Valorization of raw biomaterial waste-date stones-for Cr (VI) adsorption in aqueous solution: Thermodynamics, kinetics and regeneration studies

•The FTIR analysis was used to confirm the functional groups of Date Stones.•The adsorption capacity of Cr (VI) increases with the decrease of pH.•Experimental data were best modeled by Langmuir isotherm.•The pseudo-second order model best described the biosorption kinetics.•Results recommend this biomaterial as a low-cost and effective biosorbent.

The objective of this study is to see, if raw local Date Stones (D.S) waste can be successfully used as biosorbent for removing of hexavalent chromium Cr (VI) from aqueous solution. The characterization of this raw biomaterial has been performed using various analytical techniques such as FTIR, SEM, XRD and BET surface area. The experiment results in batch adsorption show that optimum conditions are: initial Cr (VI) concentration 100 mg L−1, pH 2, equilibrium contact time 60 min and D.S concentration 1 g L−1. The corresponding adsorption capacity was around 70 mg g−1. These results are well modeled by Langmuir isotherm and kinetics study followed the pseudo second-order model. The adjustment of models was confirmed by the Chi-square (χ2) test and the correlation coefficient R2. Thermodynamic parameters indicate that the adsorption process is spontaneous and endothermic. The chemical regeneration tests showed that, NaOH is the best eluent. Based on these results, D.S could be used as an ecofriendly and economic biosorbent for removing of Cr (VI) from aqueous solution.