Theoretical and Experimental Study of the Adsorption of Natural Red 4 Dye from Synthetic Aqueous Media Using a Low-cost Silica-smectite Composite

Abstract

Purpose: A study of the removal of dye Natural red 4 (NR4) by a low-cost silica-smectite clay labeled SSC was carried out.

Methodology: Batch tests were carried on with some processing parameters namely initial dye concentration (10 - 50 mg/L), temperature (25 - 65 °C), adsorbent dose (1 - 5 g/L), initial pH (4 - 8) and contact time (0 - 120 min).

Findings: The Energy of adsorption was less than 20 kJ/mol showing a physisorption process. Also, thermodynamics parameters such as enthalpy of activation ∆H* (19.0 kJ/mol), entropy of activation ∆S* (- 024 kJ/mol/K) and Gibbs free energy of activation ∆G* (90.57 - 100.17 kJ/mol) revealed that the adsorption of NR4 molecules onto SSC was endothermic and with no significant changes in the internal structure of the adsorbent. The pseudo-first order and pseudo-second order had a good correlation with experimental data with R² = 0.99 and R² = 0.98 respectively. Langmuir isotherm model matched well the equilibrium data with a maximum adsorption capacity Q_m of 25.55 mg/g. and a correlation value of 0.98.

Unique Contribution to Theory, Policy and Practice: The newly synthesized and characterized low-cost silica-smectite composite is effective in the adsorptive removal of natural red 4 dye from water wastes.