Recycling of lead-contaminated EDTA wastewater

Ethylene diaminetetraacetic acid (EDTA) is one of the chelating agents used in the soil washing process for the decontamination of lead-contaminated s oil. Lead-EDTA complexes in the wastewater from the soil washing process mu st be removed before the wastewater can be safely discharged. This study ou tlines a method to recycle Pb-EDTA wastewater by substituting the Pb comple xed with EDTA with Fe(III) ions at low pH, followed by precipitation of Pb ions with phosphate or sulfate ions. Fe(III) ions complexed with EDTA were then precipitated at high pH using sodium hydroxide. The resulting solution (Fe-precipitated solution) was tested on three lead-contaminated soils. Th e Fe-precipitated EDTA solution was found to have similar extraction capabi lities as fresh EDTA solution. Experimental results showed that the recycle d EDTA solution may be recycled several times without losing its extractive power. Recycled EDTA wastewater with phosphate precipitation was found to be slightly more effective than recycled EDTA solution using sulfate precip itation. The recycling procedure may be applied to wastewater generated dur ing soil washing of lead-contaminated soil, resulting in a reduction in was tewater generated and savings in the amount of EDTA used. (C) 1999 Elsevier Science B.V. All rights reserved.