Eco-Friendly Approach to Soil Remediation: Evaluating Clay-Biochar Composites for Used Motor Oil Removal Through Kinetic, Isotherm, and Thermodynamic Models

Abstract

This study investigates the efficiency of Clay-Biochar Composite (CBC) in the remediation of contaminated soil by used motor oil (UMO). The CBC was synthesized through the carbonization of acid-activated bentonite (AC) [derived from natural bentonite clay (NC)], which was combined with Loquat Seed Biochar (LSB) [derived from raw Loquat Seed (RLS)]. A comprehensive characterization for NC, AC, RLS, LSB, and CBC to assess their physicochemical properties and potential for UMO adsorption was conducted via Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), Fourier Transform Infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-Ray Diffraction (XRD), and Brunauer-Emmett-Teller (BET) analysis techniques. Additionally, the effects of adsorption parameters such as (UMO) concentration, adsorption time, and adsorbent dosage on removal efficiency were studied. At an optimal dose of 0.3 g and 50 °C, with a contact duration of 300 minutes, the CBC removed 99.89% of oil, reaching a maximum adsorption capacity of 41.62 mg. g-1. The results indicated that the Freundlich isotherm (R² = 0.995) and second-order kinetic models (R² = 0.996) more effectively fitted to describe UMO adsorption, suggesting that multilayer adsorption was involved. Also, Thermodynamic analysis showed that motor oil adsorption is spontaneous and endothermic. The ΔG° values ranged from −16.05 to −17.69 kJ/mol, while a positive ΔH° of 19.23 J/mol and a ΔS° of 54.84 J/mol. K indicates increased randomness at the solid–liquid interface. Real-world experiments, which involved examining actual contaminated soil samples, validated the practical applicability of the (CBC) for UMO remediation. CBC established the possibility of reuse, achieving 90 % oil desorption. These results showed that the CBC significantly enhanced adsorption affinity, highlighting its potential as a cost-effective and eco-friendly adsorbent for oil pollution remediation.