Efficient removal of aqueous chromium using hydrothermally activated perlite

Abstract

The removal of chromium from wastewater has received considerable attention in recent years due to its harmful environmental effects. This study evaluated the chromium adsorption capacity of activated perlite obtained by a hydrothermal process using 20% NaOH and 30% NaCl. The experiments were performed using a synthetic Cr(OH)SO₄ solution containing chromium predominantly as Cr(III), as confirmed by chromium speciation analysis. Adsorption experiments based on a factorial design assessed the effects of initial chromium concentrations (401-1482 mg L^-¹) and activated perlite dosages (10-30 g L^-¹). The Langmuir isotherm provided the best fit to the data at 273.15-298 K, yielding a maximum adsorption capacity of 133 mg g⁻¹ and a Langmuir constant of 0.09 L mg⁻¹. Kinetic data were consistent with both pseudo-first-order and pseudo-second-order models. Hydrothermal activation increased the cation exchange capacity from 90.57 to 120.52 meq per 100 g. Statistical analysis indicated that chromium removal followed a linear model relative to both initial concentration and adsorbent dosage. These results demonstrate that hydrothermally activated perlite is a promising low-cost and sustainable adsorbent for the removal of Cr(III) from tannery effluents, with potential for large-scale implementation.

Keywords: adsorption isotherm, cation exchange, chromium, factorial design, hydrothermally activated perlite, kinetics.