Treatment of Oil Refinery Wastewater Polluted by Heavy Metal Ions via Adsorption Technique using Non-Valuable Media: Cadmium Ions and Buckthorn Leaves as a Study Case

This study focuses on the removal of cadmium ions generated by oil refinery wastewater, employing an agricultural by-product. Buckthorn leaves, sourced from Baghdad and Diyala provinces, underwent preparation, including washing, drying, crushing, and sieving before being utilized in experiments. Batch experiments were conducted using simulated solutions to assess the impact of six key adsorption design parameters: pH, cadmium concentration, agitation speed, contact time, adsorbent dosage, and temperature. The highest adsorption efficiency, reaching 94.4367%, was directly correlated with contact time, adsorbent dosage, pH value, and agitation speed, and inversely related to other variables. Morphological studies on the treated adsorbent, indicated structural changes during the adsorption process, manifested as shifts in FTIR and XRD peaks, and observed pore alterations through SEM analysis. The BET test revealed a surface area of 36 m²/g, with less than 68% utilization through adsorption. Adsorption behavior was analyzed in three parts: isothermal analysis, exhibiting a strong fit to the Langmuir model; kinetic study, favoring the pseudo-second-order model; and thermodynamic characterization as exothermic, of low entropy, and spontaneous. The study also investigated the regeneration of spent adsorbent, highlighting physical activation as the more effective method, providing four reuse cycles compared to chemical activation's two. The paper extended its investigation to real oil refinery wastewater, assessing the ability of the adsorbent to compete with other contaminants. Buckthorn leaves exhibited an efficiency of 50-75% in remediating real wastewater, similar to simulated solutions. Consequently, this research proposes an environmentally sound, cost-effective means of sustainably repurposing agricultural waste to achieve zero-residue levels.