Oxidative Acidic Leaching of Ferronickel Slag for Sustainable Metals Recovery and Liability Reduction

Pyrometallurgical processing of lateritic ore produces huge amounts of ferronickel slags, which may contain valuable metals. This paper describes a novel hydrometallurgical route to recover metals from ferronickel slag samples and reduce liability matters using oxidative acidic leaching. Hydrochloric acid and hydrogen peroxide were employed as leachants. A 2^4–1 factorial fractional design with 11 experiments was employed as a screening design to evaluate HCl concentration (3.0–6.0 mol L^–1), H₂O₂ concentration (0.5–2.5 mol L^–1), leaching time (30–240 min), and solid–liquid ratio (75–125 g L^–1). HCl and H₂O₂ concentrations were statistically significant for mass and metals leaching yields, which were studied by Doehlert design with 9 experiments with a response surface methodology (RSM). More than 80 wt% of cobalt and nickel, and ~ 75 wt% of iron were leached under the optimum region indicated by Doehlert design: 5.4–6.0 mol L^–1 HCl, 0.7–1.5 mol L^–1 H₂O₂, 25 °C, 120 min, and 100 g L^–1 solid–liquid ratio. Over 70 wt% of the slag mass was dissolved. The insoluble matter is essentially Fe₃O₄ and SiO₂. Chromium was poorly leached. The mild experimental conditions, namely temperature, leaching time, and leachant concentrations make the novel route very attractive for processing medium- to low-quality ferronickel slags and for reducing the environmental impact of this liability.

Graphical Abstract