Novel insights into the kinetics and mechanism of arsenopyrite bio-dissolution enhanced by pyrite.

Arsenopyrite and pyrite often coexist in metal deposits and tailings, thus simultaneous bioleaching of both sulfides has economic (as well as environmental) significance. Important targets in bio-oxidation operations are high solubilization rates and minimized accumulation of Fe(III)/As-bearing secondary products. This study investigated the role of pyrite bioleaching in the enhancement of arsenopyrite dissolution. At a pyrite to arsenopyrite mass ratio of 1:1, 93.6% of As and 93.0% of Fe were solubilized. The results show that pyrite bio-oxidation can promote arsenopyrite dissolution, enhance S0 bio-oxidation, and inhibit the formation of jarosites, tooeleite, and amorphous ferric arsenate. The dry weight of the pyrite & arsenopyrite residue was reduced by 95.1% after bioleaching, compared to the initial load, while only 5% weight loss was observed when pyrite was absent. A biofilm was formed on the arsenopyrite surface in the presence of pyrite, while a dense passivation layer was observed in the absence of pyrite. As(III) (as As2O3) was a dominant As species in the pyrite & arsenopyrite residue. Novel and detailed findings are presented on arsenopyrite bio-dissolution in the presence of pyrite, and the presented approach could contribute to the development of novel cost-effective extractive bioprocesses. ENVIRONMENTAL IMPLICATION: The oxidation of arsenopyrite presents significant environmental hazards, as it can contribute to acid mine drainage generation and arsenic mobilization from sulfidic mine wastes. Bioleaching is a proven cost-effective and environmentally friendly extractive technology, which has been applied for decades in metal recovery from minerals or tailings. In this work, efficient extraction of arsenic from arsenopyrite bioleaching was presented through coupling the process with bio-oxidation of pyrite, resulting in lowered accumulation of hazardous and metastable Fe(III)/As-bearing secondary phases. The results could help improve current biomining operations and/or contribute to the development of novel cost-effective bioprocesses for metal extraction.

Efficient dealkalization of red mud and recovery of valuable metals by a sulfur-oxidizing bacterium.

Red mud (RM) is a highly alkaline polymetallic waste generated via the Bayer process during alumina production. It contains metals that are critical for a sustainable development of modern society. Due to a shortage of global resources of many metals, efficient large-scale processing of RM has been receiving increasing attention from both researchers and industry. This study investigated the solubilization of metals from RM, together with RM dealkalization, via sulfur (S0) oxidation catalyzed by the moderately thermophilic bacterium Sulfobacillus thermosulfidooxidans. Optimization of the bioleaching process was conducted in shake flasks and 5-L bioreactors, with varying S0:RM mass ratios and aeration rates. The ICP analysis was used to monitor the concentrations of dissolved elements from RM, and solid residues were analyzed for surface morphology, phase composition, and Na distribution using the SEM, XRD, and STXM techniques, respectively. The results show that highest metal recoveries (89% of Al, 84% of Ce, and 91% of Y) were achieved with the S0:RM mass ratio of 2:1 and aeration rate of 1 L/min. Additionally, effective dealkalization of RM was achieved under the above conditions, based on the high rates (>95%) of Na, K, and Ca dissolution. This study proves the feasibility of using bacterially catalyzed S0 oxidation to simultaneously dealkalize RM and efficiently extract valuable metals from the amassing industrial waste.

Red mud regulates arsenic fate at acidic pH via regulating arsenopyrite bio-oxidation and S, Fe, Al, Si speciation transformation.

Red mud (RM) as waste of industrial aluminum production is piling up in huge ponds. RM could be a cost-effective adsorbent for heavy metals, but adsorption is vulnerable to pH changes, metal ions speciation and the occurrence of iron bearing minerals. In this study, the precipitation and elemental speciation transformation relevant to arsenic fate in responding to the addition of RM during arsenopyrite bio-oxidation by Sulfobacillus thermosulfidooxidans was investigated. The results show that the addition of RM significantly changed the arsenic precipitation and the solution chemistry and thus affected the arsenopyrite bio-oxidation and arsenic fate. An addition of a small amount (≤ 4 g/L) of RM substantially promoted arsenopyrite bio-oxidation with formation of SiO2 @ (As, Fe, Al, Si) spherical nanoparticles that can enhance the stability of the immobilized arsenic. The SiO2-based spherical nanoparticles precipitate was mainly composed of jarosites, amorphous ferric arsenate and crystalline scorodite, and its formation were controlled by Fe3+ concentration and solution pH. An addition of increased amount of RM (≥ 6 g/L) resulted in a significant increase of the solution pH and a decrease in the Fe2+ bio-oxidation activity, and spherical nanoparticles were not formed. Consequently, the dissolution of arsenopyrite was inhibited and the release of arsenic was blocked. This study suggests the applicability of RM in mitigation of arsenic pollution from bio-oxidation of As-bearing sulfide minerals.

The effect of energy substrates on PHB accumulation of Acidiphilium cryptum DX1-1.

The effect of glucose and elemental sulfur on the growth and PHB accumulation of Acidiphilium cryptum DX1-1 was investigated. Meanwhile, the differential expressions of 19 genes related with PHB accumulation, sulfur metabolism and carbon fixed in heterotrophy, phytotrophy and mixotrophy were studied by RT-qPCR. The results showed that strain DX1-1 could accumulate PHB with sulfur as the energy substance and atmospheric CO2 as carbon resource. Glucose could improve the growth of strain DX1-1 cultured in medium with sulfur as the energy substance, and almost all the key enzyme-encoding genes related with PHB, sulfur metabolism and carbon fixed were basically up-regulated. PHB polymerase (Arcy_3030), ribulose-bisphosphate carboxylase (Acry_0825), ribulose-phosphate-epimerase (Acry_0022), and cysteine synthase A (Acry_2560) played important role in PHB accumulation, the modified expression of which could influence the PHB yield. With CO2 as carbon resource, the main initial substance of PHB accumulation for strain DX1-1 was acetyl-CoA, instead of acetate with the glucose as the carbon resource. Because of accumulating PHB by fixed atmospheric CO2 while independent of light, A. cryptum DX1-1 may have specifically potential in production of PHB.

Effects of copper exposure on expression of glutathione-related genes in Acidithiobacillus ferrooxidans.

The response of Acidithiobacillus ferrooxidans to variations in extracellular Cu exposure was investigated in terms of glutathione-related genes expression profiling based on reverse-transcription quantitative PCR analysis. The results show that the higher concentration of Cu would induce the expression of glutathione-related enzymes and cells elicited specific transcriptional responses when challenged with environmental Cu (0.08 mol l(-1)) conditions over a 60-min period. In comparison to the control, glutathione S-transferases (GST) and glutathione reductase (GR) were highly expressed when the cells were grown in the medium with copper, and the increase of glutathione and glutathione-related enzymes makes the cells acclimate to oxidative stress induced by Cu and protects the cells from toxicity caused by Cu exposure. It suggests that in order for Acidithiobacillus ferrooxidans to counteract the conditions of external Cu exposure, it modulated its expression level of GST, GR, glutathione hydrolase, and glutathione synthetase, which may protect organisms from oxidative damage. These parameters may be used to assess the biological impact of Cu in mining activities.

Sulfur oxidation activities of pure and mixed thermophiles and sulfur speciation in bioleaching of chalcopyrite.

The sulfur oxidation activities of four pure thermophilic archaea Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared. Meanwhile, the relevant surface sulfur speciation of chalcopyrite leached with the mixed thermophilic archaea was investigated. The results showed that the mixed culture, with contributing significantly to the raising of leaching rate and accelerating the formation of leaching products, may have a higher sulfur oxidation activity than the pure cultures, and jarosite was the main passivation component hindering the dissolution of chalcopyrite, while elemental sulfur seemed to have no influence on the dissolution of chalcopyrite. In addition, the present results supported the former speculation, i.e., covellite might be converted from chalcocite during the leaching experiments, and the elemental sulfur may partially be the derivation of covellite and chalcocite.

Production of Chitinase and its Optimization from a Novel Isolate Serratia marcescens XJ-01.

Production of chitinase from bacteria has distinct advantages over fungi, due to the formation of mycelia of fungi in the later phase of fermentation. A novel chitinase-producing bacterial strain XJ-01 was isolated from the Yulu fishing field of Changsha, Hunan province, China, by enrichment and spread-plate technique, sequentially. Physicochemical characterization and 16S rRNA sequencing revealed that strain XJ-01 belongs to Serratia marcescens. By optimizing the fermentation condition based on L(9)(3(4)) orthogonal experimental design, a maximal chitinase activity up to 15.36 U/ml was attained by that stain under the condition: 0.5% (NH(4))(2)SO(4) as the nitrogen source, 0.75% colloidal chitin as the carbon source, temperature of 32°C, time of 32 h and pH 8.0.

Biodegradation of di-n-butyl phthalate by Rhodococcus sp. JDC-11 and molecular detection of 3, 4-phthalate dioxygenase gene.

Rhodococcus sp. JDC-11, capable of utilizing di-n-butyl phthalate (DBP) as the sole source of carbon and energy, was isolated from sewage sludge and confirmed mainly based on 16S rRNA gene sequence analysis. The optimum pH, temperature, and agitation rate for DBP degradation by Rhodococcus sp. JDC-11 was 8.0, 30 degrees C, and 175 rpm, respectively. In addition, the effect of glucose concentration on DBP degradation indicated that low concentration of glucose inhibited the degradation of DBP while high concentrations of glucose increased its degradation. Meanwhile, the substrates utilization test showed that JDC-11 could also utilize other phthalates. Furthermore, the major metabolites of DBP degradation were identified as mono-butyl phthalate and phthalic acid by gas chromatography-mass spectrometry and the metabolic pathway of DBP degradation by Rhodococcus sp. JDC-11 was tentatively speculated. Using a set of new degenerate primer, partial sequence of the 3, 4-phthalate dioxygenase gene was obtained from the strain. Sequence analysis revealed that the phthalate dioxygenase gene of JDC-11 was highly homologous to the large subunit of phthalate dioxygenase from Rhodococcus coprophilus strain G9.