DE19731616A1 - Metal ion removal from electrolyte - Google Patents

Abstract

In a process and cell unit for material removal from an electrolyte, the electrolyte is passed through two electrolysis/electrodialysis units referred to as primary and secondary cells (1, 2). The primary cell (1) consists of an anode (6), a cathode (7) and preferably three sub-cells, separated by two separators (3, 4) to form a central chamber which separates an anode space or anolyte circulation system from a cathode (7) or catholyte circulation system, the electrolyte (11) being passed through the space containing the cathode (7) or connected to the catholyte circulation system. A second electrolyte circulation connection (12) can be produced between the catholyte system of the primary cell and that of the secondary cell (2), the secondary cell comprising an anode (10), a cathode (9), catholyte and anolyte systems and two sub-cells separated by a separator (8).

Description

The invention relates to a method and a cell unit for removing ingredients from Electrolytes such as z. B. used in surface technology or in gas scrubbers. Ty Typical representatives are nickel-containing systems that are used as galvanic baths. In the baths accumulate nickel ions due to inadequate anode and cathode reactions, that can negatively affect the nickel plating process. Particularly modern high-gloss elek trolytes have to be discarded after a relatively short time and replaced with new ones. Still is metal enrichment in rinsing water is characteristic of these processes. Described for all three In these cases, there is a need for metal removal. Dialytic processes in An Layer stacks are state-of-the-art, but it is only possible to concentrate process solutions ren, but not to carry out the process of the desired metal deposition. E.g. for ver needed process baths this method is absolutely unsuitable. Unfortunately, the exist time no satisfactory solutions that could be realized with moderate costs. Exemplary The nickel is particularly clear. While it is relatively easy to concentrate nickel to separate solutions in simple, undivided electrolysis cells (Hartinger, L .: manual the waste water and recycling technology, Munich 1991), the problem of the process conditions however, it was not sufficiently resolved. In particular, compliance with the necessary constant pH value is problematic. Buffering is ruled out in many cases, the constant adjustment Treatment with sodium hydroxide solution is usually not economically viable or leads to spoilage the process solution. There are other proposals based on electrolytic principles Removal of similar ingredients. So z. B. proposed (Läser, L .: recycling of valuable materials with a new system in electroplating and other process solutions, electroplating 88 (1997) 4, 1134-1137), cations via a separator in the electric field in the cathode compartment to enrich a cell and fill it in by adding hydroxide, which is also a metal back production stands in the way. In various articles (Blatt, W .: electrolytic nickel recoil Winnung, Galvanotechnik, 87 (1996) 4, 1118-1124; Hurschmann, H .: Metal recovery from Process water electroplating 84 (1993) 10, 3429-3432) become cation exchange membrane divided electrolytic cells proposed to prevent undesirable reactions at the anode to press. A similar principle is also applied to chromic acid regeneration (DE PS 40 32 856) agile. In a previous work (Patrick, K and Dexter, D .: Combining Elektrolysis and Dialy sis for Regeneration of Chromic Acid Etching Solution, Journal of Membrane Science 13 (1983) 327-336), the pair-wise interconnection of two sub-cells becomes a simple one Dialysers and a cation exchange membrane-divided cell presented, but z. B. in Case of nickel also does not solve the problems described. The same applies to the  Publication DE OS 41 18 725. In DE OS 195 32 784 the cathode circuit is egg ner two-chamber cell with the circuit of the middle chamber or in a sub-variant with the Catholyte circuit of a second three-chamber electrolysis cell connected. This variant, too does not allow overcoming the problems outlined above, such as metal deposition in metalli form while keeping the pH constant without the use of chemicals.

The object of the invention is to provide a method and a cell unit steep, which allow ingredients from electrolytes under problematic conditions If possible, in pure form with high effectiveness and without separating external chemical additives.

The object of the invention is achieved - starting from the preamble of the first claim - according to the features in the marked part. Fig. 1 shows the features of claim 1, wherein a combination of two sub-cells in a simple basic or multiple structure, which repeats the basic structure used multiple times, and a material flow even interconnectability of the subcells, here as a primary (1) and secondary cell (2 ) is given. The flow of material through the catholyte space shown here and delimited by the separator ( 4 ) with the cathode ( 7 ) and through the catholyte space shown here with the cathode ( 9 ), delimited by the separator ( 8 ), can be carried out simultaneously or at intervals. If an electrolyte to be treated ( 11 ) is guided from a template 14 through the catholyte space of the primary cell ( 1 ), z. B. a metal can be deposited in pure form, the pH shifting due to the side reaction of the cathodic hydrogen formation, which deteriorates the effectiveness of the metal deposition. According to the invention, this can be compensated for by a material stream ( 12 ) from the catholyte space of the secondary cell ( 2 ) into which protons produced at the anode ( 10 ) pass through the separator ( 8 ). A part ( 13 ) of the electrolyte from the middle chamber ( 5 ) of the primary cell ( 1 ) can also be used to correct the pH. In this Mittelkam mer occur through the separator ( 3 ) z. B. protons formed on the cathode ( 6 ) and via the separator ( 4 ) anions and form an acid in the case described. In principle, the middle chamber ( 5 ) could be dispensed with, but since many electrolytes contain halide ions, the three-chamber structure effectively prevents halogen formation at the anode ( 6 ). In this way, surprisingly, an almost self-regulating metal separation process is obtained under optimal conditions. A disturbing sludge formation is avoided. Another important advantage of the invention is that no costly correction or detoxification chemicals have to be added from the outside - on the contrary, even usable acid (in the case described) is obtained, which can be returned to the surface treatment process. For an application for the disposal of electrolytes, in addition to the removal of the cations via metallic deposition, removal of anions from the used process solution is also obtained. However, the invention is mainly worthwhile if ion separation processes depend to a large extent on the pH, as is the case for many systems containing nickel, zinc, iron, cobalt or chromium.

The embodiment of the invention is explained in more detail with the aid of an example ( FIG. 2). In a semi-technical electrolysis unit with a total volume of 0.0105 m ³ , two sub-cells according to FIG. 2 were interconnected under constant current operating conditions (current load 30 A). A processed standing rinsing electrolyte ( 11 ) (initial sulfate concentration: 40 g / l, initial chloride concentration: 10 g / l) was passed over a catholyte chamber of the primary cell ( 1 ) from a storage vessel with a volume of 25 l. This catholyte chamber was separated by an anion exchange membrane ( 4 ) from the middle chamber ( 5 ) into which an electrodialytic anion transport (sulfate and chloride ions) was carried out selectively. From the anode chamber of the primary cell ( 1 ), separated from the middle chamber ( 5 ) with a Nafion cation exchange membrane ( 3 ), protons entered the middle chamber ( 5 ). A second Ka tholytstromstrom ( 12 ) connected the catholyte chambers of the primary and secondary cells. The secondary cell ( 2 ) as well as the non-catholyte chambers of the primary cell ( 1 ) were initially filled with 3% sulfuric acid. At the beginning of the experiment, 1% sulfuric acid was in the middle chamber of the primary cell ( 1 ). The separator ( 8 ) in the secondary cell ( 2 ) was a cation exchange membrane (Nafion). Under the conditions of the test (test time 20.5 hours), the pH in the catholyte chambers changed from initially 5 to 5.5 at the end of the test. Pure, metallic nickel of excellent quality was deposited on the nickel plate cathodes. The nickel content of the template ( 14 ) decreased from 12 g nickel / l to 0.02 g nickel / l. A mixture of sulfuric acid (60 g / l) and hydrochloric acid (12 g / l) formed in the middle chamber ( 5 ).

Claims (10)

1. The method and cell unit for removing ingredients from electrolytes, characterized in that the electrolyte is guided by an arrangement of two electrolysis / electrodialysis units - referred to as primary ( 1 ) and secondary cell ( 2 ), the primary cell ( 1 ) preferably three types of sub-cells, separated by two separators ( 3 and 4 ), as well as an anode ( 6 ) and a cathode ( 7 ), and the electrolyte ( 11 ) is guided through the space which receives the cathode ( 7 ) or which is connected to a catholyte circulation system, and the anode space or the anolyte circulation system are separated by a central chamber from the cathode space or catholyte circuit, and that a second electrolyte circuit connection ( 12 ) between the catholyte system of the primary cell ( 1 ) and the catholyte system of the secondary cell ( 2 ), the at least of two sub-cell types, separated by a separator ( 8 ), as well as anode ( 10 ), cathode ( 9 ) and catholyte and anolyte system can be produced. 2. The method according to claim 1, characterized in that preferably the separator ( 3 ) facing the anode ( 6 ) of the so-called central chamber ( 5 ) of the primary cell ( 1 ) has a cation exchange membrane and the separator ( 4 ) facing the cathode ( 7 ) the so-called middle chamber ( 5 ) of the primary cell ( 1 ) is an anion exchange membrane, and the separator ( 8 ) of the secondary cell ( 2 ) is a cation exchange membrane. 3. The method according to claim 1, characterized in that primary and secondary cell, similar the structure of electrodialysis stacks have a multiple structure or auxiliary chambers, e.g. B. to protect the anodes. 4. The method according to claim 1, characterized in that the primary cell ( 1 ) is operated clocked without switching on the secondary cell ( 2 ) or with clocked switching on of the secondary cell via the catholyte guide. 5. The method according to claim 1, characterized in that in the central chamber ( 5 ) of the primary cell ( 1 ) resulting electrolyte for pH correction of the catholyte system of the primary ( 1 ) or secondary cell ( 2 ) is used. 6. The method according to claim 1, characterized in that an Im for quality improvement pulse operation of the cell voltages and / or the current is used.   7. The method according to claim 1, characterized in that the electrodes used a so can have said three-dimensional structure as expanded metal, fill, chips or the like. 8. The method according to claim 1, characterized in that the electrodes used from Metal, graphite, carbon; conductive or metallized plastic or conductive composite materials exist. 9. The method according to claim 1, characterized in that for accelerating the Stoffiran sportive means and measures such as internals or floats, increased convection, scramble tion, gas injection, structured electrodes, movement of the cell and / or parts of the cell or special physical methods such as ultrasound can be used. 10. The method according to claim 1, characterized in that the primary and secondary cell under construction Licher unit are made.