The aim of this study is to evaluate the potential of red mud applied as an adsorbent in the removal of dyes from the textile industry; the adsorption process was optimized using both response surface methodology and desirability function. Scanning electron microscopy (SEM), X-ray diffraction (XRD), point of zero charge (pH_PZC), nitrogen physisorption and thermogravimetric analysis techniques were used to characterize the adsorbent. Adsorption process was based on an experimental design, where contact time (5 and 60 min), pH of the medium (4 and 6.5) and adsorbent concentration (5 and 10 mg L⁻¹) were the independent variables. In addition, the kinetic mechanism and adsorption equilibrium were investigated. The results indicated that a higher removal efficiency of methylene blue was obtained at higher adsorbent concentrations (8–10 mg L⁻¹) and lower pH ranges (4.0–5.0), while increasing the adsorptive capacity is achieved by decreasing the adsorbent concentration and pH. The optimum adsorption conditions were: 60 min, a pH of the medium at 4.0 and adsorbent concentrations of 8.66 and 10 g L⁻¹. The equilibrium data were fit to the Langmuir equation (R² = 0.993) with a maximum adsorption capacity of 6.541 mg g⁻¹. Experimental measurements showed that the adsorption kinetics corresponded to a pseudo-second-order reaction (R² = 0.998) with the chemisorption as the process controlling step. The results obtained in this work indicated that red mud can be an alternative for the removal of pigments in wastewater treatment processes in an efficient and economical way.

Graphic abstract

中文翻译：

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使用亚马逊地区的赤泥作为吸附剂去除亚甲蓝：工艺优化，等温线和动力学研究

这项研究的目的是评估红泥作为吸附剂从纺织工业中去除染料的潜力。使用响应面方法和合意函数对吸附过程进行了优化。使用扫描电子显微镜（SEM），X射线衍射（XRD），零电荷点（pH _PZC），氮物理吸附和热重分析技术来表征吸附剂。吸附过程基于实验设计，其中接触时间（5和60分钟），介质的pH（4和6.5）和吸附剂浓度（5和10 mg L ^-1）是自变量。此外，还研究了动力学机理和吸附平衡。结果表明，在较高的吸附剂浓度（8–10 mg L ^-1）和较低的pH范围（4.0–5.0）下，亚甲基蓝的去除效率较高，而通过降低吸附剂的浓度和pH值可以提高吸附能力。 。最佳吸附条件为：60分钟，介质的pH值为4.0，吸附剂浓度为8.66和10 g L ^-1。平衡数据符合Langmuir方程（R ²  = 0.993），最大吸附容量为6.541 mg g ^-1。实验测量表明，吸附动力学对应于拟二级反应（R ²  = 0.998），化学吸附是过程控制步骤。在这项工作中获得的结果表明，赤泥可以作为一种有效且经济的方式来去除废水处理过程中的色素。

图形摘要