الفهرس 
CHAPTER 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
The mineral Monazite that used in the present work is produced as low-grade by-product during separation and concentration of the more abundant economic minerals, Zircon, Ilmenite, Rutile, etc. from the black sand in Rashid area that located at the shore of Mediterranean Sea, Egypt. This crude by-product Monazite sand have grade of about 47%, however, 25 kg of this low-grade mineral was subjected directly without grinding for digestion at temperature of 220 °C using sulfuric acid of 93% concentration and in ratio to the crude Monazite sand of 2.5. Digestion efficiency that achieved at these conditions were 96.6%, 92.6% for thorium and rare earth elements respectively. The product from digestion was paste of elements in sulphates form, it was dissolved thoroughly, after cooling at atmospheric temperature, using normal water to obtain a solution of rare earth elements, thorium and uranium sulfates. selective precipitation for light rare earth elements, in the form of double sulfate sodium earth elements, was carried out through adding 5% sodium chloride. The resultant precipitate was then converted it to hydroxide where its analysis reveals that its constituent of light rare earth elements (LREEs) was about 83% but it also containing significant amount of thorium (up to 13.5%).
The present study was divided into three parts; The first part deal with preparation of a high-grade concentrate of thorium that is suitable for subsequent purification processes after its dissolution from the prepared (LREEs) concentrate while the second part deal with preparation of impregnated resin with tri butyl phosphate solvent to be used in the third part of the study to extract thorium from nitric acid medium. The obtained extraction data were then applied for thorium extraction in fixed bed column system and also applied upon different adsorption and kinetic models.
Results of the first part reveal that dissolution most of thorium, that present with the prepared concentrate of light rare earth element, under different conditions were achieved at liquid / solid ratio of 20 at pH of 1.0 and 80°C with stirring for 6 hrs. Dissolution efficiency at these conditions reached to79% of thorium with only 2.8% of light trace earth. Analyzing the rest sample after thorium dissolution, it was found that its thorium content decreased to 3.3%. However, the prepared thorium precipitate from the entire leach solutions through neutralization with caustic soda produces concentrate having 45% thorium with about 48% of rare earth elements. This thorium precipitate was relatively low grade, so it was subjected to up-grading stage through another selective precipitation technique such as hydrolysis. Accordingly, the precipitate was re-dissolved in sulfuric acid then hydrolyzed using water. The efficient hydrolysis conditions were achieved at initial pH of 0.75 and dilution ratio of 25. Thorium content in the resultant final high-grade precipitate was high as 70% with almost no rare earth elements, so this thorium concentrate is suitable for subsequent purification experiments.
A polymeric resin support, commercially known as Siplite LX-16, was used to be impregnated with the organic solvent tributyl phosphate (TBP) after its pretreatment. The two common preparation methods of dry and wet impregnation were tested. Wet impregnation led to impregnate the resin to the level 1.99 g TBP / g resin at the conditions of initial solvent concentration in kerosene of 70% and its ration to resin 6.0 and left to impregnate for 24 hours at room temperature before separation, washing with hot water and then dry overnight at 50°C. In the case of dry impregnation, one gram was impregnated with 2.057 g of TBP when solvent concentration of 55% in acetone was used at solvent/resin ratio of 5.0 and contacted for 4.0 hrs in the air till complete volatilization of acetone and finally drying overnight at 50°C.
Thorium nitrate solution was prepared through dissolving an appropriate weight from the previously obtained thorium cake, that containing 70.36% Th, in the appropriate normality of nitric acid for use in the adsorption study using the prepared tributyl phosphate (TBP) impregnated Siplite LX-16 resin. Results of studying equilibrium contact time for thorium extraction revealed that the equilibrium was reached after 30 minutes of mixing, where thorium extraction efficiency reached to 70.7%. With respect to free nitric acid normality and salting out agent effects, the results show that thorium extraction requires high free normality from nitric acid rather than nitrate salt. In this regard, thorium extraction efficiency was increased with increasing nitric acid normality till 9.0 N, however, for economic considerations normality in the range 3 - 5 N may be enough to conduct the extraction step where thorium extraction efficiency was 62% to 75%. Effect of both initial concentration of thorium and solution to TBP impregnated resin ratio on thorium uptake show that the uptake increased with increasing both of them, however, the studied ranges doesn’t saturate the resin due to using low concentration of thorium during the test. Accordingly, for economic considerations it was preferable to use solutions of high thorium concentration to reduce amount of the treated solutions as well as attain saturation for the TBP impregnated resin.
Thorium elution from the loaded TBP impregnated Siplite LX-16 resin was conducted using distilled water acidified to the level of 0.1 N with nitric acid to prevent thorium from hydrolysis during desorption process. Equilibrium elution contact time was attained after 30 minutes of mixing where the eluate containing 2.26-gram Th / liter. Elution efficiency was increased with increasing the eluant to resin ratio, but high ratios must be avoided in order to produce concentrated solutions able to precipitate its constituent of thorium, however, conducting the process in columnar system can attain this purpose
The appropriate conditions of extraction and elution was applied upon fixed bed column system to study the efficient flow rate that attain maximum saturation for the resin with thorium in the extraction stage and almost complete displacement of thorium from the loaded resin with minimum amount of eluate. This efficient flow rate was 1.0 ml / min in the extraction stage while that for elution was 0.25 ml / min.
To evaluate the performance of thorium extraction from nitric acid solutions using tributyl phosphate impregnated resin, the laboratory results were applied to the different models such as Langmeyer and Freundlich adsorption kinetics as well as models of diffusion through liquid film, diffusion through spherical solid resin and also diffusion through porous materials. Results of application Langmeyer model showed that the model is appropriate while the Friendlich model is not suitable. Constants of the Langmeyer model were determined as well as the theoretical degree of saturation, which was estimated at 625 mg thorium nitrate / gram resin, which is close to the calculated and practical, as they were 605.6 and 590.13 mg thorium nitrate / gram resin. With respect to adsorption models, it is clear that the adsorption was affected by both diffusion through the liquid film as well as through solid resin grains, where R2 for the resulting straight lines were 0.9946 and 0.9993.
Finally, thorium eluate solutions resulting from elution the saturated columns were collected and precipitated selectively using hydrofluoric acid then filtered and good washed then dried. The precipitate was characterized using Scanning Electron Microscope (SEM) that showed that resultant thorium concentrate has high purity as 99%, that reflect the study achieved the aim.