الفهرس 
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Abstract
SUMMARY
The work given in this thesis deals with the decontamination of phosphoric acid from natural radioactivities especially uranium. The presence of humic substances complicate the kinetic and the extraction of uranium due to the complexes that can be formed between these substances and uranium, so the acid must be purified firstly from suspended matters and humic substances.
The thesis includes three main chapters
The introduction, the experimental, the results and the discussion.
Chapter (1); the introduction, includes importance of phosphoric acid, the different methods of producing phosphoric acid, source of natural radioactivities and also the methods of uranium recovery from wet phosphoric acid process. A literature review about the types of adsorption, factors affecting adsorption process and the main aspects related to the chemistry and radiochemistry of uranium are given. Also it covers a literature survey related to the extraction of uranium from phosphoric acid and the adsorption of humic substances from aqueous solutions.
Chapter (2): the experimental, contains detailed outline concerning the chemicals, reagents and the types of adsorbents used in this study. It contains also description of the instrumentation and experimental techniques used during this work.
Chapter (3): the results and discussion, is divided into two main parts.
Raw phosphoric acid was firstly purified from suspended matters by sand filter (particle size of sand = 64 mesh)and the obtained phosphoric acid is considered as a crude acid.
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SUMMARY
The first part contains the data obtained for the adsorption of humic substances from crude phosphoric acid. Different types of activated carbons were investigated for the adsorption process. The data obtained showed that BDH-activated carbon gives the best adsorption results. The results obtained showed that, increasing in the pH value of the acid samples causes a decrease in, the concentration of the humic substances and also in both the percent removal and the uptake values. This can be explained in terms of alteration of the charge on the adsorbent surface with changing the solution concentration. The negative charges on the surface of the activated carbon will be neutralized by hydrogen ions when the solution is concentrated (pH of the solution is decreased), and thus, the activated carbon may have more active sites. By studying the effect of contact time, on the adsorption process the results showed that, the values of the percent removal (%R) and uptake value (qe) of the humic substances increase by increasing the contact time and a plateau was reached after one day, indicating that the adsorbent is saturated at this level and the equilibrium is performed. The results also showed that as the carbon dose increases, (%R) increases and (qe) values decreases and the equilibrium is reached at 0.1 g carbon after which the plateau is formed. This result was discussed in terms of the excess of powder activated carbon PAC (BDH) inhibits good mixing and in turn prevents the pollutants to reach the PAC (BDH) particles. The adsorption of humic substances from crude phosphoric acid by (BDH) activated carbon was found to agree with Freundlich isotherm and the adsorption process was found to be exothermic The I.R spectra of crude phosphoric acid showed that the acid exhibits major bands occur that at 3441cm-i (H bonded OH), 2900 cm 1, 2840 cm-1 due to (aliphatic C-H, CH2, CH3), 2366 cm-1 due to P-OH of phosphoric acid, 1605 cm-1 (aromatic C=C and H bonded C=0 ) 1200 cm-1 (C-0 stretching and OH deformation of COOH),1074 cm-1 (C-0), 2098 cm-1 (C =N stretching ) and 700 cm -1 due to aromatic carbon bond.
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By studying the effect of temperature on the adsorption process of crude acid at different temperature (10,25,35and 45 °C), the results showed that the best removal (90.1 %) for the humic substances was registered at 10 °C. At this temperature most of the humic substances peaks disappeared as those at 1644 cm -1 due to (aromatic C=C and H bonded C=0) and at 2099 cm-ldue to isonitriles groups. By increasing temperature from 20 °C to 45 °C the removal percent decreases gradually from 89% to 80% and new additional peaks which may be due to some degradation effect for humic substances were observed. It is to be noted that the percent removal of humic substances by activated carbon is still high 80% at 45 °C due to the capability of activated carbon for the degradation effect.
Based on the data obtained, a recommended procedure for the treatment of raw phosphoric acid was proposed. After passing through the sand filter (64 mesh), 10m1 of crude acid is shaken with 0.1 g of activated carbon at temperature of 10 °C for one day. A percent removal of humic substances of about 91% and on uptake of about 200 [t.g /g are obtained. In addition, analysis of the treated phosphoric acid by the X-ray fluorescence showed that the crude acid is purified not only from organic impurities but also from some inorganic impurities.
The second part covers the extraction of uranium from crude phosphoric acid after treatment to remove suspended matters and humic substances. The different factors affecting the extraction equilibrium of U (VI) from 5M phosphoric acid by HDEHP / TOPO, HDEHP/ Cyanex-921 systems in kerosene or toluene as diluent and its stripping from the organic phase were studied in details.
The results obtained showed that addition of either TOPO or Cyanex-921 to HDEHP extractant enhances the extraction of uranium from 5M H3PO4. Also, it was found that the
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SUMMARY
distribution ratio (D) decreases by the increase of phosphoric acid concentration. This means that by increasing the H3PO4 concentration in the aqueous phase unextracted metal phosphate complexes are formed. A log- log relation between the values of D and the concentration of H3PO4 gives a straight line of slope (-2). The effect of HDEHP concentration in the presence of different- constant concentrations of either TOPO or Cyanex-921 in either kerosene or toluene on the extraction of uranium showed that the (D) values increase by increasing HDEHP concentration giving a log-log slope that varies with the concentration of the other extractants present with HDEHP. In the absence of TOPO or Cyanex-921 , the slope obtained was found to be nearly 2 . When the concentration of TOPO or Cyanex-92 1 increases, a continuous decrease in the slope is obtained to reach a value around one. The effect of TOPO or Cyanex-921 in the presence of different-constant concentrations of HDEHP in either kerosene or toluene showed that the distribution ratio increases by increasing the concentration of either TOPO or Cyanex-921 giving a log- log slope around 2 in the absence of HDEHP or at low concentration of HDEHP. As the concentration of HDEHP increases the slope decreases to reach a value around 1. This means that the interaction between the two extractants in the organic phase must be taken into
consideration.
In the stripping investigations, it was found that as the concentrations of the stripping agent increase the stripping percent increases to reach 94.2 at 1M Na2CO3, 98.1 at 1M (NH4)2CO3 and 95.7 at 0.15 M Na citrate.