Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Iron group metal
Reexamination Certificate
2000-03-27
2001-05-15
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Iron group metal
C210S634000
Reexamination Certificate
active
06231823
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to solvent extraction of metals from acidic aqueous solutions containing same. More particularly, the invention is directed to the separation of cobalt values from nickel values in aqueous acid leach solutions.
BACKGROUND OF THE INVENTION
The extraction of cobalt(II) from acidic leach liquors, which also contain nickel(II), is typically conducted by solvent extraction with a water-immiscible organic solution containing an organophosphorous acid, which extracts cobalt(II) in preference to nickel(II). Typical acidic leach liquors contain between 1 and 130 g/L nickel and between 0.3 and 25 g/L cobalt. U.S. Pat. No. 4,353,883, issued Oct. 12, 1982 to Rickelton et al., discloses a process to separate cobalt and nickel values from such aqueous solutions by contacting the aqueous solution with a water-immiscible solvent phase containing an organophosphinic acid extractant of the general formula R
1
R
2
PO(OX), where R
1
and R
2
are substituted or unsubstituted alkyl, cycloalkyl, alkoxyalkyl, alkylcycloalkyl, aryl, alkylaryl, aralkyl or cycloalkylaryl radicals, and X is either H or a salt forming cationic species. In this step, cobalt forms an organic soluble complex with the extractant that reports to the organic phase, displacing a stoichiometric amount of X that report to the aqueous phase, along with the majority of the nickel values. After extraction, cobalt in the loaded organic phase can be recovered by stripping with a suitable mineral acid to produce a high concentration cobalt product solution. During this step, the organophosphinic acid is converted to its acid form and is suitable for recycle to the solvent extraction unit operation. Before recycling, the organophosphinic acid can be contacted with a suitable base to displace the hydrogen with the corresponding salt forming radical. A similar solvent extraction process is taught in U.S. Pat. No. 4,348,367, issued Sep. 7, 1982, to Rickelton et al. These patents leave many possible problems unsolved, and in particular, do not deal with a problem of double salt formation, discussed more fully below, and which is specifically addressed by the process of the present invention.
In particular, in the Rickelton et al. patents, if X is a salt forming radical, the extraction reaction will lead to a build-up of this salt, such as sodium sulphate or ammonium sulphate, in the aqueous phase. Similarly, if X is H, the extraction of cobalt will lead to an increase in the acid content of the aqueous phase. This liberated acid has to be neutralized with an appropriate base, such as ammonium or sodium hydroxide, to retain the extractive strength of the organic phase extractant, and in so doing, will also result in a build-up of ammonium or sodium sulphate. The above patents do not address potential problems, such as double salt formation due to a salt build-up, nor do they provide a solution to these problems.
Canadian Patent 1,075,474, issued to Inco Limited (inventors Barnes and Truscott), discloses a process in which cobalt values are separated from nickel values by solvent extraction using an organic solvent phase containing a nickel salt of an organophosphoric acid extractant of the formula (RO)
2
PO(OH). The nickel salt of the organophosphoric acid may be generated by first converting the organophosphoric acid to its alkali metal or ammonium salt, and then contacting this salt solution in an organic solvent with a mother liquor from a subsequent nickel salt crystallization step, which produces nickel sulphate crystals from the cobalt solvent extraction raffinate. Alternatively, an organic solution of the acid may be contacted with a nickel base such as nickel hydroxide in an aqueous slurry, although this approach is slow and difficult to use. More preferably, the nickel salt of the organophosphoric acid is generated by mixing an organic solution of the organophosphoric acid with an aqueous solution of nickel sulphate and an aqueous alkaline solution such as sodium hydroxide in a single step. Although ammonium hydroxide is listed as an alternative to sodium hydroxide, there is no teaching of how to avoid the production of double salts or metal hydroxides. For instance, in the case of Example 1 of CA 1,075,474, if ammonium hydroxide had been used as a neutralization reagent in place of sodium hydroxide, a raffinate containing 46.7 g/L Ni and 138 g/L (NH
4
)
2
SO
4
, would have been produced, according to our calculations. Such a composition would, in our experience, result in double salt precipitation. The patent only teaches stoichiometric addition of the neutralizing agent, based on the extraction stoichiometry. In this patent, and in the patents issued to Rickelton et al., there is no mention of ammonium sulphate, the neutralization product, which would be produced if ammonium hydroxide were used for neutralization in the cobalt extraction circuit. More particularly, there is no mention of the potential deleterious effect of ammonium sulphate on the solubility of nickel during the extraction of the cobalt. There is only a teaching of minimizing the contamination of the nickel raffinate with sodium or ammonium.
Furthermore, regarding the prior art associated with the conditions at which a nickel loaded organic phase is formed, there is no mention of the role of, nor in fact, any need for, ammonium sulphate in the feed solution to the nickel loading step as now recognized by the inventors of the present invention. In CA 1,075,474, this feed solution to the nickel loading step is stream
17
in both Figures. Nor is there any recognition of a need to maintain a prerequisite ammonia concentration in this feed solution, in combination with the ammonium sulphate, to prevent the precipitation of the nickel as either a double salt or a hydroxide, hereagain as recognized by the inventors of the present invention. Thus, there is no recognition by the prior art that, as recognized by the inventors of the present application, if the process were practiced according to the patent teachings, the ammonium sulphate would have a deleterious effect, as it would promote the precipitation of the nickel as a double salt.
Overall, CA 1,075,474 can be summarized by the following equations, when sodium hydroxide is used for neutralization, with the overbar representing the organic phase and RH representing the organophosphorous acid extractant:
Extraction: 2{overscore (RH)}+CoSO
4
+2NaOH
{overscore (R
2
+L Co)}+Na
2
SO
4
+2H
2
O (1)
Stripping: {overscore (R
2
+L Co)}+H
2
SO
4
2{overscore (RH)}+CoSO
4
(2)
In reality, the base used for neutralization must be carefully selected based on the operability of the solvent extraction circuit and in consideration of the other process units, as it will accumulate in the nickel containing raffinate. If, for instance, electrowinning is selected for final recovery of nickel from the solvent extraction raffinate, it would be undesirable to use ammonium hydroxide for neutralization, as ammonium cannot be tolerated during the electrowinning step, and sodium hydroxide will be the preferred neutralization reagent.
If hydrogen reduction is selected for final nickel recovery, sodium hydroxide will be undesirable, as it will lead to sodium contamination of not only the nickel product, but also the ammonium sulphate salt, which is recovered from the barren reduction end solution by crystallization. Therefore, if hydrogen reduction is used, ammonium hydroxide will be the preferred neutralization reagent. However, this reagent has a disadvantage in that the ammonium sulphate produced during the solvent extraction of cobalt, will reduce the solubility of nickel in the raffinate, depending on the relative metals and ammonium sulphate concentrations, the temperature and the solution pH. If the solubility limit is exceeded, nickel will precipitate from solution as a nickel sulphate-ammonium sulphate double salt (NiSO
4
.(NH
4
)
2
SO
4
.6H
2
O).
If ammonium hydroxide is substituted in reaction (1) for the neutralization, the amount
De Kock Felix Petrus
Genik-Sas-Berezowsky Roman Michael
Raudsepp Rein
Bos Steven
Dynatec Corporation
Greenlee Winner and Sullivan P.C.
LandOfFree
Solvent extraction process for the separation of cobalt from... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solvent extraction process for the separation of cobalt from..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solvent extraction process for the separation of cobalt from... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2550959