EP0324843A1

EP0324843A1 - Process for separating metallic ions from aqueous solutions

Info

Publication number: EP0324843A1
Application number: EP88907053A
Authority: EP
Inventors: Rolf Marr; Heinz Lackner; Hans-Jörg BART; August Nickl
Original assignee: M&T Chemicals Inc
Current assignee: M&T Chemicals Inc
Priority date: 1987-07-13
Filing date: 1988-07-13
Publication date: 1989-07-26
Also published as: AT391464B; ATA176387A; WO1989000444A1; JPH02500452A

Abstract

Selon un procédé d'extraction d'ions métalliques, notamment d'ions de nickel, contenus dans des solutions aqueuses, on soumet les solutions pendant une première étape à une perméation fluide à travers une membrane, puis on soumet les solutions ainsi enrichies pendant une deuxième étape à une extraction usuelle à l'aide d'un solvant. La phase de la membrane utilisée pendant la première étape est utilisée comme phase solvante pendant la deuxième étape. La phase de la membrane contient un composé organophosphorique sulfureux, la phase aqueuse d'extraction a une teneur en acide minéral comprise entre 1 et 5 mol/l, le rapport entre la phase aqueuse de solution utilisée d'une part et la phase de solvant et de membrane d'autre part est toujours supérieur à 1. La perméation fluide et l'extraction par solvant se font dans un appareil du type mélangeur-séparateur, avec des séparateurs verticaux, la hauteur différentielle statique entre le mélangeur et le séparateur étant librement sélectionnable.According to a method of extracting metal ions, in particular nickel ions, contained in aqueous solutions, the solutions are subjected during a first step to a fluid permeation through a membrane, then the solutions thus enriched are subjected for a second step to a usual extraction using a solvent. The membrane phase used during the first step is used as the solvent phase during the second step. The membrane phase contains a sulfur-containing organophosphoric compound, the aqueous extraction phase has a mineral acid content of between 1 and 5 mol / l, the ratio between the aqueous phase of the solution used on the one hand and the solvent phase and of membrane on the other hand is always greater than 1. The fluid permeation and the extraction by solvent are done in an apparatus of the mixer-separator type, with vertical separators, the static differential height between the mixer and the separator being freely selectable.

Description

Process for the separation of metal ions from aqueous solutions

The invention relates to a process for separating metal ions, in particular nickel ions, from aqueous solutions, in which the solutions are subjected to liquid membrane permeation in a first stage and the depleted solutions are subjected to conventional solvent extraction in a second stage, the membrane phase from the first stage is used as the solvent phase of the second stage.

The nickel can be separated from wash water in the electroplating industry using known techniques. Evaporation, electrolysis, precipitation, liquid-liquid extraction, processes using solid ion exchangers and, in particular, membrane separation processes are suitable (Ullmanns Enzyklo¬ pädie der technical chemistry, 4th edition, vol. 17). In the case of very dilute solutions, membrane processes are particularly economical since, as a rule, less equipment and operating resources are to be expected based on the substance to be separated (J. Draxler, R. Marr: Emulsion Liquid Membranes, Part I: Phenomenon and Industrial Application, Chem. Eng. Process., 20 (1986) 319-329).

The removal of nickel from dilute aqueous solutions should be designed in such a way that, with simple process control, a good removal is obtained which is selective and provides a product which can be used. The treated wastewater should be cleaned to such an extent that the various state guidelines can be safely adhered to. For example, the legislature in Austria has set the permissible nickel content in waste water to a maximum of 3 pp (guidelines for limiting waste water emissions, Federal Ministry of Agriculture and Forestry Vienna, September 1981). Extraction methods which work with strong ion exchangers are suitable for such extensive separation. Such an exchanger is bis-2-ethylhexyldithiophosphoric acid in an organic solvent phase, since such an exchanger itself is still used very low pH values, e.g. B. at pH = 1, nickel can still increase so that the required limit values are reached. The choice of a strongly acidic ion exchanger is expedient since it is possible to obtain metal directly without additional steps, such as pH adjustment, for example.

Comparative example 1 describes an extraction process for nickel. The re-extraction takes place with hydrochloric acid. According to this process, it is possible to separate nickel from the waste water to the required extent and to selectively obtain it as a NiCl ₂ solution. However, it is a disadvantage for the electroplating industry that nickel chloride solutions can only be used to a very limited extent there, since the nickel plating baths work in a sulfate environment. Carryover of nickel sulfate into the washing solutions creates an additional need for nickel sulfate, while the electrolysis itself creates an acid requirement. Although small amounts of chloride are metered into the bath, the amounts of nickel chloride solutions obtained during the extraction of the waste water could not be consumed in this way.

A stripping of the nickel from the extract phase with sulfuric acid instead of hydrochloric acid is not technically feasible, since it was found that even after hours of contact, no significant amount of nickel can be obtained from the organic extract phase. A process control with sulfuric acid is therefore not useful. Although it is technically conceivable to carry out an extractive process in which sulfuric acid is used with an ion exchanger other than bis-2-ethylhexyldithiophosphoric acid, a weaker ion exchanger must then be used, so that the requirement mentioned above for high performance can no longer be met at low pH values.

In contrast, it is possible with liquid membrane permeation technology (FMP) to strip the nickel from the bis-2-ethylhexyldithiophosphoric acid with sulfuric acid. The sour one The stripping phase is embedded as a microemulsion in the organic extract phase, which now acts as a selective membrane (R. Marr, H.-J. Bart, A. Bouvier: Selective Metal Enrichment by Liquid Membrane Permeation, Ger.Chem.Eng. 4 (1981 )). This microemulsion has an enormous surface, which means that the extremely slow stripping effect, which is characteristic of the conventional liquid-liquid extractions, no longer occurs.

Comparative example 2 shows the results for a single-stage and comparative example 3 for a two-stage permeation system. As can be seen, in the latter it is readily possible to reduce the nickel content in the waste water to 3 ppm Ni. The advantage of the method is that an aqueous sulfuric acid can be used as the stripping phase, which has a concentration of at least 1 mol / 1 H ^ SO., But preferably 5 mol / 1. Higher sulfuric acid concentrations would favor the stripping operation, but they would damage the ion exchangers and reduce their capacity over longer periods of time. The phase ratio in the process can be set so that the emulsion phase, which consists of the stripping and membrane phases, can always be used in a ratio of less than one compared to the waste water phase.

The membrane phase is thus small in quantity. This has a positive effect on the costs of the procedure.

FMP is best carried out in a two-stage process control in equipment of the mixer-separator type. For this purpose, various types of apparatus are known from conventional liquid-liquid extraction (Handbook of Solvent Extraction, Ed. T.C. Lo et al., John Wiley & Sons, New York 1982).

In the case of liquid membrane permeation (FMP), however, special boundary conditions must be observed. Therefore, the use of conventional horizontal separators is not expedient. Because of the gravitational field of the earth, the emulsion is segregated. The specifically heavier droplets of the stripping phase in the emulsion settle down and form a very compact emulsion there. Above, a low-emulsion, almost pure organic membrane layer remains. Such an inhomogeneous emulsion is in no way suitable for further processing and on the contrary leads to a standstill of a continuous process.

However, this harmful settling effect can be prevented when using standing separators. In a standing separator, the emulsion is fed in from below, so that the emulsion separated from the wastewater phase is always subjected to a vertical impulse which counteracts gravity and thus an inhomogeneity. In contrast, in a horizontal settler only horizontal impulses occur which do not impair the effect of gravity.

Using standing settlers, it is therefore possible to carry out the settling of the emulsion from the wastewater phase in a technically safe and practically simple manner. The FMP is thus a membrane process which, with the simultaneous use of specific ion exchangers, enables very selective metal separation.

As with all membrane processes, water is always transported through the membrane due to osmotic effects, the magnitude of the osmosis being determined by the difference in ionic strength between the waste water phase and the stripping phase.

In order to keep the osmosis as low as possible, a precise control of the residence time of the emulsion and the amount of the emulsion in the mixing chamber is necessary. According to the present invention, this control is facilitated by the difference in height between the mixing chamber and the the setting chamber is freely selectable. Mixing chamber and settling chamber are independent parts and are not connected to one another in the usual compact design (Handbook of Solvent Extraction, Ed. TC Lo et al., John Wiley & Sons, New York 1982). The advantage of this design of the apparatus is that the proportion of the dispersion in the apparatus can be influenced not only as a function of the usual parameters throughput, phase relationships, apparatus volume and number of revolutions and type of stirrer, but also by the height difference between Mixer and separator. The separation of the mixing chamber and settling chamber makes it possible to set any hydrostatic counterpressure, which represents a further degree of freedom for regulating the residence times and the disperse phase portion in the mixing chamber. Fig. 1 shows such an apparatus with a separation of the mixing chamber and settling chamber.

It has been shown that in order to achieve the desired enrichment behavior it is necessary to maintain an exact residence time of the disperse phase in the mixing chamber. 2 shows a graphical representation which shows the increase in nickel in the stripping phase with increasing dwell time. As can be seen, nickel is initially transported through the membrane transport into the stripping phase and concentrated there. Due to the increasing nickel concentration, however, an osmotic gradient arises, which entails water transport, which redilutes the stripping solution again. A clear maximum of the nickel concentration at 7 minutes can therefore be seen in FIG. 2. In order to obtain a stripping phase with the highest possible nickel concentration, the emulsion must not remain in the mixing chamber longer than until the maximum concentration is reached. The required dwell time of e.g. B. 7 minutes can be set in a very exact way by choosing the above freely selectable parameters.

It also follows from the figure that in the case of a two-stage system which leads to a total residence time of 14 minutes, - i - the attainable optimum is left again.

In order to be able to reduce the nickel concentration in the raffinate to the required values with the help of the FMP, however, a two-stage implementation of the FMP would be absolutely necessary.

To avoid the disadvantages described, in the process according to the invention the solutions containing metal ions, in particular nickel ions, are subjected to a liquid membrane permeation in a first stage and the depleted solutions are subjected to a conventional solvent extraction in a second stage, the membrane phase from the first stage being the solvent phase in the second stage. is used, the method according to the invention being particularly characterized in that for the removal of nickel

a) the membrane phase contains a sulfur-containing organophosphorus compound,

b) the aqueous stripping phase contains a mineral acid content between 1 and 5 mol / 1,

c) the ratio of the aqueous feed solution phase to the solvent and membrane phase is always greater than 1 and

d) the liquid membrane permeation and the solvent extraction are carried out in an apparatus of the mixer-settler type, vertical settlers being used and the static height difference between the mixer and settler being freely selectable.

The advantage is that in a first permeation stage a major part of the nickel is optimally separated. In a second stage, in which little residual nickel and a lot of water would be transported through the membrane during permeation, the use of a conventional liquid-liquid extraction leads to an extraction of the residual nickel into the organic phase, so that the nickel concentration in the raffinate can be reduced to the required values. The organic phase preloaded with nickel can easily be used for membrane production for the FMP, without the permeation being significantly affected thereby.

The method according to the invention is explained in more detail below with reference to the figures.

Show it:

1 shows an apparatus with a separate mixing and separating chamber for liquid membrane permeation with a standing separator according to the present invention,

Fig. 2 is a graphical representation of the dependence of

Nickel enrichment in the emulsified stripping phase depending on the contact time between the wastewater to be cleaned and the membrane and stripping phase in liquid membrane permeation,

3a shows the flow diagram of a two-stage liquid membrane permeation process, and

3b shows the flow diagram of the method according to the invention with a liquid membrane permeation in the first stage and a conventional liquid-liquid extraction in the second stage.

The method according to the invention is explained in more detail below with reference to FIG. 3 and the following example 1.

In the case of the combination of permeation / extraction according to the invention, there is no difference in terms of apparatus compared to a two-stage permeation, except that the individual apparatus are switched differently. This is shown in comparison in FIGS. 3a and 3b. According to variant 3a, the nickel-containing wastewater - & - permeated in two stages in countercurrent. The loaded membrane phase is broken down by known methods. The acidic aqueous phase can be fed to baths for galvanic nickel plating, and the organic membrane phase can be eluted with fresh acid and used for renewed permeation.

In the method according to the invention, a freshly prepared emulsion (stripping acid in organic membrane phase) is permeated in a first step. This leads to the transport of nickel ions and water through the liquid membrane. The emulsion is then broken down according to known methods. The aqueous product phase is fed to the nickel bath. With the organic membrane phase, which contains the ion exchanger, the waste water is subjected to a conventional liquid-liquid extraction in a second step. The small amount of residual nickel from the permeation stage is extracted completely. No water is transported during the extraction. The wastewater obtained (raffinate) then has the required low final nickel concentrations. A new emulsion is then produced from the loaded organic membrane phase using fresh acid. As a result, the membrane phase is regenerated and the emulsion used in the permeation stage already has a slight preload. However, this pre-loading does not affect the effectiveness of the permeation stage to a detectable extent.

To carry out the process according to the invention, an organic extract phase is required which can be used both in the extraction and in the permeation. The phase preferably contains 2 to 7% bis-2-ethylhexyl-dithiophosphoric acid dissolved in technically customary aromatic or aliphatic hydrocarbons. An oil-soluble surfactant is also added to stabilize the emulsion.

The advantages of the method according to the invention are:

- The sulfur-containing organophosphorus compound, the bis-2- ethy] exyl-dithiophosphoric acid, extracts nickel even at low pH values down to low raffinate concentrations;

- The process is always carried out in such a way that, in comparison to the nickel-containing feed solution, smaller amounts of the elution or extracting agent phase are used, so that the solvent expenditure can be kept low;

- By using the liquid membrane permeation, a sulfuric acid solution can be used as the stripping phase;

- By using a combination of liquid membrane permeation and conventional liquid-liquid extraction, one obtains (an inexpensive and technically effective process design;

- By the apparatus design of the apparatus with separate mixing and settling chambers or the use of standing settlers, the special requirements of liquid membrane permeation are taken into account, so that optimal operation of the process is possible;

- The process is able to guarantee, on the one hand, the officially required low raffinate concentrations and, on the other hand, to produce selectively enriched, acidic nickel sulfate solutions; and

- The process produces usable solutions of value and significantly reduces wastewater pollution.

The invention is explained in more detail below with reference to comparative examples and examples.

Comparative Example 1

12.25 parts of an aqueous nickel phase which contains 2 g / 1 of nickel and has a pH of 4.5 are treated with 3.5 parts of an organic phase which comprises 15% bis-2- contains lo-ethylhexyl-dithiophosphoric acid, 15% isotridekanol and 70% undecane. After a contact time of 5 minutes, the initially nickel-free organic phase contains 7.0 g / 1 nickel, and 0.003 g / 1 nickel remain in the aqueous raffinate phase. The organic extract phase loaded with nickel is regenerated with 10 mol / 1 HC1. For this purpose, 1 part of aqueous phase with 3.5 parts of organic phase are contacted in two countercurrent stages for 5 minutes each. The organic phase obtained has a nickel concentration of 0.5 g / 1 Ni, the aqueous stripping phase has been enriched to a content of 22.75 g / 1 nickel.

Comparative Example 2

An aqueous nickel phase which contains 2 g / 1 nickel and has a pH of 4.5 is treated with an emulsion phase whose organic membrane phase contains 5% bis-2-ethylhexyldithiophosphoric acid, 3% oil-soluble surfactant Paranox 100 (Esso Chem.) And 92% undecane and their aqueous stripping phase contains 250 g / 1 H_S0 ₄ . The ratio of aqueous nickel phase to membrane phase to stripping phase is 30: 3.5: 1. After a contact time of 5 minutes, the initially nickel-free stripping phase contains 50 g / 1 nickel, and 0.17 g / 1 Ni remains in the aqueous raffinate phase .

Comparative Example 3

An aqueous nickel phase which contains 2 g / 1 nickel and has a pH of 4.5 is treated in a two-stage countercurrent with an emulsion phase, the organic membrane phase of which is 5% bis-2-ethylhexyldithiophosphoric acid, 3% contains oil-soluble surfactant Paranox 100 (Esso Chem.) and 92% undecane, and whose stripping phase contains 250 g / 1 H ₂ S04. The ratio of the aqueous nickel phase to the membrane phase to the stripping phase is set to 30: 3.5: 1. After a contact time of 5 minutes each, the nickel concentration is 0.2 g / 1 in the first countercurrent stage and 0.003 g / 1 in the second. The degree of nickel recovery is therefore 99.85%. - u - The nickel concentration in the stripping phase is 30 g / 1.

example 1

An aqueous nickel phase, which contains 2 g / 1 of nickel and has a pH of 4.5, is treated in countercurrent in two stages, first in a permeation stage and then in an extraction stage. The organic membrane or organic extract phase contains 5% bis-2-ethylhexyldithiophosphoric acid, 3% oil-soluble surfactant Paranox 100 (Esso Chem.) And 92% undecane. The stripping phase of the emulsion contains 250 g / 1 H ₂ S0 ₄ . The ratio of the aqueous nickel phase to the membrane phase to the stripping phase is set to 30: 3.5: 1. After a contact time of 7 minutes in the permeation stage, the nickel content in the aqueous raffinate phase is only 0.08 g / l. This amount of residual nickel is subjected to a subsequent liquid-liquid extraction. The phase ratio of aqueous to organic extract phase is 3.5: 1. After a contact time of 5 minutes, a raffinate concentration of 0.003 g / 1 nickel is found. The organic extract phase is regenerated in the emulsion preparation with 250 g / 1 H ₂ S0 ₄ . After permeation, the aqueous stripping phase then contains a product concentration of 55 g / 1 nickel. The degree of recovery of nickel is therefore 99.85%. The product solution has a concentration of 2750% compared to the input solution.

Claims

- IZ process for the separation of metal ions from aqueous solutions

1. Process for the separation of metal ions, in particular for the separation of nickel ions, from aqueous solutions, in which the solutions are subjected to liquid membrane permeation in a first stage and the depleted solutions are then subjected to a conventional solvent extraction in a second stage, the membrane phase from the first stage being used as the solvent phase of the second stage,

characterized in that

a) the membrane phase contains a sulfur-containing organophosphorus compound,

b) the aqueous stripping phase contains a mineral acid content between 1 and 5 mol / 1, - - c) the ratio of the aqueous feed solution phase to

Solvent and membrane phase is always greater than 1 and

d) the liquid membrane permeation and the solvent extraction are carried out in an apparatus of the mixer / settler type, with standing settlers being used and the static height difference between the mixer and settler being freely selectable.

2. The method according to claim 1, characterized in that bis-2-ethylhexyl dithiophosphoric acid is used as the sulfur-containing organophosphorus compound.

3. The method according to claim 1 or 2, characterized in that the content of the sulfur-containing organophosphorus compound in the solvent phase is in the range of 2 to 7%.

4. The method according to claim 1, characterized in that the ^■ organic solvent phase contains an oil-soluble surfactant.

5. The method according to claim 1, characterized in that the organic solvent phase contains a water-immiscible inert diluent, which consists of aliphatic or aromatic hydrocarbons or mixtures thereof.

6. The method according to claim 1, characterized in that the acid present in the stripping phase is sulfuric acid.