Hexavalent chromium removal performance of a locally sourced kaolin sheep wool composite adsorbent

This study reports the development and systematic characterization of a magnetized kaolin–sheep wool composite adsorbent engineered from locally available raw kaolin and waste sheep wool composite was characterized using FTIR, SEM, and XRD analyses, demonstrating successful integration of functional groups, a heterogeneous surface morphology, and a stable structural matrix highly favorable for metal binding. Batch adsorption experiments were conducted to evaluate the effects of contact time, adsorbent dosage, temperature, pH, initial \(\:Cr(VI)\) concentration, and particle size on removal efficiency. Under optimized experimental conditions of \(\:2.5 g/L\) adsorbent dosage, \(\:{20}∘\:C\) , \(\:pH\:2\) , \(\:210 min\) contact time, and a \(\:63\:μ\:m\) particle size, a maximum \(\:Cr(VI)\) removal efficiency of 99.97% was achieved. Equilibrium studies revealed a maximum adsorption capacity ( \(\:{q}ₘₐₓ\) ) of 2.48 mg/g, which was achieved at an initial \(\:Cr(VI)\) adsorbate concentration of 10 mg/L. The adsorption equilibrium data were best described by the Freundlich isotherm model ( \(\:{R}²=0.961\) ), indicating multilayer adsorption on a heterogeneous surface, while the kinetic data adhered to the pseudo-second-order model ( \(\:{R}²=0.999\) ), signifying chemisorption as the rate-limiting mechanism. Thermodynamic parameters confirmed that the adsorption process was spontaneous and exothermic ( \(\:{Δ\:}{H}∘\:=-37.82\:kJ/mol\) ). These results demonstrate serves as an outstanding and environmentally sustainable adsorbent.