Adsorptive Removal of Acid Fuchsin Dye Using By-Product Silica Fume and Laccase-Modified Silica Fume

Silica fume, also known as micro silica, is a by-product of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys. This material and laccase-modified silica fume used as alternative low-cost adsorbent materials for dye removal from aqueous solutions. The silica fume was modified to maximize its adsorption capacity. For this purpose, the laccase enzyme was purified and immobilized on silica fume. Batch adsorption experiments have been performed as a function of pH, contact time, temperature, and adsorbent dosage. The equilibrium data were analyzed using Langmuir and Freundlich adsorption isotherms. The Langmuir adsorption model provided a better fit to the data. The kinetic data were evaluated with pseudo-first-order and pseudo-second-order kinetic models. The adsorption process undergoes pseudo-second-order kinetic as proved by the high value of R2. The thermodynamic parameters such as free energy, enthalpy, and entropy were also determined. These parameters indicated that the adsorption of Acid Fuchsin dye onto silica fume and laccase-modified silica fume was a spontaneous, endothermic, and entropy-driven process. The results show that both of them, especially laccase-modified silica fume, can be used as alternative low-cost adsorbents for dye removal from aqueous colored solutions or effluents.