Document b86Q9XD3Xbx7ynOnddbp50Xk

FILE NAME: Dow Chemical (DOW) DATE: 1980 Nov 18 DOC#: DOW004 DOCUMENT DESCRIPTION: US Patent - Asbestos Treatment [Fwd: FW: dow asbestos research program] Images ( 363 of 465 ) United States Patent Pezzoli 4,234,377 November 18,1980 Asbestos treatment Abstract A method of treating asbestos comprising depositing on at least a portion o f the asbestos a material consisting essentially of at least one metal ferrocyanide. Inventors: Pezzoli; Paul A. (Midland, MI) Assignee: The Dow Chemical Company (Midland, MI) Appi. No.: 737888 Filed: November 2,1976 Current U.S. Class: Intern'1 Class: Field of Search: 1907616 2096538 162/3; 424/641; 424/646; 424/648; 424/650; 424/652; 424/654; 427/215; 427/343; 428/378; 428/443 C03B 037/00 162/3,153,181 A 427/215,343 428/378,443 424/131,144,132,147,145,2 References Cited [Referenced By I May., 1933 Oct., 1937 U.S. Patent Documents Tucker Durrant 162/153. 427/343. Other References McNab, G. et al., Nature 214, 522-523 (1967). Schnitzer et a l.,"Asbestos Hemolysis", Environ. Res. 3, 1-13 (1970). pp. 1-13. Primary Examiner: Smith; William F. Attorney, Agent or Firm: Kuszaj; James M. Claims 18 of 29 4/10/2003 10:33 PM [Fwd: FW: dow asbestos research program] What is claimed is: 1. A method o f treating asbestos comprising depositing on at least a portion o f the asbestos a sufficient amount of a material consisting essentially of at least one metal ferrocyanide to reduce the hemolytic activity o f the asbestos to at least about 9 percent hemolysis. 2. The method o f claim 1 wherein the asbestos is chrysotile. 3. The method of claim 1 wherein the metal is selected from the group consisting o f cadmium, iron (III), nickel, tin (II), and titanium (IV). 4. The method o f claim 1 wherein the metal is titanium (IV). 5. The method o f claim 1 wherein the metal is tin (II). 6. The method o f claim 1 wherein the depositing step comprises: (a) contacting the asbestos with a solution of an ionizable salt of at least a first metal to deposit at least a portion of the ionizable salt on the asbestos; (b) contacting the asbestos with a solution solution of a ferrocyanide salt of a second metal to form a ferrocyanide o f at least the first metal on at least a portion of the surface of the asbestos. 7. The method of claim 6 wherein the first metal is selected from the group consisting o f cadmium, iron (III), nickel, tin (II), and titanium (IV). 8. The method o f claim 6 wherein the second metal is selected from the group consisting of sodium and potassium. 9. The method o f claim 6 wherein the solution o f the ionizable salt has a salt concentration o f from about 1 percent by weight to about a concentration corresponding to a saturated solution o f the salt. 10. The method of claim 6 wherein the solution of the ionizable salt has a salt concentration o f from about 5 percent by weight to about 10 percent by weight o f the salt. 11. The method of claim 6 wherein the ionizable salt includes at least one member selected from the group consisting of a chloride, a sulfate, and a nitrate. 12. The method of claim 6 wherein the ionizable salt is a chloride. 13. The method of claim 6 wherein the solution o f the ferrocyanide salt has a concentration o f from about 1 percent by weight to about the concentration corresponding to a saturated solution o f the ferrocyanide o f the second metal. 14. The method of claim 6 wherein the solution of the ferrocyanide salt has a concentration of from about 1 percent by weight to about 10 percent by weight o f the ferrocyanide o f the second metal. 15. The method of claim 6 wherein the solution of the ionizable salt is an aqueous solution. 19 of 29 4/10/2003 10:34 PM [Fwd: FW: dow asbestos research program] 16. The method of claim 6 wherein the solution o f the ferrocyanide salt is an aqueous solution. 17. The method o f claim 1 wherein the depositing step comprises spraying at least a portion of the asbestos with at least one metal ferrocyanide suspended in a liquid medium. 18. The method of claim 17 wherein the medium is water. 19. A method for treating asbestos comprising: (a) slurrying the asbestos with a sufficient amount of an aqueous solution of an ionizable salt of at least a first metal selected from the group consisting o f cadmium, iron (III), nickel, tin (II), and titanium (IV), to deposit at least a portion o f the ionizable salt o f the first metal on at least a portion of the asbestos; (b) slurrying the asbestos from step (a) with an aqueous solution of a ferrocyanide of a second metal selected from the group consisting of sodium and potassium to form a sufficient amount of a ferrocyanide of the first metal on at least a portion of the asbestos wherein the ionizable salt was deposited to reduce the hemolytic activity of the asbestos to at least about 9 percent hemolysis. 20. The method of claim 19 including agitating the asbestos and the aqueous solution of the ionizable salt o f the first metal for a sufficient time to allow the ionizable salt to contact at least a portion o f the asbestos. 21. A fibrous asbestos material consisting essentially of asbestos fibers and at least one metal ferrocyanide deposited on at least a portion of the asbestos fibers in a sufficient amount to reduce the hemolytic activity of the asbestos fibers to at least about 9 percent hemolysis. 22. The material of claim 21 wherein the metal is selected from the group consisting o f cadmium, iron (III), nickel, tin (II), and titanium (IV). 23. The material o f claim 21 wherein the metal is titanium (IV). 24. The material of claim 21 wherein the metal is tin (II). 25. The material of claim 21 wherein the metal ferrocyanide is present in an amount o f from about 0.05 to about 5.0 percent by weight, based on the weight o f the asbestos. 26. The material of claim 21 wherein the asbestos has a fiber length o f at least about 0.5 microns. Description BACKGROUND OF THE INVENTION This invention relates to asbestos. More in particular, the present invention relates to a method of treating asbestos. "Asbestos" is a general term applied to a group of naturally occurring fibrous silicate minerals that are commercially important because of their fibrous characteristics. Four principal types o f asbestos 20 o f 29 4/10/2003 10:35 PM [Fwd: FW: dow asbestos research program] minerals generally enter world commerce. These are chrysotile, crocidolite, amosite and anthophyllite. O f these, chrysotile is perhaps the most important, accounting for about 95 percent o f the world's asbestos production. Chemically, chrysotile asbestos is the fibrous form o f the mineral serpentine, a hydrated magnesium silicate having the general formula Mg.sub.3 Si.sub.2 O.sub.3 (OH).sub.4. Structurally the chrysotile asbestos is believed to consist o f rolled up sheets formed from two layers. The first layer is a continuous network o f silica (SiO.sub.2) tetrahedra. This layer is interlocked through common oxygen atoms with a second layer o f magnesium hydroxide (Mg(OH.sub.2)) octahedra. The walls o f the asbestos fibers are composed o f a number of such individual sheets contorted into scrolls with the magnesium hydroxide layer on the outside. Consequently, one o f the dominant chemical features o f chrysotile asbestos is its alkaline surface characteristics. The surface modification of asbestine minerals, such as chrysotile, has attracted a good deal of attention from research workers during recent years. A large number of surface treatment methods have been proposed and evaluated for the purpose o f modifying certain predetermined properties of the asbestos fibers. These procedures include: coating the surface o f asbestos fibers with a phosphate, polyphosphate, or corresponding acid to improve the filtration characteristic o f the fibers (U.S. Pat. Nos. 3,535,150, 3,957,571); treating asbestos fibers with magnesium carbonate or an oxide o f a polyvalent metal to enhance the tensile strength o f the fibers (U.S. Pat. Nos. 1,982,542; 2,451,805; 2,460,734); coating an asbestos fabric with an insoluble inorganic oxide to render the fabric flame resistant and water repellent (U.S. Pat. No. 2,406,779); mixing a detergent organic surface-active agent with fibrous asbestos agglomerates to disperse the asbestos fibers (U.S. Pat. No. 2,626,213); and distributing small amounts of polymeric particles or a water-soluble macromolecular organic substance throughout an asbestos product to reduce dust emitted by the asbestos during handling and use (U.S. Pat. Nos. 3,660,148; 3,967,043). An area of concern to the producers and users of asbestine material has been the potential health problems allegedly associated with asbestos exposure. It has been reported by the National Safety Council that persons who inhale large amounts o f asbestos dust can develop disabling or fatal pulmonary and pleural fibrosis (asbestosis) and several types o f malignancy of the respiratory tract ("Asbestos", National Safety Council Newsletter, R & D Section, June 1974). There is also speculation that asbestos may cause various forms of carcinogenesis, particularly carcinoma of the lung, pleura and peritoneum (R. F. Holt, "Asbestosis", Nature, 253, 85 (1975)). Since the pathogenicity o f asbestos minerals is apparently unmatched by any other silicate, there has been much interest in developing a method of passivating asbestos to reduce any potential fibrogenic and carcinogenic effects on those exposed to it without adequate precaution. Existing methodology for studying the in vivo fibrogenic effects of asbestos involves direct inhalation or intratracheal administration of asbestos fibers to animals. Subsequently, the experimentally treated animals are examined, usually months later, for pathological and histochemical evidence of fibrosis. Since the incubation period for asbestos-induced diseases is reported to be unusually long, experiments of this type are complicated, expensive and time consuming. However, recent work done by R. R. Hefner, Jr. and P. J. Gehring (American Industrial Hygiene Association Journal, 36, 734-740 (1975)) shows that a relationship exists between the in vivo fibrogenicity o f asbestos and its in vitro hemolytic activity. Hemolytic activity, or hemolysis, is a measure of induced blood cell rupture when fibers are agitated with a suspension o f blood erythrocytes. Numerous other authors have also made similar in vitro evaluations of a number of particulates. 21 of 29 4/10/2003 10:36 PM irwu: r w: dow asbestos research program] The in vitro hemolytic model provides a rapid, relatively inexpensive test which reliably assesses the fibrogenic potential o f asbestos. Consequently, the hemolytic model has been employed in the present invention to test the effectiveness o f certain asbestos treating procedures found to be potentially useful in alleviating some of the health problems reportedly associated with asbestos fibers. Various materials have been examined which interact with the surface o f asbestos fibers and reduce its hemolytic activity. Such material includes disodium ethylenediamine tetraacetic acid (EDTA), simple phosphates, disodium versenate, polyvinylpyridine N-oxide and aluminum (G. Macnab and J. S. Harington, Nature 214, 522-3 (1967), and certain acidic polymers (R. J. Schnitzer and F. L. Pundsack, Environmental Research 3, 1-14 (1970). In addition, West German Pat. No. 1,642,022 discloses that asbestos coated with polyvinylpyridine N-oxide minimizes the risk of asbestosis. Some o f these known materials, such as EDTA, are solubilized in body fluids and do not reduce the long term hemolytic activity o f the asbestos. There is therefore a need to determine materials which will adhere to the asbestos and reduce its hemolytic activity. Such passivating materials should not adversely affect the useful commercial properties of the asbestos. SUMMARY OF THE INVENTION The present invention is a method for treating asbestos comprising depositing on at least a portion o f the asbestos a material consisting essentially of at least one metal ferrocyanide. Using the hemolysis test, as an in vitro screening test to assess the effectiveness o f the metal ferrocyanide treatment, it has been surprisingly found that asbestos fibers with at least one metal ferrocyanide deposited thereon have reduced hemolytic activity in comparison with untreated asbestos fibers. For the purposes of this specification, the oxidation state (valence) o f metals which commonly exhibit more than one valence is indicated by a Roman numeral in parentheses following the metal to which it refers. DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the present invention, asbestos is treated to deposit at least one metal ferrocyanide on at least a portion o f the asbestos. The method o f treating asbestos includes depositing an ionizable salt of at least one suitable first metal on at least a portion o f the asbestos. In this context an ionizable salt is defined as a salt which dissociates spontaneously into ions o f opposite electrical signs when dissolved in a suitable polar solvent, such as water, methanol, mixtures thereof and the like. Examples o f suitable first metal cations are barium, cadmium, cobalt, iron (II), iron (III), lead, manganese, nickel, potassium, silver, tin (II), tin (IV), titanium (III) titanium (IV), zinc and mixtures thereof. However other first metal cations which are capable of forming a ferrocyanide salt can also be used. The ionizable salt can be deposited on the asbestos by contacting asbestos fibers with a solution o f the ionizable salt o f the first metal, preferably an aqueous solution o f the ionizable salt of the first metal, to deposit at least a portion o f the ionizable salt on the asbestos. A number o f suitable techniques are known for depositing compounds on asbestos. These techniques include spraying the compound onto the asbestos fibers or soaking asbestos fibers in a solution of the coating compound. In the present process, a 22 of 29 4/10/2003 10:37 PM [Fwd: FW: dow asbestos research program] preferred method o f contacting the asbestos with the ionizable salt is by slurrying the asbestos in the solution o f the ionizable salt for a sufficient time to allow the surface o f the asbestos fibers to be contacted and wetted by the solution. The ionizable salt employed in the present process is preferably a chloride, a sulfate, a nitrate, or a mixture thereof o f the above first metals. More preferably, the ionizable salt is a water soluble chloride salt o f the first metal. However, any salt that will ionize in solution to produce a cation of one o f the first metals can be used in the present process. Furthermore, the ionizable salt can contain more than one type o f cation and one type of anion. For example, a mixture o f chloride salts of two first metals, or a mixture o f the chloride and sulfate salts o f the same first metal is suitable. The concentration o f the solution o f the ionizable salt employed in the present process is from about 1 percent by weight o f the salt to about the concentration corresponding to a saturated solution o f the particular first metal salt. For example, when nickel chloride hexahydrate is the ionizable salt, the concentration o f the salt in the aqueous solution at 20.degree. C. and 1 atmosphere pressure is from about 1 to about 72 percent by weight. Preferably, the concentration o f the solution o f the ionizable salt is from about 5 to about 10 percent by weight. Advantageously, the mixture of asbestos and the salt solution can be agitated at room temperature for a sufficient time to allow the solution to contact at least a portion, and preferably substantially all o f the asbestos fiber surfaces. The agitation o f the mixture is accomplished by use o f agitation means well-known in the art. These include mechanical, air, hydraulic or magnetic means for inducing agitation. Following agitation, the asbestos fibers in solution can be separated from the filtrate by any suitable solid-liquid separation technique such as vacuum filtration. The ionizable salt-treated asbestos fibers are then contacted with a solution, preferably an aqueous solution, of a ferrocyanide salt of a second metal. Examples o f suitable second metal cations are sodium, potassium or a mixture thereof. Various suitable techniques for contacting the salt-treated asbestos fibers with the ferrocyanide solution can be used as indicated previously. However, it is preferred to slurry the salt-treated asbestos fibers with the ferrocyanide solution. The salt-treated asbestos fibers are maintained in contact with the ferrocyanide solution for a sufficient time to allow at least a portion, and preferably substantially all the ferrocyanide solution to contact the salt-treated asbestos and react with the ionizable salt thereon to form a metal ferrocyanide compound wherein the cation of said compound is originally the cation of the first metal associated with the ionizable salt. The ferrocyanide solution has a concentration o f from about 1 percent by weight to about the concentration corresponding to a saturated solution of the ferrocyanide of the second metal. For example, when sodium ferrocyanide is employed, the concentration o f the salt in an aqueous solution at 20.degree. C., 1 atmosphere pressure, is from about 1 to about 32 percent by weight o f the ferrocyanide o f the second metal. Preferably, the ferrocyanide solution has a concentration of from about 1 to about 10 percent by weight o f the second metal ferrocyanide. The osAestos-ferrocyanide solution slurry is preferably agitated at about room temperature for a sufficient time to insure contact between the asbestos fibers and the solution. Following agitation, the asbestos fibers in solution are separated from the filtrate by any suitable solid-liquid separation technique, such as vacuum filtration. Preferably the filtered asbestos fibers are subsequently washed with a suitable solvent, such as deionized water, to remove any non-adherent 23 of 29 4/10/2003 10:38 PM [Fwd: FW: dow asbestos research program] ferrocyanide compound. The asbestos fibers can then be dried by any suitable techniques, such as air drying, heating, vacuum and the like. The present method o f treating asbestos has been described in terms o f initially contacting asbestos fibers with a solution of an ionizable salt of at least one first metal and subsequently contacting the thus treated asbestos with a solution o f a ferrocyanide salt o f at least one second metal to form a coating of a ferrocyanide o f at least one first metal. However, the present invention is not limited to this sequence. For example, if desired, the asbestos can initially be contacted with a solution, preferably an aqueous solution, o f ferrocyanide o f at least one second metal, for example sodium or potassium ferrocyanide. If it is desirable to have another metal ferrocyanide other than the second metal salts deposited on the asbestos, the asbestos can be subsequently contacted with a solution of an ionizable salt of at least one first metal, to deposit on the asbestos a ferrocyanide of at least one of the first metals. Suitable first metals are those that have been described previously. Alternatively, the metal ferrocyanide can be deposited on the asbestos by directly contacting the surface of the asbestos fibers with at least one first metal ferrocyanide suspended in a liquid medium, such as water. One suitable deposition technique involved suspending a particulate first metal ferrocyanide in water, spraying the suspension onto the surface o f the asbestos fibers, and removing the water by drying. First metal ferrocyanides which can be suitably applied in this manner include those that are insoluble in the suspending medium. The asbestos treated by the present method is characterized as being a fibrous asbestos material consisting essentially o f asbestos fibers with a coating of at least one first or second metal ferrocyanide deposited on at least a portion of the asbestos fibers. Suitable first metals include any metal cation capable o f forming a ferrocyanide salt. Preferably the first metal cation is barium, cadmium, cobalt, iron (II), iron (III), lead, manganese, nickel, potassium, silver, tin (II), tin (IV), titanium (III), titanium (IV), zinc and mixtures thereof. More preferably, the first metal cation is either titanium (IV), tin (II) or a mixture thereof. Suitable second metal cations are potassium, sodium, or mixtures thereof. The asbestos treated by the present invention can include chrysotile, crocidolite, amosite, or anthophyllite asbestos. Chrysotile, being the most abundant type o f asbestos, is the preferred material for treatment by the present process. The physical form o f asbestos treated includes fibrous mineral bundles o f fine crystalline fibers, or individual fibers. Preferably the asbestos is in the form o f bundles of crystalline fibers. Generally, the individual fibers o f the bundle have a fiber length o f at least about 0.5 micron, and a diameter o f at least about 0.01 micron. However, other fiber lengths and diameters can be employed. The exact mechanism by which the deposited metal ferrocyanide forms an adherent coating on the asbestos is not completely understood. It is believed that the coating is due to the alkaline outer surface of the asbestos fiber. The individual fibers are composed of a network o f magnesium hydroxide tetrahedra. The outermost portion o f the tetrahedra contains hydroxyl groups. There is some evidence that hydroxyl hydrogens are being displaced by the metal cation, to form a bond between the metal ferrocyanide and the asbestos. Since each asbestos fiber is composed o f a number o f individual sheets having outer hydroxyl groups, and because these sheets are contorted into concentric scrolls, the deposition of the metal ferrocyanide may occur on more than just the outermost exposed surface o f the asbestos fiber. Some o f the metal ferrocyanide can impregnate the interior scrolls o f the fiber and deposit on the interior hydroxyl surface present. The metal ferrocyanide that is deposited on the asbestos is preferably present in an amount o f from about 24 of 29 4/10/2003 10:39 PM