Membrane distillation and ion exchange combined process for mining wastewater treatment, water reuse, and byproducts recovery

In this paper, we propose the combination of direct contact membrane distillation (DCMD) and ion exchange (IX) as an alternative for (i) generating reuse water and (ii) recovering byproducts from the DCMD concentrate by IX, from gold mining wastewater. The DCMD showed a steady flux (5.49 L/m2.h), ions rejection >99.7%, and a permeate recovery rate of 33.9%. The batch equilibrium results showed that the Amberlyst A26 had a strong affinity for H2SO4 (2897.9 mg/g). Conversely, Amberlite IRC747 and Dowex M4195 showed affinity towards Cu (83.4 and 103.1 mg/g), Ni (26.3 and 89.9 mg/g), and Co (6.5 and 24.4 mg/g). Batch kinetics showed that the rate-limiting step was intraparticle diffusion. Batch recovery of H2SO4 (1265 mg/L) from Amberlyst A26 could be achieved with H2O. Although the recovery of Cu (198.6 mg/L, 91.5%), Ni (62.4 mg/L, 30%), and Co (20.1 mg/L, 41.3%) from the Amberlite IRC747 could be achieved H2SO4 (1 mol/L), carryover of impurities was found. On the other hand, the recovery from the Dowex M4195 with NH4OH 4 mol/L was higher and carryover was lower. The fixed-bed tests showed that the ions breakthrough followed the same order as in the batch and they reached the breakpoint faster at higher feed velocity (8 BV/h compared to 4 BV/h). Elution from the Amberlyst A26 fixed bed achieved 7497.4 mg/L of H2SO4 with only 4.1% of carryover from other ions. The Dowex M4195 elution can achieve high selectivity when increasing the eluting agents' strength (H2SO4 0.1 and 1 mol/L, followed by NH4OH 4 mol/L) are used. By that, separated fractions of Cu, Ni, and Co could be recovered by each agent.