Kinetic and thermodynamic study of magnesium obtaining as sulfate monohydrate from nickel laterite leach waste by crystallization

Abstract

According to the European Union, magnesium is considered as a critical metal, which can also be found in nickel laterite waste processing, where it is a strategic element with nickel, copper, and cobalt. For this reason, the goal of this work was to study the parameters for crystallization of magnesium sulphate under pressure based on nickel laterite leach solution through a reactor designed with separation system where monohydrate crystals were not decomposed. A magnesium monoelementary solution was used for the present study. After the reaction, the solid phase was separated with the reactor still under pressure to avoid crystals decomposition. Magnesium sulphate solubility was determined to complement the data already published in the literature and to define the solubility product from 30 to 230 °C. Pitzer interaction model made possible the Kps values were obtained at high-temperatures. The crystallization of magnesium sulphate reached the equilibrium in 5 h. At pH 5.7 and 230 °C, 81% of the magnesium crystallized. The particles presented a spherical morphology. The reactor here designed allowed the realization of crystallization at high-temperature, without crystals decomposition. The flowchart here proposed represents the novelty since it could be used for critical metals recovery from mining waste.