Comparative study of Cu, Zn, Cr, Ni, Al extraction from sewage sludge with six kinds of acids at low concentration

The effects of Low molecular weight organic acids (oxalic acid, citric acid) and inorganic acids (HCl, HNO₃) and high molecular weight organic acids (EDTA, HEDTA) on extraction of Cu, Zn, Ni, Cr, and Al from sewage sludge was studied in low concentration and economical extractable characteristics of organic acids were analyzed. The results illustrated that the extractable fraction percent of total Zn is higher than that of Cu, Cr, Ni and Al in all cases; maximum extractable fractions of Cu, Zn, Ni, Cr, and Al from sewage sludge were gained when pH of HCl and HNO₃ was 1-2; extractable fractions of heavy metals raised with the increment of the low molecular weight organic acids (oxalic, citric acid) concentration. After 24h of extraction procedure, citric acid can extract 98% of total Zn, 45% of total Cr, 5% of total Cu, 9% of total Ni and 20% of total Al. while oxalic acid can extract 95% of total Zn, 43% of total Cr, 15% of total Cu, 24% of total Ni and 30% of total Al.; extractable fractions of Cu with EDTA and HEDTA were higher than in other acids, the general extractable ability of HEDTA was better than EDTA. Comparative analysis of organic acids shows that the economic extractable order was oxalic acid >; citric acid >; EDTA >; HEDTA.