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Understanding rill erosion processes is important in the prediction of soil erosion and the prevention of soil loss. However, limited information is available concerning the impacts of rainfall on rill erosion on steep slopes. Colluvial deposits with steep slopes make up the packed material underlying the collapsing walls in benggang, which collapse due to hydraulic pressure and gravity. They contain loose materials and large amounts of coarse particles. The objectives of this study were to investigate the impacts of rainfall intensity and slope gradient on the rill erosion process, rill development and rill flow dynamic mechanisms on the steep slopes of colluvial deposits. The colluvial soils were subjected to simulated rainfall in a 5-m2 (5-m by 1-m) flume at heavy rainfall intensities (100, 120, and 140 mm h−1) and on five steep slopes (20, 25, 30, 35, and 40°). Rill erosion contributed significantly to colluvial slope erosion; on average, rills accounted for 61% of the soil loss, and the effects of slope gradient were greater than those of the rainfall intensity. After rill development, rill density, rill length, width, and depth all significantly increased. Correspondingly, the soil loss rate sharply raised and irregularly fluctuated. Moreover, the collapse of rill heads or sidewalls tended to increase the relative contribution to rill erosion and rill development. The rill flow was characterized by transitional and subcritical flow regimes. The rill flow velocity was the most sensitive hydraulic parameter, and the unit stream power provided the optimal hydrodynamic parameter to characterize the dynamic mechanisms of rill erosion on colluvial deposits. The collapse of rill heads or sidewalls could result in negative values for critical shear stress, critical stream power, and critical unit stream power of rill erosion, which were −19 Pa, −5.3 N m−1 s−1, and −0.09 m s−1, respectively. These results provide a better understanding of the mechanism of rill erosion on steep slopes.

This study aimed to compare soil physicochemical properties and mineralogical compositions, including the cohesive force and internal friction angle, using direct shear tests with designed water contents and temperatures, between noncollapsible soil and collapsed gullies. Two pedons were collected from Longmen Town (Anxi County, Fujian Province) with severely collapsed gullies that developed from granitic rocks, and another two pedons were collected from metamorphic regions (Gande Town) without soil erosion. The samples were subjected to X-ray diffraction (XRD) analysis, and their soil physicochemical properties were compared. Noncollapsible soils had superior physicochemical characteristics, e.g., these soils contained higher amounts of cations, especially total iron oxides (Fet). Furthermore noncollapsible soils were able to resist shearing due to their greater cohesive force, and the internal friction angle did not differ considerably from that of the collapsed soils. Kaolinite, illite, hydroxy-interlayered vermiculite (HIV) and gibbsite were the dominant clay minerals in the noncollapsible soils. However, in the collapsed soils, kaolinite accounted for > 85% of the total clay mineral composition. The cohesive force and internal friction angle were significantly correlated with sesquioxides of all non-collapsible and collapsed pedons, such as Fed (free Fe-oxides, 0.762**, 0.637**) and total iron (Fet, 0.783**, 0.708**), as well as magnetic susceptibility (0.650**, 0.740**) (P

Inappropriate treatments for the effluents from semiconductor plants might cause the releases and wide distributions of selenium (Se) into the ecosystems. In this study, Al/Si and Fe/Si coprecipitates were selected as model adsorbents as they often formed during the wastewater coagulation process, and the removal efficiency of selenite (SeO3) and selenate (SeO4) onto the coprecipitates were systematically examined. The removal efficiency of SeO3 and SeO4 was highly related to surface properties of Al/Si and Fe/Si coprecipitates. The surface-attached Al shell of Al/Si coprecipitates shielded a portion of negative charges from the core SiO2, resulting in a higher point of zero charge than that of Fe/Si coprecipitates. Thus, adsorption of SeO3/SeO4 was favorable on the Al/Si coprecipitates. Adsorptions of both SeO3 and SeO4 on Al/Si coprecipitates were exothermic reactions. On Fe/Si coprecipitates, while SeO3 adsorption also showed the exothermic behavior, SeO4 adsorption occurred as an endothermic reaction. The kinetic adsorption data of SeO3/SeO4 on Al/Si and Fe/Si coprecipitates were described well by the pseudo-second-order kinetic model. SeO4 and SeO3 adsorption on Fe/Si or Al/Si were greatly inhibited by the strong PO4 ligand, whereas the weak ligand such as SO4 only significantly affected SeO4 adsorption. The weakest complex between SeO4 and Al was implied by the essentially SeO4 desorption as SeO4/PO4 molar ratios decreased from 0.5 to 0.2. These results were further confirmed by the less SeO4 desorption (41%) from Fe/Si coprecipitates than that from Al/Si coprecipitates (78%) while PO4 was added sequentially.

Mulching is an effective soil conservation practice for permanent gullies in southern China. Knowledge of the sediment characteristics that occur in mulched soils of colluvial deposits could improve the utility of mulching for soil conservation. A rainfall simulation experiment was designed to evaluate the effects of mulch on the runoff, erosion, and particle size distribution of eroded sediments. Straw mulch coverage of 0, 25, 50, 75, and 95% was tested with simulated rainfall. The effective particle size distribution of the sediment was compared with the ultimate particle size distribution to investigate the detachment and transport mechanisms involved in sediment mobilization. Mulching delayed the runoff initiation time and reduced the average runoff rate. Compared with bare soil, the increased mulch coverage decreased the soil loss rate by 13.0 to 90.3%. Moreover, the peak sediment concentration decreased from 80 to 200 g L− 1 under the different mulch coverage conditions. The optimal straw application rate was 1.5 to 3.0 Mg ha− 1 in the permanent gully's deposits. The relationship between instantaneous kinetic energy of rainfall and the proportion of effective clay- and sand-sized particles was well represented using an exponential equation. The effective clay-sized sediments under the different mulch coverage conditions were 2 to 4 times more common than those of the original soil, although there were only 13.9% sand-sized particles in the sediment when the mulch coverage was 95%. The silt-sized sediment was transported as primary particles under the different mulch coverage conditions. The effective to ultimate ratio of silt-sized particles fluctuated around 1. There were depletions of clay and silt in the colluvial deposit soil with mulch cover, and the enrichment ratios of clay and silt were larger than 1 while most of the enrichment ratios for sand were

Colluvial deposits with loose, coarse material are easily erodible in permanent gullies, but the mechanisms of erosion and sedimentation during overland flow remain obscure. Hence, the processes and mechanisms of the transportation of soil particles by overland flow were investigated in this study. Experiments were carried out in a 5.0 m long by 1.0 m wide flume using colluvial deposits. The slope gradient varied from 36 to 84%, and the flow rate ranged from 0.72 L m − 2 min − 1 to 2.88 L m − 2 min − 1 . The runoff rate and sediment yield rapidly increased with increasing overland duration. Runoff and sediment were highly variable when the flume was treated with a high flow rate compared with a low flow rate, with the fluctuation of sediment concentration under the high flow rate usually reaching 500 g L − 1 . The slope gradient and overland flow rate have strong impacts on sediment transport capacity. The mean flow velocity and the unit stream power can be an optimal composite force predictor for estimating sediment transport capacity. Experimental results also revealed that the percentage of gravel-sized particles increased with increasing flow rate and slope gradient, but silt and clay fractions observed opposite trend. The average enrichment ratio (ER) of gravel was usually 2.16 L m − 2 min − 1 , the bed load transport became an important mechanism; however, the simulation model overestimated these values.

Phosphorus recovery in the form of struvite has been aroused in recent decades for its dual advantages in eutrophication control and resource protection. The usage of the struvite products is normally determined by the size which is largely depended on the hydrodynamics. In this study, flow behavior of struvite pellets was simulated by means of Eulerian-Eulerian two-fluid model combining with kinetic theory of granular flow in a liquid-solid fluidized bed reactor (FBR). A parametric study including the mesh size, time step, discretization strategy, turbulent model and drag model was first developed, followed by the evaluations of crucial operational conditions, particle characteristics and reactor shapes. The results showed that a cold model with the mesh resolution of 16×240, default time step of 0.001sec and first order discretization scheme was accurate enough to describe the fluidization. The struvite holdup profile using Syamlal-O'Brien drag model was best fitted to the experimental data as compared with other drag models and the empirical Richardson-Zaki equation. Regarding the model evaluation, it showed that liquid velocity and particle size played important roles on both solid holdups and velocities. The reactor diameter only influenced the solid velocity while the static bed height almost took no effect. These results are direct and can be applied to guide the operation and process control of the struvite fluidization. Moreover, the model parameters can also be used as the basic settings in further crystallization simulations.

The suitability of an agent for washing heavy metal contaminated soils depends not only on the efficiency of heavy metal removal but also on the persistence of the washing effect, especially for agricultural soil. Redistribution of residual heavy metals in washed soil from inert pools to labile pools can reverse the initial washing effect. In order to study the redistribution of residual Pb in Pb-contaminated soils washed with citric acid (CA), ethylenediaminetetraacetic acid (EDTA), FeCl3, and HCl solutions, washed soils were incubated under both flood and 70% field water capacity (FWC) conditions for 180 days. The Pb availability in CA-, EDTA-, FeCl3-, and HCl-washed soils varied with incubation time. Diethylenetriaminepentaacetic acid (DTPA)-Pb generally increased with incubation time, except in CA-washed soil under flood incubation condition. Pb associated with the exchangeable/acid extractable fraction (F1) increased, whereas Pb in the easily reducible fraction (F2) decreased over time, for all washed soils under flood incubation condition; the changes in the amount of Pb associated with each fraction were much smaller under 70% FWC incubation. The transformation of Pb from F2 to F1 during flood incubation was largely caused by the mobilization of Fe and Mn oxides. The mobility factors (MF) of Pb for samples under flood incubation increased with increasing incubation time while those for samples under 70% FWC incubation changed only slightly, which implies increasing environmental risks of Pb from washed soils that are flooded. Therefore, the redistribution and potential environmental risks posed by heavy metals in washed soils, especially in paddy rice soils, should be taken into account when the suitability of a washing agent is evaluated. In the present study, CA was found to be unsuitable for washing Pb-contaminated agricultural soil, whereas the FeCl3 solution was the most stable washing agent tested, as it had high removal efficiency and low release of Pb after washing.

Fluidized bed reactor (FBR) has been applied in phosphorus recovery from wastewater due to its ability on producing struvite pellets with large size, high crushing strength and purity. However, the fine struvite crystals (fines) can be flushed out of the reactor, which may result in undesirable and variable phosphorus recovery efficiencies. In this study, the influences of key factors with respect to phosphorus recovery and product quality in a FBR were investigated for the treatment of swine wastewater. The effects of process parameters were first evaluated using response surface methodology (RSM), and later, long-term pilot-scale operations were tested. Results showed that fines retention was directly related to the in-reactor saturation index (SI) and upflow velocity (vup). Decreasing SI (from 2.42 to 1.65) or vup (from 75 to 25 mm s− 1) will reduce the fines entrainment and improve the phosphorus recovery profile by 14.9 and 18.5%, respectively. Moreover, these two factors governed the quality of the struvite pellets in the pilot-scale investigations—SI showed more crucial effect to size distribution, crushing strength and morphology than vup. As to the composition, struvite (35.5–95.3% of mass fraction) and CaCO3 (2.8 to 51.4% of mass fraction) were the two major components in the pellets. Decreasing SI or increasing vup and pellet size can enhance the struvite purity. Therefore, phosphorus recovery and pellet quality can be simultaneously improved by SI and vup control without additional trapping devices or reagents. The finding is constructive for FBR system set-up and operation in either pilot- or full-scale applications, where different phosphorus recovery rates and product qualities are required.

The composition, structure and transformation characteristics of clay minerals in various size particles ( 100 nm) were an important mineral source of nanoparticles, and the 1:1 clay minerals were mainly inherited from the minerals in larger particles and transformed from 2:1 clay minerals into nanoparticles.

The sediment transport capacity (Tc) is an important parameter for analysing and controlling soil erosion processes. However, few studies have investigated the Tc of soils containing gravel (grain sizes of >2 mm) on steep slopes. Colluvial deposits on steep slopes in benggang are composed of loose materials with large amounts of gravel. This study aimed to investigate the effects of gravel content on the Tc of overland flow using colluvial deposits with a range of slope gradients and flow discharges in a nonerodible flume (4 m long, 0.12 m wide and 0.1 m high). The experiments were carried out using six gravel mass contents (0, 10, 20, 30, 40, and 50%), four slope gradients (18, 36, 57, and 84%), and four flow discharges (0. 56, 1.11, 2.22, and 4.44 × 10-3 m2 s−1). The experimental results revealed that the measured Tc increased linearly as the gravel content increased. The effects of the slope gradient, flow discharge and gravel content on Tc were significant (p

Eroded sediment is an important feature of permanent gully's development; however, obtaining the specific characteristics of the sediment transport in the gully can be difficult. Thus, a composite fingerprinting technique, incorporating uncertainty analysis, has been employed to investigate the mean relative contribution of sediment sources in permanent gullies. In this study, 31 tracers were measured at 62 different sampling sites from three layers of a gully wall [surface layer (SL), sandy soil layer (SSL), and semi-weathering rock layer (SWL)] and 36 sediment samples from the slumping deposit and alluvial fan of the gullies. The sediment source tracing procedure was therefore used to assess the relative contribution of each source. The mean relative contribution from the SL to the sediment of the slumping deposit is higher in the active gully (G1), and is relatively lower in the potentially stable (G2) and stable gullies (G3); thus there was no obvious gully bank retreat in G2 and G3. In different places of the G1 alluvial fan, the mean relative contribution of the SL, SSL and SWL ranged from 9–11, 36–43 and 46–55%, respectively. However, the sediment contribution of the SL increased in G2 and G3 due to the changes in the erosion type. The mean relative contributions of the SL were 33 ± 5 (G2) and 30 ± 3% (G3). These findings have important implications for the establishment of a scientific basis for permanent gully sediment transport management and control policies.

The relationships between the basic properties and trace elements in soil argillans and corresponding matrix soils were studied by sampling from the B horizons of 26 Alfisols in croplands of the subtropical area in Central China. The soil elements (K, Na, Ca, Mg, Mn, Co, Cu, Cr, Cd, Li, Mo, Ni, Pb, Ti, V, and Zn) were extracted by acid digestion and their contents were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The mean contents of clay and organic matter in the argillans were approximately 1.1 and 1.3 times greater than those in the matrix soils, respectively. The pH values and the contents of P2O5 and bases (K2O, Na2O, CaO, and MgO) in the argillans were higher than those in the corresponding matrix soils. Cu, Cd, Ti, and V were enriched in the argillans. Correlation coefficients and factor analyses showed that Co, Cu, Li, and Zn were bound with phyllosilicates and manganese oxides (Mn-oxides) in the argillans. Cr and Pb were mainly associated with iron oxides (Fe-oxides), while Ni was bound with Mn-oxides. Cd, Ti, and V were chiefly associated with phyllosilicates, but Cr and Mo were rarely enriched in the argillans. In contrast, in the matrix soils, Co and Zn were associated with organic matter and Fe-oxides, Cr existed in phyllosilicates, and Mo was bound to Fe-oxides. Cd, Ti, and V were associated with organic matter. The results of this study suggest that clays, organic matter, and minerals in the argillans dominate the illuviation of trace elements in Alfisols. Argillans might be the active interfaces of elemental exchange and nutrient supply in cropland soils in Central China.

Forest thinning is an important method for managing forests, changing forest structure, biological diversity and community. This study examined forest thinning effects on macrofungal diversity and the environmental factors affecting fruiting and community structure. Field surveys were conducted from 2006 to 2010 in 35-year-old Cryptomeria japonica plantations in central Taiwan. Thinning was completed in October 2007 and included control, 25% thinning, and 50% thinning treatments. Each treatment had four replications. Forest thinning and time affected macrofungal species richness observed but not abundance. Thinning influenced macrofungal community compositions; however, the difference between the two thinning intensities was not significant. The macrofungal community showed significant differences between communities of eastern and northern aspect. A redundancy analysis indicated that macrofungal communities in the C. japonica plantations were significantly affected by relative humidity, light, canopy cover, soil water content, soil temperature, soil pH value and soil texture. The fruiting of a dominant coral fungal species, Scytinopogon sp., was affected by thinning and light. The fruiting bodies of this species decreased in the 25% thinning plots and disappeared in 50% thinning plots in the first two years post-thinning, but were recorded in the third year post-thinning. After thinning, macrofungal species richness observed decreased, the community changed, and changes were associated with environmental conditions. Forest thinning decreased observable macrofungal diversity and changed the community structure, and these changes were associated with environmental variation after thinning.

Wine-processing waste sludge and alkaline substances, including KOH, NaOH, Ca(OH) 2 , and Mg(OH) 2 , were employed to prepare various dissolved organic carbon (DOC) solutions for remediating a Pb-contaminated cropland by soil washing. The Pb concentrations were 5340 and 4920 mg kg − 1 in the topsoil and subsoil, respectively. Aqueous solution treatment , general DOC treatment , and enhanced DOC treatment were proposed as treatments for the reclamation and determination of the factors affecting the removal of Pb, such as pH, initial concentration of the DOC solution, temperature, and washing frequency. The aqueous solution treatment could not remove sufficient Pb and therefore failed in the reclamation. Approximately 86.5% Pb was removed from the topsoil at pH 2.0 by the general DOC treatment undergoing two wash cycles. However, over 90% Pb was removed from the subsoil under the same conditions; only the final Pb concentration in the subsoil met the control standard, 500 mg kg − 1 . About 93% Pb in the topsoil could be removed at pH 3.0 by the enhanced DOC treatment, which was performed using a 2500 mg L − 1 DOC solution containing abundant Ca 2 + and Mg 2 + at an 80:1 liquid/soil ratio (v/v) at 40 °C for 60 min. Meanwhile, organic matter, cation exchange capacity, NH 4 + -N, as well as exchangeable K, Ca, and Mg contents increased by 125%, 22.6%, 107%, 577%, 55.3%, and 306%, respectively, and the pH in the topsoil decreased to 3.7. The use of Ca(OH) 2 and Mg(OH) 2 not only prevented washing losses of the exchangeable Ca and Mg but also increased Pb removal by 20%. However, its use decreased the availability of P in the soil.

Background Clay minerals especially organoclays modified by the introduction of organic molecules into the mineral structure show much promise for environmental remediation applications. Application of organic attapulgite (O-APG) and organic montmorillonite (O-MMT) as soil amendments to bind polychlorinated biphenyl (PCB) in contaminated soils and observe PCBs accumulated in the ryegrass shoots and roots was investigated. Results Pot experiments in greenhouse indicated that organoclays could significantly fix the PCB in soils and reduce its contents in ryegrass shoots and roots. Compared with the control, the migration of concentrations of PCB into the environment in contaminated soils is reduced by about 28.5 and 44.1%, and concentrations of PCB in ryegrass roots and shoots were reduced within the range from 57.0 to 63.0% and 49.6 to 56.5%, respectively, through addition of 6% organic attapulgite and montmorillonite. There was a negative correlation between the accumulation of PCB in ryegrass and the amount of organoclay addition. The accumulations of PCB in ryegrass roots were significantly higher than those in the ryegrass shoots. Conclusions The two organoclays had been proved effective as environmental amendments for reducing the mobility and bioavailability of PCB in contaminated soils. The results of this study provided an efficient method for the remediation of PCB contaminated soils.

The soil carbon reservoir is the largest carbon reservoir in terrestrial ecosystems and consists of soil organic and inorganic carbon stocks. Previous studies have mainly focused on the soil organic carbon (SOC) stock, and limited information is available about the soil inorganic carbon (SIC) stock. The Chinese Loess Plateau (CLP), which is located in the arid and semi-arid region of China, is an important inorganic carbon reservoir, with a thick soil layer that is rich in calcium carbonate. However, there are few reports on the SIC stock and its spatial distribution in this region. In the current study, the SIC densities and stocks for various soil types and land use patterns were evaluated based on 495 profiles with 2470 soil samples across the CLP, which were collected from the Chinese Second National Soil Survey. The results showed that in the top 1 m of soil across the CLP, the average SIC density is 17.04 kg/m(2), and the total SIC stock is approximately 10.20 Pg C (1 Pg = 10(15) g). The SIC stock of the CLP accounts for approximately 18.4% of the total SIC stock throughout China. The average values of the SIC stock in the 0-20, 20-50 and 50-100 cm depths of the CLP are 2.39, 2.92 and 4.89 Pg, respectively. Under different land use patterns, the order of the average SIC density is farmland approximate to grassland > forest in all soil layers. For the various soil types, the SIC density in the 0-100 cm layer is the highest in alkaline soil and lowest in subalpine meadow soil, whereas the SIC stock is highest in loessial soil, eolian sandy soil and sierozem, and the lowest in subalpine meadow soil. These differences are largely a result of the area occupied by each soil type and the climate conditions. The results of this study provide basic information about carbon reservoir in China and contribute to our understanding of the SIC stock on the CLP as it relates to the carbon balance of terrestrial ecosystems. (C) 2014 Elsevier B.V. All rights reserved.

The release of silicon (Si) from and the structural changes to clay minerals (i.e., kaolinite, montmorillonite (Mt), and illite) were investigated after being batch incubated with low-molecular-mass organic acids (i.e., oxalic and citric acids, LMMOA) of varying concentrations (0–0.5 mol L − 1 ) at 25 °C. Two mineral acids (i.e., HCl and H 2 SO 4 ) with varying concentrations were also reacted with Ca-montmorillonite (Ca 2 + -Mt). With increasing reaction time, the Si released from kaolinite and illite reached its maximum level after incubation with the varying LMMOA concentrations for 15 days. Quantities of Si released from the clay minerals with the LMMOA ranged from 0.22 to 114.01 μg mL − 1 (Si). Quantity of Si released with oxalic acid was higher than that with citric acid. The Si released from the clay minerals increased with increasing organic acid concentrations. More Si was released from Mt than from kaolinite and illite when incubated with the same LMMOA concentration. With increasing organic acid concentrations, the X-ray diffraction (XRD) reflection intensities of the Mt weakened, and this trend was more remarkable in the clay treated with oxalic acid than citric acid. However, no relationship between the XRD reflection intensity and the acid concentrations was noticeable in the incubated kaolinite and illite. While incubating with hydrochloric acid (HCl) and sulfate acid (H 2 SO 4 ) for 15 day incubation, amounts of Si released from Ca 2 + -Mt were generally higher than those reacting with organic acids, and more Si was released in the H 2 SO 4 treatment than that of HCl. But the XRD reflection intensities of the Ca 2 + -Mt had no distinctly change compared with those treated with the organic acids.

Separation and collection of environmental nanoparticles (ENPs) in natural systems are of paramount importance in research on their nature and physicochemical properties for understanding their associated properties of adsorbing or binding to organic and trace metal contaminants. However, efficient separation and collection of ENPs in nature system remain obscure. This study aimed to use an automated ultrafiltration device (AUD) to demonstrate efficient collection of ENPs from highly weathered red soils. Synchrotron and conventional X-ray diffraction (XRD) with oriented and random powder specimens were employed to identify the composition of clay minerals with various particle-size fractions (PSFs

This study investigates biogeochemical reductive release of arsenate from beudantite into solution in a crater area in northern Taiwan, using a combination of X-ray absorption near-edge structure (XANES) and atomic absorption spectrometry. Total arsenic (As) concentrations in the soil were more than 200 mg/kg. Over four months of laboratory experiments, less than 0.8% As was released into solution after reduction experiments. The 71% to 83% As was chemically reduced into arsenite (As(III)) and partially weathering into the soluble phase. The kinetic dissolution and re-precipitation of As, Fe, Pb and sulfate in this area of paddy soils merits further study.

Sewage sludge (SS) is used on sloping land, as a soil amendment, because of its organic matter (OM) and nutrient content. However, the presence of nitrogen (N), in acidic soils amended with sludge, and its transport in runoff can lead to eutrophication of downstream surface water. This study assesses the effects of different application methods on N transport, via runoff from plots amended with SS (0 and 120 Mg ha−1). A lateritic red soil (pH 5.2) was selected for this study, using simulated rainfall conditions. When sludge was broadcasted and mixed with surface soils (BM), the concentrations and mass losses of total N in the mixed sample (MTN), total N in the settled sample (STN), total particulate N (TPN), total suspended N (TSN), total dissolved N (TDN) and NH4+-N, in runoff water, were highest at 1 or 18 d after application. BM treatments showed initial pollution risks to surface waters, which diminished gradually with time. Whereas the concentrations and mass losses of NO3−-N, in all sludge plots, appeared to have a declining trend, after an initial ascent. Hole-application (HA) and broadcast application with hay mulch (BH) treatments prevented N loss effectively, the runoff losses coefficient of MTN increased in the order BM (0.43%) > HA (0.15%) > BH (0.03%). For sludge treatments, N was largely lost in dissolved species, while a large portion of NH4+-N was lost in particulate fraction. Nitrogen (N) losses in runoff were greatly affected by the transformation of sludge N in the soil and the modification of soil properties, induced by sludge amendment. The risk associated with the application of sludge to sloping fields, in areas of acidic soil, is an important research subject that merits further study.

Humic substances are a major component of soil organic matter that influence the behavior and fate of heavy metals such as Cr(VI), a toxic and carcinogenic element. In the study, a repetitive extraction technique was used to fractionate humic acids (HAs) from a peat soil into three fractions (denoted as F1, F2, and F3), and the relative importance of O-containing aromatic and aliphatic domains in humic substances for scavenging Cr(VI) was addressed at pH 1. Spectroscopic analyses indicated that the concentrations of aromatic C and O-containing functional groups decreased with a progressive extraction as follows: F1 > F2 > F3. Cr(VI) removal by HA proceeded slowly, but it was enhanced when light was applied due to the production of efficient reductants, such as superoxide radical and H2O2, for Cr(VI). Higher aromatic- and O-containing F1 fraction exhibited a greater efficiency for Cr(VI) reduction (with a removal rate of ca. 2.89 mmol g−1 HA under illumination for 3 h). 13C NMR and FTIR spectra further demonstrated that the carboxyl groups were primarily responsible for Cr(VI) reduction. This study implied the mobility and fate of Cr(VI) would be greatly inhibited in the environments containing such organic groups.

This study investigates the species of Cu and As (enargite) residues present in soils of the Chinkuashih area, northern Taiwan. Two pedons, on the shoulder and footslope along a toposequence, were examined for their metal partitioning and geochemical origins. The bulk soils were analyzed by sequential extraction combined with mineralogical analyses, including X-ray diffraction (XRD) and scanning electron microscopy ∕ energy dispersive spectrometer (SEM ∕ EDS) analyses. Soil pH ranged from 4.23 to 4.91 with low base saturation, and the soils can be classified as fine, mixed, thermic, Typic Kandiudults. Mineralogical study indicated that enargite and pyrite particles mainly coexisted in silt and sand fractions, particularly in lower soil horizons of the footslope, showing high contents of Cu and As. Kaolinite and illite were dominant minerals in clay fractions. The footslope accumulated more total Cu and As than that of shoulder pedon. The sequential extraction experiments resulted in high proportions of Cu remaining in residual fractions, while the most of As was bound in amorphous Fe and Al oxyhydroxide fraction. The risk analyses of Cu and As (enargite) contamination in soils of the Chinkuashih area merits further study.

Intumescent material with commercial resin, such as acrylic copolymer resin, has been demonstrated to be extremely effective in improving the fire performance of wooden materials used for indoor furnishing. This study investigates the enhancement of painted thin red lauan (Parashorea spp.) plywood by using intumescent coating with organo-clays added with different types of Cloisite 30B, Cloisite 10A and Cloisite 15A and different amounts of organo-clays (1, 3, 5 and 10%). These intumescent formulations significantly enhanced the fire retardancy of painted plywood, exhibiting lower peak heat release rates (PHRR) and extending the time to reach PHRR, as compared with plywood panels coated with intumescent coating with absence of organo-clay. Therefore, the amount of organo-clays added in intumescent is important. In additional, 3% of Cloisite 30B and 5% of Cloisite 10A further enhanced fire retardancy. The FT-IR, 27Al and 31P NMR analyses demonstrated that adding organo-clay extended the survival duration of the phosphor-carbonaceous chars structure.

Attapulgite and montmorillonite were utilized to remediate heavy metal polluted red soils in Guixi City, Jiangxi Province, China. The effects of clay minerals on availability, chemical distribution, and biotoxicity of Cu and Zn were evaluated. The results provided a reference for the rational application of clay materials to remediate heavy metal contaminated soils. From the sorption experiment, the maximum adsorbed Cu2+ by attapulgite and montmorillonite was 1501 and 3741 mg/kg, respectively. After polluted red soil was amended with attapulgite or montmorillonite and cultured at 30 and 60 days, soil pH increased significantly compared to the control. An 8% increase in the amount of montmorillonite in soil and 30 days incubation decreased acid exchangeable Cu by 24.7% compared to the control red soil. Acid exchangeable Cu decreased with increasing amounts of attapulgite and montmorillonite, with best remediation effect reached at a dose of 8%. Results also showed that the Cu poisoning effect on earthworms was reduced with the addition of attapulgite and montmorillonite. Montmorillonite showed the best effect, with the addition of a 2% dose the mortality of earthworms decreased from 60% to zero compared to the control. Our results indicated that the bioavailability of Cu in soils was reduced more effectively with the application of montmorillonite than attapulgite.

Wine processing waste sludge (WPWS) has shown effective removal of heavy metals in batch studies, but the adsorption in a fixed-bed WPWS column has not been examined and the mass transport in this column remains unclear. This study aimed to investigate: (1) the retardation factor ( R ) and the dispersion coefficient ( D ) of WPWS, employing one-dimensional convective–dispersive model with breakthrough curve (BTC) and using chromium, copper and zinc as the adsorbates; and (2) explore the adsorption mechanism of WPWS column for heavy metals. The retardation factor for various metal treatments is shown in the following order: Cr(18.3) > Cu(13.0) > Zn(7.2), indicating their binding affinity toward WPWS. The dispersion coefficients were calculated to be 2.36 × 10 −6 , 5.89 × 10 −7 and 6.83 × 10 −7 m 2 s −1 for Cr, Cu and Zn treatments, respectively. The high charge density for Cr 3+ ion makes it longer for the Cr column to attain exhaustion state, about 4.0 and 8.2 times the time required for the Cr and Zn columns. However, the least retardation and adsorption amount for Zn can be attributed to its full orbital in electronic configuration.

Chemical surfactants or bio-surfactants intercalated into layered double hydroxides (LDHs) are considered as potential organic pollutant sorbents. This study evaluates the effects of (1) using either calcined or uncalcined LDH, and various solid/solution ratios, (2) the concentrations of the chemical surfactant sodium dodecyl sulfate (SDS) or the bio-surfactant rhamnolipid (RL), and (3) reaction temperatures and times on the synthesis of SDS-LDH and RL-LDH. Small angle X-ray diffraction (SAXRD) and X-ray diffraction (XRD) patterns reveal that using 1000 mg L−1 RL intercalated 2:1 uncalcined LDH with 3 days reaction time, 0.5 g L−1 solid/solution ratio, and temperature of 65 °C to synthesize the RL-LDH, containing more organic carbon content, showing larger interlayer distance than SDS-LDH. RL-LDH shows subsequent higher efficiency of naphthalene sorption than SDS-LDH, depending on higher organic carbon contents and larger interlayer distance of RL-LDH. Since RL-LDH is environmentally friendly chemical, these results are of practical interesting in RL-LDH could be potentially employed as a sorbent for removal organic contaminants from aqueous solutions, and particularly in optimizing aquatic environment remediation technologies.

The dynamics of Cs and Sr sorption by soils, especially in the subtropics and tropics, as influenced by soil components are not fully understood. The rates and capacities of Cs and Sr sorption by selected subtropical and tropical soils in Taiwan were investigated to facilitate our understanding of the transformation and dynamics of Cs and Sr in soils developed under highly weathering intensity. The Langmuir isotherms and kinetic rates of Cs and Sr sorption on the Ap1 and Bt1 horizons of the Long-Tan (Lt) and the A and Bt1 horizons of the Kuan-Shan (Kt), Mao-Lin (Tml) and Chi-Lo (Cl) soils were selected for this study. Air-dried soil (2mm) samples were reacted with of 7.5 x 10(-5) to 1.88 x 10(-3)M of CsCl (pH 4.0) or 1.14 x 10(-4) to 2.85 x 10(-3)M of SrCl(2) (pH 4.0) solutions at 25 degrees C. The sorption maximum capacity (q(m)) of Cs by the Ap1 and Bt1 horizons of the Lt soil (62.24 and 70.70 mmol Cs kg(-1) soil) were significantly (p0.05) higher than those by the A and Bt1 horizons of the Kt and Cl soils (26.46 and 27.49 mmol Cs kg(-1) soil in Kt soil and 34.83 and 29.96 mmol Cs kg(-1) soil in Cl soil, respectively), however, the sorption maximum capacity values of the Lt and Tml soils did not show significant differences. The amounts of pyrophosphate extractable Fe (Fe(p)) were correlated significantly with the Cs and Sr sorption capacities (for Cs sorption, r(2)=0.97, p1.0 x 10(-4); for Sr sorption, r(2)=0.82, p2.0 x 10(-3)). The partition coefficient of radiocesium sorbed on soil showed the following order: Cl soilKt soilTml soilLt soil. It was due to clay minerals. The second-order kinetic model was applied to the Cs and Sr sorption data. The rate constant of Cs or Sr sorption on the four soils was substantiality increased with increasing temperature. This is attributable to the availability of more energy for bond breaking and bond formation brought about by the higher temperatures. The rate constant of Cs sorption at 308 K was 1.39-2.09 times higher than that at 278K in the four soils. The activation energy of Cs and Sr sorbed by the four soils ranged from 7.2 to 16.7 kJ mol(-1) and from 15.2 to 22.4 kJ mol(-1), respectively. Therefore, the limiting step of the Cs(+) or Sr(2+) sorption on the soils was diffusion-controlled processes. The reactive components, which are significantly correlated with the Langmuir sorption maxima of Cs and Sr by these soils, substantially influenced their kinetic rates of Cs and Sr sorption. The data indicate that among components of the subtropical and tropical soils studied, short-range ordered sesquioxides especially Al- and Fe-oxides complexed with organics play important roles in influencing their capacity and dynamics of Cs and Sr sorption.

The relationship between organic matter contents and soil aggregates of particle size ranging from >4, 2–4, 1–2, 0.5–1 to 0.25–0.5 mm in three eroded (slightly, moderately and severely) Ultisols in central China was investigated using dry-sieving and wet-sieving methods, as well as chemical analyses. In different eroded Ultisols, the size distribution percentages of >4 and 2–4 mm macroaggregates obtained by dry-sieving method were all higher than that by wet-sieving method by separately between 12.3 and 45.7%, 3.0 and 24.7% , but the percentages of 0.25–0.5, 0.5–1 and 1–2 mm macroaggregates showed opposite trend. Microaggregates ( 0.25 mm water-stable aggregates (WSA) and average of mean weight diameter (MWD) decreased from slightly eroded soil to severely eroded soil by 28.0% and 0.14 mm, respectively. The organic matter (OM) content of macroaggregate fractions from slightly and moderately eroded Ultisols rose with increasing in particle size fractions from 0.25–0.5 to >4 mm, but that of macroaggregates fractions from severely eroded Ultisols decreased with increasing in particle sizes. The percentages of >0.25 mm WSA correlated well with the OM contents of eroded Ultisols ( r 2 = 0.6573, n = 19). The OM contents of macroaggregates in eroded soils showed high correlation with that of the bulk soil, and the correlation coefficients decreased in the order of slightly > moderately > severely eroded Ultisols.

Lithium/aluminum layered double hydroxide intercalated by chloride (Li/Al LDH-Cl) was considered as a superior adsorbent for anionic compounds. This study aimed to establish the adsorption behavior of arsenate on Li/Al LDH-Cl by employing X-ray absorption spectroscopy (XAS) and adsorption kinetics. The XAS analysis demonstrated that inner-sphere complexes were the dominant arsenate adsorption configurations on the planar surfaces and edges of Li/Al LDH-Cl. Based on a kinetic study, arsenate adsorption on Li/Al LDH-Cl could be separated into fast and slow reactions. This biphasic arsenate adsorption behavior was partially attributable to: (i) two different adsorption sites associated with Li, exposing on planar surfaces, and Al, existing on the edges of double hydroxyl layers, and (ii) micropore adsorption sites within the Li/Al LDH-Cl surfaces. Activation energies derived by the Arrhenius equation indicated that the diffusion process was the rate-limiting step of arsenate adsorption on Li/Al LDH-Cl.

Wine-processing waste sludge (WPWS) has been shown to have powerful potential for sorption of some heavy metals (i.e., chromium, lead and nickel) in single-component aqueous solutions. But although most industrial wastewater contains two or more toxic metals, there are few sorption studies on multicomponent metals by WPWS. This study has two goals: (i) conduct competitive adsorption using Cr, Cu and Zn as sorbates and examine their interaction in binary or ternary systems; and (ii) determine the effects of temperature on the kinetic sorption reaction. The sludge tested contained a high amount of organic matter (38%) and had a high cation exchange capacity (CEC, 255 cmol(c)kg(-1)). Infrared analysis reveals that carboxyl is the main functional group in this WPWS. The (13)C NMR determination indicates alkyl-C and carboxyl-C are major organic functional groups. At steady state, there are about 40.4% (Cr), 35.0% (Cu) and 21.9% (Zn) sorbed in the initial 6.12 mM of single-component solutions. Only pseudo-second-order sorption kinetic model successfully describes the kinetics of sorption for all experimental metals. The rate constants, k(2), of Cr, Cu and Zn in single-component solutions are 0.016, 0.030 and 0.154 g mg(-1)min(-1), respectively. The sorption of metals by WPWS in this competitive system shows the trend: CrCuZn. Ions of charge, hydrated radius and electronic configuration are main factors affecting sorption capacity. The least sorption for Zn in this competitive system can be attributed to its full orbital and largest hydrated radius. Though the effect of temperature on Zn sorption is insignificant, high temperature favors the other metallic sorptions, in particular for Cr. However, the Cr sorption is lower than Cu at 10 degrees C. The Cr sorption by WPWS can be higher than that of Cu at 30 degrees and 50 degrees C.

Polyphenols (catechins) are vital biomolecules in tea plants, Camellia sinensis , which are well adapted to acid soils with high availability of phytotoxic Al species. Since the mechanism of Al resistance in tea plants by catechin remains obscure, this study investigates the influence of catechin on aluminum transformation. It is found that the pH of the suspensions decreased with aging. The hydrolytic precipitates of Al were subjected to surface area, X-ray diffraction (XRD), Fourier-transform infrared absorption spectroscopy (FT-IR), transmission electron microscopy (TEM), thermal, and chemical analyses. At the initial Al concentration of 2 × 10 − 2 M sample, in the absence of catechin for 180-d aging, only 59.7% of the Al is remained in the filtrate, including readily, moderately extractable and nonextractable fractions. However, in the presence of catechin, above 70.5% of the Al is present in the filtrate. The readily, moderately extractable and nonextractable Al fractions with 8-quinolinolate method are decreased with increasing concentrations of catechin after 180-d aging. Specific surface area of the Al precipitates increases with increasing concentrations of catechin. In the absence of catechin, the Al precipitates with prolonged aging are mostly crystalline gibbsite. X-ray diffraction analysis and TEM observations also show the structural distortion within the hydrolytic precipitates of Al in the presence of catechin. FT-IR spectra show that catechin substantially inhibits the formation of crystalline aluminum hydroxides. X-ray noncrystalline to poor-ordered hydrolytic reaction products of Al are formed in the presence of catechin. TEM images also show that the Al precipitates form under the perturbation of catechin are fine, shapeless and hollow colloids that are deformed and aggregated. Thermal analysis shows that the hydrolytic reaction products of Al lost their structural water gradually when catechin concentration is raised from 0 M (control) to 4.0 × 10 − 3 M, indicating that greater structural disorder occurs with increasing catechin concentration in the Al systems.

Injection of saline solutions can enhance the effect of electro-osmotic pressure. This study considers the consolidation and stability of foundation soil for building construction. Kaolinite (KGa-1) and Taipei silty clay were subjected to zeta potential (ZP), electro-osmosis and laboratory vane shear tests with injection of saline solutions. The ZP values decrease (i.e., less negative potential) with increased cationic valences and concentrations. The increased electro-osmotic permeability from injecting CaCl2 (1 N, EOC5) solution is about 172% higher than that without injection due to an increase of drained water from the cathode and the resulting increase of undrained shear strength. Average undrained shear strength for injecting CaCl2 solution over a period of 7 days is about 4 to 5 times greater than that without injection during electro-osmosis tests. Electro-osmosis tests with injection of saline solutions reveal that the increase of undrained soil shear strength (ΔSu) is proportional to the ZP tests.

In this study, we investigated the biodegradation of the phthalate acid esters (PAEs) di-n-butyl phthalate (DBP) and di-(2-ethyl hexyl) phthalate (DEHP) in compost and compost-amended soil. DBP (50 mg kg(-1)) and DEHP (50 mg kg(-1)) were added to the two types of compost (straw and animal manure) and subsequently added to the soil; they were tested as a single compound and in combination. Optimal PAE degradation in soil was at pH 7 and 30 degrees C. The degradation of PAE was enhanced when DBP and DEHP were simultaneously present in the soil. The addition of either of the two types of compost individually also improved the rate of PAE degradation. Compost samples were separated into fractions with various particle size ranges, which spanned from 0.1-0.45 to 500-2000 microm. We observed that the compost fractions with smaller particle sizes demonstrated higher PAE degradation rates. When the different compost fractions were added to soil, however, compost particle size had no significant effect on the rate of PAE degradation.

Arsenate is one of the main contaminants threatening water supplies all over the world. Layered double hydroxides (LDHs) have large surface areas and high anion exchange capacities, so they may be used to develop rapid and cost-effective methods for scavenging As from contaminated water. In order to enhance arsenate adsorption of layered double hydroxides, it is essential to have a fundamental understanding of the interactions between arsenate and LDHs. In this study, the effects of layer charge density and interlayer nitrate orientation of Mg/Al–NO 3 LDHs on the preferential adsorption of arsenate were investigated. Mg/Al–NO 3 LDHs with a Mg:Al ratio of 2:1, 3:1 and 4:1 were synthesized, using a constant-pH co-precipitation method. The adsorption maxima of As on 2:1, 3:1 and 4:1 LDHs were 1.56, 1.08 and 0.36 mmol g − 1 , respectively, following the order of their layer charge densities. In addition, nitrate orientation in the LDHs plays a significant role in determining arsenate adsorption. The low arsenate adsorption of 4:1 LDH relative to its anion exchange capacity resulted from the low degree of access arsenate has to the interlayer space, so that arsenate adsorption largely occurred on the external surface of the material. The accessibility of the interlayer of 4:1 LDH to arsenate was restricted by the small basal spacing as a result of the parallel orientation of the interlayer nitrate with respect to the hydroxide sheets. Conversely, interlayer nitrate with an orientation perpendicular to the hydroxide sheets in 2:1 and 3:1 LDHs can be exchanged for arsenate more readily. Consequently, these two LDHs exhibit greater arsenate adsorption capacity, because arsenate can be adsorbed on both their external and interlayer surfaces. The arsenate adsorption of the LDHs also was highly dependent upon the type and concentration of competing anions. The negative effect of the competing anions on arsenate adsorption by various LDHs generally followed the order H 2 PO 4 − > HCO 3 − > SO 4 2− > F − > Cl − . Due to the difference in adsorption mechanism, the arsenate adsorption of 4:1 LDH is subject to the negative impact of competing anions to a greater extent than those of 3:1 and 2:1 LDH. These results demonstrated that the preferential adsorption of arsenate by LDHs is dependent upon the nitrate orientation in these materials, as a consequence of changing layer charge density. The selective retention of arsenate for wastewater treatment can be maximized by controlling the orientation of interlayer nitrate in Mg/Al–NO 3 LDHs.

The occurrence of glauconite in Oligocene and Miocene sedimentary rocks remains obscure. This study focused on the mineralogy and occurrence of glauconite at Kuohsing (KH) and Chungliao (CL) villages, Nantou Prefecture in central Taiwan. The glauconite pellets occur mainly in siltstones and mudstones that contain abundant shell and fossils, respectively. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) with petrography microscopic investigations, and electron probe microanalysis (EPMA) were employed for this study. The glauconitic pellets show two main types of morphology. (1) Spheroidal or ovoidal glauconitic pellets consist of microcrystals of phyllosilicates in random orientation. The HRTEM study showed that the spheroidal or ovoidal pellets consist mainly of glauconitic packets, iron-rich chlorite, muscovite, biotite and low amounts of smectites. The glauconite and chlorite packets were generally arranged in random orientation in the spheroidal or ovoidal pellet. There are also low concentrations of submicroscopic quartz, apatite, and monazite in the pellets. (2) Vermicular pellets in packet sizes of glauconite ranging from several to 50 nm in thickness. Vermicular glauconitic pellets occur like a single crystal (i.e., oriented aggregation of polycrystalline glauconites). The basal planes of vermicular glauconitic pellets show cleavages, which are approximately perpendicular to the long axis of the vermicular pellets. The XRD analysis of vermicular glauconitic pellets showed glauconite and chlorite present. The EPMA indicated that vermicular glauconitic pellets contained more K and Fe than spheroidal or ovoidal glauconitic pellets. The spheroidal or ovoidal glauconitic pellets contained more glauconitic/smectite mixed-layer clays than the vermicular glauconitic pellets. The morphology, mineral constituents and chemical compositions, and submicroscopic textures, indicated that spheroidal or ovoidal and vermicular glauconitic pellets are formed from faecal pellets through neoformation.

The goal of this study was to investigate the characteristics of iron–manganese cutans and to observe information of their pedogenic processes and certain environmental condition changes in the pedogenic process of subtropical Chinese soils. The characteristics of micromorphology of iron–manganese cutans and element distribution with linear microprofiles (i.e., the vertical microprofile from cutan to matrix soil) in Fragiudalfs (FRA), Ferrudalfs (FER) and Hapludult (HAP). Cutans and matrix soils were studied by chemical analyses, optical microscopy (OM) and energy dispersive spectroscopy (EDS). The micromorphological structure of iron–manganese cutan was a thin black film with alternating color of red and brown, and about 1 mm thick of soil particles. The structures of cutan materials were denser, and the boundaries between cutans and matrix soils were clear. EDS analyses of cutans and the plasma phase of the matrix soils, showed that the contents of MnO 2 , Fe 2 O 3 and CaO in cutans were higher than those in matrix soils, while the content of SiO 2 showed the opposite trend. From the outer to inner, cutans in Fragiudalfs and Ferrudalfs can be easily fractionated into manganese-rich, iron–manganese-rich and iron-rich regions. But there were only iron–manganese-rich and iron-rich regions in cutans in Hapludult, there was no clear manganese-rich region of belt structure in it. These differences were attributed to soil-forming factors. The formation of belt structure in iron–manganese cutans would probably undergo several great change in landscapes and soil environments. It indicated that the growth of cutans was in environments of alternating wetting and drying. They gradually grew in the oxidation–reduction process on the dry or wet condition of whole bulk soils.

(137)Cs is one of the major artificial radionuclides found in environments; but the mechanisms behind fertilizer-induced (137)Cs desorption from soil remain unknown. This study aimed to investigate the kinetics and mechanisms underlying the various cations and anions that cause Cs release from soil under acidic conditions. NH(4)H(2)PO(4) (1M), 0.5M (NH(4))(2)SO(4), 1M NH(4)Cl, 1M KCl or 1M NaCl solutions were added to (137)Cs-contaminated soil. The power function model well described the short term (137)Cs desorption with the solutions. The rate coefficients for (137)Cs release from soil in NH(4)H(2)PO(4), (NH(4))(2)SO(4), NH(4)Cl, and KCl solutions were 7.7, 7.3, 6.8, and 6.1 times higher than the rate observed in a NaCl solution, respectively. The NH(4)H(2)PO(4) and (NH(4))(2)SO(4) solutions induced significantly greater (137)Cs release from the contaminated soil than the NH(4)Cl, KCl and NaCl solutions. After four times repeated extractions with the fertilizer solutions, the total amount of (137)Cs extracted by (NH(4))(2)SO(4) and NH(4)Cl solutions reached equilibrium, while that extracted using an NH(4)H(2)PO(4) solution continued to increase. The combined effect of phosphate and protons was the major mechanism behind (137)Cs release from contaminated soils, when an NH(4)H(2)PO(4) solution was used.

The aims of this study were to make use of organo-clays (i.e., Cloisite-10A, Cloisite-15A, Cloisite-30B and Cloisite-93A), to remove p -nitrophenol, phenol and aniline of organic pollutants. The organo-clays were characterized by X-ray diffraction (XRD). Sorption isotherm, kinetic and pH effect of p -nitrophenol, phenol and aniline sorbed by four organo-clays were evaluated. The d -spacings (0 0 1) of the XRD peak of Cloisite-10A, Cloisite-15A, Cloisite-30B and Cloisite-93A are 1.98, 2.76, 1.93 and 2.64 nm, respectively. The d (0 0 1)-spacings of XRD indicated that these p -nitropheno, phenol and aniline could penetrate into the interlayer of clays and expand the d (0 0 1)-spacings. The linear sorption isotherm of constant partition was employed to describe the sorption isotherms of phenols sorbed by organo-clays through hydrophobic–hydrophobic chemical reactions. The parabolic diffusion and power-function of kinetic models were employed to describe properly the kinetic experiments. The rate limiting step of the p -nitrophenol sorption reactions on organo-clays were diffusion-controlled processes (i.e., 15A, 30B, 93A) and chemical-controlled process for 10A organo-clays. The pre-exponential factor of the p -nitrophenol sorbed by four organo-clays showed the trend as follows: 10A > 30B > 93A > 15A. The efficiency of these organo-clays in removing phenol compounds in water treatments merit further study.

Goethite widely occurs in the environment and its role in photoreduction of toxic Cr(VI) to less toxic Cr(III) has been previously reported in the literature. However, natural goethite is rarely stoichiometric and usually contains certain substitutional cations, such as Mn(III) or Mn(IV), which, on the other hand, is an oxidant for Cr(III). In order to provide more insight into the fate of Cr(VI) in the environment, the influence of Mn-substitution in goethite on its Cr(VI) photoreduction capability needs to be clarified. The objectives of this study were to evaluate the adsorption and photo-transformations of Cr on Mn-substituted goethite with Mn/(Mn + Fe) molar ratios ranging from 0 to 0.1. The results showed that Cr adsorption and photo-catalytic transformation on goethite were strongly influenced by the Mn content of goethite. When the system was under illumination, Cr(VI) reduction was decreased with increasing Mn-substitution in goethite. The re-oxidation of photo-reduced product, i.e., Cr(III), at the Mn sites on the surface of goethite is responsible for the lower Cr(VI) photo-reduction capacity of Mn-substituted goethite. The role of goethite in the reduction of Cr(VI) may be overestimated unless its Mn-substituted counterparts are considered. The effectiveness of Mn sites in goethite to increase toxic Cr(VI) has important implications in determining the fate and threat of Cr(VI) contamination.

The present study describes the photocatalytic degradation of toluene in gas phase on different porous manganese oxide doped titanium dioxide. As synthesized birnessite and cryptomelane type porous manganese oxide were doped with titania and tested for photocatalytic decomposition of toluene in gas phase. The effects of the inlet concentration of toluene, flow rate (retention time) were examined and the relative humidity was maintained constantly. Thermal and textural characterization of manganese oxide doped titania materials were characterized by X-ray diffraction (XRD), thermogravemetry (TG), BET and TEM-EDAX studies. The aim of the present study is to synthesize the porous manganese oxide doped titania and to study its photocatalytic activity for toluene degradation in gas phase. Cryptomelane doped titania catalyst prepared in water medium [K-OMS-2 (W)] is shown the good toluene degradation with lower catalysts loading compared to commercial bulk titania in annular type photo reactor. The higher photocatalytic activity due to various factors such as catalyst preparation method, experimental conditions, catalyst loading, surface area, etc. In the present study manganese oxide OMS doped titania materials prepared by both aqueous and non-aqueous medium, aqueous medium prepared catalyst shows the good efficiency due to the presence of OH bonded groups on the surface of catalyst. The linear forms of different kinetic equations were applied to the adsorption data and their goodness of fit was evaluated based on the R2 and standard error. The goodness to the linear fit was observed for Elovich model with high R2 (>or=0.9477) value.

We have investigated the clay mineralogy of 3 pedons along a toposequence of perhumid forest soils facing a subalpine lake in northeastern Taiwan to gain insight into the individual factors that affect weathering rates. Toposequence of the transect was investigated from summit to footslope and at the lakeshore. The natural drainage of soils varies from well drained to poorly drained. The major minerals in the well-drained soils at the summit site were illite and kaolinite, whereas illite and vermiculite were dominant in the poorly drained soil at the footslope. In the poorly drained soils of the lakeshore site, almost permanent saturation inhibited weathering of minerals, and vermiculite, illite and illite–vermiculite were the dominant minerals. The magnitude of the mean layer charge of vermiculite was estimated by use of the alkylammonium exchange method (nC = 12). The mean layer charge of vermiculite ranged between 0.63 and 0.78 cmolc/(O10(OH)2). The distribution of clay layer charge varied with location and soil depth. Vermiculite in the surface horizons displayed lower mean layer charges, indicating stronger weathering intensity in the surface horizons. Acidification by organic acids may result in the reduction of layer charge in vermiculite, particularly at the surface. Differences in layer charge with landscape position may be due to differences in weathering processes. The drainage condition caused by topography is a critical factor in the transformation and redistribution of clay minerals. High precipitation, combined with surface runoff, enhance the variation of the type and mean layer charge of clay minerals along this toposequence.

The subtropical alpine forest ecosystem is vulnerable to acid rain deposited through the forest soils. Soil pH buffer capacity is a common index and plays an important role in buffering acidification. In this study, the pH buffer capacity of forest soils along an elevation sequence in central Taiwan was investigated and evaluated through conventional titration and mathematical calculation of proton affinity methods. High pH, cation exchangeable capacity, base saturation were observed in the low elevation site. Three phases of pH buffer capacity (pHBC) were proposed and well described the titration curve through linear fitting. The pHBCs showed no significant differences from the titration curves of various pedons and horizons. However, mathematical calculation of proton affinity potentials showed the highest correlation at the lower elevation site with soil pH (r = 0.90⁎⁎), cation exchangeable capacity (CEC) (r = 0.91⁎⁎), base saturation (r = 0.97⁎⁎), and X-ray non-crystalline sesquioxides (r = 0.68⁎⁎). It is important to evaluate the alpine forest soil pH buffer capacity by combining its proton consumption potentials.

This study aimed to investigate the physical and chemical properties of rhizosphere and bulk soils of three tea plants cultivated at two different elevations for direct comparison each cultivar planted in different soil environments. The three tea plants are Camellia sinensis CV Chin-Shin Dahpan (CSD), Camellia sinensis CV Chin-Shin Oolong (CSO), and Camellia sinensis CV TTES, No. 12 (TTE). The two study sites were located at Yangmei (YM), Taiwan Tea Experimental Station, Taoyuan County of northern Taiwan, and the Luku (LK), Fonghuang Tea Experimental Station, National Taiwan University, Nantou County of central Taiwan. Rhizosphere and bulk soils from A horizon (0–15 cm) below tea plants were sampled. The fresh tissues of tea plants were also collected for comparison. The physical and chemical properties, bioavailability of metals (i.e., Al, Fe, Mn, Cu and Zn), and fractionations of metal speciation of the rhizosphere and bulk soils were studied. The low molecular weight organic acids (LMWOAs) of the soil and fresh tissue samples were determined by gas chromatograph (GC), while the organic functional groups were determined by cross polarization magic angle (CPMAS) nuclear magnetic resonance (13C NMR) analysis. In general, the mean value of cation-exchange capacity (CEC), organic carbon, and C/N ratio of the rhizosphere soils were lower than those of the bulk soils. Bioavailability of Al shows that Al concentrations in YM soils were higher than that of LK soils. However, bioavailability of Fe in YM and LK soils showed no significant differences. Bioavailability of both Al and Fe in rhizosphere soils was higher than those in bulk soils. According to sequential multi-step extractions, the amounts of Al and Fe fractions showed the following order: residual (step 8) > metal-organic complexes-bound (steps 3 and 5) > crystalline Fe-oxide-bound (step 7). The LMWOAs concentrations in rhizosphere soils were higher than those in bulk soils. The LMWOAs exudates in soils showed the following order: oxalic > succinic > fumaric > malonic acids. Regression analysis of bioavailability of Al and Fe in YM and LK sites showed linear relationships with total LMWOAs concentrations (R2 > 0.974 to Al; R2 > 0.791 to Fe). The microbial resynthesis of alkyl-C, hemicellulose of acetal-C and aromatic-C rhizosphere soils was higher than that of bulk soils. On the other hand, the lignin of aromatic-C, phenolic-C and carboxyl-C contents of bulk soils were higher than those of rhizosphere soils. The cellulose component of O-alkyl-C contents in fresh roots at the YM site was higher than that at the LK site. From regression analysis, total LMWOAs concentrations showed high correlation with bioavailability of Al and Fe.

Pollution of agricultural lands by heavy metals has become more serious with increasing pollutants emitted from electroplate plants of northern Taiwan. This study aimed to assess the retardation factor (R) and the dispersion coefficient (D) using one-dimensional convective–dispersive model by comparing the breakthrough curve (BTC) and least squares methods. An acrylic column, with an inner diameter of 9 cm and a length of 15 cm, was uniformly packed with soil for metal leaching experiments. An unpolluted surface (0–20 cm) of the Taoyuan red soil was collected for this study. In miscible displacement experiments, a mixture of 4 mg L− 1 CdCl2, 20 mg L− 1 NiCl2, and 60 mg L− 1 ZnCl2 was leached from top of the column and the effluent was collected in increments with the aid of a fraction collector. The retardation factor (R) calculated from the least squares method was close to the R value observed from breakthrough curves. The R value showed the trend: Cd>Zn>Ni, indicating the rate of metals transport in red soils: Ni>Zn>Cd. Their reactivity was assessed within the framework of the hard–soft acid–base principle (HSAB). From sequential extractions, most of the Cd remained in exchangeable fractions, and Ni and Zn were found to exist in residual Fe- or Mn-oxides, and organic matter fractions.

In Taiwan, the average sulfate and nitrate deposited by acid rain as precipitation amount to 50 kg SO42− and 15–50 kg NO3− ha−1 year−1, respectively. The reactions of sulfate and nitrate with forest soils were not fully understood. Thus, we selected two forest pedons, namely the Dystrochrept and Hapludult of the Lien-Hua-Chi watershed in central Taiwan, to study their sorption and desorption of sulfate. Soil samples were leached with simulated acid rain solutions of various acidity and sulfate concentrations to assess their retention of cations and sulfate. The amounts of sorbed-SO42− of two pedons extracted with NaH2PO4 (0.016 M) solutions in the range 0.14–1.09 mmol kg−1 soil were higher than that of native water-soluble sulfate (i.e., extracted with H2O), in the range 0.15–0.41 mmol kg−1 soil. The amounts of native sorbed-SO42− of two pedons correlated significantly with the exchangeable Al (r = 0.91). The sorption of sulfate did not fit well the Langmuir equation. The native sulfate contents of all tested pedons were near the maximum sulfate sorption capacity. The sulfate sorption capacity and the amount of released Al correlated well with increasing acidity of simulated acid rain added. Introducing solutions of various acidity and sulfate concentrations into the leaching solution flowing through the soil column resulted in sharp increases in amount of sulfate and aluminum released in percolates after several pore volumes were replaced. High clay and sesquioxide contents at soil depths of 30–50 cm (Bw horizon) and 50–80 cm (BC) of pedon 1 retained part of the sulfate added serving as the sulfate sink. Released K, Mg and Ca showed two periods of higher leaching pattern, having a trend similar to that the electrical conductivity (EC) pattern. After leaching of simulated acid rain through the soil column, the soil exchangeable cations were decreased. The tested soils possess an acid-buffering capacity in pedon 1. Pedon 1 is composed of high clay and sesquioxide contents and possesses greater buffer capacity than that of pedon 2.

Many important sorption parameters have been determined by isothermal sorption batch experiments; however, only macroscopic and indirect results were obtained. The objective of this study was to derive the species and structural environment of Cu(II) on the surface of gibbsite (Al(OH) 3 ), pyrolusite (MnO 2 ), and amorphous silica (SiO 2 ), using the technique of extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Results show that the equilibrated pH of suspension affects significantly the species of Cu sorbed on the surface of these oxides. Sorbed species (Cu 2+ ) were present below pH 5.73 and precipitated (Cu(OH) 2 ) phases above 5.63. On the other hand, there is no EXAFS evidence that sorbent types and concentrations affect the local chemistry environment and species of Cu(II).

Summary Soils are the central organizer of the terrestrial ecosystem. Their colloidal and particulate constituents, be they minerals, organic matter, and microorganisms, are not separate entities; rather, they are constantly interacting with each other. Interactions of these components control biogeochemical reactions, namely, the formation of short-range-ordered metal oxides, catalysis of humic substance formation, enzymatic stability and activity, mineral transformation, aggregate turnover, biogeochemical cycling of C, N, P, and S, and the fate and transformation of organic and inorganic pollutants. Furthermore, the impacts of mineral–organic matter–microorganism interactions and associated biogeochemical reactions and processes on biodiversity, species composition, and sustainability of the terrestrial ecosystem deserve close attention for years to come. This paper integrates the frontiers of knowledge on this subject matter, which is essential to uncovering the dynamics and mechanisms of terrestrial ecosystem processes and to developing innovative management strategies to sustain ecosystem health on the global scale.

The mechanisms of the influence of organics on Al transformation were not fully understood. This study investigated the effect of citric acid on Al speciation in partially neutralized aluminum solution. The partially neutralized solution was prepared with 20 mmol L(-1) AlCl3 without citrate (citrate/Al molar ratio of 0, control) or with citrate (citrate to Al molar ratios between 0.1 and 3.0) at pH between 3.0 and 7.0. The nature of aluminum hydrolytic products as influenced by citrate complexation was investigated by turbidity measurement, ferron kinetic color development, peak line width in 27Al nuclear magnetic resonance (NMR) deconvolution demodule quantitative methods, and the MinteqA2 chemical speciation program. Sulfate precipitates from Al solution as influenced by citrate were examined by X-ray diffraction (XRD) analysis and atomic force microscopy (AFM). The turbidity of the Al solution increased with increasing pH values. Increases in citrate/Al molar ratio from 0 to 0.1 decreased dramatically the turbidity due to citrate complexation. The 27Al NMR peak at 6 ppm of the Al solution at a citrate/Al molar ratio of 0.5 shifted to 8 and 10 ppm in the solutions at citrate/Al molar ratio of 1.0 and 3.0, respectively. Comparison of 27Al NMR data and the data obtained from the MinteqA2 chemical speciation program, indicate that the Al-citrate complexes as revealed by 27Al NMR data are largely Al(citrate), AlH(citrate)+, and Al(citrate)(2)3- complexes (99-112%) in the pH range of 4.5-6.5. The non-detected Al fractions by the MinteqA2 program account for 82-99% of the non-detected Al fractions by NMR quantitation in the same pH range. The AFM of sulfate precipitates from solutions with low citrate/Al molar ratios (i.e., 0.01, pH 4.5, aged 40 days) shows that Al13 sulfate precipitates were ellipse-shaped. These ellipse-shaped precipitates were aggregated when solution pH increased from 4.5 to 7.0 (aged 40 days), indicating the fast hydrolytic rate of Al at high pH. The sulfate precipitates from solution with a high citrate/Al molar ratio (i.e., 0.05, pH 4.5, aged 40 days) also shows aggregate of particles, and XRD non-crystallized precipitates the hampering effect of citrate on Al precipitates.

Utilization of inorganic reducing agents, such as Fe(II) and sulfide for Cr(VI) reduction would result in an increase in solid waste production and subsequent treatment cost. Rapid decrease in Cr(VI) concentrations and less solid by-products are valuable in the remediation of Cr(VI) contamination. The enhancement of Cr(VI) reduction by organic compounds with activated surfaces allows us not only efficient uses of natural materials but also decrease of processing products. The experiments of this work were all conducted under the light in visible wavelength region. Titanium dioxides (TiO 2 ) could accelerate Cr(VI) reduction by citrate; however, illumination was necessary to initiate the redox reaction. Although Fe(III) did not show any capability of reducing Cr(VI), it could increase the removal of Cr(VI) by TiO 2 in the presence of citrate and fluorescent light. When develop remediation techniques for Cr(VI) contamination, natural sunlight or a cheaper light source (i.e., fluorescent light) can be used, instead of UV light which is often used in the current techniques of treatments of soil and water contamination.