Chelating extraction technology in removing and recovering heavy metals from municipal sludge

Abstract

Comparable heavy metal extraction efficiency using different chelating aminopolycarboxylic acids was studied with sewage sludge as well as sludge-soil mixtures. EDDS and MGDA showed only slightly lower extraction efficiency in comparison with EDTA, at solution pH 6 and 25°C. Chemical fractions of HM in the sludge were determined using sequential extraction. According to their stability in the environment (in sulphide and residual fractions) the investigated heavy metals can be ranked as follows: Cr> Pb> Ni> Cd> Zn ≈ Cu. It was found out that methylglycinediacetic and S,S’-ethylenediaminedisuccinic acids had much better biological degradation properties than widely for metal complexation used ethylenediaminetetraacetic acid – EDTA. Possibility to utilize metal-contaminated extraction solution by chelant recovery with calcium hydrosilicate was also investigated