Study of sorption of platinum, palladium and rhodium ions on a carbon sorbent

Abstract

The article is devoted to the sorption concentration of platinum (II,IV), palladium (II) and rhodium (III) ions from chloride media on a carbon synthetic sorbent. For the study of the sorption concentration of platinum group metals, the carbon synthetic sorbent Lewatit AF5 was chosen. This sorbent has high mechanical strength, high surface area, narrow pore size distribution, and low cost compared to silicate or polymer sorbents. Sorption concentration was carried out under static conditions from model chloride solutions. The concentration of analytes in the initial solutions ranged from 8 to 50 mmol/dm3. Equilibrium concentrations of metals in solutions were determined by inductively coupled plasma atomic emission spectrometry. The dependences of adsorption on contact time, free acidity and redox potential of the system were studied, and the limiting absorption values for each of the metals studied were determined. The study of the kinetic parameters of the sorption of Pt (IV), Pd (II) and Rh (III) ions was carried out from chloride solutions characterized by free acidity values of 0.01 mol/dm3. The time for establishing sorption equilibrium was determined, which was 4 hours for each of the ions. When studying the dependence of adsorption on free acidity and the oxidation-reduction potential of the system (ORP), it was revealed that with an increase in free acidity and redox potential, a decrease in sorption activity is observed, thus we can conclude that aquated complexes of platinum metals, in which metals present not in the highest oxidation state, involved in the sorption process. Processing of experimental data showed the applicability of the linear equation of the Langmuir isotherm for the description of the adsorption process, the limiting adsorption values were calculated, using which the sorption capacity of the sorbent was assessed. The sorption capacity for Pt (II, IV), Pd (II) and Rh (III) was 1.24 mmol/g; 1.16 mmol/g and 0.57 mmol/g, respectively. High values of sorption capacity, as well as a fairly short time to achieve sorption equilibrium without the use of means for the acceleration of the process, in combination with the mechanical characteristics of the sorbent, allow us to conclude that the Lewatit AF5 sorbent is promising for the concentration of platinum group metals from hydrochloric acid solutions.