Evaluation of a leaching process coupled with regeneration/recycling of the extractant for treatment of heavy metal contaminated solids.

A hydrometallurgical circuit process combining the leaching of metals with the electrolytic regeneration of the mass separating agent is an option to effectively treat heavy metal contaminated solids. This process aims towards a dosed loop utilisation of the extractant by its regeneration and recycling, enabling the use of high cost extractants and the recovery of the heavy metals as well. The circuit process, in which each cycle consists of an extraction step followed by the electrolytic regeneration of the mass separating agent and a second extraction to finally recycle the separating agent and start a new cycle, was applied on a lead contaminated soil from an accumulator manufacturing facility and for the removal of copper from a municipal solid waste incinerator bottom ash. For the first case a 0.13 M citrate solution was used at a pH of 5; for the second 10%; sulphuric acid (pH=0.5). The results showed that above 80% of lead and copper were removed from soil and ash, respectively, when the concentration of mass separating agent was controlled and kept constant. The extraction efficiency of metals from the solid materials was in the same range as the one obtained by two extaction steps using fresh extracting agent. However, due to losses of the mass separating agent the operation in a complete closed loop configuration was not possible. Nevertheless, a substantial reduction in separating agent consumption was achieved. The process proved to be suitable for treating highly contaminated materials, for which the operation parameters of extraction and regeneration are more favourable, also increasing the recovery of metals.