Mineral biotechnological applications, e.g., bioleaching and bio-beneficiation, for waste treatment and resource recovery have invited due attention owing to their economic and eco-friendly benefits in comparison to the conventional methods. Although research has progressed well, there are several aspects that are still not well understood and require more attention in view of full-scale industrial application of these processes. For example, microbe-mineral/galvanic interactions, passivation phenomenon, synergistic effects among the microbes, identification of novel and robust microbial strains, etc., require more studies to explore the fundamental aspects. In addition, mode of treatment for a wide variety of ores and/or concentrates, advances in engineering applications and scaling-up of bio-processes to industrial level along with the assessment of techno-economic feasibility, life-cycle, and environmental impact can provide numerous opportunities for the researchers to further explore the applied aspects. This paper presents comprehensive details, including the latest research, on the fundamentals and applications of bioleaching, bioflotation and bioflocculation for the readers. The key microorganisms and their mode of action, factors affecting each bio-processes and aspects related to their scale-up and industrial applications are reviewed, analyzed and compared. It is believed that the recent advances, emerging dimensions and future directions of research presented in this paper will serve as a guide for the researchers to further explore this exciting field of research.

Aluminum is produced from its primary bauxite ore through the Bayer process. Although Al is important nowadays in the development of humanity, its production leads to the generation of a huge amount of waste, called red mud. Globally, the estimation of the stock of red mud is about 4 billion tons, with about 10 million tons located in Turkey. The presence of rare-earth elements (REEs) in crucial materials such as red mud makes it a major source of these elements. A number of methods have been developed for treating red mud, which are employed globally to recover valuable products. The application of a suitable method for REE extraction from red mud is a way to overcome the supply risk, contributing to reducing the environmental issues linked to red mud pollution. The current review summarizes the research on red mud processing and examines the viability of recovering REEs from red mud sustainably, utilizing hydrometallurgy and biohydrometallurgy.

There is a growing interest in electronic wastes (e-wastes) recycling for metal recovery because the fast depletion of worldwide reserves for primary resources is gradually becoming a matter of concern. E-wastes contain metals with a concentration higher than that present in the primary ores, which renders them as an apt resource for metal recovery. Owing to such aspects, research is progressing well to address several issues related to e-waste recycling for metal recovery through both chemical and biological routes. Base metals, for example, Cu, Ni, Zn, Al, etc., can be easily leached out through the typical chemical (with higher kinetics) and microbial (with eco-friendly benefits) routes under ambient temperature conditions in contrast to other metals. This feature makes them the most suitable candidates to be targeted primarily for metal leaching from these waste streams. Hence, the current piece of review aims at providing updated information pertinent to e-waste recycling through chemical and microbial treatment methods. Individual process routes are compared and reviewed with focus on non-ferrous metal leaching (with particular emphasis on base metals dissolution) from some selected e-waste streams. Future outlooks are discussed on the suitability of these two important extractive metallurgical routes for e-waste recycling at a scale-up level along with concluding remarks.

The cyanidation of precious metals from ores and secondary resources has been classified as a hazardous process due to the release of toxic gases. The use of environmentally friendly and cost-effective processes is a suitable alternative to cyanidation. Thiourea leaching has been shown to be one of the best alternative reagents to cyanide. The present work aims to evaluate the efficiency of the thiourea leaching of gold and silver from pretreated pyrite cinders. The use of pre-chemical activation prior to leaching helped to increase the amount of free gold and silver particles. A preliminary leaching test led to the selection of Fe₂(SO₄)₃ as a suitable oxidizing agent for Au and Ag leaching. To select suitable leaching parameters, the response surface methodology (RSM) was used to optimize some parameters that can considerably affect sulfuric acid–thiourea leaching and identify the greatest interaction between them. The optimized parameters of 30 g/L thiourea, 10% pulp density, pH = 1, and 50 °C over 4 h of leaching time allowed for Au and Ag recoveries of 98.31 and 88.57%, respectively.