This research was conducted to synthesize silica from sugarcane baggase and to understand the adsorption process of nitrate ions by silica. The propose of the adsorption process was based on the best fit of experimental data to calculated fit using the equation model, proton stoichiometry, (c), e.i. the number of protons taken or released by the adsorption process, and other adsorption parameters produced by the isotherm models, such as: site density of sorbent (N_m), equilibrium constant for the adsorption process (K), energy involved in the adsorption. The product of silica from the baggase was characterized by FTIR and compared to that of silica Kiesel 60 (Merck), as well as by XRD. Data of experimental adsorption were collected by varying concentrationat the system of nitrate ions and the silica at a constant pH of 7.0 and room temperature at equilibrium time of 30 minutes. Data of proton stoichiometry were calculated from the amount of added H⁺ or OH¯ ions to maintain the constant pH of 7.0 during the adsorption experiment of each concentration studied. Experimental data fitted very well to the Freundlich isotherm equation, indicating the formation of multilayer coverage on surface sites of silica. Few amount of c indicated that adsorption process did not involve significant amount of proton. The energy involving the adsorption process was calculated from Dubinin-Radushkevich model and was 5.61 kJ/mole.   From the model, this research proposed that adsorption process of nitrate ions on silica was through physical process.

Keywords: nitrate adsorption; adsorption process; physisorption