Use of High-Efficiency Lignocellulose-Based Materials for Toxic Ions Removal: Impact of Surface Chemistry and Mathematical Modeling

Low-cost adsorbents promote the valorization of locally sourced waste materials and are still a significant challenge for removing toxic metal ions from industrial effluents. In this sense, Castor (Ricinus communis L.) stalks (CS) were activated with an alkaline solution and tested as an adsorbent to remove nickel, copper, cadmium, and lead ions. A 2^4-1 factorial design was carried out and showed a correlation and influence of the variables, such as pH, adsorbent mass, agitation rate, and initial concentration in the adsorption process. The adsorbents in their natural, activated, and saturated states were characterized. After activation, X-ray diffraction results revealed a change from cellulose I to cellulose II. The X-ray fluorescence showed that the ion exchange adsorption mechanism occurred. For the kinetic adsorption studies, the equilibrium time was reached up to 15 min. Different isotherm models described the adsorption process, with the Sips model providing the best fit to the experimental data. Five cycles of sorption/desorption using 0.1 mol L^-1 HCl elution were carried out with a minimal loss in sorption capacity and physical degradation. Nickel and copper ions exhibited the lowest desorption rates. Due to their efficiency, CS can be a promising and low-cost alternative for removing metal ions.

Keywords:
adsorption; metals; biomass; pollutants; environmental; factorial design