Studie van die Wisselwerking Tussen Reagense en Minerale by die Flottasie van Apatiet

• Main Author: Van der Linde, Gert Johannes
• Format: Dissertation
• Language: Afrikaans
• Published: ProQuest Dissertations & Theses 01-01-2015
• Subjects: Chemical engineering
• ISBN: 9798377671800

The Phosphate Development Corporation (FOSKOR) recovers apatite from foscorite ore by a process of froth flotation. Four reagents are used viz. sodium hydroxide, water-glass, nonylphenol tetraglycol ether (EMU) and a fatty acid. The fatty acid is mainly composed of a mixture of oleic and linoleic acid in a ratio of 1,2:1.The aim of this study was to investigate the influence of the first three above-mentioned reagents on the adsorption of oleic, linoleic and linolenic acids on apatite and calcite. From these results and from micro flotation tests a possible mechanism for the quantitative recovery of apatite by flotation was postulated.The amount of fatty acid that adsorbed on the minerals was measured using a radio-chemical method. In this method a very small quantity of 14c-marked fatty acid is mixed with a known concentration of unmarked fatty acid. By detennining the radio-activity of these sohitions before and after adsorption, the amount of adsorbed fatty acid can be ca1cu1ated.During the development of this technique, adsorption isotherms, displaying maxima Which chunged in heignt from day to day, were obtained. It was found that the presence of micelles in the solutions led to these results. On further investigation it was found that solutions at concentrations above the critical micelle concentration (CMC) of the fatty acids still contained fatty acid micelles even after dilution to far below the CMC. As a result all adsorption tests were done with primary standard fatty acid solutions below the CMC of the fatty acids.It was evident that the fatty acids chemisorbed on the apatite. Oleic acid adsorbed in multi layers on apatite while both linoleic and linolenic acid adsorbed as a monolayer.All three fatty acids adsorbed in a rardomly orientated manner as precipitated calcium salts on the calcite. These calcium salts of the fatty acids were physically bound to the calcite surface. The calcite was covered by a monolayer of water-glass. EMU interacted in solution with the fatty acids through their double bonds and enhanced their adsorption on both minerals at low concentrations. Water-glass had no effect on the acount of fatty acid that adsorbed on both minerals.A mixture of water-glass and EMU had no effect on the adsorption of the fatty acids on apatite, while the amount of fatty acid that can adsorb on calcite was depressed by 50%. The flotation recovery of apatite with fatty acids in the presence of this mixture was not affected while 50% less calcite was recovered.From these results it was postulated that in a flotation cell the presence of EMU and water-glass slows down the adsorption of fatty acids on calcite. As a result apatite particles can become hydrophobic more qui ckly than the calcite particles. Because the cal cite particles are covered with a monolayer of water-glass, the few particles that do become hydrophobic undergo .nsuccessful collisions with air bubbles. Almost no calcite is recovered while the apatite particles can be recovered quantitatively.