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In this study, a carbonate material (CM) and its form heated to 900°C (CM900) were used to remove Congo red (CR) from aqueous solutions. The objective was to combine the results of the characterization of the modified material, CR adsorption and spectroscopic study to propose a coherent mechanism of the CR-CM900 interaction. A bibliographical study on the adsorption of dyes by carbonates and their interactions revealed the scarcity of published works. This study will compensate somewhat for the lack of results in this field. Carbonate materials are abundant, low-cost and available in different countries around the world. The materials were characterized by X-ray diffraction and scanning electron microscopy. A solid/solution concentration of 1 g·L-1, pH of 6.9, equilibrium time of 2 h and temperature of 40°C, were found to be the optimum conditions for a maximum amount of CR adsorbed by CM900 of 288.2 against 32.7 mg·g-1 for CM. A full decarbonation of CM900 results in MgO and CaO, releases CO2 from the structure, and leads to a more porous structure. The pseudofirst-order model adequately described the kinetic data. The experimental isotherms were suitably fitted by the Redlich-Peterson model with determination coefficient and average relative error values =0.97% and <10.0%, respectively. Thermodynamic parameters suggested a spontaneous and endothermic process. Methanol easily desorbed the CR adsorbed by CM900 which maintained its adsorption capacity during three adsorption-desorption cycles. Fourier-transform infrared spectroscopy investigation before and after the dye adsorption showed that the CR-CM900 interaction involves a mechanism of outer-sphere complexation between the amine groups and the hydroxylated magnesium oxides. Understanding the interactions between dyes and carbonate materials is an important approach to develop the use of these materials in wastewater treatment. [ABSTRACT FROM AUTHOR]

Algerian dolomite was treated at different temperatures in the 600–1000°C range and characterized by XRD and SEM. The obtained samples, named dolomitic solids, were used in the removal of Reactive Black 5 (RB5) from aqueous solutions. A literature survey shows that the data about the dye adsorption by dolomites are almost non-existent. Kinetic data, equilibrium isotherms, thermodynamic parameters, pH influence, and FTIR study were considered. The kinetic mechanism is enough complex, involving different models such as those of pseudo-second-order, intraparticle diffusion, and Elovich. For all dolomitic solids, the capacity in RB5, at equilibrium, strongly increases with increasing adsorption temperature. The affinity sequence is D900 (dolomite treated at 900°C) > D800 > D1000 > D600 > raw dolomite. Knowing that D900 adsorbs 125.9 mg g−1, it appears very effective for removing reactive dyes from wastewaters. The isotherms are found to be overall well represented by the Redlich–Peterson equation. The fact that maximum adsorption occurs at isoelectric point emphasizes the prevalence of the nonelectrostatic interaction. A close agreement exists between the evolution of kinetic, equilibrium, and thermodynamic parameters, suggesting chemisorption. The process reflects for D800, D900, and D1000 a weak chemical interaction via a mechanism of inner-sphere complexation. The comprehension of the organic compound–dolomitic solid interactions constitutes a fundamental aspect for developing the application of these materials in the field of wastewater treatment. [ABSTRACT FROM PUBLISHER]