Acid settler levels

Acid settler levels. Spent alkylation acid contains a sludge consisting mostly of corrosion products. The acid sludge accumulates in the settler. There it plugs the level gauge glass laps. This is one of the most frequent causes of physical acid carry-overs. 

Figure 46.1 tells the tale. A faulty level indicator on the acid settler drum had caused the 90 percent sulfuric acid to carry over into the caustic settler drum. One pound of acid will neutralize 10 lb of the caustic solution. When I checked the pH of the circulating solution from the caustic settler, I measured a pH of less than 1. That is, the litmus paper turned red, not its normal blue. 

Several tests using countercurrent separation in mixer-settler or centrifugal extractors with simulated and genuine high-level waste showed that the recovery of An(III, IV, VI) is quantitative. The back extraction of An(III) was complete. These early flow sheets were not designed to strip U(VI) and Pu(IV). The distribution ratios of these ions at low acidities are lower than those measured with CMPO and one can guess that the stripping... 

The exhaustive U, Pu extraction step is best achieved in pulsed columns rather than in mixer settlers in order to keep the contact time lower at the very high radiation level. This operation is expected to produce as its main product a HAW raffinate that is virtually free of Pu (and Np, U) a scrub appears therefore superfluous and would dilute only the HAW. In order to attain still a good extraction efficiency within a few stages, A/O phase ratios < 3 should be avoided. This ratio corresponds to a TBP saturation by heavy metals of about 18%. Considerable amounts of Zr are therefore co-extracted, being however present essentially as inactive isotope. Either a complexing or a reductive stripping is advisable in order to keep the aqueous flow small and the acidity sufficiently high to avoid hydrolysis of Zr. 

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