Innovative dual-purpose remediation of acid mine drainage and resource recovery through membrane distillation crystallization

Abstract

The current study evaluated the innovative application of membrane distillation crystallization (MDCr) for dual treatment and resource recovery from acid mine drainage (AMD), a persistent environmental crisis in South African. This AMD was characterized by exorbitant concentrations of Ca²⁺ (2622 mg·L⁻¹), Fe²⁺ (1421 mg·L⁻¹), SO₄²⁻(9790 mg·L⁻¹) and Cl⁻ (1113 mg·L⁻¹). The current study evaluated the performance of hollow fibre polypropylene membrane in processing both acidic (pH 3.58) and neutralized (pH 6.47) feedwaters. The permeate was 3.3 kg·m⁻²·h⁻¹, 2.2 kg·m⁻²·h⁻¹ and 1.3 kg·m⁻²·h⁻¹ at 70, 60 and 50 °C respectively, which remained relatively stable at high recovery factors ( >80%). Acidic AMD promoted formation of large metal-rich ettringite and halite crystals while neutralized AMD produced small and dense ettringite, hexahydrite and jarosite crystals. This study highlighted the dual functionality of MDCr in water treatment and mineral resource recovery, offering a sustainable solution to address the AMD pollution crisis in South Africa.