Coupled mutual diffusion in aqueous calcium sulphate plus sulphuric acid solutions

Taylor dispersion method was used to measure binary mutual diffusion coefficients of calcium sulphate in water at concentrations ranging 0.0000 to 0.0100 mol dm(-3) and at 298.15 K. Experimental results are discussed based on the Onsager-Fuoss and Pikal models and compared with theoretical diffusion coefficients, calculated using different values of the mean distance of closest approach of ions, a. The influence parameter a on the diffusion of this system is also discussed. Ternary mutual diffusion coefficients (D-ik) measured by the same technique are reported for aqueous CaSO4 + H2SO4 solutions at 298.15 K and concentrations up to 0.0100 mol dm(-3). The coupled diffusion of CaSO4 (1) and H2SO4 (2) is significant, as indicated by the large negative cross-diffusion coefficients. Nernst equations are used to predict transport coefficients from limiting ionic conductivities and help to interpret both concentration dependence of the diffusion coefficients and the electrostatic mechanism for the coupled diffusion of the solutes. (C) 2021 Elsevier Ltd.