Kinetic and thermodynamic studies on the biosorption of Cr(VI), Cu(II), and Zn(II) ions onto waste biomass of rice husk

ABSTRACT Rice husk is used as a biosorbent due to its chemical composition and irregular surface. In this work, we studied the chemical modification of rice husk in order to improve the removal of Cr(VI), Cu(II), and Zn(II) ions from synthetic solutions. Rice husk was treated with distilled water (RH-H2O), solutions of sodium hydroxide 0.5, 0.25, and 0.1 mol × L−1, and different acids (0.1 mol × L−1 HCl, H2SO4, H3PO4). The biosorbents from each treatment with the highest metal ion removal efficiency were selected for kinetic and thermodynamic studies. The results showed that the greatest biosorption efficiency for Cr(VI), Cu(II), and Zn(II) ions was achieved with sodium hydroxide treatment. Furthermore, Cu(II) and Zn(II) ions were more effectively removed from aqueous solutions than Cr(VI) by the studied samples. Kinetic studies indicated that the process followed a pseudo-second-order model, with rate constants of 0.61, 4.11, and 4.75 g·(mmol·s)−1 for Cr(VI), Cu(II), and Zn(II), respectively. Analysis of the kinetic data showed that the biosorption of Cr(VI), Cu(II), and Zn(II) onto biosorbents derived from rice husk was governed by a mixed-diffusion process and interaction with functional surface groups. The biosorption process for Cu(II) and Zn(II) was found to be spontaneous, whereas it was not spontaneous for Cr(VI).