From Laboratory towards Industrial Operation: Biomarkers for Acidophilic Metabolic Activity in Bioleaching Systems

Recent advances in bioleaching and biosorption of metals from waste printed circuit boards: A review

Electronic waste, commonly known as "e-waste", refers to electrical or electronic equipment that has been discarded. E-waste, especially waste-printed circuit boards (WPCBs), must be handled carefully; as they can cause serious environmental pollution and threaten the health of local residents. The most abundant metal in WPCBs is copper, in addition to gold, aluminum, nickel, and lead, with grades that are tens or even hundreds of times higher than those of natural deposits. Due to the superiority of biorecovery methods in terms of their environmental friendliness, low capital investment and low operating costs, this study focuses on recent advances in the bioleaching and biosorption of metals from WPCBs. First, the principles, methods, and efficiency of bioleaching are reviewed in detail, particularly acidolysis, redoxolysis, and complexolysis. Additionally, six major factors (microbes, pH, temperature, nutrients, aeration, and substrate) affecting bioleaching are analyzed. The principles, kinetics, and isotherms of biosorption are then reviewed, and the factors influencing biosorption, including temperature and pH, are elaborated on. Hybrid recovery with biorecovery is explored, as these integrated strategies are conducive to achieving selective and efficient metal recovery. Finally, we discuss the advantages and disadvantages of the bioleaching and biosorption processes for metal recovery from WPCBs, particularly in terms of recovery efficiency, recovery time, and cost. Furthermore, future developments in biorecovery are also examined, along with useful ideas on how to accomplish energy-efficient metal recovery from WPCBs in the future.

The dynamics of two iron-oxidizing Acidithiobacillus strains in industrial copper sulfide heap-leaching

Several species within the Acidithiobacillus (At.) genus can derive energy from oxidizing ferrous iron and sulfur. Two bacterial strains according to their 16S rRNA gene sequences closely related to At. ferridurans and At. ferrivorans were obtained from the industrial sulfide heap leaching process at Minera Escondida (SLH), named D2 and DM, respectively. We applied statistical and data mining analyses to the abundance of At. ferridurans D2 and At. ferrivorans DM taxa in the industrial process over 16 years of operation. In addition, we performed phylogenetic analysis and genome comparison of the type strains, as well as culturing approaches with representative isolates of At. ferridurans D2 and At. ferrivorans DM taxa to understand the differential phenotypic features. Throughout the 16 years, two main operational stages were identified based on the D2 and DM taxa predominance in solution samples. The better suitability of At. ferrivorans DM to grow in a wide range of temperature and in micro-oxic environments, and to oxidize S by reducing Fe(III) revealed through culturing approaches can, in a way, explain the taxa distribution in both operational stages. The isolate At. ferridurans D2 could be considered as a specialist in aerobic sulfur oxidation, while isolate At. ferrivorans DM is a specialist in iron oxidation. In addition, the results from ore samples occasionally obtained from the industrial heap suggest that At. ferridurans D2 abundance was more related to its abundance in the solution samples than At. ferrivorans DM was. This dynamic coincides with previously obtained results in in-lab cell-mineral attaching experiments with both strains. This information increases our knowledge the ecophysiology of Acidithiobacillus and of the importance of diverse physiological traits at industrial bioleaching scales.

Progress in bioleaching: part B, applications of microbial processes by the minerals industries

This review provides an update to the last mini-review with the same title pertaining to recent developments in bioleaching and biooxidation published in 2013 (Brierley and Brierley). In the intervening almost 10 years, microbial processes for sulfide minerals have seen increased acceptance and ongoing but also declining commercial application in copper, gold, nickel and cobalt production. These processes have been applied to heap and tank leaching, nowadays termed biomining, but increasing concerns about the social acceptance of mining has also seen the re-emergence of in situ leaching and quest for broader applicability beyond uranium and copper. Besides metal sulfide oxidation, mineral dissolution via reductive microbial activities has seen experimental application to laterite minerals. And as resources decline or costs for their exploitation rise, mine waste rock and tailings have become more attractive to consider as easily accessible resources. As an advantage, they have already been removed from the ground and in some cases contain ore grades exceeding that of those currently being mined. These factors promote concepts of circular economy and efficient use and valorization of waste materials. KEY POINTS: • Bioleaching of copper sulfide ore deposits is producing less copper today • Biooxidation of refractory gold ores is producing more gold than in the past • Available data suggest bioleaching and biooxidation processes reduce carbon emissions.