Utilization of salt activated Raphia hookeri seeds as biosorbent for Erythrosine B dye removal: Kinetics and thermodynamics studies

Abstract

The use of a non-conventional precursor, Raphia hookeri seeds, (RHS) for the production of activated carbon through thermal and salt activation for the adsorption of Erythrosine B (EB) dye in an aqueous solution was investigated. The physicochemical properties of the prepared activated carbon were studied using standard methods. Scanning electron microscopy (SEM) displayed the surface morphology micrograph and Fourier Transform Infrared was used to identify the functional groups of the activated carbon. Adsorptive performance tests at various temperatures were evaluated at optimum results of 75 µm adsorbent particle size, 1 g adsorbent dosage, 100 mg/L adsorbate concentration and pH 4. An equilibration time of 90 minutes is sufficient at 30 °C for 87.78% adsorption of EB on SARHS. Experimental data were fitted into non-linearized pseudo-first order (PFO) and pseudo-second order (PSO) kinetic models. PSO better fitted the experimental data based on SSE (%), RMS and R2 results. Computations from intra-particle diffusion kinetic model reveal that intra-particle diffusion is not the only rate-limiting step governing the adsorptive process. Results from Analysis of Variance (ANOVA) confirmed that there were statistical significant differences between the adsorption efficiencies of salt activated raphia hookeri seeds (SARHS) at different time intervals (P-Value < 0.05). Tukey’s Honest Significant Difference (HSD) post hoc method was employed for the identification of the location of these differences. The values calculated for ΔG°, ΔS° and ΔH° thermodynamic parameters were −29.60 KJ mol−1, 0.089 KJ mol−1 and −0.705 KJ mol−1 respectively confirming that the adsorptive process is feasible, spontaneous and exothermic in nature.