Thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high thiosulfate consumption and the difficult recovery of dissolved gold. In this review, the four solutions to reduce the consumption of thiosulfate, including the control of reaction conditions, the use of additives, the generation of thiosulfate in situ, and the replacement of traditional cupric-ammonia catalysis, are introduced and evaluated after the presentation of background knowledge about thiosulfate consumption. The replacement of cupric-ammonia catalysis with other metals, such as nickel- and cobalt-based catalysts, is proposed. The reason is that it not only reduces thiosulfate consumption observably via decreasing the redox potential of leach solution significantly but also is beneficial to gold recovery mainly owing to eliminating the interference of cuprous thiosulfate [Cu(S₂O₃)₃]⁵⁻. Based on the comparative analysis for five common recovery techniques of rare-noble metals from pregnant leach solution, ion-exchange resin adsorption is considered to be the most appropriate to recover aurothiosulfate [Au(S₂O₃)₂]³⁻ because the resin can be employed in the form of resin-in-leach/pulp and, furthermore, is able to be eluted and regenerated simultaneously at ambient temperature. At last, how to reduce the process cost of the resin adsorption technique is discussed. In order to simplify the complex two-stage elution process for loaded resins, the traditional catalysis is suggested to be replaced.

This review is devoted to an integrated evaluation of the current use and future development of the resin adsorption technique in gold recovery from pregnant thiosulfate solutions. Comparisons are firstly made with other recovery techniques, including precipitation, activated carbon adsorption, solvent extraction, electrowinning and mesoporous silica adsorption. A detailed discussion about the recent advances of the technique in gold recovery from pregnant thiosulfate solutions is then presented from the aspects of gold adsorption on the resins and gold-loaded resin elution, respectively. On the basis of summarizing the present research, the major limitations of the resin adsorption technique are eventually pointed out and future development will also be prospected.

A series of thermodynamic calculations are performed for the roasting of pyrite in changing temperatures and atmospheres. The relationship between Δ_rG^θ and temperature in the range of T = 300–1200 K shows that, depending on the atmosphere it is in, reactions of pyrolysis, oxidation or reduction can occur. Both the pyrolysis of pyrite in an inert atmosphere and its oxidation by oxygen can form pyrrhotite (mainly Fe_0.875S and FeS), but the temperature required for oxidation is much lower than that for pyrolysis. In an oxygen-containing atmosphere, the isothermal predominance areas for the Fe–S–O system indicate that a change in temperature and oxygen partial pressure can lead the pyrite to undergo desulphurization to pyrrhotite (FeS₂ → Fe_0.875S/FeS) or iron oxides (FeS₂ → Fe₃O₄/Fe₂O₃), or sulphation to iron sulphates (FeS₂ → FeSO₄/Fe₂(SO₄)₃). The presence of carbon is beneficial to the desulphurization of pyrite under an oxidizing atmosphere since iron sulphates can be converted to iron oxides at very low levels of P_CO/P_CO2. Results presented in this paper offer theoretical guidance for the optimization of roasting of pyrite for different purposes.

The spent automobile catalysts (SAC) is the major secondary source of palladium and the production of SAC is increasing rapidly over years. The price of palladium keeps rising over the years, which demonstrates its preciousness and urgent industrial demand. Recovering palladium from the spent automobile catalysts benefits a lot from economic and environmental protection aspects. This review aims to provide some new considerations of recovering palladium from the spent automotive catalysts by summarizing and discussing both hydrometallurgical and pyrometallurgical methods. The processes of pretreatment, leaching/extraction, and separation/recovery of palladium from the spent catalysts are introduced, and related reaction mechanisms and process flows are given, especially detailed for hydrometallurgical methods. Hydrometallurgical methods such as chloride leaching with oxidants possess a high selectivity of palladium and low consumption of energy, and are cost-effective and flexible for different volume feeds compared with pyrometallurgical methods. The recovery ratios of palladium and other platinum-group metals should be the focus of competition since their prices have been rapidly increased over the years, and hence more efficient extractants with high selectivity of palladium even in the complexed leachate should be proposed in the future.