Application of Indian modified Shorea robusta bark for removal and recovery of heavy metal ions from aqueous solutions

Abstract

Studies have been carried out on the removal of copper, cadmium and lead ions from synthetic chloride solutions using modified Indian Shorea Robusta (SR) bark species. Increase of solution pH systematically increases the percentage removal of metal ions. However, the treated solutions are brown colored. On the other hand, the chemically modified bark's efficiency for removal of metal ions is systematically higher than that of the raw ones at any given pH. Kinetics of metal ions removal indicates that about 1 h reaction time is quite adequate to achieve equilibrium removal. Retention capacity of Indian bark species for Cu and Pb ions is comparable with that of the European ones. Scanning electron microscope and infrared determinations of the loaded bark saturated with copper ions suggest that the interaction of bark with the metal ions follows an ion - exchange mechanism with the release of 2 moles of H3O+ for one mole of bivalent metal ions exchanged with the bark substrate. In this study, the competitive removal of copper, cadmium and lead ions by the bark from a binary and ternary metal mixtures was studied as a function of pH at 100 ppm concentration level and compared with the single metal ion situation in a batch stirred system. The influence of pH on the removal of HMI's from the binary system showed varied difference in Cd and Pb ions percentage chelation by the bark. However, it was observed that percentage removal of metal ions was suppressed in the case of mixture of metal ions. Elution studies of bark loaded with cadmium and lead using diluted acids indicated almost full extraction of HMIs. This study suggests that the bark can be easily regenerated and reused.