Retention of heavy metals by soils in the presence of a residue from the olive-oil industry

摘要

The effect of the presence of alpechín, wastewater from the olive-oil industry, on the reaction of three soils with Cd, Cu and Zn is studied. Adsorption of Cu and Zn by all the soils studied, and Cd by one of the soils, is markedly decreased by the presence of high doses of alpechín, while Cd adsorption by the other two soils increases in the presence of the residue. Adsorption of Cu and Zn in the absence of alpechín releases considerably more Ca than the exchangeable contents at a rate of about 0.5-1 moles of Ca for each mole of metal adsorbed, and this rate is decreased in most cases when alpechín is present. The behaviour of Cd with respect to Ca release is less definite. The relationships between solution concentrations and pH show that alpechín increases the mobility of Cd and Cu in the presence of some soils, while in the case of Zn no effect is evident. It is concluded that soil carbonate is the most relevant component involved in Cu or Zn retention, and, in the presence of alpechín, part of the carbonate surface is blocked and becomes unavailable for retention. Formation of soluble Cu complexes is suggested to occur in some cases.