MANAGEMENT AND TREATMENT OF ELECTROLYTES DERIVING FROM THE ELECTROKINETIC REMEDIATION OF POROUS MATRICES CONTAMINATED BY HEAVY METALS

Abstract

Electrokinetic remediation is a technology proposed to remove several contaminants, especially heavy metals, from matrices such as soils and sediments with low hydraulic conductivity. Its most common implementation applies an electric field to the contaminated mass through electrode couples installed in wells with porous walls where specifically conditioned water is circulated. The electric field causes the electrolysis of such solutions, generating an acid front which migrates from anodes to cathodes inducing the desorption and solubilisation of contaminants, and an alkaline front which propagates backward hindering this process, and is hence tackled by dosing acids in the catholite. Electrolysis reactions, conditioning agents, and transport processes due to the electric field cause an increase in the electrolyte ionic strength and its management becomes necessary in order to: 1) avoid species precipitation in the porous matrix, on the electrodes or on the casing walls, 2) avoid the possible inversion of diffusive transport process with the risk of recontamination of the treated matrix, 3) limit the increase in electrical conductivity because the removal efficiency can be reduced and can generate waste of electrical energy. Scientific literature is mainly focused on the treatment of the contaminated matrix at laboratory scale and it rarely takes into account the field implementation of electrokinetic remediation and the problems related to the electrolyte management and treatment. Therefore, the present study aims at analysing these aspects, focusing on possible solutions, technical aspects and economical considerations