The Kinetics of Crystallisation and Dissolution of Sparingly Soluble Salts in Aqueous Solutions

Purdie, Neil (1961) The Kinetics of Crystallisation and Dissolution of Sparingly Soluble Salts in Aqueous Solutions. PhD thesis, University of Glasgow.

Abstract

In a kinetic study of the crystallisation of sparingly soluble salts from supersaturated solutions the dependence of crystal nucleation in spontaneous growth on such effects as the geometry of the apparatus, the purity of the solutions, the previous history of the water etc. , warrants the use of the more reproducible method of growth by inoculation with seed crystals. This method is used in the present work. In an adsorbed layer theory suggested by Davies and Jones, growth and dissolution are described as non-reciprocal processes. The theory has been su successfully tested in growth and in dissolution work on silver chloride, a 1-1 electrolyte and silver chromate, a 2-1 electrolyte. In the first part of this thesis the study of the dissolution of silver chloride was extended to solutions of non-equivalent ionic concentrations. These conditions effectively alter the ion distribution in the layer, the ion in excess in solution being in excess in the adsorbed layer. As in equivalent ionic concentration conditions, good first order kinetic plots were observed in accordance with the theory of diffusion control in dissolution reactions. Parts 2a. and 2b. were designed to test the adequacy of the theory to include 2-2 electrolytes. Magnesium oxalate, a fairly soluble salt, forms a very stable complex in solution, Mg2+ + Ox2- ↔ MgOx. The theory of growth requires that a second order rate equation in ionic concentrations should be obeyed, -dm/dt = k(m - mo)2. and in spite of this complex formation, growth was explained by the theory at equivalent and non-equivalent concentrations and in the presence of adsorbates. Considerable retardation was observed in presence of adsorbates and from a Langmuir adsorption isotherm treatment of results the observed rate constant approached a limiting value as adsorbate concentration was increased, illustrating that adsorption occurred only at specific crystal sites. Crystallisation was followed by conductivity, titrimetric and photographic techniques. Spontaneous crystallisation was observed at supersaturations above a certain limit, but could be eliminated by increasing the seed concentration, The rate of growth was independent of the increasing.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Inorganic chemistry, Physical chemistry
• Date of Award: 1961
• Depositing User: Enlighten Team
• Unique ID: glathesis:1961-79410
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Mar 2020 10:03
• Last Modified: 05 Mar 2020 10:03
• URI: https://theses.gla.ac.uk/id/eprint/79410