Removal of lead, zinc and iron by coagulation–flocculation

Aluminium sulfate (alum), polyaluminium chloride (PACl) and magnesium chloride (MgCl2) have been used as coagulants with Koaret PA 3230 as the polyelectrolyte to determine the effectiveness of coagulation method for the removal of heavy metals (Pb, Zn and Fe). The maximum removal of Pb(II) was observed in different distinctive pH ranges: 6.2–7.8 for alum, 8.0–9.3 for PACl and 8.7–10.9 for MgCl2, regardless of types of solution. PACl is the most effective among the coagulants used in this study. The coagulant dosage required to achieve more than 99% removal in the mixed solutions containing Pb(II) and Zn(II) increased with the initial concentrations of Zn(II), whereas, the presence of 25–45 mg/L of Fe(III) in the mixed solutions containing Pb(II) and Fe(III) reduced the coagulant dosage used for more than 99% removal of Pb(II). The concentrations of Zn(II) and Fe(III) in the mixed solutions were always below the standard discharge limits. The flocs settling time was decreased by the addition of coagulant aid and the flocs settling time was found in the sequence of MgCl2 > PACl ≥ alum.