Vanadium carbonate leaching

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. 

It has recently been discovered that the roasting of carnotite ore at 850°C in the presence of a few per cent of calcium sulphate, prior to carbonate leaching, enhances both the vanadium and uranium extraction efficiencies. A convenient way of achieving the desired conditions is to blend the ore with another carnotite ore with a high natural calcium sulphate content, when available, rather than waste the beneficial effect of the latter by treating it alone. 

The uranium anion present in carbonate solutions is [U02(C03)8] and this is associated with few other impurity anions. Absorption capacities as high as 100 to 200 mg/g of dried resin have been obtained on Amberlite IRA-400 2 and Dowex I , under conditions where competing anionic impurities such as phosphate and aluminate ions have only absorbed to an insignificant extent. The resin capacity, in both cases, is greatest at low sodium carbonate concentrations. Vanadate ion absorption can take place to an appreciable extent when vanadium is present in the carbonate leach liquor from the ore. It is, however, readily separated from the uranium, e.g. by a preliminary elution with a saturated solution of sulphur dioxide. This removes the vanadium from the resin by reducing it to a lower valency state. 

A series of processes have been patented for the separation of vanadium and uranium by anion-exchange from sodium carbonate solutions resulting from carbonate leaching of carnotite ore. None of them, however, are believed to be operated commercially. Three methods of operation are proposed with a strong base resin. These are (a) selective elution of uranium followed by elution of vanadium, (b) selective elution of vanadium followed... 

For direct precipitation of vanadium from the salt-roast leach Hquor, acidulation to ca pH 1 without the addition of ammonia salts yields an impure vanadic acid when ammonium salts are added, ammonium polyvanadate precipitates. The impure vanadic acid ordinarily is redissolved in sodium carbonate solution, and ammonium metavanadate precipitates upon addition of ammonium salts. Fusion of the directly precipitated ammonium salts can yield high purity V20 for the chemical industry. Amine solvent extraction is sometimes used to recover 1—3 g/L of residual V20 from the directly precipitated tail Hquors. 

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... 

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

It may be mentioned that starting with ash and soot from crude oil-fired stations, the resulting metals are the same, but the main leaching residue is carbon. This residue is initially burned and the ash is leached again to increase the total yield of vanadium. In the same operation, the concentration of iron is reduced by precipitation of jarosite. During leaching, the redox potential is controlled by SO2 addition to keep vanadium in its IV-valent state. 

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. 

Butler (B39) described the leaching of carnotite ores that contained high-vanadium-low-lime and low-vanadium-asphaltic-type minerals. The high-vanadium-low-lime ore (less than 2%) is roasted with 6-9 wt. % salt at 850°C and is immediately quenched in 3% hot sodium carbonate solution. The calcine is ground to 65 mesh and uranium and vanadium are dissolved by agitation leaching at 92-96°C. 93% of the uranium and 85% of the vanadium are extracted from the ore. The asphaltic tjq>e ore is roasted at 550°C and 80-85% of the uranium and 35-40% of the vanadium are extracted. The leach solution concentration was maintained between 7 and 9% sodium carbonate. The pulp density was between 45 and 50% solids. 

Chemical leach tests of the <50 p.m size fraction of dust samples collected around Owens Lake, using water (Reheis etal, 2001, and our unpublished data) and SLFs (our unpubhshed data), show that the dusts are sufficiently aUcahne and reactive to shift the pH of water and SLF to values near 10.5 and 9.5, respectively. Arsenic, chromium, vanadium, molybdenum, hthium, zinc, and other trace metals or metalloids are readily solubilized from the dusts. The trace metals or metalloids leached in the greatest quantities are those that form oxyanion species or abundant carbonate complexes in solution, and that are therefore mobilized most effectively under the alkaline conditions generated by the alkaline dusts. 

In the first process vanadium is coprecipitated and the sodium diuranate contains a nominal stoichiometric excess of sodium. The vanadium can be removed by roasting the yellow cake in the presence of sodium carbonate at 850°C followed by washing. The sodium carbonate solution from the washing is converted into sodium hydrogen carbonate and the sodium hydroxide solution into sodium carbonate by passing hot carbon dioxide into the solutions, which are returned to the leaching process. The consumption of solid sodium hydroxide is 10 to 20 kg/t ore. 

In the methods using an alkaline leach the ore is boiled either with sodium carbonate which extracts a considerable portion of both vanadium mid uranium, or with sodium hydroxide which removes vanadium only. Itnilnun may then be extracted with HC1, after which the remaining uranium and vanadium may be reclaimed, This method extracts the valuable constituents of the ore, hut much difficulty is exjwrieneed in filtering the lid solution because the liberated silicic arid clogs the filtering medium. 

The Koenig procoas consists in treating the crushed ore with a 20 per cent solution of sulfuric or hydrochloric acid at a temperature of 200° and a pressure of 225 pounds per square inch. After several hours the liquid is filtered, evaporated, and the Halts ignited to expel excess acid, then roasted with sodium carbonate. The mass is leached with boiling water, and curiam dioxide bubbled in to precipitate alumina. This method is recommended for roscoelite and vanadium-bearing sandstone. 

The nickel and vanadium in the fly ash from the burning of heavy oil can be recovered by chlorination and distillation, with 67% recovery of the nickel and 100% recovery of the vanadium.265 Another method is to leach out the nickel with aqueous ammonium chloride, followed by treatment with hydrogen sulfide to recover nickel sulfide (in 87% yield), which could be refined in the usual way.266 The vanadium was recovered next in 78% yield by solvent extraction with trioctylamine, followed by treatment of the extract with aqueous sodium carbonate to take the vanadium back into water, and finally ammonium chloride to produce ammonium vanadate. 

Dilute alkali leaching of ores, principally with solutions of sodium carbonate or ammonium carbonate, is a technique of some commercial importance. In the rare metal field, however, its use is almost entirely restricted to two elements, uranium and vanadium, which form soluble complexes in carbonate solutions. The relatively inexpensive soda-ash grade of sodium carbonate is adequate for the purpose. 

Camotite is a potassium uranyl vanadate, K2O.2UO3.V2O5.11H2O. Since the uranium is in the fully oxidized condition, leaching can usually be carried out without an oxidant, at a particle size of about 100 mesh. The vanadium dissolves on leaching, to sodium vanadate, and the uranium forms a soluble double carbonate. The reaction may be represented approximately as ... 

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. 

Vanadium ores are heated to high temperatures with sodium chloride in air to obtain water-soluble sodium vanadate, which is then leached with dilute acids so that a vanadium oxide can be obtained. The precipitate is dissolved in a sodium carbonate solution and ammonium chloride is added to precipitate NH4VO3. Intense heating of NH4VO3 causes it to decompose to V2O5, which is the commercial vanadium compound [13]. Vanadium metal can be purified by several methods including iodine refining [13]. 

Because vanadium pentoxide, V Oj, which coprecipitates simultaneously with sodium uran-ate, is always present in the impure yellow cake, at levels ranging from 5 to 6 wt.%, it must be removed by roasting the impure yellow cake with sodium carbonate at S60°C for 30 min, and after cooling the solid calcinated mass is leached with water to extract the soluble sodium vanadate, NaVOj. The leached product is filtered and the washed yellow cake is dried, while the solution from which vanadium can be recovered is stored. 

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