Camotite ores, leaching

Australian Vanadium—Uranium Ore. A calcareous camotite ore at YeeHrrie, AustraHa, is iU-suited for salt roasting and acid leaching. Dissolution of vanadium and uranium by leaching in sodium carbonate solution at elevated temperature and pressure has been tested on a pilot-plant scale... 

A similar non-aqueous process has been decribed using iso-octyl phosphoric acid, monododecyl phosphoric acid or monoheptadecyl phosphoric acid as solvents, none of which require the ammonium nitrate addition. Methyl ethyl ketone, other ketones, or kerosene are suitable diluents. The sulphuric acid usage is much less than that normally required for, for example, a dilute acid leach of the camotite ore used, since the high proportion of lime present in the ore is not taken into solution. Hydrochloric acid is preferable for backwashing the uranium. 

The camotite ore of the Colorado Plateau area contains a workable proportion of vanadium in addition to uranium, and processes have been devised for the simultaneous recovery of both elements by solvent extraction methods. The Shiprock plant in New Mexico, for example, extracts first the uranium from a sulphate leach liquor, by means of a solvent containing 10 per cent D2EHPA with 2-5 per cent TBP, in kerosene. A second solvent cycle, with different proportions of the two phosphates, then extracts vanadium from the first cycle raffinate. Sodium carbonate is then used for backwashing the uranium and 10 per cent sulphuric acid for the vanadium. 

Uranium, too, is widely distributed and, since it probably crystallized late in the formation of igneous rocks, tends to be scattered in the faults of older rocks. Some concentration by leaching and subsequent re-precipitation has produced a large number of oxide minerals of which the most important are pitchblende or uraninite, U3O8, and camotite, K2(U02)2(V04)2.3H20. However, even these are usually dispersed so that typical ores contain only about 0.1% U, and many of the more readily exploited deposits are nearing exhaustion. The principal sources are Canada, Africa and countries of the former USSR. 

Alkaline leaching is carried out by using sodium carbonate solution. In this case any U(IV) present in the ore must also be oxidized to U(VI). The uranium species soluble in carbonate leach solutions in the uranyl tricarbonate ion. The formation of this ion by solubilization of a hexavalent uranium mineral such as camotite, or a tetravalent uranium mineral such as uraninite, may be represented by the following reactions ... 

For the treatment of camotite several methods are available. The method recommended by the United States Bureau of Mines2 is as follows The ore is leached with concentrated nitric acid at 100° C., neutralised with caustic soda, and barium chloride and sulphuric acid added to the solution to precipitate the radium as barium-radium sulphate. The precipitate settles in three or four days, after which time the clear liquid is decanted into tanks and is treated with excess of boiling sodium carbonate solution in order to precipitate any iron, aluminium and chromium present. The solution now contains sodium uranyl carbonate and sodium vanadate. It is nearly neutralised with nitric acid, and caustic soda is added in sufficient quantity to precipitate the uranium as sodium uranate. After filtering, the remaining solution is neutralised with nitric acid and ferrous sulphate added, whereupon iron vanadate is thrown down. By this method it is claimed that 90 per cent, of the radium, all the uranium, and 50 per cent, of the vanadium in the camotite are recovered. 

Two of the most well-known applications of the sodium carbonate leaching of ores are the extraction of uranium from pitchblende in Canada and extraction of both uranium and vanadium from camotite, which is mined in numerous localities of the Colorado Plateau area of the United States. The latter deposits were originally worked for their vanadium content but since the 1939-45 war the emphasis has been on uranium, with vanadium a subsidiary product. 

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