CA2059428C - Recovery of nickel from uranium containing ore - Google Patents

Abstract

Nickel is found in substantial quantities in some uranium-containing ores. Recovery of uranium from such ores by the known acid leaching process includes a solvent extraction stage that leaves an aqueous raffinate containing nickel, together with other components including iron, arsenic, radium 226 and uranium. Attempts have been made to recover nickel from this raffinate but have not been successful because the costs of recovery are so high that the process is uneconomic or because the nickel obtained is contaminated with radium 226 and uranium to such a degree that the nickel is unacceptable. The present invention provides a process for obtaining from the raffinate a solution of a nickel salt that is not unacceptably contaminated with radium 226 and uranium. The process is economic and in a preferred embodiment uses only air, lime and a barium salt, preferably barium chloride, as reagents. If cobalt is also present in the ore it is recovered with the nickel.

Description

2~5~8 63147-51 The present invention relates to the recovery of nickel and cobalt from ores con-taining these metals together with urani-um.
Nickel and cobalt occur in association with uranium in many mineral deposits. A typical deposit may contain about 2%
uranium, about 1% nickel, about 1% arsenic, about 0.05~ cobalt, some iron, and minor amounts of other components. Those mineral deposits are mined primarily to recover the uranium values. The co-recovery of nickel and cobalt in uranium mills has not been practised to date because it has generally been considered that any nickel-cobalt by-product of uranium milling would be contami-nated with uranium and radium 226. Consequently the nickel-cobalt product would not be acceptable to nickel smelters or to hydro-metallurgical nickel plants.
Uranium is extracted ~rom uranium ore by a known acid leaching process. Although any mineral acid can be used in the leaching, for instance sulfuric, hydroc,hloric, nitric or phosphor-ic acid, sulfuric acid is the cheapest mineral acid and sulfuric acid is used for reasons of economy. In a typical process the uranium ore is ground and then subjected to sulfuric acid leaching in one or several stages, including a pressure leaching stage.
Between the several stages about 98% of the uranium is extracted.
Also extracted is about 50% of the nickel originally present in the ore, about 50% of the cobalt and some iron, some arsenic and some radium 226. The sulfuric acid products from the several leaching stages are combined and are then subjected to a solvent extraction to remove the uranium. The sulfuric acid is admixed ~t~5~ 8 with an organic phase that is typically composed of a hydrocarbon solvent such as kerosene and an amine. A suitable amine is a water insoluble symmetrical, straight chain, saturated tertiary amine commercially available under the trade-mark Alamine 336 ~rom Henkel Corporation. Another suitable amine is commercially avail-able under the trade-mark Adogen 364. This solvent extraction is usually carried out in several stages and uranium values enter the organic phase. Therea~ter the organic and aqueous phases are separated and the uranium value is stripped from the organic phase using a suitable reagent such as ammonium sulfate solution or concentrated sulfuric acid. Uranium is subsequently precipitated from the stripping reagent as yellow-caXe which is subjected to further processing to recover uranium.
The raffinate from the solvent extraction is an aqueous sulfuric acid solution that con-tains some residual uranium and nickel, cobalt, iron, arsenic and radium. At present, these com-ponents of the raffinate solution are precipitated and disposed of as tailings.
Attempts have been made on a laboratory and pilot plant scale to separate nickel and cobalt from the other components of the raffinate but no attempts have met with commercial success, for one reason or another.
Initial attempts were focused on conversion of nickel to nickel sulfide and solvent extraction techniques. There were found solvents that would extract high percentages of the nickel and cobalt present in the aqueous raffinate. Un~ortunately the solvents also extracted radium, to such an extent that the obtain-ed nickel and cobalt were too contaminated to be of any commercial 2~5~8 63147-51 value.
Another attempt to separate nickel and cobalt from the aqueous raffinate involved subjecting -the raffinate to oxidation with hydrogen peroxide to convert the iron from the ferrous to the ferric state, followed by various precipitation stages to obtain nickel and cobalt sulfide. Pilot scale tests were carried out and considerable data were obtained but these data revealed that the process was uneconomic, laryely as a consequence of the high cost of the reagents used for -the oxidation and precipitation stages.
Canadian Patent No. 431,614 is concerned with separating iron from iron-containing nickel solutions. It is particularly concerned with the treatment of nickel salts produced as by-pro-duct from electrolytic copper refining, although the process is said to be applicable to purification o~f iron-containing nickel salts from any source. No mention is made of uranium ores as a source. The process involves treating an impure nickel sulEate solution with hydrogen peroxide and with calcium hydroxide.
Canadian Patent No. 560,855 i'3 concerned with recovering nickel from ores of very low grade. No mention is made of uranium-containing ores. The process involves acid leaching, followed by raising the pH value, for which purpose potassium hydroxide, potassium carbonate, sodium carbonate, sodium hydrox-ide, ammonium carbonate or ammonium hydroxide can be used.
Canadian Patent No. 931,765 is concerned with recovery of nickel and cobalt from low grade nickeliferous ore. Precipita-tion of iron and aluminium impurities from an acid solution of nickel is achieved by addition of magnesia at elevated temperature and pressure. No mention is made of uranium-con-taining ores.

2~5~8 63147-51 Canadian Patent No. 1,084,716 is concerned with separa-ting copper from nickel in an acidic sulfate solution by a process involving formation of copper sulfite and thermal dissociation.
No mention is made of uranium-containing ores.
Canadian Patent No. 1,105,264 is concerned with recovery of uranium values from uranium ores that also contain siliceous material. Nickel is mentioned as a further component of the ore and a process for recovery of nickel from the aqueous raffinate after solvent extraction of uranium is described. This process includes a pH adjustment step, to a pH of about 3.5 - 4.5, and simultaneously with the pH adjustment there may be added a ferric compound to precipitate ferric arsenate to remove arsenic. There- ~ -af-ter nickel is precipitated by addition of hydrogen sulfide or sodium hydrogen sulfide, with formation of nickel sul~ide, or by addition of ammonium sulfate with formation of nickel sulfate-ammonium sulfate double salt.
Canadian Patent No. 1,139,955 is concerned with uranium solution mining processes in which stripping solutions are inject-ed underground to solubilize uranium. The stripping solution comprises an oxidant and a bicarbonate. The uranium-containing solution obtained from the mining process is frequently supersatu-rated with dissolved calcite (calcium carbonate). The calcite is precipitated but with it comes some of the uranium and also some radium, so that there is created a radioactive waste disposal problem. The precipitate is dissolved with acid, to form a solu-tion containing radium, uranium and calcium, from which uranium is removed and the radium is precipitated by adding barium sulfate or ~5~ 63147-51 strontium sulfate.
Canadian Patent No. 1,156,047 is concerned with recovery of uranium from uranium ores that also contain siliceous matter, iron and arsenic, and may contain nickel. The process involves solvent extraction to leave an aqueous acidic raffinate that may contain arsenic and nickel. It is proposed to remove arsenic from the raffinate by addition to hydrogen sul~ide to precipitate arsenic sulfide. This precipitation can be carried out in such a manner that nickel is also recovered by precipitation as nickel sulfide, e.g. by adjusting the pH to a value of about 2.5 by addi-tion of magnesium oxide. After the recovery of nickel as nickel sulfide the raffinate is treated with lime to raise the pH to a value in the range of from about 8 to about 10 and with air to oxidize ferrous iron to ferric iron, to precipitate the remaining nickel values as hydroxides and to precipitate remaining arsenic values as arsenate.
It is an object of the present invention to provide a process for recovery of nickel, and cobalt if present, from the aqueous raffinate obtained after solvent extraction in the re-covery of uranium from uranium ore by acid leaching, which processis economic and yields a product that is not objectionably con-taminated with radioactive impurities. At this time there is no recognized industry standard for acceptable freedom -from radio-active contamination. At one time the British Wall Board Industry set a requirement that nickel must have a radioac-tivity at or below 0.56 Becquerel per gram (Bq/g). It is a present object to meet or exceed this standard.

~5~8 The present invention provides a process for -the recov-ery of nickel from a nickel-containing aqueous acidic raffinate obtained after solvent extraction in the recovery of uranium from uranium ore by acid leaching, which process comprises oxygenating the raffinate and adding to the raffinate an alkaline reagent and a barium or strontium salt, the amount of alkaline reagent added being such that the pH is not raised above 7.0, and separating a solution containing a nickel salt from precipitated solids.
The raffinate can be oxygenated with air, with oxygen enriched air or with pure oxygen. It is usually preferred to use air, for cost considerations.
As alkaline reagen-ts there are mentioned sodium hydrox-ide, sodium carbonate, potassium hydroxide, potassium carbonate, ammonium hydroxide, ammonium carbonate, magnesia, magnesium hy-droxide lime (CaO) and slaked (hydrated) lime (Ca(OH)2). Of these, lime and slaked lime are normally preferred for reasons of cost.
The nickel salt obtained is the salt of the mineral acid used in the acidic leaching process for the recovery of uranium.
Usually this is sulfuric acid, so that the salt is nickel sulfate.
In the following the invention will be described with reference to sulfuric acid and nickel sulfate.
Any cobalt present in the raffinate reacts in the same manner as nickel, on an almost quantitative basis, and will be recovered with the nickel. In the following description where mention is made only of nickel it should be borne in mind that ''-.. ' :; ' Z~5~ 63147-51 cobalt may be present with the nickel.
In a preferred embodiment of the invention the oxygena-tion and the addition of the alkaline reagent are carried out in a plurality of stages. For instance, in a first vessel air is pump-ed into the aqueous raffinate and sufficient lime, preferably in the form of a slurry, is added to the raffinate to raise the pH to about 3. Raffinate from this vessel passes to a second vessel where again air is pumped in and lime is added to raise the pH to about ~. Raffinate from this second vessel passes to a third vessel where air is pumped in and lime is added to raise the pH to about 4.5. These aeration stages can be conducted at elevated pressure, up to about 350kPa (50psig), and preferably about 210kPa (30psig). Ambient temperature is suitable but a modestly elevated temperature, say up to about 50~C, e.g., 35~C, is preferred.
Raffinate from this third vessel passes to a fourth vessel where a barium salt, is added. The barium salt can be barium sulfate, barium carbonate or barium chloride, of which the chloride is preEerred. Alternatively, a strontium salt can be used instead oE a barium salt. The contents of all four vessels are subjected to vigorous agitation, so that any ~aterial that is precipitated does not settle out but remains in suspension. From the fourth vessel the treated raffinate-suspension passes to a settling tank. In this settling tanX solid waste containing iron, arsenic, radium and calcium sulfate settles out and a solution of purified nickel sulfate is separated, suitably by overflow, from the waste.

d~ ~ 9~ ~ 63147-51 The pH is not allowed to rise above 7. As the pH rises nickel is precipitated, along with the other precipitated materi-al. The maximum pH used affects the amount of nickel recovered and also the amount of iron, in particular, that remains with the nickel. The lower the pH used, the more nickel remains in solu-tion but also the more iron remains in solution with the nickel.
The higher the pH used, the less iron remains to contaminate the nickel but the more nickel is lost as a precipitated solid with the other waste materials. At pH 7 and above substantially all the nickel is precipitated. It will be appreciated that a pH
value between about 4.5 and 7 can be selected depending upon whether a high yield of nickel is required and some contamination with iron is acceptable, or whether freedom from iron contamina-tion is required and a lower yield of nickel is acceptable. It is normally preferred that the pH shall not be above about 6.
For a typical raffinate the amount of lime added should be of the order of 20 g/h of raffinate. The important considera-tion is that the amount of lime or other alkaline reagent should not raise the pH above 7. The residence time of the raffinate in contact with the air and lime is not critical. Suitable values are between about 3 hrs and 24 hrs. Vse of elevated temperature and pressure permit shorter residence times.
The barium chloride can be added after the raffinate has been treated with air and lime. The amount required will usually be less than about 1.2 g of barium chloride per litre of raffin-ate. For a typical uranium ore from the Key Lake area of Saskatchewan an amount as low as about 0.06 to 0.04 g of barium "' ' ~5~ 3 63l47-5l chloride per litre of raEfinate i5 sufficient to achieve the objective of radioac-tivity less than 0.56 Bq/g. If a level of radioactivity substantially below this 0.56 figure is desired more barium chloride can be used to achieve this. The process of the invention provides a purified solution of nickel sulfate. If desired, a crude nickel sulfate product can be obtained by evapor-ating the solution to cause crystallization of nickel sulfate.
Alternatively, an alkaline reagent can be added to the purified solution to precipitate the nickel. Suitable alkaline reagents are those mentioned above. For instance, lime can be added to the purified solution, to precipitate a product that is a mixture of nickel hydroxide and calcium sulfate. This mixture is acceptable as a source of nickel for further recovery. The amount of alkaline reagent added raises the pH to a value well above 8, preferably to about 9 - 10.
The crystallization process yields a purer product than the precipitation process. The crystallization process is more expensive than the precipitation process, however, owing to the capital cost of a crystallizer and the energy cost of the evapora-tion of a large volume of solution.
By these processes there have been obtained productsdisplaying a radioactivity of only about 0.01 to 0.01 Bq/g, well ~elcw the target of less than 0.56 Bq/g. Uranium leve]s in the products were found to be very low at about 0.00004 to 0.00016~. -The invention is further illustrated in the following examples.

2~'5~ 631~7-51 Examples 1 to 3 A sample of uranium ore from a deposit at Key Lake, Saskatchewan, was subjected to the known acid leaching process.
The ground ore was subjected to two leaching stages with sulfuric acid, a first one at atmospheric pressure that extracted about 15% of the uranium from the ore and a second one carried out at elevated pressure of abou-t 550 kPa with agitation and addition of oxygen. Thereafter uranium was removed by solvent extraction using a mixture of Alamine 336 and kerosene as organic phase. A
sample of aqueous sulfuric acid raffinate was taken from the solvent extraction. The sample had a content of free acid of about 14 g/L. The pH of the sample was adjusted to about 4 by the addition of hydrated lime with vigorous agitation to form a slur-ry. About 18 g oE hydrated lime were required per litre of raffi-nate to achieve the required pH.
Example 1 A por-tion of the slurry at about pH 4 was stirred in a container at atmospheric pressure and ambient temperature while air was sparged into it for 24 hrs. Barium chloride was then added to the slurry to remove radium.
Example 2 A portion of the slurry at about pH 4 was sparged with air in an agitated autoclave at ambient temperature and 210 kPa ~30psig) pressure for 3 hrs. Barium chloride was -then added to the slurry to remove radium.

~'5~8 63147-51 Example 3 (Comparative) A portion of the slurry at pH 4 was agitated for 36 hours without air sparging. Barium chloride was then added -to the slurry to remove radium.
The composition of the original raffinate and the composition of the product of each of Examples 1 to 3 are given in Table 1 below.

Table 1 mg/L Bq/L

pH Ni Co Fe As U 226Ra Raffinate 1.05 2400 1701400 1900 0.919 200 Example 1 4.2 2800 180 470 2 0.032 0.3 Example 2 4.1 2200 150 290 ~ 1 0.0090.45 % Removal in Example 2 2 2 79 99.9 98.9 99.8 Example 3 4.06 2800 180 550 7 0.007 1.4 The amount of radium was determined by measurement of radioactivity, in Bq/~. The increase in concentration of nic~el and cobalt in Examples 1 and 3 occurred because the volume of liquid was reduced over the period that the process was carried out.

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~ ~C~? ~ 63147-51 Example 4 A three stage continuous process was conducted at atmos-pheric pressure on a lOOL sample of raffinate.
In this test, air was sparged into each cell through a dip tube. The raffinate feed rate was 3.6L/h and the recycle rate of the treated slurry was 7.4L/h. The test conditions are given in Table 2.

Table 2 Air-sparging - Barium Chloride Addition Continuous Test Conditions Stage 1 Stage 2 Stage 3 Cell capacity (litres) 3.5 2.5 2.5 pH set point 2.0 3.0 4~0 The pH values in each stage were achieved by addition of a slurry of hydrated lime, the consumption of hydrated lime being 18.3 g per litre of raffinate. AEter st:age 3 the slurry was allowed to settle and there was obtainecl a supernatant of 68 litres volume.
The supernatant was analyzed and found to contain 0.001 mg/L of uranium and radium 226 corresponding to 10 Bq/L~ To the supernatant was added barium chloride solution at pH 5, the amount of barium chloride added being 1.2 g per litre of supernatant.
This reduced the radium 226 content to a value corresponding to 0.13 Bq/L. Calculation showed that nickel produced from the solu-tion would have a radium 226 level of 0.08 Bq/g, significantly lower than the objective of 0.56 Bq/g.

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Results are given in Table 3.

- Table 3 Air-sparging Treatment of Raffinate and Barium Chloride Addition Continuous Test Details mg/L ~

Process Procedure~ Ni Co Fe As U 226Ra Raffinate (reference) 1.05 2400 170 1400 1900 0.919 200 After air-sparging and pH adjustment 4.08 2000 130580 54 0.001 10 After barium chloride/
lime 5.0 1700 110370 7 0.001 0.13 Example 5 A batch impurity precipitation test was conducted to investigate the optimum residence time and barium chloride consumption rate. The test was carried out in a flotation cell having good agitation and air dispersing capabilities. Hydrated lime was added in slurry form to minimize localized high pH zones and the temperature was maintained at 3!;~C.
The composition of the raffinate after various residence times was determined and the results are given in Table 4.

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' 2~5~ 63147-51 Table 4 Bulk Precipitation of Raffinate - Effect of Residence Time (Batch) Residence mg/L

Time (h) Ni Co As Fe pH
(Raffinate) 2400 170 1900 1400 4 2300 150 1.7 160 5.0 2200 150 2.2 90 5.0 6 2300 150 2.2 50 5.1 7 2300 150 2.1 30 5.1 As can be seen from Table 4, residence time of about 5 hours brings the iron content down to a value below about 100 mg/L. Arsenic content dropped to below 2 mg/L after 4 hrs.
The effect of different dosages of barium chloride in removal of radium 226 was also determined and results are given in Table 5.
Table 5 Radium Removal with Barium Chloride - Effect of Dose Rate BaC12 Final mg/L Bq/L
~ate (g/L) ~ Ni co As Fe 226Ra (Raffinate) 2400 170 1900 1400 200 0.02 5.5 2200140 2.4 4.1 1.8 0.04 5.6 2200150 2.4 4.7 0.55 0.06 5.6 2200150 3 4.7 0.5 0.10 5.5 2200140 2.4 4.7 0.35 0.20 5.7 2100140 2.1 3.8 0.45 Table 5 shows that a barium chloride dose rate of about -,, . ., .,~ ~

~5~ 8 63147-51 0.02 - 0.04 g/L of raffinate results in a radium 226 content corresponding to less than 0.6 Bq/L. Calculation shows that a nickel hydroxide/gypsum product recovered from a purified raffin-ate with this content of radium 226 would have a radium 226 con-tent corresponding to about 0.05 Bq/g, well below the objective of 0.56 Bq/g.
Example 6 An impurity precipitation test was conducted under conditions to simulate a three stage pH adjustment system, with 2 10 hours at pH 1.5, 1 hour at pH 3 and 1 or 2 hours at pH 5.
Slurried lime was used and the barium chloride addition rate was 0.04 g/L of raffinate. The temperature was maintained at 35~C.
Results are given in Tables 6 and 7.
Table 6 Bulk Precipitation of Raffinate - Effect of Residence Time Residence mg/L
Time Ni Co As Fe (Raffinate) 2400170 1900 1400 2400160 4.6 220 2400150 3.6 110 Table 7 Radium Removal with Barium Chloride BaC12 Final mg/L B~/L
Rate (g/L) ~Ni Co As Fe 226Ra (Raffinate) 2400 170 1900 1400 200 0.04 5.22400 150 2.5 4.9 ~ 0.45 Metal losses 15 % 18 %

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~ g~ 8 63147-51 Example 7 A 4 litre quantity of a purified raffinate solution, i.e., a raffinate solution from which metals other than nickel and cobalt had been removed by the process of the invention, was evaporated to dryness. There was obtained a nickel sulfate product that contained radium 226 in an amount corresponding to 0.01 Bq/g and contained uranium in an amount of 0.00004%, i.e. 0.4 ~g/g. This product should be acceptable to nickel smelters and to hydrometallurgical nickel plants.
~xample 8 A 4 litre quantity of a purified raffinate solution was treated by addition of hydrated lime to a pH of 9.0 to precipitate a nickel hydroxide/gypsum product. This product had a content of radium 226 corresponding to 0.02 Bq/g and a uranium content of 0.00016~, i.e. 1.6 ~g/g. This product should be acceptable to nickel smelters and to hydrometallurgical nickel plants.

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Claims (14)

1. A process for the recovery of nickel from a nickel-containing aqueous acidic raffinate obtained after solvent extraction in the recovery of uranium from uranium ore by acid leaching, which process comprises oxygenating the raffinate and adding to the raffinate an alkaline reagent and a barium or strontium salt, the amount of alkaline reagent added being such that the pH is not raised above 7.0, and separating a solution containing a nickel salt from precipitated solids.

2. A process according to claim 1 wherein the oxygenation of the raffinate is carried out with air.

3. A process according to claim 1 wherein the alkaline reagent is slaked lime.

4. A process according to claim 1, 2 or 3 wherein the raffinate also contains cobalt and a cobalt salt is also separated in solution with the nickel salt.

5. A process according to claim 1, 2 or 3 wherein the pH
after the addition of alkaline reagent is not greater than about

6.

6. A process according to claim 5 wherein the pH after the addition of alkaline reagent is not greater than about 4.5.

7. A process according to claim 1 wherein the oxygenation and addition of alkaline reagent are carried out in a plurality of stages, followed by a stage in which a barium salt is added, and the raffinate is vigorously agitated in all stages to maintain precipitated solids in suspension until a separation stage.

8. A process according to claim 6 wherein the aeration and addition of lime are carried out in three stages, the first at a pH of about 3, the second at a pH of about 4 and the third at a pH
of about 4.5.

9. A process according to claim 1 which is carried out in a continuous manner.

10. A process according to claim 1 which is carried out batchwise.

11. A process according to any one of claims 1 and 4 to 10 wherein the aqueous acidic raffinate is a sulfuric acid raffinate and the nickel salt is nickel sulfate.

12. A process according to claim 11 which includes the further step of adding an alkaline reagent to the obtained nickel sulfate solution to obtain a crude nickel hydroxide product.

13. A process according to claim 12 wherein the added alkaline reagent is lime.

14. A process according to claim 11 which includes the further step of subjecting the obtained solution of nickel sulfate to evaporation to crystallize nickel sulfate.