Transporte de metais pesados em liner de solo compactado de aterro sanitário.

Abstract

The migration of heavy metals in soils that compose landfill base liners poses a risk of contamination of surface and groundwater bodies. In liners, the low flux speed favours the transport of metal ions by diffusion, which is associated with adsorption mechanisms between the soil and contaminants. In the Sanitary Landfill of Campina Grande – PB (SLCG), the waterproof capacity of base liners is provided by mixtures of sandy and bentonite soils, but studies regarding diffusive transport of heavy metals in these soils are scarce. This study aimed to evaluate the adsorptive behaviour of heavy metals and the diffusive transport of Nickel (Ni), utilizing a multispecies solution, in mixtures based on the soils utilized as base liners in the SLCG. The Ni was chosen because it is one of the most common species in leachates produced in landfills. In addition, Ni concentration in the SLCG leachate was higher than the limit set by standards. The mixtures were produced with addition of 10 and 20% of bentonite soil to sandy soil. Batch tests were performed using a multispecies solution of Ni, Pb, and Zn, concentrations of 0.17 to 5.96 mmol.L-1 , soil-solution ratio of 1:25, with agitation during 24 h at 22 °C. The analysis of adsorption isotherms, adsorption efficiency (AE), average distribution coefficients (Kd,médio), and joint distribution coefficients (KdΣsp) enabled to establish the selectivity order of metals in soils. Pure diffusion tests were conducted following a central composite design (CDC) in the experimental planning by varying the percentage of bentonite soil and the oncentration of metals in the multispecies solution. The results indicated that Pb was the most adsorbed metal in the batch tests, followed by Ni and Zn, both with similar concentrations. Diffusion coefficients (D*p) of Ni ranged from 7.76 to 9.63 × 10-12 m.s-2 in the solution of the equivalent contaminated layer (ECL). The content of bentonite soil was the only variable that had a significative effect on the D * p values of Ni, considering a p-value of 0.05. Thus, the use of mixtures with 20% of bentonite soil can optimize the performance of the SLCG base liners in terms of waterproofing and retention of heavy metals, and also retard the diffusive transport of Ni, representing a way to mitigate the effects of metal contamination in surface and groundwater bodies.