TW200914377A - Process & apparatus - Google Patents

Abstract

A process for reducing arsenic in an acidic liquid comprising arsenic in an oxidized form, wherein the liquid is subjected to electrolysis in a single step and in a single compartment electrolytic cell using pulsed current in the presence of a conduction salt. A reference electrode comprising an electrolyte bridge made of PTFE is also discussed.

Description

200914377 IX. INSTRUCTIONS OF THE INVENTION: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method and apparatus for the removal, recovery or removal and recovery of arsenic. More specifically, the present invention relates to a method and apparatus for the removal, recovery or removal of industrial wastewater, natural water and other liquids, and for the recovery of the stone. More specifically, the present invention relates to a process for removing, recovering or removing and recovering arsenic from hydrofluoric acid. [Prior Art] Anhydrous hydrazine is generally produced by a reaction of a mixture of fluorspar and sulfuric acid. Impurities generated in the reaction include tetra-drying, sulfur dioxide, non-volatile acids such as H2S〇4 and H3P〇4, water, and arsenic. It is desirable that the product hydrogen fluoride is purified by distillation. However, the distillation method does not allow the arsenic to be separated so that the product anhydrous hydrogen fluoride still contains an unacceptable amount of schist. The anhydrous hydrogen fluoride produced by the conventional method generally contains arsenic contained in the arsenic fluorite ore from about 20 to about 600 ppm. Since anhydrous hydrogen fluoride is used as a fluorinating agent in the production of organic and inorganic chemicals, the presence of arsenic, which is a catalytic agent, can affect the efficiency of the process in which hydrogen fluoride is used and will result in reduced catalyst life. In addition, the presence of arsenic in the feed stream and/or the production stream can cause severe corrosion of the process equipment. Dilute hydrogen fluoride has many uses. For example, it is used in metal pickling and glass button engraving. Although the existence of Kun does not have a poisoning effect on these methods, 'God will exist in the effluent and therefore must deal with the waste stream to remove arsenic. Unfortunately, the treatments known are expensive. In addition to being found in fluorite, it is also present in phosphate rock. When the disk 132210.doc 200914377 acid rock is treated with sulfuric acid to produce phosphoric acid, arsenic remains as an impurity in the product acid. Thereafter, if phosphoric acid is used in foods, arsenic must be specifically removed. Fluorite (H^iF6) is produced in large quantities as a waste product during the conversion of the limestone, which is a rock of the monophosphate, to phosphoric acid. However, volatile species such as AsF3 are present in fluoroantimonic acid. Since fluoroantimonic acid is used in fluorinated drinking water, it is important to understand that arsenic removal is necessary. Fluorine acid is also used as a starting material in the production of hydrofluoric acid.水质 Water quality regulations introduced in the United States in 2006 require arsenic in water to be ppb or less. The maximum amount of arsenic present in the water is allowed to be 50 ppb prior to the introduction of these regulations. Therefore, the requirement to remove arsenic from natural or industrial water is extremely urgent and more desirable. It will therefore be appreciated that it would be desirable to provide a method for recovering and/or removing arsenic from any liquid that may contain it. Such liquids include, but are not limited to, polyhydrofluoric acid; fluoroantimonic acids such as H2SiF6 and HSiF5; phosphoric acids such as h3P〇4; water from any source such as groundwater, river water and rainwater; leachate from accumulation yards and mines And all public and industrial effluents. A variety of methods have been proposed for the removal of clocks from water, especially water used as drinking water or from industrial effluents. These known methods can be divided into physical methods, chemistry Methods, biological methods, and electrochemical methods. Physical methods; | Membrane methods such as nanofiltration, reverse osmosis, electrodialysis, and adsorption methods. Adsorption methods include methods using active image soil or ion exchange trees, although such methods are - Stones can be removed to some extent, but their 132210.doc 200914377 all have the disadvantage of producing _ shame! > 4 V" J3A, a maternal liquid effluent that must be disposed of before disposal. In this regard, please note that the waste should be neutralized and stabilized before disposal. Even after such treatment, it is carried out in the exclusive accumulation yard of the waste. High cost, and the like comprising discarding the subsequent chemical wherein using, for example, oxygen, ozone, air, gas, acid gas time -, too much salt, Fenton (FentGn) reagent or hydrogen peroxide as oxidizing agent Γ

L, :/, physical methods, these have the disadvantage of leaving toxic waste, which must be disposed of in order to safely discard such toxic waste. In addition, if these chemical methods are used in combination with the production of anhydrous fluorinated gases, the products need to be proud of the downstream, κ ^ progressive steaming. Alternative methods include co-precipitation with iron or aluminum. These methods also produce toxic waste. Give (a) instead. The biological method involves the biological treatment of 2 with a microbial cocktail. Such microorganisms are generally growth-specific and when used = toxic compounds such as hydrazine. The main disadvantage of these biological methods is their toxicity to the side, which must be treated in order to safely discard the toxic age. Another disadvantage of biological methods is that they cannot be used in an acidic environment. For the removal of slaves known to electrification method package cut three (four) Wu price Kun AS (Vp in the group to be treated) is high concentration of acid, the use of - Hyun salt conductive L has very low conductivity of the coffee view 9 she 51_39 description The heart is self-existing::Chemical# such as the electrochemical method of the shore. This method uses an electrolytic cell and a hydrogenated hydrogen fluoride under liquidity and c force (4). During the electrolysis, I32210.doc 200914377 impurities are oxidized in the hydrogenated hydrogen. In particular, _ Oxidation to a non-volatile form that remains in solution. One of the disadvantages of this method is the need to steam the anhydrous gasification gas and produce a toxic liquid waste that must be disposed of or carefully discarded. Because anhydrous hydrogen fluoride has very low conductivity, DC will be used in the case of the party * 'measuring and still 51_9 teaches should exist - electrolytes such as potassium fluoride or other alkali metal fluorides or water. In any case. τ 'DC electrolysis efficiency is poor and produced The rate is low unless electrolyte salt or water is added. Although this method will be more effective if an alternating current is used, fluorine loss will occur and the distillation residue contains hydrogen fluoride and arsenic fluoride compounds such as HAsF6. This residue must be in a specific accumulation field of toxic waste. Stabilized and discarded. An alternative method is described in EP 〇 48〇 254. A method is described here..., water fluoride is applied by applying It is electrolyzed for the current of direct current. The reaction is carried out in an inert atmosphere to prevent the accumulation of potentially explosive gases. The disadvantage of this method is that it is necessary to complicate the exhaust gas containing not only oxide but also arsenic. And expensive washing. The reaction requires the application of a voltage of up to 50 V. Therefore, the power consumption of the reaction is extremely high, making the method relatively expensive. Moreover, due to the use of a high voltage and because the method must be carried out for a relatively long period of time, Presence—the risk that no hydrogen will be decomposed into H2 and F2, which will eventually lead to fluoride loss. As with other methods, there are also problems with the co-production of toxic liquids and gaseous effluents. Must be processed before disposal. US 55 " 437 describes - electrochemical method, which uses a pulse current from 0.5 to H) 〇〇 Hz, preferably between 1 〇 and 1 〇〇 Hz and - 132210.doc 200914377 View or less, preferably a duty cycle between (4) and 5G%. This method is suitable for solutions containing electroactive chemical species such as metal ions. The cathode is configured to It has a large surface area. ^ ^ The pole is made of 1 mm or a packed bed of particles with a surface area of 80 to 1500 m2 / g ^ _ 4 g. The cathode has at least about 10,000 The roughness factor and the double hills are selectively coated with an ion-parent resin such as a perfluorinated acid ion clock ring + 卞 bond tree. The deposited metals are copper, silver, gold, zinc, nickel, mercury, lead, uranium, thorium uranium And chromium. However, due to its high oxidation potential, this method is not suitable for; ^. Bu_.

Ύ In addition, this method is not suitable for use in highly concentrated acid media. Therefore, all known methods require the preparation of additional reagents to produce a waste stream that must be disposed of or carefully discarded. Even oxidatively based electrochemical methods leave toxic waste that must be disposed of. It is therefore desirable to provide a method for removing the stone from the liquid in a manner that does not require any residual toxic waste to be treated. In particular, it is desirable to provide a method in which it is recycled in a metal form as it can then be used in a commercial product in a variety of industries. SUMMARY OF THE INVENTION Accordingly, in accordance with the present invention, there is provided a method for reducing arsenic in an acidic liquid comprising arsenic in an oxidized form, wherein the liquid is pulsed in a single compartment cell in the presence of a conductive salt It is subjected to single-step electrolysis. The so-called "acid" means that the liquid has a 1)11 value (pH value) of 0 to 8. Therefore, any As(III) in the treated liquid will be reduced according to the following reaction: 132210.doc -10· 200914377

As(III) + 3 e_ |As When it is later reduced to the above As metal, any As(V) present in the treated liquid will be reduced to As(III), but this is all A single step reaction. The conductive salt also acts to depolarize the anode, and this minimizes or preferably prevents reoxidation of any As(III) to As(V) of the anode. Therefore, in the method of the present invention, the balance of the redox system is favorable

Replace the As metal of the most unstable thermodynamic species. Similarly, this method facilitates the slowest reaction, i.e., reduction, rather than the fastest kinetic reaction. It will be appreciated that one of the advantages of the present invention is that it can be easily isolated and recovered due to the reduction of arsenic to a metallic state. The arsenic in this state can be recycled as a commercial product suitable for industrial use. Such uses include doping in the microelectronics industry. The ability to recover and subsequently use arsenic means that the process of the present invention is particularly economically attractive. Another advantage of the present invention is that, in addition to the desired arsenic metal, no waste that must be safely disposed of or discarded is produced. The method of the present invention can be adapted to remove any concentration of arsenic in the liquid being treated, such as from tens of percent, e.g., 2% to traces, such as parts per trillion. The liquid itself can be electrically conductive. However, a liquid having a low or very low conductivity potential can be subjected to the method of the present invention due to the presence of a conductive salt. In a preferred embodiment of the invention, the method is carried out in the presence of a reference electrode. . Conductive salts of the redox potential of the standard hydrogen electrode (NHE) phase V. Any suitable conductive salt can be used, having a purity of from about 0.6 V to about -1.8 132210.doc 200914377 The most suitable salts include barium peroxide and barium. Derivative products such as barium fluoride, N2H4F, barium sulfate, barium nitrate, barium phosphate and barium hydroxide, of which fluorination is the best. Typically, <=*, the phosphonium salt is selected such that it is suitable for the medium being treated without leaving any additional impurities. Therefore, the substance to be treated is fluorinated with hydrogen fluoride, and is ideal for H3P〇4 lanthanum phosphate, and for H2S〇4 barium sulfate. Without being bound by any theory, it is believed that the conductance of the salt will increase the conductivity of the medium from which the electrolysis will occur. According to the Pourbaix diagram, it is important to increase the conductivity of the medium in order to maintain the oxidation-reduction potential in the stable region. In addition, the conductive salt acts as a depolarizing anode to prevent accidental oxidation of the anode. Another advantage attributed to the conductive salt is that it does not contaminate the solution with impurities and does not produce liquid or gaseous toxic waste. This is because the conductive salt is consumed during electrolysis and thus disappears from the liquid at the end of the operation. Preferably, the reactions of the present invention provide products that are neither toxic nor unexpected. Therefore, this method does not cause toxic substances released into the environment. For example, when 2 is a conductive salt, the product will be volatile nitrogen and hydrogenated hydrogen remaining in the reaction mixture, wherein the liquid system being treated is fluorinated. Any suitable amount of conductive salt can be added to the liquid being treated. The amount of conductive salt added in the -good configuration is dosed according to the amount that will be completely consumed at the end of the electrolysis reaction. Conductive salts are generally degradable and do not leave contaminants in the liquid that require further purification. The current applied to the tank is a pulse current. Without being bound by any theory 132210.doc •12- 200914377, it should be understood that strong acids are usually good electrical conductors. However, the chlorine acid is a weak acid, i.e., it has a low dissociation constant and thus it has extremely low conductivity at a high concentration. While some of the prior art methods suggest the use of pulsed currents, the efficiency of the reduction by Shishen in these prior art methods is poor. In this regard, please note that the slowest metal of all metals in the Shishen system in electrochemical deposition. However, in the present invention, the presence of a conductive salt overcomes several disadvantages of the prior art methods because the conductive salt also functions as a ruthenium oxidation inhibitor. The method of the present invention is thus effectively implemented using pulse current γ. The pulse current can be sinusoidal, square or digonal. The current can be symmetrical or asymmetrical. In a preferred configuration, a negative asymmetrical current is used. Any suitable current can be used. The current frequency can range from 0 to about 2_, where the frequency is approximately the best in the fine area. The duty cycle, also known as the cycle ratio, can vary between 〇 and 嶋, but is preferably from about 5 至 to about 75%. 1 A method of the invention can be used to treat any liquid containing shishen. However, in an example towel, the liquid energy of the package cut is (iv) hydrogen. Hydrogen can be undiluted == any concentration present in the aqueous solution. Under the use of undiluted house-: and brother, the electrolysis will be carried out under conditions and pressures that allow the hydrogen to be in a liquid state. Contains =: = in the treatment of fluorite, acid (including its various forms), and " text, acid mixture, acidic or neutral effluent. The β-hai method can be implemented in a continuous, continuous or batch process. The degree of electrolysis is selected to be the most suitable for electrolysis. The appropriate temperature 132210.doc -13· 200914377 degrees l is from about -60 C and about 1 〇 (temperature between TC. The optimum temperature is from about 7 ° C to about i 4 ° C. The temperature of the system can be used by any A suitable method is used to control. In one configuration, the temperature can be controlled by the circulation of the cooling liquid. In the case where the electrolytic cell has a double-layered shell, the cooling liquid is generally uncovered in the space inside the double-shell. It is also typically used to control the liquid in the storage vessel and to the exhaust gas condenser.

The method can be carried out in any suitable device. The electrolytic cell can be made of any suitable material as long as it is resistant to the composition being treated. Suitable materials include plastics such as fluoropolymers such as polyvinylidene chloride, polytetramethylene and the like. Suitable alternative materials include metals such as phono, mis, silver, platinum, stainless steel, nickel alloys, chromium, and combinations thereof. The tank that can be used for electrolysis in the eighth can be configured as appropriate. For example, it can be cylindrical, parallelepiped, spiral or tube bundle. . It is suitable for propagation in the process of the invention. Appropriate material... Made from any suitable material: = (4) Includes no money for steel, gold, steel or carbon. These can be used by Cui. In the case of the use of carbon ^ U-JO. For its various formulas, it can be its glassy form of graphite, all-gear = gemstone and the like. In the -configuration, the anode can be a carbon = and the cathode can be accompanied by a copper-free electrode with 1 , / /. The stainless steel cathode can be protected by metal stone. This is an ultra-pure vaporized ammonia used in the microelectronics industry to prevent contamination of the solution: the :: method is especially important. In the case where the nail is removed, this can also be used with a reference Thunder ^ ^ test electrode. The reference electrode can be made of any suitable material, I32210.doc 200914377, and made of a material suitable for tolerating corrosive solutions. Tetrafluoroethylene or other fluoropolymer. to make. However, the appropriate material is a reference electrode that is a ship and has a stable and fixed potential and thus allows for adjustment: the presence of a cathodic electrical t-pole that changes with the altered ion concentration during deposition. Keep the potential_ straight in the formation of As metal, the day 4 ancient H, 夂 listed in the Pourbaix diagram. It should be understood that the reduction of Kun into a gas pure 3 system is not expected. Should

The electrodes can be of any suitable configuration. For example, they may be flat plates, and the like may be another configuration including a cylindrical shape, a tubular shape, or a spiral shape. For no configuration, the electrodes can be porous or non-porous. In addition, the electrodes may be formed of spherical ions. The device can include a pulse generator. The generator provides an asymmetric pulse in the form of a rectangle that allows the commutation of the duty cycle. As indicated above, any suitable tj > test electrode can be used. The conventional reference electrode is made of a ceramic film which can be called tantalum. This membrane acts as an electrolyte bridge. "As most of the Tao Jing materials contain Si〇2', they are not resistant to hydrofluoric acid. In addition, most of the materials will be invaded by hydrofluoric acid and will be contaminated by hydrofluoric acid. To overcome these difficulties, An improved reference electrode has been provided. Thus, in accordance with the second aspect of the present invention, a reference electrode having a new design is provided which allows for extremely fine control of the electrochemical cell and overcomes In a preferred embodiment of the second aspect of the invention, the reference electrode comprises an electrolytic f-bridge made of PTFE. The bridge may comprise a conjunctiva produced by the foot! Any porous material that is resistant to hydrogenation in the acidic environment 132210.doc 15 200914377. Suitable resistance materials include sapphire or Ti〇2. The naf leg is a trademark of DuPont. The first aspect of this month The use of the second embodiment of the reference electrode of the present invention allows fine control of the electrochemical cell. The size of the trench and the pitch of the electrodes will be well known to those skilled in the art as being suitable for the liquid being processed. However, 'electrode The distance between them is in the range of about 0.1 mm to about 1000 mm. The liquid to be treated is generally pumped through the electrolytic cell. The pump can be a thin film pump. The speed is generally chosen to be compatible with the reduction rate of the arsenic of the electrode. Speeds that can be used at any suitable speed include speeds within the range of _. In particular, speeds can be within _.

The cathode (4) is set and controlled to allow the ions to be reduced to a metallic state. For an acidic medium, a potential in the range of from about +0. 3 to about _〇·6 VANHE can be used, with a standard hydrogen electrode being deleted. For a neutral medium, a potential in the range of about _0.24 to about _丨v/nhe can be used. An appropriate potential for any alkaline medium that can be used can be calculated from the P〇urbaix plot. In any case, the potential is set to avoid the formation of arsenic because of the extremely toxic gas of arsenic. A reference electrode can be used as described above. The potential control will be done using three electrodes. The measurement of the operating potential will be made between the reference electrode and the cathode. The adjustment of the cathode potential can be carried out by increasing or decreasing the potential difference Δυ between the cathode and the anode. In this mode, the anode acts as the auxiliary electrode and reaches the ionic potential of arsenic. By maintaining the current to the same current as when the positive potential is reached, 132210.doc -16- 200914377 * Change to the constant current full navigation mode (Aamperostaticspiloting m〇de). First, in batch operation, electrode deposition is performed at a constant voltage that operates at a constant potential until the diffusion limit of the medium is reached. This can be observed by the reduction in current Z. To overcome the concentration limit, the voltage is then increased and the current remains constant, which is the constant current operation mentioned above. The method of the present invention allows for the incorporation of a gas such as 4 to avoid full condensation. It has been confirmed that the method of the present invention can be integrated into a knife of another production implement or it can be provided as a mobile component for single or temporary operation. The invention will now be described, by way of example, with reference to certain drawings. [Embodiment] The electrolytic cell in which the electrochemical method of the present invention can be carried out is shown in Fig. i. The tank 1 comprises a gold plate suitable for the pole and a copper plate tank 1 suitable for the cathode, which is connected to a double wall electrolyte reservoir 2 by means of a polysilicon tube, in which the liquid is uniformly cooled. Circulate at a controlled temperature. A reference electrode 3 is immersed in the electrolyte reservoir. The fluoropolymer film pump 4 circulates the electrolyte to be purified in a loop between the tank and the reservoir. An inert flushing gas, such as nitrogen, is blown onto the electrolyte surface in the trap. The mouse flows through a colder 5 and an alkaline absorber before being discharged to the suction hood. The tank 1 is placed in a cooling vessel to maintain its temperature. An adjustable pulse current power generator 6 is connected to an A3 electrode. 132210.doc -17· These examples should not be

In 200914377 and other institutions (A3 electrode setups). One quintal for 4± test electrode bee ^_7 money is connected between the parameters, and an ammeter 8 is connected to the circuit. P is carried out by electrolysis, and the reduced arsenic partially sinks U rr ^ L, which is only in the liquid or in the electrode to form a deposit. Subsequent arsenic can be removed by any suitable method. Although methods include separation techniques such as filtration. The method of the present invention will now be described with reference to the following examples as a limitation. Examples 1 and 2 perform U secondary operation using AC power. In each operation, an electrolyzer equipped with a gold-plated stainless steel anode and a copper cathode was circulated with about 400 g of anhydrous hydrogen fluoride at a rate of 12 丨/m. The surface area of the anode and cathode is 0.5 dm2. The electrodes were set such that they were separated by approximately 2 mm ° for each run to determine the respective starting concentrations of arsenic impurities. Conductive salts are added to the solution. The temperature of the first run tank is 7 to 1)1, and the temperature of the second run tank is 9 to 14. (: The voltage of the AC is adjusted using a power generator' and allows the current to continue to run for the time listed in Table 1. The frequency is set to 200 kHz and the cycle ratio is 75%. The operating mode is constant current. The same data of the liquid was analyzed. The data corresponding to the analysis before the respective electrolytic reduction and the liquid analysis after the electrolytic reduction are listed in Table 1 〇132210.doc -18- 200914377 Operation time (h) | AC voltage temperature. As ppm begins at the end of As ppm As ppm 1 conversion % 1 72 1.3-9.1 ^7-12 106 "2.5 98 2 30 2.2-4 9-14 144 4 97 Increasing the run time will increase the conversion rate. In the - alternative configuration The running time can be reduced by using a larger surface area electrode.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a drawing suitable for a suitable electrolysis cell of the present invention; and Figure 2 is a reference electrode in accordance with a second aspect of the present invention. [Main component symbol description] 1 Electrolyzer 2 Double-wall electrolyte reservoir 3 Reference electrode 4 Membrane pump 5 Condenser 6 Pulse current power generator 7 millivoltmeter 8 ammeter 132210.doc •19-

Claims (1)

200914377 X. Patent application scope: 1 'A method for reducing arsenic in an acidic liquid containing an oxidized form of arsenic' wherein the liquid is subjected to a single-step electrolysis in a compartment electrolyzer using a pulsed current in the presence of a conducting salt . 2. The method of claim 1, wherein the conductive salt is barium fluoride, barium sulfate, strontium nitrate, hydrogen peroxide or hydrogen peroxide. 3. The method of claim 2, wherein the conductive salt is cesium fluoride. 4. The method of any one of claims 1 to 3, wherein the conductive salt is added in an amount such that f) is completely consumed at the end of electrolysis. 5. The method of any one of 3, wherein the conductive salt is degraded and does not contaminate the liquid. 6. The method of claim 1, wherein the current frequency is from about kHz to about kHz 7. The method of claim 6, wherein the current frequency is about kHz. 8. The method of any one of the preceding claims, wherein one of the duty cycles is from 100 〇 to 〇. The method of claim 8, wherein the working cycle is from about 50 to about 75%. The method of any one of claims 3 to 3, wherein the liquid containing arsenic is hydrogenated hydrogen or fluoroquinone The method of any one of the above-mentioned items, wherein the electrolysis system is carried out at a temperature of from about -6 〇 ° c to about 1 〇〇 (: at a temperature of 12.) The method of any one of claims 1 to 3, wherein a reference electrode is used, wherein a reference electrode is used, wherein the electrolysis system is carried out at a temperature of from about 7. It comprises an electrolyte bridge made of PTFE. 15. The reference electrode of claim 14, wherein the bridge comprises a by NAFION Ti02 prepared sapphire or conjunctiva. 132210.doc -2-