Nickel (Ni) and cobalt (Co) are strategic metals that have found applications in a wide range of metallurgical and industrial uses. In this study, the dissolution of a mixed nickel–cobalt hydroxide precipitate using organic acids (citric, oxalic, and malic acid) was investigated. Citric acid was found to be the best leaching agent yielding the following dissolution rates: 91.2% Ni, 86.8% Co, and 90.8% Mn. Oxalic acid resulted in low dissolution, which is likely due to the formation of insoluble metal oxalates. The impact of acid concentration, leaching time, and temperature on metal dissolution was systematically examined. The optimal dissolution conditions were identified as 0.5 M citric acid at 30 °C for 30 min, utilizing a 1/20 solid/liquid ratio and a stirring speed of 400 revolutions per minute (rpm). The attempt to use oxidants, such as potassium permanganate (KMnO₄) and hydrogen peroxide (H₂O₂), to achieve selective dissolution in an organic acid environment was not successful, which was different from that in the sulfuric acid case. As for the leaching kinetics in the organic acids, it seems that the leaching of Ni correlates with the Shrinking Core Model, specifically regarding porous-layer diffusion control. Based on the experimental results, the activation energy for the leaching of Ni was estimated to be 3.1 kJ/mol.

This paper deals with the current magnesite concentration technology and upgrading studies in Turkey, which is the second biggest magnesite and third biggest sinter magnesia producer in the world. Magnesite heat treatment and magnetic separation fundamentals are also covered. This study aims to concentrate magnesite middlings containing the silica/iron impurities from Kütahya, Turkey, by calcination and dry magnetic separation. Final calcined MgCO₃ product contains 89.57% MgO, 0.96% SiO₂, 0.43% Fe₂O₃, 2.35% CaO and 6.64% loss of ignition. The optimum particle size was determined at −8 + 0.5 mm at 1000°C. Final product is saleable for industrial applications (i.e., soil decontamination, panels, fertilizers, animal nutrition, abrasives).

In this study, a brief overview of the solvent extraction (SX) application for the separationand purification of nickel and cobalt in hydrometallurgical processing of laterite nickel ores ispresented. This paper consists of two parts: firstly, the SX of nickel and cobalt from sulphateleach solutions is described; and secondly, the development of hydrometallurgical plants forthe processing of laterite nickel ores that involve solvent extraction technique is discussed. Themost important extractants are shortly given in the first part of the study. It is seen that theextraction and separation of nickel and cobalt from the impure leach solution of laterite nickelores can be performed by either using a single extractant system that is called as a direct solventextraction (DSX) or a mixture of two or more extractant which is known as a synergistic solventextraction system (SSX). Mixed sulphide precipitation (MSP) and mixed hydroxide precipitation(MHP) processes are mentioned. This paper is also addressed advantage and disadvantages ofeach extraction system. It is shown that capital investment expenditure, operational investmentexpenditure and mineralogical content are the most important factors that can affect the selectionof the appropriate hydrometallurgical process for lateritic nickel ore.