Nickel extraction from olivine using waste acid from an electrochemical marine CO2 removal process

Abstract

Global production of nickel (Ni) and ferronickel (FeNi) alloys, critical to battery materials and stainless steel alloys, is limited to a few countries due to the distribution of laterite ores. To meet the growing demand, an alternative supply of Ni and FeNi alloys needs to be established. Laterite ores result from olivine (Mg_xFe_2−xSiO₄) weathering under tropical conditions, making olivine a promising alternative source to consider; however, the lower Ni concentration of olivine makes it less economical. One approach to lowering the process costs is using waste chemical inputs in place of expensive commodity chemicals. In this study we evaluate the feasibility of using such waste byproducts generated by a demonstration-scale electrochemical marine carbon dioxide removal system to extract Ni from olivine (0.27 wt% Ni) as FeNi alloy. Bipolar membrane electrodialysis (BPMED) technology used for ocean alkalinity enhancement generates acidic, desalinated, and basic streams using seawater and electricity. The acid stream is a waste product, and we show that it is 37% better than equal-strength commercial HCl for leaching of Ni from olivine at room temperature. A small volume of the alkaline product from BPMED is used to increase the pH of the olivine leachate to remove all dissolved silicon and the majority of the dissolved iron, while retaining most of the dissolved Ni (65%) and Mg (84%). This enriched solution is used for Ni recovery via electroplating while the spent electrolyte, rich in Mg, is suitable as an additional source of alkalinity for marine CO₂ removal. We demonstrate the recovery of Ni as a FeNi alloy with an Fe to Ni molar ratio of 1.37 : 1 and evaluate the cost-benefit of the process for various possible scenarios. Preliminary assessment indicates an overall net economic benefit from recovering Ni from olivine using the proposed method and the net benefit is expected to further increase if the overall recovery rate of Ni is improved, the price of the Ni product is increased, and the value of CO₂ credit is included.