The Potential Use of Residual Soil from Ribeira Valley (Brazil) in Mitigating Metal Contamination: A Geotechnical Characterization

The incorrect disposal of hazardous waste causes serious problems around the world. For instance, mining waste is one of the main sources of potentially toxic metals in the environment. In the Ribeira Valley region of Brazil, residues generated during lead ore smelting were improperly deposited in the Ribeira de Iguape River and on the soil’s surface without protection. An alternative solution for mitigating local contamination is verifying whether a local residual soil is appropriate to use as a mining waste landfill liner. The soil is sandy silty clay, with a plasticity index of 24%, an optimum water content, wopt, of 26.3% and a maximum dry density, ρdmax, of 1.515 g/cm3 from the Standard Proctor test. Specimens molded at an optimum compaction condition showed hydraulic conductivity of 10−9 m/s and effective shear strength parameters of c′ = 22 kPa and φ′ = 26.8°. The soil is acidic (pH 4.6), exhibits low CEC (41.4 mmolc/dm3) and presents a predominance of negative charges on the particle surface (PZSE 3.6 < pH), favoring cation retention. The hydraulic and mechanical characteristics together with the chemical properties suggest that this soil is a candidate for use as a liner. Further studies are underway to characterize its chemical contaminant retention and to complete the analysis about its suitability for the desired purpose.