Direct Extraction of Ni(II) from Acidic Polymetallic Sulfate Media with a Novel Synergistic Extraction System of DNNSA-MSL211

Abstract

Direct extraction of Ni(II) from Fe(III), Al(III), Ca(II), Mg(II), and Mn(II) is a bottleneck issue in the hydrometallurgy processes of laterite-nickel ore, spent batteries, and other secondary sources. One of the biggest challenges in achieving direct extraction of Ni(II) is the lack of stable and efficient extractants. Hence, a novel bipyridine extractant MSL211 was designed and synthesized in this paper. With its strong steric resistance and electrostatic interaction, MSL211 can form a stable eight-membered chelating ring with Ni(II), thereby having a high bonding ability toward Ni(II). Therefore, based on the high bonding ability of MSL211 toward Ni(II) and the low extraction capacity of DNNSA for Fe(III), an efficient synergistic extraction system of DNNSA-MSL211 was proposed. The synergistic extraction system of DNNSA-MSL211 realizes direct extraction of Ni(II) from Fe(III), Al(III), Ca(II), Mg(II), and Mn(II) without neutralization, precipitation, and solid/liquid separation processes, which are inevitable but problematic processes in the current hydrometallurgy processes for removing Fe(III), Al(III), and Mn(II). The effects of the molar ratios of DNNSA:MSL211, shaking time, temperature, O/A ratios, and equilibrium pH on the extraction behavior of Ni(II) were investigated. Under optimum conditions, the extraction efficiency of Ni(II) was as high as 97.62%, and the separation coefficient of Ni(II) over all impurities was greater than 400. To elucidate the mechanism of the high selectivity of DNNSA-MSL211 toward Ni(II), DFT calculations were carried out to calculate the binding energy (ΔE) and Gibbs free energy (ΔG(ext)) of the extraction process. Furthermore, this paper investigated the entire ″extraction-stripping″ process, demonstrating that the synergistic extraction system of DNNSA-MSL211 avoids neutralization, precipitation, and solid/liquid separation processes, minimizes hazardous waste generation, and shortens process flow while meeting the objectives of sustainable and clean production.