Adsorption thermodynamics and kinetics of O—butyl—N—isobutyl thionocarbamate on chalcopyrite surfaces

Abstract

O—butyl—N—isobutyl thionocarbamate (NBIB) is a novel collector for copper sulfur flotation separation. The adsorption capacity of NBIB was measured using a UV–vis spectrophotometer. The effects of the adsorption temperature, pH value, stirring time, and collector concentration on the adsorption capacity of NBIB on chalcopyrite surfaces, as well as its adsorption thermodynamics and kinetics, were investigated. Results of a pure mineral flotation experiment indicate that NBIB has a high recovery rate for chalcopyrite, strong collection capacity, and little influence by pH. The adsorption capacity of NBIB on a chalcopyrite surface increases with an increase in the collector concentration at 288, 298, and 308 K and pH 6, 9, and 12, respectively. When the equilibrium concentration reaches 0.5×10−4 mol·L−1, the adsorption capacity has a small increase range. At the same pH value, the adsorption capacity increases with an increase in the adsorption temperature. It is speculated that NBIB adsorption on a chalcopyrite surface is an endothermic process. At pH 6 and 9, little difference exists in adsorption capacity, which slightly decreases when pH increases to 12. Meanwhile, the pulp pH value has little effect on the adsorption capacity, which is consistent with the flotation test results. The adsorption capacity data were linearly fitted by Langmuir and Freundlich isotherms, and the Langmuir equation has a better correlation coefficient of the fitting curve. The adsorption process of NBIB on the chalcopyrite surface is more consistent with the Langmuir adsorption model, and it is speculated that the adsorption process may be monolayer adsorption. The parameters of the Langmuir equation are considered based on a thermodynamic formula. The results indicate that the linear fitting results are good, ∆G is negative, and ∆H and ∆S are positive. Therefore, the process of chalcopyrite adsorbing NBIB may be spontaneous, entropy-driven, and endothermic chemical adsorption. Meanwhile, the adsorption capacity of NBIB on the chalcopyrite surface increases with an increase in the adsorption time at temperatures from 288 K to 308 K. The increasing trend of adsorption capacity slows down after the adsorption time reaches 20 min. Moreover, the adsorption capacity increases with increasing temperature. Evidently, the adsorption is an endothermic process, which is consistent with the results of the thermodynamic analysis. The kinetic calculation shows that the correlation coefficients of the second-order reaction fitting curve are greater than those of first-order reaction, indicating that the second-order reaction rate equation has a better linear fitting result. The equilibrium adsorption capacity calculated by the second-order reaction rate equation is closer to the experimental equilibrium adsorption capacity. Therefore, it is speculated that the NBIB adsorption on the chalcopyrite surface conforms to the second-order adsorption kinetic model.

Keywords

• chalcopyrite
• thionocarbamate
• adsorption capacity
• adsorption thermodynamics
• kinetics