Mixer settler laboratory

The development of the novel Davy-McKee combined mixer—settler (CMS) has been described (121). It consists of a single vessel (Fig. 13d) in which three 2ones coexist under operating conditions. A detailed description of units used for uranium recovery has been reported (122), and the units have also been studied at the laboratory scale (123). AppHcation of the Davy combined mixer electrostatically assisted settler (CMAS) to copper stripping from an organic solvent extraction solution has been reported (124). 

Because of the diversity of contacting equipment available, it is unlikely that all these contactors will be available in any one laboratory or pilot plant. Consequently, unless test work is carried out on similar contactors, the system may not be optimized. Since mixer-settlers are the easiest to construct, are simple to operate, and require little room and low-flow rates, these contactors are, in many cases, the only ones used to investigate a continuous solvent extraction process. This is by no means ideal and may result in abandonment of a process that, using another type of contactor, could be found to be entirely satisfactory. 

Laboratory Extractors. Pilot-Scale Testing, and Scale-Up. Several laboratory units arc useful in analysis, process control, and process studies. The AKUFVE contactor incorporates a separate mixer and centrifugal separator. It is an efficient instrument for rapid and accurate measurement of partition coefficients, as well as for obtaining reaction kinetic data. Miniature mixer-settler assemblies set up as continuous, bench-scale, multistage, countercurrent, liquid-liquid contactors are particularly useful Tor the preliminary laboratory work associated with flow-sheet development and optimization because these give a known number of theoretical stages. 

The early experiments on solvent extraction directly from leached pulp were beset with problems such as losses of solvent in the aqueous phase and the formation of emulsions. The use of mixer-settler, pump mixer, and internal mixer-settler type contactors on a laboratory scale (Gil) has demonstrated the feasibility of uranium extraction from desanded slurries with 5-1. )% solids and from high-density slurries with 48-60% percent solids. The deemulsification rate of a synthetic slurry as a function of the temperature of the system and the pH of the slurries (T12) and the effect of extractant entrainment in the aqueous effluent on solvent extraction of uranium from slurries containing more than 40% solids (E6) have been studied. 

In 1968, an electrolytic reduction process was proposed by A. Schneider and A. L. Ayers (6) to circumvent the above disadvantages. A research program was carried out in the Allied Chemical Corporation s laboratories during the years 1968 to 1972 to develop the process and equipment. The work resulted in the development of the Electropulse Column ( 7) for the continuous (differential) electrolytic uranium-plutonium partition process, which was later scaled up, fabricated, and installed in the Allied-General Nuclear Services reprocessing plant at Barnwell, South Carolina. About the same time, a stagewise electrolytic uranium-plutonium partition process was tested on a mini mixer-settler unit in Germany. (8)... 

Laboratory Scale Contactor Tests. The feasibility of each part of the flow sheet was tested in small, commercially available mixer-settler units which had 12 or 16 stages with individual mixer and settler volumes of 15 mL and 49 mL, respectively. 

The flow sheet presented here has been shown, in laboratory tests using mixer-settlers, to be suitable for separating the the three actinides, Th, U and Pu from each other. 

A laboratory study was undertaken to determine the behaviour of neptunium in the WAK flowsheet, and to devise a procedure for its recovery. Based on static ( ) and counter-current experiments (J5), the conclusion was reached that about half of the Np is co-extracted with the U and Pu in the HA-HS mixer-settlers of WAK while the other half is rejected to the HAW, see Fig.1. It could also be shown that an increase of the aqueous acidity, or the addition of pentavalent vanadium as an oxidant into the lower stages of the HA mixer-settler (6), would increase the Np yield in the organic solvent. In the 1BX-1BS mixer-settlers where the partitioning of U and Pu is carried out by use of uranium (IV)nitrate - hydrazine nitrate, a splitting of the coextracted Np between the two product streams was observed the proportions of the (co-extracted) Np which ended up in the 1CU (uranium product) stream fluctuated from 30 to 93 % while the difference amount (from 7 to 70 %) ended up in the 1 BP (plutonium product) stream. 

A solvent extraction cycle similar to that used in the earlier work was selected (1). The flowsheet (Figure 1) was first demonstrated in laboratory miniature mixer-settlers. 

Figure 1. Solvent extraction flowsheet for laboratory miniature mixer settlers...

Reduction by HAN is slow at 2.3-2.5M HN03 in the center of the mixer-settler. Therefore, Fe2+ would be the principal re-ductant and more should be consumed as reflux increases. However, subsequent reduction by HAN prevented measurement of Fe2+ so the HAN concentration should be indicative of increased Pu concentrations. The analyses showed that 0.01M more HAN was consumed after the start of reflux. Assuming that 2 moles of ferric are reduced per mole of hydroxylamine, the ferric ion concentration was 0.02M lower after reflux than before reflux. Lowering Fe2+ and NH2S03 was sufficient to obtain Pu reflux similar to that observed in laboratory tests with 0.01M FeSA. 

Laboratory tests showed that FeSA added as a sidestream to the extraction section of the mixer-settler lowered Np losses. After Pu(VI) and residual Np(VI) were extracted, FeSA was added to reduce inextractable Np(V) to extractable Np(IV) in situ. 

Mixer-settlers are widely used, particularly in the mining industry. Vendors are available, and they are easily designed. In the laboratory, small-scale, mini-mixer-settlers are available that offer as many as 16 countercurrent stages and are capable of achieving steady state using 500 mL of feed or less. 

In selecting the contactor a number of options were available dispersed water phase in a continuous amalgam phase dispersed amalgam in a continuous aqueous phase use of packed columns and use of mixer settlers. The early work to establish the separation factor was carried out in a mixer settler which had been developed around the centrifugal glass impeller commonly used in laboratories for mercury cleaning, and mixer settlers were used in the main plant. 

Jamrack, W. D., Logsdail, D. H., and Short, G. D. C. Laboratory mixer-settlers. Progress in Nuclear Energy, Ser. Ill, vol. 2, Process Chemistry. Pergamon Press. 

Mixer-settlers consist of a mixing chamber, usually with an impeller that also pumps the liquid through the system, and a separation chamber in which the phases are separated by gravity. The size ranges fi om laboratory equipment with a volume of a few milliliters per step to... 

Separation of each element by solvent extraction is carried out in multistage batteries of mixer-settlers for each rare earth element. A minimum of 50 mixer-settler stages per stream is required to obtain a product with a purity of 4 or 5 nines. For economic and technical reasons the ion-exchange method is only used for laboratory and pilot scale production to produce small toimage of rare earths. 

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