The process of separating and purifying rare earth elements is selectively carried out by utilizing different distribution ratios of certain components in the aqueous phase in the organic phase. It is one of the important methods for the separation and purification of rare earth elements. The continuous organic phase formed by the extractant and the organic solvent is in sufficient contact with the aqueous phase containing the separated rare earth element without being mutually miscible (ie, sufficiently mixed and clarified), thereby achieving unequal concentration of the rare earth component in the two phases. The distribution achieves the purpose of separation and purification of rare earth elements.
The solvent extraction process of rare earth elements includes the selection of extraction system, the selection of extractor and extraction method, the determination of extraction separation process conditions and the implementation of extraction and stripping processes, and the post-treatment of various solutions after separation (see solvent extraction). There are single-stage and cascade-level extraction methods. In order to obtain high-purity products, cascade extraction is usually adopted. Cascade extraction has different forms such as cross-flow, co-flow, countercurrent, fractionation and reflux. Since the 1970s, the extraction and separation of rare earths has been dominated by fractional distillation, supplemented by other processes. The determination of the extractant, extraction system and process conditions is mainly based on the separation factor β A/B of the separated A and B components (or two elements):
Where D A is the distribution ratio of the A component in two phases; D B is the distribution ratio of the B component in the two phases, C A (0), C A (a) is the A component in the equilibrium organic phase and water The concentration of the phase, C B (0), C B (a) is the concentration of the B component in the equilibrium organic phase and the aqueous phase. The size of β A/B indicates the difference between the separation effect of the two components A and B. The larger the β A/B value, the better the separation effect, that is, the higher the selectivity of the extractant. If D A = D B and β A/B =1, it indicates that the two components A and B cannot be separated by the extraction system, and the size of β is related to the atomic number of the rare earth element and the extraction system.
The application of new extractants and advances in extraction theory and process research have strongly promoted the development of rare earth separation and purification technologies. Solvent extraction technology has become the main means of separation and purification of rare earth elements. It has been used to separate and purify each rare earth element from raw materials of various rare earth components. The cascade extraction theory provides the theoretical basis for the optimal design of the extraction process and has been widely used in the separation and production of rare earths.
There are five general body styles of Ball Valves: single body, three-piece body, split body, top entry, and welded. The difference is based on how the pieces of the valve-especially the casing that contains the ball itself-are manufactured and assembled. The valve operation is the same in each case.
In addition, there are different styles related to the bore of the ball mechanism itself.
Ball Valves in sizes up to 2 inch generally come in single piece, two or three piece designs. One piece ball valves are almost always reduced bore, are relatively inexpensive and generally are throw-away. Two piece ball valves are generally slightly reduced (or standard) bore, they can be either throw-away or repairable. The 3 piece design allows for the center part of the valve containing the ball, stem & seats to be easily removed from the pipeline. This facilitates efficient cleaning of deposited sediments, replacement of seats and gland packings, polishing out of small scratches on the ball, all this without removing the pipes from the valve body. The design concept of a three piece valve is for it to be repairable.
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