Adsorption ability of sugar scum as industrial waste for crystal violet elimination: Experimental and advanced statistical physics modeling

Recycling solid industrial waste into useful resources is the most critical aspect of managing waste. Herein, for detoxifying poisonous crystal violet dye (CV) in aqueous media, sugar scum (SS) as an underutilized industrial discard has been tested as a promising adsorbent.

The SS was thoroughly analyzed beforehand and after the adsorption process through various characterization techniques. Several operational factors, including pH, biosorbent dosage, dye concentration, and temperature, were optimized, reaching 24 mg.g^-1 at (pH 10, 2 g.L⁻¹ of SS, 10 mg.L⁻¹ of CV and 25 °C). The bioadsorbent's performance was assessed through a range of studies involving kinetic, equilibrium (using both conventional and statistical physics models), and thermodynamic investigations.

Based on the results, the equilibrium curves best fit the Freundlich model, indicating that multilayer adsorption occurs on a heterogeneous active sites surface. The statistical physics models provided detailed physiochemical insights, the double-layer with two energies model was most accurately describing the data, with a high saturation capability of 371 mg.g⁻¹. Most interactions occur at a single adsorption site (70 %), with the remaining 30 % at two sites, involving both parallel and non-parallel orientations. The mesoporous structure of the SS surface provides an optimum size for CV adsorption. Pore filling, Van der Waals forces, hydrogen bonding, π-π and electrostatic interactions are proposed as the possible mechanisms in the CV-SS system. Thermodynamic measurements indicate that CV adsorption is spontaneous (ΔG° < 0) and exothermic ΔH° (− 41.390 kJ mol⁻¹).

The SS recyclability was assessed, exhibiting encouraging sustainability with a slight fall in effectiveness (∼7 %) after 5 sequential usages. Altogether, this study makes a substantial contribution to the promotion of ecological water treatment strategies, which highlights the utility of using SS as an environmental alternative to water contaminant remediation.