Papers by Keyword: Arsenic

Abstract: At present, arsenic content in copper concentrates is increasing, which leads to an increase in its content in all smelting products, the largest amount of arsenic is transferred in fine dust (dust composition,%: 10-12 Zn, 11-13 Pb, 8-15 Cu , 12-14 Fe, 5-10 As). Autoclaved leaching of dusts (temperature 160-200 °C, oxygen pressure 0.4-0.8 MPa, molar ratio H₂SO₄ /(Cu + Zn) = 0.75-2.25) to obtain a copper-zinc solution and a cake containing arsenic, iron and lead was studied. Copper extraction in the solution reaches 92%, zinc 95%. Lead, arsenic and iron are concentrated in the cake. Lead from cake is extracted by leaching in sodium chloride solution (temperature 60-70 ° C, NaCl concentration 300 g / dm³). The extraction of lead into the solution is 95%, subsequently lead is precipitated as lead carbonate.

Abstract: The efficiency of iron oxy-hydrate application for cleaning aqueous media from arsenic has been studied. It is proposed to precipitate the active layer to a coarse-grained carrier to improve filterability. Metallurgical alumina and quartz sand are considered as carrier materials. Conditions for the synthesis of inorganic sorbent based on iron oxy-hydrate are established. The dependence of the sorbent capacity on the pH of the solution is determined. IR spectra of the sorbent before and after sorption of arsenic are given, and the mechanism of sorption of arsenic is proposed. The data on the capacity of the obtained sorbent modifications for the sorption of As (III) ions under static conditions are presented.

Abstract: The efficiency of application of various iron compounds for purification of aqueous media from arsenic has been studied. It is proposed to apply the active layer to a substrate of a coarser material to improve the filterability. Alumina, quartz, and crystalline sulfur are considered as carrier materials. The conditions of inorganic sorbent synthesis based on iron oxyhydrate (IOH) are determined. Effect on sorbent capacity for As (V) of the concentration of iron and sodium sulfate in the solution at the modification of alumina is determined. The results of X-ray phase analysis and scanning electron microscopy are presented. The data on the capacity of the obtained sorbent modifications for the sorption of As (V) ions under static conditions are presented. The dependence of the capacity of the sorbent for As (V) on the method of synthesis of IOH and the type of carrier is established. It is shown that the sorbent on the basis of SiO₂ possesses maximum capacity.

Abstract: Arsenic is an abundant element associated with a wide range of minerals and a major contaminant in metallurgical wastewater. For the immobilization of arsenic, iron arsenate in the very stable mineral scorodite (FeAsO₄ 2H₂O) is the preferred route. Microorganisms of the natural iron cycle living at pH below 2 and high temperatures can conduct the oxidation of ferrous iron with oxygen, which is not feasible chemically at these extreme conditions. Remarkably, at similar acidic conditions and high temperature these microorganisms can also carry out the oxidation of arsenite (As(III)) to arsenate (As(V)). Using these intrinsic features of the microorganisms, we have investigated the role of a thermoacidophilic mixed culture in the oxidation of As(III) and precipitation of (As(V) in the form of scorodite from a synthetic wastewater containing 6.7mM of As(III) and 0.5%Wt pyrite as main iron Fe(II) source. The results indicate that As(III) was completely oxidized from the synthetic wastewater in the presence of pyrite and scorodite was formed only in presence of the mixed culture at a Fe/As:1.3. This is a combination of biological oxidation and biocrystallisation accomplished to the presence of pyrite not only as the main energy source for the microorganisms, but as catalyst in the As(III) oxidation reaction.

Abstract: Rhodococcus erythropolis S43 is an actinobacterium isolated from an arsenic-contaminated soil sample, collected from an old smelter site, including an arsenic smelter, in Germany. This strain has unique features as compared to the other members of the species, namely resistance to elevated concentrations of arsenic. Here, we present the microbiological features and genomic properties of this biotechnologically relevant strain. The 6,812,940 bp draft genome is arranged into 264 scaffolds of 848 contigs. It possesses 62.5% of CG content and comprises 6,040 coding sequences and 49 tRNA genes. Bioinformatic genome analysis showed the presence of arsenic-resistance genes. A complete ars operon was found containing the arsACDR cluster coding for ArsA (efflux pump ATPase), ArsC (arsenate reductase), ArsD (chaperone) and ArsR (ars operon regulator). Our results show that the arsC mRNA level significantly increased in response to arsenite and arsenate exposure, suggesting its involvement in the arsenic resistance phenotype of strain S43. In addition, this strain showed to have a plethora of genes coding for proteins involved in oxidative-stress response, including catalase, super-oxide dismutase, glutathione peroxidase-related genes, thioredoxin and thioredoxin reductase, suggesting it is highly tolerant to oxidative conditions. Finally, genes for radiation resistance, biodesulfurization, and oil and phenol degrading pathways were also detected. Altogether this data make R. erythropolis S43 a good candidate microorganism for bioremediation of highly contaminated environments and other industrial applications.

Abstract: Arsenic contamination is considered as a global environmental problem. This metalloid is known to be carcinogenic in some forms, and is mostly found in the environment as arsenate As (V) and arsenite As (III). Several chemical methods have been established for decontamination of arsenic from ground water including biological treatments. In the present work, the effect of the anaerobic bioreduction of soluble Fe (III) by the strain Aeromonas hydrophila on arsenic immobilization has been investigated. The tolerance of this strain to arsenic concentration and the effect of the iron concentration in arsenic immobilization have been studied. The release of ferrous ion indicated the bioreduction of iron and promoted the subsequent arsenic co-precipitation, leading to the formation of various iron-bearing minerals. This precipitate has been observed and identified by Scanning Electron Microscopy and X-ray diffraction analysis as Fe₃(AsO₄)₂(H₂O)₈.

Abstract: The potential utility of mesophilic/moderately thermophilic acidophiles was investigated for immobilization of arsenic (As) as scorodite (FeAsO₄·2H₂O) at moderate temperatures (35–45 °C). Here, the acid-tolerant mesophile Thiomonas cuprina Hö5 and acidophilic moderately thermophile Acidimicrobium ferrooxidans ICP were selected as As (III)- and Fe (II)- oxidizers, respectively. Due to a difference in their optimal growth pHs, a 2-step reaction consisting of the 1st As (III) oxidation step followed by the Fe (II) oxidation + precipitation step was studied. In our previous study, the optimal [Fe (II)]_ini/[As (III)]_ini molar ratio for bioscorodite formation at 70 °C was shown to be around 1.4. However, setting the same molar ratio at moderate temperatures (35-45 °C) resulted in formation of unstable amorphous ferric arsenate. Lowering the ratio to ≤ 1.0 led to precipitation of crystalline bioscorodite with > 90% As (III) removal at 45 °C.

Abstract: Silver-catalyzed bioleaching of enargite concentrate with three bacteria (Acidimicrobium ferrooxidans ICP, Sulfobacillus sibiricus N1, Acidithiobacillus caldus KU) and one archaeon (Ferroplasma acidiphilum Y) was conducted in order to elucidate the catalytic mechanism of silver sulfide in enargite bioleaching. Whereas Cu recovery remained relatively low (43%) and Fe dissolved completely without silver sulfide, Cu recovery was greatly enhanced (96%) and Fe dissolution was suppressed (29%) in the presence of 0.04% silver sulfide. In the latter case, 52% of the solubilized As was re-immobilized, in contrast to only 14% As re-immobilization in the former. The silver-catalyzed bioleaching (at 0.04% silver sulfide) proceeded at low redox potentials within the optimal range, which likely promoted enargite dissolution via formation of intermediate Cu₂S. XAFS analysis revealed that As was mainly immobilized as As (V), which was in agreement with the EPMA results detecting ferric arsenate passivation on some enargite grains. Furthermore, formation of trisilver arsenic sulfide (Ag₃AsS₄) was detected by XRD and EPMA, covering the surface of enargite particles. An intermediate layer, consisting of (Cu,Ag)₃AsS₄, was also observed between the enargite grain and trisilver arsenic sulfide layer, implying that Cu in enargite may be gradually substituted by solubilized Ag. The overall mechanism of silver-catalyzed bioleaching of enargite concentrate will be proposed.

Abstract: This work was done to assess the arsenate (AsV ) removal from the model solution by sorbents based on Fe-oxide. Two samples were compared in sorption properties, synthetically prepared Fe-oxide and bentonite/iron oxide (ratio 2:1). The effect of pH and initial metal ion concentration was investigated. The optimum pH for arsenic adsorption by both samples was found to be about 3.0. The adsorption increased very significantly with decreasing pH for both samples. The Fe-oxide sample achieved the maximum adsorption capacity 24,1 mg.g-1 AsV at pH 3, composite sample 14,1 mg.g -1 AsV at pH 3. The adsorption of AsV on Fe-oxide sample increased with the increasing initial metal ion concentration up to 40 mg/l and then equilibrium was established, by contrast of bentonite/Fe-oxide sample shown no significant change at this concentration range.

Abstract: The use of chemical pretreatment with 10mM EDTA to enhance the arsenic microbial mobilization was evaluated in this study. The bioleaching involved the use of the indigenous sedimentary and soil heterotrophic microorganisms, whose leaching media contained 2mM EDTA. The main objectives of using the chemical pretreatment was the removal of metal surface coatings from the iron minerals, such as Cu and Zn, which inhibited the iron microbial dissolution in the soil and sediment environment and thus increasing the mobilization of the retained As. To examine the effect of the chemical pretreatment and the biological leaching on the mobilization of Cu, Zn, and As, batch and column tests were conducted within the laboratory experiments. The removal of As and Zn from the soil and sediment was greatly enhanced by the co-treatment in the batch solution conditions than in the column percolate conditions and had negative effect only for Cu. In the batch tests, the heterotrophic bioleaching of the soil and sediment was found to have a pronounced positive effect on the extraction of As and Zn.