JPH047250B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to the production of anionic acids and halogens, monovalent cationic hydroxides,
and the electrodialytic conversion of polyvalent cations to substantially water-soluble salts. Specifically, the present invention:
It relates to the electrotransfer of polyvalent cations through a cation-permeable membrane into an aqueous liquid containing an immobilizing agent that renders the polyvalent cations insoluble and ionically immobilized. In the present invention, an acid (the acid has a pH of 3 or less in a 1N solution and forms a water-soluble salt with the polyvalent cation) is used in an aqueous solution containing an insolubilizing agent for polyvalent cations. ). Soluble salts of acids prevent fouling of cation-permeable membranes by water-insoluble salts of polyvalent cations. Insolubilization of polyvalent cations prevents electrodeposition of metals in the electrochemical cell membrane and on the cathode, which requires frequent cell maintenance. As a result, from the salts of polyvalent cations to the acids and halogens of the anions and substantially water-insoluble salts of polyvalent cations or other ionically immobilized compounds with polyvalent cations, there is preferably a continuous , an effective, high capacity electrodialysis method for conversion is provided.

One embodiment of the method of the invention includes the use of chromic and other acids for use in aluminum anodizing, cadmium chromating, zinc and copper plating, metal and printed circuit etching, and metal and plastic plating. It is particularly applicable to the conversion of polyvalent cation salts.

Another aspect of the method of the invention relates to an electrodialysis process comprising an electrodialysis cell having at least three chambers separated by a cation-permeable membrane. This embodiment is particularly useful for electrolyzing sodium chloride brines containing salts of calcium and other polyvalent cations to produce chlorine and high purity caustic soda while maintaining high cell capacity.

Another aspect of the polyvalent cation salt conversion of the present invention relates to an in-cell electrodialysis method for retrieving cation-permeable membranes contaminated with salts of polyvalent cations. This in-cell remediation method of cation-permeable membranes is particularly useful for remediation of contaminated cation-permeable membranes in chlor-alkali cells where the catholyte system is unsuitable for acids.

[Problems to be solved by conventional technology and invention]

Electrodialysis is a well-known technique (U.S. Patent No.
No. 4325792, No. 3481851, No. 3909381, No.
No. 4006067, No. 3983016, No. 3788959, No.
No. 3926759, No. 4049519, No. 4057483, No.
No. 4111772, No. 4025405, No. 4358545, No.
No. 3793163, No. 4253929, No. 4325798 and No.
No. 4439293 (please refer to each specification). Electrodialysis is the movement of ions across an ion-permeable membrane as a result of an electrical driving force. The method is typically carried out in an electrochemical cell, the cell having a catholyte compartment containing a cathode and a catholyte, and an anolyte compartment containing an anode and anolyte; and the anolyte chamber are separated by an ion-permeable membrane.

Acids are used extensively in the chemical, electronics, mining, electroplating and metal finishing industries where they react with metals and other salts to form polyvalent cations and anions of each acid. form salts. The process of the conventional technology is
It does not provide a satisfactory method for regenerating and purifying acidic solutions containing polyvalent cations and recovering polyvalent metal cations. Considerably better results are obtained by using aqueous solutions of inorganic carbonates or bicarbonates, as described in my US Pat. Nos. 4,325,792 and 4,439,293. When an acidic catholyte is used in electrodialysis of an aqueous solution of a salt of a polyvalent cation, cations migrate from the acidic solution through a cation-permeable membrane into the acidic solution. Multivalent cations tend to electrodeposit as metals in the membrane and on the cathode, resulting in frequent cell maintenance. The object of the present invention is to prepare salts of polyvalent cations,
A high capacity electrodialysis process that can be used to continuously convert the anions of the salts to acids and halogens and the polyvalent cations to hydroxides and other substantially water-insoluble salts. It is about providing.

[Means for solving problems]

The present invention provides a method for dissolving polyvalent cations in an aqueous solution containing ions or agents that render polyvalent cations insoluble or ionically immobile. used for the continuous conversion of salts of polyvalent cations into water-insoluble salts of polyvalent cations with anionic acids and halogens by using soluble salts of polyvalent cations (which form soluble salts). To provide a high-capacity electrodialysis method that can Said transformation consists of said soluble salt of a polyvalent cation, preferably acidic,
From a first aqueous liquid, as a feed liquid or anolyte, through a cation-permeable membrane into a second aqueous liquid consisting of soluble salts and ions such as hydroxyl ions and other agents that render the multivalent cations insoluble. It consists of electrotransfer of cations. Said first
The anion of the polyvalent cation salt in solution converts to the respective acid or halogen. The use of soluble salts of acids in the catholyte that accepts electrically transferred polyvalent metal cations prevents fouling of the membrane with water-insoluble salts of polyvalent cations. Insolubilization of polyvalent metal cations essentially eliminates electrodeposition of metal onto the cathode and onto or into the membrane of the electrolytic cell. The result is a high capacity electrodialysis process that can be used for continuous conversion of salts of polyvalent cations. The acid produced can be used repeatedly for metal etching, metal plating, anodizing, and other applications. The substantially water-insoluble salt of the polyvalent cation can be recovered as a solid from the second aqueous liquid and can be reused or disposed of.

Another aspect of the electrodialytic conversion of salts of polyvalent cations is that an acid (the acid is soluble salts of polyvalent cations (having a pH below 3 in a normal solution and forming water-soluble salts of polyvalent cations), such as by using sodium chloride and an ionic immobilizer of polyvalent cations. , producing a chlorine and substantially salt free caustic by electrodialysis of a sodium chloride brine containing magnesium, iron and other polyvalent metal cations. Polyvalent cations and sodium cations are
From the anode brine, it is transferred electrically through a cation-permeable membrane and into the reactor chamber solution. In situ, the polyvalent cations in the reactor chamber are ionically immobilized as negatively or uncharged water-insoluble salts and chelates or complex compounds. Sodium ions are electrically transferred from the reactor chamber solution through a cation-permeable membrane into the aqueous sodium hydroxide catholyte. Chlorine is produced in the anolyte.
A mixture of salts of monovalent and polyvalent cations is
In the electrodialysis method described above, electrolysis can be performed with separation of monovalent cations and polyvalent cations and selective separation of polyvalent cations. The method described above requires ultrapure membranes to operate effectively without fouling of the cation-permeable membrane by water-insoluble salts of polyvalent cations, which increases cell voltage and reduces electrolysis efficiency. No additional brine is required. The process described above does not require dechlorination or sulfite treatment of the recycled brine to effect the removal of polyvalent cations by ion exchange. The method of the present invention is an effective method for the electrolysis of brines and other metal salts containing calcium, magnesium, iron, copper and other polyvalent cations.

Recovery of a cation-permeable membrane contaminated with water-insoluble salts of polyvalent cations is achieved by using an acid (this acid has a pH of 3 or less in a 1N solution, and a water-soluble salt of polyvalent cations) on the cathode side of the contaminated membrane. using an aqueous solution of, for example, sodium chloride, and using an acidic solution on the anode side of said soiled membrane, and removing said acid from said soiled membrane. It can be carried out electrodialytically in a cell by electrically transferring multivalent cations into an aqueous liquid consisting of soluble salts. The method described above is particularly useful for the recovery of contaminated cation permeable membranes in chlor-alkali cells with catholyte systems in which it is not appropriate to use strong acids to clean the membranes.

The cations that are electrically transferred across the cation-permeable membrane are soluble (ionically mobile) in the solution, enter the membrane at the solution-membrane interface, and pass through the polymer membrane structure to form ions. It needs to be physically mobile and able to exit the membrane into the aqueous liquid. All of the above requirements are easily met for electrodialysis of salts of monovalent cations. 1
Valent cations produce water-soluble salts and hydroxides that do not foul cation-permeable membranes. In contrast, polyvalent cations form substantially water-insoluble salts with hydroxide ions and many other anions, and aqueous solutions consisting of polyvalent cations and anions that form substantially water-insoluble salts They tend not to migrate ionically through the membrane into the membrane. If a high rate of precipitate forms in and on the membrane, ion transport may be substantially impeded and membrane discontinuation may occur. Generally, polyvalent cations form hydroxide precipitates in the PH range of about 3 and above.

The present inventor discovered that an acid (this acid has a pH of 3 or less in a 1N solution and forms a water-soluble salt with a polyvalent cation) in a catholyte consisting of an ion or an agent that makes polyvalent cations insoluble. High cell capacity can be achieved and maintained by using soluble salts of polyvalent cations, including salts of polyvalent cations, as well as anionic acids or halogens, as well as hydroxides of polyvalent cations. or other substantially water-insoluble salts. In the reactor chamber of an electrodialysis cell divided into three or more compartments, a mixture of salts of monovalent and polyvalent cations is prepared by using a soluble salt of an acid with ionic immobilization of the polyvalent cations. Concomitantly, and simultaneously, a method is provided for electrolyzing the salt while converting the anion to an acid or halogen and the monovalent cation to a substantially pure hydroxide. Soluble salts of acids are surprisingly effective in electrically transporting high concentrations of polyvalent cations through cation-permeable membranes into hydroxide-containing aqueous fluids while preventing membrane fouling and loss of cell capacity. It is. Soluble salts of acids are useful for preventing cell capacity loss in aqueous solutions of sodium carbonate or sodium bicarbonate at low concentrations, e.g.
Effective at 200ppm or less. The effectiveness of soluble salts of acids increases with the strength of the acid and the acid solubility of the polyvalent cation salt and soluble salt. The availability of soluble salts at low concentrations indicates that the anion of the salt becomes concentrated at the interface between the membrane and the aqueous liquid consisting of the soluble salt of the acid. This results in a thin film of soluble salt anions, which act as ionically mobile connections for the multivalent cations, and are expelled from the membrane into the aqueous fluid, where they become insolubilized. Soluble salts of acids do not significantly render polyvalent cations insoluble in aqueous or catholyte solutions. The above explanation is one possible reason why soluble salts of acids undergo electrotransfer of polyvalent cations.
The above description is not intended to be a limitation of the invention.

Acid (this acid has a pH of 3 or less in a 1N solution,
Moreover, any soluble salts of polyvalent cations (which form water-soluble salts of polyvalent cations) can be used in the electrodialysis method of the present invention. Salts formed with polyvalent metal cations need only be slightly water soluble. That is, it is sufficient to minimize the formation of insoluble polyvalent metal salts on the membrane, and a solubility of at least 2000 ppm is preferred. Preferred soluble salts of acids include sulfur, halogen, nitrogen, phosphorous and carbon acids, which have a pH of less than 3, more preferably 2 or less in 0.1 normal solution, and which have a PH of less than 3, more preferably 2 or less, in a polyvalent cation, preferably an electrodialysis cell. (shall form water-soluble salts with polyvalent cations present in the feed solution or anolyte). When treating mixtures of polyvalent cation salts, a mixture of soluble salts of different cationic and anionic acids can be used to provide cell capacity retention. For the treatment of mixtures of salts of polyvalent cations, it is preferred to use soluble salts of acids, which should form water-soluble salts with all polyvalent cations in the anolyte. It is believed that the above and similar variations will be apparent to those skilled in the art.

The concentration of the soluble salt of the acid in the aqueous or catholyte solution can vary over a wide range from a saturated solution to about 200 ppm. It is preferred to use high concentrations of soluble salts of acids and operate at high cell capacities (high current densities) at low cell voltages. If the anion of the soluble salt of the acid migrates back from the aqueous or catholyte solution and adversely affects the quality of the anolyte, use a lower concentration of the soluble salt of the acid and increase the conductivity with carbonate or sodium bicarbonate. It is preferable to adjust. As will be apparent to those skilled in the art, the concentration of the soluble salt of the acid is sufficient to minimize the tendency of ions or agents that render polyvalent cations insoluble in the aqueous or catholyte solution to foul the membrane. It is necessary that

The electrodialysis cell of the present invention can have two or more chambers. A two-chamber cell has an anolyte compartment and a catholyte compartment separated by a cation-permeable membrane. The anolyte chamber is
It has an aqueous anolyte and an anode consisting of a soluble salt of a polyvalent cation or a mixture of salts of monovalent and polyvalent cations and anions. The catholyte chamber is an aqueous solution consisting of a soluble salt of an acid (the acid must have a pH of 3 or less in a 1N solution and form a water-soluble salt of a polyvalent cation) and a polyvalent cation insolubilizing agent. It has a catholyte and a cathode. A three-compartment cell has a catholyte compartment, a reactor compartment, and a catholyte compartment separated by a cation-permeable membrane. The anolyte chamber contains an aqueous liquid consisting of a salt of a polyvalent cation and an anode, and the reactor chamber contains an aqueous liquid consisting of a soluble salt of an acid and an ionic immobilizer of a polyvalent cation. The catholyte chamber is
Aqueous liquids or acidic aqueous liquids or soluble hydroxides, carbonates or bicarbonates consisting of soluble salts of acids (the acids shall have a pH of 3 or less in 1N liquid) and polyvalent cation insolubilizing agents. It has an aqueous solution consisting of and a cathode. A three-compartment cell can also have an anolyte compartment, a feed compartment, and a catholyte compartment separated by a cation-permeable membrane. The anolyte can be an acidic aqueous solution with or without soluble salts, the feed solution is an aqueous solution consisting of soluble salts of polyvalent cations, and the catholyte is an aqueous solution consisting of soluble salts of acids and polyvalent cations. It is an aqueous solution of a cationic insolubilizing agent. Cells of the invention with more than three chambers can be constructed using a cation-anion-neutral ion permeable membrane and a porous separator, as long as the membrane between the anolyte and the next chamber is cation-selective. They can be combined or all separated by cation-permeable membranes. A soluble salt of an acid (the acid shall have a pH of 3 or less in a 1N solution) is used to electrolyze polyvalent cations through a cation-permeable membrane into an aqueous solution consisting of a polyvalent cation insolubilizing agent. The use of soluble salts of acids in the chamber where the conditions described above are present will be apparent to those skilled in the art.
The feed solution consisting of a salt of a polyvalent cation or the chamber between the anolyte and catholyte chambers must be in electrical communication with the cathode and the chamber must be provided with a cation-permeable separator. It will also be clear to those skilled in the art that it is necessary to separate the It will furthermore be obvious that said membranes are chosen to be resistant to chemical attack by reactants and conversion products. Therefore, if the feed solution contains a sodium chloride brine and chlorine is produced in the anolyte by electrolysis, the membrane in contact with it should be resistant to harmful attack by the chlorine. .

The reactor chamber of the electrodialysis cell of the present invention having three or more chambers is an acid (the acid has a pH of 3 or less in a 1N solution and forms a water-soluble salt with a polyvalent cation). and a selective ionic immobilizing agent for polyvalent cations. Multivalent cations are ionically immobilized as negatively charged or uncharged water-insoluble salts, chelates, and complex compounds. The concentration of soluble salts of acids and ionic immobilizers of polyvalent cations can be varied. It is generally desirable to use low concentrations of polyvalent cation insolubilizing agents to minimize the tendency of the agents to foul the membrane. It is desirable to use soluble salts of acids at high concentrations to obtain high cell capacity at low cell voltages. There are a number of agents that can be used to ionically immobilize polyvalent cations, such as soluble hydroxides, carbonates, bicarbonates, oxalic acid and its soluble salts,
Hydrofluoric acid and its water-soluble salts, phosphoric acid, hydrogen sulfide, alkali sulfides, thiosulfates, polymer acids, and ion exchange resins. There are a number of compounds that can be used to form chelates and complex compounds of polyvalent cations, with or without a negative charge (anion) (see PCLThorne and ER Roberts).
Inorganic Chemistry, Fritz Ephraim, 15th edition,
Gurney and Jackson, London, UK.289-322
(see page). Chelates and complex compounds that ionically immobilize polyvalent cations include, for example, aminoacetic acid, ethylenediaminotetraacetic acid, α-
It can be formed with agents such as hydroxy acids, dimethylglyoxime, nitrosophenylhydroxylamine, acetylacetone, 8-hydroxyquinoline, and alkali cyanides.
Ionic immobilization of polyvalent cations can be carried out in the cell or in a device outside the cell. Multivalent cations can be selectively insolubilized, chelated, and complexed to effect separation by electrotransfer, extraction, filtration, electrodeposition, ion exchange, and other chemical-mechanical methods. For example, one or more polyvalent cations may be selectively immobilized within the reactor chamber, and other polyvalent cations may be electrically transferred into a third or catholyte compartment where they become insoluble. , separation of different polyvalent cations can be performed. The reactor chamber is used to ionically immobilize polyvalent cations to enable separation of polyvalent and monovalent cations, and more than one in-cell reactor chamber or external reactor It will be obvious to those skilled in the art that it is possible to use

The anolyte of the two-compartment electrodialysis cell of the present invention is an aqueous liquid consisting of soluble salts of polyvalent cations or a mixture of salts of monovalent and polyvalent cations. Said liquid is acidic, i.e. has a pH of 7 or less, preferably a pH of 7 or less.
Have 3 or less. The concentration of polyvalent cation salts is
Can vary from ppm to saturated solution. The anolyte can contain adducts to complex ions, solubilize salts, and precipitate impurities, wetting agents, detergents, and other additives used in metal and plastic finishes. If the anolyte is not the feed to the electrodialysis cell, the anolyte can be an acidic liquid with or without soluble salts. The feed liquid to the cell is an aqueous liquid consisting of soluble salts of polyvalent cations as described above with respect to the anolyte.

The feed to a multichamber electrodialysis cell is typically circulated through feed chambers and the acid generated in the anode eluate is recovered. Similarly, the catholyte is
The precipitated or ionically immobilized polycationic compounds may be circulated through the catholyte compartment and recovered from the eluate by, for example, precipitation, filtration, ion exchange, or any other conventional means. Ru. Similarly, the liquid in the reactor chamber of a three or more chamber cell can be circulated and the eluate treated to recover polyvalent cation material. As will be apparent to those skilled in the art, the flow rate is chosen to allow sufficient time for electrolysis without variation with respect to recovery of reaction products.

Any cation permeable membrane can be used to separate the chambers of the electrodialysis cell of the present invention. The cation permeable membrane fixes the negative charges dispersed in the polymer matrix and is permeable to positively charged ions. Preferred membranes are membranes of hydrocarbon and halocarbon polymers containing acids and acid derivatives. Particularly suitable acid polymers are perhalocarbon polymers containing pendant sulfonic acid groups, sulfonamide groups and carboxylic acid groups. The membrane can be a multilayer structure of different polymers and can contain fillers, reinforcements, and chemical modifiers. Preferred membranes are substantially chemically stable to the process conditions and are conducive to economical operation and design of the electrodialysis process;
Mechanically suitable. Preferred membranes for strongly oxidizing media are perfluorocarbon membranes, e.g.
Nafion (manufactured by Dopont), which contains sulfonic acid, carboxylic acid, or sulfonamide groups. Preferred membranes for the electrolysis of sodium chloride brine in electrodialysis cells of the invention having a reactor chamber are perfluorinated membranes with high electromobility of polyvalent cations and high conductivity for separation of the anolyte brine from the reactor chamber. Carbon membranes as well as high perm selectivity (high electrolytic efficiency) hydrocarbon or perfluorocarbon membranes for separation of the reactor compartment from the catholyte compartment.

The present invention is for the electrodialysis treatment of polyvalent cations and mixtures of monovalent and polyvalent cation salts in aqueous liquids, including acids (the acids having a pH of 3 or less in 1N liquid). soluble salt of)
It is intended for use in an anolyte or aqueous solution that is in electrical communication with the cathode of an electrodialysis cell. Aqueous solutions of salts of polyvalent cations and mixtures of salts of polyvalent and monovalent cations are commonly found in the chemical industry, electronics industry, mining industry, metal finishing industry, etc. In some solutions, the desired component is the polyvalent cation; in other feed solutions, the polyvalent cation is an impurity and the purified acid is the desired component. In the chloro-alkyl process, polyvalent cations are impurities that foul the membrane in cases where continuous high throughput is desired. According to another aspect, it is desirable to separate and isolate polyvalent cations from mixtures of their salts. Yet another aspect is to separate monovalent and polyvalent cations from a mixture of monovalent and polyvalent cation salts to produce pure monovalent cation hydroxides. It is also desirable to restore fouled membranes with polyvalent cation salts. These and other aspects of the invention will be apparent to those skilled in the art.

One embodiment of the method of the present invention is to electrolytically transform a brine containing polyvalent cations (more generally, electrodialytic conversion of a mixture of monovalent and polyvalent cation salts) into chlorine and substantially pure chlorine. The purpose is to produce sodium hydroxide. This embodiment consists of using a soluble salt of an acid (sodium chloride) and an ionic immobilizer of polyvalent cations in the reactor chamber of a three-compartment electrolytic cell. The soluble salts minimize fouling of the membrane, and the ionic immobilization of the polyvalent cations allows selective electrotransfer of sodium ions from the reactor chamber to the catholyte chamber. To illustrate aspects related to this aspect of the invention:
An electrodialysis cell was constructed having an anolyte chamber containing the anode, a reactor chamber, and a catholyte chamber containing the cathode. The chambers were separated by a cation-permeable membrane. The cell has an electrolytic area of about 58 cm ² (9 in ² ) and transports the anolyte into the anolyte chamber;
Means was provided for continuously adding reactor liquid to the reactor chamber and catholyte (eg water) to the catholyte chamber. Anode is Electrode
The cathode was a stainless steel mesh. The cation-permeable membrane separates the anolyte and reactor chambers from Nafion.
membrane 417 and separating the catholyte and reactor chambers;
It was Nafion324 membrane. The membrane was obtained from Dupont. The total anode-to-cathode gap was approximately 0.76 cm (0.3 in), the cell temperature was 80-85°C, and the current density was approximately 0.31 amps/cm ² (2 amps/in ² ). Cell voltage was the anode-cathode total voltage. Chlorine is formed at the anode. Caustic efficiency was measured by the amount of caustic soda produced per unit of DC electricity. The DC power supply was from Hewlett Packard and had the means to experiment with constant current and variable voltage. The brine used as a control pure brine was 23% by weight sodium chloride (saturated solution) containing less than 0.5 ppm calcium ions and having a pH below 3. calcium, magnesium, copper,
Reagent grade chloride salts of iron and other polyvalent cations were added to the pure brine described above to obtain the anolyte of the desired composition. The reactor liquid was filtered and circulated through the reactor chamber, and the initial composition was largely maintained throughout the experiment, except that back migration of hydroxide ions from the catholyte chamber increased the PH of the solution. Optionally, adjust the pH by adding soluble salts of acids.
was adjusted and maintained. Each example maintains catholyte composition essentially constant (adjusted by addition of water);
It consists of a series of experiments in which the compositions of the anolyte and reactor chamber fluids are varied as follows. Each experiment was conducted over approximately 4 days. During the experiment, an increase in cell voltage is indicative of some fouling of the membrane and loss of cell capacity.

〔Example〕

Example 1 In a three-chamber system, pure brine was added to the anolyte compartment and the reactor compartment, and the concentration of sodium hydroxide in the catholyte compartment was adjusted to 20% by weight. The initial cell voltage is
It was 4.2 volts. After 4 days of operation, the cell voltage increased to 4.4 volts. The reactor liquid had a pH of 10.5 and contained a small amount of white precipitate (which upon analysis was calcium hydroxide). The current effect was 91%. The catholyte was then changed to 10% by weight sodium chloride and 2% by weight sodium hydroxide. The reactor liquor was changed to 22% by weight sodium chloride and 2% by weight oxalic acid. The initial cell voltage is
4.5 and after 2 hours of operation the voltage dropped to 4.2 volts. The catholyte was changed to 20% by weight sodium hydroxide and the operation continued. The initial cell voltage was 4.1 volts. After 4 days, the cell voltage was 4.0 volts and the current efficiency was 92%. A white precipitate formed in the reactor liquid, which upon analysis was a mixture of calcium oxalate and calcium hydroxide.
The pH of the reactor liquid after 4 days of electrolysis was 10. Next, calcium chloride was added to the brine to obtain a brine feed solution containing 5000 ppm of calcium ions. Cell operation continued for 3 days. At this time, the pH of the reactor liquid was maintained at about 5. Cell voltage was kept constant at 4.0-4.1 volts. The current efficiency was 91%.

Example 2 The assembled electrolytic cell of Example 1 was used. The anolyte is 1
% calcium chloride, the catholyte was 20% sodium hydroxide by weight, and the reactor liquid contained 22% sodium chloride by weight. The initial cell voltage was 4.3. The reactor liquor was passed through an ion exchange resin cartridge to remove solids, followed by an Amberlite IRC 718 ion exchange resin column to remove calcium. The pH of the reactor liquid was between 9.5 and 10 throughout the experiment. The cell voltage was kept constant at 4.2 volts and the current efficiency for 4 days was 92%. The filter cartridge contained a white precipitate, which upon analysis was determined to be calcium oxide hydrate. Calcium was removed from Amberlite IRC 718 resin by regeneration with hydrochloric acid. As the operation continued, the reactor liquor was changed to 22% by weight sodium chloride, 1% by weight sodium fluoride, 1% by weight oxalic acid, and 1% by weight sodium metasilicate. The pH of the reactor liquid was adjusted to 4 with hydrochloric acid and maintained for 3 days. The cell voltage was kept constant at 4.2 and the current efficiency was 91%. As operation continued, the reactor liquor was changed to 22% by weight sodium chloride, 2% by weight sodium metaphosphate, and 1% by weight hypophosphorous acid. The PH was adjusted to 11 and maintained at approximately 11 for 3 days. The cartridge filter contained a gelatinous precipitate, which contained calcium phosphate and calcium hydroxide. The initial cell voltage was 4.2 and the cell voltage after 3 days was 4.3 volts. As the operation continued, the reactor liquor changed to 22% sodium chloride by weight and the reactor liquor PH was adjusted to 3 and maintained at about 3. The initial cell voltage was 4.3. 1
After the time operation the cell voltage increased to 4.8 and after 2 hours it was 9.5. The catholyte was diluted to 2% by weight sodium hydroxide and sodium sulfate was added to yield a solution containing approximately 2% by weight sodium hydroxide and 4% by weight sodium sulfate. Immediately after the addition of sodium sulfate, the cell voltage began to drop and after 30 minutes, the cell voltage was 4.5 volts. The catholyte contained a white precipitate. Continuing the operation, the reactor chamber liquid was changed to a 22% by weight sodium chloride solution and this solution was circulated through the filter and Amberlite IRC 718 resin. Adjust the pH of this solution to 10,
That value was maintained. The catholyte was changed to 20% by weight sodium hydroxide. The initial cell voltage is 4.2 and 3
It dropped to 4.1 after a day. The current efficiency was 92%.
The experiment has ended. The above experiment demonstrates the recovery of a soiled Nafion 324 membrane separating the reactor and cathode chambers.

Example 3 The assembled electrolytic cell of Example 1 was used. The anolyte is 1
Pure brine containing % calcium chloride by weight, catholyte 20% sodium hydroxide by weight,
The reactor liquid was then 22% by weight sodium chloride. The initial cell voltage was 4.2. Add cupric chloride and ferrous chloride to the above brine to obtain 1% by weight cupric chloride, 1% by weight ferrous chloride and 24% by weight.
A brine feed to the anode chamber with sodium chloride was obtained. The pH of the brine was 2.5. The reactor chamber liquid was adjusted to a pH of 10 and contained 3% by weight sodium sulfite. The initial cell voltage was 4.2 and was kept constant for 4 days.
The reactor liquid contained a dark brown precipitate, which was collected on a filter and analyzed, and it was found that copper, iron,
It contained sulfur and oxygen, indicating that it was a mixture of salts. The catholyte was free of precipitates and colorless. The current efficiency was 91%. Continuing the operation, the reactor liquid was reduced to 22% by weight sodium chloride and
Converted to 0.5% by weight nitrosophenylhydroxylamine. The initial cell voltage was 4.2 and remained substantially at 4.2 for 3 days. A precipitate formed in the reactor chamber and was collected on a cartridge filter. The catholyte was free of precipitates and colorless. The operation has ended.

Example 4 The assembled electrochemical cell of Example 1 was used. The anolyte was 25 wt% pure brine containing 1 wt% calcium chloride, the reactor chamber contained 10 wt% sodium hydroxide, and the catholyte chamber contained 20 wt% sodium hydroxide. Ta. The initial cell voltage was 4.3. The cell voltage begins to rise rapidly,
After 20 minutes it was 11.5 volts. The reactor liquor was changed to 22% by weight sodium chloride and 3% by weight oxalic acid and the pH was adjusted and maintained at 8.5. The initial cell voltage was 11.2 and this voltage began to drop rapidly.
After 1 hour the cell voltage was 4.2 and after 2 days it was 4.1. The current efficiency was 92%. This example shows the effect of calcium in brine on cell voltage and membrane fouling. This also indicates the recovery of the membrane separating the anode and reactor chambers.

The foregoing examples demonstrate the ease and efficiency of producing chlorine and sodium chloride by electrolysis of a sodium chloride brine containing polyvalent cations. Ionic immobilization of polyvalent cations allows separation of monovalent and polyvalent cations and subsequent production of high purity hydroxides of monovalent cations. Soluble salts of acids prevent fouling of separation membranes and recovery of fouled membranes.

To illustrate another aspect of the invention, instead of a ruthenium-based anode, a
The same assembled cell as in Example 1 was used except that an Ebonex reduced titanium oxide anode was employed. The anode chamber is
It contained an acidic aqueous liquid consisting of sulfuric acid. The composition of the aqueous liquid in the reactor chamber (here the feed chamber) was varied as follows. The aqueous liquid in the catholyte consists of soluble salts of acids. No measurement of electrolytic efficiency was performed. Each electrolysis was performed over one day. Anolyte composition was adjusted by adding water. The catholyte composition changed with electrolysis. Multivalent cations became insoluble, and monovalent cations produced soluble hydroxides. A decrease in cell voltage is indicative of an increase in the conductivity of the catholyte or feed fluid composition. An aqueous liquid (feed liquid) was fed to the cell at a constant rate while passing through the anode chamber. An increase in cell voltage indicates fouling of the cation-permeable membrane.

Example 5 The assembly cell of Example 1 was used, modified as described above. The anolyte is an aqueous solution of 4.7 wt.% sulfuric acid, the catholyte is an aqueous solution consisting of 5 wt.% sodium sulfate and hydroxide ions formed at the cathode, and the feed solution is 3 wt.% chromic acid, 2 wt.% nitric acid, 2 wt. % sodium acetate and 5% by weight dissociated cadmium metal. The initial cell voltage is approximately
At 0.03 amps/cm ² (0.2 amps/in ² )
It was 6.2. Cell voltage ranged from 6.2 to 6.2 over 24 hours.
remained virtually constant at 6.0. The catholyte contained a white precipitate, which upon analysis was cadmium hydroxide. The feed solution was changed to an aqueous solution consisting of 5% by weight chromic acid, 3% by weight cupric chloride, 5% by weight cupric chromate, and 2% by weight boric acid. Initial cell voltage is 0.3 amps/in ²
6.8 and was maintained constant at 6.8 volts during 28 hours of electrolysis. The catholyte contained a precipitate of cupric hydroxide. No detectable chlorine was generated at the anode. The experiment was terminated, the membrane was removed from the cell, and the deposits were inspected. The membrane was substantially free of metal or salt deposits. The cathode was clean and free of deposits.

Example 5 above shows that salts of polyvalent cations and anions, such as chromates, chlorides, borates, acetates and nitrates, are added to the substantially water-insoluble form of the polyvalent cations at continuous high cell volumes. This shows the ease of converting into hydroxide and anionic acids, respectively. Soluble salts of acids (sodium sulfate) promote electromigration of polyvalent cations and prevent membrane fouling. Insolubilization of polyvalent cations by hydroxide ions generated at the cathode enables long-term use of the catholyte and recovery of polyvalent cation hydroxide for use as a solid.

Another aspect of the method of the invention is the recovery of membranes contaminated by polyvalent cation salts. To illustrate the practice of this aspect of the invention, a two-chamber electrodialysis cell was constructed by removing the reactor chamber from the cell of Example 1. The anode and cathode compartments were separated by cation permeable membranes, namely Nafion perfluorinated membranes 901 and 203. The 901 membrane described above consists of a sulfonic acid group and a carboxylic acid group, and the 204 membrane described above contains a sulfonic acid group and a sulfonamide group. For both membranes, against chlor-alkali electrolysis,
High caustic efficiency membrane. The anolyte has a pH of 2 and 5
It was an aqueous solution consisting of 20% by weight of calcium chloride and 20% by weight of sodium chloride. Two catholytes were used. The catholyte (1) is for electrolysis and dirty membrane recovery and contains 2% by weight sodium hydroxide and 20% by weight.
The catholyte (2) is for cleaning the membrane and consists of a 20% by weight aqueous caustic solution. The electrolytic conditions used were those of Example 1. The cell was operated with catholyte (1) for 2 hours before taking the initial voltage and for about 24 hours before taking the final voltage. The catholyte (1) was replaced with the catholyte (2) and the cell voltage was observed until the voltage reached approximately 10 volts. Next, add the catholyte (2) to the catholyte.
Replaced with (1). The cell was operated for approximately 24 hours and the voltage was recorded. The results of several soil and recovery cycles were very similar. The results were as follows. (a) Membrane 901: initial voltage 4.0, catholyte
(2) at 11.5 volts for 30 minutes and catholyte (1) at 3.9 volts for 28 hours.
(b) Membrane 204: initial voltage 3.9, 12.8 volts for 60 minutes with catholyte (2), 3.9 volts for 24 hours with catholyte (1). The above results demonstrate the effectiveness of soluble salts of acids (e.g., sodium chloride) in the recovery of fouled membranes, as well as in the electrotransfer of polyvalent cations through cation-permeable membranes into aqueous solutions containing hydroxide ions. This shows that. Similar experiments were performed on the anolyte, aqueous feed, monovalent and polyvalent cation salts, catholyte,
Other combinations of anodes, cathodes, membranes, insolubilizing agents, chelates with ionic immobilizing effects, and complex polyvalent cations were investigated. The results of the above experiments demonstrate that the use of a soluble salt of an acid in an aqueous liquid containing a polyvalent cation insolubilizer and in electrical communication with the cathode prevents fouling of the cation-permeable membrane and allows cation permeation. The present invention is shown to provide continuous high-capacity electrotransfer of multivalent cations across membranes.

Claims (1)

Claims: 1. A salt of a polyvalent metal cation in a first aqueous feed solution or anolyte, selected from a solution of a salt of a polyvalent metal cation and a solution of said salt and a salt of a monovalent cation. to its salt anion acid, or to a halogen if the salt anion is a halide, the method comprising: passing a cation from said aqueous liquid through a cation-permeable membrane; (b) selectively reacts with the polyvalent cation; and electrotransferring the multivalent metal cation into a second aqueous liquid comprising an immobilizing agent capable of producing an ionically immobile material selected from precipitates, complexes, and chelates of the multivalent metal cation. Electrodialysis conversion method as described above. 2 The soluble salt of the acid in the second aqueous liquid is a sulfur, halogen, nitrogen, phosphorus, and carbon acid (this acid shall have a pH of 2 or less in the 0.1N liquid)
The method according to claim 1, wherein the alkali metal salt is selected from the group consisting of alkali metal salts of 3. The second aqueous liquid comprises soluble hydroxide ions, carbonate ions, bicarbonate ions, or a mixture thereof, which reacts with the polyvalent metal cation to form a precipitate. the method of. 4. The method according to claim 1, wherein the soluble salt is a salt of an acid having a pH of 2 or less in a 0.1N solution. 5 The immobilizing agent is an alkali cyanide ion, dimethyl gloxime ion, ethylene diamino tetraacetic acid ion, nitrosophenylhydroxyamine ion, hydroxide ion, carbonate ion, bicarbonate ion, oxalate ion, silicate ion , fluoride ions, phosphate ions, sulfide ions, thiosulfate ions, ion exchange resin materials, and mixtures thereof.
The method described in section. 6. Said second aqueous liquid contains an ionic immobilizer for a portion of the polyvalent cations, and the cations are removed from said second aqueous liquid without immobilization of the other polyvalent cations. Through a permeable membrane, (a) an acid (the acid must have a pH of 3 or less in a 1N solution and form a water-soluble salt with the polyvalent cation);
(b) an immobilizing agent capable of selectively reacting with said polyvalent cation to produce an ionically immobile compound selected from precipitates, complexes and chelates of said polyvalent metal cation; 2. The method of claim 1, wherein the aqueous liquid is electrotransferred to a third chamber containing the aqueous liquid, the aqueous liquid being in electrical communication with the cathode of the electrodialysis cell. 7. The first aqueous liquid contains a salt of a monovalent metal cation in addition to a salt of a polyvalent metal cation, and the monovalent metal cation in the second chamber passes through a cation-permeable membrane. . The method of claim 1, wherein the third chamber contains an aqueous liquid having a pH greater than 7 and a cathode for an electrodialysis cell. 8. A method of applying electrodialytic conversion to a mixture of salts of polyvalent and monovalent cations in a first aqueous liquid as an anolyte, the method comprising: An aqueous solution is passed through a cation-permeable membrane to form a soluble salt of (a) an acid (the acid must have a pH of 3 or less in a 1N solution and form a soluble salt with the polyvalent cation) and (b) )
and an immobilizing agent capable of selectively reacting with the polyvalent cations and effecting ionic immobilization of the polyvalent metal cations through a cation-permeable membrane; and electrotransferring the monovalent metal cations from the second aqueous liquid through another cation-permeable membrane into a third aqueous liquid in electrical communication with the cathode and containing hydroxyl ions; The method according to claim 1, wherein the electrodialytic separation of monovalent and polyvalent cations in an aqueous liquid can be carried out effectively under high cell capacity. 9. The immobilizing agent in the second aqueous liquid selectively reacts with the polyvalent metal cation to form an uncharged or negatively charged chelate or complex compound. 9. The method according to claim 8, wherein the method is selected from materials that can be used. 10. The method of claim 8, wherein the immobilizing agent in the second aqueous liquid is selected from substances capable of reacting with the polyvalent cation to form a precipitate or a water-insoluble salt. Method. 11. The immobilizing agent capable of forming a chelate or complex compound with the polyvalent metal cation present is an alkali shead, dimethyl gloxime, ethylene diamino tetraacetic acid or nitrosophenyl hydroxyamine. 9
The method described in section. 12. The immobilizing agent capable of ionically immobilizing the polyvalent cation and forming a precipitate or a water-insoluble compound with the polyvalent cation,
selected from soluble hydroxide ions, carbonate ions, bicarbonate ions, oxalate ions, fluoride ions, silicate ions, phosphate ions, sulfide ions, thiosulfate ions, polymeric acids, ion exchange materials, and mixtures thereof. The method according to claim 10. 13. The method of claim 8, wherein the monovalent cation salt is an alkali metal halide and the monovalent and polyvalent metal cations are electrotransferred into the second aqueous liquid in the reactor chamber. 14. The method according to claim 13, wherein the alkali metal halide is sodium chloride. 15. The method according to claim 13, wherein the catholyte is an aqueous sodium hydroxide solution. 16. The method of claim 13, wherein the polyvalent metal cation is made insoluble and removed from the aqueous liquid in the reactor chamber by filtration or ion exchange. 17 (a) An acid in contact with the cathode side of the dirty membrane (this acid has a pH of 3 or less in a 1N solution, and
shall form water-soluble salts of polyvalent cations)
(b) an acidic aqueous solution in contact with the anode side of the contaminated membrane, thereby removing polyvalent cations from the contaminated membrane. 2. The method of claim 1, wherein polyvalent metal cations contaminating the membrane are converted and removed from the membrane by electrotransfer into an aqueous solution comprising a soluble salt of an acid. 18 Soluble salts of the above acids include sulfur, halogen, nitrogen, phosphorus and carbon acids (this acid is
Claim 1, which is selected from alkali metal salts having a pH of 2 or less in a 0.1N solution and forming a water-soluble salt with the polyvalent cation.
The method described in Section 7. 19 The acid in the acidic aqueous liquid is a sulfur, halogen, nitrogen, phosphorus and carbon acid (this acid is
18. The method according to claim 17, wherein the method is selected from PH of 2 or less in a 0.1N solution or a mixture thereof. 20 A chamber comprising at least a cathode chamber and an anode chamber, containing an acidic aqueous liquid comprising a soluble salt of a polyvalent metal cation, and capable of being an anode chamber but not a cathode chamber, hydroxide ions, an electrodialysis cell comprising a cation permeable membrane separating said chamber from another chamber containing carbonate ions, bicarbonate ions or mixtures thereof and which can be a cathode chamber but not an anolyte chamber; 2. A method according to claim 1, comprising passing an electric current.