Effect of the acid treatment conditions of kaolinite on etheramine adsorption: A comparative analysis using chemometric tools

The present work evaluated the effect of the acid treatment conditions of natural kaolinite (NK) regarding its efficiency in removing etheramine. The treatment was conducted using sulfuric acid at the concentrations of 1 mol L^-1 (KA-01), 2 mol L^-1 (KA-02) and 5 mol L^-1 (KA-05) at 85 °C. The obtained adsorbents were characterized by X-ray fluorescence, X-ray diffraction, N₂ adsorption/desorption isotherms, zeta potential analysis and infrared spectroscopy. The Response Surface Method was used to optimize adsorption parameters (initial concentration of etheramine, adsorbent mass and pH of the solution). The results, described by means of a central composite design, were adjusted to the quadratic model. Results revealed that the adsorption was more efficient at the etheramine concentration of 400 mg L^-1, pH 10 and adsorbent mass of 0.1 g for NK and 0.2 g for KA-01, KA-02 and KA-05. The sample KA-02 presented a significant increase of etheramine removal compared to the NK sample. The adsorption kinetics conducted under optimized conditions showed that the system reached the equilibrium in approximately 30 min. The kinetic data were better adjusted to the pseudo-second order model. The isotherm data revealed that the Sips model was the most adequate one. The calculation of E_ads allowed to infer that the mechanism for etheramine removal in all the evaluated samples was chemisorption. The reuse tests showed that, after four uses, the efficiency of adsorbents in removing etheramine did not suffer significant modifications, which makes the use of kaolinite to treat effluents from the reverse flotation of iron ore feasible.