the solution analyzed note the larger amounts of impurities in the product from the concentrated acid treatment of scheelite compared to the product obtained from the tricalcium tungstate treated according to the present invention ______________________________________ material treated with acid ca sub 3 wo sub 6 per sheelite cawo sub 4 impurity invention comparison______________________________________ca 10 15mg 26 9k 24 15si 460 1180mn 1 2fe 2 27mo 165 67cu 3 11total 691 1326______________________________________ a sample of a commercial ferberite concentrate of 250 mesh and containing 68 6 by weight of tungsten trioxide and 24 1 by weight of iron oxide feo was mixed with a laboratory grade calcium carbonate so that the molar ratio of calcium to tungsten was 4 4 1 approximately 300 g of the mixture were calcined for 4 hours at 1200 u00b0 c a 25 10 g sample of the calcined mixture was added to 365 ml of 2 n hydrochloric acid solution this quantity of acid was about 30 in excess of the stoichiometric requirements the solution was stirred for 2 hours at ambient temperature and then filtered the solid residue was washed with a small volume of 2 n hydrochloric acid the solid residue was treated with saturated ammonia solution as in example iii the recovery of tungsten in the form of tungsten trioxide obtained from the ammonia solution was 79.