Green synthesis for novel sorbent of sand coated with (Ca/Al)-layered double hydroxide for the removal of toxic dye from aqueous environment

The novel point of this study is utilization of alum as a cheap compound and cement kiln dust by-product waste resulted from cement industry in the production of layered double hydroxide (LDH) of calcium and aluminum. The gel-solution of this compound was identified by X-ray diffraction (XRD) analysis and immobilized on the sand surfaces to create new sorbent named sand coated with (Ca/Al)-LDH. To obtain the highest adsorption capacity for prepared sorbent-Congo red dye interaction, the synthesis parameters were: pH 8, (Ca/Al) molar ratio 2 and dosage of sand 1 g/100 mL. Batch and continuous studies demonstrated that the prepared material was an effective and efficient sorbent for the removal of Congo red dye from simulated wastewater. For initial dye concentration of 50 mg/L, more than 90% of this dye was removed in the batch tests under initial pH-7, time-60 min, sorbent dosage-0.2 g/50 mL and speed-200 rpm with maximum adsorption capacity of 60.64 mg/g. Sorption isotherm and kinetic measurements have formulated in precision manner by Langmuir and pseudo second-order models, respectively and this means that the dye removed by chemisorption. Also, characterization analyses signified that the new nanoparticles precipitated on the sand have significant participation in the supporting of dye sorption. Finally, the longevity of prepared sorbent in packed column increased dramatically with decreasing of flow rate and inlet concentration of contaminant as well as increasing of sorbent mass. Measured breakthrough curves were well simulated by numerical modeling for solute transport equation solved by COMSOL package.

Automated summary

This study utilized alum and cement kiln dust by-product waste to produce (Ca/Al)-LDH sorbent for effective removal of Congo red dye from simulated wastewater. The new nanoparticles precipitated on the sand surface significantly supported dye sorption, with the adsorbent's longevity in packed column increasing dramatically with controlled flow rate and sorbent mass. Numerical modeling effectively simulated breakthrough curves for solute transport equation, demonstrating the stability and efficiency of the prepared sorbent.