June, 1924
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Continuous Process for Manufacture of Sodium Tungstate and Tungstic Acid from Wolframite' By N. T. Gordon2 and A. F. Spring3 NATIONAL LAMPWORKS,GENERALEWCTRICCo.,CLBVELAND, OHIO
V
ARJOUS methods for An examination of Plates I , 2, 3, and 4 will present a unified uiew m i x t u r e has been the the extraction of of the uarious operations and emphasize the continuous production method most widely used tungstic oxide from in the Preparation of tungprinciple. The fusion mixture is prepared f r o m wolframite ore, wolframite Ores have been stic acid, and it is still in conueyed automatically to the rotary fusion furnace, and the fused suggested and Patented, mass discharged continuously info the lixiviat ing tank. The sodium favor in many but in general they may be The preparation of tungtungstate ihus formed is separated from the residue by a rotary includedin three classes: (1) sten metal used in the infilter and used either for the continuous precipitation of tungstic acid acid treatment of the concandescent lamp industry or the preparation of sodium tungsfate crystals. centrates, (2) digestion with The mechanical and chemical features in the continuous operation r e q u i r e s uniform, highof the 'plant, as well as the purity and uniformity of the products, quality tungstic acid O r SOcaustic alkali solutions, and may be of interest to chemists and chemical engineers engaged in dium tungstate, and it was (3) sintering O r fusing with alkaline carbonates a n d similar problems to meet these requirements nitrates or similar mixtures. that the process described It is not intended to discuss in this article was develthe various processes and patents, and only a few are cited oped along the lines of the Oxland method. in the footnotes which serve to illustrate the general MANUFACTURE OF SODIUM TUNGSTATE SOLUTION Sintering - or fusing - the ore with some fusion PREPARATION OF FUSION MIXTURE-Chinese wolframite 1 Received April 5 , 1924. ore, known as 70 per cent concentrates, is received in either 3 Edisoa Lamp Works, General Electric Co., Harrison, N. J. 100-pound bags or 225-pound cases. The sizes of the ore 8 Lake Erie Glass Co., Cleveland, Ohio. vary from 6 mesh and sometimes finer to pieces 3 or 4 inches * Figures in text refer to bibliography at end of article.
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Vol. 16, No. 6
FUSION MIXTURE
WASH WATER FROM FILTER
SOMUM TUNGSTATE DRAWN 111 W?M*m SOLUTION
long and about an inch in thickness. Wolframite is monoclinic in form, and although its crystals are wedge-shaped it seldom shows good crystal boundaries but generally occurs in tabular or irregular masses. On newly broken cleavage surfaces of the unweathered mineral the luster is brilliant metallic. As the ore is received it is usually gray-black, but after pulverizing it always presents a distinct brown or reddish color due to the presence of the iron oxide. It is quite brittle and is reported to have a mineralogical hardness of 5.0 to 5.5 and a specific gravity of 7.1 to 7.55. The apparent density as received varies from 197 to 245 pounds per cubic foot. A typical analysis of the ore used in this process is as follows:
....... ........... .............. Fe ............... Moisture.. WOa.. Mn
SiOr. . . . . . . . . . . . .
P................ Mo..
...........
Per cent 0.14 69.36
7.48
12.26
2.00 Trace Faint trace
................. Sn .................. Cu.................. s ................... AlzOa.. .............. Cb and T a . . ......... CaO ................. As
Per cent 0.085
0.62 Trace 0.06
1.08 0.65
0.40
As shown in Plate 1, the ore is first passed through a jaw crusher (capacity 1500 pounds per hour) into the crushed ore storage bin a t 6 to 8 mesh. It is next fed into an impact pulverizer (capacity 1000 pounds per hour), from which it is blown into the pulverized ore bin. As pulverized, 95 per cent of the ore will pass a 200-mesh screen, while only 0.10 per cent is left on an 80-mesh screen. A definite amount of pulverized ore is weighed out in the buggy, along with 10 per cent over the theoretical amount of 58 per cent soda ash (dense) required to combine with the tungstic oxide content, and about 4 per cent of commercial sodium nitrate. These materials are dumped into a pebble mill and mixed for 10 minutes before being discharged into the boot of the bucket elevator. This mixture, which will be
called the “fusion mixture,” is prepared in pebble mill charges of 750 pounds each. The fusion mixture is conveyed by means of a bucket elevator and endless belt to a storage bin (Plate 2). From this point it is supplied by gravity to the belt conveyor which feeds the furnace. The term tungstic oxide as used in this article does not necessarily signify the yellow oxide of tungsten, but is used rather as a measure of the quantity of tungsten present in various stages of the process, regardless of the exact chemical formula which should be given considering the elements with which the tungsten is combined. The weight of all substances containing tungsten is converted into the corresponding weight of tungstic oxide; thus 100 pounds WOS is equivalent to 126.7 pounds Na2W04, 142.2 pounds Na2WO4.2H20,or 107.8 pounds H2W04. FusIoN-The design of the rotary fusion furnace pictured in Fig. 1and also Plate 2 is the result of months of experimental and development work. I n these illustrations it is difficult to convey any appreciation of the problems that have been solved relative to convenient size, method of changing tubes, proper heat distribution, uniform feed, clogging, regular discharge, and many other operating conditions. Essentially, the present design of the furnace is of the inclined rotary tube type tilted at an angle of 6 degrees. The furnace is supported near the discharge end by hinged joints and a t the forward end by screw jacks which make it possible to adjust the inclination. The furnace is built upon a 8/&ch steel base plate supported by four 10-inch I-beams. It is lined with fire brick and insulated with a light, nonheat-conducting brick, while ordinary building bricks form the outside. The furnace is divided internally by baffle walls into three chambers. The self-supporting arched roof is constructed in two removable sections. A
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June, 1924
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
sheet metal hood supported above the furnace is connected to a n exhaust fan which carries away the hot flue gases. The tube, which is 14 feet 10 inches long and 14 inches inside diameter, rotates at 4 r. p. m. in a combination gas or oil-fired combustion chamber. The tube has four port holes near the end through which the fusion discharges. On each end of the tube is bolted a steel tire 21 inches in diameter which rides on 6-inch diameter dollies. The tube is driven by a 1-horsepower motor through reduction and spur gears. A horizontal roller at the discharge end rides against the end tire and takes care of the thrust caused by the angle of inclination. The weight of the complete furnace is 24 tons.
FIG.I-ROTARY FUSION FURNACE
Fuel is supplied by means of gas or oil and low-pressure air to five burners consuming about 950 cubic feet of natural gas or 7 gallons of fuel oil per hour to maintain a tube temperature of 1020" to 1040' C. The end burner (Fig. 1) is on a center line with the tube and the flame plays directly on the discharge ports. The temperature is registered by two recording pyrometers connected to low-resistance thermocouples protected by nichrome tubes. The fusion mixture is fed into the furnace by means of an automatic feeding device. The apparatus consists of a hopper, the bottom of which is a four-ply, rubberized-canvas endless belt, which discharges through a calibrated gate into a vaned conical hopper bolted on the end of the tube. The fusion mixture is fed a t the rate of 278 pounds per hour or 14Q pounds tungstic oxide per hour, and at the rate of rotation and angle of inclination of the furnace the fusion mixture is exposed to the heat about 30 minutes. The dam a t the discharge end of the tube forces all the molten fusion through the port holes into the lixiviating tank directly below. The fusion as it comes from the furnace contains approximately 55 per cent soluble tungstic oxide. The efficiency of the operation of fusing is 99.35 per cent; that is, 0.65 per cent of the tungsten trioxide in the ore is not converted into the soluble form. Several kinds of tubes have been tried in the fusion furnace and their average performances are given as follows: Life Temperature Thickness c. Inch Hours 0.6 32 1010 to 1020 Steel 0.6 48 1010 t o 1020 Wrought iron 1 317 1040 Nickel-chromium alloy Iron-chromium alloy 1 1000a 1020 t o 1040 a Tube has been in operation for 425 hours and this figure is an estimate based on the thickness and condition of the tube after that life.
TUBE
LEACHING AND FILTERING-The method of discharging the molten fusion directly into the leaching tank from the furnace
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has the advantage of finely dividing the material without cooling and crushing, and also of raising the temperature of the leach liquor to obtain the benefit of the increased solubility of sodium tungstate with temperature. The lixiviating tank is located directly under the lower end of the furnace, as shown in Plate 2. The top is 70 inches below the ports in the tube from which the fusion is discharged. The tank, 6 feet in diameter by 2 feet 9 inches in height, is constructed of welded 10-gage steel plate. It is equipped with an extra heavy, tvo-blade agitator of the plow type, which is operated at 48 r. p. m. Leading into the tank are a delivery pipe for city water and a pipe for wash water from the filter. Outlets are provided a t various heights to supply the leach liquor carrying the sludge to a common line to the filter. The tank may be filled with either water or wash water and all outlets closed until the leach liquor reaches the required specific gravity (1.70 with suspended sludge a t 80" C.) before drawing off, or water or wash water may be run in continuously a t a rate which will give an overflow of the same specific gravity. When this latter method is used a constant level of 18 inches of liquor is maintained in the tank. The problem of filtering the sodium tungstate solution from the insoluble material is being handled by using a 6-foot diameter, 8-foot face continuous filter. It was found best for this particular slurry to use a lBounce, double-fill duck cloth as the filter medium and to rotate the filter a t one revolution in 16.5 minutes. Owing to the rapidity with which $he sludge settles out, the contents of the filter tank must be kept in violent motion by means of a rotary paddle agitator and compressed air. Above the filter is a line of sprays using hot water to wash the soluble sodium tungstate from the sludge. I n order fo operate the filter and to conduct operations soon to be described, the plant is equipped with a compressor supplying 340 cubic feet of air per minute a t a pressure of 8 pounds per square inch and also with two vacuum pumps each having a capacity of 300 cubic feet per minute.
FIG. %-sTEAM-JACKETED EXPANSION Tusn FOR CONCSNTRATION OR SODIUM TUNGSTATE SHOWING PREHEATING TAN=AND R E G U L A T I N G ORIFICC AT T H E L E F T
Using a 21-inch vacuum and the least "blow" sufficient to loosen the cake, the filter will handle 150 gallons of leach liquor per hour. The clear sodium tungstate filtrate is pumped to either of the two intermediate tanks and finally to one of the 10,000-gallon storage tanks, while the wash water is pumped back into the lixiviating tank. The clear sodium tungstate solution as it comes from the filter has a specific
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gravity of 1.47, which corresponds, to about 3.: pounds of tungstic oxide per gallon, and a t this concentration is used for the preparation of sodium tungstate crystals. When used for the precipitation of tungstic acid, the solution is diluted in the storage tanks to a specific gravity of 1.27, or about 2 pounds of tungstic oxide per gallon. The residue obtained from the filter consists mainly of a slightly magnetic mixture of iron and manganese oxides of an apparent density of 82 pounds per cubic foot. An average analysis of the dry residue follows:
...............
H20..
Soluble WOs.. . . . . . . . . Insoluble W O S . .. . . . . . FesO4.. . . . . . . . . . . . . . . MnsOp.. . . . . . . . . . . . . . SiOz.. . . . . . . . . . . . . . . . . e .
Per cent 1.89 1.34 1.44
49.80 36.30 .9.05
..... .............
Cb and T a . . NazC03 . . . . . . . . . . P.. Cu... . . . . . . . . . . . As... . . . . . . . . . . .
Sn ..............
Per cent 0.67 Trace Trace Trace 0.04 0.17
Owing to the method of discharging the fusion into the leaching tank, a uniform and fine-grained residue is obtained, which may be used as a brown pigment in paints. Such paints have been observed to dry quickly and afford good service. The sludge as it comes off the filter contains about 33 per cent moisture. When this residue is dried it corresponds to approximately 32 per cent of the weight of the ore. The sludge is so washed, on the filter, that the loss of soluble tungstic oxide in this operation is 0.61 per cent of the tungstic oxide in the ore, making the efficiency of working 99.39 per cent. This figure, combined with the 99.35 per cent eEciency of the fusion operation, gives an efficiency from the ore to sodium tungstate solution of 98.74 per cent.
Vol. 16, No. 6
CRYSTALLIZATION OF SODIUM TUNGSTATE The process, as outlined to this stage, produces a sodium tungstate solution containing approximately 3.5 pounds of tungstic oxide per gallon, and has a specific gravity of 1.47 a t 20" C . This solution serves both for the preparation of sodium tungstate crystals and for the precipitation of tungstic acid. I n the manufacture of sodium tungstate crystals the solution is pumped from either a 2000 or 10,000-gallon storage tank to a preheating tank where it is heated to 90" to 100" C. This hot solution flows through a regulated arifice into a steam-jacketed expansion tube, more commonly called a "flash still," which is operated under a 20-inch vacuum. This expansion tube is constructed of 3-inch pipe and is 12 feet long. The preheating tank and expansion tube are shown in Fig. 2 and also in Plate 4,which is a general drawing of the crystallizing apparatus. The rate of flow of solution is so regulated that the concentration is raised, in the expansion tube, from 3.5 pounds to 5.0 pounds of tungstic oxide per gallon. This hot, concentrated liquor flows into 100-gallon receivers, operating under a 20-inch vacuum, which are provided with steam coils to keep the liquor a t a temperature from 75" to 85" C. The receivers, as shown in the upper portion of Fig. 3, are alternately filled and discharged. The liquor is discharged through a header, which gives an equal distribution over the surface of the 2-foot diameter by 4-fOOt face water-cooled drum which is rotated a t 1 r. p. m. By cooling the sodium tungstate liquor to 25" C. the concentration is reduced to approximately 3.9 pounds of tungstic oxide per gallon by the separation of
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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fine crystals of sodium tungstate. The rotary drum cooler is provided with a knife-edged scraper which removes the crystals together with the mother liquor. This sludge of sodium tungstate crystals and mother liquor is dropped into a %foot diameter by 12-inch face continuous filter operated a t 1/3 r. p. m. and covered with SO-mesh monel screen. Here the crystals are separated from the mother liquor, which is pumped back into the storage tank and recirculated. This process is continued until 70 per cent of the total tungstic oxide has been removed from the solution in storage. The remaining sodium tungstate solution is diluted and used for the precipitation of tungstic acid. The capacity of this apparatus is 2500 pounds of NazW04.2H20 per 24 hours, while the loss of tungstic oxide is not over 0.5 per cent. The crystals are packed in 30gallon tongue and groove barrels containing 500 pounds of Na2WO4.2Hz0. The crystals obtained by this method contain an average of 14.8 per cent moisture, while the theoretical amount of moisture for NazW04.2Hz0 is 10.9 per cent. The purity of the product is exceptionally good, as is shown by an average analysis compiled from results of the last seven runs : Per cent ~~
............ 99.20 ............... 0.011 ................... 0.002 Mn .................. None P . . .................. Faint trace NazWOi.. SiOz.. Fe As
...................
0.006
............ ..............
Mo. C a . . ............ A1
Per cent 0.017 ~
~~
~~
0.007 0.011
s . . . . . . . . . . . . . . . . 0,009 NaiCOa., . . . . . . . . 0 . 3 2 5 C1 . . . . . . . . . . . . . . 0 . 0 6 2
MANUFACTURE OF TUNGSTIC ACIDFROM SODIUM TUNGSTATE SOLUTION PRECIPITATION-ASpreviously stated, the sodium tungstate solution is diluted from 3.5 pounds of tungsten trioxide per gallon l,o 2.0 pounds of tungstic oxide per gallon before being used for the precipitation of tungstic acid. After the strong solution has been diluted to almost 2.0 pounds of tungptic oxide per gallon, there is added a concentrated solution of sodium nitrate in the proportion of 1pound of sodium nitrate to 25 pounds of tungstic oxide. The solutions are mixed by thorough air agitation and a sample is then taken for analysis. Sodium tungstate solution is pumped, from a 10,000-gallon storage tank by a centrifugal pump to a 110-gallon,constantlevel preheating tank (Plate 3), where it is heated to 85" C. by steam coils. It next passes through a calibrated tip a t the rate of 70 gallons per hour into a superheater, which consists of a steam-jacketed pipe. After being heated to 100" C. it flows directly into the precipitating kettle. Tungstic acid is precipitated from the sodium tungstate solution by commercial 20" BB. hydrochloric acid. This acid is stored in large earthenware jars and is pumped to a constant-level earthenware jar by means of a hard-rubber, single-acting, plunger pump. The acid flows through glass coils enclosed in a steam-heated jacket, where it is heated to 60" C., and then through a calibrated tip (at the rate of 40 gallons per hour) directly into the precipitating kettle. The earthenware precipitating kettle (Fig. 5 ) is set in an oil bath heated by steam coils to 138" C. The outside jacket of the kettle is made of 14-gage wrought iron and is insulated by a magnesia covering. The kettle has a capacity of 38 gallons and is provided with an earthenware cover, which is fitted tightly to the kettle by calking. A vent provided in the cover is connected to an exhaust fan which removes the steam and acid fumes. The hot sodium tungstate solution and hydrochloric acid are run simultaneously into the kettle and are kept in agitation by a steam jet, which also aids in bringing the temperature of the contents up to 106" C. The tungstic acid suspended in the hot acid liquor is continuously removed from near the bottom of the kettle by means of an air lift (Plate 3). This air lift is operated under a pressure of 3 inches of mercury and keeps 32 gallons of tungstic acid and acid liquor in
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the kettle a t all times. This method of removing the tungstic acid from the kettle has proved very satisfactory, and it is believed that this principle could be adopted to advantage in elevating chemicals where other methods are impractical. The precipitated tungstic acid and acid liquor are run continuously into one of the four 900-gallon, wooden settling tanks until it is full. Two hours are allowed for the tungstic acid to settle and then the clear acid liquor is siphoned to recovery. Another charge of the tungstic acid suspended in the acid liquor is run into the tank on top of the tungstic acid settled from the first batch and the clear acid liquor is again siphoned to recovery. The process is repeated a second time before washing the combined charges. Ninety per cent of the tungstic oxide in the sodium tungstate solution is precipitated as tungstic acid by this method. To decrease the amount of unprecipitated tungstic oxide it is necessary either to raise the temperature of the contents of the kettle or increase the amount of hydrochloric acid. To this end every effort has been made to maintain a maximum temperature in the kettle, and an excess of hydroG1oric acid is used, which is believed to be the most economical. With this excess of acid the resulting acid liquors have an acidity of about 7.8 per cent. The plant is equipped with two precipitating kettles, and since they both can be operated a t the same time the capacity of the precipitation operation is 280pounds of tungstic oxide per hour. Ten per cent of the tungstic oxide in the sodium tungstate solution is not converted into tungstic acid during the precipitation operation, but, as will be seen later, 90 per cent of this unprecipitated material is recovered and the actual loss suffered is 1per cent.
F I G . Z-VACUUM
RECEIVERS ABOVE, ROTARY COOLING
DRUM AND C O N -
TINUOUS FILTER BELOW FOR CRYSTALLIZATION O F SODIUM
TUNGSTATE
SETTLINGAND WASHING-After a settling tank has been filled the third time, the tungstic-acid suspended in the hot acid liquor is allowed to settle four hours. At the endof this period the tungstic acid has completely settled, leaving the clear acid liquor. This liquor is siphoned to recovery. The
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.
tungstic acid is thoroughly washed, using about 800 gallons of water for each wash. As soon as the last acid liquor from a tank has been siphoned to recovery, the wooden agitator is started and gradually lowered into the tungstic acid slurry. At the same time water is run into the tank. The agitator (Plate 3) works its way through the heavy slurry to the bottom of the tank and is operated a t such a speed as to keep all the tungstic acid suspended in the wash water. After the tank has been filled with water, the agitator is kept running for 5 minutes before it is stopped and hoisted to the maximum weight. When the tungstic acid has settled (6 hours are usually required), the wash water is siphoned to recovery.
frames, forming dams near the top of the drum. The under sides of these frames are grooved so that a 1.5-inch diameter asbestos rope can be fitted into them to prevent the tungstic acid slurry from leaking back on the brushes. The drum is operated under a steam pressure of 40 pounds. As tungstic acid is very easily reduced to the blue oxide, it is very important that the enamel coat be perfect to insure a uniform product. The tungstic acid slurry forms a layer in back of the dams about 0.5 inch thick a t the deepest point. As the drum is rotated and the water evaporated from the slurry, a thin layer of tungstic acid forms on the drum and is thoroughly dried by the time it reaches the brushes. The dried tungstic acid is removed from the drum by a reciprocating brush made of tungsten wire wool. The entire drier is enclosed in a wooden housing and is connected to an exhaust fan, which removes the steam and fumes. The tungstic acid as brushed from the drum is a very fine, bright yellow powder and is discharged through a chute directly into the packing containers. Thirty-gallon tongue and groove barrels are used to pack 400 pounds of tungstic acid. The capacity of the drier is about 120 pounds of tungstic acid per hour. The amount of water corresponding to the formula HzW04 is theoretically 7.2 per cent, but the tungstic acid obtained from the drier contains on the average 7.6 per cent of moisture and may vary from 6.5 to 8.1 per cent. The efficiency of this operation is 98 per cent. An average analysis of the tungstic acid produced from the process is as follows: Loss on ignition..
,
Per cent 7.38
WOa.. . . . . . . . . . . . 91.87 F e . . . . . . . . . . . . . . . 0.0488 M n . . . . . . . . . . . . . . Faint trace SiOz.. . . . . . . . . . . . O.OOfi8 P 0.0054
................
FIG. &-GENERAL
V I E W OF TUNGSTIC ACIDPLANT
The second wash is put on following the same procedure as the first, with the exception that 3 gallons of 42" B6. commercial nitric acid are added to aid in settling. It has been found that aluminium sulfate acts as a coagulant and can be used to good advantage to aid the settling of any colloidal tungstic acid. It is possible to wash tungstic acid by this method without seriously injuring the purity. After the tungstic acid has settled, the second wash water is siphoned to the sewer. The tungstic acid is washed six times, following the procedure as outlined. The average time of settling for each wash, with the exception of the first, is approximately 10 hours. If any of the washes are not perfectly clear, they are allowed to settle for a longer period; if they still contain an appreciable amount of tungstic oxide, they ars sent to recovery. In removing the final wash writer as completely as possible, the siphon is gradually lowered to the surface of the tungstic acid slurry, and in consequence a considerable quantity of suspended tungstic acid is drawn off. In order to prevent a loss, the latter portion of the wash water containing this suspended material is sent to the recovery instead of the sewer. Thirtysix hundredths per cent of the tungstic acid precipitated is lost in the wash waters. The tungstic acid slurry, after being completely washed, is thoroughly mixed into a thick sirup and run into a 300gallon, wooden intermediate slurry tank provided with an agitator, as shown in Plate 3. The slurry contains about 50 per cent moisture and is now ready for the drier. DRYINa-The tungstic acid slurry is dried by means of a rotary drum drier (Fig. 6 and Plate 3). This drier consists of a welded steel drum 3 feet in diameter by 6 feet long covered with an acid-resisting enamel, and is operated at 0.5 r. p. m. The tungstic acid slurry is run from the intermediate tank through a double trough into two adjustable wooden
Vol. 16, No. 6
Per cent A s . , . . . . . . . . . . . . 0.0148 M o . . . . . . . . . . . . . Faint trace S . . . . . . . . . . . . . . . 0.015 Ca.. ............ 0,0013 AizOa.,. . . . . . . . . . . 0.0154 Chlorides.. 0.0961
......
RECOVERY-A~~ acid liquors, the first wash water, and other wash waters containing an appreciable amount of tungstic oxide are sent to recovery. The recovery system consists of two 4000-gallon wooden tanks provided with wooden agitators and an acid-resisting pump which is used to transfer liquors from one tank'to the other (Plate 3).
FIG. 8-PRECIPITATION
KETTLE
The method of converting the tungstic oxide in liquors sent to recovery into a form in which it can again be put in process is divided into three stages: first, the tungstic oxide in the liquor is converted into calcium tungstate; second, the calcium tungstate is converted into tungstic acid; and third, the tungstic acid is converted into sodium tungstate solution. Assuming that both tanks are empty, the procedure for
June, 1924
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SER FROM VACUUM
[PUMP
the first stage of the process is as follows: When a tank contains about 3500 gallons of acid liquors and wash waters, the agitator is started and hydrated lime added until all the tungstic oxide has been converted into calcium tungstate. The agitator is stopped and the calcium tungstate is allowed to settle The supernatant liquor containing no tungstic oxide is siphoned to the sewer. This operation is repeated until the tank contains about 2000 pounds of tungstic oxide in the form of calcium tungstate. The second stage of the process is accomplished by continually adding the acid liquors to the tank containing calcium tungstate sludge while the agitator is running. Live steamis used to bring the temperature to 60" C., which aids in the conversion. After the acid liquor has finished reacting with the calcium tungstate, the agitator is stopped, and the contents are allowed to settle. The spent acid liquor is siphoned t o an acid-resisting pump, which transfers it to the other tank. It is then treated according to the procedure given under the first stage. The method of producing sodium tungstate solution from tungstic acid comprises the third stage of the process. The tungstic acid is washed three times with water to free it of calcium chloride. The first wash is transferred to the other tank by means of the pump, while the other washes are run to the sewer. After the third wash has been removed there is enough water added to produce a concentration of 2 pounds of tungstic oxide per gallon. A 10 per cent excess of commercial sodium hydroxide is added to this tungstic acid slurry and 90 per cent of the tungstic oxide is converted into sodium tungstate, The sodium tungstate, together with a small amount of sludge, is run into a continuous filter and the
clear solution used for the precipitation of tungstic acid. This cycle is continued by alternating the use of the two tanks each time an extraction is completed.
CONTROL I n order to produce efficiently sodium tungstate and tungstic acid of uniform quality and high purity, the entire process is subjected to careful analytical control. An analysis is made on each lot of raw material before it is uked in the process. I n addition, a 1-pound sample is removed from every 100 pounds of pulverized ore put into the process. Each week these 1-pound samples are thoroughly mixed and the tungstic oxide content determined. The efficiency of the process is computed from these weekly analyses. The cinchonine method is used to determine the tungstic oxide content of wolframite ore, and it is hoped that the details as carried out by W. J. King, Chemical Laboratory of the National Lamp Works, may be published at a future date. I n preparing the fusion mixture it is important that the sodium carbonate and sodium nitrate be dry, thereby avoiding the formation of lumps during storage and an uneven feed to the furnace. During the operation of the rotary fusion furnace the temperature is very closely controlled so that the insoluble tungstic oxide in the residue will be held a t a minimum. The soluble tungstic oxide in the residue is controlled by efficient washing with hot water on the filter. A small sample of residue is taken from the filter each hour and the composite sample for each 24 hours is analyzed for soluble tungstic oxide, insoluble tungstic oxide, and moisture. A sample of the sodium tungstate solution produced during the same period is analyzed for tungstic oxide content.
Thn purity of sodiiim tungstate is elicckml hy a (lnily analysis on crystals witlidrawn from the filter cach hour. Careful operation requires frequent analyses for tungstic oxide conteiit of the sodium tnngstate solution, acid liquors, wadi waters, and liqriors in tlic recovery process. Tho acidity of the liqmir in the preripitat,ing kettle is folloived regularly, and it has been found that the color of the precipitate is a fairly good indication of tlic excess of acid being used.
tnngsten lakes is a more recent development. The process" consists of mixing solut.ions of a dyestuff, a soluble compound of phospbonis, a soluble compound of tungsten, a.nd an acid in such quantities as to cause the precipitstion of the tungsten lake. Basic coal-t,ar dyes are generally used as the coloring matter. By this met.liod a double salt of tungsten is formed in the presence of the coloring matter without destroying tlic lattcr. It is claimed that tungsten lakes so produced possess a great brilliancy, are ext,remely fast to water, and are little affected by exposixre to light. These lakes arc used in printing and lithogaphing inks and in the manufacture of coated papcrs. ACKXOYLEDGXENT Tlie authors are indebted to the staff and to F. M. Ilorsey, direct,or of the Experimental Engineering Laboratory, Kational Lamp Works of the General I.:lcctric Company, for placing tile subject matter of this article a t their disposal. BIBLIOGRAPHY
Pia. 6 - R o i n ~ v DIIDMDRIERN
~ L GUARDS I REVDYED
Before drying a tank of tungstic acid, i t milst pass t( for tilng& oxide content, chloridcs, and residue nonvola 1 e in sulfur chloride. Tlic dcterniinatioiis shomn for tbe iivcrxgc analysk of tunp,stic acid et&d under the are made on dried trmgstic acid from each tank.
fJsm OF TUKGSTIC ACIDA
m QOUIUI
TUXGSTATE
Most of the applications of sodium tun8stat.e and tungstic acid are well knowri, 11-'6 bnt thcir use in ,the production of
I-Roscoe and Schorlemmer, "A Treatise on Cl~einisfry."Vol. 11, 5th e d ... 1913, . .D. 1086. 2-Tmnr. Am. Eirdroihcm. Sor.. IS, 601 (1908). 3-U. S. Piitenl 1,335.277 (March 30, l9Z0). I--French Patent 989,040 (April 8, 1908); Belgian Patent 207,299 1AuriI . . 13. 1908). 3--J. Iron Slrrl I m i . , 64, 14 (1903). R--I.'Acndemie Rogale des Sciences, Inscription e t Belles Letties de Toslourc. 1784. 7-Runner end Aartmann. "Occurrence, Chemistry, Metallui~y,and l s e s oi Tengsten," South Dakota School 01 Miner, Ruli. 12 (1918), gives valuable information OD subjecr of tungsten aiid best list ot reiercncer, in. d u d i n s 1917 =nd pait 01 1918S-.Mennicb-e, "Die Metatlurgie des Woltrnmr," 1911,contains a CY%p,ehensive tunerten compaunds, ~~
9-Chmm. Me,. E n g . 2 2 . 9 (1920). 1 W E w i n e p r i n g . 104, 432 (1917). 11-Sei. A m . Ilonihiy, 6, 135 (1921). 12-Amcricon 34nchinist. 60, 99 (1919). 13--Hess, Mineral Resources of U. S. lor 19IR. 1919. 1920, etc. 14-Fink. Mlneial Industries, 1919, 1920, 1921, etc. I5--nrl , J . Wesfern SOC.E a . , 27, 225 (1922). 1~-1, Tariff commisrioo, In(ormrtion Sriies, 279 (1920), 17--U. S. Patent 1,378,882 (May 24. 1931).
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Clarification of Yeast Extracts with Neutral Lead Acetate' By F. W. Reynolds C~reosunnnr>3 LABORATORY, BVIEAUor C m r i s m u , 'U'~sxiuaroa,D. C.
A .\lEl.HOD of pnrification and concentration of enzymeeontaming yeast ext.ract,a employing dialysis or ultrafiltration and acidificat.ion with acetic acid has recently been puhIislied.* \;\lt,h the desire to short.cn somewliat tlic time required fnr the pro , experiments on purification have subseqiieiitly been n e with neut,ral lead acetate. Neiitral lead acetate used in excess has been employed by a number of workers in defecating autolyzed yeast exiract.s, the excess lead being eliminated as sulfide or carbonate and the resulting acetic acid or a.cetate removed by dialy The writer has found t.liat efficient clarifications may be accoinplished by using smaller amounts of lead acetate, such that. no excess remains in the solution to necessitate its removal. The extract may then he dialyzed or washed on an ultrafilter to complete the pnrification. Only enough lead acetate to produce a flocculent, easily filtered precipitat,e need be added. Working with an extract of bakers' yeast,3 it was found that 10 grams of lead acetate per 1000 cc. were suffi*Received M a y 10, 1924. 9 Reynolds. Tnra Jouan*r,16, 169 (19241. I Thc erpciimental work in this connection was done by M. A. XcCaIip.
cient t o produce a flocculent precipitat.e, while 20 grams could he added before lead appeared in the filtrate. With an extract of brewers' yeast the quandities n'ere 25 and 45 grams, respectively. A nredian figure, 15 grams per liter for top yea,& extract and 35 grams for bottom yeast extract, has been used in purifying large quantities, with uniform resuits.* Tlie products of this treatment are practically the same as when excess lead is used and removed or when the dialysis-acetic acid method is employed. S o loss of inrcrtase or melihiase results, and the purified enzymes are stable as far as it has heen possible t o observe. .4 small portion of the lead precipitate, washed free of soluhle material with distilled water, is an excellent filtering medium for the removal of the turbidity or opalescence which may develop in yeast extracts after coiicentration and wauhing on an ultrafilter. It is superior to infusorial earth in that it does not adsorb the enzyme. A bottle containing a quantity of the washed lead precipitate may he kept, with a preservative, in the laboratory for convenient use, only a very small portion being required for a filtration. Prepared z i ~described In reference given in Footnote 2.
