Search

An incubation test was conducted to study the bioavailability and fractionations of exogenous arsenite [As(3)] during the aging period in three soils originated from different parent materials, including quaternary red clay, purple sandy shale and granite. The results indicated that the exogenous arsenite As(3) were totally transformed into As(V) after 120 d aging. The available As content in soils derived from the three soils generally decreased sequentially throughout the aging period in the order of purple sandy shale, granite and quaternary red clay. The pseudo-second-order model well fitted the change of available As content with aging time (P＜0.05). Soil pH, organic matter (SOM) content and the concentrations of Fe, Al and Mn oxides were the main factors influencing the red soil arsenic in aging, especially, Mn oxides played a more crucial role than Fe and Al oxides in As aging (P＜0.05). Correlation analysis revealed that the non-specially and specially absorbed As constituted the primary forms of available As.

The soil of 0-100 cm depth was collected from the wastewater-irrigated farmland in Zhangshi, Shenyang and was amended with low concentration of arsenic. Microbial-mediated speciation transformation and environmental behavior of arsenic were investigated with and without addition of sulfate. The results showed that without addition of sulfate, arsenate was significantly reduced and released into soil solution after eight days of anaerobic incubation. Above 70% of arsenic presented as arsenite. More arsenic was released from the soil of 20-40 cm depth with arsenite and total arsenicconcentration of 892.8 microg x L(-1) and 1 240.6 microg x L(-1) respectively. Compared with abiotic control, the amount of arsenic dissolved in hydrochloric acid decreased greatly in each layer of soil, moreover, almost all of arsenic was reduced to arsenite. Ferric iron was also significantly reduced to ferrous and released into soil solution simultaneously. The concentration of ferrous iron in soil solution was above 40 mg x L(-1) in solution and was 9.0-13.4 g x kg(-1) in soil solid. Above 50% of the iron dissolved in hydrochloric acid was presented as ferrous. This indicates that microbial reduction leads to reductive dissolution of iron oxides and transformation of mineral configuration in soil solid. The release of arsenic and iron was notably suppressed after addition of 10 mmol x L(-1) sulfate, with the concentration reduced by 50%. The amount of HCl-dissolvable arsenic in soil solid decreased by 50%, compared to the treatment without sulfate addition, which probably due to precipitation of arsenic sulfide. It is obvious that microbial reduction leads to reduction and release of arsenic when sulfate is absent. In the presence of sulfate, microbes may transform mobile arsenic into more stable species. Formation of arsenic sulfide mineral was probably the mechanism for arsenic fixation in soil by microbes.

Two kinds of Fe-Mn oxide impregnated GAC (FM-GAC-1, FM-GAC-2) were prepared and their arsenite removal performance were studied. The adsorption isotherm and reaction kinetic models of arsenite on the two kinds of modified GAC and influence of solution pH, temperature and co-exist anions were investigated in the study. The results showed FM-GAC-1 and FM-GAC-2 can adsorb arsenite effectively, the adsorption capacities were 32.37 mg x g(-1) and 26.67 mg x g(-1) respectively. The adsorb velocity could be predicted well by applying pseudosecond order rate equation and the chemistry reaction process was the limitation of the reaction for both modified GAC. The lower solution pH was benefit to the removal of arsenite. The adsorption capacity of FM-GAC-1 and FM-GAC-2 decreased with temperature increasing. The adsorption processes were spontaneous heat-discharge processes. Some co-exist anions can influence arsenite adsorption on modified GAC when their concentration were 200 times of arsenite. It was found that SiO3(2-), PO3(2-), NO3(-) had a significant negative influence on arsenite removal by FM-GAC-1 and SiO3(2-), CO3(2-) can markedly decrease arsenite adsorption on FM-GAC-2. As a whole, FM-GAC-1 had better arsenite removal performance than FM-GAC-2.

The comparison of calcined Mg-Al layered double hydroxides (Mg-Al CLDH) for adsorption of arsenite and arsenate anions from aqueous solution was investigated by batch method. The results show that Mg-Al CLDH is an effective adsorbent for the removal of arsenite and arsenate anions. The adsorption processes are followed 'memory effect'. When the initial concentration of arsenic is lower than 10 mg x L(-1) for arsenite and 40 mg x L(-1) for arsenate, the equilibrium concentration of arsenic is lower than 10 microg x L(-1). In the range of 4-500 mg x L(-1) for initial arsenic concentration, the maximum adsorption capacity of arsenite and arsenate on Mg-Al CLDH from 298 to 323 K is 150.46-224.03 mg x g(-1) and 149.62-224.76 mg x g(-1), respectively, which are much larger than other adsorbents. But the adsorption capacity is not reached saturation, it is continued to increase significantly. L and H model can be used to describe the adsorption isotherm of arsenite and arsenate, respectively. The adsorption data are corresponded to the Freundlich model for arsenite and Langmuir model for arsenate at lower equilibrium concentration, but corresponded to Freundlich model for arsenite and arsenate at higher equilibrium concentration. Under the same temperature and initial concentration, the adsorption rate and removal rate of arsenate are higher than those of arsenite. And they are increased with temperate but decreased with increase in initial concentration. Adsorption processes follow the pseudo-second-order kinetic model for both arsenite and arsenate. The removal rate is not influenced by the initial pH (3.0-10.0). The adsorption capacity is influenced insignificantly by ionic strength. Arsenate anions are adsorbed firstly from arsenite and arsenate solution on Mg-Al CLDH.

Objective: To study the role of glutathione (GSH), cysteine (Cys), vitamin C (VC) and ferrous ion (Fe2+) in the reduction of arsenate [As (V)] and the characteristic of reduction., Methods: The reaction conditions [(37 degrees C, pH7.0 phosphate buffer) and the concentrations of As (V) (3 micromol/L), GSH (60 mmol/L), Cys (60 mmol/L), VC (0-30 mmol/L) and Fe2+ (0-40 mmol/L)] were simulated in vitro. Arsenite[As(III)] and [As(V)] were determined by the high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS)., Results: The reduction, of As(V) and As(III) formation, increased with the concentration, of GSH (0-60 mmol/L), and reached a maximum values at the concentration of 60 mmol/L GSH, then decreased with the concentration of (60-80 mmol/L) GSH. -SH in sulfhydryl compound, could play an important role in the reduction of As(V), and at the concentration of 60 mmol/L -SH (both GSH and Cys) could reduce 60%, of As(V) to As(III) for 30 min. VC or Fe2+ could not reduce As(V) alone, but when the concentration of VC or Fe2+ reached to 10 mmol/L or 20 mmol/L, they could have a significantly synergistic effect with 60 mmol/L -SH on the reduction of As(V) (P < 0.01)., Conclusion: SH could reduce As(V) alone without any reductase. VC and Fe2+ could have a synergistic effect with -SH on the reduction of As(V).

The effectiveness and mechanism of permanganate enhancing arsenite (As(III)) co-precipitation with ferric chloride is investigated. Effects of parameters such as pH, natural organic matter (NOM) on As removal are studied. Permanganate significantly enhances As(III) removal for ferric co-precipitation (FCP) process. With Fe(III) dosage increasing from 2mg/L to 8mg/L, As removal increased from 41.3% to 75.4% for FCP process; for permanganate oxidation-ferric co-precipitation (POFCP) process, however, corresponsive As removal increased from 61.2% to 99.3% . As removal increased with higher pH for both processes; comparing to FCP process, pH had less effects on As removal for POFCP process; the presence of NOM reduced As removal for FCP process whereas no obvious reduction was observed for POFCP process. Permanganate oxidizing As(III) to As(V) is the main course for enhancing As(III ) removal; furthermore, products of permanganate reduction, hydrous MnO2 (s), also contribute to removing As. POFCP process exhibits good potential of removing As(III ) to assure chemical safety of drinking water.