Compositions – Absorptive – or bindive – and chemically yieldive
Reexamination Certificate
2000-07-24
2001-08-21
Kim, John (Department: 1723)
Compositions
Absorptive, or bindive, and chemically yieldive
C210S634000, C210S688000, C252S364000, C423S024000, C423SDIG001, C564S265000
Reexamination Certificate
active
06277300
ABSTRACT:
This invention relates to an improvement in compositions and processes for extracting metals from aqueous solutions, especially solutions obtained by leaching ores with acids, using o-hydroxyaryloximes as extracting agents.
It is known to extract metals, especially copper, from aqueous solutions containing the metal in form of, for example, a sulphate salt by contacting the aqueous solution with a solution of an o-hydroxyaryloxime in a water immiscible organic solvent and then separating the solvent phase loaded with metal, i.e. containing a part of the metal in the form of a chelate compound with the o-hydroxyaryloxime. The metal can then be recovered from the metal loaded solvent phase by stripping with acid solutions followed, for example, by electrowinning.
The reaction leading to the metal chelate compound also forms acid and causes a lowering of the pH. This reaction is reversible and proceeds to an equilibrium point which will favour formation of the chelate compound as the pH is increased. The metal salt-containing aqueous solutions from which metal e.g. copper is to be extracted will frequently be leach liquors obtained by extracting metal ores with acid and will in some cases have a low pH. Since the amount of chelate compound formed at equilibrium is lower as the pH is decreased only those o-hydroxyaryloximes which have a strong chelating power will be able to achieve a high degree of extraction from those aqueous leach liquors having very low pH or high copper content.
The advantage of high copper extraction shown by these strongly chelating oximes is to some extent offset by the large amount of copper which remains as chelate if the solvent after stripping with acid of convenient strength. While this residual copper as chelate is not lost since it can be recycled to the extraction stage, a reduction in the amount of residual copper chelate would, in the absence of any comparable-reduction in the degree of copper extraction from the aqueous solution, afford an improvement in the overall efficiency of the process.
In our UK Patent No 1549615 we show that the amount of copper removed in these cases from the solvent phase in the stripping stage is significantly increased if the solvent phase contains a defined phenol. Such compounds are sometimes called ‘strip modifiers’.
In the above specification we also disclose that certain aliphatic alcohols, such as tridecanol have similar beneficial effects.
Modifiers will not only influence the strength of the extractant, but can also affect the hydrolytic stability, the selectivity of copper extraction over iron extraction, the level of entrainment, the kinetics of the extraction and stripping stages and the generation of crud. A suitable modifier will therefore often be the result of a compromise.
‘Crud’ is a term applied to undesirable extraneous matter formed at the organic-aqueous interface or in the organic phase in the settler compartment of mixer settlers used in the solvent extraction process. It is usually an oil-water emulsion stabilised by the presence of finely divided solid material that may be either alumino silicates present in the feed, or colloidal silica precipitated during the solvent extraction operation. It can accumulate in sufficient quantities to seriously reduce the working volume of a settler leading to flooding. Where large quantities are produced it has to be removed and the emulsion broken by centrifuging. Crud can also be a source of loss of reagent by aborption on the silicacious solids component which is discarded.
In solvent extraction operations employing banks of mixer settlers operated in a continuous fashion, it is inevitable that after the primary separation of the organic and aqueous phases in the settlers, there remains some entrainment of one phase in the other. This is in the form of minute droplets that are very slow to coalesce or settle and are thus carried through with the primary phase. Tn the case of droplets of organic material entrained in the aqueous phase this represent a major loss of extractant reagent from the plant, both in organic material entrained in the discarded raffinate from the extraction circuit and in organic material transferred to the electrolyte in the stripping stage. In the latter case the entrained organic material may cause further complications by interfering with the clean deposition of copper and may cause burning of the electrodes. In the case of entrainment of droplets of aqueous in organic phase, this represents a means of physical transfer of unwanted metals such as iron present in the aqueous feed solution, that may outweigh the advantages of the high selectivity of an extractant reagent for copper over other metals. It is therefore seen to be of considerable advantage to maintain entrainment at as low a level as possible. Various physical means have been tried but it is also clearly a function of the reagent composition employed and there are distinct advantages in reagents which minimise formation of entrainment of one phase in another.
U.S. Pat. No. 4,507,268 and 4,544,532 describes the use of mixture of aldoxime and ketoxime with no or only low level of modifiers. Such mixtures will be advantageous in respect of crud formation. These formulations commercially known under the trade names Lix 864 (2 hydroxy 5 dodecyl benzaldoxime with 2 hydroxy 5 nonyl benzophenone oxime) and Lix 984 (2 hydroxy 5 dodecyl benzaldoxime with 2 hydroxy 5 nonyl acetophenone oxime) will however provide extraction with low Cu over Fe selectivity.
There is thus still a need for more efficient modifiers with good selectivity which furthermore will not favour formation of crud and avoid entrainment.
We have now found that the use of highly branched chain aliphatic or aliphatic-aromatic C-10 C-30 esters or C-14-C30 alcohols give unexpected benefits as strip modifiers. Good and unexpected selectivity for copper over iron can be achieved and the above disadvantage concerning crud formation and entrainment level can be overcome by using such compounds, particularly very highly branched derivatives.
It has also been found quite unexpectedly that the formulations in accordance with the present invention provide better hydrolytic stability than formulations based on certain mixture of aldoxime and ketoxime without modifier as claimed in U.S. Pat. No. 4,507,268.
Accordingly, our invention provides a composition for use in extracting metals from aqueous solutions of metal salts which comprises:
A. one or more o-hydroxyaryloximes containing at least 5 aliphatic or alicyclic carbon atoms which are strong metal extractants as hereinafter defined.
B. one or more branched chain aliphatic or aromatic—aliphatic alcohols containing 14 to 30 carbon atoms or esters containing 10 to 30 carbon atoms, the ratio of methyl carbon atoms to non-methyl carbon atoms being higher than 1:5, the weight ratio of A to B being in the range 10:1 to 1:3.
Preferably the methyl carbon atoms to non methyl carbon atoms ratio is higher than 1:3 and the weight ratio of A to B is 5:1 to 1:1. The esters contain preferably 14 to 25 carbon atoms and the alcohols 15 to 25 carbon atoms.
The composition may. be dissolved in an organic solvent, which for the normal metal extraction process should be water immiscible.
A further aspect of the present invention is a process for extracting metal from aqueous solution by the steps of:
a. contacting the aqueous solution containing metal with a solution in an immiscible solvent of a composition according to the present invention;
b. separating the aqueous and solvent phases, the latter containing metal complex;
c. contacting the solvent phase with an aqueous mineral acid; and
d. separating the solvent phase from the aqueous phase containing metal in the form of a salt of the mineral acid.
Preferably the metal is copper or nickel, more preferably copper itself.
o-hydroxyaryloximes generally of value for extracting metal values from aqueous solutions of metal salts are well known and include for example alkyl or alkoxysalicylaldoximes as described in Belgian Patent Nos. 796,835
Dalton Raymond Frederick
Leng John Lindley
Kim John
Pillsbury & Winthrop LLP
Zeneca Limited
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