MXPA96005210A - Synthetic mexinerite product and method for suffering - Google Patents

Abstract

An improved synthetic meixnerite having reduced levels of carbonate contamination and an X-ray diffraction pattern reminiscent of that shown in the figure is described, the meixnerite is made by combining magnesium alumina and transition alumina, preferably an alumina powder activated having a BET surface area of approximately 100 m2 / g or greater, in a substantially carbonate-free environment. A method for manufacturing this synthetic meixnerite product is also described.

Description

SYKMETIC PRODUCT DK METXNERITE AND METHOD FOR SP FAR TGACT? GJ DESCRIPTION OF THE INVENTION This invention relates to the field of the manufacture of mixed metal hydroxides or double stratified hydroxide compounds. More specifically, the invention relates to an improved synthetic meixnerite product and to a method for manufacturing the same. Meixnerite that occurs naturally exists as a secondary mineral in the cracks of serpentine rocks near Ybbs - Persenberg in Lower Austria. In its crystalline state, such meixnerite material is tabular, colorless and has a perfect basal break. The natural meixnerite is closely related to the hydrotalcite and pyroaurite in its general structure. Its infrared absorption spectrum compares favorably with those of hydrotalcite and other magnesium and aluminum double hydroxides. In some circles, meixnerite is listed even as among other hydrotalcite-like materials, or it is grouped into a wider family of "hydrotalcites." Under this latter definition, meixnerite is a member free of carbonates of the family of hydrotalcites which have only hydroxy anions. REF: 23485 Still others refer to meixnerite as a double dihydroxide stratified all hydroxyl. Meixnerite, or magnesium aluminum hydroxide hydrate, is often symbolized by the formula Mg6Al2 (OH) 18-4H20, although other representations of formula include: Mg4Al2 (OH) 14.3H20 and [Mg3Al (OH) 8] OH. 2H20. While the synthesis of meixnerite is completely new, these various manufacturing methods do not seem to be a common practice or to be commercially practical. In March 1980, G. Mascolo et al., Describes a synthesis process in Mine > ralogical Magazine, where magnesium oxide, decomposed from the basic magnesium carbonate at 650 ° C for 6 hours, is combined with alumina gel and rotated in an oven with air thermostat for one week, at 80 ° C. The resulting product is subsequently dried on silica gel. It is analyzed and contains a certain brucite compound and approximately 0.8-1.0% by weight of carbon dioxide. Six years later, I. Paush et al., Wrote about a variation in the process mentioned in the above in Clay and Clay Minerals. The same, the magnesium oxide, annealed at 1050 ° C, is combined with an alumina gel (d - Al203), MgC204 «2H20 and distilled water. This combination is heated between 100-350 ° C at a pressure of 100 MPa during various reaction times ranging from 7 to 42 days. The analysis by IR spectroscopy of the resulting product shows some contamination by carbonate, but at an intensity of less than 5% compared to the natural hydrotalcite. From a series of experiments reported by E. Dimotakis et al., In Inorganic Chemistry. vol. , 29 No. 13 (1990), synthetic meixnerite is prepared by calcining a hydrotalcite of the formula [Mg3Al (OH) 8] [CO3] 05.2H2O a 500 ° C, to form a metal oxide solution. This oxide is subsequently hydrolyzed at 25 ° C in a carbon dioxide-free environment. It is a principal object of this invention to provide an improved means for manufacturing synthetic meixnerite. It is another objective to provide a process for synthesizing meixnerite and related minerals from two or more powders. It is a further objective to make a hydrotalcite-like compound that has significantly lower carbonate levels and virtually no contamination by other anions. It is a further objective to provide a method for manufacturing synthetic meixnerite which does not depend on the use of alumina gels. It is a further objective to make an improved meixnerite product from an activated magnesium and transitional alumina which has not been completely calcined or calcined by superposition.

In a preferred base, synthetic meixnerite can be manufactured from inexpensive reagents and easily available through this process, which makes suitable the commercial scale production of meixnerite and similar materials to meixnerite. It is another object to provide an improved process for the manufacture of meixnerite which improves (in terms of yield) other known methods including those involving magnesium carbonates, magnesium hydroxides and / or aluminum hydroxides. In accordance with the foregoing objects and advantages, an improved method for manufacturing synthetic meixnerite is provided. The method comprises reacting powdered magnesium oxide with a transitional alumina with a large surface area, in a solution or suspension substantially free of carbonates. Such reaction causes a compound similar to meixnerite to be formed. The latter compound can be extracted from the solution by filtration, centrifugation, vacuum dehydration or other known separation means. In a preferred base, the transition alumina combined in this manner with activated magnesia consists essentially of an activated alumina powder having a surface area of about 100 m2 / g or greater. For some double hydroxides, powdered reagents are those that can be combined so they must first be agglomerated before being put in contact with water or steam. An improved meixnerite synthetic product manufactured by the foregoing method is also disclosed. The additional objects, features and advantages will become clearer from the following detailed description and preferred embodiments that are made with reference to the figure, which shows an X-ray diffraction pattern for a meixnerite compound manufactured by an embodiment of this invention. As used herein, the term "transition alumina" refers to alumina of a large surface area in the form of a powder or fine particulate. A preferred way to define such alumina materials utilizes the criteria of surface area measurement and ignition loss (LOI). More specifically, an alumina having a measured Brunauer-Emmett-Teller [or BET] surface area of approximately 100 m2 / g or more may be considered as having a high surface area and therefore qualifies as a transition alumina. for purposes of this invention. Aluminas having a LOI weight percentage of approximately 1.5% may also qualify as transition alumina under this definition, while typical d-Al203 does not. A particular preferred type of transition aluminas are referred to as "rehydratable aluminas".

They tend to form strong hydroxyl bonds upon contact with water and their rehydration reactions are highly exothermic. The particle sizes for such aluminas range from 0.01-200 μ, with a preferred range of about 0.1 to 10 or 20 microns. Certain activated aluminas are more suitable than others for purposes of this invention. Most are aluminas of high surface area formed by the rapid calcination of aluminas and treated at temperatures below those required for dehydration or complete calcination. Typically, such aluminas are amorphous (ie, have no microcrystalline structures), when determined by X-ray diffraction. In a more preferred base, the trivalent metal oxide powder combined with magnesia according to this invention is formed by the rapid dehydration of alumina trihydrate, usually by passing such a trihydrate through fire or hot gas for about 0.5 to several seconds. The resulting alumina derivative has a LOI value of about 4-12% by weight, and a BET surface area of about 200-300 m2 / g. A representative and preferred material is the powder line of activated aluminas sold commercially by the Aluminum Company of America (Alcoa) under its designation Series CP. Such particulate powders are available in a variety of sizes. For such powders, the number that follows the Alcoa CP designation represents the average particle size for that product; therefore, more than 50% of the particles in Alcoa CP 1 powder measure 1 micrometer or more. For the Alcoa CP-2 powder, more than 50% measure 2 μ or more, and so on for the CP-5, CP-7 and CP-100 product line from Alcoa. As used herein, magnesia or magnesium oxide refers to a product based on magnesia activated by "low cooking" at one or more temperatures between about 450 ° -900 ° C. It generally has a surface area of 10-200 m2 / g, preferably about 25-150 m2 / g and an L.O.I. which varies from 1.0 to 6.0% by weight. The percent of carbon dioxide for such material generally varies between 0.51 and 1.61%. Such criteria differentiate this preferred product from activated magnesia which has been completely calcined or completely burned. Although the latter can still produce meixnerite with longer reaction times and under more extreme reaction conditions, the percent yield of such conditions is significantly lower than that obtained from the present invention. There are average numbers for manufacturing activated magnesia products and combining them with transition aluminas according to this invention. For example, magnesium carbonate sold commercially can be heated to remove the carbon dioxide and thus form a reactive magnesia in this manner. Magnesium oxide can also be manufactured by heating magnesium hydroxides, natural or synthetic, at temperatures between 380 ° -950 ° C, or basic magnesium carbonate by heating MgCl2 with quicklime or lime. Various methods known to those skilled in the art can be used to generate magnesia powders or of various particle sizes and / or surface areas. As used herein, the term "carbonate contamination" refers to the level of carbonate (or C03 ~ 2) in the final product. Sometimes, this is established as a carbon percent which must be converted to a more representative concentration of actual carbonate contamination. Other additional divalent metal oxides, such as CaO, may be combined with transitional aluminas or other trivalent metal oxides in powder, according to the methods mentioned above. One way to summarize this mechanism is by the following chemical reaction: 6MgO + Al203 »XH20 + 12H20 -Mg6Al2 (OH) 16 (OH) 2» (3 + x) H20 in which x varies from about 0.1 to about 1.0. It is preferred that the pH be maintained at a level of 11 or higher in order to improve the total solubility of the transition alumina reagents. Additional temperature limitations with respect to the contact water solution have also been shown to be beneficial in terms of overall performance. It is preferred that this reaction be carried out at one or more temperatures between about 80 and 180 ° C. At such temperatures, yields that exceed about 85 to 90% are usually observed. Most preferred reaction temperatures are generally between about 95-150 ° C. There are several end uses for the products manufactured by the method of this invention. Most notably, such compounds can be converted to hydrotalcite or a hydrotalcite-like material by contact with carbonate or another anionic substitute.

EXAMPLES Each of the following examples is carried out at two temperatures: atmospheric boiling (or 98 ° C) and 150 ° C. Considerable conversions occur after 2 hours at atmospheric boiling. But an even greater conversion is observed after 22.8 hours (based on X-ray diffraction patterns). A double stratified magnesium and aluminum crystallized hydroxide is produced by heating a slurry of magnesium oxide and alumina at 150 ° C for 2 hours or more.

EXAMPLE 1 - Use of Activated Alumina and Oxide s Magnesium Magnesium oxide is prepared by heating hydromagnesite sold by Fisher Scientific and having the formula Mg5 (C03) 4 (OH) 2 »4H20, for 2 hours at about 475 ° C. to. Reaction to atmospheric boiling: About 52.5 grams of this MgO are charged to a reactor, with 34.2 grams of activated alumina CP-2 Alcoa (which has an average particle size of 2 micrometers). The contents of this reactor are constantly stirred and heated for 4 hours at 60 ° C. The reactor temperature is subsequently raised to 98 ° C and maintained at this temperature for an additional 18.5 hours.

A sample of the suspension, taken at 2 hours after the reaction mixture reached 98 ° C, is subsequently filtered and the solids are dried at 105 ° C. X-ray diffraction analysis shows that the solids thus produced have hydroxide present. The suspension of the reaction mixture is stirred and heated for a further 16 hours before cooling and filtering. The filter cake solid was mainly meixnerite, with some residual magnesium hydroxide. b. Reaction at 150 ° C: Another suspension of the same composition as above is constantly stirred and heated to 60 ° C, then kept at that temperature for 4 hours. Subsequently the temperature increases to 150 ° C and is maintained at that temperature for another 18.8 hours. A sample of the suspension taken at 2 hours after the reaction mixture reached 150 ° C contains meixnerite and a certain amount of Mg (OH) 2. Two additional samples are taken from the solids as the reaction suspension is cooled, and filtered, which shows only the formation of material similar to meixnerite.

EXAMPLE 2 - Use of M O Pele ized and Activated Alumina Approximately 52.5 g of magnesium oxide and 34.2 of activated alumina are mixed in a Turbula powder mixer for 2 hours. The subsequently mixed powders are formed into granules by using the hydraulic press and a pressure of approximately 2268 kg (5,000 pounds) of pressure. The resulting granules have a resulting diameter of approximately 10.2 mm (0.40 inches) and require approximately 0.50 grams of mixed powder to be formed. to. Reaction to atmospheric boiling: Ten granules, formed as described above, are placed in a beaker under a layer of deionized water. The system is brought to atmospheric boiling and kept under these conditions for about 2 hours. The only agitation that occurs is due to turbulence due to boiling water. A granule was separated into three pieces, and another in two. The rest remained complete during several fractures perpendicular to the direction of pressure. According to X-ray diffraction analysis, the granules include meixnerite-like compounds, a lower amount of Mg (0H) 2, and trace amounts of MgO. b. Reaction in liquid water at 150 ° C: Ten more granules of the above were placed in a Parr pressure reactor with a little deionized water. Subsequently the reactor was closed, heated to about 150 ° C and maintained at this temperature for about 2 hours. After the reactor is cooled, the granules are extracted and dried overnight at 110 ° C in a vacuum oven. By X-ray diffraction analysis, the granules contained a compound similar to meixnerite and smaller amounts of boehmite.

EXAMPLE 3 - Use of Magnesite and Activated Alumina A sample of ore containing magnesite, dolomite and quartz is milled to an amount smaller than 325 mesh (44 micrometers) and calcined for 2 hours at 700 ° C, resulting in a total weight loss of 46.5% . Analysis of this material shows a composition of approximately 16.9% by weight of magnesium, approximately 5.66% by weight of calcium, approximately 1.75% by weight of silicone and approximately 0.4% by weight of iron (Mg, Ca, and Si are measured by atomic absorption, and iron by qualitative spectroscopy). It is found that the carbon dioxide content is 46.2% by LECO analysis. The reactor charge consists of 750 ml of deionized water, 34.2 grams of Alcoa CP-2 alumina and 61.8 grams of the last calcined magnetite. The resulting suspension is placed in a Parr autoclave reactor and stirred constantly while heating for 4 hours at 60 ° C. to. At atmospheric boiling After heating to atmospheric boiling for 2 hours, a suspension sample is withdrawn. Subsequently, the end content is filtered, dried at 110 ° C overnight and samples taken for analysis. According to the X-ray diffraction, the solids consist of materials similar to meixnerite and tricalcium aluminate with traces of quartz. b. At 150 ° C: The reaction suspension is heated to 150 ° C and a suspension sample is extracted after 2 hours. The content of the reactor is subsequently filtered and at the end of the process a sample of the filter cake is taken for analysis. Both samples are dried at 110 ° C overnight. Each solid consists of a main quantity of maixnerite main material, tricalcium aluminate, a trace amount of quartz and traces of boehmite according to the analysis by X-ray diffraction. For comparative purposes, several samples of meixnerites are prepared by using an initial material of A1 (0H) 3 in combination with magnesium oxide described in Example 1 above. These samples also do not work like samples prepared with transition alumina using a direct comparative chromate uptake test (Cr042 ~) (to approximate the relative amounts of meixnerite-like materials present in the resulting products).

TABLE Source of Chrome Aluminum Load Time Formation (%) [vs. standard] Sample (hours) alumina 18.5 11.64 [6.82] CP-2 B Al (OH) 3 21.75 7.90 [8.52] C Al (OH) 3 22.17 7.45 [8.52] Having described the presently preferred embodiments, it should be understood that the invention is constituted within the scope of the appended claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (16)

1. A synthetic meixnerite product characterized in that it is produced by combining magnesium oxide and a transition alumina in an aqueous suspension substantially free of carbonate, the product has an X-ray diffraction pattern similar to that shown in Figure 1.

2. The meixnerite product according to claim 1, characterized in that the transition alumina consists essentially of a rehydratable alumina powder.

3. An improved synthetic meixnerite, characterized in that it has a carbonate contamination level of approximately 1.0% by weight or less, when expressed as inorganic carbon.

4. The synthetic meixnerite according to claim 3, characterized in that it has a contamination level of inorganic carbon of approximately 0.1-0.2% by weight.

5. The synthetic meixnerite according to claim 3, characterized in that it has an X-ray diffraction pattern that resembles that shown in figure 1.

6. The synthetic meixnerite according to claim 3, characterized in that it is manufactured by combining magnesium oxide and transition alumina in an aqueous suspension substantially free of carbonate.

7. The synthetic meixnerite according to claim 6, characterized in that the transition alumina consists essentially of an activated alumina having a BET surface area of about 100 m2 / g or greater.

8. A method for manufacturing a double layered hydroxide compound, characterized in that it comprises: (a) reacting at least one divalent metal oxide and a trivalent metal oxide powder in a solution substantially free of carbonate, to form a hydroxide compound double, stratified; and (b) separating the double stratified hydroxide compound from the solution.

9. The method according to claim 8, characterized in that the divalent metal oxide is selected from the group consisting of: magnesium oxide, calcium oxide and mixtures thereof.

10. The method according to claim 9, characterized in that the divalent metal oxide consists essentially of magnesium oxide powder.

11. The method according to claim 8, characterized in that the trivalent metal oxide powder is a transition alumina.

12. The method according to claim 11, characterized in that the transition alumina consists essentially of a rehydratable alumina.

13. A method for manufacturing synthetic meixnerite, characterized in that it comprises: (a) reacting powdered magnesium oxide with a transitional alumina of high surface area, in a solution substantially free of carbonate to form a compound similar to meixnerite; and (b) separating the meixnerite-like compound from the solution.

14. The method according to claim 13, characterized in that the transition alumina consists essentially of an activated alumina powder having a BET surface area of about 100 m2 / g or greater.

15. The method according to claim 13, characterized in that step (a) includes: (i) combining the magnesium oxide and the transition alumina in an agglomerate; and (ii) exposing the agglomerate to liquid water heated to one or more temperatures between about 80-180 ° C (176-356 ° F).

16. The method according to claim 15, characterized in that the magnesium oxide and the combined transition alumina in step (i) are heated to one or more temperatures between about 50-70 ° C (122-158 ° F). RESJJMEN DE LA JUVEHCIÓ An improved synthetic meixnerite having reduced levels of carbonate contamination and an X-ray diffraction pattern reminiscent of that shown in the figure is described, meixnerite is manufactured by combining magnesium oxide and transition alumina, preferably a powder of activated alumina having a BET surface area of about 100 m2 / g or greater, in a substantially carbonate-free environment. A method for manufacturing this synthetic meixnerite product is also described.