Recovery of iron(II) and aluminum(III) from acid mine drainage by sequential selective precipitation and fluidized bed homogeneous crystallization (FBHC)

Acid mine drainage (AMD) released from gold and coal mining contains a large quantity of heavy metals, thus being a threat to the surrounding ecosystem. The recovery of metals from AMD can both address the potential contamination and bring more economic profits. In this study, the sequential selective precipitation and fluidized bed homogeneous crystallization (FBHC) were integrated to recover iron(II) and Al(III) from real AMD wastewater. The selective precipitation of Fe was optimized by adjusting pH. The FBHC recovery of Al performed its best at pH 9.25 ± 0.2, molar ratio of [H₂O₂]/[Al(III)] = 2.0 and up-flow velocity (U) = 30.5 m/h. Iron(II) and Al(III) were recovered in the form of iron hydroxide (Fe(OH)₃) and bayerite (α-Al(OH)₃) pellets. Removal efficiencies were as high as 99.7% and 99.3% for Fe(II) and Al(III), respectively. A brief cost-benefit estimation was performed and showed that the estimated profit gained from field-scale recovery of Fe(II) and Al(III) would be $1.31/m³-AMD.