ORGANIC-ACIDS TO REMEDIATE A CLAY LOAM POLLUTED BY HEAVY-METALS

Weak organic acids have the capabilities of washing heavy metals witho ut seriously deteriorating the soil properties. A clay loam naturally contaminated by heavy metals was characterized physically and analyzed for its content in Cr, Hg, Mn, and Pb. At various pH, concentration, and reaction time, several weak organic acids and their salts were use d to leach out heavy metals. The optimum pH ranged from 5 to 7 for cit rate and 2 to 3 for tartarate in the case of Cr, Hg, and Mn and 2 to 7 in the case of Pb. More than 85% of Pb was removed with both citrate and tartarate at a concentration of 0.12 and 0.2 M, respectively, with in 24 h. From 86 to 99% of Hg was removed by tartarate and citrate, wh ereas up to 60% of Cr was removed. EDTA and DTPA were found to be quit e effective in removing Pb but not the other metals. Four citrate or t artarate extractions were required to remediate the experimental soil to a category A except for Hg. For Hg, remediation criteria are so str ict that only the C criteria were met after two extractions, with citr ate and tartarate, that left levels of 32 and 62 mg/kg, respectively, when a category A soil requires no more than 0.5 mg/kg.