Efficient removal of chromium(VI) from dilute aqueous solutions using agro-industrial residue based on parboiled-rice husk ash

The removal of Cr(VI) from wastewater by adsorption from agro-industrial residues remain an attractive option since combines reasonable cost with the quality of effluents treated. This paper employs of parboiled-rice husk ash (RHA) and parboiled-rice husk ash chemically treated (RHAH(+)) as adsorbents for Cr(VI). The RHA and RHAH(+) were characterized. It was studied the adsorption efficiency on adsorbent dosage, pH, chromium concentration, and interaction time. RHAH(+) presented superior Cr(VI) removal, although both adsorbents have shown satisfactory results. The best results are obtained at pH 1.0, presenting 90.9% and 97.7% of Cr(VI) removal for RHA and RHAH(+), respectively, in 5 mg L-1 of Cr(VI) concentration at about 30 minutes. The adsorption of RHAH(+) is governed by the Freundlich isotherm (R-adj(2) = 0.989) and kinetically by the pseudo-second order model (R-adj(2) = 0.991). The rice rusk ash represents an alternative low-cost and environment-friendly material that efficiently removes Cr(VI) from dilute aqueous solutions.