THE ADSORPTION OF METALS LEAD AND ZINC FROM ACID WATERS BY A BRAZILIAN PEAT

Maria Dionísia Costa dos Santos (Departamento de Metalurgia Extrativa, Centro de Tecnologia Mineral/Ministério da Ciência e Tecnologia, Rio de Janeiro, RJ, 21.949-590, Brasil ) Laurindo de Salles Leal Filho (Departamento de Engenharia de Minas, Escola Politécnica da Universidade de São Paulo, São Paulo, SP, 05508-900, Brasil)

This work investigates the removal of heavy metals of acid effluents by a Brazilian peat with high decomposition grade, emphasizing the mechanisms of adsorption of the metallic ions in the peat/solution interface.

After physical, chemical and constitutional characterization of the peat, batch adsorption essays were made in laboratory scale, with synthetic nitrate solutions of the ions lead and zinc (concentrations varying from 30 to 150 mg/L) and with natural acid effluent, from a coal mine of Santa Catarina State. Electrokinetic determinations of the peat suspensions with those electrolytes were also accomplished.

The removal of the metal was over 99% for lead and 87% for zinc, in peat suspensions of 22 g/L and 168 g/L, respectively. The adsorption data adjusted to Freundlich equilibrium isotherm. The lead concentration in the treated solution fitted the requirements for effluent discharge, while the same was not observed for zinc.

It was evidenced by the constants of Freundlich and ratified by the measurements of zeta potential, that the peat catches the divalent cations lead and zinc by two different mechanisms. The lead adsorbs specifically in the active sites of the peat surface, by coordination reactions with the polar functional groups; while zinc undergoes non-specific adsorption as counter-ion in the peat interface.

The selectivity sequence determined in the peat adsorption essays, accomplished with the effluents of coal mining, was Pb2+ > Cu2+ > Cd2+ > Fe2+ > Zn2+ > Mn2+.