Patented Mar. 3, 1942 2,275,032 UNITED STATES PATENT office 2,275,032 MANUFACTURE of BASIC MAGNESIUM CAR BONATE AND EAT NSUATION MATE RAL COMPRS ING SAME Harold W. Greider and Roger A. MacArthur, Wyoming, Ohio, assignors to The Philip Carey Manufacturing Company, a corporation of Ohio No Drawing. Application August 16, 1938, Seria No. 225,139 w 8 Claims. (C. 25-156) This invention relates to the manufacture of narily obtained from the dolomite rock during basic magnesium carbonate and heat insulation burning and from the fuel used for the burning. material comprising basic magnesium carbonate. The Solid matter is then Separated from the mix It relates especially to the production of basic ture of insoluble calcium carbonate and soluble magnesium carbonate in a finely-divided, light magnesium bicarbonate by filtration or settling, and bulky state that is particularly adapted for or by combination of these methods of separa employment in the manufacture of heat insula tion. The clarified liquor consists essentially of tion materials. about a 3 per cent. by weight solution of mag Basic magnesium carbonate is widely used in nesium bicarbonate in water. In practice, it is the manufacture of heat insulation materials. 0 not feasible to make Solutions containing more It is believed to have the chemical formula of the bicarbonate, as the carbon dioxide pres 3MgCO3.MgO2H2.3H2O. A heat insulation mate sure and time which are both necessary for the rial that is very widely used at the present time production of higher concentrations of magne and that contains basic magnesium carbonate is sium bicarbonate, are not economically available. the so-called "85% magnesia' insulation which The solution of magnesium bicarbonate is then consists essentially of 85% of basic magnesium heated rapidly, or “boiled,' at temperatures Carbonate and 15% of asbestos fiber. In such usually above 200° F., whereupon insoluble basic insulations, the basic magnesium carbonate, be magnesium carbonate is precipitated. The basic cause of its capacity for existing in the form of carbonate is then in condition for incorporation extremely finely divided particles which form a 20 into heat insulating materials. bulky and extended mass, affords high resistance For example, the suspension from the "boiling' to the transfer of heat. In addition to its re operation, consisting essentially of about a 2 per Sistance to heat transfer, the basic magnesium cent. by weight suspension of basic magnesium carbonate particles must possess sufficient co carbonate in water, may be settled and filtered hesion or binding power to allow the formation 25 until the suspension is a thick paste. The of blocks and slabs therefrom which have sufi amount of solid matter therein may be deter cient strength for handling and use. While 85% mined, for example, by titration with acid, and magnesia is mentioned, there are many other sufficient asbestos fiber or other ingredients may types of insulation in which basic magnesium be added to produce the mixture desired, and carbonate may be used. Thus it may be con 30 the paste may then be formed by filtering under bined with a number of known heat insulation pressure of conveniently 10 to 50 pounds per materials such as calcium carbonate, diatoma square inch in filter molds of desired shape, the ceous earth, colloidal clays, mineral fibers of vari excess water being expelled from the filter molds. Olus types, and the like. . : The compacted and molded mixture may then be By far the greater proportion of basic mag 35 removed from the mold and dried and trimmed nesium carbonate manufactured is obtained from to the shape desired. dolomite by the well-known Pattinson process. In In the practice of this process, there are Sev the practice of this method, dolomite rock, which eral disadvantages due to the large amount of is essentially an equimolecular mixture of cal water necessary for solution of the magnesium cium carbonate and magnesium carbonate of the 40 carbonate as bicarbonate. Large tanks and filter approximate chemical formula: MgCO3.CaCO3, presses are necessary to prepare the bicarbonate is first calcined, or "burned,' in a kiln to con solution. Also, a great amount of heat is neces vert the carbonate rock into a mixture of calcium sary to “boil' the dilute solution of magnesium Oxide and magnesium oxide, essentially of the bicarbonate in precipitating. the basic magnesi chemical formula, MgO.CaO and called dolomitic 45 lum carbonate. Large settling and filtering tanks lime. This lime is then hydrated with water to are also essential to bring the basic carbonate to form a dilute slurry of calcium and magnesium the proper consistency for subsequent use. hydroxides, both substantially insoluble in water. Basic magnesium carbonate may also be made This slurry is then treated by passing through by heating normal magnesium carbonate. Nor it carbon-dioxide-containing gas until all of the SO mal magnesium carbonate may be prepared by calcium hydroxide has been converted to in several methods known to the art, and further soluble calcium carbonate and substantially all more, may be prepared in high concentration in of the magnesia is in the form of Soluble mag water suspension. For example, normal magne nesium bicarbonate of the chemical formula: sium carbonate may be readily prepared by in Mg(HCO3)2. The carbon dioxide used is Ordi 35 troducing carbon dioxide into a suspension Of 2 2,275,032 magnesium hydroxide at a temperature be per square inch for about one and one-half hours. tween about 80° F. and about 158° F. The mag At this time the suspension consisted of normal nesium carbonate thus produced has the formula magnesium carbonate crystals and a small MgCO3.3H2O. While there are believed to be amount of magnesium bicarbonate in solution. other normal magnesium carbonates containing The suspension was then mixed with five times other amounts of combined water, it is to be, its volume (i. e., with 150 gallons) of magnesium understood that reference herein to normal mag bicarbonate liquor containing 2.9 per cent. of nesium carbonate includes any normal hydrated magnesium bicarbonate by weight, obtained from magnesium carbonate analogous in the respects dolomite as described hereinabove with reference herein mentioned to the normal magnesium car O to the Pattinson process. The mixture was then bonate produced by treating magnesium hydrox boiled at 210 F. by being passed through a ide with carbon dioxide in the manner above boiler adapted to heat the mixture rapidly and mentioned. Basic magnesium carbonate of suf to operate in a continuous manner. The result ficiently low density and of satisfactory fireness ing slurry was thickened by de-watering and was of particle size for manufacture of heat insulst 5 mixed with an amount of asbestos fiber suitable ing materials cannot, however, be made by heat for the manufacture of 85% magnesia insulation ing suspensions of normal magnesium carbonate and W8S molded at about 30 lb, per square inch in water. Further, the basic magnesium car in a filter mold to form a block which was sub bonate made by "boiling' suspensions of normal Sequently removed from the mold and dried. magnesium carbonate in Water has very poor 20 The dried block had a density of 15.7 lb. per bonding power and heat insulating blocks or cubic foot and possessed properties, including shapes made therefrom have insufficient strength Such properties as strength, toughness and high as well as unsatisfactorily high density. heat insulating efficiency, which made it highly We have now made the unexpected discovery desirable for commercial use as heat, insulation. that basic carbonate of magnesia, of low density 25 The advantages to be obtained by the process and of fineness of particle size suitable for use outlined are immediately obvious. The basic in heat insulation material may be obtained by magnesium carbonate obtained from the calcined heating normal magnesium carbonate in water magnesite in the above example was about 18% in the presence of basic magnesium carbonate pounds. The basic carbonate obtained from the produced by heating a magnesium bicarbonate 30 bicarbonate solution was about 22% pounds. solution. In the preferred application of this The Water heated to boiling to produce a total discovery, it has been found that the rate of of 41 pounds of basic carbonate was 180 gallons. production of a plant designed for utilization of If all the basic. carbonate had been produced dolonite for the manufacture of basic carbonate from bicarbonate solution, it would have been of magnesia...may be increased as much as 100 35 Inecessary to heat 23 gallons of water to boiling. per cent. Or more with Virtually no additional The saving in heat, which is a costly factor in equipment or capital cost and with resulting this process, and in plant capacity per pound economy immediately apparent to those ac of basic carbonate produced was about 34 per quainted with the art. cent or conversely stated, the production capacity In one preferred application of this invention, 0. and heat efficiency of a plant of stated size were normal magnesium carbonate, produced by treat increased about 50%. Also, the carbon dioxide ing magnesium. Oxide or hydroxide with carbon necessary to transform the magnesium oxide to dioxide gas, is mixed with magnesium bicarbonate formal carbonate is available from the excess Solution and the mixture is rapidly heated to gas produced from the burning of the dolomite. produce a slurry of basic magnesium carbonate 45 When about one-third of the basic carbonate is containing. considerably more solid matter than produced from normal magnesium carbonate and could be obtained from the same amount (vol about two-thirds from bicarbonate solution, the une) of 3 per cent. magnesium bicarbonate solu capacity of the plant may be increased by an tion, and the heat necessary for boiling the liq amount approaching 50 per cent maximum as luid per pound of basic carbonate produced is 50 the Water content of the normal carbonate slurry correspondingly less. Nearly half of the carbon is decreased, and the heat required per pound dioxide gas produced in the burning of dolomitic of basic carbonate produced is correspondingly line and subsequently used in the above described less than if all the product were made entirely Pattinson process for the manufacture of basic from bicarbonate liquor. Similarly, by increasing magnesium carbonate is not necessary for the 55 the amount of basic carbonate produced from process and is commonly allowed to escape to the normal magnesium carbonate to about 50% of atmosphere. This excess gas is available for re the total, the capacity of the plant can be in action with magnesium oxide or hydroxide in creased by an amount approaching 100 per cent, producing normal magnesium carbonate in with the production of a heat insulation such aqueous suspension. This preferred method of 60 as 85% magnesia having adequate strength and carrying out our invention is made clear by the toughness for commercial use as a heat insula following description illustrating one Way of tion. practising this invention, but it is to be under In the practice of this invention as described stood that we are not to be limited as to the above and as described hereinbelow in connection Source of either our normal magnesium carbon 65 With alternate methods of practising this inven ate or Our magnesium bicarbonate. It is desire tion, the amount of basic magnesium carbonate able that the normal magnesium carbonate produced from the normal carbonate, on the one crystals be as fine as possible and the conditions hand, and from the bicarbonate, on the other recited in the following example are adjusted to hand, may vary within wide limits. Ordinarily form this material in such condition. We prefer to produce about one-third to one Eight pounds of magnesium oxide produced half of the basic carbonate from the normal by calcining magnesite (MgCO3) at about 1800 magnesium carbonate and two-thirds to one-half F. for three hours was suspended in thirty gal of the basic magnesium carbonate from the bi lons of water at about 80 F. and was treated carbonate solution. When about two-thirds of with carbon dioxide gas under 50 lb. pressure 5 the basic carbonate of magnesia is produced from 2,275,032 3 normal magnesium carbonate and about one heat that is applied may vary within wide limits third is produced by boiling magnesium bicar between the minimum temperature necessary to bonate, insulation prepared from the resulting decompose normal magnesium carbonate into basic magnesium carbonate is somewhat more basic carbonate (about 158' F. at atmospheric brittle than when the amount of basic carbonate pressure) and the temperature at which basic produced from the normal carbonate of magnesia magnesium carbonate is excessively decomposed, is approximately half or less. However, even i. e., about 550 F. Preferably the heat that is when larger amounts of the basic carbonate are applied is sufficient to subject the mass to a produced by decomposition of the normal car temperature of about 175 F. to about 350 F. An advantage of this method is that the normal bonate in the presence of basic magnesium Car O magnesium carbonate added to the basic car bonate produced by boiling a magnesium bicar bonate prior to the forming of, for example, bonate solution, the basic carbonate has very blocks of 85 per cent. magnesia heat insulation, considerably greater toughness and effective heat inhibits drying shrinkage. This is of great prac insulation properties when incorporated in a tical importance. For example, if a slurry of heat insulation material, e.g., 85% magnesia in 5 50 per cent. by weight on a dry basis of normal sulation, than if the basic carbonate were pre carbonate and 50 per cent. by weight of basic pared entirely by decomposition of the normal carbonate produced by boiling magnesium bi carbonate. Carbonate liquor is mixed. With 15 per cent, of its In precipitating the basic carbonate from the weight on the dry basis of asbestos fiber and is bicarbonate solution containing normal magne 20 molded at, for example, 5 to 10 lb. per square sium carbonate, the mixed materials are pref inch pressure, and dried, it will be found that erably heated rapidly to above 190 F., best re there is substantially no drying shrinkage of the sults being obtained when the mixture is heated molded articles. Furthermore, the molded at about 200 F. to about 210 F. articles are sufficiently rigid after a few hours at While it is preferable to convert normal mag 25 nesium carbonate into basic magnesium car drying temperatures (about 75° E. to 350° F.) bonate in the presence of and simultaneously that no expensive shape-retaining supports are with the production of basic magnesium car needed during the Subsequent drying in spite of bonate produced by heating a bicarbonate solu the fact that the molded articles' are still quite tion by mixing normal magnesium carbonate wet. Also, trimming Scrap is reduced, as the 30 articles can be molded much nearer in dimension with magnesium bicarbonate solution and Con to the trimmed final shape. In the manufacture verting the bicarbonate and normal carbonate of 85% magnesia insulation the amount of trim into basic carbonate substantially simultaneously ming scrap is frequently as high as 30% and this as described above, it is also possible to first trimming scrap can be very iargely and almost produce basic magnesium carbonate from bicar 35 bonate solution and thereafter in the presence of entirely eliminated in the practice of this in the basic carbonate thus produced form basic vention. Moreover, by causing the normal mag magnesium carbonate from normal carbonate. nesium carbonate to decompose in the presence Thus in another modification of Our invention of basic magnesium carbonate after a heat in we prepare a slurry of basic magnesium car 40 sulating material comprising these sustances has bonate by heating a magnesium bicarbonate been molded, the resulting heat insulation can solution preferably to above 190° F (best re be made lighter and at the same time of in sults being obtained when the temperature is creased strength as compared with a heat in about 200 F. to about 210 F.). The heating Sulation material similarly prepared but compris should preferably be as rapid as possible. To ing a like amount of basic magnesium carbonate this slurry We add normal magnesium carbonate all of which is produced prior to molding. Crystals in Suspension, and we either continue In still another desirable modification of the to heat the suspension to the degree above-men invention, We form normal magnesium car tioned until the normal carbonate is changed to bonate by addition of , magnesium oxide or basic carbonate, or we allow the decomposition hydroxide to magnesium bicarbonate solution of the normal carbonate to proceed, utilizing the (instead of producing the normal carbonate in heat in the boiled slurry. The mixture is then a separate operation) and then heat the mixture concentrated by de-watering and is adaptable to rapidly. In the preferred practice of this method, the production of heat insulation or other a slurry of active magnesium oxide or hydroxide products. Alternatively, the de-watering may is introduced into magnesium bicarbonate solu take place prior to the incorporation of the 5 5 tion. The mixture is agitated more or less to hold normal carbonate. The decomposition of the the Solids in Suspension until the added mag normal carbonate may take place with or with nesium compound has been substantially com Out agitation of the mass, pletely converted to normal carbonate. It is In a third embodiment of our invention we preferable in this case that the added magnesium boil a magnesium bicarbonate solution in the (5) as oxide or hydroxide be no more than enough manner above described and produce a slurry to form about one-third of the basic carbonate of basic carbonate which we concentrate by filter produced by the subsequent boiling. If the ing or settling, or both. To this slurry we add amount of magnesium oxide or hydroxide that is a suspension or slurry of normal magnesium added exceeds that mentioned above, carbon carbonate. We may then add to this mixture" dioxide can be passed through the aqueous mix Other ingredients of a heat insulation, e. g., ture to increase the relative proportion of the asbestos fibers, and make a molded insulation bicarbonate therein. However, the relative from the aqueous mixture by molding the in amounts of basic carbonate produced from the sulation in a filter mold. Heat applied while the normal carbonate (in this instance as formed material is in the mold or after removal of the from magnesium hydroxide or oxide) and from molded material from the mold and while the the bicarbonate solution may vary within rela material is still moist, i. e., prior to or during tively wide limits as has been mentioned here drying, but before complete drying, converts the in above. normal carbonate into basic carbonate. The While we have no theory to offer to explain the 4. 2,275,032 superior results to be obtained by heating normal solution, the steps comprising adding a suspen magnesium carbonate in the presence of basic sion of normal magnesium carbonate particles to carbonate produced by boiling magnesium bi the Solution of magnesium bicarbonate and con carbonate solutions, it is readily apparent that verting the particles of normal magnesium car the presence of the latter material is essential, bonate and the dissolved magnesium bicarbonate whether the latter material is produced first Or is in the mixture into basic magnesium carbonate produced simultaneously with the production of by rapidly heating the mixture. basic magnesium carbonate from normal magne 2. A method of making basic magnesium car sium carbonate and Whether the basic magnes bonate which comprises heating a solution of um carbonate is produced from the normal mag 0 magnesium bicarbonate to convert said mag nesium carbonate before or after the mixed ma nesium bicarbonate into basic magnesium car terials are molded. It is readily possible to pro bonate and then heating finely-divided normal duce a light heat insulation materiai from nor magnesium carbonate commingled with said bas mal magnesium carbonate alone mixed with as ic magnesium carbonate thus formed to bestOS fiber providing the normal carbonate is s convert said normal magnesium carbonate into produced under very carefully controlled condi additional basic magnesium carbonate, not more tions and further providing that little or no presa than about 2% of the total basic magnesium car Sure is used. When the shape is molded. We have bonate being produced from the said normal found, howeves, that such magnesia, insulation is magnesium carbonate. exceedingly Yittle and does not have 8, scooth 2) 3. A method according to claim 2 of making and tough textire. If such insulation is pressure basic magnesium carbonate winerein the mixture molded it becomes excessively heavy and of poor of basic magnesium carbonate and normal mag insulating value and is excessively brittle. In nesium carbonate is subjected to agitation during the practice of our invention, it is possible to ob the conversion of the normal magnesium car tain exceedingly tough and strong insulating bonate into basic magnesium carbonate. blocks and shapes which at the same time Bre 4. A method of making basic magnesium car light and bulky and have high insulation eff bonate which comprises rapidly heating a solu ciency. Furthermore, in the practice of our in tion of magnesium bicarbonate to at least about vention, it is possible to utilize crystals of normal 190 F. to convert said magnesium bicarbonate magnesium carbonate too large to produce di. 30 into basic magnesium carbonate, mixing finely rectly anything out excessively heavy insulating divided normal nagraesium carbonate with the I haterials. basic magnesium carbonate thus produced and While we have specified above magnesium oi converting said normal magnesium carbonate carbonate produced from dolonite and norina in the mixture into additional basic magnesium magnesium carbonate produced from magnesite, 85 Carbonate by rapidly heating the mixture to at We do not limit ourselves to these sources. Nor least about 190° F., not more than about 50% of Elal Inagnesium carbonate may be produced from the total basic magnesium carbonate being pro Several sources. For example, magnesium salts duced from said normal magnesium carbonate. from Sea Water or salt-well bitterns may be co 5. in a method making heat insulation ma verted to magnesium hydroxide by well-known. terial wherein a semi-fluid mass comprising basic methods; and this hydroxide may be converted to magnesium carbonate and water is moided and hormal magnesium carbonate by treatment, with the molded product is dried, the steps comprising carbon dioxide gas. Alternatively, magnesium preparing basic nagnesium carbonate by rapidly Salts may be changed to normal carbonate by re heating a Solution of magnesium bicarbonate, action with soluble carbonates. The magnesium 45 making a semi-fiuid mass containing the basic bicarbonate solution also may be made from magnesium carbonate thus prepared and con magnesium compounds by methods known to the taining finely-divided normal magnesium car art. When, for example, the source of all the bonate incorporated with said basic magnesium Emagnesia is magnesium hydroxide from sea, Wa carbonate, molding, the mass, and heating the ter or from magnesite, the normal carbonate 50 molded mass prior to complete drying thereof and bicarbonate solution may both be made from Sufficiently to convert normal magnesium car this material. When the source of all the mag bonate contained therein into basic magnesium nesia is dolomite, the normal carbonate &nd bi carbonate. carbonate solution may both be made from this 6. In 8 method of making heat insulation ma material as described in our application Serial 585 terial wherein a semi-fluid mass comprising basic No. 225,140, filed August 16, 1938. In general, Anagnesin Caronate is molded and the molded the location of the plant will determine the source product is dried, the steps comprising preparing of the magnesia, and the source producing the basic magnesium carbonate by rapidly heating cheapest basic carbonate willi be nos; desirable. 8. Water Solution of magnesium bicarbonate to at it is to be noted, also, that where carbon di 80 least about 190 F., making a semi-fluid mass oxide gas is used, it may be that from any Source, containing the basic magnesium carbonate thus either substantially pure or greatly diluted, as it prepared and containing finely-divided normal is Well known to the art that the concentratio Ignagnesium carbonate incorporated with said bas is variable in practice. ic magnesium carbonate, molding the mass, and We claim: . 35 heating the molded mass prior to complete drying 1. In the preparation of basic magnesium car thereof sufficiently to convert normal magnesium bonate from a mixture of nagnesium and cel carbonate contained therein into basic mag cium hydroxides wherein the Said hydroxides are nesium carbonate, not more than about 2% of treated with carbon dioxide to convert them to the total basic magnesium carbonate in the in precipitated calcium carbonate and dissolved sulation being produced from said normal mag. magnesium bicarbonate, the dissolved nag nesium carbonate. nesium bicarbonate is separated from the pre 7. In the preparation of basic magnesium car cipitated calcium carbonate, and the dissolved bonate from a mixture of magnesium and cal magnesium bicarbonate is converted into basic cium hydroxides wherein the said hydroxides are magnesium carbonate by rapidly heating said 3. treated with carbon dioxide to convert them to 2,275,032 5 precipitated calcium carbonate and dissolved 8. A molded heat insulation material consist magnesium bicarbonate, the dissolved magnesi ing predominantly of basic magnesium carbonate um bicarbonate is separated from the pre and made by molding a semi-fluid mass com cipitated calcium carbonate, and the dissolved prising normal magnesium carbonate in admix magnesium bicarbonate is converted into basic ture with basic magnesium carbonate produced magnesium carbonate by rapidly heating said by precipitation from magnesium bicarbonate solution, the steps comprising incorporating with Solution, the said basic magnesium carbonate be the bicarbonate solution a suspension of mag sing at least about one-third of the total mixture, nesium hydroxide particles adapted to react with and heating the molded mass to decompose the magnesium bicarbonate to form particles of nor 10 normal magnesium carbonate in the molded mal magnesium carbonate, the proportions in the mass to basic magnesium carbonate whereby the mixture being controlled so that at least about basic magnesium carbonate produced by heating 50% of the magnesia occurs as magnesium bicar the molded mass acts, as a bond for the basic bonate, and converting the particles of normal magnesium Carbonate produced by precipitation magnesium carbonate and the dissolved mag 5 from magnesium bicarbonate solution. nesium bicarbonate in the mixture into basic magnesium carbonate by rapidly heating the HAROLD W. GREIDER. mixture. ROGER A. MACARTHUR.