Synthesis of poly(hydroxamic acid-co-amidoxime) chelating ligands grafted acacia cellulose for heavy metals removal

Heavy metal pollution in aqueous medium is a problem of global concern. The discharge of industrial effluents with low concentration of metals, yet promising technology should be emphasized in the problem. Consequently, a new chelating ligands containing hydroxamic acid and amidoxime functional groups was synthesized from poly(methyl acrylate-co-acrylonitrile) (Poly(MA-co-AN» grafted acacia cellulose. The poly(MA-co-AN) grafted cellulose was prepared by free radical initiation using ceric ammonium nitrate (CAN) as an initiator and the optimum percentage of grafting yield was found to achieve 344% when the concentration of acacia cellulose, Hâ‚‚SO4, CAN, MA and AN were observed at 0.062, 0.120, 0.016, 0.309 and 0.427 mol/L respectively. The optimized grafting process was carried out at 55°C for two hours. Thereafter, the conversion of the ester and nitrile groups of the grafted copolymers of cellulose into hydroxamic acid and amidoxime was performed under alkaline condition through reaction of poly(MA-co-AN) grafted acacia cellulose with hydroxylamine solution. The reaction was carried out under optimized condition by using 2.878 x 10â�»Â³mol/L of NH20H.HCI solution, adjusted to pH 13.0 and the mixture was stirred at 70°C for four hours. Then the synthesized acacia cellulose grafted copolymer and chelating resins were characterized by SEM, FTR and TG analysis. The cation exchange capacity of the resins towards hydrogen ions was found to achieve 6.50 mmol/g and low swelling property of resins was observed at 5.408 g water g-1. The chelating behaviour of resins towards a series of metal ions was investigated through batch and column techniques. In the batch technique, chelating resins showed high binding capacities towards metal ions in the order of Cu²â�o > Cr³â�o> Zn²â�o> Fe³â�o. The sorption behaviour of resins was found to be pH dependant where the highest metal ions uptake was observed at pH 5.0 towards Cu2+ ion with sorption capacities of 13.57 mg/g. The synthesized chelating resins showed fast sorption rate towards Cu²â�o and Cr³â�o ions with t½< 2 min but slow sorption rate towards Zn²â�o and Fe³â�o ions with t½< 20 min. In column technique, the flow rates were studied where fast breakthrough and saturation of resins was observed at 2.5 mL/min towards mixture of Cu2+, Cr³â�o,Zn²â�o and Fe³â�o ions solution. The treatment of two wastewater effluent from metal plating industry by column technique was investigated and it was found to be highly efficient where up to 99% of metal ions was being removed from the liquor. Therefore, the polymeric chelating resins could be applied in heavy metals removal from wastewater with promising environmental protection.