Biochar-SO prepared from pea peels by dehydration with sulfuric acid improves the adsorption of Cr6+ from water

Abstract

A new biochar was produced from pea peel residues by the dehydration process. The effect of the obtained new biochar on the ability to remove Cr6+ ions from the aqueous solution was investigated. Biochar-SO was obtained from pea peel by dehydration of biochar with 50% sulfuric acid. The obtained biochars were characterized by Fourier transform infrared (FT-IR); Brunauer, Emmett and Teller (BET); Barrett-Joyner-Halenda (BJH); thermogravimetric analysis (TGA); differential scanning calorimetry (DSC); scanning electron microscope (SEM); and energy-dispersive X-ray (EDAX) analyses. The optimum pH value for Cr6+ ion removal was determined as 1.48. The maximum removal percentage of Cr6+ ions was 90.74% for Biochar-SO of 100 mg·L−1 Cr6+ ions initial concentration and 1.0 g L−1 adsorbent dosage. The maximum adsorption capacity (Q m) of biochar-SO was 158.73 mg·g−1. The data obtained were analyzed with Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherm models. In addition, the data obtained from these isotherm models were tested using different error functions (hybrid error function (HYBRID), average percent errors (APE), the sum of the absolute errors (EABS), chi-square error (X 2), and Marquardt’s percent standard deviation (MPSD and the root mean square errors (RMS)) equations. It was the Freundlich isotherm model that best fits the experimental data of biochar-SO. Kinetic data were evaluated by pseudo–first-order (PFO), pseudo–second-order (PSO), Elovich, and intraparticle diffusion models. The adsorption rate was primarily controlled by the PSO rate model with a good correlation (R 2 = 1). The adsorption mechanism of biochar-SO to remove Cr6+ ions can be based on electrostatic interaction and ion exchange with exchangeable cations in biochar such as aluminum, silicon, and calcium ions for chromium. The results indicate that biochar-SO is a promising adsorbent for the adsorption of Cr6+ ions that can be employed repeatedly without substantial loss of adsorption effectiveness.