Green mining of mining water using surface e-precipitation

Abstract

Surface e-precipitation (SEP) is a largely unknown in separation electrochemical technique that uniquely combines the kinetic advantage of chemical precipitation with the advantages of conventional surface-based separation techniques such as electrodeposition/electrowinning (e-deposition), electrosorption, and adsorption. This work explores the potential of SEP in recovering valuable elements and removing toxic elements from mining water of a polysulfide ore origin. Without employing any reagent, in a simple batch-type laboratory setup with a carbon electrode, SEP alone or in combination with e-deposition can concentrate groups of dilute (20–30 mg/L) and ultradilute (<2 mg/L) valuable metals such as Zn, Al, Cu, Co, Ni, and rare earth elements (REE) vs gangue metals such as Mn, Fe, and an excess of Ca and Mg by an order of magnitude at highly competitive rate and energy consumption values which can reach 0.25 m3/(kg carbon ⋅ min) and 0.02 kWh/m3, respectively. The recovery and relative content of the concentrated metals can be controlled by the method design and operational variables such as applied potential, retention time (water treatment rate), and the number of stages. The uptake of Zn and Cu by SEP and e-deposition, respectively, is compared in mining waters and synthetic sulfate solutions. This comparison reveals that the ionic matrix of mining water promotes SEP but inhibits e-deposition. The comparison with the chemical precipitation at similar pH and reaction time shows that SEP has higher selectivity but lower recovery. These results demonstrate that SEP is a promising novel approach to valorizing and decontaminating acid mine drainage (AMD), process water, and metal-loaded wastewater.