Phenol removal from aqueous solution using Citrullus colocynthis waste ash

Abstract Phenol is a hazardous organic chemical that introduced into the environment by industrial and pharmaceutical discharges. As a versatile option for phenol removal, adsorption would be viable if it accompanying with low cost adsorbents. This article described a natural, very cheap and local available adsorbent for phenol removal. Phenol showed a high affinity to Citrullus colocynthis waste ash which mainly composed of SiO 2 (41.6%), Al 2 O 3 (17.3%) and MgO (15.9%). Up to 70% of phenol adsorbed in the first 30 min of agitation. The phenol removal was increased by increasing adsorbent dose (0.5–10 g/L) and decreasing pH (2–12) and pollutant concentration (10–100 mg/L). The positive value of ∆ H ° in thermodynamic data (0.06) revealed that the process is endothermic. The high and positive value of ∆ S ° (13.01) and negative values of ∆ G ° (− 5.36 to − 7.28), showed a high affinity of phenol to the adsorbent and the spontaneous nature of the adsorption. Isotherm modelling revealed that the phenol molecules adsorbed in multilayer with the maximum adsorption capacity of 173.2 mg/g. The rate limiting step in the sorption process was chemisorption, based on the kinetic data.