Electrolyte and pH effects on Pb(II)-calcite sorption processes: the role of the PbCO03(aq) complex

Batch sorption experiments were conducted under conditions of ambient temperature and atmospheric PCO2(g) to determine the effects of electrolyte type, ionic strength, and pH on Pb(II) interactions with calcite. For 0.15 M nitrate and chloride solutions at pH 8.2, no significant effect of electrolyte type on Pb sorption was observed. Varying ionic strength from 0.15 to 0.5 M produced little effect on Pb sorption in nitrate compared to chloride solutions in which Pb uptake decreased with increasing ionic strength. For a pH range of 7.3-9.4 in 0.15-0.2 M nitrate solutions, Pb sorption increased from pH 7.3 to 8.5 with a subsequent decrease in uptake out to pH 9.4. The trends in electrolyte and pH experiments correlate well with those for PbCO03(aq) speciation, indicating that this metal-ligand complex in solution dictates Pb sorption in the system under investigation.