[en] When evaluating uranium resources, one must not overlook the possibilities of recovering uranium as a by-product of other industries. The technology for recovering by-product uranium from phosphoric acid has been known for many years, but only recently have market conditions encouraged production. Even with recent improvements in process technology, many problems are still encountered in scale-up from laboratory and pilot plant operation to commercial production. Some of these problems are discussed in this review of the process technology. A recent USDOE study shows a total capital cost of US $12 million for a by-product uranium plant designed to recover 40 to 60 t U/a from 30% P₂O₅ acid provided by a phosphoric acid plant with a capacity of 155,000 t P₂O₅/a. Operating costs were estimated at US $50 to 65/kg U ($20-25/lb U₃O₈), assuming the phosphoric acid contains 120 to 160 mg U/l and a raffinate of 13 mg U/l. The quantity of uranium recovered and the operating costs are highly sensitive to the uranium content of the acid. Constraints to by-product uranium production, besides low uranium content of the acid are small-size phosphoric acid plants and high strength (>40% P₂O₅) acid. Similarly the technology for recovery of uranium from copper waste dump leach liquors has been known for several years. It was developed in the mid-1960s by the US Bureau of Mines in co-operation with Kennecott Copper Corporation at its Bingham Canyon mine near Salt Lake City, Utah. Commercial application was first realized when an ion-exchange plant to recover about 55 t U/a commenced operation in 1978. (author)