INFLUENCE OF SOIL CARBONATES IN LEAD FIXATION

Despite the progressive decrease in emissions coming from a variety of sources, lead continues to be one of the toxic metals more often foun d as environmental pollutants. Of particular concern is lead migration through the soil which may result in contamination of water supplies through;he leaching caused by water infiltration. Carbonate minerals a re frequently found in soils and those of heavy metals are usually ins oluble so carbonates in the soil could act as a sink for heavy metals for as long as the environmental conditions guarantee their stability. The influence of soil composition on the fixation of lead from aqueou s solutions of this metal has been studied. Two clayey soils with diff erent carbonate content have been used in the tests. The kinetics and equilibrium of retention of lead in the soils under different conditio ns of pH and salinity have been determined using batch and fixed-bed c olumn experiments. Carbonate precipitation and ion exchange were the m ain processes responsible for the Pb uptake by the soils and concentra tions of up to 50% were achieved. The results obtained show that carbo nates confer the soil a high immobilization capacity for lead, impedin g the advance of the contamination under natural conditions.