Promoters for froth flotation of coal

BACKGROUND OF THE INVENTION
The present invention relates to the froth flotation of finely-divided coal particles for separation of ash therefrom and more particularly to a new promoter which enhances the coal recovery in the froth flotation process.
Coalification is a natural process which results in the deposits of combustible carbonaceous solids in combination with some non-combustible mineral matter. Most coal cleaning is carried out by gravity separation methods utilizing jigs, shaking tables, heavy media or cyclones, and like techniques. The fine coal therefrom has been incorporated into clean coal or simply discarded in the past; however, due to economic and enviromental considerations gained by recovery of the fine coal fraction, fine coal beneficiation has become a necessity in most coal operations requiring any degree of preparation. Froth flotation is one method which has been practiced for cleaning the fine coal.
The use of froth flotation to effect a separation of pyritic sulfur and ash particles from coal can be achieved only if liberation of these unwanted particles from the coal has taken place. Most high-grade coals are floatable naturally due to their hydrophobic surface and typically only require a frothing agent for effecting flotation. A frothing agent imparts elasticity to the air bubble, enhances particle-bubble attachment so that the coal is buoyed to the surface of the slurry. The flotability of coal can vary within a given seam at a mine depending upon the exposure of the locale to weathering elements or the blending of coals from different seams. Butuminous and lower grade coals either possess an oxidized condition as mined or undergo oxidation (weathering) when the coal is stored or stockpiled for later processing. Coal that has been oxidized does not respond well to froth flotation. As the degree of oxidation increases, coal becomes increasingly hydrophilic and, therefore, less coal readily can be floated. Heretofore, oxidized coal which was not flotable was discarded in the tailing of the flotation process with little attempt to recover this loss being undertaken.
Recently, though, technology has emerged for practicing froth flotation of oxidized and other difficult to float coal particles. For example, U.S. Pat. No. 4,253,944 shows a promoter which is the condensation product of a fatty acid or fatty acid ester with an ethoxylated or propoxylated amine. U.S. Pat. No. 4,308,133 shows a promoter which is an aryl sulfonate. European patent application Publication No. 16914, Oct. 15, 1980, shows a promoter which is an alkanol amine-tall oil fatty acid condensate. U.S. Pat. No. 4,305,815 shows a promoter which is a hydroxy alkylated polyamine. U.S. Pat. No. 4,278,533 shows a promoter which is a hydroxylated ether amine. U.S. Pat. No. 4,196,092 shows a conditioning agent of a frother and a bis(alkyl)ester of a sulfosuccinic acid salt. United Kingdom Pat. No. 2,072,700 (and corresponding U.S. Pat. No. 4,340,467) floats coal with a latex emulsion prepared from a hydrocarbon oil with a hydrophobic water in oil emulsifier and a hydrophilic surfactant. Canadian Pat. No. 1,108,317 shows anionic surfactants which are fatty sulfosuccinates. Russian Inventor's Certificate No. 882,626 proposes a collector-frother which is an hydroxy, chloro or sulfide derivative of the methyl or ethyl ester of caproic acid.
Polish Pat. No. 104,569 proposes the use of ethoxylated higher fatty acids in coal flotation. U.S. Pat. No. 2,099,120 proposes the use of a water-soluble salt of a mono-ester of an organic dicarboxylic acid to float coal. British Pat. No. 741,085 proposes the flotation of coal by using salts of napthenic acids, cresylic acids, or rosin acids as wetting agents.
The foregoing art is consistent with accepted coal flotation principles that emulsified reagents should be used in coal froth flotation. While such promoters in the art can function in the coal flotation process, there is need for improving coal recoveries and improving the quality of the recovered coal. The present invention provides such improved high coal recoveries with improvements in coal quality utilizing a promoter which is highly effective and less expensive.
BROAD STATEMENT OF THE INVENTION
The present invention is directed to a froth flotation process for beneficiating coal wherein solid coal particles are selectively separated under coal froth flotation conditions as the froth phase from remaining solid feed particles as an aqueous phase in the presence of a coal particle collector which preferably is a fuel oil and frother. The improvement in such process is characterized by the addition of an effective proportion of a promoter comprising a non-ionic, hydrophobic, non-emulsified, aliphatic ester of an at least C.sub.10 aliphatic carboxylic acid which is devoid of nitrogen and sulfur atoms or the carboxylic acid itself. The promoter works especially well in the flotation of coal particles which have highly oxidized surfaces. Preferred promoters include fatty acids and especially higher fatty acids, and alkyl esters thereof (e.g. mono, di, and triesters).
An additional class of promoters are nitrile promoters and especially fatty nitriles having a chain length of about C.sub.10 -C.sub.30. A further class of promoters is the oxified derivatives of the fatty acid, fatty acid ester, and nitrile promoters of the present invention. Oxified derivatives for present purposes comprehend the hydroxylated, alkoxylated, epoxidized, and oxidized derivatives of such promoters. The addition of this second oxygen-functional group is very beneficial to the float. Yet another class of promoters comprise C.sub.10 -C.sub.30 higher fatty alcohols and their alkoxylated derivatives, especially propoxylated higher fatty alcohols. The promoters are non-emulsified (in water) and are non-ionic in character. The promoters are not miscible with water and form a distinct separate phase with water.
Advantages of the present invention include the ability to improve recovery of coal particles during the froth flotation process without increasing the proportion of ash in the concentrate. Another advantage is that the ash in the concentrate usually is even lower when using the promoters of the present invention. Yet another advantage is the ability to improve the coal recovery utilizing a promoter which is inexpensive and which heretofore in some forms has been considered as a waste material.
DETAILED DESCRIPTION OF THE INVENTION
A wide variety of promoter carboxylic acids and esters thereof have been determined to be highly effective in enhancing or promoting the beneficiation of coal by the froth flotation process. Aliphatic carboxylic acids are preferred for their availability and cost, though aromatic carboxylic acids function in the process too. A wide variety of aliphatic carboxylic acids have been determined to function effectively as promoters in the froth flotation of coal particles and especially in promoting the froth flotation of highly oxidized coal particles. The aliphatic carboxylic acid collectors advantageously will have at least about 10 carbon atoms and generally the aliphatic carboxylic acids will be C.sub.10 -C.sub.30 fatty aliphatic carboxylic acids and more often C.sub.12 -C.sub.22 fatty acids, such as are typically found in vegetable oils (including nut), animal fat, fish oil, tall oil, and the like. Typical vegetable oils from which the fatty acids can be derived include, for example, the oils of coconut, corn, cottonseed, linseed, olive, palm, palm kernel, peanut, safflower, soy bean, sunflower, mixtures thereof and the like vegetable oils. Fatty acids can be recovered from such triglyceride oil sources, for example, by conventional hydrolysis of the oils. Tall oil fatty acids (including tall oil heads and bottoms) also form an advantageous promoter for the process and such fatty acids can be recovered from crude tall oil by solvent fractionation techniques or conventional distillation including molecular distillation. Synthetic fatty acids are comprehended as promoters too.
The fatty acids used as promoters for the present process can be separated or purified from mixtures thereof with related fatty acids or other fatty or lipoidal materials, depending in large part upon the source from which the fatty acids are derived and the particular operation employed to recover such fatty acids. Unsaturated fatty acids in admixture with relatively saturated fatty acids can be separated from such mixture by conventional distillation including molecular distillation, or by conventional fractional crystallization or solvent fractionation techniques. Alternatively and preferably, though, fatty acid promoters for the present process can be typical in composition of the oil or other source from which such fatty acids are derived. Typical dosages of the fatty acid promoter in the froth flotation process range from about 0.005 to about 2.0 grams of promoter per kilogram of coal particles.
The ester promoters are aliphatic partial or full esters of the promoter carboxylic acids described above (e.g. an ester of a monool or polyol). The aliphatic ester moeity can be a simple lower alkyl group, e.g. methyl, or can range up to a fatty group having up to about 30 carbon atoms, though typically the upper range of the carbon atom chain length will be about 22. Accordingly, the ester promoters can be mono, di, or tri-esters of glycerol, esters of tall oil, and the like. The dosages of the fatty acid ester promoter are the same as for the fatty acid promoter from which the ester promoters are derived. It should be noted that mixtures of the fatty acids and fatty acid esters are ideally suited for use as promoters in the process of the present invention.
The ester promoters of the present invention are non-ionic and hydrophobic. Neither the promoter nor the collector, e.g. fuel oil, are emulsified in an aqueous emulsion for use in the froth flotation process. The presence of nitrogen atoms in the form of an amine or an amide has been determined to detract from the utility of the promoters during the coal beneficiation process. As the examples will demonstrate, equivalent promoter molecules with and without amine and/or amide nitrogen atoms when used in the coal flotation process result in higher percentages of coal being recovered by the promoter which is devoid of such nitrogen atoms. Nitriles, however, have been found to function effectively as promoters as disclosed below. Ether linkages also can be tolerated.
An additional class of promoters comprises the oxified derivatives of the fatty acid and ester promoters described above. By oxified promoters is meant that the ftty acid or fatty acid ester promoters contain an additional carbon-bound oxygen group in the form of hydroxyl group, an epoxide group, or a carbonyl group. This additional functionality on the promoters has been found to provide excellent recoveries of coal which recoveries often exceed the basic fatty acid and fatty acid ester promoters recovery. The oxified promoters can be naturally occurring, such as castor oil (12 hydroxy-cis-9-octadecanoic acid), or oiticica oil (4-oxo-cis-9, trans-11, trans-13-octadecatrienoic) or the like. These naturally occurring oxified triglyceride esters can be split through conventional reactions with water or alcohol and converted into their corresponding fatty acids or partial esters to form promoters ideally suited according to the precepts of the present invention. Additionally, the promoters may be synthesized from a fatty acid or fatty acid ester promoter by conventional reactions well known in the art. For example, the fatty acid or ester may be epoxidized, oxidized, hydroxylated, or alkoxylated for formation of appropriate promoters. Epoxidation is conventionally practiced by reaction of the unsaturated acid or its ester with an epoxidizing agent such as, for example, peracetic acid or the like. Additional promoters can be synthesized from the epoxidized promoter through hydrogenation, acid catalysis (e.g. with boron trifluoride or the like), to form a fatty ester ketone, acid ketone or the like, or a simple reaction with water to form a fatty ester diol or acid diol.
Additional reactions for alkoxylation (hydroxylation) include the reaction of the ester or acid promoter with an alkylene oxide, preferably propylene oxide or a higher oxide. Oxidation may be accomplished for an unsaturated acid or ester promoter through simple blowing of air through the promoter or by use of oxidizing agents, such as potassium permanganate, for example, in an alkaline solution or by using elevated temperatures in an alkaline media. Fatty acid ketones also can be prepared using similar conditions with a corresponding fatty acid alcohol or ester alcohol. The Examples will set forth the advantageous promotion effect which such promoters provide in coal flotation.
A wide variety of nitriles have been determined to be highly effective in enhancing or promoting the froth flotation of coal particles as the examples will demonstrate. The only limitation on the nitrile promoters is that such promoters be soluble in or with another reagent used during the flotation process. Such other reagents generally include the collector and the frother. So long as the nitrile promoter is soluble in the collector and/or the frother, the nitrile promoter will function effectively and efficiently in the beneficiation of coal particles by froth flotation. Suitable nitrile promoters include substituted and unsubstituted nitriles including polynitriles (e.g. dimer fatty nitrile). Advantageous nitrile promoters include fatty nitriles derived from natural or synthetic fatty substances, typically fatty or fat-forming acids. Natural fatty substances include, for example, glyceride oils, nut oils, marine oils, and tall oil. Substituents on nitrile promoters can include, for example, ether, carboxylic acid, carboxylic acid alkyl esters, amine, ether amine, amide, aromatic groups, and like substituents. Such substituents have been determined not to detract from the enhancement provided by the nitrile group of the nitrile promoters. Specific preferred nitrile promoters include fatty nitriles (e.g. C.sub.12 -C.sub.22 nitriles), dimer fatty nitriles, C.sub.12 -C.sub.22 ether nitriles, and the like. Especially preferred nitriles for use as promoters are nitrile pitches. A pitch is the residue remaining from a distillation or other purification process applied to various nitrile substances. For example, a fatty nitrile which is subjected to distillation for providing a pure fatty nitrile product has a residue or pitch which remains at the bottom of the column. Today, such nitrile pitch usually is discarded or burned for its fuel content. Such pitches, however, have been found to function efficiently and effectively in the process as promoters and, due to their cost, are especially preferred.
Synthesis of the nitrile promoters is routine and includes the cyanoethylation of a fatty material, the dehydration of an amide, and the dehydration of a carboxylic acid ammonium salt. Other techniques are suitable for forming the nitrile also as those skilled in the art will appreciate. The particular manner for forming the nitrile promoter is unimportant. Typical dosages of the nitrile promoter in the froth flotation process range from about 0.005 to about 2.0 grams of promoter per kilogram of coal particles.
The nitrile promoters may be oxified also to provide a further class of promoters for use in the process of the present invention. For example, the nitrile promoter may be epoxidized with an epoxidizing agent as disclosed above. The epoxidized nitrile promoter then may be formed into a nitrile alcohol by hydrogenation, for example, a nitrile ketone by acid catalysis with boron trifluoride, for example, or a nitrile diol by reaction with water. Additionally, the nitrile promoter may be oxidized with air or a strong oxidizing agent and a nitrile ketone may be formed by a similar reaction from a corresponding nitrile alcohol. As with the fatty acid and fatty acid ester promoters, nitrile promoters are subject to enhanced promotion by addition of this second functionality of a carbon-bound oxygen group.
A still further class of promoters are higher fatty alcohol promoters and their alkoxylated derivatives. By "higher fatty alcohol" for present purposes is meant a C.sub.12 or higher alcohol. Typically, such higher fatty alcohols will be C.sub.14 or C.sub.16 and higher alcohols often ranging up to C.sub.30 though typically such alcohols will range up to about C.sub.22 in chain length. While ethoxylated fatty alcohols do provide enhanced coal recovery, the resulting froth often is difficult to handle. Thus, it is distinctly preferred that the alkoxylated fatty alcohol promoters be alkoxylated with propylene oxide or a higher oxide. Fatty alcohols can be synthesized from corresponding higher fatty acids by conventional hydrogenation or other decarbonylation techniques known in the art. The Examples again will demonstrate the unexpected improvement in coal recovery realized by such higher fatty alcohol and alkoxylated alcohol promoters. Such results are surprising when considering that such alcohol and alcohol derivatives do not provide frothing action adequate to be termed as a frother by the coal froth flotation art.
The promoters of the present invention are non-emulsified and non-ionic, and are used with conventional collectors and frothers. Fuel oil is the preferred collector for use in the coal flotation process. Representative fuel oils include, for example, diesel oil, kerosene, Bunker C fuel oil, and the like and mixtures thereof. The fuel oil collector generally is employed in a dosage of from about 0.02 to about 2.5 gm/kg of coal feed. The precise proportion of collector depends upon a number of factors including, for example, the size, degree of oxidation and rank of the coal to be floated, and the dosages of the promoter and frother.
The frother or frothing agent used in the process is conventional and includes, for example, pine oil, cresol, isomers of amyl alcohol and other branched C.sub.4 -C.sub.8 alkanols, and the like. Preferred frothing agents by the art, however, include methyl isobutyl carbinol (MIBC) and polypropylene glycol alkyl or phenyl ethers wherein the polypropylene glycol methyl ethers have a weight average molecular weight of from about 200 to 600. The dosage of frothing agent generally ranges from about 0.05 to about 0.5 gm/kg of coal feed. The precise proportion of frothing agent depends upon a number of factors such as those noted above relative to the conditioning agent. The preferred frother is disclosed in commonly-assigned application U.S. Ser. No. 454,607, filed Dec. 30, 1982, now U.S. Pat. No. 4,504,385 and comprises a polyhydroxy frother which has been modified to contain an ester group.
Suitable coal for beneficiation by the improved froth flotation process of the present invention includes anthracite, lignite, bituminous, subbituminous and like coals. The process of the present invention operates quite effectively on coals which are very difficult to float by conventional froth flotation techniques, especially where the surfaces of the coal particles are oxidized. The size of the coal particles fed to the process generally are not substantially above about 28 Tyler mesh (0.589 mm), though larger particles (e.g. less than 14 Tyler mesh or 1.168 mm), while difficult to float, may be floated successfully. In typical commercial froth flotation operations, coal particles larger than 28 Tyler mesh, advantageously larger than 100 Tyler mesh, may be separated from both inert mateial mined therewith and more finely divided coal by gravimetric separation techniques. The desirable cut or fraction of coal fed to the process for flotation preferably is initially washed and then mixed with sufficient water to prepare an aqueous slurry having a concentration of solids which promote rapid flotation. Typically, a solids concentration of from about 2% to about 20% by weight solids, advantageously between about 5 and 10 weight percent solids, is preferred. The aqueous coal slurry is conditioned with the collector and promoter, and any adjuvants, by vigorously mixing or agitating the slurry prior to flotation in conventional manner. It should be noted that the promoters of the present invention can be used in separate form or can be premixed with the collector or the frother for use in the present invention. Any manner of incorporating the promoter into the froth flotation process has been determined to provide a much improved recovery of coal so long as all three ingredients are present in the float.
Typical commercial coal froth flotation operations provide a pH adjustment of the aqueous coal slurry prior to and/or during flotation to a value of about 4 to about 9 and preferably about 4 to 8. Such pH adjustment generally promotes the greatest coal recovery, though flotation at the natural coal pH is possible. If the coal is acidic in character, the pH adjustment is made generally by adding an alkaline material to the coal slurry. Suitable alkaline materials include, for example, soda ash, lime, ammonia, potassium hydroxide or magnesium hydroxide, and the like, though sodium hydroxide is preferred. If the aqueous coal slurry is alkaline in character, an acid is added to the aqueous coal slurry. Suitable acids include, for example, mineral acids such as sulfuric acid, hydrochloric acid, and the like. The conditioned and pH-adjusted aqueous coal slurry is aerated in a conventional flotation machine or bowl to float the coal. The frothing agent or frother preferably is added to the aqueous coal slurry just prior to flotation or in the flotation cell itself.

The following examples show how the present invention can be practiced but should not be construed as limiting. In this application, all units are in the metric system, and all percentages and proportions are by weight, unless otherwise expressly indicated. Also, all references cited herein are expressly incorporated herein by reference.
IN THE EXAMPLES
Coal subjected to evaluation was comminuted to a particle size (Examples 1-7 and 12-16) of less than 28 Tyler mesh (0.589 mm) and then dispersed in water for conditoning with the fuel oil collector and promoter, if any, for about one minute. The flotation tests used 6.67% solids slurry of the conditioned coal which was pH adjusted to 7.0 with sodium hydroxide. The frother was MIBC (methyl isobutyl carbinol) in a dosage of about 0.2 gm/kg of coal (Examples 1-7 and 12-16), unless otherwise indicated, and all tests were conducted in a Denver Flotation Machine.
The various coals evaluated contained varying amounts of ash content (Examples 1-7 and 12-16) as follows: first Ohio coal, about 33% ash; second Ohio coal, about 50% ash; Western Kentucky coal, about 15% ash; West Virginia coal, about 21% ash; and Alberta (Canada) coal, about 62% ash.
The nitrile pitch promoter was a mixture of several different nitrile pitches derived from the product of several different fatty nitriles from a commercial chemical plant operating in this country. The precise proportions and types of nitrile pitches making up the mixture is unknown. The other nitrile promoters used in the examples were derived from vegetable, animal, and tall oil fatty acids as the names indicate. The weight percent of nitrile promoter set forth in the tables refers to the nitrile promoter in the diesel oil or other collector for forming a collector/promoter reagent.
EXAMPLE 1
The ester promoters of the present invention were compared to several substantially equivalent promoters which contained nitrogen atoms in the form of amine, amide, or combinations thereof. The following promoters were evaluated.
______________________________________PromoterNo. Promoter______________________________________N1 Reaction product of a C.sub.12 -C.sub.15 alkoxy propyl tallow diamine, tall oil fatty acids, and propylene oxide (1:3:3 molar ratio, respectively)N2 Reaction product of a tallow diamine, propylene oxide, and tall oil fatty acids (1:2:3 molar ratio, respectively)N3 Reaction product of iso-decyl ether propyl amine, ethylene oxide, and tall oil fatty acids (1:1:2 molar ratio, respectively)N4 Reaction product of tallow diamine and tall oil fatty acids (1:1 molar ratio)E1 Tallow alcohol ester of tall oil fatty acidsE2 Mixture of various lower alkyl esters of soft tallow acid pitchE3 Diester of diethylene glycol and tall oil fatty acidsE4 Methyl ester of tallow fatty acids______________________________________
Each promoter was dispersed at 10% by weight in diesel oil collector which collector/promoter was employed in a dosage of 0.30 gm/kg of coal for the West Virginia coal (21% ash) and 0.85 gm/kg coal for the Alberta (Canada) coal (62% ash). The frother dosage for the very high ash Alberta (Canada) coal was increased to about 0.28 gm/kg of coal. The Control run contained diesel oil collector with no promoter. The following flotation results were obtained.
TABLE 1______________________________________ CoalRun Promoter Concentrate Ash RecoveryNo. No. (wt. %) (wt. %) (wt. %)______________________________________West Virginia CoalControl -- 20.9 10.3 23.7432 N1 24.4 13.8 26.8433 N2 28.3 12.7 31.3434 N3 30.3 9.8 34.5435 N4 30.0 10.2 35.0438 E1 36.3 10.2 41.6440 E2 39.6 14.5 43.3437 E3 40.1 10.3 46.0431 E1 40.0 9.2 46.1Alberta (Canada) CoalControl -- 21.1 28.2 40.7467 N2 15.3 31.8 31.5466 N1 18.0 31.7 34.8465 N3 24.6 33.5 49.4469 N4 33.6 33.4 59.8470 E4 40.5 41.5 71.7468 E1 40.2 37.3 72.5464 E3 43.1 42.7 73.2471 E2 45.1 37.6 74.7______________________________________
The above-tabulated results clearly demonstrate the excellent results which the ester promoters provide in the coal flotation process. The comparative promoters containing amine and amide groups consistently showed poorer promotion performance than did the ester promoters devoid of such nitrogen atoms.
EXAMPLE 2
The first Ohio coal (33% ash) was floated with several different ester promoters in two different series of runs. The diesel oil collector/ester promoter combination was used in a dosage of 1.05 gm/kg of coal. The following table displays the results of the floats.
TABLE 2______________________________________Ester Promoter wt. % Coal in Concen- Ash Re-Run Diesel trate (wt. coveryNo. Oil Type (wt. %) %) (wt. %)______________________________________Series A40 -- None 25.1 17.2 31.462 10.0 methyl tallowate 59.5 19.8 73.663 10.0 oleyl oleate 57.4 14.6 73.0Series B64 -- None 29.9 21.2 35.666 10.0 tallow triglyceride 46.2 19.5 57.867 10.0 rape seed oil 50.3 18.5 61.980 10.0 *Polyester 523 55.9 19.1 70.181 10.0 *Polyester 775 58.9 21.2 72.185 10.0 *Polyester 523 56.9 21.3 69.5 86a 10.0 *Polyester 433 58.1 20.5 70.8 86b 10.0 *Diester 200 55.5 19.1 68.987 10.0 *Diester 120 48.5 19.9 59.7______________________________________ *Polyester 523 is a medium viscosity polyester (Gardner Color 3; viscosit 36 stokes at 25.degree. C.; specific gravity 1.100, 25.degree. C./25.degree. C.; acid value 2.0; refractive index 1.514 at 25.degree. C. Polyester 775 is a high viscosity polyester (Gardner color 1; viscosity 5 stokes at 25.degree. C.; specific gravity 1.095, 25.degree. C./25.degree. C.; acid value 1.3; refractive index 1.4670 at 25.degree. C.) Polyester 433 is a low viscosity polyester (Gardner color 3; viscosity 17.0 stokes at 25.degree. C.; specific gravity 1.090, 25.degree. C./25.degree. C.; acid value 2.0; refractive index 1.5050 at 25.degree. C.) Diester 220 is the isodecyl alcohol diester of adipic acid Diester 120 is the isodecyl alcohol diester of phthalic acid.
The above-tabulated results again demonstrate the effectiveness of the ester promoters in the float. Diesters, polyeters and aromatic esters are shown to function effectively also.
EXAMPLE 3
Western Kentucky coal (15% ash) was floated in this series of runs using 0.525 gm/kg dosage of collector/promoter with the following results.
TABLE 3______________________________________Ester Promoter wt. % Coal in Concen- Ash Re-Run Diesel trate (wt. coveryNo. Oil Type (wt. %) %) (wt. %)______________________________________90 -- (1.05 gm/kg 64.4 11.7 76.3 diesel oil)91 -- (0.525 gm/kg 37.6 13.6 42.2 diesel oil)98 10.0 Diester 220 71.7 10.7 84.199 10.0 methyl tallowate 69.7 10.6 81.4______________________________________
Again, the effectiveness of the ester promoters is demonstrated to provide improved coal recoveries even at one-half the collector dosage.
EXAMPLE 4
Lots of the first Ohio coal (33% ash) were held at about 71.degree. C. (160.degree. F.) for 3 days in order to further oxide the coal. The highly oxidized coal then was floated with the following results.
TABLE 4______________________________________Ester Promoter wt. % Coal in Concen- Ash Re-Run Diesel trate (wt. coveryNo. Oil Type (wt. %) %) (wt. %)______________________________________104 -- None 28.6 25.3 32.7110 10.0 1,4-butanediol 47.9 21.4 58.7 diester of tall oil fatty acids111 10.0 ethylene glycol 49.7 20.2 59.5 diester of tall oil fatty acids______________________________________
These results demonstrate the remarkable improvements which can be realized by employing the ester promoters for floating very difficult-to-float coal.
EXAMPLE 5
The first Ohio coal (33% ash) was floated using fatty acid promoters and 0.25 gm/kg MIBC frother. The diesel oil/promoter dosage was 0.85 gm/kg coal.
TABLE 5______________________________________Fatty Acid Collector wt. % Coal in Concen- Ash Re-Run Diesel trate (wt. coveryNo. Oil Type (wt. %) %) (wt. %)______________________________________596 -- None 45.3 11.8 58.1496 10.0 Coco fatty acids 64.7 14.6 86.1597 10.0 Tall oil heads 64.7 13.4 84.2 fatty acids598 10.0 Tall oil fatty acids 68.2 14.7 87.7599 10.0 Tall oil fatty acids 65.9 13.9 87.3600 10.0 Dimer tall oil 65.6 13.2 84.9 fatty acids601 10.0 Diacid product of 68.6 14.5 88.3 linoleic and acrylic acids602 10.0 C.sub.10 fatty acid 66.9 13.7 84.9603 10.0 C.sub.12 fatty acid 67.4 15.2 84.2______________________________________
The above-tabulated results demonstrate the beneficial effect on the float imparted by the fatty acid promoters. The concentrate recovered has substantially increased while its ash content has only slightly increased. Thus, coal recovery also has substantially increased.
EXAMPLE 6
The second Ohio coal (50% ash) was floated using several different fatty acid promoters and 0.25 gm/kg MIBC frother. The diesel oil collector/fatty acid promoter blends were used in a dosage of 0.4 gm/kg of coal.
TABLE 6______________________________________Fatty Acid Collector wt. % Coal in Concen- Ash Re-Run Diesel trate (wt. coveryNo. Oil Type (wt. %) %) (wt. %)______________________________________693 -- None 28.3 28.6 40.0694 10.0 Yellow grease fatty 40.5 24.9 59.2 acids695 10.0 C.sub.12 fatty acids 41.3 27.0 56.6696 10.0 Tall oil fatty acids 42.9 25.0 60.4697 10.0 Diacid product of 47.0 27.6 63.7 linoleic and acrylic acids698 10.0 Dimer tall oil 38.1 25.4 51.8 fatty acids699 10.0 Coco fatty acids 47.2 26.9 62.7700 10.0 C.sub.10 fatty acid 45.1 28.6 55.8______________________________________
The invention again is demonstrated even for a coal that is one-half ash. The concentrate amounts recovered has increased substantially without an increase in its ash content.
EXAMPLE 7
West Virginia coal (33% ash) was floated with 0.25 gm/kg diesel oil collector and 0.2 gm/kg MIBC frother. In addition, various amine condensates and fatty acid promoters were evaluated in the floats. The promoters evaluated were tall oil fatty acids, an amine condensate promoter (reaction product of a C.sub.12 -C.sub.15 alkoxy propyl tallow diamine, tall oil fatty acids, and propylene oxide in a 1:1:3 molar ratio, respectively), and a mixture thereof. The following test results were obtained:
TABLE 7A______________________________________Promoter wt. % Coal in Concen- Ash Re-Run Diesel trate (wt. coveryNo. Type Oil (wt. %) %) (wt. %)______________________________________804 -- None 28.4 16.2 34.6801 Amine Condensate 10.0 42.0 14.8 52.3802 Amine Condensate 5.0 49.6 15.5 63.1 Tall Oil 5.0 800* Tall Oil 10.0 69.5 16.1 69.5______________________________________ *Average of two runs
The above-tabulated results demonstrate that, though the amine promoter is beneficial to the float, the presence of the amine in admixture with the fatty acid promoter is adverse to maximizing coal recovery. Note the dramatic increase in the concentrate when the fatty acid promoter is used alone.
A further demonstration of the unexpected improvement in using fatty acids as promoters was observed when comparing the tall oil fatty acid promoter with an amine promoter consisting of the reaction product of the tallow diamine, tall oil fatty acids, and propylene oxide (1:1:2 molar ratio, respectively).
TABLE 7B______________________________________Promoter wt. % Coal in Concen- Ash Re-Run Diesel trate (wt. coveryNo. Type Oil (wt. %) %) (wt. %)______________________________________804 -- None 28.4 16.2 34.6799 Amine Condensate 10.0 40.4 17.5 50.5798 Tall Oil 10.0 48.7 16.4 60.1______________________________________
These results again show the improved coal recovery which pure fatty acids provide compared to amine-fatty acid condensates. A comparison of Run No. 802 from Table 8A and Run 798 from Table 8B appears to show that the presence of the amine condensate provides no margin of improved coal recovery than is provided from the tall oil fatty acids by themselves.
EXAMPLE 8
Western Kentucky coal (about 22% ash content, particle size less than 20 Tyler mesh or 0.833 mm) and Ohio coal (about 27-28% ash content, particle size less than 14 Tyler mesh or 1.168 mm) were floated with 10% by weight of various hydroxyl-containing fatty acid and fatty acid alkyl ester promoters dispersed in No. 2 diesel oil collector (0.44 g/kg dosage) and 0.16 g/kg MIBC frother for the Western Kentucky coal, and 0.105 g/kg diesel oil collector and 0.315 g/kg MIBC frother for the Ohio coal. Runs using corresponding fatty acid and ester promoters without hydroxyl groups also are reported.
TABLE 8______________________________________ Con- Coal cen- Ash Re- trate (wt coveryRun No. Promoter Type (wt %) %) (wt %)______________________________________Western Kentucky Coal1513 None 19.5 15.2 21.11515 0leic acid 55.8 11.3 62.31514 Castor Oil fatty acids 65.7 11.9 74.21516 Methyl oleate 59.2 11.7 66.91517 Methyl ricinoleate 65.5 11.9 73.2Ohio Coal1582 None 36.9 14.1 43.41583 Soybean oil triglyceride 64.8 14.7 77.01584 Castor oil triglyceride 67.7 14.6 79.71585 Oleic acid 63.1 15.0 72.71586 Castor oil fatty acids 75.1 16.4 87.31587 Methyl Oleate 58.3 14.7 68.01588 Methyl ricinoleate 68.6 14.6 81.21589 Linseed oil triglyceride 64.9 14.2 76.71590 Boiled linseed oil triglyceride 66.3 14.4 79.31591 *Castor oil fatty acids 33.6 14.7 39.81592 *Methyl ricinoleate 29.4 14.3 34.81593 *Soybean oil 19.3 19.4 21.4______________________________________ *No MIBC or other frother added.
The above-tabulated results demonstrate that the hydroxyl group addition to the fatty acid and ester promoters provides increases coal recovery without increased ash in the concentrate. Note also should be made of the extremely large particle size of the Ohio coal which was floated successfully using the novel promoters.
EXAMPLE 9
The same types of coal (except having about 25% ash content each) and reagent dosages of Example 8 were used to evaluate epoxidized fatty acid and ester promoters (10% by weight in #2 diesel oil collector). Comparative runs using prior art olefin oxides and runs using the non-epoxidized fatty acids and esters also are reported.
TABLE 9______________________________________ Con- Coal cen- Ash Re- trate (wt coveryRun No. Promoter Type (wt %) %) (wt %)______________________________________Western Kentucky Coal1603 None 27.7 13.5 32.21636 C.sub.16 Olefin Oxide 45.4 11.8 53.9 (Comparative)1637 Soybean Oil triglyceride 44.5 11.7 52.71638 Epoxidized Soybean Oil 65.1 12.9 69.2 triglyceride1640 Methyl Oleate 46.4 11.7 54.61639 Epoxidized Tall Oil 2-ethyl 59.1 11.8 76.6 hexyl esterOhio Coal1582 None 36.9 14.1 43.41641 C.sub.16 Olefin Oxide 54.6 14.2 63.9 (Comparative)1643 Soybean oil triglyceride 60.7 12.9 73.31644 Epoxidized Soybean Oil 73.4 14.1 87.1 triglyceride1601 Epoxidized Soybean Oil 71.9 14.2 84.4 triglyceride1646 Methyl Oleate 60.0 14.8 70.71642 Epoxidized tall oil 2-ethyl 62.8 14.8 73.8 hexyl ester1602 Split Epoxidized Soybean Oil 63.6 16.1 73.6______________________________________
The above-tabulated results again demonstrate the improvement which is experienced by adding additional functionality to the fatty acid and fatty acid ester promoters.
EXAMPLE 10
Western Kentucky coal (about 22-23% ash content, particle size less than 20 Tyler mesh, 0.833 mm) was floated with 10% by weight of various propoxylated fatty acid promoters dispersed in 0.44 g/kg No. 2 diesel oil collector and using 0.16 g/kg MIBC frother. Ohio coal (about 29.5% ash content, particle size less than 20 Tyler mesh, 0.833 mm) similarly was floated with 0.33 g/kg No. 2 diesel oil collector and 0.22 g/kg MIBC frother. Propoxylation was conducted using propylene oxide (PO as used below) with the number of moles added being set forth below.
TABLE 10______________________________________ Con- Coal cen- Ash Re- trate (wt coveryRun No. Promoter Type (wt %) %) (wt %)______________________________________Western Kentucky Coal1505 None 26.3 12.4 29.11507 Tall oil fatty acids 61.5 11.7 69.21512 Tall oil + 1.5 moles PO 69.0 10.8 79.21508 Tall oil + 10 moles PO 66.7 11.7 75.81509 C.sub.16 -C.sub.18 fatty acid mixture 47.3 12.8 53.01510 C.sub.16 -C.sub.18 Fatty acid mixture + 65.4 11.0 74.6 1.5 moles PO1511 C.sub.16 -C.sub.18 Fatty acid mixture + 63.0 12.0 71.0 10 moles POOhio Coal1498 None 42.9 14.4 55.61500 Tall oil fatty acids 63.8 13.8 77.91499 Tall oil fatty acids + 74.1 15.2 88.4 1.5 moles PO1501 Tall oil fatty acids + 75.3 15.1 90.0 5 moles PO1502 Tall oil fatty acids + 74.2 15.7 89.0 10 moles PO1504 C.sub.16 -C.sub.18 69.8ty acid mixture 14.9 84.31503 C.sub.16 -C.sub.18 fatty acid mixture + 75.7 14.7 90.2 10 moles PO______________________________________
Again, the benefits imparted by the oxified (alkoxylated) fatty acid promoters is demonstrated. Also, an optimum number of moles of propylene oxide was reached. Additional moles or propylene oxide beyond such optimum resulted in no increase in coal recovery.
EXAMPLE 11
U.K. Pat. No. 2,093,735 and corresponding Offenlegungsschrift DE No. 3,107,305 propose to completely replace diesel oil collectors with vegetable oil collectors. The present invention, however, is directed to the use of vegetable oils (and other compounds) as promoters to promote diesel oil and like collectors. The heretofore unrecognized and unexpected benefit of such promoter use is demonstrated below on Western Kentucky coal (about 29% ash content, particle size less than 28 Tyler mesh or 0.589 mm) and on Ohio coal (about 32-33% ash content, particle size less than 14 Tyler mesh or 1.168 mm). The frother was MIBC at 0.135 g/kg for Western Kentucky Coal and 0.105 g/kg for Ohio coal. The triglyceride oil used in the Western Kentucky coal runs was soybean oil and rape seed oil for the Ohio coal runs.
TABLE 11______________________________________ Soybean Oil Promoter Total Dosage- Coal (wt % Triglyceride Re-Run in #2 Oil & #2 Diesel Concentrate Ash coveryNo. Diesel Oil) Oil (g/kg) (wt %) (wt %) (wt %)______________________________________Western Kentucky Coal1885 0 0.70 42.6 10.6 54.01886 20 0.70 68.0 11.0 84.81890 50 0.70 64.7 10.3 81.91891 75 0.70 64.1 10.7 80.61886 100 0.70 61.0 10.1 76.7 1888* 100 1.00 35.4 12.7 43.6Ohio Coal1928 0 0.57 58.5 15.8 72.91929 20 0.57 72.5 16.9 88.01930 50 0.57 73.3 17.2 88.81931 75 0.57 69.3 16.9 84.21932 100 0.57 60.6 15.3 75.5______________________________________ *No MIBC frother.
These results demonstrate that the fatty acid ester (e.g. triglyceride oil) was more beneficial in improving the float when used to promote or enhance the ability of conventional diesel oil or like collectors. The unexpectedness of the present invention, thus, is demonstrated.
EXAMPLE 12
The first Ohio coal (33% ash) was floated with several different classes and sources of nitriles in order to evaluate the efficacy of nitriles as promoters in the float. Diesel oil was used as the collector in all runs. The following table displays the results of such floats.
TABLE 12______________________________________ Coal Concen- Re-Run Nitrile Promoter trate Ash coveryNo. wt. % Type (wt. %) (wt. %) (wt. %)______________________________________40 -- None 25.1 17.2 31.441 10.0 nitrile pitch 46.2 15.2 58.443 50.0 nitrile pitch 41.8 16.7 51.845 2.5 soft tallow nitrile 54.1 15.2 69.044 5.0 soft tallow nitrile 54.6 14.9 69.342 10.0 soft tallow nitrile 57.2 13.6 73.146 2.5 tall oil nitrile 55.2 14.6 70.747 5.0 tall oil nitrile 58.0 14.6 74.348 10.0 tall oil nitrile 52.1 12.6 68.350 2.5 dimer nitrile 59.6 15.7 73.851 5.0 dimer nitrile 61.2 15.0 77.552 10.0 dimer nitrile 65.8 15.1 84.449 10.0 off grade hard 59.4 14.0 75.1 tallow nitrile57 10.0 coco nitrile 59.4 15.0 74.558 10.0 C.sub.14 ether nitrile 43.0 16.2 54.059 10.0 tallow amine 46.5 15.9 58.7 trimethylene nitrile______________________________________
The above-tabulated results demonstrate that several different classes of nitriles are effective in improving the selectivity of floating coal. The ash content was reduced in every run using the nitrile promoters. Moreover, more coal was recovered in the concentrate and the concentrate amount increased also. The ability to use a pitch as the basis for a highly effective and selective promoter underscores the usually intense effect which the nitrile group has in the process. The only apparent limitation on the nitrile promoter is that it be solubilized by the collector and/or frother.
EXAMPLE 13
Additional lots of the first Ohio coal (33% ash) were subjected to froth flotation using the nitrile promoters with the following results.
TABLE 13______________________________________ Concen- CoalRun Nitrile Promoter trate Ash RecoveryNo. wt. % Type (wt. %) (wt. %) (wt. %)______________________________________64 -- None 29.9 21.2 35.6 65* -- None 28.5 23.9 33.074 5.0 dimer nitrile 50.0 18.4 63.075 10.0 soft tallow nitrile 51.8 20.6 62.276 10.0 tall oil nitrile 50.4 19.7 62.4______________________________________ *Collector was Western Fuel Oil #5.
Again, the above-tabulated data demonstrates the effectiveness of the nitrile promoters in the coal flotation process.
EXAMPLE 14
In this example, the total proportion of reagents, fuel oil collector and nitrile promoter, were reduced to 0.525 gm/kg of Western Kentucky coal (15% ash). In run 90, the fuel oil dosage was 1.05 gm/kg coal and in run 90 the dosage was 0.525 gm/kg. Runs 92, 94 and 95 with the promoter also used a total dosage of collector and promoter of 0.525 gm/kg coal. The following results were experienced.
TABLE 14______________________________________ Concen- CoalRun Nitrile Promoter trate Ash RecoveryNo. wt. % Type (wt. %) (wt. %) (wt. %)______________________________________90 -- None 64.4 11.7 76.391 -- None 37.6 13.6 42.292 10.0 soft tallow nitrile 71.1 10.4 84.194 10.0 tall oil nitrile 63.7 10.7 75.595 10.0 nitrile pitch 63.0 12.4 70.1 (unfiltered)______________________________________
These results show that the nitrile promoters intensity in the process permits the total reagent concentration to be cut in half without any loss in concentrate amount or grade.
EXAMPLE 15
In order to demonstrate the efficacy of the nitrile promoters in improving the float of oxidized coal, lots of the first Ohio coal (33% ash) were held at about 71.degree. C. (160.degree. F.) for 3 days in order to further oxidize the coal. The highly oxidized coal then was floated with the following results.
TABLE 15______________________________________ Coal Concen- Re-Run Nitrile Promoter trate Ash coveryNo. wt. % Type (wt. %) (wt. %) (wt. %)______________________________________104 -- None 28.6 25.3 32.7106 10.0 nitrile pitch 42.4 19.5 53.7107 10.0 oleyl nitrile pitch 49.6 19.7 60.7112 10.0 filtered nitrile pitch 49.1 20.3 60.7113 20.0 filtered nitrile pitch 49.4 20.9 59.7______________________________________
These results demonstrate the remarkable improvements that can be realized by the present invention in floating very difficult-to-float coal. Note that the weight percent concentrate has been increased as well as has the amount of coal recovered.
EXAMPLE 16
Additional tests were conducted in the first Ohio coal (33% ash) in order to further demonstrate the present invention. The total reagent concentration (fuel oil and nitrile promoter) was 0.22 gm/kg of coal.
TABLE 16______________________________________ Concen- CoalRun Nitrile Promoter trate Ash RecoveryNo. wt. % Type (wt. %) (wt. %) (wt. %)______________________________________122 -- None 33.8 22.4 39.1118 10.0 tallow nitrile 46.6 18.4 57.1123 10.0 nitrile pitch 39.9 21.6 47.6117 10.0 filtered nitrile 52.8 19.0 63.1 pitch124 10.0 filtered amine 42.3 20.6 51.7 nitrile pitch116 20.0 filtered nitrile 54.4 19.0 66.3 pitch125 20.0 filtered amine 47.9 19.9 59.0 nitrile pitch______________________________________
Once again the efficacy of the nitrile promoter is demonstrated by the above-tabulated results.
EXAMPLE 17
Nitrile promoters were epoxidized and evaluated on Ohio coal (about 27% ash content, particle size less than 14 Tyler mesh or 1.168 mm). Flotation reagents used were 10% promoter in #2 diesel oil collector at a total dosage of 0.30 g/kg, and 0.105 g/kg MIBC frother.
TABLE 17______________________________________ Concen- CoalRun trate Ash RecoveryNo. Promoter Type (wt %) (wt %) (wt %)______________________________________1787 None 48.4 14.6 55.71790 C.sub.16 olefin oxide 55.3 14.6 65.1 (comparative)1789 Soya nitrile 59.2 14.0 69.41788 Epoxidized soya nitrile 63.5 15.0 74.3______________________________________
Again, the efficacy of the promoters of the present invention is demonstrated.
EXAMPLE 18
Western Kentucky coal (about 25% ash content, particle size less than 28 Tyler mesh or 0.589 mm) and Ohio coal (about 28% ash content, particle size less than 14 mesh or 1.168 mm) was floated using 0.315 g/kg No. 2 diesel oil collector containing 10% by weight promoter and 0.105 g/kg MIBC frother. Long chain aliphatic alcohols and alkoxylated derivatives thereof were evaluated.
TABLE 18______________________________________ Coal Concentrate Ash RecoveryRun No. *Promoter Type (wt %) (wt %) (wt %)______________________________________Western Kentucky Coal1603 None 27.7 13.5 32.21604 Tallow alcohol 52.3 12.7 61.31606 Tallow alcohol + 58.9 12.6 68.6 8 moles PO1605 Tallow alcohol + 60.0 12.2 70.7 10 moles PO1607 Tallow alcohol + 53.3 14.5 60.8 8 moles PO/EO1609 Tallow alcohol + 55.0 15.2 63.5 4 moles EO1608 Tallow alcohol + 57.3 14.5 65.5 9 moles EOOhio Coal1582 None 36.9 14.1 43.41594 Tallow alcohol 52.6 14.8 61.61596 Tallow alcohol + 63.8 15.4 74.7 8 moles PO1595 Tallow alcohol + 65.0 15.3 76.4 10 moles PO1598 Tallow alcohol + 48.8 16.4 56.0 8 moles PO/EO1599 Tallow alcohol + 50.5 16.7 62.3 4 moles EO1598 Tallow alcohol + 52.4 17.7 60.0 9 moles EO______________________________________ *PO is propylene oxide. EO is ethylene oxide.
The above-tabulated data shows the efficacy of long chain alcohol promoters and alkoxylated derivatives thereof. Not shown in the data is the superior froth texture which the propoxylated alcohol promoters displayed relative to the ethoxylated alcohol promoters.
EXAMPLE 19
Ohio coal (32.5 ash content, particle size less than 14 Tyler mesh or 1.168 mm) and Western Kentucky coal (25% ash content, particle size less than 28 Tyler mesh or 0.589 mm) each were floated with a fatty acid promoter approximately 67% C.sub.18, 30% C.sub.16 and 3% C.sub.14 fatty acids) and with varying degrees of the ethoxylates and propoxylates thereof. Polish Pat. No. 104569 proposes the use of ethoxylated higher fatty acids in coal flotation. The runs utilized 0.13 g/kg MIBC frother and 0.34 g/kg diesel oil collector plus promoter (10% by weight promoter in diesel oil collector in all runs).
TABLE 19______________________________________ Concen-Run trate Ash CoalNo. Promoter Type (wt %) (wt %) (wt %)______________________________________Western Kentucky Coal1989 Fatty Acids 54.1 15.5 61.21983 Fatty Acids +2 moles EO 53.5 14.7 60.91985 Fatty Acids +5 moles EO 48.3 15.1 54.91987 Fatty Acids +10 moles EO 49.1 16.1 55.21990 Fatty Acids +3 moles PO 55.8 14.7 63.71986 Fatty Acids +5 moles PO 60.3 14.4 68.91988 Fatty Acids +10 moles PO 58.9 15.0 67.2Ohio Coal1992 Fatty Acids 71.3 17.8 87.61993 Fatty Acids +2 moles EO 71.3 16.6 88.31995 Fatty Acids +5 moles EO 71.0 17.3 86.81997 Fatty Acids +10 moles EO 66.7 18.2 81.31994 Fatty Acids +3 moles PO 72.8 17.1 89.11996 Fatty Acids +5 moles PO 74.8 18.2 90.61998 Fatty Acids +10 moles PO 74.8 18.4 90.5______________________________________
The foregoing data shows that the fatty acid promoter neat provides better coal yields and recoveries than the ethoxylate thereof, but that the propoxylate of the fatty acid promoter improves both yield and recovery. It is believed that the emulsification strength of the ethoxylate is detrimental to the float. The propoxylate and higher alkoxylates are not emulsifiers and, thus, improve the float compared to the fatty acid promoter. The unobviousness of fatty acid and higher (C.sub.3 or greater) alkoxylates is proven.

Number	Name	Date
2166093	Harwood et al.	Jul 1939
2175093	Ralston et al.	Oct 1939
2298281	Corley et al.	Oct 1942
3298520	Bikales	Jan 1967
3301400	Bikales	Jan 1967
3353671	Bikales	Nov 1967
4394257	Wang et al.	Jul 1983
4452714	McCarthy	Jun 1984

Promoters for froth flotation of coal

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