Document zweq3R31vJx0v4GL3EzpN6k7

PLAINTIFF'S EXHIBIT UC-102 United States Patent Office 3,409,499 Patented Not. 6, 1968 12 the prior art. In accordance with that method, chrysotile 3,409,499 CHRYSOT1LE ASBESTOS FIBER DISPERSION INCLUDING MONOCARBOXYUC ACID William H. Dresber, Warwick, and Alfred W. Naumann, Saffem, N.Y, assignors to Union Carbide Corporation, a corporation of New York ...... No Drawing. Filed May 14, 1945, Ser. No. 454,005 10 Claims. (CL 142--3) asbestos is dispersed and stabilized in aqueous suspension by the use of an auxiliary, highly charged, electropostlive colloid containing a metal aluminale and a monobasic acid, which is adsorbed onto the surface of the asbestos fibers. The present invention diflers from our previous invention in that the dispersed state herein is created and stabilized by preservation of the natural electro positive (cationic) surface charge of asbestos fibers ^This invention relatesV a process for producing stable 10 developed in aqueous suspensions. Thus, while the prior ( dispersions of finely divided, chrysotile asbestos. More art has been successful in dispersing chrysotile atbeatoa 'v~paaicularly, the process comprises contacting an aqueous by enhancing the electrostatic charge of the mineral, it slurry of asbestos fibers with a carboxylicacid and ap has not heretofore been known how to disperse atbeatoa plying high speed shearing forces to the slurry. by preserving the natural charge which the mineral it Chrysotile asbestos generally occurs in mineral deposits 15 self is capable of generating. This method has the advan in the form of closely packed bundles of individual fibers. tage of avoiding contamination of the asbestos with metal These individual or ultimate fibers (sometimes referred ions or hydrolysis products which may cause undesirable to as fibrils) when separated are of colloid size having results in the end products. diameters of from about 200 to 800 A. and variable It is an object of this invention to produce a (table lengths of several microns. In aqueous suspension, as well SO suspension of finely divided chrysotile asbestos fibers as when dried, the individual-fibers have 8 tendency to which maintain their natural cationic or electropositive become associated into floes rather than^to remain sepa surface charge. It is another object of this invention to rated. For many commercial uses, however, such as in produce a dry purified asbestos product composed of finely ^ the manufacture of asbestos filled paper.''it is necessary divided chrysotile asbestos fibers which are easily redis that the individual asbestos fibers remain separated. persible in water. It is still another object of this invention Separation of asbestos fiber^bundKs may be accom to purify asbestos by a process which includes the step plished by various well known dry mechanical processes of dispersing asbestos fibers by means of a carboxylic add whereby the closely packed bundles of fibers are physical alone. ly forced apart. While this technique is relatively succes- ,Q One aspect of this invention consists of a process com ful in separating a substantial portion of the fibers from prising contacting an aqueous slurry containing from each other, and at the same time liberating most of the about 0.5-5% chrysotile asbestos with a sufficient amount "gangue" or non-asbestos impurities contained in physical of a water-soluble, monocarboxylic acid having up to 6 mixture with the asbestos, additional purification is re carbon atoms to maintain a pH of 3.8 to 6.3 and apply quired to produce an asbestos product which is substan- 35 ing high speed shearing forces to the sluny. It is critical tially free of impurities. Unfortunately, the dry mechani that the water which is used in making up the asbestos cal means, which - are conventionally used to open the slurry contain no more than about 100 p.p.m. of mono asbestos fiber bundles, also break up the impurities, thus valent anions and no more than about 10 p.p.m. of multi increasing the difficulty of separating the fine asbestos valent anions both of which constitute interfering anions. fibers from the finely ground impurities. 40 Deionized or distilled water meets these requirements. Several techniques have been proposed in the prior art According to the present invention, the chrysotile as to defibrillate and to chemically disperse asbestos fibers bestos to be treated need not be previously opened; how in water suspensions in order to obtain more complete ever, some amount of prior opening is desirable. Any of separation of individual fibrils from each other, as well the well known techniques for opening asbestos can be as from the impurities, than is possible by mechanical 4j employed. The asbestos can be opened either before It it means alone. Such chemical dispersion techniques are de added to the water, or after the asbestos slurry is formed. scribed, for example, in U.S. Patent Nos. 1,907,616; Preferably, the asbestos employed should be grade 5 to 2,661,287; 2,626,213 and 3,062,701. These prior art tech grade 7 according to the Quebec Asbestos Producers As niques have various drawbacks or disadvantages. The sociation Classification. Sufficient asbestos is added to processes described in 1,907,616 and 2,661.287 require 5u water to prepare an asbestos-water slurry containing from a large quantity of a soluble metal salt, such as aluminum about 0.5 to 5 weight percent chrysotile asbestos. If the chloride, to be present in the aqueous asbestos slurry, slurry contains less than 0.5 weight percent asbestos, the consequently there is a large quantity of anions, such as resulting asbestos dispersion will be too dilute for eco chloride ions present in the solution. This tends to limit nomical processing, even though technically feasible. the amount of asbestos which can be held in suspension, 53 When the slurry contains more than about 5 weight per to decrease the stability of the dispersed asbestos and to cent asbestos, the viscosity increases greatly, and the cause it to flocculate easily. The processes described in slurry becomes too difficult to handle. Preferably the 2,626,213 and in 3,062,701 employ organic surfactants slurry contains from about 0.1 to about 4.0 weight per for dispersing the asbestos fibers. The process described cent chrysotile asbestos. in 2,626,213 has limited utility in the production of dis- 60 -1 ilC B9DC3IU3 13 men comacieo wiin ViltP persed individual fibers, since mechanical agitation of carboxylic acid and mixed at high shear. The acid is pref the surfactant used to aid the fiber separation will cause erablv added to the asbestos-water slurry, but alternative!) foaming which cannot be tolerated. The process described the acid can be present in the water to which the asbestot in 3,062,701 has been designed to eliminate the foaming, is added. The amount of acid employed is governed b) but has the disadvantage that a true dispersion is not 05 several factors in the system, such as the amount of acid' formed. Only a temporary dispersion which quickly re soluble, non-chrysotile impurities in the asbestos and tlx verts to a clotted condition is formed. degree of ionization of the acid in aqueous solution. Th< In our previous application Ser. No. 305,217, filed amount of acid required is also governed by the conceit Aug. 28, 1963. now Patent No. 3,297,516 we described a ,, tration of interfering anions in the water used to prepan method by which a stable suspension of chrysotile asbestos 10 the asbestos slurry, the average fiber length of the asbestos can be prepared without encountering the difficulties of and the^ulp denflty'of^he asbestos dis----- The minimum pH at which dispersion occurred was 3.8 Impurities, improving the ease with which the dispersed and the maximum pH was 6.3. A pH below the minimum asbestos is separated from the impurities. of 3.8 does not result in satisfactory asbestos dispersions, Stable dispersions of chrysotile asbestos prepared ac while a pH in excess of 6.3 results in excessive foaming. cording to the present invention have a viscosity of from An alternative operational procedure is to apply me 6 about 1 to about 10 centipoises at 25* C. In this state, chanical energy to the slurry, containing the required a dispersion of asbestos exhibits a characteristic *|shim- amount of acid, at a solids concentration of up to approxi mer" or "pearlescent" appearance due to the reflection of mately 8 to 10% asbestos and then to dilute the slurry light from the alignment of the asbestos fibers in suspen to the range of 0.5 to 5.0% while applying an additional sion. The quality of a dispersion can be determined by but smaller amount of mechanical energy to the system. In this case, the amount of acid required will be the same 10 measuring the viscosity of the dispersion and recording the viscosity reading as a function of time. The lower the as if the dispersing had been done at the final slurry initial viscosity reading and the longer this reading re concentration. mains substantially constant, the better is the dispersion. The acids which are useful in the process of this in The viscosity relationships of an asbestos dispersion are vention are water soluble, monocarboxylic acids having 15 functions of the particular dispersing reagents employed, up to 6 carbon atoms. The acid may be saturated or un the pH of the dipersion, the kind and amount of anions saturated and substituted or unsubstituted. Illustrative use present and the concentrations and grade of asbestos ful acids include formic, acetic, propionic, butyric, valeric, employed. acrylic, crotonic, methacrylic, lactic, angelic, pyruvic and The stability of asbestos dispersions is expressed in tiglic. The first three listed are preferred. Acids contain 20 terms of "gel-time" which is defined as the time it takes ing more than 6 carbon atoms are not useful because they for a low viscosity asbestos dispersion to reach a viscosity cause excessive foaming. Inorganic acids, such as hydro which is out of the "dispersed" viscosity region and in chloric acid, nitrous acid, nitric acid, sulfuric acid, phos the "gel" viscosity region. The transition from the dis phoric acid, etc.; and polycarboxylic acids such as oxalic persed state to the gel stale is marked by a sudden and acid, malonic acid, maieric acid, tartaric acid, citric acid, 25 continuous rise in viscosity with an eventual leveling off etc., are not useful within the scope of this invention due in the region above 50 centipoises at 25* C. Having to their strong interaction with the charged surface of the reached the gel-point, the asbestos suspension loses the asbestos causing dispersions thereof to be very unstable. shimmer which is characteristic of asbestos in the dis In adding the acid to the asbestos slurry it is advan persed form, it acquires a homogeneous, static appearance. tageous to add the acid concurrently or just prior to the 30 The gel can range in viscosity to the point at which it application of mechanical energy to the systems. In so cannot be poured from a container. The amount of me doing a minimum amount of acid is consumed in leaching chanical energy which has been applied to the system the asbestos itself. Similarly, there is some advantage to during dispersion has little effect on the viscosity of the adding the acid in dilute form rather than in a concen dispersed phase. trated form in order to avoid localized high concentra 33 Asbestos dispersions prepared in accordance with the tions of acid. The dispersing process is extremely sensitive present invention are useful per se as a source of finely to the presence of soluble salts in the asbestos slurry at divided asbestos. These dispersions can be used as addi the time of dispersing. Likew'ise, the stability of the dis tives to cellulosic paper to improve its softness as well as persion, once formed, is extremely sensitive to the pres to aid in retention of inorganic fillers. ence of soluble salts. The effect of the presence of soluble 40 Another aspect of this invention involves the forma salts is to decrease the stability of an asbestos dispersion. tion of an asbestos dispersion according to the above-de In order to maintain a stable asbestos dispersion for rela scribed methods as a step in the purification of asbestos tively long periods of time, it is desirable that the asbestos containing finely divided impurities such as magnetite. slurry contain minimal amounts of monovalent anions These impurities may readily be separated from asbestos and negligible amounts of multivalent anions, such as sul 45 w'hich has been dispersed in water by gravity methods, fate ions, since such anions tend to flocculate the asbestos such as settling followed by decantation of the (table dispersion. Stability of an asbestos dispersion is measured asbestos dispersion, or by the use of conventional con in terms of the time for which the viscosity of the dis tinuous thickeners, centrifuges or hydrocyclones. persion remains at a relatively low value, in the order The resulting purified asbestos dispersion can be used of 1-10 centipoises at 25* C. 60 "as is" or the asbestos can be flocculated, filtered and Mechanical energy in the form of high speed shearing dried. Flocculated asbestos can be used in conventional forces must be applied to the asbestos-water-organic acid asbestos products requiring short fiber asbestos, such as a slurry in order to attain satisfactory defibrillation and filler in plastic products. subsequent dispersion of the asbestos fibers. The mechani Flocculation of the asbestos dispersion may be accom cal agitation can be accomplished with any device capable 55 plished by adjusting the pH of the dispersion outside of of rendering a high proportion of its energy into shearing the range of 3.8-6.3 which is the range within which the forces. Suitable laboratory equipment includes a Waring Blendor, the Wemco Attrition Mill, the Brookfield dispersion is stable. A state of flocculation exists when two phases become obvious--a clear solution phase and Counter-Rotating Mixer, the Vir-tis Homogenizer, as well a curd-like gel phase. The flocculated asbestos is far easier as other colloid mills. Ultrasonic "cleaning" equipment CO to filter than is the asbestos dispersion or gel. can also be used ror this purpose. In commercial prac Any form of chrysotile asbestos can be employed in tice, machines such as the conventional papermaker's the present invention. The preferred type, however, is disintegrators, beaters and refiners, such as the Valley short fiber materia] obtained from deposits near Coalinga, Beater, the Jordon Engine, and the Clafin Refiner can be Calif. Asbestos mined at this location is short fibered employed. Also, machines well known in the mineral proc 03 chrysolite asbestos which would be classified as grade 7 essing industry which provide both impact and attrition according to the Canadian Standards Classification. action, such as a wet hammermill, the Fitzpatrick Com In order to more fully described the present inven minution Machine, Micro-Pulverizer, or even a conven tion, the following examples are given by way of illustra tional ball mill, can be employed. It is preferable that the agitation of the asbestos-w-ater-organic acid slurry be 70 tion only and are not intended to limit the scope of the invention. limited to interfiber comminution, in order to preserve the EXAMPLE 1 ultimate fiber size distribution which is native to the as Three hundred milliliters of deionized water were placed bestos ore, and to prevent further size reduction of the in the glass container of a Waring Blendor. Six gr fibers. This will also lenJ to limit size reduction of the 75 mechanically opened chrysotile asbestos fiber wer ,3 409,499 5 to tbe water, then 3.0 milliliters of 1.0 molar acetic acid molar butyric acid aolution was added to the asbesios- solution were added to the asbestos-water mixture. The water mixture. Tbe mixture was blended at high speed blender was turned on at high speed (about 10,000 for three minutes. The resulting asbestos dispersion was r.pjn.) and allowed to run for three minutes. The result poured into a 300 milliliter tail-form beaker. It was noted ing asbestos dispersion was poured into a 300 milliliter g that the asbestos dispersion had a pearlescent shimmer. tail-form beaker. It was noted that the asbestos dispersion This dispersion had a viscosity of 1.0 centipoise at 25* had a pearlescent shimmer. This dispersion had a viscosity C. (as measured by a Brookfield Type LVF viscosimeter of 2.7 centipoises at 25* C. (as measured by a Brookfield using a No. 1 spindle at 60 r.p.m.) and a pH of 3.5. Type LVF viscosimeter using a No. 1 spindle at 60 r.p.m.) Within thirty minutes after the dispersion bad been pre- and a pH of 4.5. Within thirty minutes after the disper 10 pared, small dark particles settled out of the dispersion. sion had been prepared, small dark particles settled out What is claimed is: of the dispersion. 1. An aqueous dispersion having a pH of from 3.8 to The asbestos dispersion was decanted away from the 6.3 comprising from about 0.5 to 5.0 weight percent settled residue into a second beaker. Tbe residue remain finely divided chrysotile asbestos fibers, and as the sole ing in the first beaker, which had a gritty feel, was greenish jg dispersing and stabilizing agent, a water-soluble, mono- brown in color and contained small black specks of mag carboxylic acid containing up to 6 carbon atoms. netite. A portion of the decanted dispersion was floccu 2. The composition of claim 1 wherein the dispersion lated by the addition of a few drops of 10 weight percent has a viscosity of about 1 to 10 centipoises at 25* C. sodium sulfate solution. Tbe flocculated suspension was 3. The composition of claim 1 wherein tbe asbestos vacuum filtered to form a matted asbestos filter cake, 20 fibers in said dispersion are characterized by having an which was removed from the filter in a coherent mass and electropositive surface charge. dried. The dry material had a brightness of 75 percent 4. The composition of claim 1 wherein tbe mooocar- as compared to a standard magnesite block, using light boxylic acid is selected from the group consisting of having a wave length of 457 millimicrons. formic acid, acetic acid and propionic acid. The remainder of the decanted suspension was centri 25 5. The dried residue of the dispersion of claim 1. fuged at 1000 r.p.m. for five minutes. The supernatant 6. A process for the preparation of a stable aqueous liquid was decanted and flocculated by the addition of a dispersion of finely divided chrysotile asbestos fibers which few drops of dilute sodium sulfate solution. The floccu comprises: lated suspension was vacuum filtered to form a matted (1) contacting a slurry of chrysotile asbestos in water asbestos cake which was removed from the filter in a 50 containing no more than 100 p.p.m. of monovalent coherent mass and dried. The dry cake had a brightness anions and no more than 10 p.p.m. of multivalent of 85 percent when measured in the same manner as anions with sufficient water-soluble, monocarboxylic above. The high brightness of the asbestos indicates a acid containing up to 6 carbon atoms to cause the very high degree of purity. slurry to have a pH of from 3.8 to 6.3, and EXAMPLE 2 S5 (2) applying high speed shearing forces to said slurry. 7. The process of claim 6 wherein the carboxylic acid Three hundred milliliters of deionized water were is selected from the group consisting of formic acid, acetic placed in the glass container of a Waring Blendor. Three acid and propionic acid. grams of mechanically opened chrysotile asbestos fiber 8. The process of claim 6 wherein the aqueous slurry were added to the water, and then 1.0 milliliter 1.0 mole 40 contains from about 0.5 to 5 weight percent asbestos. lactic acid solution was added to the asbestos-water mix 9. The process of claim 6 wherein the water used to ture which was then blended at high speed for three prepare the slurry is deionized water. minutes. The resulting asbestos dispersion was poured 10. The process of claim 6 wherein the water used to into a 300 milliliter tail-form beaker. It was noted that prepare the slurry is distilled water. the asbestos dispersion bad a pearlescent shimmer. This 43 dispersion had a viscosity of 1.0 cenlipoise at 25* C. (as References Cited measured by a Brookfield Type LVF viscosimeter using a No. 1 spindle at 60 r.p.m.) and a pH of 4.5. Within thirty minutes after the dispersion had been prepared, small dark particles settled out of the dispersion. 60 EXAMPLE 3 Three hundred milliliters of deionized water were placed in the glass container of a Waring Blendor. Three 2,661,287 2,685,825 2,759.813 2,940,892 3,297,516 UNITED STATES PATENTS 12/1953 Barbaras ......................... 162--155 8/1954 Novak .. .............................. 162--3 8/1956 Feigley........................ 162--155 6/1960 Feigley..................... 162--155 X 1/1967 Naumann......................... 162--3 grams of mechanically opened chrysolite asbestos fiber 53 DONALL H. SYLVESTER, Primary Examiner. were added to the water, and then Vi milliliter of 1.0 A 35 1 G