Removal of heavy metals from aqueous media using native cassava starch hydrogel

Abstract

Graft copolymers of cassava starch and acrylonitrile were synthesized in aqueous solution using ceric ammonium ion as the initiator. Saponification of grafted copolymer was done by reaction with sodium hydroxide and precipitated with methanol. Grafting was confirmed by Fourier transform infrared spectroscopy (FTIR). The grafted copolymer and the hydrolyzed graft copolymer (hydrogel) were used as sorbent for the uptake of heavy metals from the aqueous media. The sorption capacity was evaluated by measuring the extent of sorption of nickel, copper, and leads metals ions, under equilibrium conditions. Using the sorption isotherm models, the Freundlich model was found suitable because of good fitness and equilibrium data yielded the following ultimate capacity values for the sorbent of the grafted copolymer: 54 mgPb/g, 64.5 mgCu/g and 71.1 mgNi/g and for the hydrogel: 72 mgPb/g, 76.6 mgCu/g and 86.5 mgNi/g. Hydrolysis increases the sorption affinity of grafted copolymer toward metal ions. Acid stripping with 2% HCl resulted in 99.6% metal recovery for the hydrogel and 52.2% for the grafted copolymer. This shows the ability of the product to be reused, upon drying between treatments.

Key words: Acrylonitrile, cassava starch, grafted copolymer, heavy metals, hydrogel, sorption.