1248
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 23, No. 11
Thermal Decomposition of Alunite' W. L. Fink, K. R. Van Horn, and H. A. Pazour ALUMINUM RESEARCH LABORATORIES, ALUMINUM COMPANY OF AMERICA, NEWKENSINGTON, PA.
The thermal decomposition of the mineral alunite, H E mineral a l u n i t e , and Northrup potentiometerK ~ 0 ~ 3 A 1 ~ 0 ~ ~ 4 S 0 3 .was 6 H ~investigated 0, by x-ray difhaving approximately type controller. A platinumfraction methods and chemical analysis. Alunite is wound tubular furnace was the composition reptransformed into submicroscopic or imperfectly formed employed for the heat treatr e s e n t e d by the formula crystallites of dehydrated alum by heating at 500-600' C. ments a t 1200" and 1400" C. Kz0.3A120~~4S03~6Hz0, has Dehydrated alum is decomposed between 700" and The changes induced by roastfrequently been considered 800' C. into Alz03(corundum) and K2SOI. A potassium ing were interpreted by soluas a possible aluminum ore. aluminate (&0,10A1zOs) is synthesized from the A1203 bility measurements and by Alunite c on t a in s conaiderand a part of the &SO( on heating between 1200' and x-rav diffraction m e t h o d s ably less a l u m i n a (37 per 1400' C. cent) than bauxite and conwhilh positively identified the crystalline phases. s e q u e n t l y could n o t be commercially used as an ore unless sufficient return could be Diffraction patterns were produced by the powder method on a General Electric x-ray apparatus equipped with a molybrealized from the potash (11.4 per cent). denum target tube, operating a t 30,000 volts and 20 milliPrevious Work amperes. The exposure periods were 24 to 48 hours. In Potash has been recovered from alunite in the form of measuring the positions of the lines, corrections were made potash alum since the thirteenth century. The industry for any dimensional changes in the films by reference to the centers a t Tolfa, Italy, where extensive deposits of alunite sodium chloride pattern which was recorded on each photooccur. The process was described by Waggaman and gram. The various reflections were rated as to intensity, five Cullen (2) in 1916 as follows: "The mineral is calcined at degrees of intensity being recognized. Samples of alunite heated from 18 to 48 hours a t 250low red heat in heaps or in kilns for about six hours. When the oxides of sulfur begin to escape, the material is removed 500" C. gave only the sharp x-ray reflections characteristic and transferred to brick bins where it is exposed to the air of the rhombohedral lattice of untreated alunite. A sample for several weeks or months, being moistened with water heated 20 hours at 600" C. gave a diffuse pattern indicating from time to time during that period. The product is then very small or imperfectly formed crystals of a new phase (X) mixed with water and, after the insoluble material has settled, and a trace of residual alunite. A specimen subjected to a the clear solution is decanted, evaporated, and crystallized." 13-hour treatment a t 700" C. produced only the sharp diffracDuring the World War when German potash could not be tion lines of phase X. The pattern of a specimen treated at imported, potassium sulfate was commercially extracted 800 " C. revealed predominant reflections of a-alumina from alunite in the vicinity of Marysville, Utah, where the (corundum) and some K&04 lines. Heating at 1000" and largest known deposits in the United States are located. 1200" C. produced sharper reflections of the alumina and The mineral was heated at about 1000" C. to produce water- K2S04. The alunite roasted a t 1400" C. was transformed soluble potassium sulfate and alumina. After leaching and entirely into a different phase ( Y ) . X-ray diffraction methods were advantageously applied filtering, the potassium sulfate was recovered by evaporating in the identification of phases X and Y . The composition of the solution. A number of methods proposed for the recovery of pure alunite would indicate that the phase X might be aluminum alumina, in addition to the potash, have been described in an sulfate, potassium sulfate, or a double sulfate of aluminum extensive survey of the literature by Edwards, Frary, and and potassium. The pattern of phase X was entirely differJeffries in 1930 (1). Most of the methods involve a pre- ent from that of K2SO4or Als(S04)3which had been heated at liminary roasting treatment to increase the rate of solution 700" C. for 16 hours. Consequently a series of samples in acid. The temperatures suggested can be classified into was made containing various molecular ratios of anhydrous three groups-500-750" C., 750-1000° C., and 1000-1600" C. aluminum and potassium sulfates and treated for 32 hours a t Although there are a number of contradictory claims in the 700" C. The x-ray photogram of the sample synthesized from patent literature, it would appear that, in the first range, equimolecular quantities was identical with that of phase X. acid-soluble sulfates are probably formed; in the second, Diffraction patterns of the samples consisting of one and oneK2S04 and AlZO3; and in the third, either alumina and half, two, and three moles of AlZ(SO4)3to one mole of showed increasing quantities of &(SO()a but predominant K2S04 vapor, or potassium aluminate. The possibility of profitable utilization of alunite in the reflections characteristic of phase X. The composition of future and the discrepancies in the literature concerning the phase X can therefore be represented by the formula Mzroasting reactions initiated the present investigation to deter- (S04)3.K2S04. It was noted that this formula is that of dehydrated alum. In order to determine whether or not the mine the mechanism of the roasting processes. crystal structures are identical, a sample of potash alum was Mechanism of Roasting Processes dehydrated a t 700" C. and found to have the same atomic Alunite containing 36.50 per cent A1203, 10.73 per cent arrangement as phase X. A chemical analysis of phase Y (i. e., alunite heated at KzO, and 1.37 per cent Fez03 was roasted for various periods at temperatures ranging from 250" to 1400" C. The roasting 1400" C.) revealed that all but 0.02 per cent SO4 had been a t temperatures up to 1000" C. was performed in a small volatilized and that the KzOand A1203occurred in the stoichionichrome-wound muffle-type furnace equipped with a Leeds metric ratio of one to ten (K~0.10A1~03). It was desired to ascertain whether the compound Kz0.101 Received July 21, 1931. Presented before the Division of Industrial A1203 could be prepared by another method. Alumina t i and Engineering Chemistry at the 82nd Meeting of the American Chemical hydrate (a&o3.3H20) was dissolved in potassium hydroxide Society, Buffalo, N. Y., August 31 to September 4, 1931.
T
IiYD USTRIAL AND ENGINEERISG CHEMISTRY
November, 1931
1249
Table I-Interplanar Spacings ( d ) and Intensities of X-Ray Reflections ( I ) a ALVNITEAFTER ALUNITEA F T h R ALUNITEAFTER ROASTINGAT ROASTINGAT ROASTING AT 600" C. 700' C. 8000 c. a A1203 KzS04 I d I d I d I d I
I d IALUNITE
5.65
4 93 3.46 3 34 2 965 2.87 2 57 2 46 2 27 2.19 2 12 2 01 1.886 1.73 1. b32 1.558 1.49 1.419 1 38 1 36 1 311 1.278 1.20
!+ E 3 2 68
1 5 2 1 2 4 2 1 1 4 4 2 2 4 2 3 2 2 3 3
2 36 2 27 1 815 1 515 1 436 1 359 1 118 1 088
5 4 3 4 3 4 3+ 3+ 3+
;
I
A.
4 08 3 61 3 46 3 24 2 99 2 85 2 652 354 2 26 2 08 2 02 1 975 1 815 1 79 1 735 1 66 1 615 1 598 1 518 1 483 1 43 1 395 1 36 1 32
2 J
1
2 1 4 3 4 3 2 2 2-t 3 + 3 1 1 1 1
3.2 3 t 3 3 2
A.
A.
4 14 3 46 3 23 3 10 2 99 2 88 2 73 2 54 2 40 2.36 2 20 2 07 1 96 735
2 3 2 1 3
3 2 2 2 2
49 SO 70 55 38
3 3 3 2 5 2
1 1 60
1 595 1 542 1 505 1 395 1 37 1 30 1 235
4
;+ E 74E
1 1
5 4 1 1
Intensity: very weak, 1; weak 2, medium, 3 , strong, 4, very strong, .?
1 545 1 51 1 405 1 375 1.235 1 185
4 1 1
5 4 5 1 4 5 1 2 4 5 4
2
A
4 145 3 73 3 36 3 11 2 99 2.885 2 65 2 495 2 40 2 36 2 22 2 OS 1 99 1 94 1 87 1 76
3 2 2 2 5 5 1 3 4 3 4 4
674 1 62 1 565 1 492 1 43 1 39 1 35 1 299
2 2+ 2 3 2 2 2
2
2
ALUNITEAFTER ROASTINGA T 1400' C. d I
A.
4 44 3 50 2 80 2 69 2 61 2 51 2 40 2.24 2 135 2.07 2 03 1 975 1 933 1 835
;+ ;
'+
E 3 1 598 1 563 1 485 1 418 1 396 1 346 1 26
2 1 3+ 4 1 4 2 2 3 1
3 2 2 2 2 1 3+ 3 2 2 5 3
1
solution and boiled, and the viscous liquid poured on a glass The x-ray results and solubility measurements indicate plate. After crystallization the product was dehydrated and that a t a temperature between 500" and 525" C. alunite besubsequently heated a t 1400" C. for 6 hours. The diffraction gins to transform into submicroscopic or imperfectly formed pattern and chemical analysis of the roasted material were crystallites of dehydrated alum, which are readily soluble the same as those of alunite roasted a t 1400" C. in sulfuric acid. This transition is substantially complete I n connection with the preceding experiment two other a t 600" C. An increase in temperature promotes crystal phases of the system KzO-Al203 were encountered a t elevated growth until a t 700" C. sharp x-ray reflections of dehydrated temperatures. One can be prepared by heating K20.Al203 alum are obtained. The larger crystals dissolve less rapidly a t 1100" C. and the other by similarly treating K20.3A1203. in sulfuric acid. A second decomposition occurs a t some These phases persist a t 1400" C. when experimental condi- temperature between 700" and 800" C. with the formation tions are unfavorable to the volatilization of the K20. of C Y - A ~ ~(corundum) O~ and K2S04crystals. Increasing the The x-ray patterns of alunite, treated a t various tempera- temperature t o 1200" C. results in crystal growth. A potastures as previously described, and those of dehydrated alum, sium aluminate (K20.10A1203) is synthesized from the alumina KzS04,and alumina are reproduced in Figure 1. The estimated relative intensities of the reflections and the interplanar distance are given in Table I. It has frequently been recorded in the literature that roasting a t temperatures from 500" to 700" C. substantially increases the rate of solution of alunite in dilute sulfuric acid The following simple experiment illustrates the variation of solution velocity with temperature: Samples of alunite which had been roasted for 21 hours a t different temperatures up to 700" C. were digested with sulfuric acid solution. A concentration of 25 per cent2 acid was selected on the basis of a preliminary determination of the rate of solution of dehydrated alum in sulfuric acid of various concentrations. The alunite samp!es (1 5 grams) were each placed in 250 cc. of the solution and maintained a t the boiling point. Water was periodically added to prevent concentration of the acid. The sample treated a t 600" C. dissolved in 1 hour. Alunite roasted a t 575O, 625". and 650" C. dissolved in 1 hour and 45 minutes. Solution of all other samples was incomplete, even after a 12-hour digestion. It would seem that the solution velocity attains a maximum a t a roasting temperature of about 600' C.
15
The effects of the various roasting temperatunis on the Figure 1-Diffraction Patterns solution velocity were quantitatively evaluated by deter1-Alunite (not roasted) 2-Alunite (after roasting at 600°C ) mining the aluminum content of alunite residues after 43-Alum (after roasting a t 7003 C.) hour digestion treatments in 10 per cent sulfuric acid at 4-Alunite (after roasting a t SOOo C.) 5-Alumina (corundum) the boiling point. The volume of solution was frequently 6 -KISOP 7-Alunite (after roasting a t 14005C.) adjusted to maintain the ratio of 250 cc. to 1.5 grams of sample. The results are shown in Table 11. and a part of the potassium sulfate between 1200" and 1400" C. The remainder of the potassium sulfate is volaTable 11-Roasting Temperatures and Solution Rates of Alunite tilized a t this temperature. ROASTINGTEMP. A1203 DISSOLVED ROASTING T E M P .41zOs DISSOLVED It was found by x-ray methods that the roasting reaction c. 470 c. 70 No roast 1 62 625 '99 72 which occurs a t 500-700" C. can be reversed and alunite 525 76 66 650 '99 67 formed by heating the decomposition products a t 170" C. in 550 99 83 675 85.29 575 99 87 700 84.80 saturated steam [ l l 5 pounds per square inch (8.08 kg. per sq. 600 99 87 .____ cm.) pressure] for 21 hours. This explains the experimental that heating under pressure is not conducive to the * T h e percentage of acid signifies per cent by volume of acid hnving a density of 1 8 4 . solution of alunite.
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INDUSTRIAL AND ENGIXEERING CHEMISTRY
Vol. 23, No. 11
Acknowledgment
Literature Cited
The authors express their appreciation to C . RI. Tucker who assisted in the investigation.
(1) Edwards, J. D., Frary, F. C and Jeffries, 2.. “The Aluminum Industry,” 1st ed., Vol. I, p. 216, McGraw-Hill, 1930. (2) n’aggaman, S. J . , and Cullen, S. J. A., U. S. Dept. A g r , Bull. 415 (1916).
Catalytic Partial Oxidation of Alcohols in the Vapor Phase-111’” W. Lawrence Faith* and D. B. Keyes DEPARTMENT OF CHEMISTRY. CNIVRRSITY OF ILLINOIS, URBANA, ILL.
APOR-phase p a r t i a l The catalytic partial oxidation of ethyl alcohol and which has a lower heat-transoxidation offers great methanol has been carried out. Different forms of fer coefficient. silver, copper, and nickel catalysts have been used. I t This was t h o u g h t t o be possibilities in solving the p r o b l e m s of m o d e r n has been found that the form of catalyst having the true b e c a u s e a c a t a l y t i c chemical industry. This has highest coefficient of heat transfer gives the highest conr e a c t i o n will t a k e p l a c e version of intermediate products. A laboratory aplargely a t the most active been shown by the excellent work of Jaeger, Downs, and paratus for obtaining duplicable results has been conS p o t s , or r e g i o n s , i n t h e others on the partial oxidastructed and described. catalyst. If the reaction is e x o t h e r m i c , this will cause tion of benzene, naphthalene, a localized accumulation of heat and therefore an increase in and anthracene. However, before this work can be extended to the oxida- temperature a t these active spots. Unless this heat can be tion of other organic compounds, much study must be made on conducted away from these localized high-temperature rethe fundamental nature of oxidation catalysis. The vapor- gions, the reaction (in this case an oxidation) will be carried phase partial oxidation of alcohols offers a convenient system to completion instead of stopping a t an intermediate point. for such a study, since all variables may be easily controlled. If the catalyst itself has a high heat-transfer coefficient, it The greatest criticism of recent work on partial oxida- should conduct the heat away from these regions and stop the tion of alcohols is that each investigator has used an entirely reaction a t the desired stage by keeping the entire catalyst a t different apparatus in his work, and that work done when a lower and more uniform temperature. using one apparatus is not duplicable when using another. I n order to show this clearly, it was decided to use several Therefore, it was decided to devise an apparatus of simple catalysts (each in two different forms), one of which had construction, which might be easily reproduced and, by means a high and one a low coefficient of heat transfer. To test of which, investigations on vapor-phase partial oxidation of this theory more thoroughly, catalysts of markedly different alcohols might be accurately and easily duplicated. activity were chosen for this reaction, i. e., silver, copper, and I n an article on ammonia oxidation, Parsons (8) has nickel. The metallic form of each of these was chosen for pointed out that platinum is much preferred to nonmetallic that form having good heat transfer, while the oxide of each, catalysts since it simplifies the local overheating problem. deposited on asbestos fiber, was chosen for the form having It was, therefore, thought probable that the form of a poor heat transfer. particular catalyst which permits the greatest amount of Apparatus and Procedure radiation will yield the best conversions of intermediate products (i. e., aldehyde and acid) in the oxidation of alcohols. The apparatus used is shown in Figure 1. In other words, that form of a catalyst which has the highest Air was Dassed through - a flowmeter, where rate of flow coefficient of heat transwas m e a s u r e d , thence fer could be maintained through a drying tower a t a more uniform temcontaining CaC12, to the perature than any form p r e h e a t e r . The preof the s a m e c a t a l y s t heater was simply a cop1 Received July 24, 1931. per coil immersed in the Presented before the Division thermostat. From the of Industrial and Engineering preheater, air could be Chemistry a t t h e 82nd Meetuhbruhon Murk ing of the American Chemical led into the furnace by Society, Buffalo, N. Y., August any one of three means. 31 t o September 4, 1931. Atfirst, stopcockawasso 9 P a r t I, “Studies in Liqturned that air passed uid Partial 0 x i d a t i o n -1,” IND.E N G .C H E M . ,21, 1227 through carburetor A , (1929); P a r t 11, “Studies in and thence through stopLiquid Partial Oxidation-11,’’ cock d, to tube leading to I b i d . , 23, 561 (1931). 8 S u b m i t t e d b y W. furnace. Previously, alLawrence Faith in partial fulcoho1 had been let into filment of the requirements for carburetor A by means the d e g r e e of doctor of philosophy i n chemistry i n the of the dropping funnel Graduate School of the Unishown. F i g u r e 1 A p p a r a t u s for V a p o r P h a s e P a r t i a l O x i d a t i o n of Alcohols versity of Illinois.
V
