Evaluation of Illitic-Kaolinite clay as an adsorbent for Cr3+ removal from synthetic aqueous solutions: Isotherm, kinetic, and thermodynamic analyses

Abstract

This study explores the adsorption capabilities of Illitic-Kaolinite clay (IKC) as an effective adsorbent to remove chromium ions from aqueous solutions. To provide comprehensive insights into the adsorption process, the IKC material was characterized using several techniques including X-ray diffraction (XRD), X-ray fluorescence (FX), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM-EDX). Qualitative mineralogical analysis of IKC reveals the presence of illite with minor amounts of kaolinite. The investigation encompassed an array of experimental parameters, such as adsorbent dosage (50-500 mg), adsorption contact time (0-180 min), solution pH (2-6), initial Cr3+ ion concentration (10-200 mg.L−1), and temperature (25-55°C), in order to understand their influence on the adsorption process. The results indicated a clear connection between the efficiency of chromium removal and increases in pH, concentration and temperature, leading to improved chromium removal efficiency. The maximum adsorption capacity of IKC for chromium ions were evaluated as 14.27 mg.g−1. The adsorption data for chromium ion exhibited strong conformity to the Freundlich isotherm model (R²=0.98), while the kinetic data showed a significant correlation with the Elovich model (R²=0.993), suggesting that chemisorption governs the rate-limiting step. Thermodynamic analyses confirmed spontaneous and feasible adsorption, indicated by the negative value of ΔG. The positive values of ΔH and ΔS further revealed the endothermic nature of the process and an increase in molecular disorder at the solid-liquid interface during adsorption. The findings of this study provide valuable insights into the potential of Illitic-Kaolinite clay as an efficient and cost-effective adsorbent for the removal of heavy metals contaminants from aqueous solutions. This contribution supports ongoing efforts to address water pollution and purification challenges.