CONTROL OF LEAD CORROSION BY CHEMICAL TREATMENT

Laboratory corrosion studies with lead pipe in the presence of orthophosphate or polyphosphate show that orthophosphate ions are most effective in controlling lead leaching. XPS analysis indicates that the mechanism differs for the two phosphate species; orthophosphate interacts directly with the lead surface whereas polyphosphates require calcium ions to develop a self-limiting protective barrier. Pilot plant testing using a pipe loop fabricated from lead, soft solder, copper, and a brass faucet simulating household water usage with typical on-off cycles established equilibrium corrosion rates for the above materials over five to eight months in two waters. Both high-hardness high-alkalinity and low-hardness low-alkalinity waters in the Pittsburgh, PA, area were treated with zinc-orthophosphate. Both lead and copper materials meet the U.S. Environmental Protection Agency (EPA) proposed maximum contamination levels (MCLs) of 0.015 mg Pb/L and 1.3 mg Cu/L.