Catalytic mechanism of manganese ions and visible light on chalcopyrite bioleaching in the presence of Acidithiobacillus ferrooxidans

The bioleaching of chalcopyrite is low cost and environmentally friendly,but the leaching rate is low.To explore the mechanism of chalcopyrite bioleaching and improve its leaching rate,the effect and mechanism of manganese ions(Mn^(2+))and visible light on chalcopyrite mediated by Acidithiobacillus ferrooxidans(A.ferrooxidans)were discussed.Bioleaching experiments showed that when both Mn^(2+)and visible light were present,the copper extraction was 14.38%higher than that of the control system(without Mn^(2+)and visible light).Moreover,visible light and Mn^(2+)promoted the growth of A.ferrooxidans.Scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS)analysis revealed that Mn^(2+)promoted the formation of extracellular polymeric substance(EPS)on the surface of chalcopyrite,changed the morphology of A.ferrooxidans,enhanced the adsorption of bacteria on chalcopyrite surface with light illumination,and thus promoted the bioleaching of chalcopyrite.UV–vis absorbance spectra indicated that Mn^(2+)promoted the response of chalcopyrite to visible light and enhanced the catalytic effect of visible light on chalcopyrite bioleaching.Based on X-ray photoelectron spectroscopy(XPS),the relevant sulfur speciation of chalcopyrite before and after bioleaching were analyzed and the results revealed that visible light and Mn^(2+)promoted chalcopyrite bioleaching by reducing the formation of passivation layer(S_(n)^(2-)/S0).Investigation into electrochemical results further indicated that Mn^(2+)and visible light improved the electrochemical activity of chalcopyrite,thus increasing the bioleaching rate.

Microbiologically influenced corrosion of cable bolts in underground coal mines:The effect of Acidithiobacillus ferrooxidans

Reports on corrosion failure of cable bolts,used in mining and civil industries,have been increasing in the past two decades.The previous studies found that pitting corrosion on the surface of a cable bolt can initiate premature failure of the bolt.In this study,the role of Acidithiobacillus ferrooxidans(A.ferrooxidans)bacterium in the occurrence of pitting corrosion in cable bolts was studied.Stressed coupons,made from the wires of cable bolts,were immersed in testing bottles containing groundwater collected from an underground coal mine and a mixture of A.ferrooxidans and geomaterials.It was observed that A.ferrooxidans caused pitting corrosion on the surface of cable bolts in the near-neutral environment.The presence of geomaterials slightly affected the p H of the environment;however,it did not have any significant influence on the corrosion activity of A.ferrooxidans.This study suggests that the common bacterium A.ferrooxidans found in many underground environments can be a threat to cable bolts'integrity by creating initiation points for other catastrophic failures such as stress corrosion cracking.

Mechanism of electro-generative-leaching of chalcopyrite-MnO_2 in presence of Acidithiobacillus ferrooxidans

To clarify the role and mechanism of Acidithiobacillus ferrooxidans (A. ferrooxidans) in bio-electro-generative-leaching (BEGL), an experiment was made on the electro-generative leaching of chalcopyrite-MnO2 in the presence of the bacteria which grew respectively in Fe(Ⅱ) and S0 media. A dual cell system with chalcopyrite anode and MnO2 cathode was used to study the relationship between time and both of electric quantity and dissolved rate of the two minerals in BEGL. The results show that the dissolved rates for Cu2+ and Fe2+ under the action of the bacteria cultivated by S0 medium are almost 2 times faster than those by Fe(Ⅱ). And the leaching ratio for Mn2+ and the electric output increase by near 3 times. The oxidation residue of chalcopyrite was characterized by SEM and XRD, whose patterns are similar to those of raw ore in BEGL. The mechanism of anodic reaction for CuFeS2-MnO2 leaching in the presence of A. ferrooxidans cultivated by S0 medium is proposed as a successive reaction of two independent sub-processes. The first stage is the dissolution of chalcopyrite to produce Cu2+, Fe2+ and sulfur, and the second stage is bio-oxidation of sulfur, which is the control step of the process. However, dissolution of MnO2 lasts until the reaction of chalcopyrite stops or the ores exhaust in two types of leaching.

Bio-oxidation of galena particles by Acidithiobacillus ferrooxidans

This paper deals with the bio-oxidation of galena particles （-80 meshes） using Acidithiobacillus ferrooxidans and compares it with Fe^3＋ oxidation. Experimental results show that, at least, 0.00197 mol galena was leached from lOOmL pulp （density of 3.8%） with 39 days＇ bio-oxidation, as compared to 0.00329 mol galena by Fe^3＋ with 9 days＇ oxidation. Because Fe^3＋ was constantly consumed, leaching by Fe^3＋ almost stopped after 9 days. Large amounts of lead sulfate were detected in both bio-oxidation and Fe^3＋ oxidation of galena. A. ferrooxidans followed a unique growth pattern during the bio-oxidation of galena. In the initial 15 days, the bacteria attached themselves to the galena surface with the formation of erosion pits similar in shape and length to those of the bacteria, and there were hardly any bacteria suspended in the solution. After 15 days, suspended bacteria increased. It is thus suggested that A. ferrooxidans may directly oxidize galena.

Isolation, identification and arsenic-resistance of Acidithiobacillus ferrooxidans HX3 producing schwertmannite

Schwertmannite, a ubiquitous mineral present in iron oxyhydroxides formed in iron- and sulfate-rich acid media, favors incorporation of some toxic anions in its structure. We reported an iron-oxidizing bacterial strain HX3 from a municipal sludge that facilitates the formation of pure schwertmannite in cultures. Ferrous iron oxidation by the isolated strain HX3 was optimum at an initial pH of 2.0-3.3 and temperature of 28-35°C. Pure schwertmannite was found through bacterial oxidation of ferrous iron at an initial pH 2.8and temperature 28°C. Following 16 S rDNA gene sequence analysis the bacterial strain HX3 was identified as Acidithiobacillus ferrooxidans. The arsenic-resistance A. ferrooxidans HX3 showed the potential of environmental application in arsenic removal from the As（Ⅲ）- and iron-rich acid sulfate waters directly by As（Ⅲ） adsorption or the formation of schwertmannite in the environment.

Synthesis of plant-based biogenic jarosite nanoparticles using Azadirachta indica and Eucalyptus gunni leaf extracts and its application in Fenton degradation of dicamba

Bio-jarosite,an iron mineral synthesized biologically using bacteria,is a substitute for iron catalysts in the Fenton oxidation of organic pollutants.Iron nanocatalysts have been widely used as Fenton catalysts because they have a larger surface area than ordinary catalysts,are highly recyclable,and can be treated efficiently.This study aimed to explore the catalytic properties of bio-jarosite iron nanoparticles syn-thesized with green methods using two distinct plant species:Azadirachta indica and Eucalyptus gunni.The focus was on the degradation of dicamba via Fenton oxidation.The synthesized nanoparticles exhibited different particle size,shape,surface area,and chemical composition characteristics.Both particles were effective in removing dicamba,with removal efficiencies of 96.8%for A.indica bio-jarosite iron nano-particles(ABFeNPs)and 93.0%for E.gunni bio-jarosite iron nanoparticles(EBFeNPs)within 120 min of treatment.Increasing the catalyst dosage by 0.1 g/L resulted in 7.6%and 43.0%increases in the dicamba removal efficiency for EBFeNPs and ABFeNPs with rate constants of 0.025 min^(-1) and 0.023 min^(-1),respectively,confrming their catalytic roles.Additionally,the high efficiency of both catalysts was demonstrated through five consecutive cycles of linear pseudo-first-order Fenton oxidation reactions.

A.ferrooxidans对高硫煤矸石去除酸性水体中Cr(Ⅵ)的强化作用

本研究考察了Acidithiobacillus ferrooxidans(A.ferrooxidans)联合高硫煤矸石(富含FeS2)对模拟煤矿酸性水体中Cr(Ⅵ)的去除效果.结果表明,处理Cr(Ⅵ)初始浓度为50mg/L的模拟煤矿酸性废水(pH=2.5)时,投配率为6.67~33.33g/L高硫煤矸石可使Cr(Ⅵ)去除达到良好效果.50mg/LCr(Ⅵ)在24h内即可完全被高硫煤矸石中的FeS2还原成Cr(Ⅲ),且在反应终点时(120h),6.67,13.33,33.33g/L高硫煤矸石对还原产物Cr(Ⅲ)的吸附去除率分别为7.1%、20.2%、29.1%.然而,在高硫煤矸石的还原和吸附作用下,大部分的Cr仍以Cr(Ⅲ)形式残留在酸性水体中,且高硫煤矸石的大量投加也给水体带来了Fe^2+、Fe^3+、SO4^2-等二次污染物.在高硫煤矸石-Cr(Ⅵ)体系中引入A.ferrooxidans和9K培养基后,A.ferrooxidans介导的Fe^2+生物氧化及产物Fe^3+水解矿化过程可促进部分Fe^2+、Fe^3+、SO42-等向次生铁矿物(包括施氏矿物和黄钾铁矾)转变,从而使模拟酸性水体中残留的Cr(Ⅲ)通过次生铁矿物的吸附或共沉淀作用被清除.在A.ferrooxidans强化作用下,模拟煤矿酸性废水中Cr(Ⅵ)在96h即可达到99.4%的去除率.

多金属硫化精矿中铜、锌和铁的生物浸出

利用嗜温混合菌Acidithiobacillus ferrooxidans,Acidithiobacillus thiooxidans和Leptospirillum ferrooxidans对低品位复杂Cu-Zn-Pb-Fe-Ag-Au硫化精矿在曝气生物浸出反应器中进行生物浸出。该菌种为从塞尔维亚Bor地下铜矿的酸性溶液中筛选出一种嗜热嗜酸菌。营养液为p H 1.6的9K营养液。87%的矿物粒度大于10μm,矿浆密度为8%(w/v)。在测试条件下,锌、铜和铁的浸出率分别达到89%、83%和68%。动力学分析表明,浸出过程与Spencer-Topley模型相符,受局部反应扩散控制。

Inhibition of hematite on acid mine drainage caused by chalcopyrite biodissolution

Even though biodissolution of chalcopyrite is considered to be one of the key contributors in the formation of acid mine drainage(AMD),there are few studies to control AMD by inhibiting chalcopyrite biodissolution.Therefore,a novel method of using hematite to inhibit chalcopyrite biodissolution was proposed and verified.The results indicated that chalcopyrite biodissolution could be significantly inhibited by hematite,which consequently decreased the formation of AMD.In the presence of hematite,the final biodissolution rate of chalcopyrite decreased from 57.9%to 44.4%at 20 day.This in turn suggested that the formation of AMD was effectively suppressed under such condition.According to the biodissolution results,mineral composition and morphology analyses,and electrochemical analysis,it was shown that hematite promoted the formation and accumulation of passivation substances(jarosite and Cu2-xS)on chalcopyrite surface,thus inhibiting the biodissolution of chalcopyrite and limiting the formation of AMD.

Biodesulfurization of vanadium-bearing titanomagnetite concentrates and pH control of bioleaching solution

Vanadium-bearing titanomagnetite concentrates were desulfurized with Acidithiobacillus ferrooxidans （A. ferrooxidans）. The sulfur content of the concentrates was reduced from 0.69wt% to 0.14wt% after bioleaching for 15 d with a 10% pulp density at 30℃. Maintaining a stable pH value during biodesulfurization was critical because of high acid consumption, resulting from a combination of nonoxidative and oxidative dissolution of pyrrhotite in acid solution. It is discovered that the citric acid-disodium hydrogen phosphate buffer of pH 2.0 can control the solution pH value smoothly in the optimal range of 2.0-3.0 for A. ferrooxidans growth. Using the buffer in the volume fraction range of 5.0%-15.0% stimulates A. ferooxidans growth and improves the biodesulfurization efficiency. Compared with the buffer-free control case, the maximum increase of biodesulfurization rate is 29.7% using a 10.0vol% buffer. Bioleaching provides an alternative process for desulfurization of vanadium-bearing titanomagnetite ores.

Bioleaching of spent Ni-Cd batteries and phylogenetic analysis of an acidophilic strain in acidified sludge

Biohydrometallurgy is a novel method to recycle discarded batteries,in which sewage sludge is used as microorganisms and culture due to the presence of indigenous Thiobacilli.A two-step continuous flow leaching system consisting of an acidifying reactor and a leaching reactor was introduced to achieve the bioleaching of spent nickel-cadmium(Ni-Cd)batteries.The acid supernatant produced in the acidifying reactor by the microorganisms with ferrous ions as the substrate was conducted into the leaching reactor to dissolve electrode materials.The efficiency of a batch treatment of batteries was examined.The results showed that the complete dissolution of two AA-sized Ni-Cd batteries with 0.6 L/d acid supernatant took about 30,20,and 35 days for Ni,Cd,and Co,respectively.But the dissolution ability of the three metals was different.Cd and Co can be leached mostly for pH below 4.0 while the complete dissolution of Ni can be achieved for pH below 2.5.Meanwhile,a strain(named Thiooxidans.WL)accounting for the reduction of pH in the acidified sludge was isolated and sequenced.It was identified to be 100%similar to Acidithiobacillus ferrooxidans strain Tf-49 based on 16S rDNA sequence analysis.The relevant phylogenetic tree constructed indicates that the strain should be classified into genus Acidithiobacillus ferrooxidans.