Influence of adsorption parameters of basic red dye 46 by the rough and treated Algerian natural phosphates

The paper reports on the adsorption behavior of basic red dye 46 from aqueous solution onto rough and treated Algerian natural phosphates. Adsorption tests were realized in static mode on natural rock phosphate and treated samples by sifting, chemical or thermal way. The adsorption process was evaluated as a function of various operating parameters such as contact time, pH of the medium, temperature, concentration, agitation speed and adsorbent mass. The adsorption ability depends mainly on the nature of mineralogical species as well as on the smoothness of the grains. It was found that the dye has more affinity for the carbonate-rich than for the phosphate-rich material. The amount of the dye adsorbed increases with the mass of adsorbent. The adsorption process was pH-dependent with a high adsorption capacity at pH 8. The chemical and thermal treatments performed on different phosphate samples have affected negatively their adsorption capacity of the dye used. The experimental isotherm data were analyzed using the Langmuir, Freundlich and Temkin models. The equilibrium data fit well the Langmuir isotherm. The calculations of the maximum amounts (qm) obtained from this model have shown that it is the fine fraction (T) which adsorbs the highest amount (28.5 mg g−1), followed by the coarse fraction (C) (15.62 mg g−1) and raw phosphate (RP) (14.7 mg g−1). The best results were obtained for dye concentration of 15 mg g−1, adsorbent mass of 3 g L−1, agitation speed of 300 trs min−1, and pH 8 at 20 °C. The experimental data were analyzed using three kinetic models: the pseudo first order, pseudo second order and intraparticle diffusion models. The linear regression, standard statistics of root mean squared error (RMSE) was carried out to support the best fit kinetic models. Based on the low RMSE values, the pseudo second order model is the one that best describes the adsorption of basic red dye 46 on phosphates. The results obtained in this study suggest that Algerian natural phosphates may be used as an efficient and low cost sorbent material for organic pollutants, and thus represent a promising alternative for eliminating dyes from industrial wastewaters.