Hexavalent chromium adsorption from aqueous solution using orange peel modified with calcium chloride: equilibrium and kinetics study

Abstract

Background: Adsorption technology using residual biomass has gained attention as a low-cost alternative for removing Cr (VI) ions from aqueous solutions. Objectives: This work attempts to study the effect of orange peel modification with CaCl2 on Cr (VI) ions uptake in batch and continuous system. In addition, pH and particle size were evaluated to determine suitable values for carrying out adsorption process. Methods/Analysis: OP-CaCl2 and OP biosorbents were characterized by FT-IR analysis in order to identify their functional groups. The pH of heavy metal ions solutions was adjusted to 2, 3, 4 and 6 and adsorbent particle size was varied in 0.355, 0.5 and 1 mm. Experimental data for batch experiments were used to calculate adsorption isotherms and kinetic. The results of adsorption on packed-bed columns were fitted to dynamic models. Desorption process was also studied to determine reusability of biomass. Findings: It was found that hydroxyl, carboxyl and aliphatic groups are the main contributors to adsorption process. The highest removal yield (86%) was achieved at pH of 2 and particle size of 0.355 mm. The chemical reticulation with CaCl2 did not improve adsorption capacity of orange peel biosorbent. Kinetic and isotherm models that best fit experimental data were Elovich´s and Freundlich´s, respectively. Regarding continuous systems, data obeyed Yoon-Nelson and Dose-response models with R2 =0.99. Desorption study with HCl reported a removal yield of 43.7% for second cycle of biosorbent use. Novelty/Improvement: These results suggested that orange peel is a suitable biosorbent alternative for removing Cr (VI).