Comparison of Single and Two-Stage Ballasted Flocculation Processes for Enhanced Removal of Arsenic from Mine Water

AbstractSingle-stage and two-stage treatment processes using ferric sulphate (Fe2(SO4)3) coagulation, lime precipitation, ballasted flocculation, and sedimentation were compared for the removal of high concentrations (i.e., 60  mg/L) of arsenic in a synthetic mine water (SMW). Single-stage treatment was found to reduce arsenic to 0.39±0.04  mg/L in As(V) SMW and 0.78±0.07  mg/L in As(III) SMW using either preoxidation with KMnO4 or higher pH and coagulant dose compared to As(V) (i.e., 9.0 to 9.5 versus 5.5 to 6.0 and 151 versus 76  mg Fe/L), above a proposed national discharge guideline of 0.10  mg As/L. The two-stage treatment process was able to reduce total arsenic concentrations to 0.004±0.002  mg/L for As(V) SMW using coagulation and ballasted flocculation alone in Stage 2, 0.010±0.008  mg/L for As(III) with oxidation upstream of the second coagulation stage, and 0.037±0.006  mg/L for As(III) with pH adjustment downstream of it. The two-stage process was shown to achieve optimum performance at colder...