The solvent extraction unit of both systems contained four extraction and four stripping stages through which aqueous and organic phases flowed continuously and counter-currently. Each stage of the United Nuclear system consisted of a conventional mixer-settler. Each stage in the extraction circuit of the C-E Natco SX pilot utilized a throttled centrifugal pump for fluid transport while mixing was achieved with a Penberthy Hondalle eductor mounted on the discharge of each pump. The intake of each pump received organic recycle and advance while the intake of each eductor received aqueous advance. Early tests utilizing the centrifugal pumps for mixing as well as fluid transport indicated that rather severe emulsions could be created under such intense mixing conditions. The eductors provided sufficient mixing intensity to produce greater than 97% extraction efficiency without creating stable emulsions.
Operating data on the C-E Natco SX system were obtained during seven days of continuous operation from October 23 until October 30, 1980. Ambient temperature during this period ranged from -10° C to 18° C. Low ambient temperatures necessitated adding live steam to the organic surge vessel on a continuous basis to maintain a temperature of 28.9° C in the E-1 extractor.
Aqueous carryover in the pregnant organic from the extraction circuit may result in a contaminated pregnant strip liquor and product. During the 7 day test period the feed to the SX systems contained a high iron content of approximately 3 g/l and aqueous carryover in the United Nuclear system was causing unacceptable iron levels in the yellow cake product. To control this problem United Nuclear utilized a fresh water wash of the pregnant organic to remove iron. As a result the iron content of the pregnant strip liquor was maintained at approximately 55 mg/l. This figure represents a four day average. During this same period the iron content of the pregnant strip liquor from the C-E Natco SX system averaged 50 mg/l without a fresh water wash of the pregnant organic.
