Heavy metal adsorption by different minerals: application to the remediation of polluted soils

We studied the heavy-metal adsorption capacity of various minerals in order to evaluate their potential for the reduction of metal mobility and bioava ilability and their possible application for the remediation of polluted so ils in the Guadiamar valley. The study (batch tests) of zinc adsorption cap acity of clays (sepiolites, palygorskites, and bentonite from different min eral deposits) and a soil unaffected by the toxic spill at the P3 site (Pue nte las Doblas) showed a relative low adsorption capacity for Zn2+. In the case of the sepiolite from Orera deposit, the maximum retention capacity wa s obtained for Cd2+ (8.3 mg g(-1)), followed by Cu2+ (69 mg g(-1)), and fin ally Zn2+ (5.7 mg g(-1)). We conclude that the capacity of adsorption of th e clays and soil P3 is insufficient to immobilise heavy metals because of t he high pollution levels of the soils in the Guadiamar valley. Only goethit e (from Cerro del Hierro and Sierra de la Culebra) has sufficient adsorptio n capacity (between 3 and 4 mg g(-1)) to immobilise As in the highly pollut ed soil. Zeolite (NaP1), synthesised from Los Barrios fly ash, showed high retention efficiency for monovalent and divalent cations. Thus, the leachin g and ionic exchange tests performed with mixtures of soil with pyrite slur ry and NaP1 zeolites showed a high reduction on the mobility of Tl, Zn, Cd, Mn and Co (between 63 and 100%). The retention efficiency (for some of the metals considered) depended, not only on the ionic exchange capacity of th e NaP1 zeolite, but also on the decrease of the acidity induced by the zeol itic product. (C) 1999 Elsevier Science B.V. All rights reserved.