April 10, 1945. ?. c. ????lsoN 2,373,528 METHOD OF RECOWERING MAGNESIUM COMPOUNDS Filed Aug. 13, 1941

AORNEY Patented Apr. 10, 1945 2,373,528

UNITED STATES PATENT OFFICE METHOD of RECovERING MAGNESIUM. ??M???NDs Thomas C. Atchison, Princeton, N.J., assignor to Johns-Manville Corporation, New York, N.Y., a corporation of New York Application August 13, 1941, serial No. 406,577 5 Ciams. (CI. 23-67) This invention relates to magnesium carbonate wasted when pipe lines, boilers, etc., are stripped compositions of the type suitable for insulating of old magnesia insulating materials. Also, min purposes. It relates particularly to a method of erals, either calcined or uncalcined, containing recovering magnesium compounds from materials relatively large proportions of magnesia. Walues, previously wasted and utilizing the recovered ma such as serpentine, chrysotile, etc., but which are terials in the process of manufacturing magne difficult to carbonate, may be utilized as a Source. sium carbonate compositions in the conventional of raw material in the operation of my present process heretofore practiced. invention. Through the use of the carbonating Heat insulating materials containing basic procedure, as will be described in more detail magnesium carbonate are generally made by 0. below, the magnesia components in these prod forming an admixture of basic magnesium car ucts, some of which were previously considered bonate and asbestos fibres, the fibres being pres waste materials, may be readily recovered, and ent to impart binding characteristics and addi the resulting recovered magnesium compounds. tional strength to the product. The mixture of may be used in preparing new magnesium com the basic carbonate and fibres is placed in suit is pounds for various purposes. . able molds shaped in accordance with the desired It is, therefore, an object of this invention to design of the final product, and thereafter the recover magnesium compounds formerly lost in molded product is subjected to a drying action. waste materials and sludge which will thus in . In forming the heat insulating material the pro crease the plant capacity for the production of portions of the fibre and the basic magnesium 20 magnesium carbonate products by about 20-25 carbonate are so proportioned that the final prod per cent. The plant capacity will be increased uct contains. about 85 per cent of basiç magne to this degree, since the volume of the materials sium carbonate. This product is generally re passing through the equipment need not be in ferred to in commerce as 85 per cent magnesia. creased in order to make the recovery of the In preparing the basic magnesium carbonate 25 magnesium compounds from the waste products, used in 85 per cent magnesia, a considerable pro ' effective. The recovered products are merely en portion of the magnesium compounds obtained as tered into the regular production cycle and the a result of following the conventional procedure concentration of the magnesium solutions may of manufacturing magnesium carbonate mate be increased without detrimental effects which rials... are lost in waste water and waste sludges. 30 were previously encountered prior to the utiliz It has been estimated that magnesium com -ation of the present invention. V pounds to the extent of 20-25 per cent of the It is also an object of this invention to recover magnesia values in the raw materials have been the magnesium compounds formerly lost in waste lost in the waste waters and sludge which have materials at a negligibly increased cost in oper always in the past been discarded. recover 35 ating expenses. The recovery operation may also ing the magnesia values from the w astewaters be applied to recover magnesia values from trim and sludge a considerable reduction in cost of mings, old magnesia insulation materials and dif the manufacturing operations will be obtained. ficultly carbonatable minerals. The necessary It is known that an aqueous suspension of cal- . equipment for carrying on the present process cium carbonate and magnesium carbonate, as, for 40 is not very expensive, and the increased overhead example, 80 per cent calcium carbonate and 20 expense as a result of the equipment and Operat per cent magnesium carbonate, could be treated ing costs will be very small as compared to the with a large excess of strong carbon dioxide gas value of the magnesium compounds now recove - to dissolve the magnesium carbonate forming a ered but previously lost. . . magnesium bicarbonate solution and leaving the 45 It is a further objec, of this invention to ma calcium carbonate undissolved, but no economi terially reduce the amount of steam required cal method has thus far been developed to apply for precipitating the magnesium bicarbonate so the above separation to plant operations. . lutions, inasmuch as the concentration of the Large quantities of magnesium carbonates have magnesium bicarbonate solution can be materi also in the past been wasted in the form of trim 50 ally increased. Previously, it was undesirable to mings obtained during the sizing and finishing have too high concentrations of the magnesium operations of crude molded basic magnesium car bicarbonate solutions because of the fact that a ... bonate products. These trimmings are usually in substantial proportion of the magnesium com the form of a dust and small lumps. Additional pounds precipitated from the solution and were . . quantities of magnesium compounds have been 55 thereby lost in the waste waters and sludge. 2 2,878,528 However, through the application of the present is converted into a water-soluble magnesium novel procedure more fully described herein, the bicarbonate and the calcium hydroxide is con resulting increase in decomposition of the mag verted into a substantially water-insoluble cal nesium bicarbonate solutions is no longer of any cium carbonate. significance, since the decomposed material is 5 The magnesium bicarbonate solution contain recovered. Thus, since the magnesium bicarbon ing the water-insoluble calcium carbonate is ate solutions may now be used at higher concen thereafter pumped to a settling tank wherein the trations, the amount of steam formerly required water-insoluble components are permitted to set for boiling magnesium bicarbonate solutions to tle to the bottom of the tank. A small percent precipitate the magnesium carbonate may be re 0. age of the magnesium bicarbonate solution has a duced. tendency to precipitate in the form of normal Additional objects and benefits of the present magnesium carbonate (MgCO3.3H2O) which will invention will be apparent to those skilled in the settle with the calcium carbonate components art from the more detailed description of the in the bottom of the tank. novel method hereinafter set forth. "?? The substantially clear and sludge-free mag Broadly stated, the present invention includes nesium bicarbonate solution is then pumped to the treatment of waste sludges and other diffi a precipitator and the Solution is subjected to a cultly carbonatable materials containing retained hêating operation. During the heating the mag or absorbed soluble magnesium carbonate and nesium bicarbonate will precipitate from the solu insoluble magnesium carbonate with carbon di f) () tion in the form of an insoluble magnesium car oxide gas to form water soluble magnesium comi benate which may be in the form of normal mag pounds. The Water-soluble magnesium com nesium carbonate or the basic magnesium car pounds are then separated from the water-insol bonate, and this reaction is accompanied by the uble compounds, and the resulting solution con evolution of considerable carbon dioxide. The taining the water-soluble magnesium compounds 5 precipitated magnesium carbonate is then placed is used in conjunction with fresh magnesium into a filter or other dewatering device to remove compounds in the regular manufacturing cycle. the major portion of water, and the magnesium The invention will be illustrated by a more carbonate slurry is thereafter placed into suit complete description in connection with the at able molds of any desired shape, followed, if nec tached drawing, which shows a flow sheet of the essary, by the application of pressure. If fibres preferred embodiment of the method for recov are added to the material, the fibres may be ering magnesium compounds from waste mate added after a substantial proportion of the water rials. The broken line portion of the flow sheet has been removed from the slurry, that is, after is the conventional method heretofore used in the slurry has been passed through the filter. manufacturing basic magnesium carbonate prod 5 The lime sludge obtained from the lime sludge ucts. The portion of the flow sheet in heavy thickener contains a substantial proportion of lines illustrates the procedure followed in my in precipitated magnesium carbonate, retained or vention in recovering the magnesium compounds absorbed magnesium bicarbonate solution, cal from the Waste materials. cium carbonate, and other compounds. The per In the drawing illustrating a conventional 4 centage of magnesia values in these sludge prod method of manufacturing basic magnesium çar lucts, previously wasted, is very high, and it is bonate, dolomite mineral (composed primarily of , advantageous to recover these magnesia values magnesium carbonate and calcium carbonate) in order to increase the plant capacity over nor and coke are fed to a kiln and subjected to rela mal operations. tively high temperatures to convert the mag The sludge obtained from the lime sludge thick nesium carbonate and the calcium carbonate to ener is mixed with additional water until the magnesium oxide and calcium oxide, respectively. mixture forms a comparatively thin slurry. It is During the calcining action, carbon dioxide gas preferable that the slurry be diluted with water is evolved as a result of the reduction of the to Such a degree that the concentration of the magnesium carbonate and calcium carbonate to 5 O magnesium carbonates is at least below 1.5 per the respective oxides. The CO2 gas is utilized in cent expressed as basic magnesium carbonate the high concentration carbonator and the low (approximately six grams of MgO per liter or 0.6 concentration carbonator, as will be described in per cent). It has been found that if a slurry more detail below in the Subsequent steps of the be diluted still further so that the concentration Operation. 5 of the magnesium carbonates would be approxi After the dolomite ore has been sufficiently cal mately .5 per cent concentration expressed as cined to form magnesium oxide and calcium basic magnesium carbonate (two grams MgO per oxide, the materials are subjected to a slaking liter or 0.2 per cent), more satisfactory results operation. In this operation water is mixed with are obtained. Highly dilute solutions are desir the oxide mixtures and thereafter the slurry of 60 able in order to obtain effective separation of the slaked materials, composed primarily of the the magnesium compounds from the insoluble magnesium hydroxide and calcium hydroxide, is calcium compounds. If the concentration of then pumped to a series of high concentration the magnesium carbonates is too high, a consid carbonating tanks where the mixed hydroxides erable proportion of the magnesium compounds . are subjected to the action of carbon dioxide gas. 65 will be lost with the calcium carbonate sludge In the high concentration carbonating tanks, which is discarded in a subsequent operation of the concentration of the magnesia is in excess of the present proceSS. 1.5 per cent expressed as basic magnesium car Trim materials, waste or discarded basic mag bonate (approximately six grams MgO per liter, nesium carbonate materials, difficultly carbonata or 0.6 per cent). The carbon dioxide gas is bub- 70 ble minerals, or other products containing mag bled through the magnesium hydroxide and cal nesia values, are added at this point of the oper cium hydroxide mixture in sufficient quantity to ation if such products are to be used in the react with the magnesium and calcium con Operation. It is desirable to break or crush the pounds to form carbonate compounds. The Sub products into a relatively fine condition and sus stantially water-insoluble magnesium hydroxide 75 pend the pulverulent materials in a large volume 2,378,5as 3. ?? yelethe supended materiai,hp????? pre ing carbon dioxide through the mixture, and erably be diluted to such a degree that the con after carbonation of the diluted sludge 98 per cent of the magnesia was found to be in solution. centration of the slurry will not exceed the con The magnesium bicarbonate solution was then centration of the diluted sludge as described Separated from the undissolved solids and added above. Highly dilute solutions are desirable in Order to obtain effective solution of the mag to the hydrated slaked dolomite entering the nesia values during the Subsequent carbonating proceSS. Another example of the application of my in action.The highly diluted slurry is then- subjected to a vention, in order to illustrate the effectiveness carbonation action in a series of low concentra O thereof, is directed to the treatment of a mix tion carbonating tanks. In this operation carbon ture of plastic and calcined magnesium oxide. In dioxide gas is passed through the diluted lime this Operation a slurry of a mixture of plastic and sludge mixture and/or other magnesia-contain calcined magnesium oxide in sufficient quantity ing materials until the water-insoluble magnesium to give a total concentration of 1.75 per cent, compounds have been converted into water-solu 15 expressed as magnesium basic carbonate (0.65 ble magnesium compounds. per cent plastic and 1.10 per cent magnesium From the low concentration carbonators the oxide), was carbonated with substantially pure sludge is pumped to a thickening or settling tank carbon dioxide gas at 40 lbs. gauge pressure. As and the water-insoluble calcium carbonate com a result of the carbonating action, 84 per cent ponents and other insoluble components are pei'- 20 of the total available magnesia entered into so mitted to settle to the bottom of the tank. The lution in forty minutes. However, when in ac highly diluted magnesium bicarbonate solution is Cordance with my invention the same quantity of separated from the settled calcium carbonate plastic (0.65 per cent available magnesia ex sludge and pumped back into the manufacturing preSSed as magnesium basic carbonate) was sub cycle either into the saker or into an accumulator 25 jected to carbonation at 40 lbs. gauge pressure thickener tank. If no calcium carbonate Com for twenty minutes, all the plastic was dissolved. ponents are present, as, for example, when treat The magnesium oxide was then added to the so ing waste trim or other basic magnesium car lution in the same quantity as used above, that bonate materials, the settling tank operation may is sufficient to give a potential concentration of be omitted, since no calcium carbonate is pres 3) 1.10 per cent, or a total concentration of 1.75 per ent. In this case the magnesium bicarbonate so cent. The magnesium oxide suspended in the lution may be pumped directly to the slaker or magnesium bicarbonate solution was then sub into the accumulator. The recovered magnesium jected to further carbonation, and after twenty bicarbonate solution will react with the calcium minutes of carbonation at 40 lbs. gauge pressure, ' * hydroxide or slaked - calcined dolomite in the ac 35 99 per cent of the total available magnesia wa cumulator to form a substantially water-insoluble found to be in solution. magnesium hydroxide. The two specific illustrations demonstrate the The recovered magnesium bicarbonate solu effectiveness of the present invention. It will tion may be reacted, if desired, with other water be noted that substantially all of the magnesia. soluble hydroxides, such as hydroxides of the 40 enters into solution as magnesium bicarbonate alkaline earth metals or the alkali metals. Among when the substantially insoluble magnesia com the water-soluble hydroxides of the alkaline ponents are treated in accordance With the de earth metals, such compounds as barium hy scribed procedure. . droxide or strontium hydroxide are satisfactory The method of recovering magnesium com compounds to precipitate the magnesium bicar 45 pounds from Waste materials and waste sludges bonate as magnesium hydroxide. Hydroxides of results in not only increasing the capacity of the alkali metals include sodium hydroxide, potas plant by about 20 to 25 per cent, but also en sium hydroxide and ammonium hydroxide, and ables the use of higher concentrations of mag may be used in place of the calcium hydroxide nesium bicarbonate Solutions. Even though mag described in the example. Calcium hydroxide is nesium compounds tend to precipitate from the ordinarily used in my operation, but it is under solution at the higher concentrations, the mag stood that other hydroxides as described above, nesia values are readily recovered from the waste may be used to precipitate the magnesium bicar waters and sludges. Furthermore, since higher bonate solution and are included within the scope concentrations of bicarbonate solutions can be of the present invention. Calcium hydroxide may used Satisfactorily without loss of too much of ordinarily be considered sparingly soluble as the magnesia value, less steam will be required compared to the solubility of, for example, so to heat the magnesium bicarbonate solution in dium hydroxide, but when compared with the the precipitator due to the smaller volume of substantially insoluble magnesium hydroxide it solution. Thus, when all the factors are consid may be construed as substantially water-soluble, ered, it will be evident that a substantial saving and for the purpose of the present Specification in operation and increased capacity are effected. It is desirable that the recovery of the magne and claims, calcium hydroxide will be defined as sium compounds from the lime sludge material water-soluble in conjunction, with other water or other magnesia products be effected at very soluble hydroxides described above. 65 low concentrations. If the solution is diluted to As an illustration of the procedure showing the such a degree that a very low concentration of effectiveness and high recovery of magnesia val magnesium compounds exists in the solution, sub ues in lime sludge, 1000 gallons of lime sludge stantially complete recovery of the magnesium was diluted with 6500 gallons of water. The di compounds is obtained. luted mixture had a concentration of magnesium . The concentration of the carbon dioxide gas carbonates of 0.67 per cent expressed as magne used in the carbonation of the waste materials sium basic carbonate. The solids in the sludge and other sludges is preferably high. It is also were found by gravimetric analyses to be con desirable to have relatively high pressures forcing posed of 78 per cent calcium salts and 22 per the gas through the carbonator in order to ob cent magnesium salts. The diluted mixture was 75 then subjected to a carbonating action by pass tain effective carbonation of the magnesium Com 4. 2,873,528 pounds. If the gas used in the resaturation re sions, forming a dilute aqueous suspension of action has a carbon dioxide content in excess of Waste magnesium carbonate products of the said 50 per cent by volume, excellent results will be manufacturing operation having a magnesium obtained. If the concentration is lower, the re concentration calculated as magnesium oxide in action will be slower, but satisfactory results will the range .2%-6%, subjecting said dilute suspen be obtained although more time will be required sion to a secondary carbonating treatment with before the treated materials may be added to the carbon dioxide under conditions adapted to con fresh stock in the accumulator thickener. Gases. vert substantially all of the magnesium carbonate under relatively high pressure, as, for example, 60 present to soluble magnesium bicarbonate, con to 100 pounds per square inch, in the carbonating O verting the dilute bicarbonate liquor thus formed units tend to accelerate the conversion of the to magnesium hydroxide, and using the thus water-insoluble magnesium compounds into Wa formed magnesium hydroxide to increase. above ter-soluble magnesium compounds. 0.6% the normal concentration of magnesium ox The details given are for the purpose of illus ide in the aqueous magnesium hydroxide. Sub tration, not restriction, and variations within the jected to the primary carbonation treatment. spirit of the invention are intended to be included 4. A cyclic process for increasing utilization of in the scope of the appended claims. magnesia Values in the manufacture of magnesi I claim: um carbonate insulation products, which com 1. The process of recovering magnesium car prises, slaking calcined dolomite to form a dilute bonates from difficultly carbonatable magnesium 20 aqueous slurry of magnesium hydroxide and cal compounds which comprises, forming a dilute cium hydroxide, subjecting the slurry to a pri aqueous suspension including substantially Water mary carbonation with carbon dioxide to produce insoluble magnesium compounds having a mag Soluble magnesium bicarbonate and insoluble cal nesium concentration of about 0.2-0.6% ex cium carbonate, separating the calcium carbo pressed as magnesium oxide, subjecting the aque 2 5 nate from the magnesium bicarbonate liquor as ous suspension to the action of carbon dioxide gas a lime sludge, heating the magnesium bicarbo under conditions adapted to convert the water in nate liquor to precipitate magnesium carbonate soluble magnesium compounds into water soluble and molding said product to shapes which are magnesium bicarbonate, Separating Water insOlu then cured and trimmed to dimensions, and re ble compounds from the magnesium bicarbonate covering magnesia values from waste magnesium Solution, admixing a water soluble hydroxide and carbonate containing products of the said manu magnesium hydroxide with the magnesium bicar facturing operation by forming an aqueous slurry bonate solution, reacting the magnesium bicarbo suspension thereof with a magnesium concentra nate solution with the water soluble hydroxide to tion calculated as magnesium oxide in the range form substantially water insoluble magnesium .2%-.6%, subjecting said dilute suspension to a hydroxide, and subjecting an aqueous suspension secondary carbonating treatment with carbon di of the magnesium hydroxide having a concentra oxide under conditions adapted to convert sub tion calculated as magnesium oxide above 0.6% stantially all of the magnesia values to soluble to the action of carbon dioxide under conditions magnesium bicarbonate, separating the dilute adapted to produce magnesium bicarbonate. 40 magnesium bicarbonate liquor thus formed from 2. The process of recovering magnesia in a suit any insoluble residue of the treatment, and mix able form for use in manufacturing molded mag ing the dilute bicarbonate liquor, water, and cal nesium carbonate products which comprises, cined dolomite in the hydrating zone in such pro forming a dilute aqueous suspension including portions as to give a magnesium oxide content calcium carbonate, magnesium carbonates and 45 above .6% in the slurry suspension subjected to water soluble magnesium bicarbonate, said suis the primary carbonation treatment. pension having a magnesium concentration of 5. The cyclic process of preparing magnesia in substantially 0.2%-0.6% expressed as magnesi a form suitable for use in manufacturing molded um oxide, subjecting the aqueous suspension to magnesium carbonate products, which comprises the action of carbon dioxide gas to convert the 50 calcining a dolomite ore forming a mixture of water insoluble magnesium carbonates into Water calcium oxide and magnesium oxide, hydrating soluble magnesium bicarbonate, separating in said oxides and forming a dilute aqueous suspen soluble calcium carbonate from the magnesium Sion of calcium and magnesium hydroxides, sub bicarbonate solution, adding calcium hydroxide jecting the mixed hydroxides to the carbonating and magnesium hydroxide to the magnesium bi action of carbon dioxide gas and separating the carbonate solution, reacting the magnesium bi thus formed water-soluble magnesium bicarbo carbonate solution with the calcium hydroxide to nate solution from the precipitated calcium car form substantially water insoluble magnesium . bonate sludge, and recovering magnesia, values hydroxide, and subjecting an aqueous suspension including Soltible bicarbonate and insoluble car of the magnesium hydroxide having a concentra 60 bonates from the said sludge by forming an aque tion calculated as magnesium oxide above 0.6% Ous slurry suspension of the sludge with a mag to the action of carbon dioxide under conditions nesium concentration calculated as magnesium adapted to produce magnesium bicarbonate. oxide of less than 0.6%, subjecting the aqueous 3. A cyclic process for manufacturing magnesi Slurry mixture to the action of carbon dioxide gas um carbonate insulation products which corn 65 to convert the precipitated magnesium carbonate prises, calcining magnesium carbonate and slak to a water-soluble magnesium bicarbonate, sep ing the resulting magnesia to form a dilute aque arating the Water-insoluble calcium carbonate ous slurry of magnesium hydroxide, subjecting from the magnesium bicarbonate solution, and the slurry to a primary carbonation with Carbon finally mixing the magnesium bicarbonate solu dioxide to produce soluble magnesium bicarbo 70 tion, water, and the calcined dolomite in the hy nate, heating the magnesium bicarbonate liquor . drating zone, in such proportions as to provide a to precipitate magnesium carbonate, concentrat magnesium oxide content above 0.6% in the sus ing the magnesium carbonate by filtration to a pension subjected to the primary carbonation molding consistency and molding, curing and treatment. trimming shaped products to specified dimen 75 THOMAS C. ATCH ISON.