الفهرس 
EXPERIMENTALOnly 14 pages are availabe for public view
 |  | from | 100 |  |  |
| | | from | 100 | | |
Abstract
This thesis is mainly concerned with the purification of locally industrial phosphoric acid to the food grade quality. The input phosphoric acid is obtained from Abu Zaabal for Fertilizers and Chemicals Co., at Abu Zaabal, Cairo, Egypt. This acid contains a lot of impurities and a P2O5 content of 45.5%.
The thesis is divided to four chapters. The first chapter is the introduction and a literature survey on the various methods used for phosphoric acid purification such as solvent extraction using different solvents (alcohols, ketones, amines, ethers, and hydrocarbons), ion exchange, precipitation, electro-deposition method and etc.
The second chapter is the experimental, it is concerned with all chemicals, reagents, and stock solutions needed in the present work. Besides, a number of wet and instrumental analytical techniques, that were used for the quantitative determination of major, and minor and trace element components during the present work. Thus wet chemical methods were adopted for the determination of (Fe, Ca, Mg and Cl ions), whereas instrumental method of analysis used involved, flame photometry for Na, and K, spectrophotometry for (P2O5, B, U, SO4, REE, F, Th, Zr and Si) and finally atomic absorption spectrophotometry for Co, Pb, Ni, Cu, Zn, Cr, Cd, V, Mo, Sr, Al, Ti, As, Mn, and Ba).
The second chapter includes also cooling, desaturation and concentration of the impure phosphoric acid used . Thus the acid was left to cool for about 24 hours in a slowly justified tank to allow all super-saturated salts to precipitate. After filtration of the acid was concentrated to 57.75% P2O5 by evaporation under reduced pressure in a rotatary evaporator. Solvent extraction procedure, stripping procedure and post treatment of the purified acid, through adsorption on carbon column and concentration under reduced pressure are also included in chapter 2.
The third chapter deals mainly with the results and discussion. It starts with the results of complete chemical analyses for major, minor and trace elements in the input phosphoric acid in the present study. It is quoted that the phosphoric acid contains 57.75 % wt P2O5 and a lot of metallic and non metallic impurities. The third chapter also deals with the purification of the phosphoric acid ( 57.75% wt P2O5 ) by solvent extraction method using an organic mixture of methanol and hexanol with phase ratio of 1 part of phosphoric acid, 4 parts of n-hexanol and 0.5 part of methanol. The extraction process is divided mainly to two steps, extraction and stripping. The relevant factors affecting the extraction of P2O5 from phosphoric acid were studied. The first factor is the effect of different solvents on the extraction of the impurities which are acetone, ethanol and methanol, where it was found that methanol is the best because its effect on losing P2O5 is the lowest and its ability for precipitation of impurities is the highest.
The second factor is the effect molecular weight of different aliphatic alcohols, from n-C4 to n-C8, where it was found that the extraction decreases with the increase of the molecular weight or the number of carbon atoms of the alcohols.
The third factor is the effect of molecular weight of aliphatic alcohol on the settling time, it is found that the ease of separation of the organic and aqueous phase increases with increasing the molecular weight of the solvent.
The fourth factor is the effect of initial phosphoric acid concentration, where seven different initial acid concentrations were used, the extraction of P2O5 increases as the concentration of the acid increases in the range 36.72% up to 67.52%. Afterwards, at higher acid concentration there was difficulty in the separation of the two phases from each other, as the raffinate turns very viscous.
The fifth factor is the effect of methanol phase ratio on the extraction of P2O5, where three different amounts of methanol was added for extracting the metallic impurities, namely 0.25, 0.5, and 1 part per volume of methanol are mixed separately to a constant volume of 1 part of impure phosphoric acid. It was found that the best mixing phase ratio of methanol is 0.5 part.
The sixth factor is the effect of n-hexanol phase ratio on the extraction process, the O/A phase ratio is varied from 1:1 to 5:1. It was found that the optimum O/A phase ratio for extraction of P2O5 occurs at a ratio of 4:1.
The effect of n- hexanol phase ratio on the separation time was also studied in the seventh factor, where it was found that the higher phase ratio O/A = 4/1 gives better separation.
The eighth factor is the effect of mixing time on the extraction process, where it was found that the extraction increases slightly from 0.5 to 25 minutes, and remains constant after that, this shows that, a mixing time of 25 minutes is the best for the extraction of P2O5.
The ninth factor is the effect of temperature, where the experiments were carried out using an electric thermostat, the temperature is regulated from 5°C to 80°C. It was found that the extraction of P2O5 increases slightly as the temperature increases until room temperature, after that extraction decreases at higher temperatures between 40°C and 80°C. Therefore the optimum temperature for the extraction process is taken as the room temperature.