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Soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) play a vital in plant growth, and their stoichiometric ratios (RCN, RCP, RNP, and RCNP) are important indicators of the elemental balance in the soil ecosystem. However, the effects of land-use change (from natural forest to high-intensity orchards) on dynamics of SOC, TN, TP, and their stoichiometric ratios along the deep soil profile remain poorly understood, especially in the red soil of Southeast China. Therefore, in the present study, we selected the high-intensity managed pomelo orchard systems (7-year-old and 20-year-old) of Pinghe County developed from the natural forest and investigated their soil nutrients distribution and stoichiometric ratios at a depth of 0–200 cm. We found that conversion of natural forest into highly managed pomelo orchard systems effectively increased the SOC (5.01 to 9.05%), TN (98.80 to 126.79%), and TP (507.50 to 1914.65%) contents in the depth of 0–20 cm. On the contrary, in this same depth, RCP and RNP consistently decreased with increasing planting years, while no significant differences were found in RCN between 7-year-old and 20-year-old pomelo orchards. Nonetheless, planting year affected the SOC, TN, RCN, and RCP in the deep soil at 0–200 cm, while TP and RNP at 0–80-cm soil depth. These findings strengthen our understanding of soil nutrients and stoichiometry changes as a result of land-use change and could also provide a vital resource for the evaluation of different land uses.

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.

Past studies have shown that dissolved organic carbon (DOC) washing can effectively remove heavy metals from contaminated soil. In this study, we used alkaline DOC solutions for remediation of arse...

In pursuit of highyield, blind application of a large number of nitrogen fertilizer in tea plantation has not only seriously affected the quality of tea, but also resulted in environmental degradat...

Increasing temperature and nitrogen (N) deposition are major drivers of global change that will influence plant-soil systems. We aimed to understand how plant stoichiometry and nutrient limiting types could change with continued warming and N inputs in subtropical regions. In 2014, the experiments were established in 30 mini-plots (2 × 2 m) with the following treatments: control, high N addition, low N addition, warming, warming + high N addition, and warming + low N addition. We sampled the leaf and root of Cunninghamia lanceolata and soils to assess their elemental and stoichiometric variables and δ15N under all six conditions. Both experimental warming and N fertilization consistently induced an increase in fine-root N, P, and N:P. The N:P ratio of the mature green-leaf and soil was 7.24–11.63 and 4.79–6.56, respectively. On average, C. lanceolata showed higher proportional P resorption, but lower N resorption. The δ15N enrichment factor significantly increased in the warming and N addition treatments. N addition decrease leaf N content, and increased the plant growth, which was due to the effect of the N dilution of C. lanceolata. In subtropical regions, N-limitation affects the growth of C. lanceolata, and the concurrent increase in warming and N fertilization should help relieve N-limiting conditions.

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.

Removal of arsenic (As) from water supplies is needed to reduce As exposure through drinking water and food consumption in many regions of the world. Magnetite nanoparticles (MNPs) are promising and novel adsorbents for As removal because of their great adsorption capacity for As and easy separation. This study aimed to investigate the adsorption mechanism of arsenate, As(V), and arsenite, As(III), on MNPs by macroscopic adsorption experiments in combination with thermodynamic calculation and microspectroscopic characterization using synchrotron-radiation-based X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). Adsorption reactions are favorable endothermic processes as evidenced by increased adsorption with increasing temperatures, and high positive enthalpy change. EXAFS spectra suggested predominant formation of bidentate binuclear corner-sharing complexes ((2)C) for As(V), and tridentate hexanuclear corner-sharing ((3)C) complexes for As(III) on MNP surfaces. The macroscopic and microscopic data conclusively identified the formation of inner-sphere complexes between As and MNP surfaces. More intriguingly, XANES and XPS results revealed complex redox transformation of the adsorbed As on MNPs exposed to air: Concomitant with the oxidation of MNPs, the oxidation of As(III) and MNPs was expected, but the observed As(V) reduction was surprising because of the role played by the reactive Fe(II).

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.

Soil clays (< 2,000 nm) (SC) and soil nanoclays (< 100 nm) (SNC) were used as adsorbents for removal of Cu(II) from aqueous solution. The experiments were conducted with variables including pH, interaction time, concentration of Cu(II) and temperature. Four kinetic models have been employed to investigate adsorption mechanisms, and the experimental data more closely resemble a second-order process of the kinetic model. Adsorption studies on soil nanoclays have been shown to be highly effective in removing of Cu(II) from aqueous solution. This adsorbent is widely available as a natural material, is mechanically stable and, most importantly, it is environmentally appealing. The maximum Cu(II) adsorption capacity of soil nanoclays (31.7 mg/g) is more than three times higher than natural soil clays (10.2 mg/g). Our study demonstrates that soil nanoclays can be used effectively for removal of Cu(II) from aqueous systems to achieve environmental cleaning purposes.

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.

The products of Al hydrolysis play significant roles in terrestrial and aquatic environments, particularly through their binding of nutrients and pollutants. However, the effect of catechins on the crystallization of Al precipitates and the resultant surface alteration of Al transformation products on their kinetics and mechanisms of adsorption of Cd still remain to be uncovered. The objective of this paper was to investigate the kinetics of Cd adsorption on the Al precipitates formed under the influence of catechin. The experiments were conducted with initial catechin/Al molar ratios, interaction time, concentration of Cd ions, and temperature as the variables. Six kinetic models were employed to investigate adsorption mechanisms, and data resembled more closely a second-order process. The structural perturbation of Al precipitates by catechin, resulting in the development of their microporosity and alteration of surface and charge properties, substantially enhanced the rate constants of both fast and sl...

Wine processing waste sludge (WPWS) has been shown to be an effective sorbent for sorption of nickel, lead, and chromium, but the sorption of copper (Cu) in aqueous solution by WPWS has not been conducted. The objective of this study was to explore the sorption mechanism of WPWS for copper. Infrared analysis revealed carboxyl was the major functional group inWPWS. The WPWS sorption isotherms of copper were only well described by Langmuir sorption isotherm. The maximum adsorption capacity (Qm) was 14.26 mg/g at 50 8C. A pseudo- second-order sorption kinetic model successfully described the kinetics of copper sorption onto WPWS. The Gibb free energies (DG8) ranged from � 20.69 to � 24.29 kJ mol -1 , and the DH8 and DS8 were 5.048 kJ mol -1 and 91.05 J mol -1 K -1 , respectively. The trend of the intra-particular diffusion rate is the opposite of the adsorption constant of the pseudo- second-order equation. Water Environ. Res., 84, 733 (2012).

This study examined the change in the speciation of cadmium (Cd) in contaminated rice paddy soils with prolonged submergence. Three Changhua soils (CH1, CH2, and CH3) from central Taiwan and three Taoyuan red soils (TY1, TY2, and TY3) from northern Taiwan with different levels of heavy metal contamination were selected for the study. The Cd, Fe, Mn, soil pH, and Eh in soil solutions were determined as a function of submerging time. During submergence, the Fe and Mn concentration increased, while the SO4 2− concentration decreased. The concentrations of Cd immediately increased in the soil solutions after a short submerging time and then decreased with further submergence. The sequential extraction showed that the exchangeable fraction decreased and the oxide-bound fraction increased after submergence. According to preliminary calculations of the MinteqA2 program, sulfate cannot be reduced to sulfite or sulfide under the soil Eh and pH values observed for the soils after prolonged submergence. Thus, the observed decreases of sulfate concentration may result from sulfate reduction in the micro-environments, which cannot be accounted for by the thermodynamic calculation. The reduction of sulfate to sulfide may subsequently result in the formation of CdS precipitate, which attributes to the decreases of Cd concentrations in the soil solutions after prolonged submergence.

Purpose Biochar amendments can alter phosphorus (P) availability in soils, though the influencing mechanisms are not yet fully understood. This work investigated the adsorption and desorption of P on ferrihydrite (F, a Fe-oxide widely distributed in surface environments) in order to evaluate the interactions between P and Fe-oxide in the absence or presence of biochar (F or ferrihydrite–biochar (F–B) interaction) in soils.

BACKGROUND: Tea plants are always cultivated in acid soils in hilly regions and their growth can be dependent on to soluble aluminium (Al). The mechanism of Al detoxification and the influence of Al on phenolic compounds (i.e. catechin) in the roots of tea plants has remained obscure. This study aimed to investigate the influence of Al changes on the concentrations of phenolic substances in tea plants through hydroponic experiments. RESULTS: Tea plants were cultivated in nutrient solution containing 1.5 and 2.5 mmol L−1 Al, and these treatments enhanced the growth of new buds and roots. Aluminium stimulated the uptake of Ca, Mg, K and Mn, whereas the uptake of Fe, Cu and Zn was retarded. Moreover, total phenol concentrations in tea plant tissues increased with increasing Al concentrations. In general, catechin concentrations in leaves increased with increasing Al concentrations in the hydroponic experiments. High correlation coefficients were obtained between Al and (−)-ECG (r2 = 0.85, P < 0.01) and between Al and total phenols (r2 = 0.92, P < 0.01). CONCLUSIONS: The Al concentration in tea plants indeed increases catechin concentrations and plays an important role in the growth of tea plants. Copyright © 2011 Society of Chemical Industry

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.

Cadmium (Cd)-contaminated soils are of concern because of their possible effects on ecosystems and human health. Millet (Setaria italica (L.) Beauv.) is moderately tolerant to salinity and poor soil fertility as well as pristine soils contaminated with trace elements. It has been hypothesized that low-molecular-weight organic acids (LMWOA) exuded into the rhizosphere may play important roles in Cd uptake by millet. Thus the objectives of this study were to assess the LMWOA exudations of millet in Cd-contaminated soils and to evaluate the capacity of millet to remove Cd for phytoremediation. Millet was grown for 3 weeks in soils containing between 0 and 1,000 mg Cd kg−1. These soils and plant tissues were analyzed for Cd content after harvest. The Cd accumulated in millet tissues was significantly increased with increasing Cd-amended rate. The total LMWOA concentrations in root exudates were significantly correlated with the amount of Cd accumulated in millet shoots and roots. High levels of Cd amendment stimulated secretion of LMWOA, a process capable of reducing Cd toxicity via the formation of Cd-organic complexes (Cd-LMWOA), thereby detoxifying the contaminated soil.

Contents and properties of heavy elements in iron-manganese cutans and the corresponding matrix soils of three subtropical Chinese soils (Fragiudalf, Ferrudalf, and Hapludult) were investigated to discern the effect of soil-forming factors on the enrichment of heavy elements in the iron-manganese cutans with respect to the matrices. Results showed that the contents of clay, organic matter (OM), bases, and heavy metal elements were higher in the cutans than in the matrices. Cutans in the Fragiudalf had a neutral pH and higher content of OM and bases than those in the other soils. The cutans in the Ferrudalf were acidic, with increased contents of Fe and Mn oxides. The cutans in the Hapludult were more acidic and clayey than the cutans in the Fragiudalf and the Ferrudalf. Moreover, the contents of free Fe oxides and ratios of extractable noncrystalline Fe oxide/free Fe oxide (Feo/Fed) in the cutans of the Hapludult were higher than those in the other cutans. Compared with the corresponding matrices, the contents of heavy-metal elements in cutans of Hapludult increased more than those in other iron-manganese cutans. The varimax orthogonal factor rotation of factor analysis was chosen to make the statistical test a good fit to show the elemental distribution between the cutans and their corresponding matrices. The results revealed that Mn oxides played a leading role in the enrichment of most heavy metals for the cutans in the Fragiudalf. In the Ferrudalf, Fe oxides strengthen the migration process of the metals to the cutans. For the cutans in the Hapludult, the influence of Mn oxides on the enrichment of heavy metals decreased, and the impact of clay and Fe oxides increased with respect to the cutans in other soils. The factors that affected the heavy metals were the least for the cutans of the Ferrudalf compared with those in the cutans of the Fragiudalf and the Hapludult. The transport of heavy metals from the matrix soils to iron-manganese cutans in the three soils was mainly influenced by the different soil-forming environments and soil compositions. Statistical analysis indicated that the soil-forming factors that affected the enrichment of heavy metals in the cutans were more prominent in the Ferrudalf than in the Fragiudalf and the Hapludult.

Interactions of toxic Cr(VI) with renewable biomaterials are considered an important pathway for Cr(VI) removal in ecosystems. Biomaterials are susceptible to dissolution, and their dissolved derivatives may provide an alternative to surface-involved pathway for scavenging of Cr(VI). In this study, dissolved organic carbon (DOC) derived from Neurospora crassa biomass was investigated. The proportion of Cr(VI) reduction by DOC to that on biomass was determined to evaluate the importance of DOC to Cr(VI) reduction. A rapid increase in DOC concentration from 145.6 to 193.7 mg L(-1) was observed when N. crassa-biomass was immersed in 0.01 M KCl solution at pH of 1-5, and polysaccharides, peptides, and glycoproteins with carboxyl, amide, and -NH functional groups, are the major compositions of DOC. On reaction of 96.2 microM Cr(VI) with N. crassa-biomass or DOC, it was estimated that DOC contributed approximately 53.8-59.5% of the total Cr(VI) reduction on biomass in the dark. Illumination enhanced Cr(VI) reduction via photo-oxidation of biomass/DOC under aeration conditions, which formed superoxide for Cr(VI) reduction. At pH 1, photoinduced Cr(VI) reduction by DOC proceeded more rapidly than reduction on the biomass surface. However, at pH >3, with a decrease in Cr(VI) reduction by DOC, photon-excited biomass may become an important electron source for Cr(VI) photoreduction.

Todorokite-type manganese oxide octahedral molecular sieves (OMS-1) have been extensively studied due to their potential applications as materials. In this study, a nanofibrous todorokite-type, tun...

Todorokite is one common manganese oxide in soils and sediments and is commonly formed from layered Na-buserite. Aging processes can alter the physicochemical properties of freshly formed Na-buserite in natural environments. However, it is not clear whether and how aging affects the formation of todorokites. In the present paper, Na-buserite with aging treatment was employed to prepare todorokite at atmospheric pressure to investigate the effects of aging treatment of Na-buserite on the formation of todorokite. Four aged Na-buserite samples, which are produced through oxidation of Mn2+ in concentrated NaOH medium by O2 with aging for 3, 6, 9, and 12 months, were employed to investigate the effects of aging processes on the transformation from Na-buserite to todorokite by Mg2+-templating reaction at atmospheric pressure. The manganese oxides were examined using X-ray diffraction (XRD), elemental analysis, determinations of the average manganese oxidation number, infrared spectroscopy (IR), and transmission electron microscopy (TEM). The XRD, IR, and elemental analyses indicate that aging treatment can alter the substructure of the freshly synthesized Na-buserite. During the aging process, some of the Mn(III) may migrate into the interlayer region or disproportionate to form Mn2+ and Mn4+ from the layer of Na-buserite and the concomitant formation of layer vacancies. The interlayer Mn3+ or Mn2+ occupied above or below the layer vacancy sites and become corner-sharing octahedral. XRD analyses and TEM clearly show that the transformation from Na-buserite to todorokite was promoted by aging treatments. The alterations of substructure of aged Na-buserites can promote the rearrangement of manganese to construct a tunnel structure during the transformation from layered manganese oxides to tunnel-structure todorokite at atmospheric pressure. The transformation from Na-buserite to todorokite was promoted by aging treatments at atmospheric pressure, and it is more suitable to explore the origination of natural todorokite in Earth surface environments using aged layered manganese oxides.

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.

Electro-osmotic chemical treatment is an innovative method to improve the strength of soft clays for geotechnical engineering purposes; the effectiveness of the treatment may be related to treatment time, the concentration of the solutions injected, and to variation of pH in the clay. The objective of this study was to investigate the relationship between the above-mentioned factors and the improvement in strength when calcium chloride solution was used as an injection material. A series of tests was carried out by injecting different concentrations of calcium chloride solution into a kaolin suspension, for different treatment times, during electro-osmosis. After the tests, the pH, cone resistance, water content, and concentration of Ca 2+ in the kaolin at different locations were measured and analyzed. The results show that the concentration of Ca 2+ in the kaolin, the pH, and the strength were increased near the cathode with increases in concentration of CaCl 2 and treatment time. An insignificant increase in strength, due to ion exchange over the entire specimen, for short treatment times of 2 to 24 h, was observed because of a small increase in concentration of Ca 2+ and in pH. During long-term treatment (120 h), a considerable increase in concentration of Ca 2+ (137.0 mg/g) and pH (pH = 10) was observed near the cathode. This led to a pozzolanic reaction, which in turn caused a significant increase in the mechanical strength of the kaolin.

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.

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.

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.

Aluminum and iron oxides have been often used in the coagulation processes during water purification due to their unique surface properties toward anions. In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse. In this study, surface properties and molecular structures of Al/Si and Fe/Si coprecipitates were characterized using spectroscopic techniques. Also, the selenite removal efficiency of Al/Si and Fe/Si coprecipitates in relation to their surface and structural properties was investigated. While dissolved silicate increased with increasing pH from Fe/Si coprecipitates, less than 7% of silicate was discernible from Al/Si samples over the range from acidic to alkaline conditions. Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates. In Al/Si coprecipitates, core-shell structures were developed with AlO6/AlO4 domains as the shells and Si frameworks polymerized from the SiO2 as the cores. However, Si framework remained relatively unchanged upon coprecipitation with Fe hydroxides in Fe/Si samples. The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

A liquid fertilizer obtained through food-waste composting can be used for the preparation of a dissolved organic carbon (DOC) solution. In this study, we used the DOC solutions for the remediation of a Zn-contaminated soil (with Zn concentrations up to 992 and 757 mg kg(-1) in topsoil and subsoil, respectively). We then determined the factors that affect Zn removal, such as pH, initial concentration of DOC solution, and washing frequency. Measurements using a Fourier Transform infrared spectrometer (FT-IR) revealed that carboxyl and amide were the major functional groups in the DOC solution obtained from the liquid fertilizer. Two soil washes using 1,500 mg L(-1) DOC solution with a of pH 2.0 at 25°C removed about 43% and 21% of the initial Zn from the topsoil and subsoil, respectively. Following this treatment, the pH of the soil declined from 5.4 to 4.1; organic matter content slightly increased from 6.2 to 6.5%; available ammonium (NH4(+)-N) content increased to 2.4 times the original level; and in the topsoil, the available phosphorus content and the exchangeable potassium content increased by 1.65 and 2.53 times their initial levels, respectively.

Wine processing waste sludge (WPWS) has been shown to be an effective sorbent for the sorption of heavy metals (i.e., chromium and nickel), but the mechanism of removal of hexavalent chromium [Cr(VI)] by WPWS remains obscure. The aims of this study were to determine the effects of temperature, initial concentration of Cr(VI), and particle size on the removal Cr(VI) using WPWS. The characteristics of WPWS were determined, and sorption mechanism studies were also performed. The WPWS used was a deposit mixture containing considerable quantities of chemical coagulation as well as activated sludge precipitation from the settling basins of a wastewater treatment plant. Differential scanning calorimetry (DSC) analysis revealed that the WPWS comprised abundant labile carbohydrates and few aromatic structures. According to the IR spectrum, carboxylic groups were the most important functional group in WPWS, interacting with chromium species by protonation and redox reaction. All kinetic experiments were conducted a...

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.

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).

Wine processing waste sludge (WPWS) has been shown to be an effective sorbent for sorption of some heavy metals (i.e., lead and chromium), but the sorption mechanism of heavy metal by WPWS has rema...

Layered double hydroxides (LDHs) are known as ‘anionic clays’. They comprise a class of material with positively charged octahedral double hydroxyl layers and exchangeable anions. The Li/Al LDH term includes a group of LDHs with Li/Al octahedral double hydroxyl layers. We have demonstrated a modifed method, using Li/Al LDH-OH (OH− as interlayer anions) as the starting material, for preparing Li/Al LDH-X (X represents interlayer anions, including dioctyl sulphosuccinate (DOSS), dodecyl sulphate (DDS), mercaptoacetate (MA), EDTA, Tiron and dichromate) under mild acid conditions (pH in the range 4 to 5). However, in the case of acidsensitive anions, Fe(CN)64−, Li/Al LDH-Fe(CN)64− can be prepared by a two-step procedure using Li/Al LDH-DOSS or similar compounds as intermediates to react with acid-sensitive anions under mild alkaline conditions (pH ≈ 9).

Lithiophorite consists of alternatively stacked MnO 6 octahedral sheets and LiAl 2 (OH) 6 octahedral sheets. Its applications in laboratories and industries have been hindered by sophisticated operation procedures, long reaction time, or impurities existing in the final product. We proposed a fast and simple method, mixing birnessite, aluminate and lithium hydroxide together (designated it as the BAL method) in high alkaline conditions (pH > 13), and treating it hydrothermally at 423 K for 6 hours to prepare pure lithiophorite. A specific reaction between lithium cations and aluminate anions plays as a key role in the BAL method. Due to this specific reaction, Li x Al n (OH) m +z complexed cations can form and penetrate into interlayers of birnessite to replace sodium cations. In high alkaline conditions (pH > 12), Li x Al n (OH) m +z complexed cations become smaller and are soluble. Thus, the higher alkaline Li x Al n (OH) m +z complexed cations can penetrate into interlayers of birnessite at a higher rate. Furthermore, impurities, such as lithium intercalated gibbsite (LIG), aluminum oxyhydroxides and aluminum hydroxides are not stable in high alkaline conditions. Consequently, pure lithiophorite can be easily obtained within 6 hours in high alkaline conditions.

Lithiophorite is a naturally occurring phyllomanganate which has been identified in soils and ores. Studies on a synthetic version have shed light on the conditions required for the formation of lithiophorite. In this study, we successfully prepared lithiophorite under highly alkaline conditions. In addition, we found that Li+, Al3+ and hydrothermal treatment are all necessary for the formation of lithiophorite. Lithiophorite, birnessite and Li-intercalated gibbsite were examined by infrared (IR) spectroscopy. The Mn oxide sheets of lithiophorite and birnessite were found to have quite similar structural environments. On the other hand, the LiAl2(OH)6 sheets are affected more markedly by the Mn oxide sheets. After intercalation, the symmetry of the six interlayer OH groups of LiAl2(OH)6 is reduced and they are divided into two groups occupying different sites, corresponding to the IR absorption bands at 3480 and 3312 cm−1, respectively.

The objectives of this study were to investigate selected physical and chemical properties, and availability of metals in rhizosphere and bulk soils of Tsuga and Yushania of alpine forests. The pH of rhizosphere soils was lower than bulk soils. Mean CEC, organic carbon, carbon/nitrogen (C/N) ratio, and clay contents in rhizosphere soils were greater than in bulk soils Concentrations of exchangeable potassium (K) and magnesium (Mg) were also greater in rhizosphere soils than in bulk soils. The availability of aluminum (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in rhizospheres was influenced by the ionic species and concentrations, which depend on the pH change and chemical compositions of root exudates.

The volcanic ash of the Mount Pinatubo in Philippines was used in this study. The major drawbacks of this ash for growing agricultural crops are nitrogen (N) and iron (Fe) deficiencies with low organic matter contents. The main objective of this study is to investigate the wheat grown on the volcanic ash to and determine the nutrient status across its rhizosphere using a rhizobox system. Either oxamide or polyolefinresin‐coated urea (PORCU) along with potash and phosphate fertilizers was applied to each rhizobox containing the volcanic ash. Plants were grown on the central compartment (CC) of the rhizobox. The nutrient status was examined by the assessment of distribution patterns of NH4 +‐N, NO3 ‐‐N, Ca2+, Mg2+, K+, Cl‐, SO4 2‐, PO4 3‐, and associated pH. Although NH4 +‐N in both oxamide and PORCU treatments was accumulated to a somewhat considerable extent of the rhizosphere. The rhizosphere effect was more prominent in oxamide treatment. While NO3 ‐‐N concentrations in either of the treatment ...

Abiotic transformation of As(III) to As(V) is possible which would decrease As toxicity. This study investigated the potential applications of zero-valent Al (ZVAl) or Al wastes, such as Al beverage cans, for converting As(III) to As(V) in an acidic solution under aerobic conditions. Results showed that As(III) could not be oxidized by ZVAl within 150 min reaction at pH 1 because of the presence of an oxide layer on ZVAl. However, 85 μM As(III) could be completely oxidized with the addition of Fe(II) or POM due to the generation of a Fenton reaction or the enhancement of H2O2 production, respectively, on the ZVAl surfaces. Because Fe(II) or polyoxometalate (POM) exhibited more stable at low pH and scavenged rapidly the H2O2 produced on the aerated ZVAl surfaces, OH radical productions were more efficient and As(III) was rapidly oxidized in the ZVAl/O2 system with theses two catalysts. The catalytic oxidation kinetics of As(III) in the presence of Fe(II) or POM were best described by zero-order reaction, and the rate constants increased with a decrease of pH from 2 to 1. Following the oxidative conversion of As(III) to As(V) in the ZVAl/Fe/O2 system, As(V) was removed by the newly formed hydrous Al/Fe precipitates by increasing the solution pH to 6. Nonetheless, the As(V) removal was incomplete in the ZVAl/POM/O2 system because the hydrolyzed products of POM, e.g., PO 4 3 − , inhibited As(V) removal due to the competitive adsorption of the oxyanion on Al precipitates. Discarded Al-based beverage cans exhibit a higher efficiency for As(III) oxidation and final As removal compared with that of ZVAl, and thus, the potential application of Al beverage cans to scavenge As in solutions is feasible.

Sewage sludge (SS) applied to sloping fields at rates that exceed annual forest nutrient requirements can be a source of phosphorus (P) in runoff. This study investigates the effects of different slopes (18, 27, 36, and 45%) on P in runoff from plots amended with SS (120 Mg ha). Lateritic soil (pH 5.2) was exposed to five simulated rainfalls (90 mm h) on outdoor plots. When sludge was broadcast and mixed with surface soils, the concentrations and loss in runoff of total P in the mixed sample (MTP), total P in the settled sample (STP), total particulate P (TPP), total suspended P (TSP), and total dissolved P (TDP) were highest at 1 or 18 d after application. Initially, pollution risks to surface waters generally increased to different degrees with steeper slopes, and then diminished gradually with dwindling differences between the slopes. The runoff losses coefficient of MTP increased in the order 36 > 45 > 27 > 18%. The initial event (1 and 18 d) accounted for 67.0 to 83.6% of total runoff P losses. Particulate fraction were dominant carriers for P losses, while with the lower slopes there was higher content of P per unit particulate fraction in runoff. Phosphorus losses were greatly affected by the interaction of sludge-soil-runoff and the modification of soil properties induced by sludge amendment. It is recommended to choose lower slopes (

Biosorption, as an effective and low-cost technology treating industrial wastewaters containing Cr(VI), has become a significant concern worldwide. In this work, acid-modified byproducts of beer production (BBP) were used to remove Cr(VI) from aqueous solutions. Removal of Cr(VI) increases as the pH is decreased from 4.0 to 1.5, but the maximum of total Cr removal is obtained in a pH range from 2.0 to 2.5. Nearly 60% of the initial Cr(VI) (100 mg L −1 ) was adsorbed or reduced to Cr(III) within the first 10 min at pH 2.0. The Cr(VI) removal capability of acid-modified BBP materials was almost completely retained after regenerating with acid. FT-IR and XPS spectra revealed that carboxylate and carboxyl groups on the surface of modified BBP materials play a major role in Cr(VI) binding and reduction, whereas amide and other groups play a minor role in the Cr(VI) removal process.

Removal of selenium oxyanions by the binary oxide systems, Al- or Fe-oxides mixed with X-ray noncrystalline SiO(2), was previously not well understood. This study evaluates the adsorption capacity and kinetics of selenium oxyanions by different metal hydroxides onto SiO(2), and uses X-ray absorption spectroscopy (XAS) to assess the interaction between selenium oxyanions and the sorbents at pH 5.0. The binary oxide systems of Al(III)- or Fe(III)-oxides mixed with SiO(2) were prepared, and were characterized for their surface area, point of zero charge (PZC), pH envelopes, X-ray diffraction analysis (XRD), and then macro-scale adsorption isotherm and kinetics of selenite and selenate, micro-scale adsorption XAS. The adsorption capacity of selenite and selenate on Al(III)/SiO(2) is greater than on Fe(III)/SiO(2). Adsorption isothermal and kinetic data of selenium can be well fitted to the Langmuir isotherm and pseudo-second-order kinetic models. Based on simple geometrical constraints, selenite on both the binary oxide systems forms bidentate inner-sphere surface complexes, and selenate on Fe(III)/SiO(2) forms stronger complexes than on Al(III)/SiO(2).

The objective of this study was to provide fundamental knowledge of arsenate sorption on lithium/aluminum layered double hydroxide intercalated by chloride (Li/Al LDH-Cl) and further to reveal the contribution of exposed positive charge surface of Li/Al LDH-CI created by intercalating LiCl into Al(OH)3 layers to arsenate sorption. Therefore, sorption isotherms, envelopes and extended X-ray absorption fine structure (EXAFS) technique were employed to examine the reaction of arsenate on Li/Al LDH-Cl and on gibbsite. Based on an isotherm study, the sorption maximum of Li/Al LDH-Cl for arsenate was approximately six times higher than that of gibbsite. Sorption envelopes of arsenate on Li/Al LDH-Cl displayed a pH-sensitive behavior from pH 4.0 to 7.0, but it was insensitive to pH above pH 7.0, approaching to the pHpzc of Li/Al LDH-Cl (7.22). This transformation with shifted pHs illustrated that there were two types of reaction sites within Li/Al LDH-Cl that participate in arsenate sorption; one is pH-sensitive and the other is not. From EXAFS analysis, arsenate sorbed on Li/Al LDH, reacted not only with Al in the edges of Al-(OH)3 layers, but also with Li located in the vacant octahedral sites within Al(OH)3 layers; however, the decreasing intensity of As(V)-Al shells with increasing pH represented there were fewer As(V)-Al complex existed at higher pH, i.e., the complex between arsenate and Al is pH-sensitive. The superior sorption capability of Li/Al LDH-Cl to that of gibbsite could be attributed to the intercalated Li cations which served as the permanent sorption sites and made the surface of Al(OH)3 have high affinity to arsenate.

The complexation of Fe(II) with organic ligand results in the decrease of redox potential, and enhances the reduction ability of Fe(II). An important example is the use of Fe(II)-organic complexes to accelerate Cr(VI) reduction. Dissolved O(2) and light can potentially affect Cr(VI) reduction; however, these two factors have not been adequately evaluated. A batch technique was used to investigate the Cr(VI) reduction as influenced by the light and dissolved O(2) using N-hydroxyethyl-ethylenediamine-triacetic acid (HEDTA) and Fe(II) solutions. The oxidation of Fe(II) by dissolved O(2) was rapid in the presence of HEDTA at low pH; nonetheless, the oxidation proceeded slowly when HEDTA was absent. Although Cr(VI) could be reduced by free Fe(II) at low pH, the reaction was considerably slower than that of systems involving HEDTA. The enhancement of Cr(VI) reduction by Fe(II) in the presence of high concentrations of HEDTA was achieved as a result of two processes. First, HEDTA acted as a ligand for expediting electron transfer between Fe(II) and Cr(VI). Secondly, HEDTA served as a reductant for Cr(VI) under illumination.

Cr (VI) sorbed more Cr in Cr (VI) in Ca (NO3)2 (0.01 M) electrolytes than in 0.001 M Ca(NO3)2 solution. Nonspecific anions influenced Cr (VI) sorbed by the Taoyuan acid soils in the order: Cl- < ClO4 - < SO4 2-. On the other hand, in the alkaline soils, these three electrolyte solutions showed slight differences in Cr(VI) sorption. In the experiment replacing phosphate by Chromate in the Taoyuan acid soils, the amount of Chromate desorbed by phosphate increased with increasing Cr (VI) concentrations and decrease with increase in equilibration time. However, Cr (VI) desorption was not affected by equilibration time in the alkaline Si-Lo soils.