Enhancement of uranium ion flux by consecutive extraction via hollow fiber supported liquid membrane
✍ Scribed by A.W. Lothongkum; P. Ramakul; W. Sasomsub; S. Laoharochanapan; U. Pancharoen
- Publisher
- Elsevier
- Year
- 2009
- Tongue
- English
- Weight
- 316 KB
- Volume
- 40
- Category
- Article
- ISSN
- 1876-1070
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✦ Synopsis
Monazite ore is a yellow to reddish-brown natural phosphate of the rare earths, mainly the cerium and lanthanum metals, usually with some uranium and thorium. Yttrium, calcium, iron, and silica are frequently present. The monazite processing to separate the desired rare earths for use is shown in Fig. 1, which generates a byproduct, trisodium phosphate. Two grades of trisodium phosphate, a food grade and a technical grade, are extensively used. Food grade is used as an additive in cheese processing. The technical grade is for many applications, e.g., in boiler-water treatment, testing of steel parts after cleaning or pickling, industrial detergents such as degreasers for steel, and heavy-duty domestic cleaners for toilets and floors (http://www.thaipoly.com). The monazite processing is composed of five essential units: 1. ore digestion unit, 2. trisodium phosphate crystallization unit, 3. dissolution unit, 4. initial precipitation unit, and 5. cerium separation unit. Monazite was digested with concentrate NaOH solution at a temperature of 140-150 8C to convert phosphate compounds of rare earths to hydroxide compounds. The hydroxide compounds of uranium, thorium and other rare earths, and a by-product trisodium phosphate were separated by filtration. Trisodium phosphate was sent to the crystallization unit, whereas the hydroxide compounds were then dissolved with HCl to remove the gangue and undigested components. The uranium and thorium in chloride solution were selectively precipitated with NaOH solution at pH 4.5-5.0 and the remaining mixed rare earths were all precipitated into mixed hydroxide cake at pH 11. Cerium in mixed hydroxide cake was later separated by leaching with HNO 3 (Suanmamuang and Laoharochanapan, 2002). Unfortunately, uranium has high solubility in water, therefore, filtration is not a suitable technique to separate uranium from trisodium phosphate solution, and it contaminates in the crystal of trisodium phosphate. The contaminated uranium is traditionally separated from trisodium phosphate solution by either ion-exchange or chemical precipitation. In general, uranium is a radioactive element which is useful at the front and back ends of the nuclear fuel cycle. However, uranium is known to cause serious environmental damage and acute toxicological effects in mammals, and its compound are potential carcinogens (Agency for Toxic Substances and Disease Registry, 2000;Clayton and Clayton, 1994). Due to safety and economic considerations, therefore, finding a new method to