Search

In order to reveal the occurrence characteristics and speciation transformation of mercury in the sewage treatment plant, the sewage of each process unit in Mai dao sewage treatment plant was taken as the research object, the total mercury (THg), particulate mercury (PHg) and dissolved mercury (DHg) in the samples was determined for 7 consecutive days. The results showed that the THg in influent water was 474.6±148.4ng/L, and had a large daily variance, and that in effluent was 27.8±8.2 ng/L. THg in wastewater was closely related to the degree of organic pollution. PHg accounted for a larger proportion in raw sewage (PHg/THg was 73.5%), and the proportion of DHg increased after treatment. The total removal efficiency of THg was 94.1%, and PHg contributed a lot. The removal of mercury mainly occurred in the secondary biological treatment process.

Landfill refuse is a mixture of inorganic minerals and organic matter that is capable of undergoing complexation and redox reactions due to its active functional groups. Organic matter often combines with minerals in landfill refuse and it remains unclear whether this combination involves electron transfer. Therefore, the effects of landfill refuse composition on reductive dechlorination and speciation transformation of heavy metals were investigated in this study. Results show that landfill refuse comprises protein- and humic-like substances, aliphatic structures, and a large number of hydroxyl, carboxyl, quinoid and other active functional group. The electron donating capacity (0.09–0.26 μmol/g(C)) of landfill refuse was found to be higher than its electron accepting capacity (0.03–0.23 μmol/g(C)), indicating that electron donating groups (hydroxyl) were the main redox-active moieties, facilitating the reductive dechlorination of pentachlorophenol (PCP) by microorganism. Fe2O3, FeO and SiO2 were the main inorganic minerals affecting PCP dechlorination. The speciation distribution of heavy metals in landfill refuse was determined by the BCR sequential extraction method. Results showed that Zn and Ni have high potential migration capacity, poor stability and the highest bioavailability, while Cr, Cu and Pb are relatively stable and have weak migration potential. The oxygen- and nitrogen-containing functional groups, aliphatic structures and aromatic carbon in landfill refuse can promote the transformation of Ni and Cr from an unstable to stable state. Protein-like substances exhibit a strong Cu binding ability, allowing Cu to combine with organic matter more easily than other assessed heavy metals. Both Fe2O3 and FeO affected the stability of Cu. FeO promoted the stabilization of Zn, whereas Fe2O3 and SiO2 promoted Cu instability. These results could provide some references for the treatment of organic chlorides and the stabilization of heavy metals in landfill refuse in China.

Wet flue gas desulfurization (WFGD) system of coal-fired power station can synergistically remove arsenic from flue gas. However, the detailed mechanism of arsenic removal by desulfurization slurry and its further migration and transformation from gas to desulfurization products still remains unclear. In this study, two important factors, the Fe3+ concentration and the pH value, were investigated for their effects on arsenic removal, redistribution and transformation in a lab-scale reactor. The results show low Fe3+ concentration (≤1 mg L-1) in slurry may lead to the decrease of particle size and the increase of Zeta potential of gypsum particles, thus promoting arsenic removal from flue gas, while more Fe3+ (10–500 mg L-1) could reduce its removal due to the increase of mass transfer resistance. Arsenic removal efficiency decreases with pH value rising. The slurry with Fe3+ is easier to remove As(III) from flue gas than As(V) due to the strong polarity of AsCl3(g). Either increasing Fe3+ concentration (pH = 5.5) or rising pH value (Fe3+ concentration = 50 mg L-1) can promote arsenic migration from desulfurization wastewater into gypsum. At any pH value, Fe-gypsum has a stronger ability to adsorb As(V) than As(III). Acid leaching model test indicates the arsenate incorporated into gypsum lattice can reach 12% without Fe3+, but the presence of Fe3+ hinders the arsenate doped into gypsum crystal, which is less than 1%. This raises the potential environmental risk of further utilization of gypsum due to the unstable arsenic speciation. The main arsenates substituting SO42- doped into gypsum lattice are HAsO42- and AsO43-.

The bioleaching experiments of chalcopyrite were conducted with mixed mesophilic culture (30 degrees C), moderately thermophilic culture (45 degrees C) and extremely thermophilic culture (65 degrees C), respectively. During bioleaching, the S/Fe/Cu speciation was analyzed by synchrotron radiation (SR) based X-ray diffraction (XRD) and S, Fe and Cu K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the chalcopyrite dissolution could be significantly promoted by these mixed cultures, and the promotion effects were enhanced with the increase of bioleaching temperature. For all bioleaching tests, the formation of intermediates S, jarosite and secondary minerals (chalcocite, bornite and covellite) was detected, in which the formation of bornite, chalcocite and covellite was just related with redox potential. The formation of bomite could accelerate chalcopyrite dissolution, while the decrease of bioleaching microorganisms could reduce chalcopyrite dissolution. (C) 2017 Elsevier Ltd. All rights reserved.

Sanitary landfill persists as a predominant sludge disposal method in particular in China. In this study, successive subsurface sludge samples (0.3 m deep) were collected from a bioreactor landfill unit where an anaerobic process took place during a 500 d period. The sludge samples were analyzed for total concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) and their species distributions, together with selected sludge chemical properties. In addition, the sludge samples were subjected to phytotoxicity testing. The results showed that the mobilities of Cd and Ni were decreased with landfill time, while the mobilities of Cr, Cu, Pb and Zn remained consistently low over the landfill period. The residual amounts of all these heavy metals were increased with landfill time, suggesting that the anaerobic sanitary landfill is an effective sludge stabilization method to reduce the ecological risk of these heavy metals. The increase in the sludge pH value with landfill time tended to promote the precipitation of heavy metals. Moreover, the sludge stabilization was found to be indicated by the formation of humic substance (HS) and volatilization of volatile matter (VM). The germination index (GI) values of barley (Hordeum vulgare L.) and Chinese cabbage (Brassica rapa chinensis) seeds grown in the 500 d anaerobically stabilized sludge were approximately 5.2- and 4.1-times higher than the values of those grown in the fresh sludge. The final sludge extract did not cause any significant inhibitory effect on the germination of the two types of seeds.

Aerobic composting has been used for a long time for bioconversion of manure wastes, however, its application has been limited due to slow transition of organic matters and influence of heavy metals and antibiotics residues. Compost with lime addition can speed up the composting process, while its effects on the evolution of organic matters, heavy metals and antibiotics need to be further investigated. In this research, the effects of lime amendment on organic substances changes was assessed by the spectroscopic characteristics. Besides, chlortetracycline (CTC) removal and Cu, Zn chemical speciation transformation were also evaluated. Results showed that the humic acid-like substances region of fluorescence regional integration (FRI-EEM) increased from 20.5% to 40.9% and 20.6%–32.6%, respectively, in lime addition treatment and control after 15 days of composting, indicating that the addition of lime remarkably improved the transition of organic matter and accelerated the maturity process. Besides, 94.04% of CTC in the manure was removed when lime was added, higher than 86.10% in the control group. The transformation of zinc from exchangeable and reducible into oxidizable and residual fractions was improved while the transformation of copper was affected slightly. Therefore, lime is a suitable amendment material for manure composting, which can accelerate the transition of organic matters due to the regulation of composting pH, as well as eliminate harmful CTC and bioavailable heavy metal, thus promoting the further utilizing of organic substance.

In this work, palygorskite was used to immobilize Pb using a sorption-calcination method. The speciation transformation of Pb during the process was characterized using surface complexation modeling (SCM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), 27Al and 29Si solid state nuclear magnetic resonance (NMR) spectroscopy and field emission scanning electron microscopy (FESEM). Results showed that Pb was adsorbed at permanently charged sites in the form of outer-sphere surface complexes at pH

The mobility of plutonium (Pu) in groundwater is dependent of its speciation distribution and transformation. The speciation and transformation kinetics of Pu(IV) and its colloids in highly saline groundwater have, however, been rarely studied. In the present study, groundwater (Ionic strength 1 M) from Dunhuang region, NW China, was collected for investigating the speciation, transformation kinetics and fate of spiked Pu (IV) with aging time. The results showed that ~99% of the spiked Pu (IV) (over initial concentration c0 range 2.5 × 10−10–7.8 × 10−7 mol·L−1) was easily associated with the natural colloids and transformed into relatively unstable Pu pseudo-colloids in 1 day, which then gradually deposited and/or adsorbed on the container walls with aging. The suspended Pu pseudo-colloids decreased in similar exponential models, with rate equations r(t) = −3.1 × 10−10e– t/4 and −1.3 × 10−8e–/3 for c0 = 1.25 × 10−9 mol·L−1and 4.17 × 10−8 mol·L−1, respectively. The chemical speciation of the suspended colloidal Pu was dominated by “Fe/Mn Oxides” at the early time, while “Carbonates” with slower depositing rate (r(t) = −6.9 × 10−12e– 0.149t) dominated it (~82%) at equilibrium state. Whatever the c0 was, the concentration of dissolved Pu (i.e., the apparent solubility of Pu) kept at 0.7 × 10−11 mol·L−1 over aging. The valence of dissolved Pu was dominated by Pu(IV) at early time, while Pu(V + VI) would become dominant (~95%) at equilibrium state with transformation rate of r(t) = −92.9e– t/16.6 + 96.9. The equilibrium times of Pu deposition (and/or adsorption), speciation transformation of the suspended colloidal Pu, and valence change of the dissolved Pu were 30 d, 80 d and 120 d, respectively. The kinetic process for each Pu species could be well fitted with exponential model. These results suggest that the majority of released Pu(IV) into highly saline groundwater will be easily associated with natural aquatic colloids and then become immobile in short time due to deposition (and/or adsorption) onto the environmental medium, but potential migration risk caused by stable suspended Pu colloids cannot be ignored.

In this study, polymetal(iod)s-contaminated mining soil from the Huainan coalfield, Anhui, China, was used to investigate the synergistic effects of biochar (BC), raw coal (RC), and hydrothermally treated coal (HTC) on the immobilization, speciation, transformation, and accumulation of Cd, Cr, and Pb in a soil-plant system via geochemical speciation and advanced spectroscopic approaches. The results revealed that the BC-2% and BC-HTC amendments were more effective than the individual RC, and/or HTC amendments to reduce ethylene-diamine-tetraacetic acid (EDTA)-extractable Cd, Cr, and Pb concentrations by elevating soil pH and soil organic carbon content. Soil pH increased by 1.5 and 2.5 units after BC-2% and BC-HTC amendments, respectively, which reduced EDTA-extractable Cd, Cr, and Pb to more stabilized forms. Metal speciation and X-ray photoelectron spectroscopy analyses suggested that the BC-HTC amendment stimulated the transformation of reactive Cd, Cr, and Pb (exchangeable and carbonate-bound) states to less reachable (oxide and residual) states to decrease the toxicity of these heavy metals. Fourier transform infrared spectroscopy and X-ray diffraction analyses suggested that reduction and adsorption by soil colloids may be involved in the mechanism of Cd(II), Cr(VI), and Pb(II) immobilization via hydroxyl, carbonyl, carboxyl, and amide groups in the BC and HTC. Additionally, the BC-2% and BC-HTC amendments reduced Cd and Pb accumulation in maize shoots, which could mainly be ascribed to the reduction of EDTA-extractable heavy metals in the soil and more functional groups in the roots, thus inhibiting metal ion translocation by providing the electrons necessary for immobilization, compared to those in roots grown in the unamended soil. Therefore, the combined application of BC and HTC was more effective than the individual application of these amendments to minimize the leaching, availability, and exchangeable states of Cd, Cr, and Pb in polymetal(iod)s-contaminated mining soil and accumulation in maize.

The control and characterization of microbial extracellular electron transfer (EET) reaction-mediated soil arsenic mobilization is still not well understood, which has limited the application of biotechnologies for the remediation of contaminated wastes. In this study, we developed an improved soil bioelectrochemical system (BES) that can decrease the dissolution of As-bearing Fe/Al oxides from anoxic submerged soil by more than 80 % under the application of a 0.9 V external voltage. Combining the results of chemical property and microbial characteristic analyses indicated that an applied voltage was accompanied by a dramatic increase in acetate oxidization and soil substrate bioavailability, facilitating electron transfer reactions for methanogenesis, whereas the applied voltage exhibited a negative effect on microbial EET activities for As/Fe reduction. Subsequently, an additional dual-chamber configuration was employed for comparison and to study the effect of bacteria-electrode interactions on arsenic mobilization; we found that the bioanode and biocathode had reverse effects on the release of As/Fe, suggesting a correlation between the disparate microbial communities and EET-mediated reaction mechanisms on the electrodes. Overall, this study is vital to expand the knowledge of the intimate links between arsenic speciation transformation and microbial electron transport system activity, improve our understanding of BES operation and move towards its application.

The release of arsenic (As) during municipal solid waste (MSW) incineration results in a new sources of anthropogenic arsenic contamination. Arsenic toxicity depends not only on the quantity but also on its speciation. At high temperatures, arsenic is predominantly present as vapors (As 2 O 3 (g)) and its speciation transformation is determined by the interactions between As 2 O 3 (g) and inorganic compounds. In this study, synchrotron X-ray absorption near-edge structure (XANES) was used to investigate the speciation transformation of arsenic during MSW combustion and flue gas cooling process. However, arsenates in various forms are hardly distinguished by using XANES alone. Considering that various arsenates are of different thermal stability, the thermal stability of arsenic in MSW incineration fly ash was examined to provide detailed information regarding arsenic speciation in the ash samples. To further understand the relationships between arsenic and inorganic compounds, the sequential extraction procedures of arsenic in the ash were conducted. The results show that the oxidation of As 2 O 3 (g) during MSW combustion is incomplete and is continuously performed in flue gas cooling process. The physical adsorption of As 2 O 3 (g) is favored at low temperature by ash particles, especially by the injection of CaO in the flue gas. Various kinds of arsenates are formed due to the interactions between As 2 O 3 (g) and Ca, Fe and/or Al compounds. Some of the arsenates are thermally unstable and are decomposed when the fly ash was heated at 1323 K. Part of arsenic is stabilized in the ash matrix including some un-oxidized As(III) which remained stable even when the ash was heated at 1323 K.

Antimony (Sb) is not an essential element for humans and plants although it can be used to treat some human diseases, such as schistosomiasis. Sb contamination has been documented in many regions around the world, particularly in China. The Sb contamination in the environment often stems from anthropogenic activities such as mining, smelting, and shooting. Within the latest decade, great progress has been made in research examining the physiochemical behavior of Sb in the environment, including 1) the extent of Sb pollution around the world particularly in China; 2) the mechanisms and factors influencing Sb migration in soils, especially the adsorption/desorption of Sb by minerals or organic materials; 3) the transformations influencing speciation catalyzed by soil microbes; 4) to a lesser extent, the toxicity of Sb to plants and soil animals. In this review, we highlighted the current knowledge with respect to 1) how soil physicochemical properties (including water regimes, pH, organic materials and Eh), and soil organisms will affect the soil bioavailability of Sb, and subsequently the uptake of Sb by plants; 2) the uptake pathway of antimonite and antimonate, the translocation of Sb from roots to shoots, and the redistribution and toxicity of Sb in plants.

To better understand migration of K and Cl caused by interaction of KCl with organics, KCl-loaded model compounds (cellulose, xylan, lignin and pectin) were pyrolyzed within 300–800 °C using a fixed-bed apparatus. The amounts of different chemical occurrences of K and Cl in chars were quantitatively determined by sequential chemical fraction analysis combined with ICP-OES and IC. Morphologies and occurrence modes of Cl and K were further examined via XPS and SEM-EDS. Big differences in K and Cl migration were observed among four samples, and the distinction was closely related to types of organic functional groups. At temperature of below 500 °C, a low proportion of K was released from four samples, while amounts of water-soluble K was transformed into organically-bounded form via different ion-exchange reaction mechanisms, thereby promoting Cl release. About 46.93–53.31% and 32.47–41.75% of organic-K, presumably formed by reaction of KCl and methoxyls, were detected in lignin and pectin chars, apparently higher than that in xylan and cellulose chars. At the same time, amounts (71.98–81.83%) of Cl was released from doped pectin, followed sequentially by lignin (35.12–52.34%), cellulose (18.56–35.68%), and xylan (10.67–18.65%). Part of released Cl was recaptured by active carbon sites, thereby forming organochlorine, and C-Cl generation followed a sequence of lignin > xylan > cellulose > pectin. As pyrolysis proceeded, cellulose exhibited highest K release due to decomposition of organic-K, while a considerable of char-K with high thermal stability still retained in other samples. Mechanism on migration of K and Cl caused by reaction of KCl with organics was proposed.

The recovery of rare earth elements (REEs) from coal ash has gained growing attention as a promising resource recovery strategy. Compared to extensive studies on REE occurrence in coal and coal ash, few studies have investigated REE behaviors during coal combustion processes. This study investigated the mineralogy, oxidation state, and structure changes of twelve representative REE-bearing phases during heating up to 1500 °C using complementary thermal analysis, in-situ X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray absorption spectroscopy (XAS), in order to better understand and predict REE behaviors during coal combustion processes. It was found that: (1) REE-lignin and REE-chitosan complexes, hydrated Y2(CO3)3 and Ce2(CO3)3, bastnasite, and REE-doped calcite transformed to corresponding oxides after heating, accompanied by Ce(III) oxidation; (2) hydrated YPO4 and CePO4 formed corresponding anhydrous REE phosphates after heating with no evident Ce(III) oxidation; and (3) apatite, monazite, xenotime, and zircon barely altered during heating, although Ce(III) in apatite was partially oxidized and Y local structure became more disordered in apatite, monazite, and zircon. These results are consistent with previous studies on REE speciation in coal and coal ash and provided an in-depth understanding on REE behaviors during coal combustion, including mineral transformations and retention of REE-bearing phases. XAS analysis revealed that due to the co-existence of different REEs, mineralogical changes, and local structural distortion of REE-bearing phases during combustion, quantification of REE speciation in coal ash using XAS should be interpreted with caution and cross-validated by other techniques.

Differential utilization of isomers pyrite and marcasite by Acidianus manzaensis were comparatively studied, besides the iron and sulfur speciation transformation of the minerals was also investigated based on synchrotron radiation X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the biooxidation of pyrite was faster than marcasite. The bioleached surface of both pyrite and marcasite are serious corroded, and the Fe (III)-containing species as well as jarosite were gradually produced, and more elemental sulfur species were formed on the marcasite surface than that for pyrite. It demonstrates the mineral structure does affect the biooxidation of pyrite and marcasite, and the more precipitated elemental sulfur might be one of the reasons leading to lower oxidation rate of marcasite by A. manzaensis.

The utilization and speciation transformation of alpha-S-8 and mu-S by the typical mesophilic acidophilic strain Acidithiobacillus ferrooxidans ATCC 23270 were investigated. A. ferrooxidans cells first acclimated to the energy source alpha-S-8 or mu-S, respectively. The results of cell growth and sulfur oxidation behavior showed that the strain grown on alpha-S-8 entered slowly (about 1 d later) into the exponential phase, while grew faster in the exponential phase and attained higher maximal cell density and lower pH value than that on mu-S. After bio-corrosion, both of the two sulfur samples were evidently eroded and modified by A. ferrooxidans cells. After growth of A. ferrooxidans, the surface composition of amorphous mu-S became 63.1% mu-S and 36.9% alpha-S-8, and that of orthorhombic alpha-S-8 became 68.3% alpha-S-8 and 31.7% mu-S, while the surface compositions of alpha-S-8 and mu-S in sterile experiment were not changed, indicating that these two elemental sulfur species can be interconverted by A. ferrooxidans.

Metal species in rhizosphere soil profoundly influence their mobility and phytoavailability. Clarifying the speciation transformation of heavy metals helps understand their translocation and accumulation in plants. Single extraction, selective sequential extraction (SSE) and X-ray absorption near-edge structure (XANES) spectroscopy were employed to investigate the speciation transformation of lead (Pb) and its influence on metal accumulation in tea plants after the addition of tea polyphenols (TPs). Pb content was decreased in young leaves and stems, whereas increased in roots, after TPs were amended to soil. Both SSE and XANES analysis suggested bioavailable Pb was transformed to organically bound Pb after the addition of TPs. The increased percentage of organically bound Pb might be fixed in the cell wall of plant root through a ternary complex formed between the Pb-organic matter complex and cell wall components. Therefore, Pb translocation from roots to young tissues was decreased. Pb phytoavailability change was driven by its speciation transformation after the addition of TPs. Combined SSE and XANES spectroscopy represent powerful tools to study metal speciation transformation in plant and soil systems.

During the last few decades, considerable research efforts have been extended to identify more effective remediation treatment technologies to lower the (129)I concentrations to below federal drinking water standards at the Hanford Site (Richland, USA). Few studies have taken iodate into consideration, though recently iodate, instead of iodide, was identified as the major species in the groundwater of 200-West Area within the Hanford Site. The objective of this study was thus to quantify and understand aqueous radioiodine species transformations and uptake by three sediments collected from the semi-arid, carbonate-rich environment of the Hanford subsurface. All three sediments reduced iodate (IO3(-)) to iodide (I(-)), but the loamy-sand sediment reduced more IO3(-) (100% reduced within 7 days) than the two sand-textured sediments (∼20% reduced after 28 days). No dissolved organo-iodine species were observed in any of these studies. Iodate uptake Kd values ([Isolid]/[Iaq]; 0.8-7.6 L/kg) were consistently and appreciably greater than iodide Kd values (0-5.6 L/kg). Furthermore, desorption Kd values (11.9-29.8 L/kg) for both iodate and iodide were consistently and appreciably greater than uptake Kd values (0-7.6 L/kg). Major fractions of iodine associated with the sediments were unexpectedly strongly bound, such that only 0.4-6.6 % of the total sedimentary iodine could be exchanged from the surface with KCl solution, and 0-1.2% was associated with Fe or Mn oxides (weak NH2HCl/HNO3 extractable fraction). Iodine incorporated into calcite accounted for 2.9-39.4% of the total sedimentary iodine, whereas organic carbon (OC) is likely responsible for the residual iodine (57.1-90.6%) in sediments. The OC, even at low concentrations, appeared to be controlling iodine binding to the sediments, as it was found that the greater the OC concentrations in the sediments, the greater the values of uptake Kd, desorption Kd, and the greater residual iodine concentrations (non-exchangeable, non-calcite-incorporated and non-Mn, Fe-oxide associated). This finding is of particular interest because it suggests that even very low OC concentrations

In this review, we summarized the uptake, translocation and metabolism mechanisms of selenium (Se) in plants. Water-soluble Se, including selenate, selenite and some organic selenium, was the predominant form taken up by plants. The active uptake of selenate in plant could be mediated by high affinity sulfate transporters. The mechanism of selenite uptake was not well understood, however, recent studies suggested that selenite uptake was probably mediated by Pi transporters. The translocation of Se from root to shoot was dependent on the form of Se supplied. The selenate taken up by plants was readily translocated to the shoots and reduced to selenite in leaves, then converted to organic Se compound. By contrast, most of the selenite taken up by plants in the roots and only a small fraction was translocated to the shoots. Se could be assimilated to seleno amino acids or selenoprotein after plant uptake, and then involved in the metabolism of plants.

The sulfur utilization and speciation transformation of two elemental sulfur species (orthorhombic alpha-S-8 and amorphous mu-S) by thermoacidophilic Archaea strain Acidianus manzaensis YN-25 was comparatively studied. The results of cell growth and sulfur oxidation behavior showed that A. manzaensis cultured on mu-S grew faster (about 24h earlier to reach stationary phase than that on alpha-S-8) and produced more H+ and SO42-. Results of scanning electron microscopy indicated that the surfaces of mu-S and alpha-S-8 were differently bio-corroded by A. manzaensis into loose porosities and pits, respectively. Fourier transform-infrared spectroscopy analysis indicated both mu-S and alpha-S-8 were adsorbed by the cells. X-ray diffraction and Raman spectra analysis indicated that mu-S was mostly converted into alpha-S-8 after A. manzaensis cell growth while alpha-S-8 was not transformed into a different allotrope. The fitted result of sulfur K edge XANES spectra further showed that the mu-S after growth of A. manzaensis were composed of 92.1% alpha-S-8 and 7.9% mu-S, while no change in composition for alpha-S-8 was found. (C) 2013 Elsevier Ltd. All rights reserved.

Pure nano-Al-13 and aggregates at various concentrations were prepared to examine their stability and potential role in coagulation processes and natural systems. Alkalinity titration experiments showed that the hydrolysis of Al-13 solutions exhibits significant difference from that of the normal Al(III) solutions. The transition OH/Al ratio (pH points) shifts from normal 2.5 to higher values (similar to 2.9). No significant structural rearrangement takes place during Al-13 aggregation. The aggregates exhibit stability during short aging up to 1 month. The Al-b species obtained by Ferron assay in the initial aging period no longer corresponds to Al-13. The aggregates disappear quickly in Al-27-NMR detection with increasing B value (OH/AI ratio) maintaining efficient Ferron reactivity. This shows that the Al-b in Ferron assay corresponds with Al-13 only under certain conditions. (C) 2012 Elsevier B.V. All rights reserved.

Arsenic (As) speciation transformation often accompanies adsorption-desorption when exogenous arsenide is poured into soil. Disregarding the speciation transformation when evaluating adsorption-desorption of As can greatly influence the experimental results. In this study, batch experiments were conducted, and the results in dicated that exogenous monomethylarsonic acid (MMA) or dimethylarsinic acid (DMA) added to fluvo-aquic soil collected from agricultural area in Beijing of China, was completely converted into As(V) after cultivated for 60 or 90 days. However, when exogenous As(V) was added to the soil, no speciation transformation of As(V) was observed. Furthermore, although the total As concentration, which was 6.55 or 11.55 mg/kg in aqueous extracts of the soil to which MMA or DMA had been added, respectively, remained stable after cultivated for 30 or 60 days, the As speciation transformation of MMA or DMA into As(V) in soil still occurred. Differences in As speciation can result in different fates and behaviors of As in soil, and As speciation transformation should be taken into ac count when evaluating the adsorption-desorption of As.

Sulfur speciation transformation during bioleaching of pyrite-containing sphalerite concentrate by thermophile Sulfolobus metallicus (S. metallicus) at 65 A degrees C was investigated by X-ray diffraction (XRD), diffuse reflectance Fourier transform infrared spectroscopy (FT-IR) and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). The results show that the presence of S. metallicus effectively enhances the dissolution of the mineral. The yield of zinc increases from 0.5 g/L in sterile control to 2.7 g/L in bioleaching. The pyrite in the concentrate facilitates zinc dissolution in the early stage, but has hindrance role in the late stage for the formation of jarosite. Sulfur speciation analyses show that jarosite and elemental sulfur are main products in bioleaching process, and the accumulation of jarosite is mainly responsible for the decline of leaching efficiency.

This paper presents a systematic study of the biometric leaching sequencing batch experiment. The major process parameters include the inoculation amount of bacteria(5%) and substrate concentration(4g/L)(elemental sulfur). The chemical speciation transformation takes place in Biology leaching were measured by sequential extraction techniques. Through which before and after the leaching we can Analyze the filter mechanism and leaching ability. According to Cd, Pb content of each chemical speciation before and after the leaching, the release rules of different chemical speciation for each elements in every sampling period were calculated. This paper also analyzed the leaching ability of different chemical speciation in different leaching condition. The results indicated that,Cd drains out through the indirect mechanism, Pb drainings is mainly completes by direct machine-made and the indirect mechanism combined action.

Phosphorus (P) speciation, burial, and transformation are poorly constrained under low-oxygen conditions. Sequential chemical extraction techniques, in-situ incubation, and laboratory incubation were employed to explore P cycling in the low-oxygen area of coastal Rushan. The study determined that the total P concentrations in the coastal area of Rushan Bay were higher than those of other China shelf seas, and largely affected by anthropogenic activities. The phosphate (DRP) fluxes in the study area calculated using an incubation method (0–1960 μmol m − 2 day − 1 ) and measured based on pore water gradients (1.5–50.4 μmol m − 2 day − 1 ) were both highly correlated with oxygen conditions. Sediment incubations showed that DRP diffusion from the sediment mainly originates from Fe–P and Auth-P dissolution and that Org-P recycling contributed only a small portion of the total released P pool. The benthic phosphate flux can be 60 times higher under low bottom-water oxygen levels of 63–150 μmol L − 1 than under oxygen levels exceeding 150 μmol L − 1 in the study area. The P accumulation rates and burial efficiencies in this study area ranged from 16.5–33.3 μmol cm − 2 year − 1 and 81.1–83.4%, respectively, and were regulated by the oxygen level and diffusive DRP flux. This study indicates that low oxygen levels between 63 and 150 μmol significantly govern P transformation and preservation in the sediment and P pools in the water column.

The speciation transformation of elemental sulfur mediated by the leaching bacterium Acidithiobacillus ferrooxidans was investigated using an integrated approach including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and X-ray absorption near edge spectroscopy (XANES). Our results showed that when grown on elemental sulfur powder, At. ferrooxidans ATCC23270 cells were first attached to sulfur particles and modified the surface sulfur with some amphiphilic compounds. In addition, part of the elemental sulfur powder might be converted to polysulfides. Furthermore, sulfur globules were accumulated inside the cells. XANES spectra of these cells suggested that these globules consisted of elemental sulfur bound to thiol groups of protein.

Flocculation of kaolin suspension with aluminium fractal polycations was investigated as a function of aluminium concentration and pH. Aluminium flocculants included Al(13) and Al(13) aggregates with OH/Al ratio of 2.6 and 2.8, respectively. The flocculation kinetics and floc size distribution were monitored by light scattering. The characterization of flocculants showed that the tridecatmer Al(13) and bridged [Al(13)](n) with out-sphere structure were the dominant species for all flocculants in a wide pH range. The coagulation results indicated that the pre and in situ-formed [Al(13)](n) play a key role in removing particles. With the increasing concentration of [Al(13)](n), coagulation mechanisms were transformed from charge-neutralization, electro-patch coagulation to bridge-aggregation. Moreover, sweep-flocculation was involved at higher dosage besides other three mechanisms when amorphous aluminium oxides formed. Hence, chemical interaction between particles and flocculants evolved from surface adsorption to surface precipitation for aluminium polycations by virtue of species transformation.

The biogeochemical cycle of sulfur can directly affect the speciation transformation of heavy metals in soils and their accumulation in plants. The toxicity of heavy metals in plants can be alleviated by their complexation with sulfur compounds like phytochelatins or metallothiones, consisting of the major mechanisms of phytodetoxification. Sulfur deficiency is becoming one of the limiting factors that influence Chinese agricultural production. Although the applications of sulfur fertilizer in soil have received much attention in recent years, the interaction mechanism of heavy metal with sulfur metabolism has not been studied extensively. In this paper, we reviewed current research advance on the impact of sulfur on the speciation transformation of soil heavy metals and their accumulation in plants, discussed the effect of sulfur on the detoxification mechanism of heavy metal in plants and provided further research prospective in this field.

Nutrient delivery to the Belgian coastal zone is to a great extent through the Scheldt estuary. We have measured the phosphate (PO4), poly-phosphate (poly-P), dissolved organic phosphorus (DOP), particulate inorganic phosphorus (PIP) and particulate organic phosphorus (POP) concentrations at the freshwater tidal limits of the Scheldt estuary, along the salinity gradient and in the coastal zone during one year. In addition, nitrate (NO3), nitrite (NO2), ammonium (NH4), dissolved organic nitrogen (DON) and particulate nitrogen (PN) were determined in the freshwater Scheldt sub-basin and NO3, NO2 and NH4 in the Rupel sub-basin, the Scheldt estuary and the coastal zone. The behaviour of each P species along the continuum from the freshwater tidal limits to the coastal zone is discussed. Phosphorus (P) and nitrogen (N) budgets were made for the Scheldt sub-basin during the productive period (May–September). The main P and N transformation processes were identified as PO4 sorption, algal uptake and nitrification. Retention of P and N in the entire freshwater tidal area was estimated. In the brackish part of the estuary, there was no net source or sink of dissolved inorganic nitrogen (DIN). Desorption of PO4 was the most important transformation process for P along the salinity gradient. The PO4 pool increased and the PIP pool decreased, while total P behaved conservatively. Mass balance calculations show that the transformation of particulate P to PO4 enhances the PO4 flux from the Scheldt to the coastal zone.

On the basis of the heavy metal (Cd, As, Pb, Zn, Cu, Cr, and Ni) control problem during the thermochemical recovery of phosphorus (P) from sewage sludge (SS), P-enriched sewage sludge ash (PSSA) was calcined at 1100 °C. The effect of organic chlorinating agent (PVC) and inorganic chlorinating agent (MgCl2) on the fixed rate of P removal and the speciation transformation of heavy metal was studied. The removal of heavy metals Cd, Pb, As, Zn, and Cr exhibited an increasing tendency with the addition of chlorinating agent (PVC). However, an obvious peak under 100 g Cl/kg of PSSA appeared for Cu, owing to the presence of carbon and hydrogen in PVC. MgCl2 was found to be more effective than PVC in the removal of most heavy metals, such that up to 98.9% of Cu and 97.3% of Zn was effectively removed. Analyses of heavy metal forms showed that Pb and Zn occurred in the residue fraction after calcination. Meanwhile, the residue fraction of Cr, Ni, Cd, and Cu exhibited a decreasing tendency with the increase in the added chlorinating agent (MgCl2). Losses of P from PSSA were around 16.6% without the addition of chlorinating agent, which were greatly reduced to around 7.7% (PVC) and to only 1.7% (MgCl2).

The speciation transformation, influencing factors, as well as bioavailability of mercury (Hg) in soil of the water-level-fluctuating zone in the Three Gorges Reservoir Area were simulated. The results showed that Hg in soil under alternative dry-wet condition could be transformed and released. The total Hg content in the soil was decreased by 28.9% after two "wet-dry" cycles. The percentages of the six Hg species (water-soluble, exchangeable, carbonate-bound, humics-bound, organic-sulf and residual Hg) were 6.1%-16.8%, 5.8% -12.9%, 4.5%-17.7%, 12.5%-29.9%, 5.3%-12.8%, and 34.5%-51.6%, respectively. It was found that Hg in soils was dominantly residue Hg, whose percentage tended to decrease under alternative dry-wet condition. The percentage of humics-bound Hg increased gradually and an increase of the percentage of bioavailable Hg (including water-soluble, exchangeable, carbonate-bound, and humics-bound Hg) after two wet-dry cycles were observed. Bioavailable Hg could be easily absorbed by aquatic organisms to enter the food chain, which might increase the ecological risk of Hg in the reservoir.