Reaction of NTA with Metal Carbonate
Carbonates are common forms of heavy metal ion solids. Solid lead carbonate,PbCO3, is stable within the pH region and alkalinity conditions often found in natural waters and wastewaters. An example similar to the one in the preceding section may be worked, assuming that equilibrium is established with PbCO3 rather than with solid Pb(OH)2. In this example it is assumed that 25 mg/L of trisodium NTA is in equilibrium with PbCO3 at pH 7.00 and a calculation is made to determine whether the lead will be complexed appreciably by the NTA. The carbonate ion, CO32-, reacts
with H+ to form HCO3-. As discussed in Section 3.7, the acid-base equilibrium reactions for the CO2/HCO3-/CO32- system are