Toxic Metals Removal from Industrial Sludge by Using Different Leaching Solutions

The safety of the environment from the industrial sludge has become a serious concern in India with the rapid increase in industrialization. The indiscriminate disposal of sludge from industries leads to the soil, groundwater and surface water pollutions. To avoid the high costs associated with the disposal of large volumes of sludge, it can be used in some building materials or can be used as fertilizer. As the accumulation of heavy metals in plants causes a threat to living beings, it has to be pretreated to remove heavy metals from the sludge to the required level before its application to soils. The heavy metals from the sludge can be reduced/separated by washing with a suitable fluid. In the present study, column leaching tests were conducted with five leaching solutions, i.e., distilled water, 0.1 N HCl, 0.1 N EDTA, 0.1 N HCl + 0.1 N EDTA and 0.1 N FeCl3to know their removal efficiencies of heavy metal ions of Cu, Zn, Ni, Cd, Pb, Fe and Cr present in the industrial sludge. It was observed that distilled water was able to remove only few metal ions Cu, Zn and Ni in lesser quantities. 0.1 N HCl has removed Cd, Cu, Zn and Ni ions with a removal efficiency of 50%. With 0.1 N EDTA, the metal ions Cd, Cu and Zn have attained a removal efficiency of 80% and other metals have attained almost 50%. Using 0.1 N HCl + 0.1 N EDTA and 0.1 N FeCl3, all the heavy metals were leached out with removal efficiencies of (different metals) 71–98%. From this study, it was found that 0.1 N HCl + 0.1 N EDTA and 0.1 N FeCl3were the most suitable solutions to remove heavy metals from the industrial sludge. Using the results of column leaching tests, the migration rates of different metal ions were determined which are used to design the soil washing program at the site to treat the similar sludge.