Adsorption Modeling of Cr^+3 on Volcanic Tuff-Based Geopolymer

In the current work, geopolymer was synthesized from volcanic tuff and was then used as a sorbent for Cr^+3 from aqueous solutions. An adsorption batch experiment was conducted to study the factors affecting the adsorption process. The obtained results showed a high removal efficiency of geopolymer (96 %) against 70 % for the volcanic tuff with an uptake capacity of 21.24 and 14.76 mg/g for both materials, respectively. The removal efficiency increased with increasing the pH up to 5, geopolymer dosage, contact time up to thirty minutes, temperature, and the decrease of Cr^+3 initial concentration in the studied ranges. The validity of the isotherm models to the experimental data can be ranked in the order of Langmuir Temkin Frundilch Dubinin–Radushkevich. The kinetic study showed that the second order model provided the best fit with R^2 of 0.97 against 0.44 and 0.62 for the first order and the intra-particle model. The sorption process can be described as endothermic, monolayer, physical, and of a high ion affinity to the surface of the geopolymer. The results obtained buttressed the applicability of using a volcanic tuff-based geopolymer for the Cr^+3 removal as a low-cost natural material at low concentrations.