Home – Home – Jornals – Chemistry for Sustainable Development 2022 number 4

As an alternative to mercury release by cementation on metallic aluminum, for the purpose of improving the purity of commercial selenium, we investigated the processes of selective sorption of mercury ions from the technological solutions of selenous acid onto styrene-divinylbenzene Lewatit MP 68 resin. The isotherms of mercury ion sorption are obtained, the main quantitative parameters and limiting stages of the process are assessed. It is established that for a low degree of resin filling with the sorbate (with the equilibrium concentration of mercury ions in solution ≤0.4 mmol/dm³) and for the sorbent - sorbate type interaction, the distribution coefficient decreases initially, and then increases while the sorption ability increases and the structures of sorbate - sorbate type are formed. The degree of mercury extraction from solution (β) is inversely proportional to the equilibrium concentration of mercury ions in the solution ( С_eq) and is described by the linear equation: β = -133.5 С_eq + 99.81. Experimental data processing shows the simultaneous occurrence of the stages of external (film) and internal (gel) diffusion, which is evidence in favour of mixed diffusion sorption mode. The rate constants of external diffusion are approximately three times larger than the rate constants of internal diffusion. It is shown that the kinetic equations of pseudo-first and pseudo-second order models provide satisfactory description of experimental data, and that the difference between determination coefficients is not large ( R_i² > 0.98). The values of thermodynamic functions of mercury sorption within the temperature range 298-333 K were determined: -Δ G = 2.35-2.99 kJ/mol, Δ H = 3.1 kJ/mol, Δ S = 18 J/(mol•K). The practical significance of the revealed sorption parameter (dynamic exchange capacity of Lewatit MP resin is 68-269 g/dm³, specific volume of solution for resin saturation in the dynamic mode is 3800, element content in saturated resin is, %: Hg ~26.0, Se <1.0) is due to their involvement in designing the industrial installation.