The leaching of pentlandite by Acidithiobacillus ferrooxidans with a biological–chemical process

Influence of organic acids on pentlandite bioleaching by Acidithiobacillus ferrooxidans LR

Bioleaching is a bio-hydrometallurgical process of solubilizing metals from low-grade sulfide ores by microbial action employing chemolithoautotrophic microorganisms capable of promoting redox reactions. Organic acids have been applied in bioleaching once can act in two different ways; providing hydrogen ions for mineral acidolysis and complexing metals due to their chelating capacity. This study investigates the synergy of different organic acids (acetic, ascorbic, citric, lactic, and oxalic) and Acidithiobacillus ferrooxidans LR pentlandite bioleaching. The addition of oxalic acid had a positive effect on the Ni extraction during pentlandite biological-chemical leaching after 15 days, and the yields observed were 45.6% (26.5 mg Ni/g ore). The yields for Co extraction were meager, and Co extraction values were found to only 2.8% (1.6 mg Co/g ore) in the presence of citric acid. A design of experiments with mixtures was used to evaluate the interaction of organic acids in bioleaching. According to simplex-centroid experiments, only citric acid presented a statistically significant effect and has contributed in a synergistic form in pentlandite biological-chemical leaching in the presence of A. ferrooxidans. This study provides a new synergistic bioleaching system to improve Ni and Co extraction from sulfide ores.

Properties of realgar bioleaching using an extremely acidophilic bacterium and its antitumor mechanism as an anticancer agent

Realgar is a naturally occurring arsenic sulfide (or Xionghuang, in Chinese). It contains over 90% tetra-arsenic tetra-sulfide (As4S4). Currently, realgar has been confirmed the antitumor activities, both in vitro and in vivo, of realgar extracted using Acidithiobacillus ferrooxidans (A. ferrooxidans). Bioleaching, a new technology to greatly improve the use rate of arsenic extraction from realgar using bacteria, is a novel methodology that addressed a limitation of the traditional method for realgar preparation. The present systematic review reports on the research progress in realgar bioleaching and its antitumor mechanism as an anticancer agent. A total of 93 research articles that report on the biological activity of extracts from realgar using bacteria and its preparation were presented in this review. The realgar bioleaching solution (RBS) works by inducing apoptosis when it is used to treat tumor cells in vitro and in vivo. When it is used to treat animal model organisms in vivo, such as mice and Caenorhabditis elegans, tumor tissues grew more slowly, with mass necrosis. Meanwhile, the agent also showed obvious inhibition of tumor cell growth. Bioleaching technology greatly improves the utilization of realgar and is a novel methodology to improve the traditional method.

The use of (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone for controlling acid mine drainage through the inhibition of Acidithiobacillus ferrooxidans biofilm formation

The aim of this study was to determine whether acid mine drainage (AMD) production can be decreased by (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone (furanone C-30) in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans). The effects of furanone C-30 on A. ferrooxidans biofilm production were determined by crystal violet staining and confocal laser scanning microscopy (CLSM). Biofilm-related gene expression was investigated using real-time RT-PCR. Finally, the effects of furanone C-30 on AMD production were evaluated. The results show that furanone C-30 inhibits the production of extracellular polymeric substances (EPS) and biofilm formation and significantly down-regulates the expression of biofilm-related genes. The decreased EPS production led to reduced pentlandite attachment and biofilm formation on pentlandite. Furthermore, the dissolution of both nickel and copper were inhibited by furanone C-30 without new acid formation. This study provides a promising biochemical method to control AMD.