Studies of the chemistry of orthophosphate and iron(III) on the 001 surface of muscovite

Abstract

This thesis involves an investigation into the adsorption of orthophosphate onto and the desorption of orthophosphate from, a muscovite mica surface which has been soaked in an aqueous solution of an iron(III) salt. The system which is formed by adsorbing orthophosphate onto the iron(III) salt. solution treated muscovite may be described (see 4.5. Models of Surface Complex, p.43 for justification) as an Orthophosphate-Iron(III)-Muscovite Surface type system. There are two main reasons why this type of system was investigated. 1. Inorganic Surface Chemistry. In studying adsorption by a surface, the nature of both the adsorbate and the surface must be known before an interpretation of the experimental results can be attempted. Lack of such fundamental knowledge makes interpretation of the results of some experiments on the physical adsorption of gases by solids, difficult - in some cases the exact nature and purity (presence or absence of adsorbed films) of the surface is uncertain. These difficulties are less serious in the present investigation because of the following advantages of the muscovite surface:- (a) The nature of the muscovite surface is well established (see 2.1. Structure of Muscovite, p.8 ) and the surface is readily prepared. Muscovite has perfect basal cleavage and is thus readily split into thin flexible sheets, the surfaces of which are smooth down to a molecular level. However, ready cleavage is sometimes prevented by crystal twinning, i.e., in crystallising, the muscovite has grown about two or more nuclei. (b) For the system investigated, it is thought that chemisorption from solution, rather than physical adsorption, is involved. Hence the presence of physically adsorbed molecule films (nitrogen, oxygen, carbon dioxide from the air) is probably unimportant.