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Sequential Extraction and Photocatalytic Recovery of Lead from Model Contaminated Soils

Abstract This work explores the technical feasibility of a two-step process for the treatment of lead contaminated soils. The first step is an extraction by chelation of lead from soil. The second step is the photocatalytic treatment of the metal-chelate extract with UV radiation and particulate TiO2 catalyst, to achieve lead deposition onto TiO2 , thus immobilizing it. Low toxicity organic chelating agents (EDTA and citric acid) were tested on a range of soil types (clays, peat and loam) artificially contaminated with lead to assess treatment feasibility. Extraction efficiencies were higher for EDTA than for citric acid. Near 100% metal recovery efficiency is achieved in short times for both extraction and photocatalytic steps with the clays and loam tested. Our previous work estimated the cost for chelatants used here to be US$1.30-1.50 per ton of soil, and illumination costs US$0.01 per gram of lead treated. The high efficiencies achieved here, together with the estimated low costs, are encouraging results for application of this treatment process to lead-containing soil, and may be extended to similar removal and re-immobilization of other heavy metals.