Fluoride feed solution preparation

Initial experimental studies on flux and fluoride rejection were conducted using synthesized TFC RO membrane. Feed solutions prepared from CaF and NaF were pressurized at 10 bar across the membrane. The TDS of feed sample was 820 ppm. The fluoride concentration in feed and permeate, flux and reject streams are listed in Table 4.3 for constant water recovery of 50% in permeate. 

A continuous nitrate/fluoride process has been proposed to take advantage of the ready solubility of columbite ore in a mixture of nitric and hydrofluoric acids, and thus allow the feed solution to be prepared in a cheap and simple manner. The feed contains 45 g/1. of niobium, about 25 g/1. of tantalum and is 8N in hydrofluoric acid and 3N in nitric acid. It is extracted in six stages with three volumes of solvent, together with an additional stage for acid equilibration . A half volume aqueous strip solution is also 8N in hydrofluoric acid and 3N in nitric acid. About 99 per cent of the niobium is extracted into the solvent and is then backwashed in a second extractor with three volumes of 0-5N hydrofluoric acid. The solvent finally passes to a single-stage backwash extractor for removal of tantalum by sodium carbonate solution. 

The simplest feeding system would involve a manually prepared fluoride solution and a flow-paced feed pump that introduces the fluoride solution into a water supply at a fixed rate. The requirements for auxiliary equipment are minimal. This system would include a platform scale, dissolving tank with a manual paddle or electric mixer for stirring, and a solution tank with a solution feed pump, this is all the equipment needed. Depending on the type of pumps (non-positive displacement) used to feed the fluoride solution, a vacuum breaker can be incorporated into the design of the pump feeding system to prevent pulling unmetered quantities of fluoride solution into the water system in the event of a low-pressure situation. 

In the feed preparation step, uranyl sulfate solution from the reactor core and thorium oxide from the blanket system, freed of D2O and suspended in ordinary water, are fed into the dissolver tank. The di.s.solvent is 13 N nitric acid to which has been added catalytic amounts (0.04 N) of sodium fluoride. When short-cooled thorium is being processed, potassium iodide is added continuously to the dissolver to provide for isotopic dilution of the large amount of fission-produced which is present. The dissolver solution is continuously sparged with air, and the volatilized iodine is removed from the off-gases in a caustic scrubber. 

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