Recycling EDTA solutions used to remediate metal-polluted soils

Abstract

The objective of this research was to investigate the recycling of ethylenediamine-tetraacetic acid (EDTA) used for the removal of trace metals from contaminated soils. We successfully used Na 2S combined with Ca(OH) 2 to precipitate the trace metals allowing us to recycle the EDTA. The results of batch and column leaching experiments show that both Ca-EDTA and Na-EDTA are powerful chelating agents with a similar soil remediation potential. The major advantage of Ca-EDTA is the preservation of soil organic matter. We found that Na 2S was capable of separating the metals Cd, Cu and Pb from EDTA; however, the precipitation of Zn required the addition of Ca(OH) 2. After reusing the reclaimed EDTA seven times, over a 14-day period, EDTA reagent losses ranged from 19.5% to 23.5%. Successive washing cycles enhanced the removal of trace metals from contaminated soils. The metal sulfide precipitates contain high concentrations of metals and could potentially be recycled.