Chromium adsorption using waste tire and conditions optimization by response surface methodology

Chromium adsorption was investigated using waste tire adsorbent (WTA) and the process variables (pH, adsorbent dosage, Cr ions initial concentration, contact time) were optimized through response surface methodology. Initial metal ions concentration (20–820 mg/L), pH (1.0–9.0 for Cr(VI) and 1.0–5.0 for Cr(III)), contact time (288–1440 min) and adsorbent dose (0.1–2.1 g/100 mL) were selected and optimized as experimental variables, which affected the Cr adsorption significantly. The optimum conditions for maximum Cr(VI) adsorption were found as; 336.63 mg/L initial concentration, pH 4.8, contact time 882.5 min, whereas for Cr(III), the optimum levels of process variables were 1.2 g/100 mL and 337 mg/L, 3.0, 910.18 min and 1.3 g/100 mL solution, respectively. The sorption capacities were 105.84 and 174.55 mg/g for Cr(VI) and Cr(III), respectively. At optimized conditions, 79.6% (214.72 mg/g) Cr was sequestered from tannery effluents. The Langmuir isotherm and pseudo-first order kinetic model fitted well to the Cr adsorption data. The FTIR study revealed the involvement of hydroxyl, amino and carboxylic acid functional groups in the adsorption of Cr ions.