Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
1999-07-08
2004-03-09
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C423S024000
Reexamination Certificate
active
06702872
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the recovery of copper from copper ores.
BACKGROUND OF THE INVENTION
In processes for the recovery of copper from copper-containing ores in which copper is first extracted from the ores using an acid leach solution, followed by contacting the acid leach solution with organic solvent solutions containing oxime extractants, problems have been found with the processing of ores from certain locations such as ores from some areas of Chile. In particular, unacceptable degradation of the oximes has been found to occur, resulting in very high levels of oxime requirements per ton of copper produced from the ore, which of course results in a serious economic disadvantage.
SUMMARY OF THE INVENTION
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”.
It has been discovered that the copper ores that cause degradation of oxime extractants are those in which the ores contain concentrations of nitrate ions, which are taken up by the aqueous acid leach solutions. When organic water-immiscible solvent solutions containing oxime extractants come in contact with the nitrate-containing acid leach solution, especially those containing nitrate levels above 10 g/l, nitration and/or hydrolysis of the oximes has been found to take place, resulting in large losses of oxime extractants. In addition, buildup of the nitrated oximes, which become loaded with copper as a copper complex and which cannot be effectively stripped under commercial operating conditions, causes viscosity of the organic solvent solutions to increase to unacceptable levels, resulting in such problems as loss of copper values, increased entrainment of the organic phase in the aqueous phase, and precipitation of the nitrated oxime copper complex from the organic phase. In some instances, the above problems have resulted in oxime extractant consumption of about eight times the oxime consumption when aqueous acid leach solutions which do not contain nitrate ions are processed in an otherwise identical manner.
In investigating the above problems it was discovered that
a) the presence of oxime extractant modifiers and/or additives significantly increased the rate of oxime degradation;
b) the presence of large quantities of aldoximes in the oxime extractants significantly increased the rate of oxime degradation;
c) when the pH of the acid leach solution was reduced to a pH range of from 2.25 to 3.1 oxime degradation was significantly reduced; and
d) an electromotive force of 550 mV or larger in the copper-pregnant acid leach solution in contact with the oxime-containing organic solvent solution significantly increased oxime degradation.
Accordingly, the present invention relates to the following process variants, used individually or in combination, for reducing oxime extractant degradation from contact with nitrate ion-containing copper pregnant acid leach solutions;
A) use of oxime extractants in water-immiscible organic solvent solutions wherein the solutions do not contain any modifiers or kinetic additives for the oxime extractants;
B) use of oxime extractants containing only ketoximes or a mixture of ketoximes and aldoximes in which the ketoxime:aldoxime molar ratio is less than 1:1.2, preferably less than 1:0.5, and more preferably 1:0.25 or less;
C) reducing the acidity of the acid leach solution to a pH in the range of from 2.25 to 3.1 prior to contact with the oxime-containing organic solvent solution;
D) reducing the electromotive force in the nitrate-containing copper-pregnant acid leach solution to less than 550 mV before contact with the organic solvent oxime extractant solution.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The solvent extraction process for extracting copper from copper ores typically involves the following steps:
1. Aqueous acid leaching of the copper ore using a strong acid to form an aqueous acid leach solution containing copper ions and often relatively small quantities of other metal ions. The aqueous leach acid solution dissolves salts of copper and other metals if present as it trickles through the ore. The metal values are usually leached with aqueous sulfuric acid, producing a leach solution having a pH of 0.99 to 2.0.
2. The copper-pregnant aqueous acid leach solution is mixed in tanks with an oxime extraction reagent which is dissolved in a water-immiscible organic solvent, e.g., a kerosene or other hydrocarbons. The reagent includes the oxime extractant which selectively forms a metal-extractant complex with the copper ions in preference to ions of other metals. The step of forming the complex is called the extraction or loading stage of the solvent extraction process.
3. The outlet of the mixer tanks continuously feeds to a large settling tank, where the organic solvent (organic phase), now containing the copper-extractant complex in solution, is separated from the depleted aqueous acid leach solution (aqueous phase). This part of the process is called phase separation. Usually, the process of extraction is repeated through two or more mixer/settler stages, in order to more completely extract the copper.
4. After extraction, the depleted aqueous acid leach solution (raffinate) is either discharged or recirculated to the ore body for further leaching.
5. The loaded organic phase containing the dissolved copper-extractant complex is fed to another set of mixer tanks, where it is mixed with an aqueous strip solution of concentrated sulfuric acid. The highly acid strip solution breaks apart the copper-extractant complex and permits the purified and concentrated copper to pass to the strip aqueous phase. This process of breaking the copper-extractant complex is called the stripping stage, and the stripping operation is repeated through two or more mixer-settler stages to more completely strip the copper from the organic phase.
6. As in the extraction process described above (step 2 and 3), the mixture is fed to another settler tank for phase separation.
7. From the stripping settler tank, the regenerated stripped organic phase is recycled to the extraction mixers to begin extraction again, and the copper is recovered from the strip aqueous phase, customarily by feeding the strip aqueous phase to an electrowinning tankhouse, where the copper metal values are deposited on plates by a process of electrodeposition.
8. After obtaining the copper values from the aqueous solution, the solution, known as spent electrolyte, is returned to the stripping mixers to begin stripping again.
The oxime extractants used in the above process are oxime extractants of the hydroxy aryl ketone oxime type or a mixture thereof with hydroxy aryl aldoximes. A general formula for such oximes is given on formula I shown below:
in which A can be:
(ii) R′″or
(iii)H
where R and R′ can be individually alike or different and are saturated aliphatic groups of 1-25 carbon atoms, ethylenically unsaturated aliphatic groups of 3-25 carbon atoms or OR″ where R″ is a saturated or ethylenically unsaturated aliphatic group as defined; n is 0 or 1; a and b are each 0, 1, 2, 3, or 4, with the proviso that both are not 0 and the total number of carbon atoms in R
a
and R′
b
is from 3 to 25, R′″ is a saturated aliphatic group of 1-25 carbon atoms or an ethylenically unsaturated aliphatic group of 3 to 25 carbon atoms, with the proviso that the total number of carbon atoms in R
a
and R′″ is from 3-25. Preferred compounds where A is (i) above are those in which a is 1, b is 0, R is a straight or branched chain alkyl group having from 7 to 12 carbon atoms and where R is attached in a position para to the hydroxyl group. Among those, the more preferred compounds are those wherein R′″ is methyl and R and a are as designated. Compounds wherein n has a value of 0 (i.e. hydroxybenzophenone oxime compounds) can be prepared according to methods disclosed in Swanson U.S.
Hein Hans C.
Mattison Phillip L.
Virnig Michael J.
Andrews Melvyn
Cognis Corporation
Drach John E.
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