MXPA97000395A - Suspension of stabilized magnesium hydroxide, hydration at pressure, from calcinated magnesite, and procedure for your production - Google Patents

Abstract

A suspension of magnesium hydroxide under pressure, stabilized and a process for its production from calcined magnesite is described, according to one embodiment of the invention, a mixture comprising calcined natural magnesite and water is hydrated under pressure to provide a hydrated pressure suspension, then the hydrated pressure suspension is deagglomerated, if desired, chloride ions and cationic polymer can be added to further stabilize the suspension

Description

SUSPENSION OF STABILIZED MAGNESIUM HYDROXIDE, HYDRAATED PRESSURE, FROM CALCINATED MAGNESITE, AND PROCEDURE FOR ITS PRODUCTION FIELD OF THE INVENTION This invention relates to a method of production of a suspension of magnesium hydroxide pumped, stable, by hydration or pressure and stabilization of calcined natural magnesite.

BACKGROUND OF THE INVENTION Magnesium hydroxide in the form of a suspension is useful as a pumpable source of magnesium oxide for various chemical treatments, including but not limited to the following: (1) pH adjustment, including residual acid and neutralization of acidic wastewater; (2) wastewater treatment, including precipitation of heavy metal contaminants; (3) purification and neutralization of acid vapors in flue gases or treatments with gas evolution; and (4) production of specialty magnesium compounds (for example ftgSQi,, M N? 3, M Cl2, etc.), as a source of magnesium. By supplying magnesium hydroxide in the form of a suspension of at least moderate quality, it eliminates a wide range of potentially dangerous operations for the extinguishing of the Mog powder (due to the exotherm of drainage). The suspensions of magnesium hydroxide of the quality have Additional advantages include the tendency to be easily handled and stored, and the tendency to be reliably dosed at will toward chemical treatments.Indeed, such magnesium hydroxide suspensions can be -transported to the point of application and stored for periods of time. from days to several weeks under constant and intermittent agitation without incurring adverse effects such as sedimentation of solids and excessive viscosity. Products of magnesium hydroxide hydrated at atmospheric pressure of inferior quality manufactured from calcined natural magnesite are common, but in many cases do not have the desirable characteristics They can cause numerous manufacturing difficulties including the following: product dehornomogeneity; obstruction of transport lines, valves, treatment equipment and storage equipment; formation of an impacted bed of non-pumpable magnesium hydroxide solids at the bottom of storage tanks and treatment vessels; insufficient or inconsistent loading speed to treatments; excessive energy costs to transport / pump the product; and high maintenance costs for systems that incorporate the product. At present, however, it is believed that the only suspensions of magnesium hydroxide of moderate to high quality available are the synthetic magnesium hydroxide products manufactured from the soluble magnesium present in brine and seawater fields. For economic reasons, these synthetic magnesium hydroxide suspensions are generally produced in close proximity to the sources of brine or rnar water.

BRIEF DESCRIPTION OF THE INVENTION In view of the foregoing, there is presently a need for a magnesium hydroxide suspension product of at least moderate quality that can be produced from geographical sources of natural magnesite ore that are not required. and attached to the brine fields and coastal areas currently necessary for the production of synthetically manufactured magnesium hydroxide products. For the time of the invention, it is not economically feasible to produce a suspension of magnesium hydroxide from calcined natural magnesite which is of sufficient stability to be stored for long periods or transported over long distances, without sedimentation in an impacted bed. However, the present inventors have developed a process for the production of an aqueous suspension of pumpable stabilized magnesium hydroxide of moderate quality which is manufactured from calcined natural magnesite. In particularA process for the production of a stabilized magnesium hydroxide suspension in which a mixture containing calcined natural magnesite and water is hydrated under pressure to provide a precursor suspension of hydrated magnesium hydroxide under pressure has been developed. A key aspect of the stability of the final product is based on the smergisic reaction between two stabilizing additives: chloride ions and cationic polymer. These additives, together with the precursor suspension of hydrated magnesium hydroxide under pressure, are treated through a diffuser to provide a stabilized suspension. The magnesium hydroxide suspension made with the method of the present invention has many advantages. including but not limited to the following: (1) hydration time is significantly reduced compared to hydration at atmospheric pressure, which results in reduced production cycle time; (2) the particle size distribution of the magnesium hydroxide of the product of the invention is smaller than that of the atmospheric hydrates, contributing to improved stability of the suspension; (3) maintenance costs are reduced compared to atmospheric hydrates since the hydration step under pressure produces hydrate particles that are easier to deagglomerate and stabilize than hydrated particles at atmospheric pressure; (4) pumping and agitation costs are low in relation to atmospheric hydrates; (5) The costs of emptying to remove solids settled or agreed to from the bottom of storage or treatment vessels, ducts, transportation containers (eg, tank trucks), etc., are lower than those of atmospheric hydrates; (6) already installed pipe systems and networks are susceptible to conversion of another alkaline hydroxide (such as that produced from lime) to magnesium hydroxide, or from a magnesium hydroxide quality premium to a magnesium hydroxide of moderate quality; (7) the end user can avoid changing the arrangement of the application system and operating procedures, or scaling the existing equipment to facilitate the use of the suspension of magnesium hydroxide from calcined magnesite; (8) the procedure is not necessarily linked to particular geographical areas for economic delivery of raw materials, allowing the facilities that employ the treatment to be located strategically to supply established markets as targets, with the advantage of relatively low shipping costs of the product.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of flrrhenius based on the hydration reaction at atmospheric pressure of calcined natural magnesite. Figure 2 is a schematic diagram of a possible embodiment of the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In accordance with one embodiment of the invention, the The main treatment requirements for the production of a stable, pumpable, moderate-quality magnesium hydroxide suspension from calcined natural magnesite are (1) hydration under pressure, and (2) stabilization. , the term "moderate quality" suspension encompasses the following characteristics: (1) percent solids by weight is at least 50%, preferably 55-65%, (2) Brookfield viscosity - room temperature is 50-900 centipoise (cps), preferably 50-300 cps; (3) the void / flow characteristics are such that more than 80% by weight, preferably more than 90% by weight, of the sample is poured by gravity after 7 days of undisturbed sedimentation; (4) after 7 days of gravity sedimentation without disturbance (without agitation), the water separation is less than 2.5 cm, preferably less than 1.2 cm, with the height of the water separation being measured in a normal cylindrical polyclinic bottle 240 rnl, (5 c OD x 13.6 crn in height); and (5) the settled solids are easily resuspendable with minimal agitation intensity. For many applications, the property of resuspension is much more critical than the homogeneity of the long-term suspension since thermistor agitation can be provided at the point of application.

Hydration under pressure In the endeavor to manufacture a magnesium ludrox product from calcined magnesite, the inventors have unexpectedly discovered that the hydration under pressure of calcined magnesite, preferably in the presence of chloride ions, can result in an improved quality product. to high, at competitive cost. The magnesite of the present invention is preferably obtained from natural sources. Large deposits of natural magnesite are found, for example, in the United States, Canada, China, Korea, Australia, Greece, Spain, Brazil, Turkey, Austria, Czechoslovakia, Russia, Ukraine, Yugoslavia, Italy, India ', Nepal and South Africa. The chemical composition of the calcined natural magnesite preferably comprises about 85 to 99% by weight of MgO (on calcined basis), and is derived by the thermal decomposition of magnesite ore (MgC 3) to form magnesium oxide (MgO) and carbon dioxide (CO2). The typical chemical composition of MgO and different major impurities of the calcined magnesite ore of the present invention are summarized in the IR table.

PICTURE Í SCALE OF TYPICAL SECURITIES MgO,% by weight 86.0 - 98.0 (calcined base) CaO 0. 70 - 4.0 1O2 0. 25 - 11.0 FH2O3 0. 06 - 0.85 The calcined natural magnesite used in the practice of the present invention is preferably divided as finely as commercially as possible, preferably by passing it through a 20 mesh screen, preferably through a 100 mesh screen. The calcined natural magnesite used in the practice of the present invention can be manufactured using drying ovens of different designs including static arrow kilns, rotary kilns, Herreshoff kilns, pitch kilns, etc. The hydration of the calcined natural magnesite comprises the reaction between magnesium oxide, MgO, and water to produce magnesium hydroxide, Mg (0H) 2- fl atmospheric pressure and at temperatures less than, or equal to, 100 ° C, however , the complete hydration of calcined natural magnesite takes up to one day. The reactive portion is moisturized. ivarnent e quickly at accessible temperatures at atmospheric pressure, but the least reactive portion < -e hydrates slowly extremely under these conditions. By contrastThe inventors have found that hydration under pressure provides a convenient method of hydration of calcined natural magnesite, apparently "overcoming the resistance to pore diffusion and mass transfer as discussed in Example 3 below. which occurs hydration, super-atmospheric pressures and the corresponding saturation temperatures dramatically increase the hydration rate of the calcined natural magnesite in question, for example, the hydration time is reduced by periods of the order of days, under pressure atmospheric, to periods of the order of hours or minutes, at super-atrnospheric pressures In the realization of hydration under pressure, it is preferred to couple the hydration equipment with a heat recovery medium to allow the reutilisation of the heat generated during hydration (an exothermic reaction) For example, if the trat is selected Intermittent heat, the last batches can be reheated with energy released from the current batch, using recovery heat transfer. The exoterrna can also be used effectively to overcome the barrier of the activation energy of the hydration reaction and accelerate hydration. Of course, the energy can be recovered if a continuous mode of treatment is selected. Depending on the volume, operating pressure, construction material and treatment mode (intermittent or continuous), selected hydration vessels may be, for example, stirred vertical pressure vessels. "fine suitable for intermittent treatments), horizontal vessels, agitated by inclined cylindrical vanes to improve the discharge of the container (more suitable for continuous treatment), etc. The hydration pressures are preferably 0.07 to 10.5 Kg / crn2, preferably 1.75 to 7 Kg / crn2, with the actual pressure selected based on capital costs, energy costs, etc.

Stabilization The magnesium hydroxide suspensions of the invention are preferably stabilized by subjecting the hydrated suspension to chemical and mechanical treatment. The mechanical treatment of the hydrated suspension of the invention is preferably carried out to deagglomerate the product and disperse any desired additive. Commercially available equipment that can be used for this purpose includes high-speed cut-off mixers and blenders such as high-speed dispersion sheet tandem slurry mixers, homogenizer / reagents, in-line static mixers, agitated holding tanks and other suitable devices. The chemical stabilization of the hydrated suspension of the invention is preferably effected by the addition of chloride ions and cationic polymer. As shown in the examples below, the chloride ions and the polymer "cationic provide a product of surprisingly high stability that is easily resuspendable with intermittent stirring." Any solid sediment of the magnesium hydroxide suspensions of the present invention is soft, as opposed to a viscous impacted bottom solid that is formed without the addition of none of these materials Prior to the present invention, it was not known that the addition of chlorides to magnesium hydroxide suspensions could contribute to the stability and suspending properties of the product In fact, the chlorides are intentionally removed from the product. magnesium hydroxide suspensions based on brines and seawater by washing It is known that chloride ions accelerate different corrosion processes, however, chloride ions are added intentionally to the magnesium hydroxide suspensions according to the present invention, which results in an unexpected increase in stability and resuspension properties. Preferred sources of chloride ions for the practice of the invention include calcium chloride, sodium chloride, aluminum chloride, magnesium chloride, potassium chloride, io, ammonium chloride, hydrated species such as CaCl2-H2? CaCl2-2H2 ?, CaCl2.6H2 ?, MgC1.6H2 ?, AICI3.6H2O, etc. The preferred chloride salt is calcium chloride, which can be added for example as a CaCl2 brine or as ground pellets of dry CaCl2. According to one embodiment of the invention, the chlorides are charged to the hydrator before the hydration reaction. Chlorides tend to cause a larger particle size distribution leaving the hydrator, but larger agglomerates can be deagglomerated to produce a suspended product that is more stable than one without chlorides. For example, a hydrated pressurized suspension with a larger hydrate particle size distribution can be deagglomerated by passing it through one of the mechanical devices discussed above. The chloride ion concentrations used in the practice of the present invention preferably range from 0.01 to 2.5% by weight of dry MgO, preferably from 0.2 to 0.5% by weight of dry MgO. It is observed that the calcined magnesite reagent is inherently low in chlorides, with chloride concentrations in the order of 0.001 to 0.01,% by weight of dry MgO. Together with the chloride ions, the addition of the ionic polymer stabilizes the suspension by means of smergistic action and produces a material easily suspended.

It is known that cationic polymers are useful for adjusting viscosity within an acceptable range. However, before I prese. The invention was not known that cationic polymers could be used to improve the stability and resuspension properties of magnesium hydroxide suspensions. In fact, the fact that the cationic polymers are used to lower the viscosity, "*" suggests that the resulting product exhibits a decrease in stability. This is because in general it is known that solids sediment more quickly in fine viscous solutions than in more viscous solutions. However, the inventors have found, on the contrary, that the stability can be increased with such additives. The cationic polymer is preferably added after hydration, since the cationic polymers are generally unstable at the preferred hydration temperatures for the practice of the invention. Preferred polymers include cationic species, particularly preferred are polyamine polymers. The preferred anion for the polymer is the chloride ion. Preferred polymer concentrations vary from 0.01 to 2.0% by weight based on the weight of suspension, preferably from 0.1 to 0.20% by weight based on the weight of the suspension. Ideally, the polymer should produce a product with a viscosity of 50-900, preferably 50-300 centipoise.

It will be clear to one skilled in the art that almost an infinite number of processing facilities can be constructed to carry out the present invention. One of these facilities is shown in Figure 2. The different hydration and stabilization apparatuses shown in Figure 2 reflect the commonly available equipment of normal construction. Referring now to Figure 2, the calcined natural magnesite stored in the storage silo 11 passes through the valve 22 to the band weed feeder 12. The calcined natural magnesite introduced by means of the band weigher feeder 12 is mixed then with water from the treatment water supplier fl in a wet mixing unit 14 with an attached piston pump 13. An amount of chloride ions F is charged to the mixture of the - Calcined natural magnesite and water leaving the wet mixing tank unit 14 and the resulting mixture enters the hydrator 15, where a vapor load B is introduced to achieve the appropriate hydration temperature and pressure. Depending on whether the process is going to start or is operating continuously, the heat of reaction may be sufficient to maintain the temperature and pressure of the hydrator, eliminating the need for external steam. The resulting hydrated suspension then enters the vaporization vessel 17, where the vapor that is vaporized is passed through the reflux condenser 15. The steam is condensed with a cold water inlet Cl emerging as a cold outlet C2. The condensed vapor is returned to the hydrator 15 to reuse its sensible heat. The hydrated suspension is then pumped through the pump 19 or through the exchange! of heat 18, where the suspension is cooled by the cold water inlet attached to Cl, which emerges as a cold water outlet C2. 1-a cooled suspension that emerges from the heat intercooling 18 «then goes to the equalizer tank diffuser 20 where it is mixed with treatment / cooling water from the water stream to adjust the percent solids to the scale set as white, as required. The suspension of the diffuser equalizing tank 20 is then released where it is combined with cationic polymer of the stabilizing polymer input stream E, and the resulting mixture is introduced to a first diffuser 21. The suspension emerging from the first, --- • "diffuser 21 passes through intermediate equalizer tank 23 and enters second diffuser 22. The stabilized suspension finally emerges as an output stream H. Many additional treatment schemes will become readily apparent to those skilled in the art. For example, the scheme in Figure 2 is a continuous treatment scheme, but intermittent and semi-intermittent treatments can be made readily apparent. As another example, the scheme shown in Figure 2 comprises two separate diffusers, but several steps can be made through a single diffuser if desired.

Ib La1 ', different sources of chloride ions, cationic polymers, treatment equipment, treatment parameters, etc., for use in a particular application of the present invention, can be evaluated, for example, by using the of 7 and 14 days discussed below to determine the optimal treatment for the desired application. The invention will be clarified considerably with the following examples, which are intended to make only 10 copies of the use of the invention.

EXAMPLES Example 1 r5 Table IB summarizes a laboratory analysis of «Chinese calcined natural magnesite used in the examples. Of course, the percent scale of MgO and the major chemical impurities may vary a bit with natural magnesite calcined from other sources, or even within magnesite. calcined tornado from a single source. The above Ifl chart lists different scales of percent MgO and major chemical impurities that can be expected for a given sample of calcined natural magnesite. > ? TABLE IB Samples of magnesium hydroxide suspension containing 55 to 57% by weight of solids were produced from the calcined natural magnesite as follows: (1) A laboratory autoclave was charged with the calcined natural magnesite, water, and a solution of 23% CaCl 2 started in superlative amounts necessary to provide a chloride concentration of 0.5% by weight (based on MgO) and a product of 55-57% by weight of magnesium hydroxide solid (based on the suspension). (2) The mixture of step (1) was hydrated under pressure in the autoclave, heating and pressing the autoclave L8 at 7Kg / crn2 (164 ° C), maintaining at 7Kg / crn2 lasting 10 minutes, then cooling the sample to near ambient temperature for safe handling in the laboratory. However, in field practice, it may be necessary as small as 11 ° C of its cooling to avoid damage downstream of the equipment. The heating period can be approximately 50 minutes and cooling approximately approximately 80 minutes. Therefore, the "" "'total residence time in the autoclave was 140 minutes. (3) 1000 pprn (pure polymer base, aggregate based on weight of suspension) of cationic polymer (Nalco) was added. 91DA054, an aqueous solution of polyamines) to the product from step 2 while mixing at low speed with a dispersion sheet? Har. (4) Then the suspension was treated through an APV Gaulin Model 15MR-8TR laboratory furnace, and the Our samples were removed after one, two, and three phases.The samples retained after hydration (without cationic polymer and treatment in the homogenizer) are compared based on the particle size of the magnesium hydroxide in Table 2. with samples of the product that had been provided with cationic polymer and treated with the furnace The polymer was added only to the stabilized products The distributions of particle size in all cases were measured with a Micromeritics Sedigraph 5100.

PICTURE It is evident from table 2 that the particle size distribution is improved with respect to the stability of the suspension passing through the homogenizer. The previous samples were subjected to stability tests of 7 and 14 days and the results summarized in tables 3 and 4, respectively. Spill tests were carried out using 240 ml normal cylindrical polycarbonate bottles (5 c OD x 13 c height). For many applications, LdS resuspension properties are much more critical than the homogeneity of the long-term suspension, because intermittent agitation can be provided at the point of api lation. The limiting period for homogeneity for suspension is the time of transportation to the application site, which may vary from as little as hours to several hours.

TABLE 3 TABLE 4 The results presented in tables 3 and 4 show that two stabilization phases resulted in a soft sediment even after 7 and 14 days of undisturbed sedimentation. Without adequate stabilization, the magnesium hydroxide solids settle and form a highly viscous impacted settlement. The presence of chlorides is also important for the final product. In tests too developed in suspension samples that were not provided with the fluorides, only the clear layer of water separation is poured after 7 days of static sedimentation. In the majority of cases where chloride was not added, a non-pourable sticky layer of bottom solids is formed within the first 24 hours of undisturbed sedimentation.

-, Obviously, this condition makes the hydroxide free of magnesium. The effect of chlorides on the particle size distributions for magnesium hydroxide made with and without 0.5% by weight of chlorides (based on dry MgO) added to the hydrator prior to hydration was also investigated. The results are summarized in Table 5 for samples as they come out of the hydrator (without polymer treatment or ovenification). Table 5 clearly shows that the addition of chlorides increases the particle size of the Mg (0H) 2 product apparently resulting from agglomeration. However, the particle size of the sample treated with chloride was almost returned to the treated levels without chloride after only one passage through the diffuser at 105 Kg / cm 2 (see Table 2, column 3).

TABLE 5 Example 2 Magnesium hydroxide suspension samples were prepared using the same formulation as in Example 1, but a different mechanical diffuser was used. A Silverson high-cut mixer (Laboratory batch mixer) was used in place of the APV Gaulin 15MR-8TA homogenizer. Different replaceable mixing heads were used in the Silverson mixer to determine those that produce an acceptable magnesium hydroxide suspenetion product. Samples of 250 ml of suspension were treated for 5 minutes with the laboratory batch mixer. The product samples are described below in Tables 6 and 7. The percent of solids varies in these samples from 57 to 62% by weight. In both table, samples with and without cationic polymer have been treated with the high speed mixer using the different mixing heads. The product samples were characterized by different measurements that included percent solids and 7-day spill tests. In addition, after 5 months of undisturbed sedimentation, the samples were shaken slightly to resuspend the settled solids and the viscosity was measured by means of the "roos fiener". Finally, the particle size distribution was also investigated. As can be observed for some of the samples, the qualitative determination of the resuspension property, as determined by testing the bottom solids with a glass stirring rod, was favorable despite the pourable weight fractions less than 80 %.

Table 6 £ J1 ? fi Notes and comments in Table 6: (L) After undisturbed sedimentation for 0 months, the samples were shaken slightly. The viscosity was then determined by means of a Brokfield viscosimeter, RVT, # 2 needle at LOO rpm. (2) Layer of sedimented solids (5.7 c) very pourable and easily resuspendable by application of slight agitation; will < .that the relatively low fraction of dumping is due to thixotropy or plastic rheology of Bmgham. Very light cutting / agitation makes pourable solids pourable. (3) Bottom suspension layer (1.7 cm) very pourable by application of light cutting without formation of viscous on the bottom. Resusable. (4) Bottom suspension layer (1.7 cm) is easily poured by light cutting application; Little formation of viscose - in the background. Very light thickening of the layer of solids sedimented. (5) Bottom suspension layer (3 cm) is easily poured by light cutting application; Very little viscous formation in the background. (6) Bottom suspension layer (6.8 c) is easily poured by light cutting application. Thickening light around the walls of the container, but there is no formation of viscous in the bottom. (7) Very soft bottom suspension layer (6 crn) with no viscose formation on the bottom; easily resuspended and made 2 1 The thickening on the walls of the container is proof of spillage. (8) Bottom suspension layer (< 3.8 crn) very soft with slight thickening on the walls of the pour test container; easily resuspended by application of light cutting / ag11acion. ("3) Bottom suspension layer (1.3 c) was very thin with slight cut. There is no formation of viscous in the bottom.

Caudro 7 In the eight samples shown in items 6 and 7, it is evident that the qualitative tests and the viscosity measurements at 5 months (5 months of undisturbed sedimentation followed by light agitation) ) that with intermittent and moderate agitation (from 3 to 5 on an agitation scale of 1 to 10) to resuspend sedimentary solids, the suspension of magnesium hydroxide is useful for many applications. Due to its quantitative nature, it does not recognize that the suspension is pumpable with the bottom solids that are quickly resuspended after applying a light cutting force, to overcome, for example, Bmgham plasticity or deformation velocity 0 of resistance to flow Table 7 also clearly shows the beneficial results obtained by the addition of cationic polymer, for example, compare the 7-day percentages for samples with polymer (92.6% by weight). that) and without polymer (27.75 by weight) when using the fine-perforated emulsion sieve in relation to the Silverson mixer. The particle size distributions summarized in Table 7 show that the aforementioned increase is stably observed by addition of cationic polymer and is not due to a change in the particle size distribution of the resulting suspension.

Example 3 Oe carried out laboratory studies to investigate the apparent kinetics of the hydration reaction of calcined magnesite. Although the details of the reaction mechanisms could not be established with certainty, speed limiting phenomena based on approximate energies of activation can be recognized. The results of these tests can be used to contrast the disadvantages of atmospheric hydration with the effectiveness of pressure hydration. The results of these studies are summarized in the flrrhenius graph of Figure 1. From Figure 1, it was determined that the slope to the left of the vertical solid line was approximately -350 ° K, which corresponds to? an apparent activation energy of approximately 2.9 kJ / g-rnol. Since the apparent activation energy was less than about 4 kJ / g-mol, it is believed that pore diffusion and mass transfer control the reaction rate in this domain. On the other hand, the slope of the data points to the right of the vertical line is approximately 3600 ° K, corresponding to an apparent activation energy of approximately 30 kJ / g-rnol. Since the activation energy is greater than about 12 kJ / g-mol, it is believed that the intrinsic surface reaction controls the kinetics in this regime. In summary, based on the experimentally determined values of the apparent activation energy, it is believed that the speed of hydration under atmospheric pressure is the calcined magnesite in question is limited by pore diffusion and mass transfer. at temperatures between about 60 ° C and 82 ° C. In terms of process and energy economy, this is a disadvantage since in general, the process speeds limited by mass diffusion or pore transfer increase only as a fractional power of the temperature. The total result is a decreased return on higher hydration temperatures and external energy costs. No claims are made in the present invention with respect to the understanding of the fundamental mechanism of the effectiveness of hydration under pressure in decreasing the hydration time. However, it seems likely that the , - super-atmospheric pressures can provide the driving force (differential pressure) to "pump" water through the labyrinth of pores in which the vast majority of the surface of reactive MgO resides. With the pore diffusion and the expired mRNA transfer resistors, the intrinsic surface reaction (chemical conversion of MgO to Mg (0H) 2) probably controls the rate of hydration. In this situation, the reaction rate generally increases exponentially with the increasing hydration temperature. The higher rate of return on external energy costs and economy of the process are thus likely advantages of low pressure under atmospheric hydration. Other embodiments of the invention will be apparent to those skilled in the art from consideration of this specification or practice of the invention described herein. It is intended that the specification and the examples be considered only as exemplary, with the scope and real spirit of the invention indicated by the following - * 'and? Indications.

Claims (2)

1. ; j NOVELTY OF Lñ INVENTION CLAIMS A process for the production of a suspension of stabilized magnesium hydroxide which comprises the steps of providing chloride ions to a mixture comprising calcined natural magnesite and water, and then hydrating under pressure the mixture to provide a precursor suspension of magnesium hydroxide hydrated under pressure; pr-oveer polymer catiomco to the precursor suspension of magnesium hydroxide hydrated under pressure; and deagglomerating said precursor suspension of hydrated magnesium hydroxide under pressure to provide a suspension of deagglomerated and stabilized magnesium hydroxide comprising 50 to 65% by weight of solids. 2. The method according to claim 1 characterized in that said chloride ions are provided in an amount ranging from 0.01 to 2.5% by weight of dry MgO. 3. The method according to claim 1 further characterized in that said chloride ions are provided in an amount ranging from 0.2 to 0.5% by weight of dry MgO. 4. The method according to claim 1 further characterized in that said chloride ions are provided by one or more of, calcium chloride, sodium chloride, ammonium chloride, potassium chloride, magnesium chloride, ammonium chloride and c hydrated from them. 5. The method according to claim 1 further characterized in that said chloride ions are provided from calcium chloride. 6. The method according to claim 1 further characterized in that at least a portion of said chloride ions are provided by means of associated ammoniums in said cationic polymer. 7. The method according to claim 1 further characterized in that said cationic polymer is provided in an amount ranging from 0.01 to 2.0% by weight, of the weight of the suspension. 8. The method according to claim 1 further characterized in that said cationic polymer is provided in an amount ranging from 0.1 to 0.2 X by weight, of the weight of the suspension. 9. The method according to claim 1 further characterized in that said cationic polymer is a polymine. 10. The method according to claim 1 further characterized in that said hydration or pressure is carried out at pressures ranging from 0.07 to 10.
2. 2 Kg / cm2. 11. The method according to claim 1 further characterized in that said hydration under pressure is carried out at pressures ranging from 1.7 to 7 Kg / cm2. 12. The method according to claim 1 further characterized in that said suspension of the second comprises 50 to 65% by weight of additives. 13. The method according to claim 1 further characterized in that said deagglomerated suspension comprises from 57 to 62% by weight of solids. 14. - The method according to claim 1 also characterized in that said calcined magnesite is "finely divided and is able to pass through a sieve of bad l 2. 15. The method according to claim 1 further characterized in that said calcined magnesite is finely divided and capable of passing through a 100 mesh screen. The method according to claim 1 further characterized in that the Exothermic heat associated with the hydration step recovers.