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Vol. 14, No. 7
Recovery of Platinum from Used Contact Mass at the Old Hickory Powder Plant’.’ By A. L. Kibler 3306 PIEDMONT AvE.,
I
N July 1920 there appeared an interesting account3of the scientific detective methods which were employed in bringing t o light the theft of approximately 2300 oz. of platinum from the War Department. It will be remembered that the stolen platinum represented the platinum which was present a t the Old Hickory Plant a t the time of the Armistice in the form of platinic chloride solution from which the metal had been recovered by a simple evaporation t o dryness and a n ignition, either in the form of platinic chloride or ammonium chloroplatinate. It is perhaps not so generally known t h a t this platinum constituted only a comparatively small part of the total platinum accumulated by the War Department, by far the larger part of which was in the form of contact mass designed for use in the manufacture of sulfuric acid. An account of the recovery of the valuable metal from the immense quantities of contact mass which the cessation of the war left in the hands of the War Department would appear t o be of interest to the chemical world. The Old Hickory Powder Plant, the world’s largest smokeless powder plant, was designed to manufaciure a million pounds of smokeless powder a day, starting from the ultimate raw materials -raw cotton, sodium nitrate, sulfur, alcohol, and benzene. I n addition t o the powder plant, as such, there were therefore plants for the purification of raw cotton, and for the manufacture of nitric acid, sulfuric acid, ether, and diphenylamine. Each of these plants was laid out on a vast scale. The sulfuric acid, with which we are particularly concerned in connection with the subject of this article, was supplied by thirty complete sulfuric acid plants of the largest proportions, arranged in the form of fifteen twin sulfuric acid lines. For each plant there were four “converters” for the catalytic oxidation of sulfur dioxide to sulfur trioxide, each converter containing approximately 4000 11)s. of contact mass, arranged on five circular screens or shelves of heavy iron wire. The two lower screens held contact mass of 0.15 per cent platinum content; the next two screens held contact ma& containing 0.20 per cent of platinum, while the upper screen held contact mass containing 0.30 per cent of platinum. Each sulfuric acid plant contained, therefore, approximately 16,000 lbs. of contact mass containing approximately 32 avoirdupois pounds of platinum or 466.5 troy ounces. The thirty plants would therefore contain approximately 14,000 oz. of platinum. Five of these plants, however, had not been supplied with contact mass a t the time of the Armistice. The platinum for the manufacture of the contact mass for these plants was on the premises in the form of platinic chloride and it was the platinum from this material-or the larger part of it-the theft of which was reported in the article above referred to. I n addition to the 400,885 lbs. of contact mass contained in the sulfuric acid plants at the Old Hickory Powder Plant, 112,941 Ibs. of contact mass were also in use in the second great smokeless powder plant of the War Department, located at Nitro, W. Va. This mass was shipped t o the Old Hickory Powder Plant t o be worked up for the recovery of its platinum content along with the larger amount a t the latter plant. April 7, 1922. Published by permjssion of the Chief of Ordnance.
1 Received
2
Chem. Met. Eng., 28 (1920),93;THISJOURNAL, 12 (1920), 815.
BALTIMORE,
MARYLAND
HISTORICAL I n October 1920, the writer of this article was requested by the Ordnance Department of the War Department to undertake the task of recovering the platinum from the entire amount of contact mass then located a t the Old Hickory Powder Plant. At t h a t time the opinion seems t o have been general in the Ordnance Department that the platinum which was stolen had been recovered from contact mass and that a n adequate plant for the recovery of platinum was in evistence a t the Old Hickory Powder Plant, and the writer was so informed. When he arrived a t Jacksonville on November 1, 1920, however, he found t h a t practically no preparation had been made for the work t o be carried out and t h a t the process proposed for use had been worked out only on a laboratory scale by a method which was practically a n analytical laboratory method. The contact mass at the Old Hickory Powder Plant, like t h a t used in the majority of contact process sulfuric acid plants in the United States during recent years, was prepared by spraying fused, grained magnesium sulfate with a solution of platinic chloride and roasting this sprayed mass to reduce the platinum salt t o metallic platinum. Such contact mass, as well a.; all contact mass in which a stable soluble salt is used as the carrier, is covered by the Schroeder p a t e n t 4 Among other advantages claimed for such contact material is the ease of recovery of the platinum which is expressed in the following language: Inasmuch as the furnace gases, even after purifying, still contain traces of dust, the contact bodies in the course of time become covered with thick impenetrable layers, which diminish their eficiency. To lay bare the surface, it is only then necessary to stir the contact body in water and t o evaporate the salt solution thus formed. The dust is thereby dispersed throughout the entire mass and can no longer diminish the penetrability of the surface. Finally the dust may be readily separated from the platinum after dissolving out the salts which serve as the vehicle. For this purpose it is only necessary t o boil with concentrated muriatic acid the slime which has been separated from the salt solution, whereupon the particles of dust pass into solution while the platinum black remains behind in a pure condition. T h a t the recovery of platinum from contact mass is not as simple as would appear from the above quotation is a matter of common knowledge among sulfuric acid manufacturers and platinum dealers. In developing the process which is here described two sets of mutually opposed factors operated t o restrict the logical and orderly development of an economical and efficient recovery plant. These factors were: 1-The recovery plant was to be a temporary affair, to be scrapped a t the completion of the work for which it was designed. For this reason the purchase of expensive apparatus was prohibited except in case of absolute necessity, and the use of makeshift appliances from stock already in the possession of the Government and on the ground a t the Old Hickory Powder Plant was encouraged. 2-It was discovered, after the construction of the recovery plant was almost completed and the e p i p m e n t purchased, t h a t the funds from which the work was t o be done would expire on June 30, 1920, and that all activity must cease on t h a t date. Plans had been submitted and equipment purchased on the basis of the turnover of 15,000 lbs. of contact mass per week, a t which 4U. S. P. 636,925, November 14, 1899.
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rate the complete recovery could not be completed until October of that year. In order to meet this emergency the proposed output of the plant had to be more than doubled and the recovery plant had t o be operated continuously with three working shifts. During the actual operation of the plant the main object, therefore, was t o recover the bulk of the platinum in a condition suitable for storage before June 30, 1920, and a high percentage of recovery, the purity of the recovered platinum and accurate current control of the recovery process were all subordinated t o this object. ACCOMPLISHMEKTS Of the 513,826 lbs. of contact mass on hand a t the Old Hickory Powder Plant, 133,830lbs. were shipped away a s such t o be stored or otherwise disposed of by the Government. I n addition to this, 36,755 lbs. of unroasted mass, containing all its platinum in soluble form, were withdrawn for other purposes. These withdrawals left 343,241 lbs. to be worked for platinum recovery. The amount of platinum which this should contain is shown in Table I. TABLEI Mass Lbs. 166330 124684 62227 Deductions for samples NET..
343241
400 -
. , . . . . . . . . . . . . . .,342841
Supposed P t Content Per cent 0.15 0.20 0.30 Av.
0.20
P t Content Troy Oz. 3418,Q 3638.8 2721.8 97?6..5
12 9764.5
These figures are based on the amount of platinum which was supposed actually t o have been sprayed on the magnesium sulfate in the manufacture of contact mass, calculated to give the platinum percentages shown. There were, however, unavoidable losses of platinum between the time t h a t the platinum solution was sprayed and the time t h a t the contact mass was delivered t o the recovery plant t o be worked for platinum, The operations involving loss are the following: 1-When the solution of platinic chloride was sprayed on the granulated magnesium sulfate. 2-When the sprayed mass was roasted. 3-When the roasted mass was transferred to the converters. 4-During the operation of the converters. 5-During the unloading of the converters and the transfer of the mass t o the recovery plant.
It should also be noted that the above tabulation assumes a normal platinum content in the entire weight of contact mass as delivered t o the recovery plant. This would include the not inconsiderable amount of sand, iron rust, and other impurities which the mass picked up during its handling and use. It is believed t h a t the discrepancies caused by the abovenamed factors would amount to from 5 t o 10 per cent of the platinum content shown in the above tabulation, and t h a t 7.5 per cent is a conservative figure to use as a basis of calculation. Deditcting 7.5 per cent of 9764.5 oz., we have 9032 oz. as the actual amount of platinum t o be recovered. There were actually recovered 8812 troy oz. of platinum sponge. The exact purity of this sponge is not known. The several lots varied considerably in purity, and there were also variations in the several parts of the same lot. Accurate analyses would have necessitated very thorough blending of large amounts of platinum sponge which would have involved considerable loss of platinum and more time than was available. Moreover, as has been pointed out above, the Ordnance Department was not so much concerned with the purity of the recovered platinum or with an accurate control of the process as i t was in the completion of work within the limited time. Some analyses were made on imperfectly blended samples and these analyses indicated a purity of about 94 per cent. On this basis the platinum sponge recovered contained 8283 troy oz. of actual platinum. On the
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basis of these calculations a recovery of 91.7 per cent has been achieved. Of the remaining 8.3 per cent or 749 troy oz., 400 t o 500 troy oz. of recoverable platinum have been accounted for in the residues left from the plant operations, the working of which was impossible within the limited time. Adding 450 oz. t o the 8283 oz. recovered, we have 8733 oz., or a 96.7 per cent recovery. CONSTRGCTION AND INSTALLATION OF PLANT Active work on the construction of the platinum recovery plant was begun during the last week of December 1920. The building, which was designated for the recovery work prior t o November 1, 1920, was one of the poacher houses previously used for the purification of nitrocellulose. This building was about 75 f t . wide and 290 ft. long. The equipment previously used in it for purifying nitrocellulose consisted of four rows of large wooden tubs approximately 13ft. in diameter and 11f t . deep, together with machinery for agitating the contents of the tubs. The tubs were built on foundations consisting of parallel walls of brick covered with concrete, approximately 2 f t . high and 1 f t . thick. Previous t o the arrival of the writer a t Old Hickory three of these tubs in one row a t one end of the building had been elevated t o a height about 4 f t . above their old foundations, the three opposite tubs in the next row had been torn down and the parallel walls which served as their foundations had been closed a t the ends, thus making three rectangular concretelined tanks, measuring approximately 13 f t . by 7 ft. by 2 ft. deep. It was decided to use this end of the building for the recovery plant and the opposite end for storage of materials and supplies. This left about 105 f t . in the center of the building which could not be used. The construction of the plant and the installation of machinery were practically completed by the first of March 1921. The principal items of construction and installation are listed below: 1-Alteration of small building for use as a laboratory and office, and installation of laboratory equipment. %-Partition across poacher house t o enclose the portion t o be used in the recovery process. 3-Installation of 40 h. p. locomotive type steam boiler with complete system of steam pipes, radiators for heating entire plant and for use in the process. 4-Installation of lighting and power service wires for laboratory and plant. 5-Installation of telpherage system with 350 f t . of 30-in. tram track, with two inclines, for delivering contact mass, acid, etc., from the storage room t o the solution tubs and other points in the recovery plant. 6-Installation of 30 h. p. motor for t u b agitators, 10 h. p. motor for telpherage system, other motors for air compressors, three centrifugal pumps, centrifuges, and exhaust fans. 7-Installation of water pipes and connections. 8-Construction of two heating tables 30 f t . by 5 ft., heated by oil burners, one a t each end. Each table was constructed of fire brick and fire clay slabs and contained a layer of about 3 in. of sand on the heating surface. Above each table and enclosing it a large fume hood and exhaust flume were constructed, the exhaust fan being placed so that the fumes were siphoned out of the hood and did not pass through the fan. Sliding doors on each side gave access t o the heating surface of the table. 9-Construction of a roasting oven for final stage of platinum purification. The heating chamber was constructed of fire clay slabs and measured 7.5 f t . by 2.5 ft. by 16 in. high. It was heated by an oil burner and was so built that the gases from the combustion of the oil could not enter the heating chamber b u t circulated around three sides of it. 10-Installation of four Sharples supercentrifuges and one centrifugal laundry wringer. 11-Installation of laundry dryer. 12-Construction of vault for platinum storage. 13-Installation of three 30-gal. earthenware jars, three 75gal, earthenware jars, and twelve 264-gal. earthenware jugs, with connections. 14-Wire fence around entire plant. 15-Repair of concrete-lined save-all tank 50 f t . by 100 ft. by 6 to 7 f t . deep for storage of spent aqueous liquors.
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Construction had advanced sufficiently by the middle of February 1921 for operations to begin on an experimental scale, and active and continual operation was begun about the first of March.
Vol. 14, S o . 7
sand could have blown into the converters while they were being filled or i t could have been carried in by careless workmen. There was also present a considerable quantity of soluble silicates which formed silicic acid gel when in the presence of acid liquors and caused great difficulty at various steps in the operaOUTLINE OF PROCESS tion. It was impossible t o filter any of the acid solutions on The process as finally worked out was as follows: account of this silicic acid. SOLUTION OF CONTACT MASS-solution of the water-soluble 1-Solution of the water-soluble portions of the contact mass in hot water. portions of the mass was carried out in large wooden tubs which 2-Allowing the charge to settle. were originally designed as poacher tubs in the purification of 3-Separation of insoluble portions by means of the Sharples pyrocellulose for smokeless powder. They measured approxisupercentrifuge. mately 13 f t . in diameter and approximately 11 f t . deep. One 4-Concentration of the platinum sludge by means of weak foot in depth held approximately 1000 gal. of water. A normal hydrochloric acid. charge for these tubs was 15,000 lbs. of contact mass and 6000 &-Separation of concentrated platinum sludge from the weak gal. of water. The optimum conditions for charging this amount acid wash by means of the Sharples supercentrifuge. were as follows: 6000 gal. of water were run into t h e t u b and 6-Digestion of the “concentrated sludge” in aqua regia, evaporation of aqua regia t o dryness, addition of two separate heated with steam t o 65’ t o 70” C. The contact mass was then portions of hydrochloric acid followed after each addition by fed into the t u b at such a rate as to require 7 t o 8 hrs. for the evaporation to dryness, extraction of the platinic chloride formed addition of 15,000lbs., the temperature during the addition not by means of two to three treatments of dilute hydrochloric acid, the solution being siphoned off after each treatment, the whole being allowed to exceed 90’ C. The agitators were kept running throughout the time of charging and for 3 hrs. thereafter at the procedure repeated two or three times. 7-Precipitation of platinum as the ammonium chloroplatinate constant speed of about 15 r. p. m. The agitators were then by the addition of ammonium chloride to the hydrochloric acid stopped and thecharge allowed to stand from 24 t o 36 hrs. Ocextract. casionally the charge settled sufficiently to allow several feet in %-Washing the ammonium chloroplatinate several times with depth of the liquid to be siphoned off from the top of the charge. alcohol, separation of the wash liquors being effected by allowing More often, however, a sufficient amount of solid matter was held to settle and siphoning off through glass siphons. 9-Final separation of the ammonium chloroplatinate from in suspension t o necessitate the centrifuging of the entire charge. the alcoholic wash liquors by means of a centrifugal laundry When this was the case centrifuging was started from the 0.75-in. wringer. outlets with which the t u b was provided a t distances of about 1 10-Drying the ammonium chloroplatinate in a laundry dryer. f t . apart, beginning with the opening nearest the top of the liquid. 11-Roasting the ammonium chloroplatinate to platinum In this way the charge was drawn off through the centrifuges sponge. without agitating the charge until there were about 1.5 to 2 ft. 12-Recovery of platinum from the waste acid and alcohol of charge in the tub. A t this depth a considerable amount of liquors by precipitation with zinc solution in aqua regia and sludgy material began to be collected in the centrifuges, and it subsequent purification as above described. was very difficult to make a clean separation between the solid DETAILSOF PROCESS and the liquid on account of the large amount of solid and the high specific gravity of the liquid. A t this point the charge DESCRIPTION OF CONTACT ivAss-’I’he contact mass as unloaded was usually diluted with water to about twice its volume. The from the converters was usually of a light gray color and granular agitators were started and run for a few minutes until the charge form, the size of the granules being approximately such as would was thoroughly mixed. I t was then allowed to settle from pass through a 0.5-in. mesh screen. I n the converters which had 0.5 to 1 hr., and again centrifuged, starting from the top openbeen in use for the longest time the granules had frequently ings as before, A much better separation was then secured on coalesced into large soft lumps containing a considerable quantity account of the lowering of t h e specific gravity of the solution. of sulfuric acid. This was particularly noticeable in the mass When large amounts of solids again began to collect in the cenfrom the top screens in the converters and was probably due to trifuge bowls, a second dilution was given and sometimes a a condensation of sulfuric acid on the mass. The mass also third and a fourth, depending on the nature of the charge. contained considerable quantities of iron rust from the interior The sludge obtained after such dilutions was almost free from of the converters and the screens. Some of the iron rust was magnesium sulfate. in the form of very fine dust and was probably carried over The centrifuge bowl in which the sludge was collected was a mechanically by the current of sulfur dioxide from the other monel-metal cylinder, approximately 30 in. long and 4.5 in. apparatus through which i t had passed. This iron was particularly troublesome in the process, being very difficult to separate outside diameter, with 0.5-in. wall. It revolved at a speed of 16,000 r. p. m. from the platinum. It was also very troublesome in analytical The liquid t o be centrifuged passed into the bowl through a work since i t was particularly difficult to get into solution, some central hole at the bottom, the solids in the liquid adhered to of i t not going into solution even on long boiling in aqua regia. Fusion with sodium carbonate proved the best way to get this the walls of the revolving bowl by centrifugal force, and the clear liquid passed out of the bowl at the top. When approxiparticularly insoluble form of iron oxide into solution for analytmately 10 lbs. of solid material had been collected the centrifuge ical work. There was also a considerable quantity of granular magnesium hydroxide or oxide in the mass. This was probably was stopped, and the bowl was taken out and emptied into pans. formed by roasting the mass t o so high a temperature as to The sludgy material thus obtained contained practically all the break down the magnesium sulfate. I n one case nearly two platinum from the original mass and a large quantity of other materials, chiefly iron rust, insoluble magnesium salts, sand, barrels of these coarse granules were shoveled out of a solution and gelatinous silicic acid. t u b after the treatment of a 15,000-lb. charge of contact mass. The effluent from the centrifuges was usually quite clear. The solutions of such charges were, of course, alkaline in characIt was first run into the rectangular sump tanks previously deter. scribed. When a sump tank was full i t was tested for dissolved The impurity present in the largest proportion was ordiilary sand. This may have come from the tops of the preheaters platinum, If there was no appreciable amount of platinum in which were covered with a layer of several inches of sand for solution and if the liquor was clear i t was pumped out and run insulation and were located very close to the converters. The into a large concrete-lined save-all tank for storage. If i t con-
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tained dissolved platinum i t was heated with steam, and hydrochloric acid and zinc were added t o precipitate t h e platinum. After cooling i t was again run through t h e centrifuge. If the liquor was not clear it was centrifuged again before running to the save-all tank. The contact mass which has been in actual use in converters was usually slightly acid t o methyl orange after being dissolved in water. Occasionally a charge was found which was slightly alkaline. This was the case with many of t h e charges of the Nitro mass. This alkalinity was due to the presence of magnesium hydroxide which might have been formed by a n overheating of the mass. A t times magnesium hydroxide was present in very large quantities, so large as to make i t impracticable to dissolve i t with acid. In one case after t h e addition of 250 gal. of commercial hydrochloric acid the charge wa4 still alkaline and, as stated above, 2 bbls of coarse magnesium hydroxide mixed with sand were shoveled out of the bottom of the t u b after the charge was run out. Charges which were alkaline settled better than acid charges but usually yielded a very much larger quantity of sludge than the acid charges. On one occasion two charges whichwerestrongly acid in reaction were neutralized with milk of lime t o facilitate settling. The charges then settled rapidly and about 3 f t . of clear water were siphoned off from the top of the charge. An immense amount of voluminous, slimy sludge, however, was found at the bottom of these charges. In one case there were almost a thousand pounds of this sludge and i t contained calcium salts which gave very great difficulty throughout all the remaining processes and even showed up in the platinum sponge. The best practice consisted in centrifuging the charges just as they were without the addition of either acid or alkali. When charges were alkaline the amount of granular magnesium hydroxide was usually so large as to make i t impracticable to dissolve i t by the addition of acid and, moreover, the addition of acid caused appreciable amounts of platinum to go into solution in the liquor. If the charge was acid the addition of alkali caused the precipitation of large quantities of iron, magnesium salts, and other compounds. It was sometimes found t h a t 15,000 lbs. of contact mass were too much for 6000 gal. of water, and in this case the charge was cut down accordingly. This was especially the case with contact mass which had been in use for some time. I n the case of mass from the first converters which were p u t into operation a t t h e Old Hickory Powder Plant, the charge of mass for 6000 gal. of water was reduced to 10,000 lbs. These charges were strongly acid with sulfuric acid and contained large lumps of material which had apparently been formed by the condensation of sulfuric acid within the converters. With these charges i t was found impossible to obtain a complete separation of the liquid and solid with t h e centrifuges unless the concentration of the solution was lowered by the addition of more water. In all cases when the charge had been run out through the centrifuges to within 6 to 10 in. of the bottom, the remainder of the charge was run out through a 4-in. opening in the bottom of the t u b into the concrete-lined sump tank opposite the tub, being passed through a coarse mesh copper screen to catch large sized gravel and other foreign material which the contact mass contained. Prom the sump tanks i t was pumped to a series of bath tubs which were located over the centrifuges a t a sufficient height to give head enough t o run well through the centrifuges. T h e material which collected on t h e screen was washed thoroughly with water until the water coming through the screen was clear. The material then remaining on the screen was collected in barrels and designated “sandy residues.” There was a very wide variation in the amount of sludge obtained from t h e several charges. Some charges yielded less than 100 lbs. of sludge, while others yielded nearly 1000 lbs. The two charges t o which milk of lime was added, as previously
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referred to, yielded very voluminous sludges containing large quantities of insoluble calcium salts, iron hydroxide, magnesium hydroxide, sand, etc. Of t h e charges not so treated the variations in weight were usually due t o magnesium oxide or hydroxide, iron oxide, and sand. The average amount of time required to clean u p a charge completely after the centrifuging began was 56 hrs., four centrifuges being used, and centrifuging being carried on 24 hrs. per day, 7 days per week. WEAK ACID CONCEKTRATION-It was discovered t h a t the sludge obtained from the several charges could be very materially reduced in bulk and weight by a weak hydrochloric acid treatment, with a n acid sufficiently weak t o pass through the centrifuges without very rapidly attacking the centrifuge parts. The total amount of sludge obtained from the twenty-five charges of contact mass was over 5000 lbs. This was reduced t o 2000 lbs. by the weak acid treatment.
The weak acid treatment was carried out in a battery of stoneware jars consisting of two 75-gal. jars and three 30-gal. jars, all of which could be emptied through faucets into a 10-gal. crock from which the centrifuge was fed. The jars were filled with a charge in a ratio of 12.5 lbs. of sludge to 1 gal. of hydrochloric acid (31 per cent HCl), and 4 gal. of hot water. The sludge was put in the jars, and the acid was added and stirred up for several minutes with a wooden paddle. The hot water was then added and the whole again stirred. It was then allowed to stand from 18 to 24 hrs., or until cool enough t o centrifuge. Occasionally, if a sludge was quite alkaline in character, it was necessary to add an additional amount of acid and water in order to make i t centrifuge properly. Approximately 500 lbs. of sludge could be charged into the battery of jars a t one time, although this was usually more than the one centrifuge which was allotted t o this work could handle in one dav’s time. PURIFICATION. Aqua Regia Treatment-In principle the purification stage consisted of a n aqua regia treatment of t h e concentrated sludge in order t o carry the platinum into solution, a complete evaporation of the aqua regia solution in order to eliminate the nitric acid, solution of the platinum chloride in hydrochloric acid, separation of the hydrochloric acid solution of platinum from the residual solid matter, precipitation of the platinum in the form of ammonium chloroplatinate by the addition of ammonium chloride, separation and washing of the ammonium chloroplatinate, drying of the ammonium chloroplatinate, and roasting i t t o sponge.
Approximately 5 lbs. of concentrated sludge in a large silica dish (about 6-gal. capacity) were placed on the hot table. About 10 qts. of commercial hydrochloric acid were then added. This was thoroughly heated and mixed b y means of wooden paddles. About 3 pints of nitric acid were then added very carefully, a little a t a time, to avoid violent frothing. In the beginning the amount of nitric acid to be added a t a time should be not more than 25 cc. or even less. Kitric acid should be added until a further addition causes no bubbling or frothing. One part of nitric acid t o three parts of hydrochloric acid was usually sufficient. The contents of the dish were then allowed to evaporate just to dryness. The residue could not be allowed to become caked since this was likely t o break t h e dish. A small amount of hydrochloric acid was then added in such a way as to moisten the entire residue and this was again evaporated to dryness. About 3 qts. of hydrochloric acid and 5 qts. of water were then added t o the contents of the dish and digested until the residue was loose from the dish and thoroughly disintegrated. The disintegration can be assisted by t h e use of wooden paddles. The entire contents of the dish were then poured into a 10-gal. crock, the dish being washed out with just sufficient water t o
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transfer the contents. Several dishes were ernptied into one 10-gal. crock until t h e crock was almost entirely full. T h e crocks were then allowed to stand for 24 hrs. or longer, until complete settling had occurred and the supernatant liquid was clear. The clear liquid was carefully siphoned off into 10-gal. crocks by the use of 0.25-in. glass siphons, the crocks being tilted gently so t h a t t h e clear liquid might be siphoned as completelv as possible. The residue left in the crock after siphoning was treated with I part hydrochloric acid and 2 parts hot water, with stirring, so that the solid residue was thoroughly mixed with the hot dilute acid. This was again allowed to cool a n d settle and the clear liquid also siphoned off and added to the liquid previously siphoned. The residue which was now in the crock was returned to the silica dishes and the entire process just described was repeated, using the aqua regia treatment and two weak hydrochloric acid extractions. The residue then usually contained from 0.2 t o 0.4 per cent of platinum and was set aside in containers for final disposal by the Government. Occasionally, however, a third and even a fourth aqua regia treatment was necessary. The process above described was adopted because filtration of the strongly acid, hot solutions was found t o be particularly difficult and very slow. T h e objections to the siphoning process are, first, that i t leaves a small amount of impurities in the finished platinum sponge, and, second, i t is not possible to strip the residues quite as free from platinum as could be done with a suction filter. Precipitation-The clear liquors which had been siphoned off after the several hydrochloric acid extractions were treated with a hot concentrated solution of ammonium chloride in order to precipitate the platinum as ammonium chloroplatinate-a highly colored yellow salt. H o t solutions of ammonium chloride were used because a much larger amount of ammonium chloride per unit of volume could be added, thus obtaining the most insoluble medium for the ammonium chloroplatinate. For the same reason, t h e first portion of ammonium chloride was sometimes added in solid, finely powdered condition. After the precipitation, about 2 per cent of 95 per cent alcohol was added in order to facilitate the settling of the ammonium chloroplatinate. If any oil was present, which was usually the case and which came from the centrifuges, a considerable amount of yellow salt might float in a scum on the surface. This scum was made to sink b y the addition of a few drops of ether and gentle agitation of the surface. Unless the nitric acid had been completely removed b y evaporation of the aqua regia in t h e preceding stage, violent frothing was likely to occur on t h e addition of alcohol, either a t this stage or the following stages where the precipitate was washed with alcohol. This frothing was sometimes so violent as to cause the loss of practically the entire contents of t h e crock if precautions were not taken. The crocks were allowed to stand undisturbed for 12 hrs. after precipitation. A t the end of this time the clear superiiatant liquid, which had previously been tested in ordertodetermine whether precipitation had been complete, was carefully siphoned off through glass siphons as completely as was possible without drawing over some of the yellow salt. T h e yellow salt from several crocks was usually concentrated into one crock at this stage and the crock filled u p with alcohol. This was again allowed t o stand for 24 hrs., or until settling was complete. The supernatant liquid was siphoned off as before and a second alcohol wash was given. It was found advantageous t o repeat this alcohol wash three times. All liquids siphoned off from t h e yellow salt were stored in 264-gal. earthenware jugs, a supply of which was available on the plant. These were afterwards treated for the recovery of the dissolved platinum as will he described later. The alcohol used in this process was colored with methylene blue t o discourage its use as a beverage. Separation of the Ammonium Chloroplatinate from the Wash
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Liquor-After the third alcohol wash the yellow salt, in the form of a thick sludge, was transferred to a 75-gal. jar which was located on a n elevated platform over an ordinary centrifugal laundry wringer. The revolving basket of the wringer was approximately 10.5 in. deep and 26 in. in diameter and revolved at about 1150 r p. m. The sides, perforated with about 0.25-in. holes, were lined with a very heavy woolen filter cloth. T h e sludge in the 75-gal. jar was diluted with alcohol t o t h e consistency of thin cream and fed through a rubber hose, with constant stirring, into the center of the revolving wringer bowl. The rate of feeding had t o be very carefully controlled by means of a n earthenware stopcock and could be learned only by experience. A slight over-balancing of the bowl by the collection of too much material on one side would cause such violent vibration that the wringer might have to be stopped and the charge dipped out and returned t o the storage jar. When properly fed t h e alcohol passed through the woolen filter cloth, leaving the yellow salt in the form of a comparatively dry cake, packed against the walls of t h e bowl. By careful feeding as much as 40 Ibs. of yellow salt were collected in one charge. The average weight of the charge was about 25 lbs. It was removed from the wringer by scraping down from the sides with a large spoon and scooping it into enameled dish pans, in which i t was dried The yellow salt as it came from the wringer contained about 18 per cent volatiles, niostly alcohol. It was dried by placing t h e pans containing the wet salt on racks in a laundry dryer. This dryer consisted of a galvanized iron box, 6 5 ft. by 8 ft. by 8 f t . high, lined on three sides with double coils of steam pipe. It heated in a very short time and attained a temperature of 95" to 100"C. The yellow salt was sufficiently dried if left in the dryer over night. Roasting of Yellow Salt-For the roasting of the yellow salt, 36-qt. graphite crucibles with tops and lined with zirconia v, ere provided. These crucibles were sufficient to handle the amount of yellow salt which was originally designed t o be roasted at one time. With the speeding up of the process, however, they were entirely insufficient, and time did not allow the purchase of a n additional supply, since they were not carried in stock. Two very large graphite crucibles, such as are used in brass foundry works, were found in the shop area of the powder plant. They held approximately 1.5 gal. each, but were still not sufficient to hold the large amounts of yellow salt which had to be roasted at a time. The large silica dishes which were in use in the aqua regia treatment of the sludge proved entirely satisfactory for the roasting process, except t h a t they were awkward in shape and were so large that they could not be provided with covers. I n the larger roasts two of these silica dishes were used and filled with yellow salt t o within 4 in from the top. By the use of all these expedients and by carefully arranging the vessels in the roasting ovens, a n amount of yellow salt sufficient to yield 1000 oz. of platinum sponge was roasted at one time. The muffle furnace which was used for roasting was constructed in such a way t h a t t h e combustion gases could not pass through the heating chamber but circulated completely around it. It was heated by means of an oil burner with a steam jet. The following is a description of a typical furnace run: T h e several crucibles and silica dishes containing the yellow salt were carefully placed in the furnace in such a position t h a t they could be withdrawn with tongs while the furnace was still hot. The temperature of the furnace, while being charged, was usually 400" or 500" F. The door was then closed and sealed. The oil burner was lighted and kept going for approximately 24 hrs., during which time the temperature rose to approximately 1300' F. Dense white and yellow fumes began to appear when the temperature of the furnace reached approximately 500' F. These continued for 12 to 15 hrs. By the time the temperature had reached 1300" F. the fumes had practically ceased. The burner was kept on for about 2 hrs. after the fumes ceased to issue from t h e
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THE JOURNAL OF INDUSTRIAL A N D ENGINEERIhTG CHEMISTRY
furnace. T h e fire was then shut off and the furnace allowed to cool to a temperature a t which it could be opened and the crucibles taken out. The yield of platinum sponge from the dried yellow salt usually ran a little over 100 per cent of theory, owing to the presence of impurities. These impurities were chiefly silica with a little iron. The lowest yield obtained was 93.7 per cent of theory, in a case where the yellow salt was not completely dried. The highest yield obtained was 107.7 per cent of theory, the result of the fact t h a t this roast was made up largely of platinum recovered from various residues and contained a larger amount than usual of impurities. T h e next highest yield was 103 per cent of theory. Recouery of Platinum f r o m Wastes-During the operation of the processes described in this report several waste products collected which contained considerable platinum. Those described below were treated to recover the platinum which they contained : 1-Oily drippings from the centrifuges. 2--ilcid effluent from the centrifuges after the weak acid treatment of the sludge. 3-Acid liquors siphoned off from the precipitation crocks after the precipitation of ammonium chloroplatinate with ammonium chloride. 4-Weak alcohol wash liquors obtained by siphoning off from the crocks and effluent from the laundry wringer. &Rags which were used in cleaning the centrifuge bowls and other pieces of apparatus. The treatments for the several waste products itemized above ’ are enumerated consecutively below: 1-The oil and water were separated in vessels having a bottom faucet. When settling was complete the water was drawn off from below and run through the centrifuge to recover the suspended platinum. The oil was burned off in a n open iron kettle and the residue treated with aqua regia on the hot table. 2-The weak acid water which contained approximately 15 oz. of platinum per 100 gal. was treated with zinc to precipitate the platinum. It was then run through the centrifuge to recover the precipitated platinum. 3-Same treatment as for (2). &Several 264-gal. jars of alcohol waste were distilled to recover the alcohol. The residue left after most of the alcohol was distilled off was precipitated with zinc and centrifuged. This process, however, proved too slow with the facilities which were available. It was found by laboratory tests that platinum could be precipitated practically completely in the presence of considerable alcohol if a large excess of zinc were used and a considerable time allowed for the reduction. The remaining alcohol liquors, were, therefore, precipitated directly with zinc and centrifuged. &The rags were burned in an open kettle and the ashes treated with aqua regia on the hot table. All the platinum sludge obtained from the above-mentioned waste products was turned on t o t h e hot table for purification with aqua regia treatment and worked up with the rest of the platinum sludge and was not kept separate. The amount of platinum recovered from these residues was probably in the neighborhood of 800 troy ounces. RECOVERABLE PLATIXUM
IN
RESIDUES
It is very difficult t o make an intelligent estimate of the platinum contained in the residues left in the Platinum Recovery Plant owing chiefly t o the difficulty of obtaining average samples. Some analyses have been made of the various residues but i t is believed t h a t they can serve as an indication merely and not as the basis of an intelligent estimate. As nearly as can be ascertained the amounts of platinum in the various residues left in the Plant were the following:
. 1-The
save-all tanks. These contained approximately 225,000 gal. of liquor which was nearly a concentrated solution of magnesium sulfate. It is estimated that there may be 100
641
oz. of platinum in solution in this liquor and 50 0 2 . in the form of fine sediment on the bottom. 2-Approximately 1000 lbs. of residue from the silica dishes, which should contain 100 oz. of platinum. 3-Approximately 1500 lbs. of sandy residues shoveled from the bottom of the solution tubs and washed. This should contain 100 oz. of platinum. 4-Approximately 500 lbs. of magnesium hydroxide shoveled from the bottom of some of the solution tubs. This should contain 25 oz. of platinum. &Approximately 200 gal. of wash liquor from the yellow salt. This should contain 30 oz. of platinum. 6-A clean-up of the solution tubs by knocking them down and scraping them and a clean-up of all the equipment used in the platinum plant should yield 50 0 2 . of platinum. All these sources account for about 455 troy ounces.
FINANCIAL STATEMENT On November 1, 1920, there was an unobligated balance of approximately $23,561.66 of the allotment for the recovery of platinum On March I, 1921, there was an unobligated balance of approximately $8,367 84. The sum of $15,193 82 represents approximately the co3t of the construction of the plant and the purchase of the initial apparatus. This sum includes the cost of four centrifuges for $6,800.00 Between March 1 and June 30, three additional allotments, totaling $18,500 00, were made. On June 30, the unobligated balance was approximately $1,840.74. T h e sum of $25,027.10, therefore, represents approximately the cost of operating the plant, although i t includes some rather large items for maintenance and the purchase of supplies and additional equipment. The total amount of money expended between November 1, 1920, and June 30, 1921, was approximately $40,220 92. Figuring the actual amount of platinum recovered as 8283 troy ounces, the cost of recovery has been $4 865 per ounce. These figures do not take into account the value of the residues, from which the Government will probably realize an appreciable sum, and the value of the equipment which has been purchased and which remains the property of the Government CONCLUSION Owing t o the conditions under which the work here described was conducted no very extended laboratory work was carried out, though many problems of an unusually interesting nature presented themselves. However, some investigations of a pressing nature were conducted and some interesting results were obtained which, while not complete, may be made the subject of a separate article in the near future I n connection with the chemistry of platinum, reference might here be made to the excellent “Bibliography of the Metals of the Platinum Group” published as Bulletzn 694 by the U. S. Geological Survey, and also to “The Detection and Estimation of Platinum in Ores,” Techaical Paper 270, of the Bureau of Mines. As this article goes to press the attention of the author has been directed to a review of “Technical Records of Explosives Supply 1915-1918, published by the Ministry of Munitions and Department of Scientific and Industrial Research, H. M. Stationery Office, London, 1921” in which the following statement appears: “Of special interest is **** the recovery of the magnesium sulfate and platinum, together with the separation of platinum and iridium, from contact mass.” The publication reviewed is, unfortunately, not available t o the author, and no comment can be made by way of comparison between the method therein described and t h a t described in this article.
ACKNOWLEDGMENT The writer desires t o express his indebtedness to Dr. Charles
E. Munroe of the National Research Council, Washington, D. C., for valuable suggestions in the compilation of this article and for his assistance in preparing it for publication.
