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

Single-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 operating temperatures (i.e., 3 versus 23°C). [ABSTRACT FROM AUTHOR]