Bio-hydrometallurgical applications have been receiving more attention globally for processing of several metal bearing wastes. Developments in bioleaching enable this technique to be utilized as an alternative process for extraction of metals (ex-copper, gold, etc.) from complex ores or even concentrates, consequently solving several environmental issues. Organic and inorganic reagents or additives used during the process have been seen to affect the leaching efficiency of microbes for metal dissolution. The present review discusses the influence of certain organic–inorganic reagents and other materials or additives on the growth, oxidation activity, and bioleaching efficiency of acidophiles on metal dissolution.

Talc is a naturally hydrophobic gangue mineral in most sulfide ores. However, talc has vast applications in the cosmetics, paper, and paint industries due to its high chemical stability, and its demand continues to grow. Since flotation is the most effective beneficiation technique for upgrading sulfides, the high hydrophobicity of talc has made its selective separation challenging. This paper explored the different properties of talc and the different factors that affect its flotation separation performance as a proven versatile beneficiation technique. Surface properties, zeta potential measurements, contact angles, and other factors affecting the talc flotation efficiency were discussed in detail. It was observed that the surface face/edge ratio (particle size) has a direct relationship with the level of talc hydrophobicity. Talc surfaces are negatively charged in a wide pH range (pH 2–12). Different depressants have already been studied; however, most of them showed low selectivity. The addition of ions such as Ca²⁺ could enhance talc depression. Pretreatment methods such as ultrasonic and thermal treatments were reported to decrease the talc floatability. It was demonstrated that the development of new selective depressants or pretreatment options for talc flotation requires attention in future investigations to improve its selective separation.

Failure to recycle valuable metals from lithium-ion batteries (LIBs) could directly lead to various environmental issues, such as ecological toxicity with inevitable impacts on environment and society health. This study presents a green process for selective recovery of Li from spent LIBs based on a ternary deep eutectic solvent. The effects of solid-to-liquid ratio, temperature, and variations of deep eutectic solvent (DES) component concentrations on the selectivity of the leaching process were studied. A ternary DES based on choline chloride, urea and ethylene glycol was found to be more selective than conventional binary DESs and made it possible to extract the Li in the lower temperatures (75–100°C). In such temperatures, DESs present better viscosity and higher stability. In the optimum conditions, 92.83%, 1.61%, 0.72%, and 0.42% recoveries were obtained for Li, Co, Ni, and Mn, respectively. Kinetic modeling indicates that mixed control models were best fitted to all data. Moreover, the results indicated that the activation energy for Li extraction is 21.15 KJ/mol. Pearson correlation assessment relieved that L/S was the most effective factor with a positive impact (r > +0.5) on Li recovery among all variables. Furthermore, temperature impacts the selectivity of the leaching process. The illustrated selectivity coupled with biodegradability and the possibility of re-utilization of the DESs opens a novel way for the greener recovery of values from wastes.

This paper assesses rutting and fatigue behaviours of polyphosphoric acid (PPA)-modified binders using the advanced tests of multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS). The PG 58-22 binder was selected as the unmodified binder and the PPA contents ranged from 0.5% to 1.5% with 0.5% increment being added to it. The MSCR test was applied at 40°C, 55°C, 70°C and the performance grade (PG) temperatures of the binders to consider a wide range of high temperatures. To further explore the role of high stress level on the creep and recovery behaviour, the stress of 12.8 kPa was selected to be added to the MSCR standard procedure. Moreover, the LAS test was conducted at the intermediate temperature of 25°C to evaluate the fatigue resistance of the PPA binders. MSCR tests indicate that, for all the selected temperatures and stresses, increasing the PPA content causes the non-recoverable compliance (Jnr) and the percent recovery (R) values to be improved. Despite the positive effects, modification of the PG 58-22 base binder with the PPA additives does not ensure an acceptable rutting performance at the field temperatures equal to or higher than the PGs, because of the high Jnr values compared to the American Association of State Highway and Transportation Officials (AASHTO) MP 19-10 limits and also the negative R values of the PPA binders at these circumstances. On the other hand, LAS tests indicate better resistances of the PPA binders to fatigue than that of the PG 58-22 unmodified one. As the PPA content increases, the fatigue performance significantly increases.