USE OF BIOCHAR GENERATED FROM SPENT COFFEE GROUNDS FOR THE REMOVAL OF Zn(ll) FROM AQUEOUS SOLUTIONS

摘要

The main focus of this study is to evaluate five types of biochar as adsorbents for Zn(ll) removal from aqueous solutions. Five different biochar samples (CB300, CB400, CB500, CB600 and CB700) were prepared through pyrolysis of spent coffee grounds (SCG) at 300, 400, 500, 600 and 700 °C, respectively.Materials characterization was carried out with respect to pH, elemental composition, higher calorific value and point of zero charge (pHpzc). Adsorption studies included assays to determine the effect of initial pH, agitation period, adsorbent dose and initial metal concentration on Zn(ll) removal. Adsorption kinetics and isotherms were also studied, through these experiments.The optimum conditions for Zn(ll) removal using SCG-derived biochars resulted: an initial pH=5, an agitation period of 4 h and an adsorbent dose of 25 g/L. The materials produced at 600 and 700 °C were provided the best results regarding Zn(ll) adsorption, having no significant differences from each other.Fitting the experimental data to mathematical models showed that the pseudo-second order model best described the adsorption kinetics, suggesting chemisorption as that the limiting step. Furthermore, for what concerns adsorption equilibrium each biochar was best fitted by different isotherms. Specifically, the linear isotherm best fitted the data for CB300 and CB600, the Freundlich isotherm described best the data for CB700, while the Langmuir model was better for CB400 and CB500.