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Subject: search.filters.subject.Calcium Sulphate

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    Dissolution Rates of Ionic Solids: Part 2.—Calcium Bisfdihydrogen phosphate) Monohydrate+Anhydrite (Calcium Sulphate)
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (12), 1974) Barton, Allan F. M.; McConnel, Stephen R.
    The dissolution rate of commercial superphosphate fertiliser was studied at 25, 35 and 45°C using a rotating disc of the solid material. The kinetics were followed by means of a calcium ion-selective electrode and spectrophotometric analyses. The initial process was observed to consist predominately of calcium bis(dihydrogen phosphate) monohydrate dissolution and was transport controlled with an apparent activation energy of 13 ± 3 kJ mol–1. Thereafter diffusion of dissolved monocalcium bis(dihydrogen phosphate) monohydrate through a porous layer of increasing thickness determined the rate of dissolution.
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    Dissociation Constant of Calcium Sulphate from 25 to 50°C
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (6), 1973) Ainsworth, Richard G.
    The e.m.f. of the cell Ag, AgCl | CaCl2(/Hi), CaSO4(/n2) | Ca-cxchange membrane | CaCl2(0.1 mol kg-1) | AgCl, Ag has been determined at 25,40 and 50°C. Errors associated with drifting of the calcium ion-exchange electrode have been minimised by using a rapid method to determine E& and the Nernstian slope factor of the electrode pair before determining the e.m.f. of the above cell. The data were used to calculate values of the thermodynamic quantities Kd, AGO, A//O, ASO and ACO for the dissociation of the CaSO4 ion-pair.