Heap leaching of lead contaminated soil using biodegradable chelator [S,S]-ethylenediamine disuccinate

The feasibility of heap leaching Pb contaminated soil using biodegradable chelator [S,S]-ethylenediamine disuccinate ([S,S]-EDDS) in concentrations ranging from 10 to 40 mmol kg(-1) was assessed in a laboratory study. Treatment with 40 mmol kg(-1) [S,S]-EDDS was the most efficient, removing 31.3% of soil Pb and producing a waste washing solution with a peak Pb concentration slightly exceeding 10 mM. The removal of Pb from simulated washing solution containing 10 mM Pb by biodegradation of the Pb-[S,S]-EDDS complex and sorption of the released Pb on a vermiculite/soya meal/Slovakite based permeable bed was completed in 7.5 days. Lead recovery from washing solutions with higher molarity was significantly slower. Lead fractionation and bioavailability were assessed 6-months after soil treatment. Heap leaching removed Pb proportionally from carbonates (approx. 25% Pb) and organic matter (> 50% Pb), the two main Pb-bearing soil fractions,and increased the small pool of Pb soluble in the soil solution. The latter had no effect on Pb phytoavailability. Accumulation of Pb in leaves of the reported hyperaccumulator species Thlaspi goesingense was < 20 mg kg(-1) in all treatments, comparable to the Pb concentration in lettuce (Latuca sativa). Soil treatment with 40 mmol kg(-1) [S,S]-EDDS reduced concentrations of Pb orally-accessible in the stomach and intestine phase from initial 234.0 and 52.5 mg kg(-1) to 157.8 and 29.7 mg kg(-1), respectively, according to Ruby's test. Our results indicate that heap leaching of Pb with [S,S]-EDDS is not a viable remediation option for the tested soil and conditions used.