Extraction of silica from sugarcane bagasse ash and its utilization in zeolite 4A synthesis for CO 2 adsorption.

Sugarcane bagasse ash (SCBA) is a solid waste containing a high amount of silica (SiO 2 ) 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 CO 2 . This work demonstrates an alternative extraction method of SiO 2 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 (SiO 2 -P and SiO 2 -PS) with a purity of 98 wt%. Both SiO 2 samples and SCBA were utilized to synthesize zeolite NaA for CO 2 adsorption. The CO 2 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 CO 2 adsorption behavior of all samples correlates well with the Toth model. The CO 2 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 CO 2 .