Review of the potential role of electrokinetics technology in tailings dewatering and minerals recovery

Abstract

Water is employed as a cost-effective media of transporting tailings; a mixture of ground waste ore, water and chemicals used in metal extraction processes. Tailings are conveyed in pipelines from the plant to the tailings dam. From the dam, the water should be recycled back to the processing plant but herein lies the challenge. The hydraulic conductivity of fine-grained tailings is very low such that instead of draining, the water tends to accumulate in the dam. Not only does this led to pore water pressure build up which undermines the dam's stability, but it also causes massive water losses by evaporation more so in arid regions. Dewatering of tailings prior to disposal has emerged as a solution that can be used to conserve water by producing paste or thickened tailings. Thickened tailings have higher shear strength, lower volume and they reduce dam closure costs. Filtered tailings can also be used as underground backfill for mine cavities or transported with conveyor belts and trucks to a designated point. The main limitation is that the benefits of dewatering are mainly technical and they do not yield a direct financial return. Processes that increase mineral production are vital in mine operations. Apart from the residue of the targeted metal, most tailings contain base metals like copper, nickel and zinc. Some mines have already established systems to extract valuable minerals from tailings; these include DRDGold, Lonmin and Sibanye mines in South Africa. Dewatering systems are designed to be in close contact with tailings and if they can perform the dual function of recovering water while extracting metals, they would fully meet the demands of the mining industry. One of the most efficient techniques which can harness both dewatering and metal extraction is electrokinetics. Electrokinetics involves the application of an electrical current to induce the flow of water from the anode to the cathode in a process called electroosmosis. Electrokinetics also induces the migration of ions in a phenomenon termed electro migration. The metal cations precipitate at the cathode where they are collected and dried. This paper evaluates the viability of using an electrokinetic system to dewater and extract metals from tailings. Introducing a mineral extracting function could well be the key to increase the usage of tailings dewatering techniques by mines.

Towards a Circular Economy in the Mining Industry: Possible Solutions for Water Recovery through Advanced Mineral Tailings Dewatering

“…The expected level of metal(loid)s in water is influenced by various physicochemical characteristics of the solid material, such as pH, grain size, mineralogy, chemical composition, and speciation. These factors play a crucial role in determining the bioavailability of these metal(loid)s and assessing the potential risks that mine wastes pose to the soil, water, and wildlife in the surrounding area [85,86]. Table 1 presents the general characteristics of mineral tailings or sludge from various sources.…”

“…They achieve a higher solids concentration in the underflow (45%-60%) and yield stresses of less than 30 Pa through enhanced settling facilitated by flocculants or coagulants. While effective, their high use of flocculants can escalate operational costs [85,101,127]. In large copper mining operations, this technology is favored due to its superior performance in handling higher solids content and its flexibility compared to conventional thickening methods.…”

“…The current promotes the movement of water within the sludge towards the electrodes, causing the water to be separated from the solid components and eventually discharged in a more concentrated form. The most efficient method involves using direct current (DC) or alternating current (AC) and voltages ranging from 10 to 200 V to assist in pressure dewatering (PDW) [85,175,176]. Furthermore, raising the voltage (or current density) results in a drier sludge cake.…”

“…Cost-effective electrode materials like aluminum, copper, and steel are frequently employed in these processes due to their electrical conductivity and widespread availability. Nevertheless, a notable challenge associated with using these materials as electrodes is their susceptibility to rapid corrosion [85,179].…”

Electroosmotic Dewatering of Iron Ore Tailings: A Laboratory Study to Improve Geotechnical Properties

“…Valenzuela et al [27] obtained lower moisture levels in their electroosmosis experiments for copper leaching than those obtained from gravity drainage tests. By using electrokinetic and electroosmosis techniques together, precious metals are obtained from mine wastes, while at the same time, the water in the tailings can be recovered and fed back to the plant [28].…”