AU2003246312A1

AU2003246312A1 - A long term-stabilized suspension for covering iron mineral, a process for its production and application

Info

Publication number: AU2003246312A1
Application number: AU2003246312A
Authority: AU
Inventors: Ricardo Benavides-Perez; Jose-Gertrudis Bocanegra-Rojas; Cesar-Emilio Zertuche-Rodriguez
Original assignee: Servicios Industriales Penoles SA de CV
Current assignee: Servicios Industriales Penoles SA de CV
Priority date: 2003-06-18
Filing date: 2003-09-16
Publication date: 2005-01-13
Also published as: CA2470286A1; BR0302076A; RU2004118102A; MXNL04000047A; AU2006202581B2; AU2009200667A1; RU2374036C2; AU2006202581A1

Description

A LONG TERM-STABILIZED SUSPENSION FOR COVERING IRON MINERAL, A PROCESS FOR ITS PRODUCTION AND APPLICATION.

BACKGROUND OF THE INVENTION.

A. FIELD OF THE INVENTION.

This invention relates to a stabilized magnesium hydroxide suspension and more particularly to a long term-stabilized magnesium hydroxide suspension, having a stability of at least three months without substantially settling and without forming a hard solid substrate for covering briquettes, particles, pellets or powder of iron mineral and also of several materials in order to avoid the adhesion between each other and thus an agglomeration of briquettes, particles or pellets when stored or submitted to a heat treatment at a high temperature, on Direct Reduction Furnace or Blast Furnace, and a process for its production and application.

B. DESCRIPTION OF RELATED ART.

In some treatments of briquettes, particles or pellets of materials such as dolomite, magnesite, iron ore, etc., in which it is necessary to sinter a plurality of briquettes, particles or pellets inside furnaces at high temperatures, exists a tendency of said briquettes, particles or pellets to adhere to each other producing an agglomerate or clustering of briquettes.

One of these treatments is the direct reduction iron of mineral iron pellets inside a furnace at high temperatures, and also in production of steel in a Blast Furnace. When the sintering is complete, usually, some or all of the pellets are agglomerated in a solid mass, forming clustering, making necessary to apply a mechanic shock thereof in order to separate each pellet form the agglomerate.

In order to avoid the agglomeration of the pellets during sintering, there were tested several compounds which must be applied to the pellets surface before the sintering process. Among these compounds, there were tested slurries of magnesium hydroxide, calcium hydroxide, bauxite and even cement, but none of these compounds produced the expected results and had some disadvantages when used for the purpose above referred. Some of the principal disadvantages, in common with all the compounds previously mentioned, are that the compounds must have to be continuously stirred in order to maintain a constant concentration, and that once the compound was applied to the pellets, the compounds proved to have a very bad adherence to the briquettes, particles or pellets, since the cover, once it dries, tends to separate from the particles only by the movement produced by the normal manipulation of the particles.

The magnesium and particularly the magnesium hydroxide have a great number of applications, such as neutralizer for acid effluents, heavy metals removal, to make easy slag removal, as well as for pharmacological purposes and paste detergent production.

The typical methods for the production of magnesium hydroxide are: Production of magnesium. hydroxide by reacting calcined dolomite or limestone with sea water or magnesium chloride brines.

Production of magnesium hydroxide by thermal decomposition of magnesium chloride brines.

Production of magnesium hydroxide by burning natural magnesite (magnesium carbonate) in order to obtain magnesium oxide, which afterwards is hydrated with water in order to convert into magnesium hydroxide.

Production of magnesium hydroxide by hydrating magnesium oxide.

Production of magnesium hydroxide by reacting sodium hydroxide with magnesium sulfate (Epsom Salt).

Production of magnesium hydroxide from sodium hydroxide and magnesium chloride brines.

From ammonia or ammonium hydroxide with magnesium chloride brines.

The trials firstly started by using a magnesium hydroxide paste obtained by: mixing burned dolomite and magnesium chloride brine in order to obtain a reaction between both compounds, washing and filtering the product of said reaction until to obtain a suspension having a high covering power (surface area covered by each gram of substance), and a viscosity of approximately 1,000 centipoises, which may be pumped by any kind of pumping means such as a centrifuge pump, a diaphragm pump or a peristaltic pump. Said suspension was subsequently conditioned by the incorporation of additives for improve the fluidity of the suspension, and to resist the transportation of pellets or briquettes without to unglue of said pellets or briquettes.

When is necessary to send the magnesium hydroxide paste or suspension to places far away from the Production Plant, as well as for further processing, it is necessary to store a magnesium hydroxide suspension for long terms in a storage container. Under such circumstances, the solid particles of the suspension normally tend to settle down producing a hard solid substrate as a hard cake in the bottom of the storage container, which is often very difficult to remove. The remaining suspension under such circumstances, results useless because it doesn't have the required magnesium hydroxide concentration or the required particle size in suspension and therefore it has to be poured from the storage container and discarded in order to remove the hard solid cake from the bottom of the container, increasing costs and high raw material loses.

Therefore, it would be highly desirable to produce a magnesium hydroxide suspension which can be used for covering briquettes, particles, pellets or powder iron and several kinds of materials in order to avoid the agglomeration of a plurality of particles when stored or submitted to a heat treatment on Direct Reduction Furnace or Blast Furnace, and also having the product good adherence properties and which can be stored for long terms without substantially settling and cake formation.

U. S. patent No. 4743,396 disclose a magnesium hydroxide slurry, for very specific purposes, having a concentration of 50% by weight or higher of Mg(OH) 2 and 0.1 to 5% of a sulfomethylated polyacrylamide which allow the slurry to be pumped through pipelines.

Furthermore, U. S. patents No. 4'164,521 (involving the use of a polyanionic polymer containing at least 50% mole of repetitive units derived from an acrylic acid and a polycathionic polymer); 4'412,844 (involving the use of 1.0 to 8.0% of a water dispersible, oil-soluble emulsifying agent); 4'155,741 (including an encapsulated material); and 3'957,674 (including at least 0.5% of sodium naphtalen-sulfonate), all of them disclose suspensions which when stored, showed some settlement but with the difference that when they are agitated, they recover their concentration and physical properties, but all of them do not mention a long term stability of about three months.

Because of its nature, a stabilized suspension can be more easily pumped than one which is not stabilized because the non-stabilized suspension tends to form thickened particles and solid substrates complicating or even impeding to be pumped.

PCT published patent application No. PCT/AU95/00446 discloses an example of a magnesium hydroxide suspension having both characteristics of pumping and stability for about seven days without substantial agitation.

However, up to now, there is no suspension in the market having a long term stability of about three months and which can be used for covering briquettes, particles, pellets or iron powder.

In accordance with the present invention, this document describe a 50-70% magnesium hydroxide suspension, called "Femag HL" having a solid content between about 52% to 72%, a water content of 28% to 48%, a viscosity of about 1000 centipoises a mean particle size of about 2 microns, a pH value greater than 10.5, an equivalent magnesium oxide content of 34% to 48%, a specific gravity of 1.40 to 1.60, and including one or more anionic polyelectrolytes, at a concentration of at least 25%, in an amount of about 0.5 to 2.5% in dry basis, and an compound such as applicated to the suspension didn't unglue to the pellets or briquettes, during the transportation process, at a concentration of at least 30% in an amount of 0.5 to in dry basis, showing a stability of at least three months without substantial agitation, and which be used for covering briquettes, particles, pellets or powders of iron mineral and several kinds of materials in order to avoid the agglomeration thereof when treated at high temperatures on Direct Reduction Furnace or Blast Furnace; is provided by a new process which will be disclosed below.

Because of the mean particle size (of about 2 microns) in combination with the use of the anionic polyelectrolytes, the three months stability of the "Femag HL" product is guarantee. In fact this product requires only somewhat (not vigorous) agitation once a day, in order to keep it fluid without experimenting particle thickening or substantially settlement forms a hard cake.

Regarding the process for producing such magnesium hydroxide suspensions, these can be produced by adding a soluble alkaline material to an aqueous salt of magnesium at atmospheric pressure and at a temperature from near ambient temperature to about 1000C.

U. S. patent No. 5'487,979 disclose a process for the production of magnesium hydroxide suspension, by pressure hydrating burnt natural magnesite in the presence of chlorine ions and a cationic polymer (polyamide).

U. S. Patents Nos. 5'143,965; 4'548,733; 4'430,248; 4'230,610; 4166,040; and 4'166,041 disclose representative processes for producing magnesium hydroxide suspensions, by using ultrasonic mixing steps and some cationic polymers such as the ammonium metacriloxiethyl-trimethyl-methasulfonate and the polyacrylic acid, among others, showing more or less stability, but none disclosing a stability in the range of about three months.

It is therefore highly desirable to provide a new process for producing a magnesium hydroxide suspension which can be used for covering briquettes, particles, pellets or powders of iron mineral and also of several kinds of materials in order to avoid the agglomeration of a plurality of briquettes, particles, pellets or powders when stored or submitted to a heat treatment on Direct Reduction Furnace or Blast Furnace, and that in addition, could be stored for long terms without substantially settling and cake formation.

The process to manufacture the "Femag HL", in accordance with the present invention, comprising basically produce a Mg(OH) 2 paste, by means of different raw materials, washing and repulping the paste in order to reduce the soluble salts; 7 reduce the particle size until approximately 2 microns average; and include additives to improve the fluidity and stability of the suspension, and compounds that improve the resistance to the transportation of pellets or briquettes without unglue of said pellets or briquettes; and finally to provide a long term stability to the suspension which has a stability of at least three months without substantial agitation, and which do not settle down forming a hard solid cemented cake, which can be used for covering briquettes, particles, pellets or powders of iron mineral and also several kinds of materials, in order to avoid the agglomeration of a plurality of briquettes, particles, pellets or powders when stored or submitted to high temperatures on Direct Reduction Furnace or Blast Furnace; said suspension being applied to said briquettes, particles, pellets or powders by. means of a plurality of spraying nozzles, applying the "Femag HL" on the pellets surface, which are passed under said spraying nozzles by means of a conveyor belt, or any other way adequate to cover surface of briquettes, particles, pellets or powders.

The "Femag HL" suspension has a high covering power, of minimum 5 m I2/g, and it can be applied on the surface of the briquettes, particles, pellets or powders, as a diluted suspension at different concentrations between 4 and Furthermore, the "Femag HL" suspension adheres strongly to the briquettes, particles, pellets or powders so it does not separate from the surface of the briquettes, particles, pellets or powders during the transportation, manipulation and different treatment phases.

By covering the briquettes, particles, pellets or powders with "Femag HL" there are obtained the following benefits: Lesser maintenance costs of conveyor belts, rollers, sieving devices, etc.

Easier product manipulation procedures, because it's a suspension.

8 Lesser emanation of hazardous and polluting elements to the environment.

When the "Femag HL" is used for covering iron ore pellets to be treated by high temperature in order to reduce the iron ore, it is obtained high quality reduced iron pellets.

High productivity on Furnaces, working to more than 1,000 'C.

Improving the slag fluidity, and impurities removal.

SUMMARY OF THE INVENTION.

It is therefore a main objective of the present invention, to provide a magnesium hydroxide suspension, calcium hydroxide suspension, dolomite suspension, bauxite suspension, etc. for covering briquettes, particles, pellets or powders of iron mineral and also of several kinds of materials, for avoiding its agglomeration thereof when treated at high temperatures on Direct Reduction Furnaces or Blast Furnace, having good adherence properties and a high covering power of the suspension.

It is another object of the present invention, to provide a stable magnesium hydroxide suspension of the above disclosed nature, having a stability of at least three months withodt substantial agitation, having a very low tendency to settle down and forming a hard cemented cake.

It is still main object of the present invention, to provide a stable magnesium hydroxide suspension, of the above disclosed nature, having an Mg(OH) 2 content of about 50% to It is also a main objective of the present invention, to provide a stable magnesium hydroxide suspension, of the above disclosed nature, having a solid content of about 52% to 72%.

9 it 'is still a main objective of the present invention, to provide a stable magnesium hydroxide suspension, of the above disclosed nature, having a mean particle size of about 2 microns.

It is jet a main objective of the present invention, to provide a stable magnesium hydroxide suspension, of the above disclosed nature, having a viscosity of about 1000 cp. (less than 1500 a pH value over 10.5, an equivalent magnesium oxide content of 34% to 48%, a specific gravity of about 1.4 to 1.6 a water content of about 28% to 48%, an anionic polyelectrolyte, at a concentration of at least 25%, in an amount of about 0.5 to 2.5% in dry basis, and a compound type styrene acrylic emulsion, at a concentration of at least 30% in an amount of 0.5 to in dry basis, which requires only somewhat of movement once a day to keep its fluid nature.

It is also a further main objective of the present invention, to provide a process to produce an magnesium hydroxide suspension for covering briquettes, particles, pellets or powder of iron mineral and also of several kinds of materials, for avoiding its agglomeration thereof when treated at high temperatures on Direct Reduction Furnace or Blast Furnace, having good adherence properties and a high covering power of the suspension, and having a stability of at least three months without substantial agitation, having a very low tendency to settle down and forming a hard cemented cake, including conditioning the magnesium hydroxide paste at a size of about 2 microns, incorporating an anionic polyelectrolyte, at a concentration of at least 25%, in an amount of about 0.5 to 2.5% in dry basis, and adding an compound type styrene acrylic emulsion, at a concentration of at least 30% in an amount of to 5% in dry basis.

These and other objectives and advantages of the present invention will be apparent to those persons having ordinary skill in the art, from the following description of the invention, referring to specific examples of practice.

DETAILED DESCRIPTION OF THE INVENTION.

The invention will be described in the following by making reference to a preferred embodiment and some specific examples of the process and materials used to produce the "Femag HL" magnesium hydroxide suspension which can be used for covering briquettes, particles, pellets or powder of iron mineral and also of io different materials, in order to avoid the agglomeration thereof when treated at high temperatures on Direct Reduction Furnace or Blast Furnace, and having a stability of at least three months without substantial agitation, and which has a very low tendency to settle down forming a hard solid cemented cake.

The magnesium hydroxide Mg(OH) 2 used as a raw material to produce "Femag HL" can produce it from the next different Processes: Production of magnesium hydroxide by reacting calcined dolomite or limestone with sea water or magnesium chloride brines Production of magnesium hydroxide by thermal decomposition of magnesium chloride brines.

Production of magnesium hydroxide by burning natural magnesite (magnesium carbonate) in order to obtain magnesium oxide which afterwards is hydrated with water in order to obtain magnesium hydroxide.

Production of magnesium hydroxide by hydrating Magnesium Oxide Production of magnesium hydroxide by reacting sodium hydroxide with magnesium sulfate or Epsom salt.

I

From ammonia or ammonium hydroxide with magnesium chloride brines.

The magnesium hydroxide of the any of the above reactions, it's one of the raw materials necessary for the stable suspension of magnesium hydroxide named "Femag HL", and comprising: washing the magnesium hydroxide; filtering and repulping the magnesium hydroxide solids in order to obtain less than 0.6% of chloride values; dispersing the agglomerated solid particles in a dispersing equipment for a minimum 5 minutes; adding one or more anionic polyelectrolytes at a concentration of at least in an amount of about 0.5 to 2.5% in dry basis; conditioning and micronizing the magnesium hydroxide solids in order to reduce the particle size until approximately 2 microns; adding an compound type styrene acrylic emulsion, at a concentration of at least 30% in an amount of 0.5 to 5% in dry basis; dispersing the product from the above step; and storing the so obtained "Femag HL" suspension in a storing tank wherein it can be stored for at least three months without substantially agitation without experimenting tendency to settle down forming a hard solid cake in the bottom of the storage tank, nor particle thickening of the solid particles of the suspension and which can be used to cover briquettes, particles, pellets or powders of iron mineral and different materials.

12 Furthermore, although the stable magnesium hydroxide suspension with particle size of 2 microns present less tendency to settle down, this alone still does not guarantee the long term stabilization which is desired and therefore, the anionic polyelectrolyte is necessary for the obtainment of the desired stability in combination with the particle size.

The anionic polyelectrolytes are macromolecules originated from monomeric units with ionizable groups as opposed to a simple electrolyte such as the sodium chloride in which the cathion Na+ and the anion CI are relatively small and similar in size. A polyelectrolyte is characterized by a macro ion which is the vertebral column (a large ion and similar number of charged groups connected by bonds) and an equivalent number of independent small charges and of opposite charge. Because of their high molecular weight, these are also known as dispersant resins.

Examples of anionic polyelectrolytes are the sodium polyacrylate, the ammonium poly(styrene/maleate), among others.

The following are examples of the specific process for obtaining the magnesium hydroxide suspension "Femag HL", in accordance with the present invention: EXAMPLE 1 It was prepared a sample of "Femag HL" and was divided in three portions.

Each portion was diluted with good quality water in order to obtain concentrations of 1, 2 and Adhesion tests were carried out for each of the samples by covering iron mineral pellets with each of the portions. An additional adhesion test was carried out using a sample of cement at a concentration of 15% for comparison purposes, as well as another adhesion test using a control sample having no adhesion additives.

13 The 5 samples were placed inside a laboratory reactor in order to carry out the iron mineral reduction (change of iron oxide to metallic iron) and the following results were obtained: Sample of clustering Control, without additives 87 Cement suspension at 15 "Femag HL" suspension at 5 4 "Femag HL" suspension at 2 "Femag HL" suspension at 1 19 The best results were obtained with the "Femag HL" suspension at 5% due to the lesser quantity of agglomerated pellets produced at the reactor exit, and the "Femag HL" has better results even at against cement at EXAMPLE 2 It was prepared a sample of "Femag HL" and was divided in six portions.

Two portions were diluted with water in order to obtain a concentration of 2%, another two portions were diluted at a 3% and the last two portions were diluted at a Each portion was used to cover iron mineral pellets. Three samples were maintained with 2, 3 and 5% of concentration, and three samples were air blew in order to eliminate the water excess and to determine if the adherence to the pellets decreases.

The 6 samples were placed inside a laboratory reactor in order to carry out the iron mineral reduction and the following results were obtained: 14 Sample of clusterinq "Femag HL" suspension at 2 "Femag HL" suspension at 2 air blew 19 "Femag HL" suspension at 3 11 "Femag HL" suspension at 3 air blew 14 "Femag HL" suspension at 5 6 "Femag HL" suspension at 5 air blew 11 It can be concluded that by air blowing the samples before placing them inside the reactor, it is loosed only a little bit the effectiveness of the "Femag HL", but obtaining low level of agglomerated pellets.

EXAMPLE 3 There were prepared four samples of the "Femag HL" suspension adding different quantities of the styrene acrylic compound to each sample, from 2% to The four samples were diluted with water until obtain a final concentration of which were used to cover iron mineral pellets. Subsequently the pellets covered with the samples of "Femag HL" were placed inside a reactor in order to carry out the iron reduction and the following results were obtained regarding to the adherence of the "Femag HL" to the pellets. It was also evaluated as a control sample a suspension of cement at a concentration of 15% without any additive.

Sample of clustering "Femag HL" suspension with 2% of additive 14 "Femag HL" suspension with 3% of additive 9 "Femag HL" suspension with 4% of additive 8 "Femag HL" suspension with 5% of additive 8 Cement suspension at a 15% without additive 28 From the above experiment it can be concluded that the lesser percentage of remnant agglomerates were obtained with 4% and 5% of additive compound.

EXAMPLE 4 There were prepared three samples of the stable "Femag HL" suspension, using as a raw material natural magnesite (magnesium carbonate) which was burned at a temperature of 9000C in order to obtain magnesium oxide.

After obtaining the magnesium oxide, water was added to said magnesium oxide in order to obtain magnesium hydroxide and to adjust its concentration at a The suspension obtained was divided in a first a second and a third portion, to which were added 3% and 5% of the styrene acrylic compound respectively, and diluted with water in order to obtain a magnesium hydroxide concentration of Each sample was used to cover different iron pellets which afterwards were placed inside a laboratory reactor in order to carry out an iron reduction at a temperature of 950'C.

16 As a test or control sample, other iron pellets were covered with a cement suspension at a 15% of concentration and placed inside the same reactor. The following results were obtained: Sample of clustering "Femag HL" suspension with 1% of additive "Femag HL" suspension with 3% of additive 9 "Femag HL" suspension with 5% of additive 8 Cement suspension at a 15% 26 The best results were obtained with the "Femag HL" suspensions having a 3% 0io and 5% of additive, showing also that "Femag HL" suspension can be produced with another different raw material.

Finally it must be understood that the long term-stabilized "Femag HL" suspension, or calcium hydroxide suspension or bauxite suspension, etc. for covering briquettes, particles, pellets or powder iron and the process for its production and application of the present invention, is not limited exclusively to the above described and illustrated embodiments and that the persons having ordinary skill in the art can, with the teaching provided by this invention, make modifications to the long term-stabilized magnesium hydroxide suspension for covering iron mineral and the process for its production and application of the present invention, which will clearly be within the true inventive concept and scope of the invention which is claimed in the following claims.

Claims

1. A long term stabilized magnesium hydroxide suspension, called "Femag HL" which can be used for covering briquettes, particles, pellets or powder of iron mineral, and also of several kinds of materials for avoiding its agglomeration thereof when treated at high temperatures on Direct Reduction Furnace or Blast Furnace, having a solid content of about 52% to 72%; a water content of about 28% to 48%; a viscosity of about 500 to 1,500 cp.; an average particle size of about 1 to 3 microns; a Mg(OH) 2 content of about 50% to 70%; a pH value of over 10.5 an equivalent magnesium oxide content of 34% to 48%; a specific gravity of 1.4 to 1.6; and including at least one anionic polyelectrolyte, at a concentration of at least 25%, in an amount of about 0.5 to 2.5% in dry basis and an compound that improve the resistant to handle the pellets or briquettes during the process, at a concentration of at least 30% in an amount of 0.5 to 5% in dry basis; which can be stored for at least Is three months without substantial agitation, and without experimenting substantial settlement and solid hard substrate formation.

2. The long term stabilized magnesium hydroxide suspension called "Femag HL" as claimed in claim 1, wherein the anionic polyelectrolyte is selected from the group consisting in sodium polyacrylate and ammonium polystyrene/maleate.

3. The long term stabilized magnesium hydroxide suspension called "Femag HL", as claimed in claim 1, wherein the compound to improve the handle of the pellets or briquettes during the process is selected from the group consisting in styrene acrylic emulsions.

4. A process for the production of long term stabilized magnesium hydroxide suspension called "Femag HL" which used in its elaboration magnesium hydroxide solids, of any of the following Processes: Production of magnesium hydroxide by reacting calcined dolomite or limestone with sea water or magnesium chloride brines Production of magnesium hydroxide by thermal decomposition of magnesium chloride brines. Production of magnesium hydroxide by burning natural magnesite (magnesium carbonate) in order to obtain magnesium oxide which afterwards is hydrated with water in order to obtain magnesium hydroxide. Production of magnesium hydroxide by hydrating Magnesium Oxide Production of magnesium hydroxide by reacting sodium hydroxide with magnesium sulfate or Epsom salt. Production of magnesium hydroxide from sodium hydroxide and magnesium chloride brines. From ammonia or ammonium hydroxide with magnesium chloride brines.

A process for the production of a long term stabilized magnesium hydroxide suspension called "Femag HL", from magnesium hydroxide solids, and comprising: a) washing the magnesium hydroxide solids; b) filtering and repulping the magnesium hydroxide solids in order to obtain agglomerated solid particles having less than 0.6% of chloride values; c) adding at least one anionic polyelectrolyte, at a concentration of at least in an amount of about 0.5 to 2.5% in dry basis. d) dispersing the agglomerated solid particles in a dispersing equipment; 19 e) grinding the dispersed product, to reduce the particle size so that at least the 50% of the ground product have a particle size of about 2 microns; f) adding an compound type styrene acrylic emulsion, at a concentration of at least 30% in an amount of 0.5 to 5% in dry basis; and g) dispersing the product of step f) in a dispersing equipment.

6. The process as claimed in claim 5, wherein the step d) is carried out in a minimum 5 minutes.

7. The process as claimed in claim 5, wherein the step e) is carried out in a sand mill using high density balls, as milling media.

8. The process as claimed in claim 5, wherein the anionic polyelectrolyte is selected from the group consisting in sodium polyacrylate and ammonium polystyrene/maleate. DATED THIS SIXTEENTH DAY OF SEPTEMBER 2003 SERVICIOS INDUSTRIALES PEFIOLES S.A. DE C.V. BY PIZZEYS PATENT AND TRADE MARK ATTORNEYS