Clarifying filtration of leachates in the recovery process of valuable metals from mine tailings

Abstract

In this study, various clarifying methods for removing fine suspended solids from leachates produced by the leaching of solid mine tailings with H₂SO₄ are presented. The focus was on clarification using vacuum filtration, vacuum filtration with flocculant addition, centrifugation filtration, column filtration, and sedimentation. Experimental work was carried out on leachates obtained from leaching mine tailings under different acid-concentration conditions. The effects of flocculant type and dosage, vacuum filter pressure differential, filtration conditions, filter cloth type, and centrifugation parameters on turbidity reduction and clarifying performance were evaluated. The results showed that the best overall performance was achieved when using a flocculant during vacuum filtration. This enabled fast clarification, relatively high filtration rates, and low vacuum pressure requirements. By directly adding a nonionic polyacrylamide flocculant to the slurry and performing one-step clarifying filtration, filtration rates of approximately 4.5 m³/m²·h were achieved at vacuum pressures below 0.4 barg. This method produced very clarified filtrates with turbidity values below 10 NTU (< 27 mg/L TSS). Flocculant addition also improved cake permeability and dewatering, which results in drier cakes, faster filtration, and reduced filter cloth blocking. Multi-step clarification filtration of the prefiltered slurry further improved the filtrate quality, and turbidity values below 1 NTU (< 4 mg/L TSS) were achieved after re-clarification. Centrifugation was also found to be an effective clarifying approach, especially at 4000 ×g combined with flocculant addition. Using this method, turbidity values reached below 10 NTU. Conversely, deep-bed filtration using glass beads as bed material showed limited clarifying performance for TSS removal. Overall, the study showed that using flocculants in clarifying filtration is a promising and practical method for producing clarified leachates appropriate for downstream hydrometallurgical metal recovery operations