Comparison of adsorption equilibrium models and error functions for the study of sulfate removal by calcium hydroxyapatite microfibrillated cellulose composite

Sorption, mechanism, and behavior of sulfate on various adsorbents: A critical review

Sulfate decontamination has drawn widespread attention due to its harmful effects by broad human and animal exposure in recent decades. Adsorption is one of the most promising methods for sulfate decontamination. This review categorized various sulfate adsorbents, discussed the adsorption behavior, and introduced effective adsorbents in detail in terms of their preparation, characterization, and affecting factors on adsorption efficiency. Moreover, adsorption mechanisms of sulfate on different adsorbents are reviewed based on the intermolecular interaction, equilibrium, thermodynamic, and kinetic studies. Among natural bioadsorbents, synthesized-organic, and synthesized-inorganic adsorbents chitin-based shrimp shells (156 mg/g), bagasse pith cellulose-based (526.32 mg/g), and ZrO(OH)₂/Y-Zeolite (284.22 mg/g) showed the significant capacity for sulfate uptake from aqueous solution, respectively. Although natural adsorbents have been proved to be inexpensive and efficient, they are not as popular as synthesized adsorbents for sulfate decontamination in recent years due to their low recoverability and reusability. The adsorption mechanism of sulfate to various adsorbents is generally attributed to electrostatic interactions, covalent or ionic bonding, and hydrogen bonding. Based on equilibrium studies, sulfate adsorption processes were done mainly homogeneously for most of the adsorbents; however, there are some exceptions of the heterogeneous adsorption process of sulfate, which is done mostly for adsorbents that remove sulfate through hydrogen and covalent bonding. The kinetic studies illustrated that both film diffusion and pore-diffusion could control sulfate uptake by the various adsorbents. The thermodynamic studies showed that the sulfate adsorption is endothermic and spontaneous except for the sulfate removal by polypyrrole-modified activated-carbons and LDH-HPI mine waste, which requires energy for adsorption.

Hydrothermal synthesis of LaFeO3 nanoparticles adsorbent: Characterization and application of error functions for adsorption of fluoride

The adsorption of fluoride from aqueous solution by lanthanum ferrite nanoparticles (LaFeO₃ NPs) synthesized by the hydrothermal method has been investigated. This experimental study was conducted on a laboratory scale. The effects of various operating parameters such as pH (3-11), LaFeO₃ NPs dosage (0.1-1.0 g/L), contact time (15-120 min), temperature (303-318 K), and initial concentration of fluoride (15-40 mg/L) on fluoride adsorption were studied. The results showed that under optimal conditions of fluoride concentration of 20 mg/L, pH of 5, LaFeO₃ NPs dosage of 0.9 g/L, temperature of 308 K, and contact time of 60 min, maximum percentage removal of 94.75 % was obtained. The process of fluoride adsorption on LaFeO₃ NPs was found to depend on the Freundlich adsorption and Koble-Corrigan isotherm models. The monolayer adsorption capacity of LaFeO₃ NPs was 2.575 mg/g. The kinetic data fitted best into the pseudo-second-order model considering the values of the regression coefficients (r²) and error functions used. The thermodynamics study indicated that the adsorption process was exothermic (ΔH°< 0) and spontaneous (ΔG°< 0) in nature. It could be concluded that the synthesized LaFeO₃NPs can be used as an effective adsorbent for fluoride ions removal from aqueous solutions.