Optimization of basic red 29 dye removal onto a natural red clay using response surface methodology

In this study, a natural red clay, a low-cost and abundant adsorbent, was investigated for the removal of Basic Red 29 dye from aqueous solutions. The effects of key parameters such as pH, adsorbent dose, initial dye concentration, contact time, and ionic strength on the adsorption capacity of red clay were systematically studied and optimized using response surface methodology. The suggested model was approved with high correlation coefficient (R2 = 0.9994) and (Radj2 = 0.9985). Furthermore, the model's p value was found to be < 0.001 and an F-value of 1215.41 indicates the model's high significance. According to the analysis of variance (ANOVA), the linear effects of dye concentration and adsorbent dose were the determining factors that affect the dye removal efficiency. The adsorption capacity predicted by the model under optimum conditions (initial dye concentration of 129.25 mg/L, adsorbent dose of 1.07 g/L, and contact time of 41 min) was reached a value of 108.79 mg/g. The adsorption process followed the Langmuir isotherm model with a maximum adsorption capacity of 303.03 mg/g and was well described by the pseudo-second-order kinetic model. The effect of ionic strength revealed the importance of electrostatic interactions in the adsorption process, which was further supported by the proposed adsorption mechanism based on protonation/deprotonation and electrostatic attractions and repulsions between dye molecules and clay surface functional groups. Red clay demonstrated superior adsorption capacity for Basic Red 29 dye removal compared with other adsorbents reported in the literature. The regeneration experiments showed the effectiveness and reusability of red clay as an adsorbent. Additionally, a germination test was performed to confirm the low toxicity of the treated water after adsorption onto the red clay. The outcome of this research showed that red clay can be classified as a good and efficient adsorbent in dye removal.