Investigation and optimization of cadmium ion adsorption from wastewater using raw and activated carbon of Pterocarpus santalinoides fruit

Abstract

Treatment of heavy metal polluted water still remains a serious challenge for some developing countries without centralized wastewater systems. This study examined the potential of raw and activated carbon from Pterocarpus santalinoides fruit as an adsorbent for the removal of cadmium ions from contaminated water. Instrumental techniques such as fourier transform infra red spectrophotometer (FTIR), scanning electron microscopy (SEM), and atomic absorption spectrophotometer (AAS) were used to characterize the adsorbents. The study analyzed the effect of various factors, including adsorbent dosage (0.1 – 0.5 g), cadmium concentration (10 – 50 mg/l), contact time (20 – 100 min), and temperature (30 – 70 ℃), respectively, on the adsorption of Cd2+ ions. The experimental findings revealed that the adsorbents have a high adsorption capacity for the removal of Cd2+ from aqueous solutions. Adsorption isotherms and kinetic models were applied to access the adsorption mechanism of cadmium removal. The Langmuir adsorption isotherm and pseudo-second-order model were found to fit the equilibrium data. Additionally, the adsorbents’ efficiency were evaluated using central composite design (CCD) adapted from response surface methodology (RSM). Using adsorption percentage as a response, a 30 run experimental matrix was generated by the CCD based on the interaction effects of the four earlier stated variables. According to the results obtained, a linear model was generated, which indicated good predictability and results agreed with the experimental data. The contact time and adsorbent dosage were predicted to have a positive effect on the adsorption process. At optimal conditions of adsorbent dosage (0.5 g), contact time (100 min), cadmium concentration (46.93 mg/l), and temperature (70 ℃), a desirability of 84 % was achieved by a numerical optimization approach demonstrating cadmium ion adsorption of 93 % for the raw and activated carbon from Pterocarpus santalinoides fruit.