Adsorptive removal of cadmium (II) from wastewater using activated carbon synthesized from stem of Khat ().

Introduction: Cadmium is among the most hazardous heavy metals, posing the greatest risk to human beings and the environment. Adsorption with activated carbon prepared from agricultural waste is the most effective way to remove cadmium (II) from wastewater. In this study, activated carbon prepared from the stem of Khat ( plant was used for the removal of cadmium (II) from wastewater.

Objective: To evaluate the efficiency and mechanism of the removal of cadmium (II) from wastewater using Khat (Catha edulis) stem activated carbon at different operating parameters.

Method: Proximate and Fourier transform infrared analyses were conducted to characterise the prepared Khat stem-activated carbon. The effects of initial cadmium concentration, adsorbent dose, pH, contact time, and agitation speed on the cadmium removal efficiency of Khat stem-activated carbon were evaluated. Furthermore, isotherm and kinetic models of adsorption were used to evaluate the mechanism of cadmium removal.

Result: The proximate analysis indicated that the activated carbon derived from Khat stems possesses a bulk density of 0.58 g/cm and surface area of 615 m/g. Additionally, the prepared Khat stem activated carbon has 4 %, 14 %, and 22 % of moisture content, ash content, and volatile matter, respectively. Furthermore, the proximate analysis indicated that the Khat stem activated carbon has a porosity of 55 %. The Fourier transformed infrared spectroscopy result indicated the presence of phenolic, alcoholic, and carboxylic acid functional groups on the surface of Khat stem activated carbon. The experimental data showed a better fit with the Langmuir isotherm model (R-squared and chi-square value of 0.9727 and 1.3936, respectively) and the pseudo-second-order kinetic model (R-squared and chi-square values of 0.9032 and 0.2179, respectively). The highest adsorption efficiency of cadmium (97 %) was attained at an adsorbent dose of 0.125 g, a contact time of 30 min, an initial cadmium concentration of 20 mg/L, a pH of 5, and an agitation speed of 100 rpm at room temperature (25 °C).

Conclusion: The results obtained in this research demonstrated that activated carbon from Khat stems can be employed as an economical, ecologically friendly, easily accessible and efficient activated carbon to remove Cd (II) from wastewater.