Studies of the chemistry of orthophosphate and selected cations on the 001 surface of muscovite

Abstract

In this thesis, an investigation has been made into the phenomena of adsorption of orthophosphate onto and desorption of orthophosphate from, a muscovite mica 001 surface which has been soaked in an aqueous salt solution. The salt solutions used in this thesis contained the following cations: Aluminium(III), Iron(III), Calcium, Magnesium, Barium, Strontium, Nickel, Copper(II), Sodium, Potassium, and Ammonium. This 001 Muscovite surface-Cation-Orthophosphate system was investigated for two main reasons: 1. As a fundamental study in inorganic surface chemistry. Before interpretation of results of adsorption studies can be attempted, the nature of the adsorbate and the surface involved must be known. In many adsorption studies, the nature of the adsorbate is known (e.g. carbon dioxide on charcoal), but the exact nature of the surface is not known. Muscovite has a surface which is simple, well-known, is a crystal cleavage plane and is therefore smooth down to molecular dimensions. Muscovite can be split into thin flexible sheets which are gas and water tight. These sheets are readily mountable on a frame designed to expose a known area of the sheet with reproducible geometry to the window of an end-window geiger counter. 2. Soil Chemistry. Much work has been done by soil chemists in attempts to explain the "fixation" of phosphate by some soils. When phosphate, in the form of fertilizer, is added to soils, only a small fraction is used by the plants and the greater fraction is "fixed" in a form said to be unavailable to plants. This phenomenon will become a serious economic problem when the supply of cheap phosphate for fertilizer manufacture has been exhausted.