Removal of lead from aqueous solutions with sodium caprate

Lead was removed from aqueous solutions by precipitation using sodium caprate [CH3(CH2)(8)COONa]. For a feed concentration of 7 mM (1450 ppm) lead and a mole ratio of caprate to lead of 2, the percentage removal of lead and the percentage loss of caprate were 99.5 +/- 0.2 and 0.8 +/- 0.3, respectively. The effects of pH and the concentrations of lead, calcium, chloride, and nitrate in the feed on the removal step were determined. At a mole ratio of caprate to lead of 2.0, the equilibrium concentrations of lead and caprate were independent of the feed concentration of lead. Decreasing the pH of the feed decreased the removal of lead but did not affect the loss of caprate. The presence of calcium, chloride, or nitrate in the feed did not affect the removal of lead. Sodium caprate was regenerated by adding HNO3 to the lead caprate precipitate to form capric acid from which sodium caprate was recovered by adding NaOH. Based on the amount of caprate used in the lead removal step, a percentage recovery of 98.9 +/- 0.3 was achieved.