The effect of phosphate on the sorption of copper by acid soils

The sorption of copper from copper nitrate solutions by eight acid soils developed over granites or amphibolites was increased significantly by treatment with phosphate. Addition of phosphate did not significantly alter the Z-potentials of the clay fractions of these soils, and the effect of phosphate was not increased by applying it to the soil in advance of the copper solution. These findings suggest that the influence of phosphate on copper sorption was not due to its increasing the electrostatic attraction of Cu2+ ions by soil particles, or to reaction between Cu2+ ions and sorbed phosphate. Rather, MINTEQA2 simulations suggest that the addition of phosphate raised pH, and hence the formation, in solution, of readily sorbed Cu–P species.