Chromium (III) Sequestration by Oats Straw and Agave Baggasse: Sorption Mechanism

Agro-waste materials such as oats straw (OS) and agave baggasse (AB) have functional groups which are able to bind metal ions. The agro-waste materials studied in this research (acid washed) were chemically characterized and their chromium sorption and desorption capacity was obtained. HNO3, NaOH and EDTA (at different concentrations and temperatures) were used to regenerate partially saturated biosorbents. Finally, the chromium (III) sorption mechanism was discussed. The results demonstrated that OS and AB contain carboxyl and hydroxyl functional groups. The chromium (III) removed by acid washed OS and AB was 2.48 and 9.85 mg/g, respectively. Based on chromium (III) removed and ions released (mainly H and Ca) during the sorption process, it was suggested that the main sorption mechanism was ion exchange: for each mol of CrOH adsorbed 1 mol of Ca and 2 mol of H were released to the solution. On the other hand, the highest chromium desorption was obtained by using an EDTA solution at 55°C. Oats straw and agave baggasse are capable of removing cations from aqueous solution. Preliminary results show that chromium (III), as CrOH, is exchanged by Ca and H during the sorption process. In addition, an EDTA solution could be used to regenerate the chromium loaded biosorbents.