Cadmium adsorption onto naoh activated palm kernel shell charcoal

Abstract

This research aimed to convert the charcoal produced from palm kernel shell pyrolysis into activated carbon nanoparticles for use in the adsorption of cadmium, which is one of the most toxic (e.g., carcinogenic) heavy metals. In particular, the adsorption capacity, adsorption isotherm, and adsorption kinetics of cadmium onto the produced charcoal were determined. Pyrolysis of palm kernel shells at 380°C resulted in liquid smoke, tar, and charcoal. The charcoal was ground with a ball mill until it reached nanoparticle size. Subsequently, it was chemically activated by soaking it in a 0.1 N NaOH solution for 24 h. The pre- and post-activation charcoal was characterized using a scanning electron microscope (SEM). The carbon activated nanoparticles were then used in cadmium adsorption experiments at various contact times (30, 60, 90, 120, 150, and 180 min), several initial cadmium concentrations (30, 60, 90, 120, and 150 ppm), and two stirring speeds (100 and 150 rpm). The results showed that maximum adsorption capacity was reached at 22 mg/g with more than 97% adsorption efficiency. Two adsorption models, i.e., Langmuir and Freundlich, were used to interpret the equilibrium data. At the 100-rpm stirring speed, the Langmuir isotherm indicated a maximum adsorption capacity (qm) for cadmium of 22.37 g/mg (Kl = 0.131 mg/g, with a constant correlation of R2 = 0.915). The Freundlich isotherm gave values of n = 1.503, Kf = 2.877 mg/g, and R2 = 0.969. Therefore, these two models are considered suitable for describing the equilibrium cadmium adsorption isotherm in the presence of NaOH-activated palm kernel shell charcoal.