US3718729A - Defluorination of wet process phosphoric acid - Google Patents

Defluorination of wet process phosphoric acid Download PDF

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US3718729A
US3718729A US00124099A US3718729DA US3718729A US 3718729 A US3718729 A US 3718729A US 00124099 A US00124099 A US 00124099A US 3718729D A US3718729D A US 3718729DA US 3718729 A US3718729 A US 3718729A
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acid
percent
silica
defluorination
process according
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A Amin
R Bristow
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Occidental Chemical Corp
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American Cyanamid Co
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/234—Purification; Stabilisation; Concentration
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/234—Purification; Stabilisation; Concentration
    • C01B25/237—Selective elimination of impurities
    • C01B25/2372—Anionic impurities, e.g. silica or boron compounds
    • C01B25/2375—Fluoride or fluosilicate anion
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/08—Compounds containing halogen

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  • ASHOK BABUBHA/ AM/A/ ROBE/PT LEE BR/STUW BYWQW ATTORNEY PATENTEDFEBZTIQYS 3718'729 snzjl'I 12 0F 1 l 4 5 6 7 a 9 /0 '2', PER HOUR INVENTORS.
  • the present invention concerns a process for defluorinating wet process phosphoric acid which contains dissolved aluminum.
  • defluorination of wet process phosphoric acid containing undesirable amounts of fluorine can be achieved by admixing the acid with an amount of silica at least about stoichiometrically equivalent to the fluorine to be removed therefrom and heating the silica acid mixture in the range of from about 75 C. to about l05 C. but below the boiling point of the mixture. Removal of fluorine as SiF, is then achieved by establishing a gas-liquid interface with the heated mixture wherein said interface is sufficient to establish a stripping ratio of from about 0.5 to about 20. The vaporized Sil is thereafter removed from the presence of the acid mixture while maintaining its tem perature above the condensation temperature of SiF,.
  • reaction scheme which prevails where silica is added to wet process phosphoric acid containing from about 0.8 percent to about 2.2 percent or higher by weight of dissolved aluminum can be expressed by the following reaction scheme:
  • ZAIF an 2 2A1+ 2H,F, l.
  • Equation I shows the concentration of dissolved silicon, denoted by X, at a very low level, whereby the total value of the term k [Al X is minimized.
  • the preferred level of silicon concentration is expressed by the ratio: (wt. %F/wt. %Si) Since dissolved Si concentration is inversely proportional to the degree of stripping, there is a preferred or critical degree of stripping which corresponds to the preferred or critical range of silicon concentration. The degree of stripping is indicated by the ratio; mn/M (called the stripping ratio herein).
  • the SiF stripping can be conveniently achieved by one of three methods.
  • the first method of the present invention involves the mass transfer of acid by spraying into a current of inert gas. This can be achieved, for example, by
  • the second process involves the use of sparging with a current of inert gas whereby the gas bubbles are sufficiently small size to establish the previously indicated stripping ratio.
  • This can be achieved by introducing a stream of gas at the base of a high speed turbine blade stirrer such as that described in FIG. 1 of the attached drawings.
  • M is the total volume of acid to be defluorinated
  • m is the volume being contacted with air per hour
  • n is the fraction of dissolved silicon removed from the acid m by stripping. It is obvious that the values of n can range from O to 1 depending on the acid/gas interface area which has been created.
  • the third process which can be employed in the practice of the present invention employs a combination of sparging with an inert gas and an acid spray recycle as described in methods one and two above.
  • the instantaneous defluorination rate is related to the dissolved silicon concentration and the stripping ratio.
  • the amount of fluorine which is transferred to the inert gas in a recycle spraying process such as that described above must be equal to the amount of fluorine lost by the acid. This can be expressed by the following equations:
  • Equation 3 is a general expression which can be used in the analysis of both the spraying, sparging and spraying-sparging methods described above. In the sparging type procedures, where it is not physically possible to measure the stripping ratio, it can be determined by the use of these equations, by measuring the rate of defluorination and dissolved silicon concentration at any given time.
  • Equation 4 The defluorination of wet process phosphoric acid containing high concentrations of aluminum can further be described by Equation 4 below. This equation is derived by means of the kinetic Equation 1 above and the material balances of the process. The equation is as follows:
  • Equation 4 The concentration of dissolved silicon can be expressed using a derivation of Equation 2 above:
  • Equation 6 The value of the reverse reaction rate constant k; is found by measuring dF/dt, d F/dt and X at any given time from the start of the defluorination and then employing this data in Equations 3 and 4 above. The data obtained by experimental defluorination and computer simulated runs is in very close agreement.
  • the preferred quantity of silica employed in the practice of the present invention is from about 0.8 to about 2.0 pounds of silica per pound of fluorine contained in the acid to be defluorinated. It is also preferred to employ silica having a surface area from about 10 to about 500 square meters per gram. It is generally preferred to employ diatomaceous silica or spraydried silica gel as the silica source.
  • the preferred inert gas is air; however, other inert gases such as carbon dioxide, nitrogen, argon and the like may be employed in lieu thereof or in combination therewith.
  • FIG. 1 is a diagrammatic representation of a sparging apparatus suitable for use in the defluorination of the present invention.
  • FIG. 2 is a diagrammatic representation of a spraying apparatus which is suitable for use in the practice of the present invention.
  • a suitable apparatus suitable for conducting the spray-sparge process of the present invention may be envisioned as an embodiment of both the spraying elements of FIG. 2 and the sparging elements of FIG. 1.
  • FIG. 1 it can be seen that the defluorination is effected in an insulated reactor 1 adapted to receive a stream of stripping air through conduit 2 which is optionally heated by means of the heat exchanger 3.
  • the conduit is adapted to discharge the air stream beneath the motor driven turbine blade agitator 4 whereby said air stream is dispersed throughout the wet process phosphoric acid contained in the reactor in the form of minute air bubbles.
  • the reactor is further equipped with a valved air port 5 to allow air to be drawn through the reactor above the acid surface to strip the dispersed acid droplets and an exit port 7 to permit withdrawal from the reactor of the fluorine containing gases which have been stripped from said acid droplets. Withdrawal is achieved by actuation of the blower 9.
  • the reactor is further equipped with insulation 8 to aid in the maintaining of the phosphoric acid temperature and heating means, such as, tracing 6, in the reactor dome and exhaust conduit to permit heating of the vessel walls in contact with the fluorine containing gases to a temperature above the condensation temperature or dew point of said gases.
  • the reactor is also equipped with a means for circulating the acid mixture to facilitate the mixing of the acid, silica and air and to permit the maintenance of proper temperature for the acid defluorination process.
  • a conduit 16 having its inlet orifice disposed in the bottom of the reactor is equipped with a circulation pump 17 of such capacity to provide a recirculation rate of at least about 3 percent per minute, and preferably, between about 3 percent and percent per minute of the total acid mixture under treatment.
  • conduit 16 is equipped with a valve adapted to permit the flow of the acid through heat exchanger 19 whereby the temperature of the recirculating acid may be adjusted as desired prior to the reintroduction of the acid to the reactor via conduit 20.
  • the valve 18 is further adapted to permit withdrawal of the defluorinated acid through conduit 21 into storage tank 22 from which it may be withdrawn through conduit 23 by opening valve 24.
  • removal of the fluorine-containing gases is effected by actuation of blower 9.
  • said blower may be vented into the atmosphere without disruption of the process of the present invention. It is preferred to exhaust the fluorine-containing gases into a scrubbing tower 10 to prevent atmosphere contamination and to recover the fluorine-containing compounds.
  • silica In operation of the apparatus of FIG. 1, it is generally preferred to charge about 1.1 pound or a slight stoichiometric excess of silica per pound of fluorine contained in the acid to be defluorinated.
  • Diatomaceous silica or spray-dried silica gel having a surface area betweenabout l0 and about 500 square meters per gram and preferably between 10 and square meters per gram is employed as preferred silica sources.
  • the silica may be charged through port 5 or other suitable conduit (not shown).
  • the wet process phosphoric acid which is also charged into the vessel through port 5 or other suitable conduit (not shown) has a P 0 content between about percent and 62 percent with a preferred range of from about percent to about 54 percent with a fluorine content of from about 0.3 percent to about 3.0 percent.
  • the percent of dissolved aluminum generally expressed as aluminum oxide, will typically be in the range of from about 0.8 percent to about 2.2 percent. In each case, the percents indicated are by weight.
  • the acid feed is generally maintained at a temperature of from about 75 C. to about 105 C. but below the boiling point of said acid. It is generally preferred to employ a sparging air stream having a temperature of between about 24 C. and about 105 C.
  • the sparging gas at a rate of from about 1 to about 5 cubic feet of air per minute per ton of acid to be defluorinated; however, depending on such factors as the acid impurities, the P,O, aluminum and fluorine content, the temperature, degree of agitation, silica concentration and its solubility in the acid, as little as about 0.5 or as much as about 10.0 cubic feet of air per minute per ton of acid may be required to establish the indicated stripping rate for the defluorination of the present invention.
  • shut down of the reactor can generally be avoided by directing a stream of recycled acid from conduit 20 onto the acid surface.
  • An unexpected degree of inhibition of the defluorination is caused by failure to maintain the interior surfaces of the reactor dome at temperatures above the dew point of the effluent gas, i.e., above about C. Where insufficiently high temperatures are achieved, the SiF, condenses on the reactor walls where it decomposes to SiO and HF by reaction with water vapor.
  • Heating of the reactor dome may be achieved by any convenient means as, for example, by electrical heating elements or by passage of hot gases through conduits provided within the reactor walls.
  • FIG. 2 illustrates another type of air-acid contacting vessel which may be utilized in the defluorination process of the present invention.
  • the wet process phosphoric acid to be defluorinated is charged through inlet 28 into holding tank 29.
  • the acid is then delivered to the insulated reactor 25 through conduit 30 by gravity or pump means herein not shown.
  • Acid circulation rate is approximately 7 percent to 10 percent per minute of total acid tonage being treated. Shorter defluorination time can be achieved by increasing the recycle rate. Recycle rates below 3 percent result in impractical high defluorination times.
  • Diatomaceous silica or spray dried silica gel having a surface area of about 15 to about 30 sq. m/gram for the diatomaceous silica or about 320 to about 500 sq. mlgrarn for the silica gel is introduced through conduit 53 into vessel 52 which is equipped with a motor driven agitator 51.
  • the vessel is then charged with phosphoric acid through conduit 50 connected to the acid recirculating line.
  • the acid/silica mixture is pumped into reactor 25 either via conduit 49 through circulating pump 46, conduit 47, holding tank 29 and conduit 30 or through the circuit which includes conduit 45 and circulating pump 43, etc.
  • Silicon tetrafluoride is released from the acid in reactor 25 and the mixing vessel 52. It is then withdrawn from said vessels through the insulated and traced conduits 33, 55 to the gas scrubber inlet 56.
  • the insulation and tracing prevent decomposition of SiF, on the walls of the exhaust conduit and refluxing of the fluorine into the acid.
  • approximately 2 to 16 cubic feet of air per minute per ton of acid is utilized for the air stripping. If the specific velocity of stripping gas drawn through the system is excessive acid mist is entrapped in the effluent gas and the fluorosilicic acid obtained by aqueous scrubbing of the gases is contaminated and valueless.
  • scrubbing tower 57 with air scrubbed with an aqueous solution of fluorosilicic acid introduced through conduit 58 and sprayed over the gas stream by means of nozzles 59.
  • the sprayed acid is recirculated from tower 57 via conduit 62 and holding tank 63, conduit 64, recirculating pump 65.
  • the scrubbed exhaust gases exit through conduit 60 through port 61 into a second scrubbing tower 67.
  • the gases are scrubbed with a stream of fresh water which enter the tower via conduit 68 and is sprayed over the gases with nozzles 69.
  • the rescrubbed gases exit through conduit 70 with the assistance of exhaust fan 71, whereafter the purified exhaust gases are admitted into the atmosphere via exhaust port 72.
  • the fluorosilicic acid scrubbing solution from the second tower is returned to holding tank 63 via conduit 73 whereafter it is recirculated through the first scrubbing tower 57.
  • the fluorosilicic acid concentration in the scrubbing unit reaches about 20 to about 25 percent, it is withdrawn from the system through conduit 66 by opening a valve therein (not shown).
  • the acid withdrawn therefrom may be marketed as such or subject to further treatment.
  • Reaction temperature of the wet process phosphoric acid in vessel 25 is maintained by insulation 26 up to acid level. Decomposition of the SiF is prevented by the heating means 27 such as electric tracing or conduits within the wall through which hot fluids or gases are passed in the reactor dome and gas exit lines. In the mixing vessel 52 heating means 54 are only required in the dome to prevent condensation or refluxing of the SiF, formed.
  • the air inlet of the reaction vessel 74 may optionally be equipped with a heating means (unshown) to assist in maintaining the reaction temperature. As previously stated, the contents of the reaction vessel are primarily heated by the heat exchange 36. This can be done by passing steam through conduit 37 and valve 39 and out a steam exit conduit 38.
  • Control of the steam flow and thus the reaction temperature can be automatically achieved by means of a temperature recording controlling device 40.
  • This device can be positioned in conduit 34 which is adapted within the reaction vessel 25 to optionally permit the introduction of steam or an air stream into the reaction vessel by opening valve 39 and/or other valve means (unshown).
  • the defluorinated acid can be supplied to a car loading station or storage vessel 48 by actuating pump 46 and opening a valve means (unshown) into vessel 48.
  • EXAMPLE 1 A 4,000 gram sample of wet process phosphoric acid containing 1.46% A1 and 0.85% F was defluorinated at 85 C. in an air sparged vessel, fitted with a 2 inch diameter turbine rotating at a speed of 350 RPM. A stoichiometric amount of diatomaceous earth was added. The air spraying rate was 0.5 liters per minute.
  • Equations 3 and 4 the values of the stripping ratio mn/M and the reverse reaction rate constant k; were then calculated to be 1.54 and 12.2, respectively.
  • EXAMPLE 2 A defluorination run similar to the above was carried out at 105 C. using a wet process acid containing 1.48% A1 0 and 1.03% F. From the defluorination kinetic data dF/dt and a! at time t 1 hour were calculated. The value of k, 1.45 at 105 C. was obtained from a separately carried out defluorination run in which an extremely high stripping ratio was employed. From these data, the values of k;, and mn/M were calculated to be 468 and 3.334, respectively.
  • FIG. 12 was plotted. This plot shows the criticality of the stripping ratio and the ratio of F /Si in the acid, on the defluorination time.
  • FIG. 3 shows the defluorination kinetic data from several runs in which wet process phosphoric acid containing various A1 0 concentrations was defluorinated at a stripping ratio of about 6 and a temperature of about 85 C.
  • FIG. 4 shows three simulated defluorinations carried out with the use of the analog computer as previously described for the acid compositions and operating conditions of Example 1, except that the stripping ratios were changed.
  • Run A was carried out at a stripping ratio of 0.15; Run B at a stripping ratio of 0.5; and, Run C at a stripping ratio of 15.43.
  • the defluorination times required to reduce the fluorine concentrations in the acids to 0.2 percent in Run C and Run B were 3.6 hours and 19 hours, respectively; whereas, the fluorine concentration of the acid at 20 hours time in Run A was still only 0.35percent.
  • EXAMPLE 5 This batch defluorination run using the process of the present invention was carried out to show the importance of dissolved silicon concentration levels on defluorination rates at two different stripping ratios. During the first 1.5 hours of the run, high stripping ratio of 25 was used. In the rest of the batch run, the stripping ratio was decreased to 0.3 by reducing the agitator speed from 1,800 RPM to 60 RPM.
  • the defluorination was carried out on a 4,000 gm. acid sample employing a 0.5 liter/min. air rate and a reaction temperature of 85 C.
  • the A1 concentration was 1.46 percent.
  • FIG. 6 graphically shows how the decrease in rate of fluorine removal and increase in concentration of dissolved silicon is effected.
  • EXAMPLE 7 The following tests demonstrate the necessity for providing the reactor dome, etc. with an additional heating means to avoid condensation and decomposition of SiF on the surfacesthereof.
  • EXAMPLE 9 Effects of Air Rate and Tip-Speed of the Impeller on Defluorination 1n the following tests 2.7 liters of wet process phosphoric acid, sp.g. 1.69, was placed in a 4-liter flask equipped with (1) an impeller driven by a variable speed motor, (2) an air sparger and (3) a heating mantle. The acid analyzed 53.3% P O 0.64% F, 1.08% Al O 1.61% Fe O 2.00% S0 and contained 1.57 percent solids. The acid was heated in all tests to 85 C. and maintained at this temperature during treatments. Results obtained are set forth in Table IV below.
  • Defluorination experiments on larger scale were carried out using 400 to 500 gallons of wet-process acid.
  • the agitator was a four-bladed turbine type with one horsepower motor.
  • Diatomaceous earth was added in the amount of 1 lb. per lb. of fluorine in the acid. All experiments were carried out at 85 C.
  • the agitator tip speed was ft/sec. The results are set forth in Table V below.
  • Pore V01. 2.4 0.64 0.2 5.0
  • Pore V01. 1 .0 0.64 0.2 6.0
  • EXAMPLE 12 In the following tests wet process phosphoric acid having from 0.64 percent to 1.33 percent fluorine, 1.08% to 2.66% A1 0 and from 48.2% to 54.52% P 0 was treated with a stoichiometric amount of silicic material selected from the group consisting of diatomaceous silica, amorphous silica, ground sand and sodium silicate. The mixtures were heated to about 85 C. and treated with (1) air sparged into the reactor beneath the acid surface, (2) air passed through the acid in a packed column or (3) by recirculating the acid from the reactor and spraying it as time droplets over the surface of the acid in the reactor.
  • silicic material selected from the group consisting of diatomaceous silica, amorphous silica, ground sand and sodium silicate.
  • a process for the formation of phosphoric acid having a P/F weight ratio equal to or greater than 100 from wet process phosphoric acid containing an undesirable amount of fluorine as aluminum fluoride complexes, from about 0.8 percent by weight to about 2.2 percent by weight of dissolved aluminum and a P 0,, percent by weight of from about 45 percent to about 62 percent comprising the steps of a. admixing said wet process acid with an amount of silica at least about stoichiometrically equivalent to the fluorine to be removed therefrom;
  • a process according to claim 1" wherein volatilizing the SiF is effected by acid spraying employingabout 2 to 16 cubic feet of air per minute per ton of heated mixture.
  • silica is selected from the group consisting of diatomaceous silica having a surface area of from about to about 30 sq.m.lgram and spray dried silica gel having a surface area of from about 320 to about 500 sq.m.lgram.
  • a process according to claim 1 wherein the volatilizing of the SiF, is effected by air sparging employing from about 0.5 to about 10 cubic feet of air per minute per ton of heated mixture.
  • volatilizing of the SiF. is effected by air sparging employing from about 1 to about 5 cubic feet of air per minute per ton of heated mixture.
  • silica is selected from the group consisting of diatomaceous silica or spray dried silica gel wherein the surface area of the silica is in the range of between 10 and 40 sq.m.lgram.
  • a process for the defluorination of wet process phosphoric acid containing from about 0.3 percent to about 3 percent by weight of fluorine as aluminum fluoride complexes, from about 0.8 percent by weight to about 2.2 percent by weight of dissolved aluminum and a P 0 percent by weight of from about 45 percent to about 62 percent comprising the steps of:

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4083937A (en) * 1974-07-09 1978-04-11 Toyo Soda Manufacturing Co., Ltd. Process for preparing pure phosphoric acid
US4086069A (en) * 1975-02-25 1978-04-25 Prorea S.A. Method for simultaneously concentrating and purifying phosphoric acid
US4377560A (en) * 1981-07-13 1983-03-22 Occidental Research Corporation Process for producing low aluminum content phosphoric acid from high aluminum matrix
US5002744A (en) * 1990-05-11 1991-03-26 Imc Fertilizer, Inc. Method for defluorinating wet process phosphoric acid
CN115285954A (zh) * 2022-08-12 2022-11-04 宜都兴发化工有限公司 一种提高湿法磷酸生产浓缩工段氟收率的方法

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS516894A (en) * 1974-07-09 1976-01-20 Toyo Soda Mfg Co Ltd Seiseirinsanno seizoho
DE2938850B1 (de) * 1979-09-26 1980-06-26 Uhde Gmbh Verfahren zur Entfluorierung von Phosphorsaeure
US5236679A (en) * 1992-05-06 1993-08-17 Freeport-Mcmoran Resource Partners Removal of aluminum contamination during production of phosphoric acid
CN110467166A (zh) * 2019-09-20 2019-11-19 瓮福达州化工有限责任公司 一种湿法磷酸脱氟方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2933372A (en) * 1956-11-02 1960-04-19 Int Minerals & Chem Corp Method of defluorinating phosphatic material
US2987376A (en) * 1956-12-27 1961-06-06 Int Minerals & Chem Corp Method for defluorination of phosphoric acid
US3151941A (en) * 1960-05-02 1964-10-06 Smith Douglass Company Inc Defluorination of peosphoric acid
US3193351A (en) * 1961-07-05 1965-07-06 Nat Distillers Chem Corp Removal of fluorine from wet process prosphoric acid
FR1456263A (fr) * 1964-11-30 1966-10-21 Eerste Nl Cooperatieve Kunstme Procédé de défluoration de l'acide phosphorique

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2933372A (en) * 1956-11-02 1960-04-19 Int Minerals & Chem Corp Method of defluorinating phosphatic material
US2987376A (en) * 1956-12-27 1961-06-06 Int Minerals & Chem Corp Method for defluorination of phosphoric acid
US3151941A (en) * 1960-05-02 1964-10-06 Smith Douglass Company Inc Defluorination of peosphoric acid
US3193351A (en) * 1961-07-05 1965-07-06 Nat Distillers Chem Corp Removal of fluorine from wet process prosphoric acid
FR1456263A (fr) * 1964-11-30 1966-10-21 Eerste Nl Cooperatieve Kunstme Procédé de défluoration de l'acide phosphorique

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4083937A (en) * 1974-07-09 1978-04-11 Toyo Soda Manufacturing Co., Ltd. Process for preparing pure phosphoric acid
US4086069A (en) * 1975-02-25 1978-04-25 Prorea S.A. Method for simultaneously concentrating and purifying phosphoric acid
US4377560A (en) * 1981-07-13 1983-03-22 Occidental Research Corporation Process for producing low aluminum content phosphoric acid from high aluminum matrix
US5002744A (en) * 1990-05-11 1991-03-26 Imc Fertilizer, Inc. Method for defluorinating wet process phosphoric acid
CN115285954A (zh) * 2022-08-12 2022-11-04 宜都兴发化工有限公司 一种提高湿法磷酸生产浓缩工段氟收率的方法
CN115285954B (zh) * 2022-08-12 2023-10-27 宜都兴发化工有限公司 一种提高湿法磷酸生产浓缩工段氟收率的方法

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IT954349B (it) 1973-08-30
ZA72647B (en) 1972-10-25
GB1383832A (en) 1974-02-12
DE2212576A1 (de) 1972-09-21
AU3865272A (en) 1973-08-09
AU462975B2 (en) 1975-06-26

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