Distribution of antimony between carbon-saturated iron and synthetic slags
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Reactant Mill solution NazSO4 NaOH
H202
Concentration 0.25 M 2.5 M 2.6 M
Feed Rate 23 ml/min 50 ml/min to maintain pH 4 to 5 1.7 ml/min
Table IV. Product and Barrens Data from the High-Vanadium Process Compared with Those from the Low-Vanadium 60 ~ Neutral Process
Allowed*
60 ~ Neutral Process
High-Vanadium Process
V 1000 ppm 300 pprn 100 ppm Mo 1000 ppm 20 ppm 50 ppm Na 500 ppm 100 ppm 300 ppm Barrens U -95 ppm 92 ppm *Typical values; allowable levels vary among different purchasers of yellow cake.
Attempts to explain, in any simple way, the effectiveness of the added feed of sodium sulfate solution in processing high-vanadium solutions lead to apparent logical contradictions, as may be seen in the following paragraph. A proper analysis of this system would be quite complicated. It should be noted parenthetically here that it was determined in initial, exploratory experiments that dilution of the reactant feeds, as an alternative to addition of the diluting feed, did not result in a satisfactory product. The experimental result that dilution of the bulk solution in the reactor permitted more complete precipitation of uranium, free of vanadium, compels one to conclude that when a diluting feed was present, uranium entering the reactor was effectively precipitated at a lower vanadium concentration. This conclusion, although qualitatively attractive, needs to be reconciled with the previous observation tl] that the precipitation takes place in a very short time, before the reactant feeds have mixed appreciably with the bulk solution, so that it would seem that dilution of the bulk solution (i.e., dilution of the vanadium) should not greatly affect the environment in which precipitation takes place. The experimental fact, however, that the process succeeds with the diluting feed and fails without it undeniably indicates that precipitation occurs in a different environment when the diluting feed is introduced. It might be postulated that the success of the modified neutral process depends to some extent upon the geometry of the addition of the feeds to the reactor. It finally seems necessary, in any attempt to explain the effect of the diluting feed, to take into account the fact that this precipitation consists of addition of material to the existing crystals in the suspension rather than nucleation of new crystals. When the concept of homogeneous processes is abandoned, it is possible to think in terms of a phase containing reactants in solution and a second phase, the barrens, containing suspended crystals of uranium peroxide upon whose surfaces the freshly 136--VOLUME 22B, FEBRUARY 1991
added uranium deposits. In spite of the formidable complication of a thorough kinetic analysis of such a system, it at least might permit one to avoid what at first seem to be logical contradictions. In conclusion, it has been shown that the problems encountered in continuous precipitation of uranium peroxide from a uranium mill solution containing a high level of vanadium can be eliminated by the addition of a sodium sulf
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