•The adhesion properties of L. ferriphilum LJ02 on refractory gold-bearing pyrite were shown to be important for the biooxidation process.•Environmental factors, such as temperature and pH, could impact the adhesion characteristics of L. ferriphilum LJ02 on the surface of refractory gold-bearing pyrite.•The passive layer generated from the biooxidation process could hinder the adhesion biooxidation process of L. ferriphilum LJ02 on refractory gold-bearing pyrite.Leptospirillum ferriphilum (L. ferriphilum) is a widely used microorganism in the commercial biooxidation process. Its ability to adhere to sulfide ores when grown in sulfide mineral substrates is very important for the entire biooxidation process. However, few studies have investigated the ore adhesion properties of L. ferriphilum. In this paper, the effects of temperature, pH and the passive layer of the sulfide ore surface on the ore adherence properties and biooxidation capacities of L. ferriphilum LJ02, which was screened by our laboratory, were investigated. The results of these experiments showed that both the contact and non-contact leaching mechanism were evident during the sulfide biooxidation process. L. ferriphilum LJ02 preferred the contact leaching mechanism to the non-contact leaching mechanism. Within the experimental range of temperatures from 36 °C to 46 °C, the OAR (ore adhesion ratio) of L. ferriphilum LJ02 increased initially and then decreased with the temperature. The optimum OAR was 0.84 at 41 °C. Within the experimental pH range of 1.1 to 2.0, the OAR of L. ferriphilum LJ02 decreased with pH. The optimum OAR was 0.87 at pH 1.1. It was also found that the OAR of L. ferriphilum LJ02 could be reduced by the passive layer on the surface of the sulfide ore, which was generated during the biooxidation process. Moreover, it seems that the OAR of L. ferriphilum LJ02 was proportional to the sulfide biooxidation efficiency.

•High desilication efficiency was existed for the layer crystal structures materials by Paenibacillus mucilaginosus BM-4.•The Al/Si ratio was improved through bioflotation of mixed minerals by Paenibacillus mucilaginosus BM-4.•There exists the electrostatic adsorption process of Paenibacillus mucilaginosus BM-4 on kaolinite.•There exists the Langmuir isotherm adsorption process of Paenibacillus mucilaginosus BM-4 on bauxite.World reserves of bauxite include vast quantities of ore which are sub-economic due to high levels of reactive silica. It would lead to the substantial loss of caustic soda during Bayer processing. With the gradual reduction of the economic reserves of high-grade ore, people began to focus on the desiliconization treatment of the low-grade ore at reasonable cost. Biodesilication by silicate bacteria (such as Paenibacillus mucilaginosus) has been known as a potential technology for its characteristics of environmental protection, energy saving and sustainable development. In this paper, one silicate bacterial isolate with high desilication ability was screened, identified, and named as Paenibacillus mucilaginosus BM-4. The optimum cultural pH and temperature of BM-4 were also determined experimentally as 8.0 and 30 °C, respectively. Under these optimum cultural conditions, silicate ores were bioleached by BM-4. It seems that the stratified structures silicate ores, such as kaolinite and chlorite, were more readily to be leached by BM-4.On the other hand, the float-abilities of BM-4 on kaolinite and bauxite were also investigated. With the experimental results shown that there existed the electrostatic adsorption process between BM-4 and kaolinite, and the Langmuir isotherm adsorption process between BM-4 and bauxite. It was observed that the float-abilities of bauxite were significantly depressed by BM-4, while the those of kaolinite were enhanced. The bioflotation test of the mixture of bauxite and kaolinite (mass ratio 5:1) through BM-4 were carried out by a modified Hallimond tube. With results shown that the Al/Si ratios of this mixed minerals were improved from 3.05 to 8.60 after bacterial conditioning due to bauxite depression. Eventually, 83.0% of Al2O3 were recovered from the mixed minerals by BM-4.

Klebsiella pneumoniae ECU-15 (EU360791), which was isolated from anaerobic sewage sludge, was investigated in this paper for its characteristics of fermentative hydrogen production. It was found that the anaerobic condition favored hydrogen production than that of the micro-aerobic condition. Culture temperature and pH of 37 °C and 6.0 were the most favorable for the hydrogen production. The strain could grow in several kinds of monosaccharide and disaccharide, as well as the complicated corn stalk hydrolysate, with the best results exhibited in glucose. The maximum hydrogen production rate and yield of 482 ml/l/h and 2.07 mol/mol glucose were obtained at initial glucose concentration of 30 g/L and 5 g/L, respectively. Fermentation results in the diluent corn stalk hydrolysate showed that cell growth was not inhibited. However, the hydrogen production of 0.65 V/V was relatively lower than that of the glucose (1.11 V/V), which was mainly due to the interaction between xylose and glucose.

The power−time curves of the micelle formation process were determined for quasi-surfactants [mono(2-ethyl-hexyl)-2-ethyl-hexyl phosphate nickel and mono(2-ethyl-hexyl)-2-ethyl-hexyl phosphate cadmium] and two kinds of solvent, n-chain alkanes (decane, dodecane, and tetradecane) and single-ring aromatic hydrocarbons (benzene, toluene, and dimethylbenzene), with sec-octyl alcohol by titration microcalorimetry. The critical micelle concentration (cmc), aggregation number (n), formation constant of the micelle (K), and thermodynamic functions (ΔrHmθ, ΔrGmθ, and ΔrSmθ) are obtained. For different quasi-surfactants and solvents, the relationships between the solvent properties with the cmc and the thermodynamic functions of the surfactants are discussed.

The power−time curves of the micelle formation process were determined for three kinds of quasi-surfactants [lithium di(2-ethyl-hexyl) phosphate, sodium di(2-ethyl-hexyl) phosphate, and potassium di(2-ethyl-hexyl) phosphate] and five kinds of alkanes (octane, decane, dodecane, tetradecane, and hexadecane) with sec-octyl alcohol by titration microcalorimetry. The critical micelle concentration (CMC), aggregation number (n), formation constant of micelle (K), and thermodynamic functions (ΔrHmθ, ΔrGmθ, and ΔrSmθ) were obtained. For different quasi-surfactants and homologue of the alkanes, the relationships between the carbon number (N) of the alkanes with the critical micelle concentration (CMC) and the thermodynamic properties of the quasi-surfactants are discussed. It can be concluded as follows: (1) The microcalorimetric method is a good method to study the process of micelle formation. (2) The CMC decreased with an increase of the carbon number (N) of the alkanes, and the relative order of the CMC of different quasi-surfactants was D2EHPA(K) > D2EHPA(Na) > D2EHPA(Li) at the same carbon number. (3) The aggregation numbers (n) and formation constant of micelle (K) increased with an increase of the carbon number (N) of the alkanes. The relative order of different quasi-surfactants was D2EHPA(K) > D2EHPA(Na) > D2EHPA(Li) at the same carbon number. (4) The ΔrHmθ and ΔrSmθ increased, while ΔrGmθ decreased with an increase of the carbon number (N) of the alkanes. The relative order of the different quasi-surfactants was D2EHPA(Li) > D2EHPA(Na) > D2EHPA(K) at the same carbon number.

•The biooxidation of the concentrate under different DO and CO2 levels was studied.•Microbial community structure was detected under different DO and CO2 levels.•The cellular ROS level under oxygen-rich condition was measured.•Bacterial growth and energy utilization were found to be decoupled.Biomining microorganisms obtain energy from the oxidation of reduced sulfur and iron (II) by using dissolved oxygen (DO) as the electron acceptor. Carbon dioxide, the carbon source for biomining microorganisms, is essential for biooxidation. However, to date, no published reports exist regarding the effect of reactive oxygen species (ROS) and the CO2 content in an oxygen-rich condition (when oxygen is sufficient) on the biooxidation process. In this study, a microbial community was used to oxidize refractory sulfide gold concentrate in a 1.5 L experimental stirred tank reactor. The effects of DO in a slurry and the CO2 content in the intake gas on the biooxidation process, bacterial growth and microbial community were investigated. It was found that the biooxidation efficiency increased at first and then decreased as the DO level elevated, while the content of ROS significantly increased within the bacteria cells. Under an oxygen-rich condition, the biomass increased as the CO2 content increased, while the biooxidation efficiency first increased and then decreased. These changes revealed that the oxidation activity of biomining microorganisms was inhibited by a high CO2 content and that bacterial growth and energy utilization were decoupled. Leptospirillum ferriphilum-like bacteria and Sulfobacillus thermosulfidooxidans were the dominate strains in the experiment. As the DO increased, the relative proportion of L. ferriphilum-like bacteria in the bacteria community first increased and then decreased, while S. thermosulfidooxidans showed the opposite trend. With an increasing CO2 content in the intake gas, the relative proportion of S. thermosulfidooxidans increased, while that of L. ferriphilum-like bacteria decreased.

While multiple theories exist regarding the effect of dissolved oxygen (DO) on the biooxidation of minerals, few studies have been performed the cellular or molecular scale (e.g., genetics) and the mechanism remains unclear. In this paper, the effects of DO concentration on the biooxidation process of refractory sulfide gold ores by Acidithiobacillus ferrooxidans were investigated in the experimental stirred tank bioreactors (STRs). The results indicated that higher biooxidation and cell growth rates were correlated with higher DO concentration. The biooxidation process was restricted at 1.2 ppm DO due to oxygen limitation. Furthermore, the effects of DO on cellular and molecular scale were studied for the first time. The results demonstrated that the oxygen uptake rate (OUR), the Fe2+ oxidation activity and the rus gene expression of A. ferrooxidans all increased with the DO concentration, which might be responsible for the increase of the biooxidation rates with the DO concentration. This study provides insight into the potential impact of molecular-level mechanisms of DO in the biooxidation process of minerals.Highlights► The biooxidation process by Acidithiobacillus ferrooxidans was restricted at 1.2 ppm DO. ► Both the oxidation rate and the cells grew rate increased with the DO concentration. ► The oxygen uptake rate, the Fe2+ oxidation activity and the expression levels of the rus gene of A. ferrooxidans increased with the DO concentration.