DE2510534A1 - Electrochemical purifcn. of liq. effluents polluted with fluorides - using aluminium anode to form insol. cpds. with fluoride ions - Google Patents

Abstract

In an electrochemical process for the purificn. of an ionising liq. by elimination of fluoride ions capable of forming an insol. aluminium cpd. an electric current is passed between the anode which has an area of its immersed surface made of aluminium, aluminium alloy or an insol. aluminium cpd. and a cathode via an electrolyte formed from a supply of the ionising liq. so as to produce an insol. cpd. of aluminium with fluoride ions, the insol. prod. then being eliminated while the purified liq. is collected separately. Used for purificn. of industrial, liq. effluents such as rinse water from electroplating processes, drainage from cooling towers and gas scrubbers. This is an uncomplicated continuous process which is readily adapted to automatic control. The electrochemical action completes the purificn. process without chemical additives or further pH adjustment. No diaphragm is required between cathode and anode.

Description

Method and cell for the electrochemical removal of fluoride ion from an ionizing medium. The invention relates to methods of treating of liquids for the purpose of removing impurities or contaminants these liquids. In particular, the invention relates to electrochemical Treatment of exhausted treatment solutions, rinsing water, e.g. electroplating rinses, Wastewater streams and effluent or cleaning streams such as those from cooling towers and wet sprinkling of contaminated gases and the like. The invention relates to also on the construction of electrolytic cells in which aluminum, aluminum alloys are used as anodes or insoluble aluminum compounds can be used.

To previous methods of removing waste fluorides from liquid or aqueous media included processes of chemical precipitation, ion exchange, adsorption and contact with alumina to turn the waste into acceptable to convert different compounds or to focus them and make them easier to make discardable. The chemical processes often require an acidification to get low to achieve pII value; a chemical additive to effect a reaction such as precipitation, to precipitate the reaction products; and the separation of the solid precipitate from the liquid. Industrial waste containing high levels of fluoride, need a two-stage treatment.

The serial precipitation removes fluoride down to 10 to 20 mg / l. A further reduction can be obtained down to a salary of 1 mg / l, with long contact with activated aluminum oxide and its regeneration needed.

Such processes experience higher capital costs and higher labor costs.

However, by following the method of the present invention, one can now with no pH adjustment of the enema or the effluent and no chemical additives, both Effectively remove ionic as well as non-ionic contaminants by removing them converts into insoluble compounds. The insoluble aluminum compounds or Complexes of the contaminating ions such as fluorides, which with the electrode metal are easily removable from the aqueous medium in which they are formed were originally present, which facilitates the cleaning of the medium.

According to the invention, contaminating fluoride ion is obtained from an aqueous one Medium of industrial drains removed by an electrochemical method which the formation of an insoluble aluminum fluoride compound or a complex of Containing contaminating ions, being an anode made of aluminum, aluminum alloy or an insoluble aluminum compound is used. The fluoride turns into an insoluble, converted to less toxic form. The method is based on removing other contaminants Ions, for example suspended solids, applicable. The invention relates also apply to electrolytic cells and devices that are used to carry out of the process are useful.

According to the invention is a method for electrochemical removal a contaminating fluoride ion from an ionizing medium, the fluoride ion is capable of an insoluble aluminum compound, a complex, or with others Substances to form a common precipitate, characterized in that one an electric current between an anode, which is a surface or a Partial surface made of aluminum, aluminum alloy or an insoluble aluminum compound having, and a cathode through which the ionizing medium can pass, wherein the ionizing medium contains the ion to be removed, so that anodically an insoluble one Aluminum compound, compound type or a complex is formed while the cathodic Reaction with the aqueous medium evolves hydrogen and forms a hydroxyl ion insoluble products are produced; and that these insoluble substances are removed from the aqueous medium removed. In preferred embodiments of the invention, the Contamination, which is initially toxic, is transformed into a non-toxic or less toxic, insoluble form transformed and removed.

For example, the fluoride ion is converted into insoluble complexes and removed as an aluminum complex, which can be thought of as a non-stoichiometric one Mixture of aluminum hydroxide and aluminum fluoride. The invention also relates on devices such as electrolytic cells which have anodes attached to their Surfaces at least parts made of aluminum, aluminum alloy or insoluble aluminum compound possess, and which have a structure that the continuous flow of to be detoxified aqueous media through the anodes, whereby blockages or Avoid covering the anodes with emptying, insoluble reaction products will.

The object of the invention is applicable to the treatment of various Liquids which can be precipitated, co-precipitated or complex-forming with aluminum Impurities or

Contain toxins like such liquids, which result from the industrial: ~: metal surface treatment, chromate conversion coatings, the chemical industries - paper mill drains, sanitary and urban sewage, aluminum processing etc. result. Brackish water, which is high in fluoride and other toxic ions can also be treated by this method but it is primarily useful for removing dangerous ions like fluorides.

As a by-product of the process, the hazardous ingredients can can often be obtained in a usable form. Even if it is decided that it is uneconomical is to use the recovered products, possibly because of the inclusion different Impurities, the solid forms are more easily discarded than the dilute ones Solutions of the initially present toxin.

The subject invention in its most preferred embodiments chemically complexes a toxic impurity of a liquid medium into one less toxic form, for example fluoride in insoluble aluminum fluoride in flocculating form, which helps to remove the less toxic product and by forming a complex with it or by some other physical means or chemically combining with this to form a removable solid, a gel or a flocculating material according to the following synergistic Reactions: 1) A1 (OH) 3 and Al2 (F) 6 usually require a special # individually pH range for complete precipitation, but in the presence of the aluminum complex from A12 <F) 6 and A1 (OH) 3 there is less tendency for the pH sensitivity; 2) Complete coprecipitation is achieved over a much wider pH range away due to the synergistic effects; 3) achieved complete failures you in a shorter dwell time.

Such reactions can be caused by using dilute solutions of the impurity and at appropriate pH values close to the neutral point treated. Previous methods were more or less aimed at removing suspended matter Solids or the production of flocculating substances using specific pH ranges.

The reaction of the invention does not require the presence of one Diaphragm or other separating means between the anode and cathode parts the electrolytic cell and because of the self-control of the pH value in the subject of the invention is in in many cases an adjustment of the conductivity or the pH value not mandatory.

Albeit the subject matter primarily to the removal toxic fluoride contamination from waste or

Treatment currents is directed, so it is also useful for Removal of compounds that contain fluorine and phosphate, leaving the soluble Form on reduction either an insoluble solid, preferably with complex formation generated with aluminum hydroxides or oxides, or a gas. In cases where the gas is also poisonous, of course, precautions must always be taken to prevent the gas extract or chemically convert it into a non-toxic or disposable form.

The various methods, devices, operations, constructions, Conditions, details, applications and advantages of the invention are evident from the following description in conjunction with the illustrative drawings preferred embodiments of the devices used to carry out the Procedure.

Fig. 1 is a schematic representation of a device for removing of impurities from liquids according to the method according to the invention; Fig. Fig. 2 is a plan view of an electrochemical cell for use in accordance with the present invention when removing contaminants from aqueous solutions; Fig. 3 is the view a central vertical section along plane 3-3 of FIG. 2; Fig. 4 is the view a central vertical section along line 4-4 of FIG. 2; and Fig. 5 is that View of a horizontal section along plane 5-5 of FIG. 3.

The electrolytic cell 11 in Fig. 1 contains anodes 13 made of aluminum, Aluminum alloy or insoluble aluminum compound, where the # anodes have a Anode busbar 17 are connected to a direct current source 15. Also contains the cell cathodes 19, which via cathode busbar 23 with the negative output are connected. In the illustrated cell, the anodes and cathodes are monopolar and a number of them are shown. However, different numbers can also be used can be used on anode-cathode combinations, both larger and smaller, and both bipolar and unipolar arrangements can be used.

The pump 25 draws out an aqueous liquid medium or solution 27 the tank 29 or other source through inlet line 31 and emptied the solution through line 33 into electrolytic cell 11. The flow meter 37 measures the flow of the solution containing the impurity to be removed, so that the flow can be controlled by adjusting the pump speed, valve 78 and the amount passing through valve 67 can be controlled. The solution, which now insoluble derivative of the impurity, for example aluminum hydroxide-aluminum fluoride complex Contains in flocculated, precipitated form, now flows through line 39, through valve 41, and line 43 into the settling tank 45, where precipitant is added to to coagulate the flocculation. The coagulate 47 is by sedimentation from the flowing solution stream removed. The clarified solution now goes through line 49 into the storage tank 51 or into another reservoir, or in some cases through a drain line therethrough which is connected to a drain pipe, a return line or another suitable stream. Instead of using a settling tank, it can be used in in some cases it may be desirable to use continuous filter devices, to remove the insoluble precipitate from the treated liquid.

In Figs. 2 to 5, the electrolytic cell 61 has a cup-shaped Base part 63, a cylindrical central section 65 and a flanged top part 66, with all parts being connected to one another in a liquid-tight manner and as a container serve for the electrolyte and the electrodes used. The container is made mainly made of polyvinyl chloride or chlorinated polyvinyl chloride, but can other plastics and inert building materials can also be used. Within the cylindrical body is a holder 71, which at several points 73 is grooved to support the electrodes 75. The electrode holder 71 has a open lower part with a support 77 which extends over it and the angled Electrodes, anodes 79 and cathodes 81, holds. Electric current goes to the anodes 79 carried by line 83, connection 85 and bracket or rail 87, while the Connection to cathodes 81 by means of line 91, connection 93 and rail 95 he follows. Inlet 101 carries liquid into the cell and outlet 103 is for provided the drain with suspended insoluble material. The top flange 105 is connected to the cell body and is used to hold various other Cell parts.

As illustrated, the electrolytic cell is monopolar with alternating Electrodes of different signs. However, you can do so in a known manner a bipolar arrangement can be modified.

In addition to removing the aforementioned toxic contaminants the present methods and devices are capable of other ionizable to treat fluorine-containing compounds which may accompany those mentioned above. This group includes tungstates, silicates, fluorosilicates and phosphates and various Forms of such substances of higher and lower acidities and higher and lower Oxidation stages, for example perborates, bisulphates, sesquisilicates, etc. If the aluminum oxide or hydroxide complex of such a substance or a Aluminum salt of this is less soluble than the concentration of the substance to be treated Medium, the substance is usually removable by the process. Even in in some cases where such materials are quite soluble, they tend to be due to the flocculation reaction products to be adsorbed and their concentrations are decreased.

The active surfaces of the anodes consist at least partially of a material, which as a result of the electric current aluminum in the aqueous Medium releases. It is not essential that the aluminum releasing compound or the aluminum donating material must cover the entire surface of the anode, however usually it makes up at least 50% and preferably over 90% of the anode surface area made of, and in most preferred cases, the entire electrode consists of such Material. Mixtures of aluminum, aluminum alloys and insoluble aluminum compounds can be used. The cathodes are preferably also made of aluminum, to facilitate their use as anodes when it is desired to increase the current To reverse cleaning purposes, to increase the life of the cell, etc., you can the cathodes also, as mentioned above, of other suitable electrode materials exist. Because the cathode in terms of removing the contaminating ions is relatively inert from the aqueous medium to be treated, is the nature of the cathode material not critical, but it should be compatible with the anode and the electrolyte and should of course not insolubilize the soluble impurity to be removed affect.

The electrolytic cell used can have any structure, in which the electrodes are mounted in any suitable configuration and the electrodes can be either monopolar or bipolar. However, they are vertical Stack of monopolar aluminum electrodes in which each electrode is monolithic, preferred. Equivalent shapes such as sieves, perforated curved sheets, mixtures of seven and holed Sheets, solid sheets, rods and Grains can be used to encourage the best currents. Also can to use electrodes of the various materials already mentioned and the Anodes and cathodes can be the same or different. In some cases like it may be desirable to use different materials for individual anodes or several such materials can be used in one anode or cathode.

The assembled electrolytic cell with electrodes, framework, Ladders, pipelines and seals are usually sized to accommodate the specific intended application and dimensions, openings and Constructions can be varied in a suitable manner.

The inventive method can be used at various concentrations the anionic contamination in the ionizing medium can be applied. In general the proportion of such contamination is less than 1% in the medium, although sometimes as much as 15% can be present. Usually because of the limiting Effect of solubilities of complexes and other insoluble derivatives of impurities, the initial concentration of impurity not less than 0.03 parts per million.

In most cases it will be 1 to 5,000 parts per million. The current density range in A / dm2 is within 0.0054 to 54, preferably -0.11 to 1.1, and especially from 0.21 to 0.32 for both bipolar and for unipolar arrangements. The voltage is usually 0.1 to 50 volts, preferably 0.5 to 20 volts and especially 5 to 15 volts in a unipolar arrangement. The current is in the range from 0.5 to 20,000 A, preferably from 2 to 1,000 A per cell module and especially from 50 to 5,000 A for unipolar cells. For bipolar cells lies the voltage in the range of 500 to 5,000 when the current is 0.5 to 50 A. For unipolar configuration the current is high and the voltage low, whereas the reverse is usually true for biplar cells.

The pH will be within the range of about 4 to 11, preferably held in the 6-10 range. The pH should be such that the insoluble Derivative or the complex form of the impurity such a sufficiently low solubility possesses that the treatment decreases the concentration in the aqueous medium, wherein such a reduction usually to less than half that initially present Amount takes place. Usually the concentration drops to less than 5 Parts per million, and preferably less than 1 part per million, with reductions to less than 0.1 parts per million, 0.01 parts per million, and even 0.000 Parts per million are not uncommon. Of course, both the pH and also the electrical conditions are usually set or controlled, to effect the most desirable removal of contamination, with such adjustments depend on the type of contamination. The temperature of the treated Contaminated solutions are normally in the range from 10 to 50 ° C., preferably at about 15 to 300C, and is often initially ambient temperature, which is reflected by the electrolytic reaction increases to about 0 2 to 20 C above ambient temperature.

The residence time of the contaminated medium to be treated in the Different devices can vary widely, being as low as 0.001 Minutes can be as long as an hour, but usually will be at least 5 seconds or 0.1 minutes. The residence time is determined by the amount of electricity, where 6 coulombs is the theoretical amount found to be about the charge is the amount it takes to convert one milligram of fluoride ion to aluminum fluoride. When using continuous processes and electrolytic cells with a single It has been found that a 50 to 200% excess of electricity often occurs is required, this excess generally being about 100%. After this the insoluble compound or the aluminum complex of the impurity is formed it can be filtered off by conventional measures or it can be replaced in the drainage liquid.

To speed up the separation of the insoluble complex from the liquid to help and to aid in the removal of other insoluble matter after the treated liquid is removed from the electrochemical cell, this can furthermore with a suitable polyelectrolyte or a suitable coagulant be treated. Among the most useful of such substances are the polyfunctional ones Polyelectrolytes and most preferred of these are the water soluble polymers U.S. Patent Application 304,221 entitled Mater Soluble Polyfunctionalized Polymers of Alpha, Beta-Unsaturated Active Hydrogen-Containing Monomers, "being the description of this application is to be regarded as part of the present application.

Treatment with polyelectrolyte or other coagulant or Flocculant is preferably effected prior to separation of the flocculant or other insoluble matter from or after the effluent from the treatment cell. Such treatment can be repeated, but there is usually one treatment sufficient. The treated and separated drain can be used for treatment other or the same electrochemical cell or it can be returned cascaded to other such cells for subsequent treatments. In such a case, a polyelectrolyte treatment or equivalent can be used Apply treatment to aid in removing the insolubles, however usually the treatment is carried out only after the final treatment or after the initial and finishing.

The following examples are only intended to illustrate the Invention without saying anything about its scope. Unless otherwise stated is, all parts of the data relate to weight and all temperature data OC. The examples given mostly relate to the removal of low concentrations of fluoride in the form of complexed fluoride ions from waste water, because this is an important one and difficult problem is, which has been solved according to the invention is. Nonetheless, it is obvious that there are many other impurities can also be removed using the same or slightly modified methods.

Example 1 In a device of the type shown in Figs 3 is illustrated, the device having a volume of 76 liters and with multiple aluminum anodes and cathodes and spacers made of polyvinyl chloride Is equipped with a thickness of 0.76 mm, one brings an aqueous solution with a Fluoride ion content, which corresponds to 25 parts per million sodium fluoride.

The flow of this solution is at a rate of 19 liters held every minute. The pH of the incoming solution is 4.5 and the reaction is carried out without making pH adjustments by adding acid, Base or buffer, solely through the generation of hydroxyl ions at the cathode. Man applies a DC voltage of 10 volts and the flowing current is 50 A. Die Current density is 0.212 to 1.1 A / dm2 and is preferably kept at 0.27 A / dm2. The electrochemical reaction required to work in this example takes 6 to 12 coulombs to reduce 1 mg sodium fluoride.

For oxidations or reductions of other substances are proportional Amounts of electricity used according to Faraday's law. The response is monitored by periodically withdrawing samples of the aqueous medium and through analyzes, both standardized photoelectric means and specific ion electrodes applies.

On analysis it is found that the fluoride content is 0.001 part per million has been reduced. Because of the excellent reduction in fluoride content the liquid medium is neither cascaded to other cells nor returned.

Instead, the liquid medium flows directly into waste drainable. If the experiment is repeated using a contaminated rinsing liquid which comes from the electroplating of metals, one obtains similar ones excellent results. The following is a comparison of the initial and final concentrations of the components of such a rinsing liquid given: initial concentration final concentration (Parts per million) (parts per million) sodium fluoride 25 0.001 iron 0.4 0.001 S04 120 SiF4 + SiF6 15 0.01 pH value 4.5 6.8 Table 1 shows a comparison between not consumable electrodes like carbon and consumable electrodes like aluminum for their effect on fluoride ion. The advantage of using the consumable Aluminum electrode is obvious.

Effect of electrode material on fluoride ion Electrode fluoride ion concentration material voltage current time before after coal 5 V 0.05 A 1.6 hours 50.5 T. per # Mill. 50, l T. each M.

Coal 15 V 0.15 A 1.6 hours 60.2 T. per mill. 59.1 T. per mill.

Aluminum 5 V 0.13 A 0.5 hours 55.2 T. per mill. 0.2 T. per mill.

The technical progress of the subject matter of the invention results from the above.

The invention is not limited to those reproduced here by way of example Embodiments turned off alone. Within the scope of the invention, there are manifold to the person skilled in the art Deviations and changes are readily available.

- patent claims -

Claims (10)

Claims 1. A method for the electrochemical removal of Fluoride ion, which is capable of an insoluble aluminum compound or Form complex from an ionizing medium, characterized in that between an anode, which has a surface or partial surface made of aluminum, Aluminum alloy or insoluble aluminum compound, and a cathode, an -electric current through the ionizing medium, which is to be removed Containing fluoride ion, allows to pass, so that an insoluble aluminum compound or complex with the fluoride ion is generated, and that this insoluble material removed from the ionizing medium. 2. The method according to claim 1, characterized in that the removed Fluoride ion is a toxic ion which is dangerous to animal life; that the ionizing medium is aqueous; that the fluoride before the production of the insoluble Aluminum compound or the complex in a concentration of 0.0 to 50,000 Parts per million is present; that the electric current is direct current or essentially Is direct current; that the current density is 0.0054 to 54 A / dm2; that the electrolyte without intermediate position of a diaphragm freely in connection with anode and cathode stands; that the anode surface is aluminum or aluminum alloy; and that the pH of the aqueous medium is in a range in which the solubility the insoluble aluminum compound or the complex with the fluoride ion is lower is than 5 parts per million in the aqueous medium. 3. The method according to claim 1 and 2, characterized in that the supplied electrical charge about 100 to 500% of the theoretical charge for conversion of the fluoride present into the insoluble aluminum compound or into the complex form is. 4. The method according to claim 1 to 3, characterized in that one the aqueous medium, which contains fluoride, continuously through an electrolytic Can pass cell, the electrodes of which are covered by the medium, the Residence time of the fluoride-containing aqueous medium in the cell from 0.001 minutes to to one hour and the supply of electrical energy to cells 2 to 5 Faraday per equivalent weight of contaminating ion reacted. 5. The method according to any one of the preceding claims, characterized in, that the aqueous medium containing the fluoride ion to be removed, continuously passing through an electrolytic cell; that the residence time of the fluoride-containing aqueous medium in the treatment cell is 0.1 minutes to one hour; that after completion of the treatment, the treated medium is continuously removed removed from the cell together with insoluble metal salt or complex des Fluoride ion; that the pH of the effluent from the cell to a range of 4 to 11, at which pH there is essentially no soluble fluoride compound or complex is present; and that the insoluble fluoride compound or the Complex removed from the aqueous medium. 6. Electrochemical cell for performing the method according to claim 1 to 5, characterized by a number of essentially parallel anodes (13) and cathodes (19), which are in a non-conductive framework in a cell body (11) are stored, the frame and the electrodes located therein together the cell body are removable and the anodes on their surfaces Aluminum, aluminum alloy or an insoluble aluminum compound , and a passageway for electrolyte flow through the cell with the electrodes is in place. 7. Electrochemical cell according to claim 6, characterized in that that the anodes and cathodes are flat and in grooves of a cell framework in their Position to be held. 8. Electrochemical cell according to claim 7, characterized in that that the electrodes are mounted vertically, that the frame is moved vertically upwards is removable from the cell body, and that means are provided for feeding contaminated aqueous medium to the cell volume as well as to remove the treated Medium from the cell to its upper part. 9. Electrochemical cell according to claim 8, characterized in that that this is monopolar and that the electrodes are made of aluminum. 10. Electrochemical cell according to claim 6, characterized in that that the cathodes on their surfaces are aluminum, aluminum alloy, insoluble Have aluminum compound or carbon or coal.