Enhancement of bio-oxidation of refractory arsenopyritic gold ore by adding pyrolusite in bioleaching system

Pyrolusite was added in the bioleaching process to enhance the bio-oxidation process. Bioleaching tests at different dosages of pyrolusite ore, pH and inoculation amounts of Acidithiobacillus ferrooxidans were studied. The results showed that the time of the bio-oxidation process was decreased obviously and the arsenic leaching rate reached 94.4% after the bioleaching. The bio-oxidation of arsenopyrite and the effective extraction of manganese from pyrolusite were achieved by the bioleaching process. After bioleaching, the leaching rate of gold from the reaction residues reached 95.8% by cyanide leaching. In the bio-oxidation process, pyrolusite increased the redox potential of the solution to accelerate the bioleaching rate. The experiment showed that there were two reaction modes in the bioleaching process.

Novel two-step process to improve efficiency of bio-oxidation of Axi high-sulfur refractory gold concentrates

In order to improve the bio-oxidation efficiency of Axi refractory gold concentrate, a two-step process including a high temperature chemical oxidation and a subsequent bio-oxidation, combined with p H control during the bio-oxidation step was used. The results revealed that the optimum mode was to maintain solution p H at 1.0-1.2 during the biological oxidation stage. Under this condition, the activity of mixed culture could be sustained and the formation of jarosite could be diminished, thus the oxidation efficiency was improved. The oxidation levels of iron and sulfur were improved by 12.50% and 15.49%, and the gold recovery was increased by 21.02%. Therefore, the two-step process combined with p H control is an effective method for oxidizing the biohydrometallurgical process of Axi gold concentrate, and it will have a broad prospect of application in dealing with complex refractory gold concentrate.

Research status of carbonaceous matter in carbonaceous gold ores and bio-oxidation pretreatment

Carbonaceous gold mines are important refractory gold ores. The previous results demonstrate that the carbonaceous matter is mainly composed of elemental carbon, organic acid and hydrocarbons. The dissolved aurocyanide complex is robbed by adsorption of carbonaceous matter, which is similar to activated carbon in cyanide leaching of gold. The pretreatment methods of carbonaceous gold ores were introduced, including high temperature roasting, bio-oxidation, chemical oxidation, competitive adsorption, barrier inhibition and microwave roasting. Recently, bio-oxidation was developed rapidly due to its advantages such as mild conditions, simple processes, low energy consumption and friendly environment. The known microorganisms related with bio-oxidation pretreatment mainly are chemolithotroph bacteria such as Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans. The researches on decomposing and passivating carbonaceous matter were commenced by Phanerochaete chrysosporium, Pseudomonadaceae and Streptomyces setonii. Finally, the main problems were analyzed and the application prospect of this technique was looked forward.

Well-controlled stirring tank leaching to improve bio-oxidation efficiency of a high sulfur refractory gold concentrate

For the high sulfur refractory gold concentrate with 41.82%sulfur and 15.12 g/t gold,of which 82.11%was wrapped in sulfide,a well-controlled stirring tank leaching was carried out to improve the bio-oxidation efficiency.Results show that bio-oxidation pretreatment can greatly improve the gold recovery rate of high-sulfur refractory gold concentrate,and at the optimum pH 1.3 in this study,compared with the process without pH control,the oxidation rate of sulfur increased from 79.31%to 83.29%,while the recovery rate of gold increased from 76.54%to 83.23%;under this condition the activity of mixed culture could be sustained and the formation of jarosite could diminish.The results also displayed that for the high sulfur refractory gold concentrate,the recovery of gold is positively correlated with the oxidation rate of sulfur,and the recovery rate of gold increases with the increase of sulfur oxidation rate within a certain range.

Effect of As(Ⅲ)on kinetics of Fe^(2+)bio-oxidation

Fe^(2+) bio-oxidation influenced by toxic metal ions released from the dissolution of arsenic-bearing gold ores was investigated.Fe^(2+) bio-oxidation by moderately thermophilic microorganisms was studied under different initial concentrations of Fe^(2+) and As(Ⅲ),and Monod equation was used to fit the Fe^(2+) bio-oxidation under different conditions.Results showed that the Fe^(2+) bio-oxidation rate increased as the initial Fe^(2+) concentration increased until it reached 12 g/L.As(Ⅲ)severely inhibited Fe^(2+) bio-oxidation.When the As(Ⅲ)concentration was 8 g/L,9 g/L Fe^(2+) was more than 200 h.The Monod equation fitted the Fe^(2+) bio-oxidation well.In the absence of As(Ⅲ),the maximum specific growth rate of the culture and the substrate affinity constant were 0.142 h^(−1) and 0.053 g/L,respectively.As(Ⅲ)inhibited Fe^(2+) bio-oxidation via competitive inhibition,and the inhibition constant was 0.0035 g/L.

Chinese Bio-oxidation Gold Extraction Technology Reaches International Advanced Level

In Liaoning, Hunan, Guangxi, Guizhou, Gansu, Sichuan, Anhui, Jilin and other provinces in China, there is a wide occurrence of metal quantity over 1000 tons of refractory gold ores, principally because of low gold recoveries and become ＂stay mine＂. Features of refi＇actory gold ores are： gold in micro-particles or a microscopic state that is wrapped in pyrite, presence of arsenopyrite and other sulfide minerals or disseminated in the crystal lattice of sulfide minerals; harmful impurity elements such as arsenic, carbon, mercury, antimony, copper with high content are closely related with the gold, and these elements affect the contact reaction between the gold and solvent extraction, making the recovery of the gold extraction process low. In the past 20 years, overseas countries have developed the application of the roasting oxidation method, hot acid （alkali） oxidation, bacterial oxidation and flash chlorination oxidation technology to solve this problem.Among these, biological oxidation has developed rapidly in the domestic market and gold enterprises abroad because of its low investment in infrastructure, low production costs, less environmental pollution, simple process and easy control, etc.

Studies on bio-oxidation of coal mine gas by a biofilter

A new biofilter technology was used to control the methane concentration in the coal mine. The results indicate that the biofilter achieves a steady methane removal capacity of 1 470 mg/（Loh） after 30 days start-up. More than 90% of the methane can be removed with an empty bed retention time （EBRT） of 5.6 min when the inlet concentration of methane （IMC） is lower than 70 mg/L （10%, V/V） and about 80% when IMC is at 105 mg/L （15%, V/V）. The biofilter is still a reliable method to control methane concentration as an auxiliary means to boost coal mine production safety together with aggrandized ventilation and drainage technologies, even though the removal efficiency of methane is not very satisfactory with a high IMC （〉10%） or a short EBRT （〈3.8 min）.

Pool bio-oxidation and fitting analysis of low-grade arsenic-containing refractory gold ore

To overcome the limitations of geography,climate,and ore characteristics on the ore beneficiation process,biooxidation studies on low-grade arsenic-bearing refractory gold ore by pool leaching were carried out,as well as process fitting analysis.The gold particles are encapsulated by pyrite and arsenopyrite.After 60 days of biooxidation,the oxidation rates of arsenic,sulfur,and gold were 39%~69%,24%~41%,and 49%~83%,respectively.The inoculated Acidithiobacillus ferrooxidans,Ferroplasma acidiphilum,and Leptospirillum ferrodiazotrophum could all mediate the initial pyrite/arsenopyrite oxidation and the Fe^(2+)oxidation reaction,but only the former could mediate the subsequent sulfur compound oxidation.When compared to daily bacterial circulation and bacterial replacement every ten days,aeration improved the gold leaching rate by 14%~22%.The Boltzmann model could fit both the arsenic and sulfur bio-oxidation,with model fit variances greater than 0.98.Based on the experimental and fitting results,the bio-oxidation cycle was determined to be 60 days,and the bio-oxidation mechanisms are summarized.This study has significant practical implications for the rational utilization of gold resources and provides theoretical and practical guidance for similar gold ores.

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.

Pyrite Surface after Thiobacillus ferrooxidans Leaching at 30℃

In order to investigate the effect of Thiobacillusferrooxidans on the oxidation of pyrite, two parallel experiments, which employed H2SO4 solutions and acidic solutions inoculated with ThiobaciUus ferrooxidans, were designed and carried out at 30℃. The initial pH of the two solutions was adjusted to 2.5 by dropwise addition of concentrated sulphuric acid. The surfaces of pyrite before exposure to leaching solutions and after exposure to the H2SO4 solutions and acidic solutions inoculated with Thiobacillus ferrooxidans were observed by scanning electron microscopy （SEM）. There were a variety of erosion patterns by Thiobacillusferrooxidans on the bio-leached pyrite surfaces. A conclusion can be drawn that the oxidation of pyrite might have been caused by erosion of the surfaces. Attachment of the bacteria to pyrite surfaces resulted in erosion pits, leading to the oxidation of pyrite. It is possible that the direct mechanism plays the most important role in the oxidation of pyrite. The changes in iron ion concentrations of both the experimental solutions with time suggest that ThiobaciUus ferrooxidans can enhance greatly the oxidation of pyrite.

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.

The Aerobic Biodegradability of Mono-fluorophenols by the Activated Sludge

By measuring the respiratory oxygen consumption, a study on the aerobic biodegradability of 2-fluorophenol, 3- fluorophenol and 4-fluorophenol was conducted using activated sludge acclimated by themselves respectively. The experimental results showed that bio-oxidation ratios of 2- fluorophenol, 3- fluorophenol and 4- fluorophenol were 25.30%, 35.28% and 36.60% respectively, and the constmdng rate constants were 0.009 3, 0.013 3 and 0.014 5 L/ gSS. h respect/vdy. The aerobic biodegradability of the mono-fluorophenols decreased in the order of 4- fluorop- henol〉3 - fluorophenol 〉2 - fluorophenol, resulting mainly from the different octanol/water partition coefficient and the different steric parameter of the fluorophenols which can affect the penetration of fluorophenol into cell membrane.

Pretreatment of copper-bearing refractory gold ores by bio-heap leaching

The refractory gold ores associated with rich copper and trapped in pyrite and quartz were studied. With conventional technique （all-sliming cyanidation）, the gold recovery rate is only 51.78%. To eliminate the negative effects of copper and pyrite on cyanidation and increase the gold recovery rate, the investigation on bio-heap leaching pretreatment was made, by which Cu would be dissolved and gold would be liberated from pyrite. The experiment adopted mixed bacteria, mainly ThiobaciUus ferrooxidan （named T.fl ）, as the bacterial catalyst for bio-preconditioning and was carried out in a PVC column with a diameter of 20 cm and a height of 1.3 m loaded with gold ores. The temperature was controlled between 28 and 30℃, the pH value was kept between 2.0-2.5, and the flux of sprinkling bacterial liquid was maintained 0.80 L/h. After 45-day＇s bio-oxidization, among the samples sizing from 0 to 5 mm, the oxidation rates of Cu, Fe and S were respectively 44.62%, 28.16% and 25.46%, and the gold recovery rate by cyaniding increased to 80.35%. The bio-heap leaching pretreatment can therefore effectively dissolve Cu and liberate gold from pyrite and lead to the increase of gold extraction.

Intensified bioleaching of low-grade molybdenite concentrate by ferrous sulfate and pyrite

Intensifying effects of ferrous sulfate and pyrite on bioleaching of low-grade molybdenite concentrate were studied in this paper. The experimental results show that the oxidation dissolution of molybdenite can be accelerated with the addition of either ferrous sulfate or pyrite in bi- oleaching medium. Pyrite has better enhancing effect than ferrous sulfate, and the highest molybdenum leaching rate in pyrite-added solutions is 20.85 %, increasing by 12.64 % compared with that in 9 K leaching system. Molybdenum leaching rate does not increase linearly with the increase of the addition of either ferrous sulfate or pyrite in each type solution. Great amounts of [NH4Fe3（SO4）2（OH）6] and [KFe3（SO4）2（OH）6] with different morphologies will be deposited on molybdenite ores when the additions of Fe from ferrous sulfate or pyrite exceed that from 9 K leaching system by 0.5 times, and these deposits hinder the oxidation dissolution of molybdenite to some extent.

In-situ neutralize methane emission from landfills in loess regions using leachate

In loess regions, landfilling is the predominant solid waste disposal and loess is usually used as landfill cover soil. However, the methane(CH_4) bio-oxidation activity of virgin loess is usually below 0.01 μmol/(h g-soil). In this study, we proposed a method to improve CH_4 removal capacity of loess by amelioration with mature landfill leachate, which is in-situ, easily available, and appropriate. The organic matter content of the ameliorated loess increased by 180%, reaching 19.69–24.88 g/kg-soil, with more than 90% being non-leachable. The abundance of type I methane-oxidizing bacteria and methane monooxygenase gene pmoA increased by 5.0 and 79 times, respectively. Consequently, the maximum CH_4 removal rate of ameliorated loess reached 0.74–1.41 μmol/(h g-soil) at 25°C, which was 4-fold higher than that of water-irrigated loess. Besides, the CH_4 removal rate peaked at 10 vt% CH_4 concentration and remained at around 1.4 μmol/(h g-soil) at 15°C–35°C. The column test confirmed that the highest CH_4 removal efficiency was at 30–40 cm below the surface, reaching 26.1%±0.4%, and the 50-cm-thick loess layer irrigated with leachate achieved more than 85% CH_4 removal efficiency. These results could help to realize carbon neutrality in landfill sites of global loess regions.