REMEDIATION OF SOILS POLLUTED BY HEAVY-METALS USING SALTS OF ORGANIC-ACIDS AND CHELATING-AGENTS

Various weak organic adds and/or their salts were tested for the remed iation of a loam and a sandy day loam naturally polluted by heavy meta ls for over three years against two strong synthetic chelating agents (EDTA and DTPA). Among 7 weak organic acids and/or their salts, citrat e, tartarate and oxalate were found to effectively remove Cd, Cu, Pb a nd Zn from the two soils in double extractions, at a wide range of pH. Citrate removed 80 to 99.9% of all four metals within 24 h at pH from 23 to 7.5. Tartarate removed 84 to 99.9% of all metals from both soil s within 24 h at pH from 2.1 to 6.7. Oxalate alone is not effective in removing metals particularly Fb but with ammonium citrate (1:1 ratio) removed effectively 82, 70, 99.9, and 99.9% for Cd, Pb, Cu and Zn, re spectively at pH from 2.6 to 5.8. Zinc met the Quebec A level soil cle an-up criteria after two extractions whereas Cu and Pb reached the B l evel. Probably, two more extractions with these weak organic acids and /or their salts are required to meet the A level for the soil dean-up criteria for Cd, Cu and Pb. EDTA and DTPA removed 75 to 99.9% of the h eavy metals within 24 h at pH from 3.5 to 9.0 for both soils. Citrate and tartarate were found to remove heavy metals from two contaminated soils, as effectively as EDTA and DTPA. But compared to EDTA and DTPA they removed 80% less macronutrients from the soil and improve its str ucture. Weak organic acids and/or their salts therefore can be used as an environmentally friendly remediation technique.