DE2325760C3 - Process for separating metals by liquid-liquid extraction - Google Patents

Description

The invention relates to a method for separating metals by liquid-liquid extraction, in which an aqueous solution containing the metals is mixed with an organic solution, which at least contains an extractant which releases hydrogen ions, the pH value of the water phase by adding of a neutralizing substance is regulated after the extraction equilibrium has been reached Phases are separated from one another, and optionally co-extracted from the organic phase obtained in this way Metals can be removed by washing as well as the extractant back to its original Form which releases hydrogen ions is converted.

A large part of the extraction agents used for liquid-liquid extraction have an acidic character, d. H. these substances are able to give off hydrogen ions, which are replaced according to the following formula can. In the formula, HA stands for any extraction agent belonging to the aforementioned group:

eJJ +

In this way, the extractant binds metals, which in the process move from the water phase to the extractant-containing one Pass over the organic phase, an equivalent amount of hydrogen ions passes at the same time into the water phase, which leads to a drop in the pH value of the water phase.

It is well known that when working with acidic extractants of the aforementioned type of The transition of the metal according to the above formula from the water phase to the organic phase is therefore strong depends on the pH of the aqueous solution, as each metal has only a very narrow pH range in which one effective extraction is possible because, as stated above, the pH during extraction decreases and the pH of the starting solution does not increase because of the precipitation of metal hydroxides can be, the effectiveness of the extraction decreases with increasing acidity, finally a state of equilibrium is achieved; depending on the metal concentration of the starting solution in the water

Lüserphase possibly still considerable amounts of a to be separated Metal.

A method of the aforementioned known type is described in US-PS 34 79 378, in which an aqueous solution containing the metals is mixed with an organic phase. This contains a organic extractant which acts selectively for the metals in question and a part of the aqueous extracted in the organic phase. After the subsequent separation of the two phases, one contains one the organic phase containing the metals and an aqueous phase free thereof. Part of this aqueous phase is the The mixture is fed back into the circuit. In order to maintain a certain pH value, the aqueous phase added to this controlling agent

From US-PS 36 25 655 an analyzer is known that automatically determines the acidity and basicity of a chemical process stream The content of a sample of acid or base is measured by potentiome-

jo tric titration determined

The apparatus has, inter alia. a titration cell in which the liquids during the Titration can be mixed. The end point of the titration is determined by means of two electrodes that are inserted into the mixture immerse, measured potentiometrically. Via the electrical potential formed between the electrodes the amount of titration liquid required to set a certain pH value is controlled is.

Surprisingly, it has now been found that the shortcomings of the known method mentioned at the beginning Working according to the method according to the invention, the main features of which emerge from claim 1, can be eliminated. The pH regulation at issue is based on the observation that the pH values of the water phase of the dispersion in the mixed state are measured can. These pH values are repeated with the same dispersion acidity and are comparable with one another and do not differ significantly from the acidity of the water phase. Based on the so The continuous measurement data obtained, the dosage of the neutralizing agent can be regulated so that the required pH value is achieved in each case. the

Vi pH measurement can be carried out regardless of whether the water phase is present in the extraction stage in dispersed or undispersed form. The neutralizing agent can be metered in by generally known methods in which

bo the control based on the measurement results obtained he follows

The procedure according to the invention offers the advantage that even when working with highly concentrated Metal salt solutions the entire capacity of the extracting agent is used to the full. Surplus treatment stages superfluous, and there is no time difference (delay) between reaction and control. Both the water phase and the organic phase

can be fed back into the mixing vessel, but with regard to neither of these two phases there is an absolute need for recirculation. The desired pH value can easily be achieved and can be precisely and reliably constant despite any changes that may occur in the course of the process because the control can be easily automated. The pH control is independent of the others Process changeable so that they can be varied without changing the pH values occurs Another great advantage is that with a multi-stage extraction system the pH control value of each individual stage can be selected independently of the other stages, so that even the most difficult separations by choosing the most favorable pH gradient between the individual Stages become a relatively simple matter.

In general, it is advisable to equip the mixing tank of each stage with its own pH control unit to equip, so that the aforementioned independence of the pH regulations from each other is guaranteed. In many cases, however, it is not necessary to regulate the pH in all stages, but rather in some Extraction stages the pH value through the regulation in the neighboring stages with sufficiently high accuracy in desired range can be kept.

In most cases, the pH values during the extraction can be chosen so that a particular Washing stage for the organic phase unnecessary; in certain cases, however, the inclusion is a such a level quite justified.

The regeneration of the extractant, i.e. the back extraction of the metals into a water phase, can take place according to known methods. Possible for this include: Treatment with mineral acid solution, whereby the metal is obtained as an aqueous solution, as well as direct reduction from the organic phase with With the help of gaseous hydrogen, the metal is then obtained in powder form

The washing and back-extraction stages can also be carried out with the pH control according to the invention equipped, if a particularly selective separation of metals takes place in these stages target. In most cases, however, the treatment in these stages is carried out in a way that pH control cannot makes necessary

The method according to the invention can be used in connection with any acidic character having extractants are used. Such means are e.g. B. the organic phosphoric acids the general formula

R ₁
O

R ₂ -O- P == O
OH

where Ri is an alkyl, aryl or alkylaryl radical or Hydrogen and R2 an alkyl, aryl or alkylaryl radical embody, as well as the corresponding thio compounds. These acidic extractants also include the carboxylic acids, such as. B. the naphthenic acids

and the acid of the formula (C ₇ HiS) ₂ CH ₃ CCOOH, the substituted carboxylic acids, such as. B. «-Bromolaurylic acid, the sulfonic acids and hydroxyoximes, such as Se-diethyl-γ-hydroxy-e-dodecyloxime, 2-hydroxy-5-dodecylbfinzophenoxime and 2-hydroxy-5-nonylbenzophenoxime. Furthermore, when working according to this method, extraction solutions can be used which, in addition to one acidic extractant, also contain a second or more other acidic extractant. The extraction solution can also contain neutral extractants and other additives, e.g. B. alcohol.

In order to achieve more favorable physical properties, the extractants are usually in shape of solutions used where the diluent is hydrocarbons or hydrocarbon mixtures, especially kerosene, serve; however, other solvents or diluents can also be used come. In certain cases, undiluted extraction media] can also be used.

Due to its nature, the method according to the invention is not bound to certain metals, but rather on the separation and recovery processes that work according to the liquid-liquid extraction principle all metals applicable.

The neutralizing agent to be added is generally an alkali, but you can do this if special reasons require that acids are also used. The neutralizing agent is in the generally in an easily metered form, in liquid or gaseous state, e.g. B. ammonia, Sodium or potassium hydroxide, sodium carbonate or the like. In aqueous solution or ammonia in gaseous form or mixed with other gases such as air, nitrogen, etc. If it is to be put to the pH control Allow accuracy requirements, but solid neutralizing agents can also be used, e.g. B. Lime, magnesium oxide, etc. A possible acid addition always takes place in the form of a solution (dilution).

In the process of US Pat. No. 3,479,378, neither the pH of the dispersion, i.e. H. the mix in the Mixing zone, is determined, nor is the neutralizing agent depending on this continuously measured value this dispersion added in the mixing zone so that these measures that the essence make up the invention should not be suggested by this document. Rather, the person skilled in the art is of Refrain from this procedure because US-PS 34 79 378 gives the clear indication that it is much cheaper is to add the agent for adjusting the pH of the recirculated aqueous solution, instead of feeding it directly into the mixing zone. This reference has the advantage that the Let the acidity of the aqueous phase and the balance of the extraction reaction be better controlled. So can the person skilled in the art of this publication may at best have a prejudice against the teaching according to the invention remove.

Also in the analyzer according to US Pat. No. 3,625,655, the pH value is determined after a Separation of the phases in a secondary line branched off from the main circuit of the process and after the removal of the sample to be determined from this vertical column and its transfer into the Titration device. This publication is therefore also unsuitable for providing an indication of this to the person skilled in the art give that it advantageously has the pH value of an organic phase and an aqueous phase

Determine the dispersion and based on the determined pH value directly the neutralizing agent of this Should add dispersion. Rather, this prior art leads the person skilled in the art away from the one according to the invention Teach away, since he must assume that the most accurate and best results will then be achieved if a separation of the dispersion into the organic and the aqueous phase is first achieved and then the aqueous phase is examined for pH.

In contrast, the invention enables a much faster and more accurate monitoring of the pH value and thus a much more optimal management of the extraction, while during the separation the phases according to the method according to the two aforementioned documents have a time delay results, which can give rise to considerable disturbances, especially if it is taken into account that the pH value in the Range from 2 to 7 can be subject to very rapid fluctuations, which are correspondingly disadvantageous Have an effect on the extraction result. According to the invention, the measurements of pH and the addition of the neutralizing agent can be carried out at essentially the same point, whereby one Compared to the method of US-PS 34 79 378 work in the mixing zone with a higher pH can, because the pH value of the mixture present there (with the equilibrium pH value after the Extraction reaction) higher than the pH value of the extraction solution fed in (or that in the circuit recycled aqueous phase) may lie.

example

Batch tests were carried out in the laboratory to separate the metals zinc and cadmium from the Metals cobalt and nickel carried out the sulfates of the aforementioned metals containing aqueous solution and di (2-ethylhexyl) phosphoric acid solution (HDEHP) were placed in a glass vessel in a volume ratio of 1: 1 mixed together. pH electrodes were immersed in the dispersion; after that it was 6 percent Ammonia water added until the desired

Table 1

pH value was reached. After mixing for an additional 10 minutes, the phases were separated from one another and analyzed; the pH of the obtained water phase was measured. The starting solution for the experiment No. 1 contained 14 g Zn / 1, 5 g Cd / 1, and 5 g Ni / L Der Experiment 2 was carried out using the same procedure with a solution containing 5 g of Cd / 1.5 g of Co / 1 and 5 g Ni / 1 contained

Dispersion
pH

Water phase _{Εγ η} pH%

Eco

Experiment No. 1 2.45 2.5 95.6 6.0 1.7 0.7 0.75 M. 3.0 3.0 99.5 20.2 3.5 1.0 HDEHP 3.5 3.5 99.9 46.0 8.3 1.5 4.0 4.0 99.97 78.0 35.2 2.1 Experiment No. 2 2.4 2.4 - 49.0 2.3 1.1 0.5 M. 2.7 2.7 - 66.7 3.6 1.4 HDEHP 3.0 3.05 - 79.6 12.6 2.9 3.6 3.6 - 94.2 30.9 8.4 4.0 4.05 - 96.4 50.9 21.6

E = extraction percentage.

The result shows that the zinc is to a very large extent from the can separate other metals; if even higher demands are made in this regard, so can can of course be worked with several levels. Also the separation of cadmium from cobalt and nickel can be done effortlessly when working with a few levels.

example

Zinc was separated from a cobalt-nickel solution in a six-stage continuous extraction device. In addition to the aforementioned metals, the starting solution also contained magnesium and ammonium sulfates; Due to the previous treatment stages, their pH was approx. 5. The zinc was extracted in four stages, all of which were equipped with their own pH control. Because of the high pH of the starting solution, the pH was brought to 1.5 in the first stage with the aid of sulfuric acid. In the subsequent bo extraction stages, the pH was regulated with the aid of 25 percent ammonia water. The zinc was back-extracted from the organic phase in two stages with the aid of sulfuric acid solution (dilute sulfuric acid) which contained 150 g of H ₂ S (VI.
bs The starting solution was fed into the system at a rate of 75 l / h; the phase ratio during the extraction was O / A == 1. During the back extraction the phase ratio was

Ο / Α = 3.6. The temperature during the extraction was 6O ⁰ C. With this method were in the individual stages the daily mean values compiled in Table 2 achieved.

Table 2

Water phase Co Ni Zn Organic phase Zn pH g / l g / l g / l Co g / l g / l

extraction 4.4 4th stage 3.9 3rd stage 2.8 2nd stage 1.5 1st stage 4.9 Injected good Back extraction 2nd stage 1st stage

11.7 6.0 0.0004 19.9 0.0015 19.0 0.12 13.9 5.4 12.3 6.3 7.5 0.046 0.013 0.82 0.003 0.82

8.0 7.0 1.8 0.012

0.009 0.005

0.025 0.13 5.4 7.5

1.9 0.015

With four extraction stages, the zinc content of the cobalt solution was reduced from 7.5 g / l to 0.4 mg / l will; only 0.1% of the cobalt contained went off together with the zinc solution.

Example 3

The following is a method of separating the metals zinc and copper from the metals cobalt and Nickel described. The separation is much easier thanks to the pH-regulated extraction than previously. A sulfate solution with the following metal content was specially prepared for this extraction experiment: Co 25 g / l, Ni 10 g / l, Zn 10 g / l and Cu 10 g / l. as A 0.75 M-HDEHP lamp oil solution, which also contains 20 percent by volume of 2-Hy- droxy-5-nonylbenzophenoxime contained. For comparison purposes, a parallel experiment was also carried out with a mere 0.75 M HDEHP solution

The tests were carried out with a volume ratio of O / A = 1.2 under control of the desired pH value carried out in each individual batch test; the pH control was based on continuous pH measurement in the dispersion. A mixture of ammonia and air was used as the neutralizing agent Test results are compiled in Table 3.

Table 3

pH

Experiment No. 1 3.04 99.3 44.8 4.0 2.0 0.75 M HDEHP 3.50 99.9 71.7 7.5 4.0 4.09 99.9 85.8 16.0 3.0 Experiment No. 2 1.27 37.4 33.0 0.3 2.0 0.75 M HDEHP + 20% by volume 2.08 89.6 68.2 1.0 2.0 Oxime 2.86 99.2 93.3 4.1 3.0 3.71 99.9 98.8 17.1 3.0

The results obtained show that when working with HDEHP solution, the pH range that is suitable for separating copper from nickel and cobalt, is quite narrow, but can be expanded by adding the oxime to the solution In this case, three to four stages are required to separate the aforementioned metals.

When it comes to separating the metals zinc and copper from one another, it is just a HDEHP solution more effective than the aforementioned mixture.

Example 4

Comparative extraction tests were carried out with two different extraction solutions: 0.9 M naphthenic acid 230 SP in lamp oil and 03 M Nickel naphthenate in lamp oil The latter solution had such a composition that it was in equilibrium with an aqueous solution which contained 03 M nickel and had a pH of 7 would have.

The starting solution for these extraction experiments was sulfate solution, which contained 25 g Ni / l, 10 g Cu / l and 10 g Zn / 1 and its pH value was 1.

When extracting with nickel naphthenate, the pH could be influenced by varying the phase volume ratio V _or g / V _aq . The relationship between the pH value and the

10

th phase ratio is shown in Table 4, in which the extraction result obtained is also recorded. to For comparison purposes, parallel tests were carried out with naphthenic acid using the same phase ratio as carried out when working with naphthenate and the pH value by direct control on the same value raised.

Table 4

pH

Nickel naphthenate

Naphthenic acid

Ez _n

0.53 3.6 23.0 0.9 27.0 2.2 0.83 4.6 97.7 6.3 96.9 9.0 1.0 5.2 99.68 21.6 99.67 19.5 2.8 5.8 99.93 92.2 99.95 93.5

As can be seen from the table, there are no significant extraction results between the obtained extraction results Differences.

However, working with the salt form presents several difficulties: Converting the acid into salt form often leads to the formation of a third phase; the ratio between the salt and acid parts of the extractant can possibly shift slightly with the consequence that the pH value during the extraction process varies although the ratio of the phase currents can be kept under control; the extraction result is, if the ratio of the phase currents changes, generally subject to very strong changes, because in addition to the pH value, the relationship between the extractant and the to extracting metals changes and this latter change in the same direction as the pH change works.

By working with immediate pH control, all of these deficiencies can be avoided, and the Control values can be selected according to the current situation. That too The phase ratio can be changed without affecting the pH values during the extraction will.

Claims (2)

Patent claims: 1. Process for separating metals by liquid-liquid extract clay, in which one the metals containing aqueous solution is mixed with an organic solution, which at least one Contains extractant which releases hydrogen ions, the pH value of the water phase through The addition of a neutralizing agent is regulated after the extraction equilibrium has been reached Phases are separated from one another, and optionally co-extracted from the organic phase obtained Metals are removed by washing, as well as the extraction agent back to its original, Form which releases hydrogen ions is converted, characterized in that the pH value is directly in the dispersion is measured, and based on this measurement result in the dispersion as much neutralizing agent is given that the water phase receives the desired pH 2. The method according to claim 1, characterized in that the extraction in a multi-stage Device according to the countercurrent principle using pH control in an or several stages in the form that happens with the help of independent pH controls the optimal pH gradient is generated between the individual extraction stages.