Carbonaceous sulfidic gold ores are commonly double refractory and thus require pretreatment before gold extraction. In this paper, the capacity of pre-bio-oxidation can simultaneously decompose sulfides or deactivate carbonaceous matters (CM) from a double refractory gold ore (DRGO) using pure cultures of A. ferrooxidans or L. ferrooxidans, and a mixed culture containing A. ferrooxidans and L. ferrooxidans was investigated. The results showed that direct thiourea leaching of the as-received DRGO yielded only 28.7% gold extraction, which was due to the encapsulation of sulfides on gold and the gold adsorption of CM. After bio-oxidation, thiourea leaching of the DRGO resulted in gold extraction of over 75–80%. Moreover, bio-oxidation can effectively reduce the adsorption of carbon to gold. XRD, SEM-EDS and FTIR analysis showed that many oxygen-containing groups were introduced on the surface of DRGO during bio-oxidation, while the C=C bond was cleaved and the O–C–O and C–N bonds were degraded, causing a decrease in active sites for gold adsorption. Moreover, passivation materials such as jarosite were formed on the surface of DRGO, which might reduce the affinity of CM for gold in solutions. In addition, the cleavage of the S–S band indicated that sulfides were oxidized by bacteria. This work allows us to explain the applicability of pre-bio-oxidation for degrading both sulfides and CM and increasing gold recovery from DRGO in the thiourea system.

The thiourea (TU) leaching of gold from refractory ores can be considered an alternative to cyanidation. However, the high reagent consumption causes an increase in cost, which seriously limits its use. In order to effectively reduce the TU consumption, it is necessary to analyze the influencing parameters of gold recovery and TU consumption and apply them to the prediction of the TU leaching process. This paper investigated six potential influencing parameters and used grey relational analysis (GRA) to analyze the relational degree between each parameter and gold recovery and TU consumption. Then, the artificial neural network (ANN) model was established to simultaneously predict the gold recovery and TU consumption in the TU gold leaching process. The results of the GRA indicated that the leaching time, initial pH, temperature, TU dosage, stirring speed, and ferric iron concentration were all well related to the gold recovery and TU consumption. Therefore, the incorporation of these parameters can significantly improve the ANN model validation. The predictive results noted that the prediction accuracy of gold recovery varied from 94.46% to 98.06%, and the TU consumption varied from 95.15% to 99.20%. Thus, the predicted values corresponded closely to the experimental results, which suggested that the ANN model can accurately reflect the relationship between the operational conditions and the gold recovery and TU consumption. This prediction method can be used as an auxiliary decision-making tool in the TU gold leaching process, and it has broad engineering application prospects in engineering.

It is vital to remove cadmium from wastewater because of its potential harm to the natural environment and human health. It was found that sulfate-reducing bacteria (SRB) had a good fixing effect on Cd under a strict anaerobic environment. However, there are few reports on the immobilization effect and mechanism of SRB on Cd in an anoxic environment. This study revealed the effects of initial Cd²⁺ concentration, initial SO₄²⁻ concentration, temperature, pH, and C/N ratio on the immobilization of Cd²⁺ by SRB in aqueous solution under an anoxic environment. The experimental results showed that under the conditions of initial concentration of Cd²⁺ within 0 mg/L~30 mg/L, initial concentration of SO₄²⁻ within 1200 mg/L, temperature within 25 °C~35 °C, pH neutral, and C/N ratio of 20:1, the immobilization rate of Cd²⁺ by SRB is above 90%. The characterization results showed that bioadsorption and chemical precipitation were the main mechanisms of SRB immobilization of Cd²⁺ in an anoxic environment.

This paper studied the leaching effect of various strains on the heavy metal contaminated soil around the mining area of Dong’an County, Hunan Province. By measuring the form of heavy metals of antimony and arsenic in the soil and the concentration of heavy metals in the solution, the remediation effect of microorganisms in different pH conditions and different soil environments on the heavy metal contaminated soil was explored. The results showed that Acidithiobacillus thiooxidans(A.c) and Acidithiobacillus thiooxidans(A.t) had better leaching effect. Under the initial conditions of pH equal to 1, 10% bacteria content and 10 g/L S, the active metal components in the soil could be dissolved. The results showed that microorganism could remediate the soil contaminated with heavy metals and make the available metal components in the soil reach the safety standard.