UTILIZATION OF
ALUNITE THROUGH FUSION WITH ALKALI SULFIDES E. 0.HUFFMAN AND F. K. CAMERON Alunite University of North Carolina, Chapel Hill, N. C. is completely decomperature and time of fusion. At 625" to 650" C. a fusion of posed by fusion 5-hour duration yielded better than 85 per cent of the alumina in water-soluble form; a t 725" to 750" C. a fusion of 1.5 to with sodium sulfide 2 hours was sufficient to make water-soluble better than 92 or with mixtures of coal per cent of the alumina. There was marked decrease in the and either sodium sulfate or water-soluble alumina produced, if either the time of melt or potassium sulfate. When sothe temperature of the melting were increased further. A dium sulfate is used, a satisfactory melt held a t 800" C. for an hour and a half yielded only 67 per cent of the alumina in water-soluble form, and one held for recovery of alumina is effected readily, 2.25 hours a t the same temperature yielded only 57 per cent but recovery of potassium as a pure salt is of the alumina in water-soluble form. difficult and may not be practicable. When Reduction of Sodium Sulfate potassium sulfate is used, fusions are more easily effected, recovery of alumina apThe optimum temperature for the reduction of sodium sulfate to the sulfide is higher than that for the decomposition of proaches perfection, and potassium alunite by the sulfide. According to Budnikov(l), best results may be completely recovered as are obtained with a mixture of 2.5 to 3 parts anhydrous sodium the sulfate and the carbonate. sulfate to 1part of carbon, a t a temperature of 850"to 1000" C. Recovery of 'e pure potasThe main reaction seems to be sium salt can be acNa$Od 4CO +NaZS 4C02 33,400 calories complished readand is therefore strongly exothermic. The carbon dioxide as ily by standfoimed is reduced by excess carbon to carbon monoxide, and ard procethe composition of the gas phase with respect to this comdures. ponent varies 94 to 99.3 per cent. Prolonged heating lowers
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HE mineral alunite, KzS04.A12(S04)g2A12Os.6H20, is decomposed by fusion with sodium sulfide. It has been suggested that the large deposits of this substance in the Tushar Mountains, Piute County, Utah, might be commercially available, since sodium sulfate is abundant in solution in the Great Salt Lake and in deposits of Glauber's salt in the neighborhood, and cheap coal is readily available for its reduction to t'he sulfide ( 3 ) . This paper records results from a laboratory investigation of the proportions of ore, fuel, and reagents, the optimum temperatures and recovery of values from the melts. It is shown that potassium sulfate, recoverable from the alunite itself, is preferable to sodium sulfate, as it is more readily reduced; potassium sulfide is more efficient in decomposing the alunite than is sodium sulfide; and the recovery of pure salts from the melt is easily accomplished.
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the yield of sodium sulfide, sulfur dioxide escaping. A series of runs was made to find the best conditions. For this purpose a supply of coal (Pocahontas) was prepared, ground to 100 mesh. An analysis showed in percentages: moisture, 1.05; total carbon, 83; fixed carbon, 70.52; ash, 3.5; volatile matter, 24.88; available hydrogen, 4.9; and sulfur, 1.0. The anhydrous sodium sulfate was crushed to 30-40 mesh. Closed crucibles were found advisable to maintain reducing conditions, and the addition of sodium chloride' facilitated the reaction and increased the yield. The best results, 94 to 94.5 per cent yield of sodium sulfide extracted from the melt by water, were qbtained by holding a mix of 1 part sodium sulfate, 0.5 part coal, and 0.1 part sodium chloride a t 900" C. for an hour and a quarter.
Decomposition of Alunite by Fusion with Sodium Sulfate and Coal Since a higher temperature is required for the best production of sodium sulfide than is desirable for the decomposition of alunite by sodium sulfide, a compromise must be found if the two operations are to be carried on simultaneously. This is desirable for economic and engineering considerations. A number of runs were made varying the proportions of reagents to alunite, the temperatures, and time of roasting.. It was necessary to use closely covered or partly closed vessels in which to make the roasts, to maintain a reducing atmosphere. Typical results are given in Table I.
Decomposition of Alunite by Sodium Sulfide A considerable excess of alkali is required for the complete decomposition of alunite. It is convenient to assume the conversion of all the alumina in the mineral, to sodium aluminate, NaA102, although the conversion is largely to NaaAIOs. With sodium sulfide, an excess of 89 to 90 per cent appears to give the most satisfactory results. This proportion of sodium sulfide was added to 200-gram samples of alunite in a series of runs to find the optimum tem420
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The reduction to sodium sulfide did not show any direct relation to the production of recoverable alumina. For satisfactory recovery of the latter it was necessary to use a t least 2 parts of sodium sulfate to 1 of alunite and to maintain the temperature a t 850' to 900" C. for upwards of 3 hours. Recoveries better than 90 per cent were obtained without difficulty.
until the solution became saturated with respect to sodium chloride. Further evaporation to a crystallization end point would be accompanied by separation as solid of these salts and some potassium chloride. After evaporation of about sixsevenths of the water and cooling, it was calculated for one of the solutions that the salts remaining in solution would contain 27 per cent potassium, and a mixture richer in potassium would precipitate on cooling. Actually, whenever these mother liquors from the precipitation of alumina were concentrated by evaporation and cooled, relatively large masses of Glauber's salt separated, leaving a mother liquor enriched with respect to potassium salts. It is well known that, in complex salt solutions and especially a t lower temperatures, final equilibrium conditions are rarely obtained without long standing. Relative rates of crystallizations are of primary importance in determining the order and amounts of salt separations. A procedure could be developed, possibly, which would be economically feasible, but efforts to recover a pure potassium salt were discontinued because of the results of experiments which will now be described.
Extraction of the Melt
Reduction of Potassium Sulfate to Sulfide
TABLEI. RECOVERY OF ALUMINA FROM ALUNITE FUSEDWITH SODIUM SULFATE, SODIUM CHLORIDE, AND COAL Na?SOi Parts 1.72 1.72 2.33 2.08 2.07 1.80 2.20 1.90 2.00 2.00
Coal Parts 1.72 1.26 1.17 1.04 1.04
0.96 1.10 '1.01 1.00 1.00
NaCl Parts 0.17 0.14 0.23 0.21 0.21 0.18 0.22 0.19 0.20 0.20
Temp. Time Hr. C. 950 3 2 950 900 3.25 860 to 900 3 3.5 900 3 900 858 to 900 3 750 3 860 to 900 3 860 to 900 3
NaaSOi Reduced Per cent 52.6 54.5 82.4
45.5 71.0 86.8 81.0
90.5 83.5 84.2
A120a Reoovered Per cent 76.5 79.0 83.2
85 91.35 85.5 92.00 74.6 77.0 80.6
Potassium sulfate, mixed with coal in the proportions of 1 Fusions were made in a specially designed furnace, using part to 0.4 part coal and heated to 900' C. for 75 minutes, 200-gram samples of alunite with appropriate amounts of was reduced more quickly and smoothly than was the corsalt and coal. A white substance deposited in the flues. It responding sodium salt. There appeared to be no advantage was insoluble in water and small in amount. It was not in adding a chloride. The reduction was found to be better examined further. There was no evidence of volatilization than 92 per cent, an easily reproducible result. It was not of either potassium or alumina. considered necessary to fuse alunite with the recovered sulfide. Soluble silica in the melt was studied by J. A. Taylor. The percentage in the precipitated alumina varied with the Decomposition of Alunite by Fusion with efficiency of the recovery of the alumina. In a case when but Potassium Sulfate and Coal 19.3 per cent alumina was recovered from the alunite, the In a typical case, 25 grams of alunite with 69.4 grams of alumina contained 1.32 per cent silica or 0.26 per cent on the potassium sulfate and 29.1 grams of coal a t 900' C. for 3 basis of alunite treated. In a typical case when the recovery hours gave a pasty mass which cooled to a dense reddish solid. of alumina was 37.5 per cent of the alunite containing 0.66 This solid dissolved readily in water, from which was precipiper cent silica, the percentage of the latter on the basis of tated and recovered 97.5 per cent of the alumina in the alunite. alunite was essentially the same, 0.25. The alunite contained Analysis of an aliquot showed practically 100 per cent recovery 0.95 per cent silica, and apparently a fourth was rendered of potassium, much of it, however, in the form of carbonate. soluble by the alkaline fusion. That it might be much greater For a commercial development it would be essential to reif a highly siliceous alunite or coal where employed was not cover from this solution the potassium salt or salts for subseinvestigated, since both low-silica alunite and coal are availquent fusions. Consequently, a series of fusion tests was made able in abundance. with mixtures of potassium carbonate and sulfate. Samples The amount of water requisite for elutriation of the melt of ground alunite, each weighing 25 grams, were mixed each depended on the history of the latter. On the average, 1.6 with 10 grams of powdered coal and the mixed salts, and grams of water per gram of melt were adequate for conifused at 900' C. for various times. Table I1 gives the data plete solution a t 100' c., whereas about 2.7 grams of water for four typical cases. The results show that a 3-hour fusion were necessary a t room temperature. In order to effect is more than ample if the total proportion of added potassium thorough washing of insoluble residues, somewhat larger is sufficient and that the recovery of alumina is favored by proportions of water were actually used. The melt was the presence of a relatively large proportion of potassium agitated with the water a t about 100" C. until there was no carbonate. In the first and fourth tests' cited, examination further solution and the small insoluble residue, coming mainly from the coal, was allowed to settle. The supernatant liquid was decanted and the residue washed on a filter. The washTABLE11. RECOVERY OF ALUMINA FROM ALUNITEFUSED ings were added to the hot mother liquor, and carbon dioxide WITH POTASSIUM SULFATE, POTASSIUM CARBONATE, AND COAL was passed through until precipitation of alumina was comAlnOa Insol. Matter i n &so4 KaCOa Time Recovered Charge plete. Sulfur dioxide also precipitated the alumina, a fact of Parts Parts HI. Per cent Per cent possible importance since sulfur dioxide and carbon dioxide both are components of the stack gas. The freshly precipitated alumina is soluble in an excess of sulfur dioxide while silica is not; if necessary, a separation might be effected by utilizing the stack gas. On cooling, sodium carbonate separated as a solid from the of the insoluble residues indicated the presence of undecommother liquor from which the alumina had been removed. posed alunite. I n the second and third tests the decomposiA further precipitation of sodium bicarbonate was effected tion seemed to be complete. In all cases the insoluble residue by saturating with carbon dioxide. It appears desirable to was relatively large, the coal used in these tests having an ash follow what would happen by evaporating a t 100' C. in the content appreciably higher than that used in the experiments light of the Trona Company's experience as described by with sodium sulfate. Teeple (4). We would expect, a t first, precipitation of anOne of the solutions from which alumina had been precipihydrous sodium carbonate, then burkite ( 2 S a ~ S 0 ~ , N a ~ C 0 tated ~ ) was found to contain (in grams) : potassium carbonate,
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not be necessary to provide for more evaporation than the water used in extracting the potassium aluminate. The operations involved are simple and easily controlled and mechanical losses can be kept a t a small minimiun. The effectof the last vsould he only a slight decrwse in the output of potash salts.
Acknowledgment .4cknowledgment is made to J. Claude Redford, of Philadelphia, whose generous assistance made possible this investigation.
Literature Cited (1) Bodnikov. P. P.. Chem.-Zto., 51. 821. 842, 8GZ (1927). C!) Hill. A. E.,and Moskowitz, Sam.. J . Am. Chem. Soc., 51, 2396 (1929). (3) Huffman,E. O., and Cameron, F. K.. Ixn. EN@. CEIBX.,26. 1108 (1934). (4) Teepla, J. E., “Indnatrid Dwelopment of Searle’s Lake Brines.” A. C. S. hlonogmph 49, New Ymk. Chernionl Catalog Co., 1929.
H e o l r v m November 7, 1835. Presented before the Division of Industrial and Bngineeiing Chemiatry st the ‘30th .Meeting of the hmerioan Chemiesl SoDietY, Sell Fmneisoo. Calif., luaust 19 to 23, 1935.
PRESSED FOAM GELATIN s. E. SHEPPARD AND J. H. nuDsoN Eastman Kodak Company. Rochester. N. Y.
HE two principal aspects of the prohleni of finishing gelatin as a product ready for use are (1) the economv of the f i n i s h e process and (2) the actual utkty or convenience of the IesufG ant product. Gelatin has been prepared in a grcat number of forrns-e. g., sheets, flakes, powder, strings, pearls, spraydried powder. Each has certain advantages and disadvantages. In presenting this new mode of preparation, the object has been chiefly the development of a gelatin product (a) absorbing and dissolving in water with maximum rapidity and (6) not excessively bulky.
the liquor with an air lift through a baffle-type emulsator (Figure I). T h e foam is passed on t o a chill roll o r a belt which is passing over a chilled %urface, so t h a t t h e foam s t r u c t u r e is set. Gellinz or setting is extremely rapid, and it has even been possible to flow the foam onto a cold water surfacewhich set and conveyed the foam. In any case the set sheet of foam is taken from the first conveyor into airdrying sections, either in batch or on continuous driers. The time of drying is relatively reduced, although no great difference can be effected in this regard for gelatin, since ultimately it is controlled by the total amount of water to he evaporated and the diffusion path in the gelatin. The dried crepe or foam is then taken either continuously or in short sections and compressed. This is done by passing the hand. sections. or sheets of dried P . ~ P ~hPP Y
New Method The new form’ is obtained by producing a foam from the gelatin liquor, setting the foam layer, drying in situ, and then compressing the dried foam or sponge. To obtain a foam or crepe giving the greatest advantages in and after the suhsequent compression stage, controlled agitation is applied to the liquor. This may be effected by beating or by passage through so-called colloid mills, but a better method is to pass *Sheppard. 8. E., and Hudson. I. E. (to Esatman Kodak Co.), U. 9. Patent 2,wO,042 (May 7.1’335).
FIGURE
2.
(LEFTTO RIGHT)GX~LATZN saEeTs, GBI.ATIN F FOAMGELATIN
L
~ c ~ ~ ~~ ~~ , ~
E The ~ ~average E D diameter of the cells depends upon the conditions of foaming and largely
