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.