Enhancement of Coal Fly Ash as a Bleaching Adsorbent for Crude Palm Kernel Oil through Physical and Chemical Activation

Abstract

Coal fly ash, a major by-product of coal combustion, contains high levels of SiO2 and Al2O3, making it a promising low-cost adsorbent. Despite its widespread use in wastewater treatment, its application as a bleaching adsorbent for crude palm kernel oil (CPKO) remains limited. This study investigates the effectiveness of physically and chemically activated coal fly ash as an alternative adsorbent for CPKO bleaching. Physical activation was performed through calcination at 150 and 300 C, while chemical activation employed 0.5 M phosphoric acid (H3PO4) and oxalic acid (H2C2O4). Adsorbent dosages ranged from 0.1% to 2.0% (w/v), and all experiments were conducted in triplicate. Two-way ANOVA revealed that both activation method and adsorbent dosage significantly affected residual beta-carotene concentration (p < 0.001), with a significant interaction between the two factors. Calcination at 300 C increased beta-carotene removal from 24.86% to 36.58%, while chemical activation further enhanced adsorption performance. H3PO4-activated fly ash achieved the highest beta-carotene removal efficiency of 51.22% at a dosage of 0.5%, resulting in the lowest residual beta-carotene concentration of 1.44+-0.11 ppm. Although commercial bleaching earth provided superior color reduction, activated fly ash produced refined, bleached, and deodorized palm kernel oil (RBDPKO) with acceptable quality, including moisture content below 0.1% and free fatty acid levels of approximately 1.01%, comparable to commercial products. XRD analysis indicated increased crystallinity and AlPO4 formation after phosphoric acid activation, while FTIR confirmed the presence of phosphate functional groups that contributed to enhanced adsorption capacity. These results demonstrate that H3PO4-ctivated coal fly ash is a sustainable and effective alternative adsorbent for palm kernel oil bleaching.