3,170,762 United States Patent Office a tented Feb. 23, 1965 - inton 2 Therefore, practically any available lime source may 3,170,762 MANUFACTURE OF MAGNESJM HYDROXDE be used for the process according to the invention, irre Carneia Bein-Ari, Raaaat Gaia, and Warren . Fuchs, spective of its degree of purity and the nature of the Mount Carmel, Haifa, Israel, assigisors to Negev Phos accompanying minerals. Thus, for example, bituminous phates limited, Hakirya, Israel limestone may be used. This possibility is economically No Drawing. Filed Oct. 2, 1961, Ser. No. 142,008 attractive since the off-the-mine mineral already contains Claims priority, application Israel, Oct. 12, 1960, the fuel necessary for calcination so that no external 14,490/60; Dec. 9, 1960, 42,445/60 source of energy is required. Another example of a 5 Caims. (C. 23-201) . source of limestone which may be utilized in accordance 10 with the present invention is the CaCO3-phosphate mix The present invention concerns the production of mag ture being the rejects of phosphate beneficiation nesium hydroxide from brines containing magnesium operations. chloride. The latter possibility is of considerable practical im Magnesium hydroxide is required mainly for conver portance as it enables to combine the production of mag sion into magnesium oxide which latter is needed, i.e., in nesium hydroxide in accordance with the invention with the manufacture of refractories. -- the beneficiation of calcareous rock phosphate. The In the so-called sea water or brine process for the beneficiation procedure concerned is of the kind wherein production of magnesium hydroxide, the latter is pre the rock phosphate, which may be the run-of-the-mine cipitated from a brine containing magnesium chloride ore or a produced concentrate by any known method, by means of calcium hydroxide resulting from calcina 20 e.g. flotation, is calcined for conversion of the calcium tion and subsequent slaking of some natural calcium carbonate contained in the ore into quicklime, the calcined carbonate ore, e.g. dolomite. While this procedure is mass is wet-slaked for the conversion of the quicklime economically attractive because of the great abundance into calcium hydroxide, and the latter is removed from and consequential low price of lime, it has the disad the phosphate...... vantage that the precipitated magnesium hydroxide is as 25 By wet-slaking the calcine mass, i.e., slaking with the a rule contaminated by numerous impurities. This makes aid of an amount of water in excess over that required necessary the application of elaborate purification pro for hydration, the resulting calcium hydroxide is slurried cedures which are rendered difficult because of the semi in the excess water. Upon separation of this slurry from colloidal nature of the precipitate. the phosphate residue, e.g., by decantation, the calcium The invention consists in a process for the production 30 hydroxide carries off an appreciable amount of phos of magnesium hydroxide by precipitation from brines phate which cannot be retrieved in an economically containing magnesium chloride, comprising the steps of satisfactory way by known methods and is given up as reacting the brine with ammonia, separating the result lost. In conventional wet-slaking rock phosphate up ing magnesium hydroxide precipitate, cycling the mother grading processes, the POs recovery is thus apt to be as liquor into contact with lime, recovering ammonia from 35 low as 60 to 70%, that is 30 to 40% of the rock phosphate the resulting calcium chloride. solution and recycling the are lost. - recovered ammonia back into the brine for precipitation The present invention provides for an integrated process of a further quantity of magnesium hydroxide. Com in which the calcium hydroxide slurry resulting from plete recovery of ammonia from the calcium chloride wet-slaking of calcined calcareous rock phosphate is solution is best done by heating. 40 combined with the production of magnesium hydroxide. The calcium chloride brine obtained in this process The calcium hydroxide is in this manner converted into may either be rejected or utilized in any suitable way. water soluble CaCl2 leaving behind it as residue the Analysis has shown that the magnesium hydroxide entrained phosphate which may be easily separated and precipitates obtained in accordance with the invention are is thus retrieved. 99.9% pure. - 45 Therefore one embodiment of the invention consists in A magnesium chloride liquor suitable for the purposes an integrated process for the production of magnesium of the present invention is, for example, water from the hydroxide and upgrading of calcareous phosphate ore Dead Sea (Israel), because of its high magnesium chlo comprising the basic steps of calcining the ore, wet-slak ride congentration. However, the invention is in no ing the calcined ore and separating from the slaked mass way limited to this possibility and any other MgCl2 brine 50 a calcium hydroxide slurry carrying with it some amount may be used, provided it does not contain ions whose of phosphate, which process is characterized in that the hydroxides are less water soluble than Mg(OH)2. separated slurry is treated with ammonium chloride for Thus in accordance with the invention the exchange producing an aqueous solution of calcium chloride and of the Cl ions of the magnesium chloride brine for ammonia in mixture with solid phosphate, the solution is OH ions supplied by the calcium hydroxide takes place 55 separated from the solid phosphate, ammonia is recovered. indirectly with the aid of a closed NH-NHC cycle from the solution and introduced into an aqueous mag without the brine and the lime ever coming into mutual nesium chloride brine, thereby producing a magnesium contact. Rather than that the brine and the line are hydroxide precipitate in mixture with an aqueous am kept in separate vessels in one of which occurs the reaction monium chloride solution, this solution is separated from MgCl, oH. Mg(OH) 60 the magnesium hydroxide precipitate and the ammonium while in the other the reaction . . . . chloride is recycled for reaction with another portion NHCl of calcium hydroxide slurry obtained by the wet-slaking Ca(OH) - CaCl2 + NHa of calcined carbonaceous phosphate ore. takes place. The OH, ions are supplied to the first The slaking of the calcined ore is preferably performed vessel by the ammonia recycled from the second one 65 at boiling temperature. while the Cl ions required in the second vessel are The separation of the phosphate from the aqueous supplied by the ammonium chloride recycled from the solution of calcium chloride and ammonia as well as, first one. Figuratively speaking, the ammonia thus the separation of the magnesium hydroxide precipitate serves as a selective carrier which delivers to the brine 70 from the aqueous solution of ammonium chloride may be the required hydroxyl ions while leaving behind all im effected by any conventional solid-liquid separation purities accompanying the lime. method. - 3,170,762 3. The complete recovery of ammonia from calcium into the slurry and the mixture was stirred for 2 hours. chloride solution is best done by heating. The ammonium chloride dissolved and reacted with the The above integrated process thus produces pure mag calcium hydroxide, whereby a calcium chloride-ammonia nesium hydroxide and at the same time provides for a solution was formed over a sediment of phosphate. The nearly 100% POs recovery in the upgrading of calcare 5 sediment was separated and amounted to 35 kg. It was ous rock phosphate. re-combined with the upgraded rock phosphate, whereby As a rule the calcium hydroxide siurry separated from the POs recovery was raised to nearly 100%. the slaked ore is dilute, and various measures may be From the separated solution the ammonia was dis taken in order not to encumber the subsequent treatment tilled off and the distillate introduced into 1200 liters of the slurry with ammonium chloride and the distilla 10 of Dead Sea water whereby a precipitate containing 98 tion of ammonia by the handling of too much water. For kg. of Mg(OH)2 was formed. The supernatant liquor example, the slurry may be concentrated, e.g., to a contained 180 kg. of NHCl. The ammonium chloride solid: liquid ratio of about 1:4 or 1:5, and Solid am was used again in the phosphate upgrading process, either monium chloride may be dissolved in the slurry thus con as a solid after the evaporation of the aforesaid NHCl 15 solution, or by contacting this solution, possibly some centrated. Or the slurry may be concentrated further, what concentrated by evaporation, with a concentrate or even to dryness or near-dryness, and this concentrate or solid residue obtained by the complete or near-complete residue be admixed with an aqueous solution of ann evaporation of the calcium hydroxide-phosphate slurry monium chloride, separated from the slaked phosphate ore. The invention is illustrated by the following examples We claim: to which it is not limited. 20 1. A process for the production of magnesium hydrox Example 1 ide comprising continuously feeding an aqueous calcium hydroxide suspension into a first vessel and an aqueous To 100 ml. of Dead Sea water containing 19.9 g, of magnesium chloride solution into a second vessel, estab MgCl, was added 100 ml. of a 10% aqueous ammonia 25 lishing between the two vessels a ciosed cycle by continu solution (64% excess of ammonia). A precipitate of 8.2 ously flowing gaseous ammonia from said first to said g. of Mg(OH) was obtained, which was 99.9% pure. second vessei and continuously flowing an aqueous am After filtration, the mother liquor was reacted with 15 monium chloride Solution from said second to said first g. of calcined bituminous limestone containing the equiva vessel, continuously discharging an aqueous calcium chlo lent of 10.4 g. of Ca(OH)2, which resulted in the in 30 ride solution from said first vessel and withdrawing pre mediate expulsion of 4.8 g. of NH3. An additional quan cipitated magnesium hydroxide from said second vessel. tity of 5.2 g of NH3 was recovered by steaming. The 2. A process which comprises calcining a calcareous entire amount of recovered ammonia was recycled to the rock phosphate, wet-shaking the calcined product, sepa Mg(OH)2 precipitation stage. rating the resulting aqueous suspension of calcium hy It will be appreciated that in practice the process ac 3 5 droxide and withdrawing the remaining enriched rock cording to the invention is carried out in a continuous phosphate as a first product; continuously feeding said manner by continuously feeding ammona and brine into suspension into a first vessel and a magnesium chloride the vessel in which the Mg(OH)2 is precipitated, con solution into a second vessel, establishing between the tinuously withdrawing from this vessel Mg(OH)2 and two vessels a closed cycle by continuously flowing gase mother liquor, leading the mother liquor continuously 40 ous ammonia from said first to said second vessel and into a second vessel where it is reacted with lime, with continuously flowing an aqueous ammoniuin chloride so drawing continuously from that second vessel the formed lution from said second to said first vessel, continuously CaCl brine and continuously adding fresh lime into this discharging an aqueous calcium chloride solution from vessel. In this manner a continuous NH3-NH4Cl cycle is Said first vessel, withdrawing a phosphate containing prod formed in which the quantity of NH3 is constant but for 45 llct from said first vessel as a second product, and with operational losses while the reactant spent is line, simi drawing precipitated magnesium hydroxide from said sec ond vessel as a third product. lar as in conventional processes. 3. A process according to claim 2, comprising concen Example 2 trating said calcium hydroxide Suspension prior to feed ing the same to said first vessel. Run-of-the-mine calcareous phosphate ore from Oron 50 4. A process according to claim 1, comprising heating (Israel) was concentrated by flotation to yield a concen said first vessel for a complete expulsion of ammonia. trate containing 30.9% of POs and a proportion of cal 5. A method of producing magnesium hydroxide in a cium carbonate corresponding to 8.47% of CO2 and closed cycle process, said method comprising fortning first 10.76% of CaO. and second reaction zones, reacting in the second reac 1 ton of this concentrate was calcined at about 1000 55 tion zone magnesium chloride and animonia to yield mag C. for 2 hours, whereby it lost 80.2 kg. of CO2 (95% nesium hydroxide and ammonium chloride and reacting CO-expulsion). The calcined ore was slaked at the in the first zone calcium hydroxide and ammonium chlo boil with 5 tons of water during 20 minutes, then the ride to yield ammonia and calcium chloride, the ammo coarse phosphate was allowed to settle and the super nium chloride produced in the second reaction zone being natant slurry of calcium hydroxide admixed with a 60 fed to the first reaction zone while the ammonia pro smaller proportion of phosphate fines was removed by duced in the first reaction zone is fed to the second re decantation. action Zone whereby magnesium hydroxide is produced Sample analysis of an aliquot portion of the decantate utilizing only magnesium chloride and calcium hydroxide showed that the total amount of suspended solid matter as starting substances. thus removed amounted to 167 kg., containing 35.9 kg. of 65 PO, being 11.5% of the POs contents of the rock References Cited by the Examiner phosphate concentrate used as a starting material. UNITED STATES PATENTS The calcium hydroxide-phosphate slurry was concen 663,840 12/00 Zitt ------23-201 trated by evaporation to a total volume of about 800 70 1,348,933 - 8/20 Dolbear ------23-201 liters. The solid:liquid ratio (weight/weight) was then 1,910,169 5/33 Kaselitz ------23-201 about 1:4. 1986,509 1/35 MacIntire ------23-201 180 kg. of solid ammonium chloride, being approxi 2,603,555 7/52 Hulme ------23-201 mately the stoichiometric equivalent of the calcium hy droxide contained in the slurry, where then introduced 15 MAURICE A. BRINDISI, Primary Examiner.