Removal of Anionic Dye from Aqueous Solution Using Treated Laterite Adsorbent: Response Surface Methodology Approach

Abstract: This study investigates the removal of Congo red (CR) dye from aqueous solution using treated laterite (TL) as a low-cost adsorbent. The effects of pH, contact time, initial dye concentration, adsorbent dosage, and temperature on adsorption efficiency were evaluated. Equilibrium was established within 90 minutes, with negligible temperature effects observed. Response Surface Methodology (RSM) with Central Composite Design (CCD) was employed to optimize three adsorption parameters: pH (4–7), initial dye concentration (10–50 mg/L), and adsorbent dosage (200– 1500 mg). ANOVA analysis revealed that all three factors were statistically significant (p < 0.001), but initial concentration exerted the strongest influence (F-value = 256.94). Significant two-way interactions were identified between pH and dosage (p = 0.000, F = 32.36) and pH and concentration (p = 0.015, F = 8.64). The quadratic model demonstrated excellent fit with R² = 0.9707 and adjusted R² = 0.9442. Optimal conditions for maximum dye removal were determined to be pH 4.8, an initial dye concentration of 52 mg/L, and an adsorbent dosage of 850 mg. These findings demonstrate that treated laterite is an effective, sustainable adsorbent for the removal of anionic dyes from textile wastewater.

Keywords: Congo red dye; Treated laterite; Adsorption; Response surface methodology; Central composite design; ANOVA; Wastewater treatment.