Recovery of EDTA from complex solution using Cu(II) as precipitant and Cu(II) subsequent removal by electrolysis

Ethylendiaminetetraacetate (EDTA) is a chelating agent widely used in industry and agriculture. Resistant to chemical and biological degradation EDTA represents a serious ecological problem. In order to avoid the outlet into the environment a new method of EDTA recycling has been proposed. The method involves substituting of the metal ions in EDTA complexes by Cu(II) and formation of an insoluble Cu(2)EDTA.4H(2)O compound at the excess of Cu(II) ions in weakly acidic solutions. Cu(II) ions substitute such metal ions as Ni(II), Zn(II), Co(II), Cd(II), Ca(II) and Mg(II). After treatment of the precipitate with water only, acidic or alkaline solutions the copper from the suspension formed can be removed by electrolysis. The highest current efficiency under galvanostatic conditions is in alkaline solutions, however, the highest yield of EDTA recovery is in acidic solutions. FT-IR investigations and chemical analysis of the precipitate formed have shown that in acidic and in alkaline solutions, H(4)EDTA and Na(2)H(2)EDTA.2H(2)O were formed, respectively. Electrolysis in acidic solutions gives the best results, i.e. the formed H(4)EDTA contains the highest amount of EDTA (95%) and the lowest amount of copper (0.01%). (C) 2004 Elsevier B.V. All rights reserved.