Extraction of silica from sugarcane bagasse ash and its utilization in zeolite 4A synthesis for CO₂ adsorption

Sugarcane bagasse ash (SCBA) is a solid waste containing a high amount of silica (SiO₂) and is suitable to utilize as a silica source for synthesizing zeolite NaA. SCBA is typically calcined at high temperatures before silica extraction. The method is not environmentally friendly because it consumes energy and produces CO₂. This work demonstrates an alternative extraction method of SiO₂ from SCBA by treating it with hydrochloric (HCl) and sodium hydroxide (NaOH) solution. The obtained mixture was separated by paper filter No. 1 (P) and a combination of paper filter and syringe filter (PS). The solution was neutralized by HCl solution, producing silica (SiO₂-P and SiO₂-PS) with a purity of 98 wt%. Both SiO₂ samples and SCBA were utilized to synthesize zeolite NaA for CO₂ adsorption. The CO₂ adsorption capacities of NaA-P and NaA-PS were 4.30 and 4.10 mmol g_adsorbent ^-1, in the same range as commercial NaA. The capacity is influenced by the total basicity of zeolite. The CO₂ adsorption behavior of all samples correlates well with the Toth model. The CO₂ adsorption kinetics agrees well with the pseudo-second-order kinetic model. Overall, this work shows the successful extraction of silica via using a direct NaOH solution, yielding high-purity silica sufficient for synthesizing zeolite NaA, a promising adsorbent of CO₂.