Effects of Mixed Chelators on the Leaching of Zinc in Contaminated Soils under the Co-planting System

To study the influence of mixed chelators (MC) on Zn leaching in two contaminated soil (acid soil with pH 4.63 and neutral soil with pH 6.51) with Pb-Zn mining wastewater under the co-planting system, a outdoor soil column (100 cm) leaching experiment was conducted with three treatments as follows: without plants and without MC (CK), co-planting of S. alfredii and Z. mays without MC (CP), and co-planting amended with MC (CPMC). Field conditions of the soil, including bulk density and profile, were reproduced in the soil columns. The concentration of Zn in leachates at 20, 40, 60, 80 and 100cm depth of soil column was measured on day 13 and day 6 before application of MC and on day 2 and day 8 after application, respectively. The soil pH and Zn concentration at each depth was measured before and after the experiment. The results showed that on day 2 after application of MC, the Zn concentration in leachates at each depth of both neutral and acid soil increased significantly. On day 8, the concentration of Zn in leachates at each depth of neutral soil and at 80 and 100 cm depth of acid soil was still significantly higher. However, the mobility of Zn on day 8 decreased substantially compared with that on day 2. The DTPA-extractable Zn concentration in both acid and neutral soils showed no significant differences among the CP, CPMC, and CK treatments. The DTPA-extractable Zn in acid soil and the total Zn in both soils showed a trend of downward migration. The results also indicated that in Zn-contaminated soil, the addition of MC might enhance the potential risks of greater Zn contamination in groundwater.