Remobilization of zinc from Ell-Ren river sediment fractions affected by EDTA, DTPA and EGTA

Ell-Ren river, enriched with heavy metals, is one of the heavily polluted rivers in Taiwan. Batch tests were used to illustrate the remobilization abilities of three chelating agents (ethylene-diaminetetraacetic acid, EDTA; diethylenetriamine pentaacetic acid, DTPA; ethylene glycol-bis (ú]-amino ethyl ether)-N-N′-tetraacetic acid, EGTA) on zinc, as well as to realize the variation and transformation of zinc contents in sediment binding fractions (exchangeable, bound to carbonates, bound to Fe/Mn oxides and bound to organics) as affected by chelating agents and pH. It has been found that DTPA had higher remobilization effect on zinc than EDTA. EGTA could release only little amount (5%) of zinc as its dosage was up to 500 mg/L. At neutral pH, both DTPA and EDTA had higher remobilization effects than at acidic or alkaline conditions. Remobilizations of zinc from sediment affected by both DTPA and EDTA were mainly released from “bound to carbonates” fraction. Meanwhile, the zinc content of “bound to organics” fraction also increased with increasing EDTA dosage, which could be attributed to the transformation from “bound to carbonates” and “bound to Fe/Mn oxides” fractions.