US2163702A - Flotation process - Google Patents

Description

Patented June 27, 1939- PATENT OFFICE 2.163.702 'FLorA'rroN rnocnss Robert C. Bled, West Conshohocken, Pa., assignor to Separation Process Company, a corporation 01'. Delaware No Drawing.

Claims.

This invention relates to the froth flotation concentration of oxide ore minerals, and more particularly to the use of stable aqueous colloidal dispersions, or emulsions, of mixtures of fatty acids and mineral oils as collecting reagents. It is of especial utility for the selective, differential separation of fine oxide ore minerals from pulps containing a substantial proportion of slimes, and particularly to obtain satisfactory 10 separations at low pulp temperatures.

The practice ofthe invention,-and a maximum of the advantages that may be derived therefrom, can best be explained by reference to its use in the flotation concentration of fine calcite, for purposes of cement manufacture, from pulps of argillaceous limestones, marls and chalks. Such pulps are usually extreme examples, with respect to the proportion of slimes, but it is to be under- I stood that the invention is of utility in treating 2o coarser pulps, and for the recovery of other oxide ore minerals.

As an example of the latter, reference will be made hereinafter to the beneficiation of Florida pebble phosphate materialsand an example will be given to illustrate the recovery'of phosphate from a de-slimed pulp typical of the pulps now treated by froth flotation in the Florida district.

In many of the natural limestones, marls and chalks, the constituent minerals are so fine that an extremely fine grinding is necessary to free the mineral bonds, or at least to release a suificient proportion of the. mineral or minerals occurring in excessive quantity, to permit 'the desired elimination. The resulting pulps are not readily amenable to froth flotation, under usual conditions, because of the abundance of slimes. A limited de-sliming is usually undesirable, in view of weight losses, and is impractical in the many cases where the natural mineral particle sizes are 40 sofine that the actual calcite separations are made in the lower micron size 3 fractions. 1 The calcite. and quartz slimes are especially desirable in cement manufacture, as intimate contact of fine particles is essential to produce uniform and I 5 complete reactions in burning the ultimate mixture to clinker, and accordingly, under such conditions, the slimes should be subjected to flotation to recover the calcite at least.

Most of the natural materials contain alumina so in too great abundance to makethem suitable Application September 10, 1937, Serial No. 163,307

for the manufacture of modern types of cements in which the proportion of tri-calcium aluminate is low. In the raw materials, all tangible quantities of alumina are silicates, especially the micas, but several silicates may be present in the same material, other common forms being the feldspar minerals, kaolin or kaolinite. Thenatural flneness of the micaceous matter and the ease with which it is reduced in grinding causes serious contamination of the froth, as the fine particles are easily trapped, probably mechanically, not only due to fineness but also because of the shape of the particles which gives them a much slower settling rate than the other tailing minerals.

It has been discovered that light stage oiling flotation circuits are essential to eifect satisfactory diiferential separations of calcite from such pulps. In relatively warm pulp, oleic acid is a satisfactory collector, but, as the temperatures are reduced, dispersion is incomplete and' the consequent partial over-oiling causes decreased grades of concentrates due to the heavy flocculation. Its disadvantages include the difiiculty in obtaining accurate control and dispersion of the small quantity used at each oiledstage,and the cost of the reagent relatively to the low commercial value of Portland cement. The less expensive high titre fatty acids, such-as fish oil acid, have high collecting power but are unsatisa factory as they cannot be uniformly dispersed and controlled in quantity. The heavy flocculation occurring in pulps of normal temperatures makes them unsatisfactory, as little improvement can be made in the grade and the concentrates are too heavily matted for satisfactory froth cleaning. Fish oil fatty acid compares favorably with oleic acid in relatively coarse de-slimed pulps, at water temperatures above average.

The common emulsions of fatty acids are unsatisfactorycollectors for use in calcite pulp of the types described. Those stabilized by amine soaps produce heavy, matted froths of low-grade, difficult to clean by froth flotation and difilcult to thicken, the scum floating on the surface of the thickener frequently carrying up to 5% of the weight ofv the'calcite. Fatty acid emulsions stabilized by the sodium soaps produce excessive froths-that cannot be controlled in'stage oiling circuits and these emulsions are usually unstable, "particularly in cold weather. Similarly, emul- I0 sions stabilized by sulphonated alcohols. produce excessive frothing and low-gradeconcentrates. Emulsions stabilized with the sulphonated oils, as described and claimed in my co-pending application Serial No, 163,306, filed September 10, 1937, are satisfactory with respect to frothing characteristics and grade and weight recoveries.

The sodium soap collectors, such as sodium oleate, usually produce excessive froths of low grade. An exception to this is saponified refined talloel, as described and claimed in the application of Vogel-Jorgensen, Serial No. 151,203, filed June 30, 1937. When'the pulp does not contain excessive quantities of the finer slimes, the collecting power of this reagent canbe increased and its frothing characteristics reduced and controlled by the use of increasing quantities of a mineral oil.

- It is accordingly among the purposes of the invention to provide stable oil in water emulsions of mixtures of fatty acids and mineral oils, that can be used in high water dilutions to effect complete dispersion in the pulp and to permit accurate and uniform control of the small quantities introduced at each of the oiled stages, to the end that selective differential separation can be made of the oxide ore mineral. It is a further' purpose to provide collecting reagents of high selectivity and collecting power, but of low cost.

It is also a purpose to control the frothing char-' acteristics, whereby the froth balance of the cells can be controlled by additions of the usual frothing agents such as crysilic acid and alcohol frothing agents, especially in stage oiling circuits. It is a further purpose to provide collecting reagents that can be used at all ranges of pulp temperatures, T including temperatures just above freezing. These reagents may beprepared from common materials without special equipment.

In general, the invention comprises the use of oil in water emulsions of mixtures'offfatty acids and mineral oils as collecting reagents for calcite and other oxide ore minerals. The oil in water ratios are preferably relatively high to obtain accuracy in controlof the small quantities introduced at each flotation stage and to obtain rapid and complete dispersion in the pulp. Relatively high ratios are also desirable for convenience in handling and also to avoid possible instability as well as inversion to water in oil emulsions at low temperatures. The preferred ratio is 1:33, but ratios are satisfactory down to 1:20. Greater ratios offer no apparent advantage-in 5 dispersion and the increased volume is less convenient to handle. Lower ratios are diflicult to disperse infine pulps, and the fullest advantages of the emulsions are not obtained. Usually, emulsions of oil in water ratios in the neighborhood of 1:-10 and lower are partially unstable at average temperatures, a light scum being formed sometimes with floating granules or agglomerates .of soapy appearing matters However, if these emulsions .are used promptly or under conditions of agitation little decrease in efllciency results from the moderate separation. Rebolling and stirring the emulsion disperses the separated matter and it is preferable to increase the dilution to avoid re-separation. Emulsions prepared with low water ratios should be diluted while still hot, as at ratios of about 1:5 and lower an apparent inversionto a water in oil emulsion takes place. or at least dense easy soap-like masses form which cannot 75 readily be handled or-dispelsed.-

Although the term emulsion has been applied to these reagents, it is possible that at least some of them are not true emulsions in the generally accepted sense.- Just .what effects produce stability in water is not fully understood. Of the emulsions described in the first example appearing hereinafter, a 1:33 oil in water emulsion of equal weights of talloel and medium fuel oil has the appearance of a solution, being clear, bright orange-yellow, whereas those produced similarly with oleic or fish acid are translucent or cloudy but highly dispersed. The emulsions in which the mineral oil component is a heavy fuel oil such as commercial oil No. 6 or bunker C have a dense green color and the appearance is that of the usual emulsions.

The emulsions are prepared by stirring the mixture of fatty acid and mineral oil, the relative proportions of which will be described hereinafter, and then adding a caustic alkali in quantities at least equal to that necessary to saponify the fatty acid and preferably a considerable excess. The usual saponifying reagents such as sodium and ammonium hydroxide may be used, but sodium hydroxide is preferred for economy and convenience and also because the resulting emulsions appear to have greater selectivity. The preferred proportions of sodium hydroxide by weight, for example technical grades of 94% purity, range from 20 to 25% by weight to the total weight of the faty acid oil and mineral oil. A proportion of about 25% is preferred as the resulting emulsion is clearer or more highly dispersed and'is stable at all temperatures above freezing. Proportions of sodium hydroxide below 20% usually do not produce permanently stable or substantially clear emulsions. For example, an emulsion prepared with equal parts ingly, an excess of sodium hydroxidebeyond that necessary to saponify the talloel is desirable and preferably in proportions of 20 to, 25% by weight.

Mineral oils throughout a wide range of specific gravities, as from kerosene to bunker C, are satisfactory for use as a component of the mixture. However, those of medium weight such as commercial fuel oils Nos.. 3 and 4 produce the -most satisfactory flotation results, especially in fine pulps, and are easily dispersed. The heavy grades, such as No. 6, can be dispersed .but more care is necessary in mixing as the sodium hydroxide solution is added, as described hereinafter. These emulsions are relatively heavy and are less satisfactory than those described above, but no loss in efiiciency is apparent in connection with coarse pulps. l v

The sodium hydroxide is first dissolved in from 4 to 10 parts of water, and while still warm, or

after heating, is slowly added and vigorously' mixture is then brought to the boiling point and slowly boiled usually from 3 to 5 minutes, stirring being continued during this time. When lumps have disappeared, the desired oil in water dilution is made simply by adding the necessary quantity of cold water, preferably before the mixture has cooled. The heavier fuel oils that have not been substantially deca'rbonized require especial care while the sodium hydroxide solution .is added, for, if additional water is not added when lumps tend to form, a heavy carbonaceous sludge, carrying soapy masses, will separate from the emulsion. When prepared as above described, however, the carbonaceous matter separates freely as a thin scum floating on the S111.- face, which may readily be removed by skimming, or syphoning the emulsion from below the carbonaceous film.

The preferred relative proportions of fatty acid and mineral oil depend upon the character of the pulp and particularly its fineness. In general, the collecting powerof the emulsion increases with increasing proportions of mineral oil up to a proportion-equal to the weight of the fatty acid,

and without reducing, and in some cases improving, the grade of the concentrate, as will appear hereinafter. Greater than equal proportions of fuel oil result in rapidlydecreasing calcite weight recovery. Further, the preferred proportions of mineral oil also depend upon the frothingcharacteristics of the fatty acid, and especially the increased frothing efiect produced by saponifioation. One of the important features of the present invention is the control of froth volume by properly proportioning the mineral oil, increasing quantities sharply reducing the froth volumes 'produced. Especially in light stage oiling circuits, it is desirable to use relatively large proportions of mineral oil whereby the froth balance of the cells can be controlled accurately by additions of normal frothing agents, such. as crysilic acid and an alcohol frothing agent identified hereinafter. Under average conditions, the most satisfactory weight recoveries, with reference to grade ofconcentrates, and under satisfactory frothing conditions, are produced by emulsions comprising approximately equal proportions of fatty acid and mineral oil. In the presence of the fatty acid, themineral oils have high collectingpower, and with relation to grade, the collecting power of the emulsion is greater than that of the equivalent of its fatty acid content, and in some cases greater than an equal weight of .fatty' acid, such as oleic acid.

In general, emulsions produced from mixtures .comp'rising more than 70% of mineral 'oil tend to become unstable. -When the proportion sub stantially exceeds 50%, the resulting emulsion is unsatisfactory for calcite recovery, ,as described above', but is satisfactory for the beneficiation of phosphates, particularly when additional mineral oil and sodiumhydroxide are added to the pulp as will be indicated'in the second example to be given hereinafter.

Further, it, will be obvious that large proportions are desirable in view of the relatively high cost of fatty acid as compared with mineral oil.

For a better understanding of the practice of the invention, reference is made to the following examples: First example The first example comprises seven comparative tests, made under equivalent flotation conditions. 7

acid content, and has, when properly employed,.

excellent qualities with reference to both grade and weight recoveries, actually exceeding oleic acid, which is commonly believed to be the most effective collector of oxide compounds of alkaline earth metals.

Two emulsionsof each of the fatty acids were used in the tests, one each being a mixture with commercial No. 3 fuel oil and the other a mixture with commercial kerosene. In all cases equal proportions of fatty acid and mineral oils were mixed as previously described, and 25% by weight of sodiumv hydroxide in 25% solution in water was added to the mixture, together with additions of water during the mixing period, to make theaqueous dispersion complete. The oil in Water ratio was 1:33.

The material treated was an argillaceous lime.- stone and the test specimens were identical in chemical composition and physical analysis. It may be characterized as one of medium fine ness, by comparison with those described above.

The pulp temperatures were F., dilutions were 20% dry solids and the pulps had a normal alkalinity of pH 7.8. Rougher flotation time in a Fa'gergren flotation machine was five minutes, the emulsions being added in five stages at one minute intervals. The frothing agent used was a mixture of branched and straight chain aliphatic monohydric alcohols boiling between about 152 C. and about 162 C. obtainable along withv methanol by the catalytic hydrogenation of carbon oxides. It is especially satisfactory in fine pulps of this type as it has little or no collecting capacity and disperses rapidly in pulps. It is especially to be noted that the quantity of frother used in eachcase is approximately 25% more than would be used in normal fatty acid flotation,

including the useof oleicacid, thereby demonstrating the control of frothing characteristics that may be exercised with large proportions of mineral oil. The quantities of collecting reagents, under the heading Reagents in the last column of the table, mean the total weight of both the fatty acid oil and the mineral oil. The '7 average CaCOa content of each test specimen was 69.5%, by titration.

results to be given hereinafter would be comparative. The talloel component of the reagents Concentrates Relects Lba /ton Test are tees: asse ass. Mew new Emma l 79. 7 (3g: 2) 93. 6 20.3 22. 7 '6. 4 0. i 0. 6 Talloel and fuel oil. 2 vac & i 91.6 24.0 us 8.4 0.04 as Talloel and fuel oil. a 71. 2 g 84. 1 2s. 8 a0. a 12.6 I act a Fish acid and fuel oil. i e1. 9 3.2 82.0 3?. 1 39.5 13.0 0.04 a 5 o acid and fuel oil. 5 "11.5 23.3 87.0 23.5 31.2 13.0 0.04 as Talloel and kerosene.

e9. gt-g v 85.0 30. a 33. e 1e 0 o. 04 e 5 Fish acid and kerosene. 65. 4 I (3. 2) 80. 6 34. 6 39. 2 l9. 4 0. 04 0. 5 Oleic acid and kerosene.

quantity of the latter up to 4.0-lbs. perton of The figures in parentheses are the grade of the froth concentrates after cleaning by froth flotation without the addition of collecting reagents. It will be seen, from test No. 1, that the emulsion of talloel and medium fuel oil produced the most effective concentration by reference to both gradeand weight recoveries. A slightly greater quantity of this emulsion is required to complete the rougher concentration, but it will be seen in test No. 2, in which a lesser quantity was used, equal to that required for the most eflicient of the other emulsions, that this reagent is superior to the others. This is of especial interest as it is the least expensive of the three fatty acids used. It will be seen from test No. 3 that the emulsion of fish oil and fuel oil is superior to emulsions of oleic acid in pulps of this character. It will also be apparent that the emulsions including fuel oil are more efficient than those in which kerosene was used.

Second example lowing physical analysis:

Per cent Plus 28-mesh sieve 4. 31 Plus 35-mesh sieve 15. 70 Plus 48-mesh sieve 22.38 Plus -mesh sieve 29. 7'7 Plus l00-mesh sieve 1'7. 94 Plus 150-mesh sieve 8. 89 Minus 150-mesh sieve 1.01

The emulsion was prepared from a mixture of equal weights of talloel and No. 4 fuel oil and had an oil in water ratio of 1:15. This was added to a dense pulp, of dry solids, together with suillcient additionalfuel oil to bring the totalfeed, and additional NaOH to bring the total quantity of the caustic soda up to 0.5 lb. per ton of feed. These additions were made to make the reagent quantities identical in proportions to those normally used commercially at a plant operating in the Florida district, so that the was .57 lb. per ton. The pulp was conditioned for 5 minutes and then diluted to 22% dry solids for flotation, the flotation time being 2 minutes. The results were as follows:

These recoveries compare favorably with those produced with other reagents. 'As compared with raw talloel, fuel oil and sodium hydroxide, the grade of the concentrate is somewhat higher but with a corresponding decrease in weight recovery. However, cleaning was much better because the froth was light. I

Although the pulps used as calcite test specimens have been described herein as of medium fineness", and others as relatively coarse it is to be understood that the latter calcite pulps are actually largely "slimcs as this term is used in the art, by comparison with commercial pulps' of other oxide ore minerals, such as the deslimed phosphate pulp described above, as will appear more fully by reference to the physical analyses of the two examples.

I claim:

1. A method of concentrating oxide ore minerals by froth flotation which comprises incorporating in'a pulp of the mineral ,a quantity of an aqueouspre-formed emulsion of a mixture of a fatty acid oil and a mineral oil, in which the proportion of fatty acid oil is equal to at least 30% of the weight of the mineral oil, stabilized by a quantity.of caustic alkali'in excess of that necessary to saponify the fatty acid, and

, subjecting the pulp to froth flotation.

2. A method of concentrating oxide ore minerals by froth flotation which comprises incorporating in a pulp of the mineral a quantity of an aqueous pre-formed emulsion of a mixture of a fatty acid oil and a mineral oil, in which the proportions by weight of fatty acid oil and mineral-oil are about equal, stabilized by a quantity of caustic alkali in excess of that necessary to saponify the fatty acid, and subjecting' the pulp to froth flotation.

3. A method of concentrating oxide ore minerals by froth flotation which comprises incorporating in a pulp of the mineral a quantity of an aqueous pre-formed emulsion of a mixture of a fatty acid oil and fuel oil, in which the proportion of fatty acid oil is equal to at least 30% of the weight of the fuel oil, stabilized by a quantity of caustic alkali in excess of that necessary to saponify the fatty acid, and subjecting the'pulp to froth flotation.

4. A method of concentrating oxide ore minerals by froth flotation which comprises incorporating in a pulp of the mineral a quantity of an aqueous pre-formed emulsion of a mixture of refined talloei and a mineral oil, in which the proportion of tall e], by weight, is equal to at least 30% of the weight of the mineral oil, stabilized by a quantity of caustic alkali in excess of that necessary to saponify the talloel, and

subjecting the pulp to froth flotation.

5. A method of concentrating oxide ore minerals by froth flotation which comprises incorporating in a pulp of the mineral a quantity of proportion of talloel, by weight, is at least equal to that of the fuel oil, stabflized by a quantity of caustic alkali in excess of that necessary to saponify the talloel, equivalent to 20 to 25% of sodium-hydroxide of the weight of the mixture, and subjecting the pulp to froth flotation.

"I. A method of concentrating oxide ore min-- erals by froth flotation which comprises incorporating in a pulp of the mineral a quantity of an aqueous pre-formed emulsion of a mixture of fish oil fatty acid and a mineral oil, in which the proportion of fish oil fatty acid.

by weight, is equal to at least- 30% of the weight.

of the mineral oil, stabilized by a quantity of caustic alkali in excess of that necessary to saponify the fish oil fatty acid,- and subjecting the pulp to froth flotation.

8. A method of concentrating oxide ore minerals by froth flotation which comprises incor-" porating in a pulp of the mineral a quantity of an aqueous pre-formed emulsion of 'amixture of fish oil fatty acid and fuel oil, in which the proportion of fish oil fatty acid, by weight, is at least equal to that of the fuel oil, stabilized by a quantity of caustic alkali equivalent to 20 to 25% of sodium hydroxide of the weight of the mixture, and subjecting the pulp to froth flotation.

9. A methodvof concentrating calcite by 'froth flotation from argillaceous pulps, which comprisesincorporating in a pulp a quantity of an aqueous pre-formed emulsion of'a mixture of a fatty acid and ,a mineral oil, in which the proportion, by weight, of the fatty acid is at.

least equal to that of the mineral oil, stabilized by a quantity of caustic alkali equivalent to 20 to 25% of sodium hydroxide of the weight of the mixture, and subjecting the pulp to froth flotation.

10. A method of concentrating finely divided calcite by froth flotation from argillaceous pulps containing a substantial proportion of slimes, which comprises incorporating in a pulp, in a stage oiling froth flotation circuit, quantities of an aqueous pre-formed emulsion of a mixture of fatty acid oil and a mineral oil, in which the proportion of the fatty acid oil, by weight, is at least equal to that of the mineral oil, stabilized by a quantity of caustic alkali equivalent 'to 20 to 25% of sodium hydroxide of the weight of the mixture, and in which the oil in water ratio is within 1:20 to 1:33.

- ROBERT C. RED.