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 bioavailability and their possible application for the remediation of polluted soils in the Guadiamar valley. The study (batch tests) of zinc adsorption capacity of clays (sepiolites, palygorskites, and bentonite from different mineral deposits) and a soil unaffected by the toxic spill at the P3 site (Puente las Doblas) showed a relative low adsorption capacity for Zn2+. In the case of the sepiolite from Orera deposit, the maximum retention capacity was obtained for Cd2+ (8.3 mg g(-1)), followed by Cu2+ (69 mg g(-1)), and finally Zn2+ (5.7 mg g(-1)). We conclude that the capacity of adsorption of the clays and soil P3 is insufficient to immobilise heavy metals because of the high pollution levels of the soils in the Guadiamar valley. Only goethite (from Cerro del Hierro and Sierra de la Culebra) has sufficient adsorption capacity (between 3 and 4 mg g(-1)) to immobilise As in the highly polluted soil. Zeolite (NaP1), synthesised from Los Barrios fly ash, showed high retention efficiency for monovalent and divalent cations. Thus, the leaching and ionic exchange tests performed with mixtures of soil with pyrite slurry 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 the NaP1 zeolite, but also on the decrease of the acidity induced by the zeolitic product. (C) 1999 Elsevier Science B.V. All rights reserved.