Agro-waste materials such as oats straw (OS) and agave baggasse (AB) have functional groups (mainly carboxyl and hydroxyl) 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. Functional groups, equilibrium constants, surface charge distribution and ATR-FTIR analysis were the parameters used to characterize these biosorbents. The adsorption of chromium (III) was carried out at 25°C, pH 4, and an initial concentration of 20 mg of Chromium (III)/L in batch reactors. HNO₃, NaOH and EDTA (at different concentrations and temperatures) were used to regenerate partially saturated biosorbents. Also the chromium (III) speciation diagram was computed. Finally, the chromium (III) sorption mechanism was discussed based on Ca²⁺ and H⁺ released.

The results demonstrated that oats straw and agave baggasse contain carboxyl and hydroxyl functional groups. 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 Ca²⁺) during the sorption process, it was suggested that the main sorption mechanism was ion exchange: for each mol of CrOH²⁺ adsorbed 1 mol of Ca²⁺ 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.

Agro-waste materials such as oats straw and agave baggasse are capable of removing cations from aqueous solution. Preliminary results show that chromium (III), as CrOH²⁺, is exchanged by Ca²⁺ and H⁺ during the sorption process. In addition, an EDTA solution could be used to regenerate chromium loaded biosorbents.

Keywords: Oats straw, Agave baggasse, Chromium (III), Sorption, Mechanism.