Sodalite zeolitic materials produced from coal fly ash for removal of congo red dye from aqueous solutions

Abstract Coal fly ash (CFA) is an excellent source of silica–alumina precursor that can be used for the copious and continuous manufacturing of zeolitic materials. This study provides a novel strategy to prepare zeolitic sodalite from CFA as adsorbents for Congo red (CR) dye removal under variable conditions. Sodalite crystals (S) were prepared by a calcination of sodium–aluminum silicate derived from CFA in either absence or presence of cetyltrimethylammonium bromide (CTAB) surfactant (CTAB-S). SEM, XRD, FTIR, and N 2 adsorption measurements were demonstrated. XRD results confirmed the presence of mullite and quartz as main components in CFA which converted to sodalite phases after calcination in existence of CTAB. SEM revealed that agglomerated larger particles were formed in S sample without adding CTAB, whereas smaller spherical particles aggregated together upon adding CTAB to form zeolitic structure (CTAB-S). FTIR showed the characteristic absorption bands of sodalite related to oxygen-containing Si and Al groups. Batch adsorption isotherm studies were conducted to evaluate the maximum adsorption capacities of S and CTAB-S, which were amounted to be 152.7 and 184.8 mg/g, respectively. Adsorption of CR dye was fitted with Freundlich isotherm. Kinetic results perfectly matched with pseudo-second-order model and intraparticle diffusion. Thermodynamic findings indicated that the adsorption of CR dye over both samples was endothermic and spontaneous in nature. CTAB-S sample showed the best reusable adsorbent, according to reuse experiments employing water as a desorbing agent. Overall, it can be concluded that CFA-derived sodalite can be used as an effective adsorbent for anionic dyes removal from wastewater.