Effects of pyrite and sphalerite on population compositions, dynamics and copper extraction efficiency in chalcopyrite bioleaching process

Bioleaching as an Eco-Friendly Nano-Factory for Sustainable Inorganic Waste Management: Current Advancements, Challenges, and Opportunities

Inorganic waste management and metal recovery technology pose significant challenges to the global research community and policymakers. Bioleaching is an economical, eco-friendly, and sustainable technology used for extracting metals and nanoparticles from inorganic waste streams, including e-waste, fly ash, ore, spent batteries, and petroleum catalysts. Valuable metals are recovered from these waste materials by microbial action. Bioleaching occurs by redoxolysis, acidolysis, and complexolysis processes. The present review provides insights into global trends and hazards of e-waste while also discussing the bioleaching of metals and nanoparticles from various inorganic wastes. In addition, the review focuses on the mechanistic pathway of the bioleaching process and computational aspects, such as the response surface method employed for enhanced recovery of metals from solid waste materials. Various physicochemical and biological parameters influencing metal bioleaching, as well as economic impacts and challenges affecting the bioleaching of metals from solid wastes, are discussed.

Bioremediation of cadmium-contaminated paddy soil using an autotrophic and heterotrophic mixture

Cadmium (Cd) pollution poses a serious risk to human health and ecological security. Bioremediation can be a promising and effective remediation technology for treating Cd contaminated soils. In this study, seven heterotrophic strains were isolated from Cd contaminated soil and 7 autotrophic strains were isolated from acid mine drainage. Cd removal efficiencies were compared after leaching with autotrophic bacteria (Att-sys), heterotrophic isolates (Htt-sys) and cooperative leaching systems (Co-sys) in laboratory agitating reactors. The results indicated that Cd removal efficiency of Co-sys (32.09%) was significantly higher than that of Att-sys (23.24%) and Htt-sys (0.74%). By analyzing the soil microbial community in different bioleaching systems, we found that the addition of heterotrophic isolates significantly promoted the growth of some heavy metal resistant inhabitants (Massilia, Alicyclobacillus, Micromonospora, etc.), and Co-sys had a minor effect on the growth of soil indigenous microbes. In Co-sys, the content of the four Cd fractions all decreased compared with other leaching systems. The analysis of soil physicochemical parameters during the leaching process showed that pH and ORP (oxidation reduction potential) were not the only determinants for Cd removal efficiency in Co-sys, synergistic metabolic activities of autotrophic and heterotrophic strains may be other determinants. This study demonstrated that cooperative bioremediation may prove to be a safe and efficient technique for field application in heavy metal soil pollution.

Bioremediation can be a promising and effective remediation technology for treating Cd contaminated soils. Cooperative bioremediation using heterotrophic and autotrophic mixtures proved to be an efficient, short-term bioremediation strategy for heavy metal contaminated soil.

Walnut Shell Powder Can Limit Acid Mine Drainage Formation by Shaping the Bacterial Community Structure

The formation of acid mine drainage (AMD), which results from the oxidation of sulfur minerals by air and water, can be accelerated by acidophilic and chemolithotrophic bacteria such as Acidithiobacillus ferrooxidans. Our previous study revealed that walnut shell powder and its phenolic component inhibit the growth of A. ferrooxidans. However, their inhibitory effect on AMD formation in the environment needs verification. We established a bioleaching system to test whether walnut shell powder and its phenolic component can limit AMD formation. Our results showed that lignin and cellulose isolated from walnut shell decreased metal ion concentrations through absorption, whereas the phenolic component increased pH by downregulating the expression of Fe²⁺-oxidizing genes and rus operon genes of A. ferrooxidans. Only walnut shell powder showed an excellent ability to curb AMD by binding metal ions and increasing the pH value. On probing deeper into the alteration of the bacterial community structure in the bioleaching system, we found that the bacterial community became more diverse-the amount of A. ferrooxidans decreased and that of some non-acidophilic bacteria increased. The bacterial community in samples treated with walnut shell powder or its phenolic component had low abundance in the pathways of metabolism and energy production, as determined by phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt). In other words, preponderant microbes, mainly A. ferrooxidans, lacked energy to grow well in the treated samples. Our findings provide a practical applicability of walnut shell powder to reduce leaching from a complex environmental community.

Relationships between galvanic interaction, copper extraction and community dynamics during bioleaching of chalcopyrite by a moderately thermophilic culture

A moderately thermophilic culture was enriched and adapted to bioleach chalcopyrite at high pulp density. In order to further improve copper extraction, effects of galvanic interaction on bioleaching performance and community dynamics were investigated by adding pyrite. Copper extractions were improved by 2.91 and 1.97 times in the initial and the final stages when pyrite was present, respectively. However, it did not benefit chalcopyrite dissolution in the middle stage. Community dynamics analysis showed that succession of the attached cells was significantly different from community dynamics of the planktonic cells. One of planktonic populations always dominated the communities in most cases, while no species had absolutely competitive advantages in the attached communities. In addition, the presence of pyrite had significant effects on planktonic and attached community structures, and could accelerate planktonic community succession.