Studies on interference of adsorption of heavy metal ions on chelating sorbents from cassava and Amidoxime-modified Polyacrylonitrile-grafted-Cassava Starch

Abstract

Polyacrylonitrile (PAN) is ideal polymeric matrix for adsorption due to its tolerance to most solvents, thermal stability and abrasion resistance. In this study, active nitrile group was converted into amidoxime functional group to form a chelating sorbent. Cassava starch (CS) that contains hydroxyl moiety is well known as effective biosorbent for the removal of heavy metal ions in aqueous solution. Batch adsorption was performed to study the interference of adsorption of heavy metal ions on the chelating sorbents prepared from cassava and Amidoxime-modified Polyacrylonitrile-grafted-Cassava Starch. It was found that the removal efficiencies of amidoxime-modified poly(AN-g-CS) towards Cu(II) ions was 43%, whilst the removal efficiencies towards Cr(III) and As(III) were 47% and 29% respectively. It was also shown that the presence of binary and ternary ions concentration greatly affects the sorption capacities of the adsorbents. The sorption capacities of the heavy metal ions was in the order As<Cu<Cr. The presence of Cr³⁺ reduced the removal efficiency of Cu²⁺ from 56.02mg/g to 25.89mg/g (46%), while As³⁺ reduced it to 24.32mg/g (43%). In a Ternary system, Cr³⁺ and As³⁺ jointly reduced the removal of Cu²⁺ to 22.56mg/g (40%). This study demonstrates that amidoxime-modified poly(AN-g-CS) has potential to be applied as good adsorbent to remove heavy metal ions from aqueous solution but interference by co-metals is noteworthy.

Keywords: cassava starch; amidoxime; graft copolymerization; heavy metal ions, hydroxylamine hydrochloride; oxime group; polyacrylonitrile.