Insights Into the Interactions of Sulfate Adsorption From Elaeis guineensis Wastewater Effluent Onto Limestone Adsorbent Through Statistical, Kinetic, and Isotherm Studies

A novel surface-interaction study using the raw limestone (adsorbent) and the sulfate present in Elaeis guineensis wastewater effluent (adsorbate), or what is well known as palm oil mill effluent (POME), has unveiled the physicochemical interactions underlying the removal process of sulfate via the adsorption method. The adsorption of sulfate from POME on limestone adsorbent was conducted in a batch technique in order to study the optimum percentage removal of sulfate. The experiment was performed with multiple conditions, namely the amount of the adsorbent (0.2–1.0 g), pH (2–13), contact time (60–300 min), and initial concentration (50%–90%). The best parameters for every condition were utilized after each experiment. The highest removal efficiency of each parameter for POME was found to be 0.6 g, pH 13, 240 min, and an initial concentration of 90% was 39.64%. The results were analyzed with a hypothesis t-test and paired t-test by comparing the t-calculated and t-critical values. The results showed that the t-calculated values were within the acceptance region, verifying the statistical significance and reliability of the results. The adsorption isotherm and kinetics study were determined by considering the parameter effects, initial concentrations, and contact time. The adsorption kinetics in the present study were best fitted to the Elovich kinetic model with a correlation coefficient (R² = 0.9834), signifying a good fit. The adsorption process also followed the Dubinin–Radushkevich isotherm model, as proved by an R² value of 0.9676, indicating physical adsorption was dominant on the heterogeneous limestone's surface.