Abstract
This article describes how selectively anionic organic molecules could be removed from aqueous medium using naturally available gypsum (GS) adsorbent. Gypsum (CaSO4.2H2O) shows strong interactions with anionic dye molecules while it dos not show any affinity towards cationic dye molecules. We have shown the removal efficiency of gypsum taking chlorazole yellow (anionic dye) and methylene blue (cationic dye) as examples of adsorbates. The GS has been to be even more effective than activated carbon in attaining chlorazole yellow (CY) removal. Three well-known kinetic equations e.g. pseudo-first-order, pseudo-second order and intraparticle diffusion were exploited to interpret the experimental data. Results show best fitting with second order kinetic process with excellent regression coefficient (r2 = 0.99) for the adsorption process. The equilibrium data were analyzed exploiting some adsorption isotherm models. It was apparent that the Freundlich isotherm model superbly fitted for CY dye adsorption process. And the maximum adsorption capacity, Qm, was obtained as 12.85 mg g−1 at room temperature. The negative values of Gibb’s free energy change (ΔGo) suggests that the CY dye molecule adsorption process is spontaneous in nature. Moreover, negative enthalpy change (ΔHo) indicates the exothermic nature of the adsorption process. The outcome could be exploited where anionic organic molecules are required to be separated, selectively.
Highlights
Nowadays, the increasing world population has created exponent of an alarming contamination of surface and ground water
The Chemical Oxygen Demand (COD) of the Chlorazol Yellow (CY) solution was determined before and after the adsorption process following the method prescribed by American Public Health Association (APHA) (Arami et al 2006)
It is clearly seen from this figure that the concentration of CY molecules fallen more rapidly when gypsum was used as adsorbent instead of activated carbon (AC)
Summary
The increasing world population has created exponent of an alarming contamination of surface and ground water. Textile and dyeing industries are playing an important role on economic and industrial. Removal of dye molecules from wastewater is extremely difficult and is a most thought-provoking matter in environmental network and industries. Several methods such as coagulation, sedimentation, filtration, oxidation, adsorption (Islam et al 2019; Youcef et al 2019; Acar et al 2015), photo catalytic degradation (Gotoh et al 2004; Miyah et al 2018), biodegradation (Hasnat et al 2005)
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