Studies in the Quartz Series: The Solubility of Siliceous Dusts

Clelland, David Watson (1951) Studies in the Quartz Series: The Solubility of Siliceous Dusts. PhD thesis, University of Glasgow.

Abstract

1. Chemical aspects of pneumokoniosis are reviewed and the development of the 'solubility theory' of silicosis is traced. The general validity of, and some important exceptions to, this theory are discussed. 2. The effect of pre-treatment with various salt solutions, acids and buffers (pH 2-11) upon the solubilities of siliceous dusts has been investigated; and the existence of a high-solubility layer on the surface of such dust particles has been demonstrated by extractive solubility methods. Comparative solubility data have been obtained for five siliceous dusts - rock crystal, silica sand from Loch Aline, fused amorphous silica, olivine, and ortboclase felspar. Analytical methods are described for estimating 'colloidal' and 'dissolved' silica in silicic acid dispersions. The dispersion in a solvent of appreciable amounts of 'colloidal' silica from siliceous dust surfaces is shown to be connected with the dissolution of the high-solubility layer. The known effect of the addition of metallic aluminium to liquid/ siliceous dust systems has been further investigated, and also the effect of aluminium upon the composition of the resulting silicic acid dispersions. 3. The nature of the high-solubility layer is discussed, and the effect of grinding upon the density of quartz has been investigated. It is concluded that prolonged grinding of quartz converts a portion of it to the vitreous state. It is suggested that this conversion is a similar process to the formation of a Beilby layer produced by polishing, that the high-solubility layer is similar in nature to the Beilby layer, and that it is produced on the dust particle surfaces by the grinding process in the formation of the dust. 4. By employing a polishing treatment it was found possible to regenerate a new high-solubility layer on dust particle surfaces from which the original layer had previously been removed. Such a regeneration by purely mechanical means is considered to emphasise the similarity in nature of the high-solubility and Beilby layers. 5. The adsorption of a number of dyestuffs on silica dust surfaces has been investigated and it has been found that from a wide range of dyes only those of the basic class are adsorbed. The colour ions of these dyes in solution are positively charged, and it has been shown that the siliceous dust particles employed are negatively charged in water suspension. It is suggested, therefore, that the adsorption mechanism is ionic in character. The presence of a high-solubility layer on the surfaces of quartz dusts has been found to have a major effect upon their adsorptive properties. 6. Pre-treatment by X-ray irradiation is shown to increase the solubilities of five siliceous dusts (rock crystal, Loch Aline sand, fused amorphous silica, olivine, and orthoclase felspar) from which the high-solubility layers had been previously removed; the three almost pure silica dusts (rock crystal, Loch Aline sand, and fused amorphous silica) exhibiting the greatest changes after such treatment. The additional silica yielded into solution, due to the irradiation treatment, is shown to be mainly in the colloidal form. Similar treatment has been found to cause a slight increase in the solubility of a Loch Aline sand dust with its high-solubility layer intact; while no measurable change in solubility was effected by similar irradiation of a rock crystal dust with its high-solubility layer.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Inorganic chemistry, Occupational safety
• Date of Award: 1951
• Depositing User: Enlighten Team
• Unique ID: glathesis:1951-78833
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 14:49
• Last Modified: 30 Jan 2020 14:49
• URI: https://theses.gla.ac.uk/id/eprint/78833