Adsorption of cadmium using modified palm oil fuel ash: kinetics, isotherms, and thermodynamic evaluation

Contamination arising from industrial wastewater significantly affects both human health and the environment. Industrial wastewater commonly contains heavy metals, which are among the most prevalent pollutants. Even in small quantities, heavy metals can harm humans and animals. Cadmium is one of the most hazardous elements among these heavy metals. Palm oil fuel ash (POFA) is generated as a byproduct when biomass from palm oil, including kernel shells and fiber, is burned in a boiler. The POFA underwent modification with sulfuric acid, showing promise for utilization as activated carbon. Therefore, the objective of this study is to evaluate the kinetics, isotherms, and thermodynamic properties associated with the cadmium (II) ions adsorption onto the modified POFA. The kinetic studies were performed using modified POFA. The adsorption isotherms were performed using different initial concentrations of cadmium (II) ions. The thermodynamic properties were evaluated at 15 to 45 °C using 5 mg/L cadmium (II) ion. The concentrations of cadmium (II) ion were analyzed by atomic adsorption spectrometry (AAS). The uptake process of cadmium (II) ions was found to adhere to a pseudo-second-order rate and a monolayer, aligning well with the Langmuir isotherm model, which offers a superior fit. The thermodynamic spontaneity of the adsorption is indicated by the negative ΔG° value between -388.21 to –7638.59 kJ/mol, which increases from 288 to 318 K, respectively. Higher temperatures demonstrate less adsorption feasibility. The adsorption process appears to be endothermic based on the positive ΔH° value of 69,247 kJ/mol. Moreover, there is an increase in energy distribution between the modified POFA and cadmium (II) ions, as evidenced by the positive ΔS° of 242.15 J/mol.K. In conclusion, the modified POFA has a significant potential for removing cadmium (II) ions from wastewater due to its superior efficacy and inexpensive availability. Effective use of modified POFA could lessen harmful environmental effects while also resolving the issue of dumping these wastes.