November, 1946
1181
INDUSTRIAL AND ENGINEERING CHEMISTRY LITERATURE CITED
Anon., Modern Packaging, 17, 103 (1943). Bloomfield, G. F., J . Chem. Soc., 1943, 289; Rubber Chem. Tech., 17, 1 (1944).
Bloomfield, G. F., J . Chem. Soc., 1944, 114: Rubber Chem. Tech., 17, 759 (1944). Bruson, H. 9., Sebrell, L. B., and Calvert, W. C., ISD. ESG. CHEDI.,19, 1033 (1927). Buizov, B. V., and Kusov, A. B., J . Rubber I n d . (U.S.S.R.), 12, 46 (1935). Burger, V. L., Donaidson, U’.E., and Baty, J. A., A S T N B u l l . No. 120 (1943); Rubber Chem. Tech., 16, 660 (1943). Dawson, T. R., and Schidrowita, P., in Davis and Blake’s “The Chemistry and Technology of Rubber”, A.C.S. Monograph 74, pp. 656-77, New York, Reinhold Publishing Corp ., 1937. Endres, H. A., Rubber dgc, 55, 361 (1944) ; Rubber Chem. Tech., 17, 903 (1944). Farmer, E. H., Endeavour, 3, 72 (1944). Field, J. E., The Goodyear Tire & Rubber Co., unpublished work
Fishei:H. L., Chem. Rev., 7, 51 (1930). Fisher, H. L. (to B. F. Goodrich Go.), U. S. Patent 1,605,180 (Nov. 2, 1926).
Fonrobert, E.. Inaugural dissertation for doctor’s degree, Konigl. Christian-Albrechts-Universitat,Kiel, 1913. Garvey, B. 8. (to B. F. Goodrich Co.), U. S. Patent 2,168,279 (Aug. 1, 1939).
Glasstone, S., Textbook of Physical Chemistry, p. 520, X . Y . , D . Van Nostrand Co., Inc., 1940. Harries, C., and Fonrobert, E., Ber., 46, 773 (1913). Jones, F. A., Trans. Inst. Rubber I n d . , 17, 133 (1941). Jones, W.-4., and Winkelmann, H. A . (to B. F. Goodrich Co.), U. S. Patent 1,751,517 (Mar. 25, 1930). Kirchhof, F., Gummi-Zt., 46, 497 (1932). Kurta, S. S . , and Lipkin, XI. R., IXD. ENG.CHEY.,33, 779 (1941).
(21) Lawson, W., U. S. Patent 2,018,678 (Oct. 29, 1935). (22) McGavack, J., IND.ENG.CHEY.,15, 961 (1923). (23) Medvedchuk, P. I., Aldoshin, F. D., Marovich, V. P., and Repman, -4. V., J . Gen. Chem. (U.S.S.R.), 12, 220 (1942); Rubber Chem. Tech., 18, 24 (1945). (24) Memmler, K., “The Science of Rubber”, translated by R. F. Dunbrook and V. N. Morris, pp. 159-230, New York, Reinhold Publishing Corp., 1934. ( 2 5 ) Meyer, G. (to I. G. Farbenindustrie), U. S. Patent 2,166,604 (July 18, 1939). (26) Powers, P. O., “Synthetic Resins and Rubbers”, p. 266, New York, John Wiley & Sons, Inc., 1943. (27) Schidrowitz, P., Trans. Inst. Rubber I n d . , 11, 458 (1936). (38) Schidrowita, P., and Redfarn, C. A , , J..Soc. Chem. Ind., 54, 263T (1935). (29) Sibley, R. L., I n d i a Rubber World, 106, 244, 347 (1942) : Rubber Chem. Tech., 16, 111 (1943). (30) Soll, J. ( t o I. G. Farbenindustrie), U. S. Patent 2,157,185 (Jan. 16, 1940) ; J. So11 and A . Koch, German Patent 619,211 (Sept. 25, 1935). (81) Staudinger, Hermann, and Staudinger, Hansjurgen, J . prakt. Chem., 162, 148 (1943); Rubber Chem. Tech., 17, 15 (1944). (32) Thies, H. R., IND. ENG.CHEM.,33, 389 (1941); Rubber Chem. Tech., 14, 398 (1941). 133) Thies, H. R., and Clifford, A. M., IND.ENG.CHEM.,26, 123 (1934). (34) Tiemann, F., Ber., 33, 3710 (1900). (35) Vanderbilt Rubber Handbook, 8th ed., p. 314, New Y-ork, R. T. Vanderbilt Co., 1942. (36) Weber, C. O., Ber., 33, 779 (1900). (37) Whitmore, F. C., “Organic Chemistry”, p. 45, New T o r k , D. Van Nostrand Co., Inc., 1937. PRESENTED before the Division of Rubher Chemistry a t the 109th Meeting of the A M E R I C A N C H E I r x c a L SOCIETY, Atlantic City, N. J. Contribution S o . 130 from the Goodyear Research Laboratory.
Extraction of Alumina from Clay ’
OTTO REDLICH, C. C. JIARCH, JI. F. ADAMS, F. H. SHARP, E. IC. HOLT, AND J. E. TAYLOR The State College of Washington, Pullman, Wash. T h e old problem of extracting alumina from clay is particularly important for the Pacific Northwest. A method is presented which, by a combination of sulfurous and sulfuric acids as leaching agents, leads t o alumina in a few, comparatively simple steps and at a minimum expense for reagents. Silica, the only major impurity, is removed by dissolution in alkali and reprecipitation of pure aIumina. Extensive laboratory tests indicate that all operations proceed smoothly and furnish high yield.
T
HE main aspects of the problem of alumina extraction from clay are generally known. Up t o the present alumina, the intermediate in aluminum manufacture, has been produced almost exclusively from bauxite. T h e deposits of this ore in the United States are insufficient. T h e only abundant domestic raw material is clay. The innumerable attempts at developing a method of alumina extraction from clay have been discussed by Frary and Mason (b). I n the Pacific Sorthwest a clay process would be of particular interest because the transportation differential for alumina (or the differential for bauxite in connection with the high fuel cost) is the economic disadvantage t o the new aluminum plants. The high fuel cost is a srrious obstacle t o clay processes such as those of Buchner or Pedersen. On the other hand, the Pacific Northwest is in a favorable position regarding electric power and the availability of sulfur dioxide in the flue gases of sulfide ore smelters.
For these reasons, our attention was focused on the use of sulfurous and sulfuric acids and electrolytic recovery of the reagents. -4process of leaching clay with sulfuric acid, converting the aluminum sulfate t o sodium aluminate, and recovering the reagents by electrolysis was previously described by one of the authors ( l a ) . SULFITE PROCESS
The essential steps i n producing alumina from clay by means of sulfurous acid were already considered “prior art” by Raynaud (14) in 1900. The recent modification of this method described in the patents of Th. Goldschmidt A,-G. is one of the few clay processes ever carried out o n a commercial or semicommercial scale (2, 6 , 7, 18). The inventors of the Goldschmidt group described a number of improvements i n several United States patents: calcination (-@), leaching (25),precipitation (Zd),decomposition ( 7 A ) . Corresponding British patents do not contain more and the German patents disclose far fewer details than the ;imericsn specifications. The essential points of these patents are based on the discovery of monobasic aluminum sulfite, A1201.2S02.rH20, a s well-defined cryytalline phase. The existence of this compcund has been confirmed by Huber (8), Rosenkrantx and Huttig ( l 7 ) ,and Bartz ( 3 ) . The technical progress claimed in the Goldschmidt patents consists of the practically complete precipitation, under certain conditions, of silica-free monobasic aluminum sulfite from silicacontaining leach liquors. We have not been able to confirm this result.
1182
INDUSTRIAL AND ENGINEERING CHEMISTRY
WATER SUPPLY
7 1\
CONSTANT FLOW RATE DEVICE
/
U
'1 Figure 1.
1-1
I
I
Leaching of Clay w i t h Sulfurous Acid
Vol. 38, No. 11
:tluminum sulfito with incrcaying tcmporwiurc :it :I .illfur dioxide pressure of' o n e ntmosphcrc. This is easily c-xl)l:iiiictl action c'ffcct. Our ;in:ilysc-s of aluminum sulfite wlutions of various concentr:itioni, obtained undir a sulfur tiiosidc pressurc of i)ne :itmosplierv, indicate that the aluniiria is present mainly : I + :in ion Al(SOa)2-. The decrease in the oxitlc with incrciihinp tem1)~xiconcentration o t Ircc sition of this ion a n c l t l i t formiturv grc:itl>- favors tlie tion of more basic coml Obviously the :ittainable final conwntration is 1:irgi.r :it L: higher sulfur tliosidc pressure. Tliis means n.aj adolitcd in the patent of Fulda, Wiedbrauvk, and Biichc ( 2 5 ) , Tvhich also p i e scribes that t h t flow velocity 0 1 the leaching liquor tic mnint:iiiii.tl a t a point \vlicrc prccipitntion of basic aluminum sulfite is pwycntcd. The flax rntc to l ~ eused is intliwtcd in no 0 t h n-:iy than by reference to this desired effert. I n vieiv of the great expense involvc'd in the IIW of ii corrusiunresistant- autoclave, it was considered desirable to obtain a higli final conccntrat ion a t atmospheric pressure. Acid :ilumiiium sulfite solutions tcncl to supersaturation. From Tamniann's investigations (2.3)i t is ne11 known t h a t this tcxndency may bc clue t o a small numhcr of sceds. t o x lon- rate of crystal growth, or t o both factors. T h e nllization of monobasic aluminum sulfito proceeds veri- slow the second type‘. To long therefor(. :ivoitl :i Inserting gloss ~ ~ oplugs o l between the six columns of the 1cac.hing battery proved t o be a simple and reliablc device to product: final conceiitriztions of 40 to 50 grams of alumina per liter :it 55 O C., or u p t o twice t h e equilibrium concentration. .Isthe amount o f material held back by the filters is small, this'devicc c a n easily be used on a n industrial scale. Table I gives the results of a n 8-day period from a continuous, 6-week leaching test in which various conditions (temperature, flow rat(., r h y I(%:ichingtimc) ivcrc csnmined. I'hr systcm had iion:iI,y s t a t e a t ( 1 1 ~ :.start of t h c . X-cl:iy pt.umetl that the :iluniiria contciit 01 tlrc y s Iy cqual a t thc' G t : i r t nntl tlic end i ) f t l i v poriotl. Ex~eryd:iy t h r cwlurnn ncnrc>.t t o thc li(1uor inl)ul x i > remolctl, :ind :I Crc?.Ghl>-r1i:ii.gc.d voluinri ,in vital. Hp. Net leaching r o l u r i tions): 1.85 liters (liquor) C o c k , Wash., clay calcined a t 800° C., s p . gr. 0.69 liters (clai-) = 2.54 1 Trariousfactorshave been examined by batch tests 2.38. Ignition loss of (11. ed clay, l.'iIi&. h v . charge 321 prariis per ( 2 6 ) and continuous countercurrent leach. I n accolumn. Total Icnclririi: tiriie, 1!11 h clay portion leached 144 h r . f liquor passed cordance n-ith two of the Goldschmidt patents (25), i t has been found t h a t a temperature of 50-60° C. and countercurrent flow give the best results. The dissolution rate v a s lower with residwil clays (deCalcined c l a y 40 0 ' ; i 2370 E. 1028 100 $2 6 Leach liquor l ( j O n . I. I i 1 .52'; l i 41. 801 78.0 36.1 posits near Mica and Freeman, Wash.) than with a Leach residue 10 7 ' . 18100. 103 18.7 . . ... N o t accounted ior . . ... .... 34 3.3 .... transported clay (Castle Rock, Wash.). S e t leaching voluirie rr,(juirrii i i i s > r~,ir!\ o u t p u t of one unit alumina: 2 . 5 X I 9 l / S O l X 24 X Below 50" C. the dissolution rate drops rapidly. 365 years.literc,'gran> = O.O(i'3 > ~ " I Y l i t e r t kg. = 0.00'3 yeur.cubic mnters/metric t o n = T h e upper limit is practically determined by the 2 . 2 0 years.cuhic i w t a h o r t t n i i . .'XI> :ippropriatc niidition is t o be made for t h e gas phase. rapid decrease in the solubility of monobasic j ' ,
~
November, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
T A B L E 11. BATCH PRECIPIT.4TION O F BASICL4LU\IISUM S U L F I T E AT AT\IOSPHBRIC PRESSL-RE (690-700 JIM. 3 I E R C U R Y ) Te.1 Nu.
278
0 11 13 25 :3 0
G!) IiU 69 c; 9
..
30.8 35.4 34.4 {I 3 8 0
127 02 87 -13 40
0.65 0.67 0.40
2i0
0
..
36 8 35.1
0 6.i 0.tiY 0.04 0.63
28.i 22.,
127 116 114 110 102 79 73
0.66
30.9
0 13
40.4 26.8 19.3 4.9
84 65 37
...
0.14
0 17
31.0
0.13
0 21
30.9
0.24
...
10
23 29 :i3 46 ?St
283
0 30 39 85 132 0 3G 59 85 182
287
0
B 3
c,
11
13 24
37 -_
--,
J
.> i
00 02 (i8
6.5 69 74 i9
G .i i1 7.5
7'9 ..
72 72 76 80 80 80
..
32.0 30.8
1.1
1G
40.4 24.5 9.0 8.6 1.9
76 40 28 14
0'73 0.70 0.70 0.55
37.9
...
0.70
...
83 58 40 34 22
...
0.32
O.(ii 0.64
0.72 0.70 0.70 0.52
... ... ... ... ...
0 Gl
0.30
... ... .. ... ... ...'
9.0
,
alumina. I n a preliminary discussion (15) the volume was estimated a t 0.087 cubic meter. Appropriate space for the gas phase niust be added to these figures. The tank volume required for obtaining a certain final concentration of aluminn in the liquor depehds appreciably on the nature of the clay and on the desiretl yield. -4 tank volume of this size does not require an unrcasonably high investment. Precipitation. If sulfur dioxide is expelled from aluminum sulfite solutions by boiling, practically the total alumina content quickly precipitates in the forin of a highly basic sulfite of varying conipo.ition. It was found that the same result can be obtained at any temperature by applying vacuum. I n general, the precipitates arc slimy and practically unfilterable. Only a t fairly high dilutions arc \vel1 filterable though still fluffy and voluminous precipitates obtained. Since dilution of the liquor would involve serious tcchnicul disadvantages, precipitation tctsts were carried out by dropping leach liquor into a hot portion d tlic same liquor from which the major part of aluminum sulfite liad been previously removed. Another way of precipit:ition consisted in dropping the liquor through a tube agairiit a stream of steam. Both methods furnish easily filterable precipitates in a quick, continuous operation. The precipitation of a highly basic sulfite is known to be efhcicnt in removing iron if air is carefully excluded, especially \r-hile the precipitate is being washed. Ferrous ion in contact with the precipitate reacts with oxygen instantaneously t o form insolublc ferric oxide. But the products obtained by quick precipitation contain, probably bl- :itlwrption, practically all the si1ic:i of' tile leach liquor. K i t h tlic clay samples and leach methods used in the present investigation, this amounted to about 1.5-2 grams of silica per 100 grams of alumina. Monobasic aluminum sulfite, .11,0,.2SOa.zH20, crystallizea from t,hc leach liquor under appropriate conditions, especially if a sufficient sulfite concentration is maintained, The Goldschmidt p t e n t of' Wiedbrauck and Biiche ( S i ) i n which this compound is first described, asserts that this compound crystallizes practically f r w of silica. There is a weak point in the Goldschmidt patents. If conditions are maintained under which the monobasic sulfite crystallizes a t a n appreciablc rate and to a tcchnically appreciable estcnt, the solution is unstable not only with respect to the monobasic sulfite but also with respect to the highly basic, fluffy
1183
precipitate. unfortunately c ~ c nn small nrnount of the 1nttc.r cnrries along enough silica t i l make the eep:iration entirely insufficient. The precipitation of tlic, monob ic sulfite TT:E c:iri,ied out in ('on iuous, and under pressure. three series of testa-batch. In a11 cases heating n-as cnrrietl out sloivly to I)rei'c,nt loc*:ilsupc'rheating aiitl undue loss of sulfur cliosiclc. M-liil(, the pnteiit o f Kiedhr:lucli and Biiclic. ( 2 . ; : u w s n t c m p i x i t u r c ot' S2.5' C. a t :itnioxphei,ic pressure, n .lightly 11,n.cr temper: t ure limit was to be expected in Pullman, K : i . ~ I i , ,on :iccount of' tliix 1on.t.r ntmosplic,ric pre.swrc. The result.< of some of t h c h i t c h precipitxtioiii iiw cornpilcd iu T:tl)le 11. l'licse tc,.-ts n - e i ~carried out n.:tli SO0 ml. o f 1e:ich li(1uor ivliich x i s stirrcatl except in test 279. The liquor used in tests 278 and 279 \viis more tiinn 2 months old. Becniiic some colloidal :ilumin:i might have formed in the solution during this period and caused formation of somc fluffy preciliitnte, tlie follo~ving tests n-erc carriecl o u t n i t h f r i ~ ~ I ipreparetl 1~liquor. I n no test was a silicu content lower than 0.13 pram per 100 grams of silica obtained; this result v a s definitely unsatisfactory. h s n-as to be expected, thc silicu content n-as lower if tntion proceeded more slcn.1-y. T h e tinit: required sufficient removal of silica n-as so long t h a t tlie corresponding tank volume would represent a serious cost item. Table I1 also shows that the iron content of the precipitate is high (the leach liquors contained about 6 grams of ferric oxide per 100 grams of alumina). The low efficiencyof theiron s q x i r n tion is in accord with the patent of Fulda, K e d b r a u c k , and Biirlie ( 2 1 ) . The precipitates obtained from iron-coiitainiiig solutions have a slight broivnish-ycllon- tinge. Oxidntioii to n ferric compound was safely avoided in these tests. It is to be concludixd that tlie basic sulfites of aluminum arid iron form mixed cryatnls. The tests on continuous precipitat,ion wcre carricd out in a tilted Pyrex tube, 45 mm. in outside diamcxter and 1000 mm. long. The tube m-as heated by three independently controlled coils of Sichrome wire (65' C. near the input, 80" C. near the output). During a period of'9 days, 10.7 liters of freah leach liquor wcro sent through the column. Of a total alumina content of 438 grams, a n amount of 291 ( 6 6 5 ) n-as recovered in thc: precipitate. The precipitate contained 0.66 gram of si1ic:i per 100 grams of alumina. On t>heaverage, tlie liquor pasbed fhrough the tube in 25 hours. The low yield and tlic slownc~ssof precipitation would
TABLE 111. PHCCIPITATIOX OF A ~ O S O B . ~ S I C A L ~ x SCLFITE I ~ ~ ~ CSDER HIGHER PRESSK-RE Test SO.
1490
Input Ppt. FiltrFte
Amount, Granis Total AlzOs Si02 580 18.4 0.33 57 13.9 0.23 . 4.1 0.11
..
Input Ppt. Filtrate
580 48
Input Ppt. Filtrate
580 47
1494 1497
1191
14'93
1499
791
792
Weight R -___ SiOz/ Fez081 AlzOa AlzOs 1.80 5.8 1.66 0.28 2.59 25.3
5.8
Llole Ratio,
sod
.\ I
2 03
....
1.87
....
....
18.4 13.8 3.5
0.33 0.32 0.08
l.b0 2.32 2.21
. ..
18.4 13.5 4.5
0.33 0.23 0.10
2.16
22.8
,..
1.94
Input Ppt.
580 48
18.4 12.3
0.33 0.24
1.80 1.93
5.8
....
Input Ppt. Filtrate
530 54
18.9 13.5 2.0
0.30 0.20 0.11
1.80
5.8
...
46
1.93
3.0
Input Ppt. Filtrate
580 52
18.4 12.9 3.3
0.33 0.23 0.10
1.80 1.93 3.1
5.8 0.35 30
1.81
17.3 10.9
0.04
.. . . ... .
0.41
.. .. ... .
4.1 0.27 11.5
1.24
2.7
29.0 12.2 14.0
0.91 0.22 0.72
3.14 1.82 5.15
0.25 9.6
Input Ppt. Filtrate Input Ppt. Filtrate
.. .
.. .
... 580 ..36. 810 40 ...
1.80 1.08
!.+S
.,
,
30.7 5.8
...
5.0
1.83
....
....
....
2.07
.... .... ....
f
.
.
.
1.74
....
1184
1 7
-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 38, No. 11
a systematic error in the analytical method used for determining small amounts of silica in alumina, in the basic sulfite, and in similar substances. S o satisfactory method has been found in the literaHEAT EXCHANGER CALCl M A T I O N ture, The amount of silica in a sample of rcasonable size is too low for the standard gravimetric: ABSORPTIOU SO2 LEACH method. The colorimetric molybdate method of Jolles and Neurath ( 9 A ) and later investigators is satisfactory for samples of practically pure S U L F I T E - SULFATE water. I n the present case various sources of LIQUOR error cause, in general, erratic results which are always too low. One of the authors developed a colorimetric method which has proved satisfactory LEACH in numerous checks ( 1 ) . It was believed that some reagent not mentioned ALUMINUY in the patents (24) might keep t h e silica in soluSULFATE tion, As tests 1491, 1493, and 1494 indicate, the LIOUOR flotation agents used do not produce this effect. I Whatever explanation may be preferred, the patt ent application of Wrigye, Ginsberg, and Holder I ( 7 A ) appears to confirm the present results. The application, published while this work was being carried out, contains t h e following statement: HZSO4 PLANT SULFATE "Impurities are removed by dissolving the crude alumina hydrate in alkali liquor and precipitating it afterwards according t o the known method." I t would be difficult t o understand why a n alkaline purification step should be added if the assertions of previous patents (b4) were valid. SULFATE DILUTE The considerable disadvantages involved in the I precipitation as well as in t h e decompositipn of monobasic aluminum sulfite could perhaps be Figure 2. Flow Sheet of Sulfite-Sulfate Process accepted if a pure product were immediately obtained. If an alkaline step is included, the method described in the following section is undoubtedly far alone be grave obstacles in a n industrial process. Even under superior. these conditions a n entirely unsatisfactory product was obtained. Although these results aroused considerable doubt about the Goldschmidt patents (84) we realized t h a t their principal emSULFITE-SULFATE PROCESS phasis is on precipitation a t higher pressure. A number of test< The sulfite method has one important economic advantage: were therefore carried out in a lead-lined autoclave of one liter I t does not require a basic reagent. We desired to retain this capacity which was kept in a n air thermostat and was violently advantage as far as possible in a process which could be combined shaken. The results are given in Table 111. The tests were mith t h e valuable new features of the electrolytic method precarried out under somewhat varied conditions chosen, as before, viously referred t o ( 8 ) . t o furnish high purity rather t h a n high yield and quick reaction. The sulfite-sulfate method is based on the fact t h a t alumina T h e leach liquor used in tests 1490-1499 was about one year old, can be precipitated in the form of a basic sulfate by expulsion of t h a t of tests 791 and 792 was freshly prepared. I n tests 1491, 1493, and 1494 small amounts of flotation agents, such as laurylamine hydrochloride, were added t o the liquor. I n tests 14901494 liquor was immediately heated in t h e autoclave to 100" C. TABLEIv. PRECIPIT.4TION O F BASIC ALa.\fINUM SULFATE a n d kept there a t 100-105° C. for about 5 hours. I n test 1497 --Amounts, 3IillirnolesTest t h e liquor was heated t o 70" C. in a stream of sulfur dioxide, then No. Conditions A1201 SO8 FezOa SiOt treated in t h e autoclave a t 95-100' C. for 8 hours. I n test 1499 1506 10 ml. sulfateliquor 7.0 20.5 ... ... t h e liquor was heated t o 65" C., transferred t o the preheated 118 ml. sulfiteliquor 36.9 0.5 ... .. . Liquor after pptn. 0 . 4 4 (1 .0%) . . . . . . . .. autoclave, heated during 1hour from 65" to 95' C., and kept there 1507 10 mi. sulfate liquor 7.0 20.5 .. . ... for 4 hours. The same procedure was adopted for test 791, ex67 ml. sulfite liquor 21.0 1 4 ... ... cept t h a t t h e heating from 65" to 95" C. was extended over 2 Liquor after p p t n . 0 . 5 3 (1 . 9 7 c ) ... ., , ... hours. I n test 792 the liquor was quickly heated in the auto1250 3i00 71 8 I509 1.8liters sulfate liquor 13.2 liters sulfite liquor 4140 280 170 220 clave to 65", heated during 7 hours t o 95' C., and kept a t this Liquor after p p t n . 139 (2.656) ... 232 temperature for 3 hours. 5330 3520 i ini 2.72 kg. ppt. The results are surprisingly poor, The possibllity cannot be safely excluded t h a t , by some chance or under certain conditions TABLE v. PRECIPITATION O F BASICALUMINUbl S C L F a l s not defined in the patents and unknown to the authors, a pure [570 ml. of a soln. were uaed which contained (in moles o r gram ions p e r liter): product may be obtained. B u t one can safely conclude t h a t the 0.361 AlzOl, 0.284 S O , - - , 0.027 F e + + , 0.123 N a + , 1.62 S O L Boiling temp. was reached after 24 min.] process described in the patents (24) does not lead to the desired Time, rnin. 24 34 44 54 64 result as a technically usable method. AlzOa pptd.. % 96.5 97.7 98.6 99.1 09.3 It is difficult to find a n explanation of this failure of the GoldSOs expelled, 70 97.1 99.7 ... 99.9 100.0 HpO evapd., grams 47 114 154 187 230 Schmidt research group, which had proved its competence and high ability in other patents. The simplest explanation would be SYELTER
I
I
Q
.
November, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEv-1. DISSOLUTION O F BASIC ALUMINUM 4.0 !v SODIUM HYDROXIDE SOLUTIOX
SULFATE I N
(14.0-gram samples of basic sulfate, containing 3.00,gramg AIsOs, were digested with 110% of the equivalent a m o u n t of alkali required for Na.4102) 70of AI2O3Undissolved after: Temp., 30 min. 120 min. c. 10 min.
-
b0 75 100
TABLE VII.
...
5.7 0.7
2.5
9.4
CLAY LEACHING WITH ACIDS
...
0.5
...
SCLFCRIC . 4 S D STJLFCROUS
(Continuous leach in a battery of eight columns identical with those de-
scribed in Table I. Castle Rock, Wash clay calcined a t 750° C. Ignition loss of dry clay 19.0%, of calcined clay: 2.8%. Av. charge, 290 rams per
Total' leaching time 360 hr.: each clay portion leachef 192 h r . : liquor passed khrough t h e system in 32 hr.) .------Amounts A1,ZOs -1!203 Available Total available Calcined clay 37.6y0 4322 g. 1630 g. ( l o o % / 53 4 g . h . 27 91. 1479 8. (90 7 % ) Leach liquor .... 2300 g. 142 6. (8 7 % ) Leach residue N o t accounted for .... 9 g. ( 0 6 % ) h-et leaching volume required for yearly output of one unit alumina: 0.093 years.cubic rneters/metric ton 3.0 years.cubic feet/short ton.
column.
....
3
sulfur dioxide from aluminum sulfite solutions which contain a certain amount of sulfate. The main disadvantage of all former uses of this method can be traced to the introduction of a basic reagent which remains in the mother liquor after the alumina is precipitated in the form of a basic salt. I n the alunite leach with sulfurous acid of Spence and Llewellyn (21) alkali is taken from the ore. I n Bjorkstedt's process (4, 16) ammonium bisulfite is added to the aluminum sulfate solution. While the recovery cost of potassium sulfate in an alunite processcarried out under favorable fuel conditions might be bearable, a I similar operation would lay too heavy a burden on a clay process, especially if fuel costs are high. For this reason it appeared desirable to develop a process which permits the separation of alumina from the leach liquor without any basic reagent. I t has been found that this objective actually can be realized. An aluminum sulfite leach liquor is mixed with an aluminum sulfate liquor in such proportion that more than three equivalents of alumina are present for one equivalent of sulfate; as soon as sulfur dioxide is expelled, basic aluminum sulfate precipitates in an easily filterable form. The mother liquor is practically free of both alumina and sulfate, except for sulfate bound to iron or other impurities (Table IV). The sulfate and sulfite liquors were mixed and boiled until the escaping steam was free of sulfur dioxide. The precipitate was filtered and washed with cold water. I n test 1509 these operations were carried out most of the time in an atmosphere of nitrogen. The alumina lost in the filtrates is given in per cent of the total alumina used. The data of Table V indicate that sufficiently complete precipitation is obtained in a short time. I t i s necessary to make use of the heat contained in the sulfur dioxide-steam mixture, and perhaps also to support t,he expulsion of sulfur dioxide by blowing steam into t'he liquor. This method has a number of advantages. If air is excluded during precipitation and washing of the basic sulfate, iron stays in the mother liquor. This separation is remarkably efficient, as already found by Spence and Llcwellyn and other authors using similar processes. Spence and Llewellyn also stated the solubility of the basic precipitate in acids. As the results reported in Table VI show, the precipitate dissolves readily also in dilute alkali a t 75" C. Compared with the straight sulfite method and with Bjorkstedt's process, there i s the advantage that the precipitate is
1185
practically free of sulfite; the recovery of sulfur dioxide is therefore limited to a single operation-namely, precipitation. One principal advantage of the present method is the fact that it permits efficient leaching. While the major part of the alumina is extracted from fresh clay by means of sulfurous acid, the required amount of aluminum sulfate liquor is easily obtained by treating the residue of the sulfite leach with sulfuric acid. Various leaching arrangements were tested. The most efficient is the following: Partially depleted clay is leached with sulfuric acid. Before the acid is completely neutralized, sulfur dioxide is blown in to prevent hydrolysis. The sulfate liquor, together with the additional amount of water required, is introduced into the sulfite leach system. Table VI1 shows the result8 of a continuous leaching test. Both concentration of leach liquor and efficiency are appreciably higher than in the straight sulfite leach (Table I). Other tests indicate that the concentration can be increased a t least t o 60 grams of alumina without appreciable loss of efficiency and probably even a t a smaller volume of t h e leach system. By addition of the required amount of concentrated sulfuric acid, the basic precipitate is easily converted into neutral aluminum sulfate. The conversion to alumina will be discussed in the next section. The sulfite-sulfate method fits particularly well into thr economic situation of the Pacific Northwest. The only raw materiala required (clay and sulfur dioxide) are abundant, and there is already a wide market for the products (aluminum sulfate and alumina) in the paper and aluminum industries. Sevcral advan-
CALCINED
Figure 3. Flow Sheet of S u l i i t e S u l f a t e Process w i t h Electrolytic Recovery
-
I SULFITE
LEACH
SULFITE
SULFATE
LEACH
I
SULFATE LIOUOR
PRECIPITATION
LIQUOR
ALUMINUM
SULFATE
DISSOLUTION
1
I ALUMIMATE. LIQUOR
AUTOCLAVE
SILICA
PURIFIED ALUMINATE
I
SODIUM SULFATE SOLU T I 0 N CALCIUATIOW
ELECTROLYSIS
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
tages can be attained by a combination of the sulfite-sulfate proccss with the sulfur dioxide recovery from smelter gases, provided the smelter is not too far from a suitable clay deposit. One advantage is the use of waste hcxt from the smelter addition, the sulfite-sulfate method presents the opportunity of improving the recovery of sulfur dioxide by means of basic aluminum sulfate solution as absorptionliquor. I t is n.cll known that the sulfate content of this liquor continuously rises by inevitable oxidation of a small fraction of the absorbed sulfur dioxide. The simplest and most rational use of the aluminum sulfate thus formed is kresented by the sulfite-sulfate method. The ~ippropriate amount of absorption liquor is bled off and combined n-ith aluminum sulfite liquor. The flow sheet of Figure 2 indicates the economic advantapcs of a n integrated combination consisting of smelter gas recovery, clay leaching plant, and sulfuric acid plant. The combination permits remarkable flexibility, :is thc relative amounts of the products-sulfur dioxide, sulfuric :ic.id, alumina, and aluminum sulfate-can be varied n-ithin wide limits so that the operation can hc adapted to the market situation. ALUMINA
The sulfite-sulfate method just d i s c u s d opens an efficient n:ty t o obtain moist, highly basic aluminum sulfate. The conversion of this intermediate product, however, presents several problems. At .first, simple calcination of the basic sulfate seems t o be the best way of converting t o alumina. But the necessity of recovering the sulfate in the form of a dilute mixture of sulfur dioxide and trioxide makes direct calcination less advantageous. It has been found that tlie sulfate can be extracted from the basic sulfate by leaching with approximately the stoichiometric amount of sodium hydroxide solution. I n one test 16.40 grams of basic aluminum sulfate (21.4% A1~03,10.7%, SO,)Tmrc tligested with 11.47 ml. of 4.0 A' sodium'hydroxidc solution for a half hour a t 70" C. The precipitate contained only a trace of sulfate, The loss of alumina in the filtrate was l.5yo of the amount used. -1fter a n extraction of this kind the remaining alumina c a n be dried and calcined, while electrolysis of the filtrate furnishes the sulfuric acid and sodium hydroxide solutions which are to be re-used. This process is probably the best way t o obtain impure alumina-Le., a product containing 1 to 2yc silica. Iyhile it may find a limited practical application, it was not considered a solution of the problem. Three methods of silica removal have becn investigated: (a) The precipitation of silica from the mixed liquor before precipitation of the basic aluminum sulfate; some promising results have been obtained and this way is still being examined. ( b ) Iceeping the silica in solution during precipitation of the basic sulfate; this has been attempted by means of flotation agents like lauryl compounds, but the results w r e unsatisfactory. (c, The removal of silica after precipitation; this method furiiiihes positive results and Kill be discussed in some detail. The only practicable way of removing silica from basil: aluminum sulfate appears to be dissolution in alkali, desilication of the alumillate solution, and precipit,ation of pure alumina. The reagents are recovered by the usual methods or 115- electrolysis a s previously described (1%). The desilication of n solution of sodium aluminate by heating in the autoclave is a long established procedure. Recently it has received considerable attontion i n sinter processes, especially in Russia (9, 10, 11, 2 2 ) . .1dditio1: of lime promotes the precipitation a t the cost of considerable loss of alumina. This has been confirmed in a number of pmliminnry tests. Ited mud, too, has been suggested as promoring ngent. Probably any material which presents a sufJirit.nt surface for adsorption will act as a satisfactory collector. It v a s considered desirable to check the results Icported in the literature, especially as the concentrations of alumina and sodium llydroxide of the present process may be lower t h a n in the processes in which alkaline desilication was used previously. The
Vol. 38, No. 11
folloTving procedure \vas adopted in thcso tests: Basic nlumi~ium sulfate n-as precipitated from sulfite and sulfate liquors obtairic-d from clay, The x-et precipitate was dissolved in ll0?& of the timount of sodium hydroxide required t o form sodium su1l:ite :andsodium aluminnte. 'l'he solution, about 400 ml., \viis t i ( ~ a 1 c din mi iron autoclnx-r of one liter capacity to 130' C'. for 6 liciuie, I n the kist of t h i w tesrs*the siilution contniricd 27.7 grams :ilumiii:i, 0.104 grkirn i'cxt,ric. iixitli,, ~ i n t 0.326 l gram silica. . U t w t l r c :autoclave tre:itni(>nt, the wlution w n t a i n c d 27.4 grams :iIumiii:i, 0.003 Ki':im ferric oxide, and 0.007 gram silic.:i. Thus rhv ratio of hilica to :ilnniin:i \v:i> rvtluccd from 1.90 to 0 . 0 2 6 5 . few lxevious tert.* gnve tlie same dcsilirntion cfftcr i n 3 :inti 6 hours, ' l ' h ~ ~are y not quoted here because tlie lcntl pns1ic.t of tile :iutocl:ivc' was n t t : i r k e d in these t , This iiitcrfc~i.c,iic~e W:IS c,liminatcti i n ttic h k t t e x t by coveri Iic gaskixt l v i t h ril~i.1.f o i l . The desilication effwt is so good that a shorttxr trt~itnic~iit : I t :t lovxr tcmperntulc m a y be expected to be sufficient. 'l'lie 8 o ~ u tioii introtluccd into the autoclave contairietl a amall amount of iron purposc>ly rc.t:iined as a collector of the silica. The iron c~ontent111 thcx ~)ui,ific~l wlution i a extrr.mcily low, as ~vouldbe IXIwct id. 'j- rcsult of the twt- on :ilkal;ne dwilicat ioti link of the sulfite-bulfat (, prcives 'lie flon. slicct of Figure 3 e i v c n )l(tm like alumina extiac,tion fro snrily w q u i r ( ~ sa consiclerable number of 01 s,ider:ible amount of equipment, As i:ir as c a n b e conclud
