Development of Low Cost Adsorbents from Agricultural Waste Biomass for the Removal of Sr(II) and Cs(I) from Water

Abstract

For the purpose of remediating aquatic environment polluted by radioactive elements such as Cs(I) and Sr(II), two types of adsorption gels were developed using biomass wastes as feed materials: a Ca-type pectin based cation exchanger for the removal of Sr(II) prepared from orange waste and a polyphenol enriched bio-sorbent for Cs(I) prepared from tea leaves. The former was prepared by means of saponification of the methyl ester portion of orange pectin in orange juice residue using lime water. Due to the chemical similarity of Ca(II) and Sr(II), the Ca(II) ions in the saponified orange juice residue (SOJR) are easily replaced by Sr(II) during adsorption. The latter was synthesized by means of cross-linking condensation reaction with concentrated H2SO4. The adsorption of Sr(II) and Cs(I) increased with increasing pH of the solution, suggesting that these metal ions were adsorbed onto active sites of these bio-sorbents through a cation exchange mechanism. These modified biomass adsorbents were found to exhibit high adsorption capacities and fast adsorption rates for the tested metal ions. That is, the adsorption capacity of SOJR for Sr(II) was evaluated as 0.83 mmol/g whereas that obtained for the cross linked tea leaves (CTL) gel with regards to Cs was 1.22 mmol/g. In comparison to the adsorption capacities of other adsorbents, it was concluded that the SOJR and CTL displayed excellent potential for the adsorption of Sr(II) and Cs(I), respectively. Thus, the combined uses of SOJR and CTL gels can be expected to work as a promising alternative to remove radioactive Sr(II) and Cs(I) from polluted water.