Chemical Modification of Starch Microcrystals and their Application as an Adsorbent for Metals in Aqueous Solutions

Starch microcrystals have the advantages of native starch grains but with higher specific surface area and numerous active sites. In this study, tapioca starch microcrystals were made by sulfuric acid hydrolysis and then chemically modified with succinic anhydride in an aqueous alkaline medium. The succinylated starch microcrystals were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The adsorption properties of the succinylated starch microcrystals in aqueous solutions were studied at different time periods (1 to 60 min), pH (2 to 7), and metals concentration (100 to 2000 mg/L) for different divalent metal ions such as Cu(II), Zn(II), Cd(II), and Pb(II). The results showed that the starch microcrystals were successfully succinylated, and their adsorption equilibrium for divalent metal ions was reached within 1 min. The adsorption capacity in high metal concentration was 147.7 mg/g for Cu(II), 143.2 mg/g for Zn(II), 216.4 mg/g for Cd(II), and 216.0 mg/g for Pb(II)). The metal-adsorption of succinylated starch microcrystals followed the Freundlich isotherm.