Kinetic, isotherm and thermodynamic studies with linear and non-linear fitting for cadmium(II) removal by black carbon of pine cone

In this study, black carbon from pine cone (BCPC) and acidic-modified BCPC (MBCPC) powder as a popular agricultural waste in the southeast of Iran were used for cadmium removal from aqueous solutions. The effect of various factors, such as surface chemistry and dosage of adsorbent, contact time, size of particles, initial concentration of cadmium, temperature, and pH of aqueous solutions, was investigated. The results show cadmium removal with usage of the mentioned adsorbents increased after acidic modification. It was noteworthy in this work that the removal percentage of pollutant was above 90% for suggested biosorbents. The obtained experimental data for optimum conditions were selected to model the adsorption behavior of the materials with usage of six isotherm equations via non-linear fitting method and the residual root mean square error estimation for each model. The adsorption of cadmium preferably fitted Khan and Langmuir-Freundlich isotherms for BCPC and MBCPC adsorbents, respectively. The kinetic studies via linear fitting method proved the second-order kinetic was the applicable model for the adsorption process. Thermodynamic studies show the adsorption process of cadmium onto BCPC and MBCPC was spontaneous and endothermic.