Separation of chromium(VI) by adsorption onto garlic peels: kinetics, thermodynamic and isotherm study

Abstract

Garlic peel, an agriculture by-product, was modified using nitric acid as a simple method. Therefore, this study aims to remove and/or minimize of Cr(VI) ions from aqueous media using HNO3 modified garlic peel (HNO3-GP). Scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy analysis of the HNO3-GP, as a solid phase extractor, were performed. The operational parameters of the adsorption such as solution pH, initial concentration of analyte, adsorbent dose, temperature and shaking time were per-formed. The equilibrium data of Cr(VI) showed a better fit with Langmuir isotherm model with R2 = 0.9956 and adsorption capacity equals to 31.7 mg/g. Moreover, the kinetic data of analyte retained revealed that the present system fitted well with pseudo-second-order kinetic model (R2 = 0.9918). Thermodynamic studies indicated that the retention step was endothermic and spontaneous in nature depending on the value of ΔH° (118.292 J/mol) and ΔG° (–117.41 kJ/mol). The positive value of ΔS° (394.39 J/mol·K) confirmed that the biosorption process was carried out with high randomness on the surface of HNO3-GP. The results showed that the proposed adsorbent (HNO3-GP) provides an effective and economical approach in highly minimization or almost removal of Cr(VI) ions from the aqueous solution.