Froth Flotation of Iron Ores ADSORPTION OF STARCH PRODUCTS AND LAURYLAMINE ACETATE NORMAN F. SCHULZ AND STRATHMORE R. B. COOKE University of Minnesota, Minneapolis 14, M i n n .
. T
HE separation of minerals from their ores is accomplished in froth flotation by causing the surfaces of particles of selected minerals to become hydrophobic and then buoying these parti-
a
cles out of the aqueous ore pulp by attaching them t o air bubbles. The basic phenomenon underlying the production of these hydrophobic surfaces, and, therefore, the whole flotation process, is that of controlled selective adsorption by these particles of a semipolar compound known as a collector. The control of this adsorption process is vested in the use of collectors showing inherent selectivities, augmented by the use of activators and depressants. Starches or their derivatives, when added to certain flotation pulps, act as selective depressants and improve the separations obtained. There are few froth flotation processes in which certain loosely defined starch products have not been tried a t one time or another. Many such instances have been reported in the periodical and patent literature for both sulfide and nonsulfide mineral separations (6-8,10-13,16, $8, 8.4, 26, $9). The present investigation was concerned primarily with how the various products made from cornstarch were able t o influence the collection and flotation of siliceous gangue from low grade hematite ores in froth flotation processes. Since this influence is probably some function of the adsorptive properties of the starch employed, some means were devised for measuring the adsorptions of starches and collectors on minerals.
then hot distilled water was added; the benzene was distilled off, and the starch was solubilized as described. When a starch product was not completely dissolved by this treatment, the insoluble portions were removed by centrifugation of the concentrated reagents before diluting for use in the adsorption tests. The concentrations of the cleared reagents were determined by comparison with standard dextrose solutions through the use of a wet combustion analytical procedure using dichromate in acid medium as oxidant (28). Table I lists the various starch products investigated, with identifying characteristics of each.
TABLE I. STARCH PRODUCTS INVESTIGATED” Product Pearl
Identifying Characteristics Globe pearl starch No. 144. A whole starch produced from corn with a minimum of alteration during manufacture. Only partially solubilized by hot water
A-Fraction
Amylose straight-chain fraction of cornstarch. Separated from cbrnstarch b y coacervation with a polar solvent. Soluble in hot water if carefully prepared (18,87) Amylopectin, branched-chain fraction of cornstarch. Complementary t o A-fraction, less soluble in water
B-Fraction Aminoethyl
Whole cornstarch containing approximately one (-0CHzCHnNHn) group per each 10 glucose units (8). Soluble in h o t water
Oxidized starch
Whole cornstarch t h a t has been subjected to NOn oxidation. Product is 18.97 carboxyl groups by weight, with approxirnately 75% of t%e theoretically available terminal (-CHaOH) g r w p s oxidized to carboxyls. Soluble in hot water
Gum 3502
British gum type of modified cornstarch, completely soluble in cold water
Dextrin
Dextrin 156. Pyrodextrin type of modified corn starch, oombletely soluble in cold water
DextroRe
Anhydrous dextrose, reagent grade
Potato
Idaho potato starch. Similar in properties and preparation t o earl starch, b u t more soluble in hot water
TEST MATERIALS
STARCH.Cereal grains such as corn, rice, and wheat, or vari-
+
ous roots and tubers are the raw materials from which starch is normally manufactured. The molecular weights and configurations, granule sizes, and trace impurities vary slightly with the source material. Raw cornstarch consists of a mixture of molecules having the general formula (CeHlo06), where z may have any integral value up to 1000 or more, and where the glucose units may be arranged linearly (amylose or A-fraction), or in highly branched aggregates (amylopectin or B-fraction). Although the glucose units, CSH~OO~, of which starch is composed are fairly stable, the bonds between these units in a starch molecule are relatively weak. For this reason, the properties of a starch product will vary greatly with the physical and chemical conditions of manufacture and, in the case of the starch reagents used here, with the manner of preparing the solutions (18, 99). The bonds between units are easily ruptured by the action of certain enzymes, by living organisms, and by acid hydrolysis. By heating in water to rupture the granules, starch dissolves to give a colloidal solution. Common practice in flotation plants is to solubilize the whole starch by heating in 1 to 10% caustic soda solutions. I n this paper, no distinction is made between colloidal and molecular dispersions of starch or of other organic materials. The term ‘Lsolution”is applied to all nonsettling dispersions of organic compounds. Weighed quantities of the air-dry starches were dispersed in distilled water, p H = 6.5, and solubilized by boiling or by heating for 1 hour a t 125” C. Those starches that would not disperse without clotting in cold water were first dispersed in dry benzene;
a All products tested except the potato starch and dextrose were supplied by C0r.n Productskefining Co., New York, N. Y. The coke numbers are those assigned by this company.
Starch solutions prepared in caustic media were similarly prepared by adding caustic soda during the solubilization. The excess caustic soda was then neutralized with sulfuric acid. In the preparation of causticized starch, the initial material was of secondary importance because the combination of heat and caustic causes slow progressive degradation of the starch (18, 29). This was shown by the shift in the absorption spectrum of the iodine complex of pearl starch as the temperature or caustic concentration during solubilization was increased (see Figures 1 and 2). The wave length of maximum light absorbancy by an iodinestarch complex decreases as the lengths of the available starch chains decrease ( 2 , 20, 26). To avoid decay of dilute starch solutions by living organisms, every effort was made to maintain aseptic conditions in the solutions. Solutions as dilute as 10 mg. per liter remained unaltered for 3 weeks or more when properly Aterilized by heat. LAURYLAMINE ACETATE. A weighed quantity of air-dry, relatively pure Iaurylamine acetate (99 +yo,supplied by the Research
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 45, No. 12
The Brazilian mineral was a very pure, fine-grained, specular hematite having a few large pores visible under a hand lens. The Mesabi hematite was obtained by hand-picking lump. from a11 iron ore stock pile. Both were crushed, ground in a sample pulverizer, and kept dry until used. T o attempt was made toleachor otherwise clean thrse hematites. ADSORPPlOV
600
700
BOO
WAVELENGTH, miilimicrons
Figure 1.
Starch-Iodine Complex Spectral -4bsorption Curves
EfIect of caustic on pearl starch gelatinized at 93' C.
Division of .41inour and Co.) was dissolved in hot distilled water, +hen immediately cooled, and diluted t o the desired concentra-ion. S e w solutions were prepared each day. Dilute neutral solutions of the amine and various starches were miscible in all proportions without formation of a third phase. MISERALS. The descriptions of the minerals used in this in7:estigation are summarized in Table 11. Surface areas were measured by air permeability (17 , 19) and by krypton adsorption 3-5), the latter value being the one used in the adsorption calculations. In the krypton adsorption measurements, the area occupied per niolecule of krypton a t liquid nitrogen temperatures was assumed to be 19.5 sq. A. Comparisons between the air permeability and krypton adsorption areas indicate that only the Mesabi hematite had a large internal surface due to pores. The Ottawa sand used as a source material for the ground quartz was leached with boiling concentrated hydrochloric acid, hot concentrated dichromate-sulfuric acid solution, and dis-illed water prior to a 4-hour dry-grind in a porcelain Abbe pebble mill. The product was recovered and kept dry until used. A small portion of the ground quartz, which was again leached in boiling concentrated hydrochloric acid and washed with demineralized water, showed no significantly different results when 'eqted by routine adsorption procedures.
-4dsorption may be defined ds the phenomenon by hhich tlispersed matter in one phase becomes concentrated a t the interfaces of a system consisting of two or inore immiscible phaqe;. A. applied specifically to the problem a t hand, the adsorbate., starches and collectors, are presumed to collect a t the mineral-liquor interfaces in aqueous ore pulps. The adsorbate may be actually in ('ontact with and bound to the mineral surface, or may be meiely concentrated in the liquid phase near that surface. In this investigation, the concentration of adsorbate in the bulk of the liquid phase was determined by chemical analysis before and after contact with a known quantity of finely divided mineral of measured specific suiface. The adsorbate abstracted from the liquid phase was assumed to have been adsoibed by the mineral surface. Other investigators have studied adwlption hy measuring directly the accumulation of adsorbate hy a bed of solid particles (14, 16). Neither procedure distinguishes hetueen the two types of adsorption mechanisms mentioned above. TESTPROCEDURE. The adsorption test procedure consisted in agitating a measured quantity of a dilute solution of the organic material under examination 13 ith a weighed portion of finely ground mineral of measured specific surface. All testy were made at room temperature of 25' to 30 C., and, unless otherwise specified, a t neutral pH. The adsorption processes neared completion in the first few minutes of agitation ( I ) , but the time of contact allowed in most cases was 1 hour to assure reproducible results. Excessive time and agitation of pulps containing starches introduced uncei tainties due to attrition and the possibility of decay and alteiation of the starch through the action of living organism.: piesent in the unsterilized minerals. Freqhly boiled distilled x-atei , essentially carbon diuuitlr-l , was used in diluting reagents and mineral pulps. 3Ien~u1rmcii ti of the p H of the pulps were made after adsorption. Pulps containing no surface-active agents were syitated ti\placing them in large stoppered borosilicate glass te-t tube. a i i d rotating them end over end a t about 50 r.p.m. Pulps containing laurylamine acetate were carefully swirled by hand in Er Ienmeyer flasks to avoid foaming, Where two or more reagent3 weie used i n the same pulp, the dry mineral was added to the premixed reagents. No attempt was made to standardize or otherwise regulate pulp densities in routine adsorption tests, since the conti olling factors ~1ere the exposed surface area of the mineral and the concentrations of organic materials in the liquors. For analysis, the pulps were centrifuged and the cleaied liquors O
TABLE 11. Mineral Mineral density, gram/cc.
CHARACTERISTICS O F 1fINERALS TESTED Brazilian XIeqabi HemHematite, atite Ore, 62.4% Fe Quartz, Si02 69.8% F e
Size analysis + 6 5 mesh 65/200 mesh -200 mesh
Surface area. sa. cm. /gram Air permeability IirvDton adsorution Krypton adeorbtiod air permeability
2.65
12.0% 88.0%
2800
5890 2.15
4.97
as.i% 76 5 %
4.32
0.04% 34.63470 6S,33%
3740
1102
2,060 128,600
3.4
62.4
Ratio for quartz agrees with that obtained by air permeability and ethane adsorption (17). a
December 1953
'"I
INDUSTRIAL AND ENGINEERING CHEMISTRY
I
I
I
I
2769
I
d W
P0
3
1.0
5 3
3
00
200
800
(QQO
RESIDUAL CONCENTRATION, Mg./L
RESIDUAL CONCENTRATION, Mg./L.
Figure 3.
.4dsorption of Starch Products on Quartz
analyzed to determine the concentrations of organic materials remaining therein by a dichromate oxidation procedure (28). The quantity of starch or other material adsorbed was then calculated from the difference between its initial and final concentration in the pulp liquor. Changes in the proportions of the various constituents present in a starch solution as affected by partial degradation (23) or by selective adfiorption on minerals were detected colorimetrically through the use of the starch-iodine complex. The results were qualitative only, based on the fact that the greater the proportion of long starch chains in a solution, the longer is the wave length of maximum light absorbancy of its iodine complex ( 2 , 2 0 , $0). Colorimetric examinations of starch-iodine 'complexes were made on suitable aliquot portions of the starch solutions. The pH of the sample was adjusted to between 5 and 6; 0.500 ml. was added of a standard iodine solution containing 10 grams of iodine and 15 grams of potassium iodide per liter, and the resulting mixture was then diluted t o 100 ml. The absorbancy curve for the preparation was determined with a Beclcman spectrophotometer, Model DU, having 1.00O-cm. Corex cells, against a blank solution containing an identical amount of iodine reagent. TEST RESULTS
The amount of starch abstracted from solution was directly proportional t o the surface area of the mineral added and was
Figure 4.
Adsorption of Starch Products on Brazilian Hematite
clearly a function of the concentration of reagent remaining in the bulk liquid (see Figures 3, 4,and 5 ) . Since starch is not normally surface-active-Le., does not accumulate in air-water interfacesit may be concluded that it was adsorbed by a direct binding between the starch micelles and the mineral surfaces ( 9 , 2 1 ) . Adsorption data for the porous Mesabi hematite cannot be compared directly with those for the quartz or Brazilian hematite because of large uncertainties in the relative surface areas accessible to the various adsorbates. Laurylamine acetate was adsorbed from aqueous solutions by either hematite or quartz (see Figure 6). It is assumed throughout this work that the area occupied per molecule of krypton in surface area measurements is 19.5 sq. A., as against 16.8 assumed by Gaudin and Bloecher ( 1 4 ) . Table I11 contains original data for adsorption of laurylamine acetate on quartz and values interpolated from a smoothed curve of Gaudin and Bloecher's data obtained by radioactive tracer technique. Both sets of data are based on the 16.8 factor for krypton. The agreement is within experimental error except a t high amine concentrations. The adsorption isotherms for laurylamine acetate on quartz and the two hematites tend to converge into a single curve a t low concentrations. Comparison of the curves for quartz (line Q of Figure 6 ) and for pure hematite (line B ) indicates t h a t adsorption of laurylamine acetate is appreciably greater on hematite than on quartz. The curve given for Mesabi hematite (line M ) seems to contradict this conclusion, since it lies below the quartz isotherm.
s:
w
'",
2"
010
d w m
&
a 8 8l 0.01
35 a001
RESIDUAL CONCENTRATION, Mg./L.
[Figure 5.
Adsorption of Starch Products o n Mesabi Hematite
10
loo
1000
10,0013
RESIDUAL CONCENTRATION, M W L .
Figure 6. Adsorption of Laurylamine Acetate on Minerals from Neutral Aqueous Solutions
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 12
Figure 9. Adsorption of hlixtures of Dextrin and Dextrose on Rrazilian Hematite
Figure 7. Adsorption of Mixtures of Globe Pearl Starch and Dextrose on Brazilian Hematite
However, it is possible that a considerable portion of the surface area of the blesabi hematite, as measured by krypton adsorption, was not accessible to the larger laurylamine radicals so that the effective surface area was less than the measured value.
I
,I , I I
I I I I I
, I
I
e
COMPOSITION, 7, DEXTROSE
Figure 10. Adsorption of Mixtures of Dextrin and Dextrose on Quartz
.
-
COMPOSITION, % DEXTROSE
Figure 8. Adsorption of Mixtures of Globe Pearl Starch and Dextrose on Quartz
The exact position of the amine collectol in the boundary layer between the solid and the liquid phases of the mineral pulps is uncertain, because it accumulates readily in air-solution interfaces. Horever, the fact that laurylamine acetate functions as a collector in a flotation circuit provides evidence that it must be rather
TABLE 111.
A D S O R P T I O N OF
LAURYLAMIXE ACETATE
OR'
QCARTZ
hrmly bound to the mineral surfaces, because the ai1 bubbles aiid floated particles hold together during the flotation process. 9 shift toward the shorter wave lengths was noted in the adsorption spectra of the iodine complexes of starch solutions that had been exposed t o hematite or quartz surfaces. It was somen-hat more pronounced for starches treated with hematite than for those treated with quartz, indicating that either the longer itarch chains were preferentially adsorbed, or mechanical agitation caused rupture of some of the long chains. The additional fact that unsubstituted starches that have undergone pronounced degradations, such as gums and dextrini;, were adsorbed to a less extent than whole, native starches supports the preferential adsorption hypothesis. Adsorption tests were made for mixtures of pearl starch and dextrose, and for mixtures of dextrin and dextrose, on pure hematite and on pure quartz. Since it was not possible to distinguish the different starch products of the mixtures, the results have been plotted as three-dimensional graphs having as coordinates, initial composition, initial coriceiiti ation, and total carbohydrates adsorbed (Figures 7 to 10). Data were also obtained for adsoiption of dextrin-dextrose mixtures on hematite from solutions initially containing 5 mg. of laurylamine acetate per liter (Figure 11). The results obtained from mixture adsorption tests indicate that even though dextrose itself is only slightly adsorbed on minerals, its presence in small amounts tends to increase the adsorption of other starch products, especially on hematite. This can be demonstrated by considering the ordinate of the curve in Fig-
Mg./Sq.~ JI. ~ & tion,[ M g ,& ~ Laurylamine ~ ~ Acetate ~ Adsorbed, ~ ~ ~ ~ ' /L. Schulz and Cooke Gaudin and Bloccher 3.5 10.5
13.5 34.0 73.0 157 287 408 446
1705 3640
OB
0.06
0.M
0.10 0.12 0.18
0
0 0%;
0.16
0.27
0.43
0.62
0.91
1.09 1.5
1.9
0.25 0.40 0.61
0.79
0.84 3.5
12.5
December 1953
INDUSTRIAL AND E N G I N E E R I N G CHEM'ISTRY
2171
sorption of the amine was very slight for quartz, and also for hematite at low amine concentrations. The gum did have a noticeable effect on amine adsorption by hematite when the initial amine concentration was 300 mg. per liter or more (see Figure 15). The presence of calcium chloride in the starch solutions caused increased adsorption of the starch. This is shown in Figures 16 and 17. The effect was not noticed for laurylamine acetate. The effect of p H on starch adsorption was largely dependent on the starch characteristics, being small for pearl starch, moderate for dextrin 156, and large for gum 3502 (Figure 18). In general, increased p H decreased the starch adsorption. Laurylamine acetate adsorption was not appreciably affected by changes in p H on the acid side, and at pH values greater than 8, the limited solubility of the compound interfered with adsorption tests. CONCLUSIONS
*
Figure 11. Adsorption of Mixtures of Dextrin and Dextrose on Brazilian Hematite from Solutions Containing 5 Mg. of Laurylamine Acetate per Liter
ure 9 a t 25% dextrose and 1000 mg. per liter initial concentration. The values of the ordinates in Figure 9 were obtained b y measuring the total carbohydrate adsorption by a quantity of hematite having a total surface area of 1.87 sq. meters from 50 ml. of each test solution. H a d the two components been adsorbed independently, the value of the ordinate in question would have been the sum of the one a t 0% dextrose, 750 mg. per liter (2.61 mg. per sq. meter), and the one a t 100% dextrose, 250 mg. per liter (0.17 mg. per sq. meter), or a total of 2.78 mg. per sq. meter. The value obtained experimentally was 3.08 mg. per sq. meter, nearly 11% greater than the calculated value. 2.0
Starches are adsorbed b y hematite and quartz surfaces from aqueous solutions. This adsorption is dependent upon the mineral, type of starch, pH, and the presence of other soluble substances; it is a function of starch concentration. The compositions of starch reagents may be altered by selective adsorption of specific molecular components on mineral surfaces, and by their manner of preparation.
5
ccd 1.s I
0-
3 (3
5
0.0 0
ccf5
d
z
r
0-
K x ) 2 0 0 x x ) 4 0 0 5 0 0
INITIAL AMINE CONCENTRATION, Mg./L.
1.0
a
s
I 0-
I
a 05
8 n
W
4
00
W
Z
3
i d m W
a w
2
K
H
)
2
w
~
4
o
o
INITIAL GUM CONCENTRATION, Mg./L.
x
x
)
Figure 14 (Upper). Adsorption of Gum 3502 on Brazilian Hematite as a Function of Initial Laurylamine Acetate Concentration
z
Z0.O0
0.0
100
INITIAL
200
300
400
GUM CONCENTRATION, Mg./L.
so0
Figure 12 (Upper). Adsorption of Gum 3502 o n Quartz as a Function of Initial Laurylamine Acetate Concentration Figure 13 (Lower). Adsorption of Laurylamine Acetate o n Quartz as a Function of Initial Gum 3502 Concentration
A small amount of laurylamine acetate in the pulp liquor also increased the total carbohydrate adsorption as is seen by comparing Figure 9 with Figure 11. This effect was also shown by adsorption tests employing mixtures of gum 3502 and laurylamine acetate (Figures 12 to 15). Laurylamine acetate had rather a large effect on the adsorption of the gum on quartz and a somewhat smaller effect for hematite. The effect of the gum on ad-
Figure 15 (Lower). Adsorption of . Laurylamine Acetate on Brazilian Hematite as a Function of Initial Gum 3502 Concentration
The adsorptions of laurylamine acetate by quartz and by hematite surfaces are of the same order of magnitude. The data obtained by chemical analysis agree well in the intermediate concentration range with those obtained elsewhere by radioactive tracer technique. Adsorption of laurylamine acetate by hematite and quartz is not appreciably affected by the presence of the starch product, gum 3502. Adsorption of gum 3502 on quartz increases with Iaurylamine acetate concentration in the pulp, passes through a maximum, and then decreases as the amine concentration continues to increase beyond the optimum value. A similar effect occurs with hematite, but it is much less pronounced, and the maximum gum adsorption occurs at a much lower amine concentration.
2772
INDUSTRIAL AND ENGINEERING CHEMISTRY
Small quantities of calcium chloride increase the adsorption of starch from neutral solutions by either hematite or quai tz. but have a negligible effect on the adsorption of laurylamine acetate by these tn-o minerals.
Vo!. 45, No. 12
I
5
u
Y 02
r" d
W
m
K
8 0
os
a
e I"
01
5
2 4
0- 0.4
w m
e 0
00
v, Q
a c z
3
200
400
600
800
RESIDUAL CONCENTRATION, Mg /L
Figure 17. Effect of Calcium Chloride and pH on Adsorption of Gum 3.502 on RTesabi Hematite
02
0 9 5
00
REFEREKCES 200
400
600
1000
800
RESIDUAL CONCENTRATION, Mg./L
Figure 16. Effect of Calcium Chloride and pII on Adsorption of Gum 3502 on Qtiartz
(1) (2)
-hendt, O., Rolloidchem. Beih., 7, 212 (1915). Raldwin, R. R., Bear, R. S.,and Rundle, R. E., ,J. A m . ( ' h e m .
(3)
Beebe, R. A., Beckwith, J. 13., and IIonig, ,J. AI., Ihl'd., 67, 1554
Soc., 66, 111 (1944). (1945).
Rloecher, F. W., .Jr., Trans. Am. Inst. Mininy M e t . Engrs., 190, 255 (1951): illin. Eng. T P 3013B (March 1951). ( 5 ) Brunauer, S., Emmett, P. H., and Teller, E., J . Am. Cheni. S'oc.,
(4)
T h e effect of pH, where investigated, is t o decrease starch adsorption at values above 8. Adsorption of laurylamine acetate is not affected appreciably between pH 4 and 8. Unaltered starches are adsorbed to a greater extent than highly degraded ones. Substitution of aminoethyl groups into starch molecules increases the adsorption considerably.
30-
60, 309 (1938). (6) Clemmer, J. B., Clemmone, B. H., Ranipacek, C., Williams, 31. F., Jr., and Stacy, R . H., U . S. Bur. Mines, Repi. Inyest. 3799 ( 1 945). (7) Clemmer, J. B., Doerner, 1%.A., and DeVaney, F. D., TXITLS. A m . Inst. Mining M e t . Enyra., 155, 550 (1943). ( 8 ) Cooke, S. R. B., Schulz, X. F., and Lindroos, E. W., I b i d . , 193, 697 (1952).
I
(9)
Delaney, J. C., Kleinberg, J., and Argersinger, W. J., ,Jr., J . Ani..
Chem. Soc., 72, 4277 (1950). (10) DeVaney, F. D., Eleventh Annual Mining Symposium, Univxsity
pH.55
I
of blinnesota, pp. 65-71, 1950. DeVaney, F. D., IND.ENG.CHEW,38,20 (1946). (12) DeVaney, F. D., U. S. Patent 2,483,890 (1949). (13) Freundlich, H., and Greensfelder, R. S.,Rolloicl-Z., 48, 318 (11)
(1929). (14)
Gaudin, A. BI.,and Bloecher, F.W., Jr., Trons. Am. I/it;t. Miningil.let. Engrs., 1 8 7 , 4 9 9 (1950).
Gaudin, A. M., and Chang, C . S.,Ibid., 193,193 (1952). Iverson, H. G., C. S.Bur. hlines, Rept. Invest. 4570 (1949). (17) Johnson, J. F., Axelson, J . , and Piret, E. L., Chem. Eng. P r o g ~ . , (15) (16)
45, 708 (1949).
pii.106
e
RESIDUAL CONCENTRATION,
Mg /L.
Figure 18. Effect of pH on Adsorption of Gum 3502 on Brazilian Hematite
The data obtained b y iodine-complex colorimetry indicate that Etarch molecules with the longer chains are preferentially adsorbed by minerals. Since starch is not normally surface active, its adsorption by minerals must constitute direct bonding between starch and mineral surfaces. Laurylamine acetate, although surface active, must also be bonded to the mineral surfaces to cause the firm attachment of floated particles t o air bubbles in flotation machines ACKNOW LEDGM EYT
This work was supported b y a fellowship grant of Corn Products Refining Co. and b y the Mines Experiment Station of the University of Minnesota, in cooperation with the School of Mines and Metallurgy, University of Alinnesota, Minneapolis, blinn.
(18)
Lansky, S., Kooi, AI., and Bchoch, 1'. J., J . Am. Chem. Soc., 71,
(19) (20) (21) (22) (23) (24)
Lea, F. M., and Nurse, R . 137.,J . SOC.Chem. Ind., 58, 277 (1939). hleyer, K. H., and Bernfeld, P., Helc. Chim. Actcr, 24, 389 (1941). Miles, F. D . , Trans. R o y . Sue. (London),A235, 125 (1935). Morton, R. J., 1T. S.Patent 2,551,893 (1948). Rakvain, hI.8., J . Buss. Phys. Chem. Soc., 48, 1319 (1916). Ravitz, R. F., Tmns. A m . Inst. Mining M e t . Engrs., 153, 528
4066 (1949).
(1943).
(25) Rey, &I.,and Brevers, H.,Ibid., 153, 536 (1943). (26) Rundle, R. E., Foster, J. F.. and Raldnin, R. R., J . A m . C'lcenz. Sue., 66, 2116 (1944). and Wolfram. 11. L., "Advances ( 2 7 ) Schoch, T. J . , Pigman, W. " Vol. 1, pp. 247-77, S e w York, in Carbohydrate Chemis (28) (29)
Academic Press, Inc., 1945. Schula, N. F., Snccl. Chew?.,25, 1762 (1953). Vedensky, D . N., and Duschak, I,. H., Eng. :Win. J . , 133, 334 (1932).
RECEIVCD for review Ala>- 1, 1953.
Acc~r'rsrrSepteirlber 28, 1933.
