WO2021079368A1

WO2021079368A1 - Novel flux / mineralizer for cement clinkering and method of manufacture thereof

Info

Publication number: WO2021079368A1
Application number: PCT/IL2020/051108
Authority: WO
Inventors: Tamer ANDREA; Nadav DOBRIN; Sharon Krumbein Rubin; Simon VOLIN
Original assignee: IMI Tami Institute for Research and Development ltd
Priority date: 2019-10-24
Filing date: 2020-10-22
Publication date: 2021-04-29

Abstract

This invention discloses a method for producing a flux / mineralizer for cement clinkering that contains CaF₂ and other residues of fluoride salts. The flux / mineralizer is produced by mixing an aqueous solution of hexafluorosilicic acid with one or more carbonates or carbonate evaporates such as limestone, marl, chalk, dolomite, oil shale, etc. In contrast to methods known in the art, the inventive method does not require any step of separation of silica, purification of the reaction product, or pH adjustment. A novel flux / mineralizer produced by the method is also disclosed.

Description

NOVEL FLUX / MINERALIZER FOR CEMENT CLINKERING AND METHOD OF

MANUFACTURE THEREOF

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Pat. Appl. No. 62/925,249, filed 24 October 2019.

FIELD OF THE INVENTION

[0002] This invention relates generally to fluxes and mineralizers for use in cement production and methods of manufacture thereof. It relates particularly to fluxes and mineralizers produced from the reaction of hexafluorosilicic acid and carbonates.

BACKGROUND OF THE INVENTION

[0003] As awareness of the impact of human activities on the environment has grown, there has been an increasing interest in reducing the amount of energy used in, and the amount of pollution produced by, industrial processes. In the specific case of cement production, for example, typical cement kiln operating at a temperature of 1450 °C requires about 1600 kcal per kg of cement. Thus, even a reduction of 100 °C in the kiln burning temperature could result in an energy savings of on the order of 150 kcal per kg of clinker; see, for example, Energy Conservation Potential in the Cement Industry (Conservation Paper No. 26); Washington, D.C.: Federal Energy Adminstration, 1975.

[0004] Fluxes and mineralizers have long been known in the cement industry, especially in the white cement industry, as additives that can reduce the clinkering temperature and accelerate the rate of the clinkering process, thereby reducing the energy required in the kiln. A "flux" is a substance that lowers the reaction temperature of a reaction or the melting point of a substance to which it is added. "Mineralizer" is a term used in the art to describe a substance that promotes the formation of clinker compounds without participating directly in the reactions that form them. Mineralizers can also lower the temperature at which the clinker melt begins to form, so in practice, there is not necessarily a distinction between two; see, for example, http://www.iipinetwork.org/wp-content/Ietd/content/improved-bumability-using- mineralizers .html .

[0005] Metallurgic fluorspar (60 - 96% CaFi) has long been used as a flux and mineralizer for cement clinkering. As it is only produced in China (which is responsible for >50% of world production), Mexico, Mongolia, and South Africa, for many potential consumers, it is not readily available.

[0006] The synthesis of CaF2 from the reaction of hexafluorosilicic acid (henceforth "FSA") with substances containing calcium carbonate such as limestone (eq 1) is well-known in the art:

H₂SiF₆ + 3 CaC0 3 CaF₂(s) j + Si0_2*H₂0 + 3C0₂(g)† (1)

The synthetic methods known in the art generally require a complicated separation step to remove the silica, and are liable to formation of significant amounts of foam due to the C0₂ liberated during the reaction.

[0007] British Pat. No. 1239078 discloses the synthesis of CaF₂ from the reaction of FSA with CaCO, at a molar ratio of at least 3:1 and a temperature above 50 °C. Flocculants are added in order to precipitate the silica produced in the reaction.

[0008] U.S. Pat. Nos. 4031193 and 4078043 disclose the production of CaF₂ from the reaction between FSA and CaCO, at a pH of 2 - 6 in the presence of sulfate or aluminum ions, with the best results being obtained when the molar ratio of aluminum to FSA is between 1 :7 and 1 : 100 and that of sulfate to FSA is between 1:5 and 1:20. U.S. Pat. No. 5698027 discloses a similar method for producing a Portland cement clinker. In the method disclosed, FSA was reacted with CaCO, in the presence of sulfate or aluminate at a pH of 2 - 6. Separation of silica from the CaF₂ product was required.

[0009] U.S. Pat. No. 4135941 discloses formation of cement clinker by direct application of FSA on argillaceous and calcareous materials and burned in a kiln at 1200 - 1500 °C to form cement clinker. lwt% FSA (24%) was thoroughly blended with fine (<50 mesh) dry feeds. The mixture was then clinkered at different temperatures and for varying times.

[0010] Production of CaF₂ (92% - 95%) and silica from the direct reaction of 6 - 8% FSA with 10% excess CaC0₃ in a pH range of 4.3 - 5.5 has been reported (Zorya, L.; Krot, V. React. Kinet, Mech. Catal. L 1993, 50, 349 - 354). The product was purified by intensive steps such as centrifugation, washing, drying, and cation exchange.

[0011] A study of the critical parameters in the production of CaF₂ from CaC0₃ and FSA was performed (Arabadzhiev, D. M., Stafilov, T.; Stefov, V. Geologica Macedonica 2003, 17, 83 - 86). It was found that a product containing 94 - 97% CaF₂, <1% CaC0₃, and <3% Si0₂ (m/m, calculated for dry substances) can be obtained, but that complete realization of the reaction depends on the quality of the starting materials, the mass ratio between carbonate and water in the initial suspension, the concentration of FSA that is introduce into the suspension, the pH necessary to complete the reaction, the time for adding the acid and mixing the suspention, and the method of separation of the products and their treatment all influence the final product yield.

[0012] It has been reported (Albustami, S. F.; Hilakosa, S. W. Procedia Engineer. 2014, 83, 286 - 290) that silica gel formation from the reaction of FSA with several calcium compounds can be avoided if the pH of the reaction is kept at about 5. The gelling was more significant with CaC0₃ and ground limestone than with other calcium compounds.

[0013] International (PCT) Pat. Appl. Pub. No. WO2017/217876 discloses a flux containing CaF2 and amorphous silica in a ratio of 4:1 or less. The flux was prepared by reacting FSA with Na₂C0₃ in the presence of up to 10% NaCl or CaCh and up to 20% Ca(OH)2 at a pH > 8 and a temperature of 60 - 80 °C. The product was separated by filtration, centrifuging, washing, and drying.

[0014] Despite the decades of research and development, a simple, low-cost method for production of a cement flux / mineralizer from FSA that is not labor- and energy-intensive, in particular, a method that does not require separation of silica from the flux, remains a long-felt, but as yet unmet need.

SUMMARY OF THE INVENTION

[0015] The invention disclosed herein is designed to meet this long-felt need. It provides a novel and simple method for producing a flux / mineralizer that, in contrast to methods known in the art, does not require any steps of separation of silica or purification; can be performed at ambient temperature; does not require any pH adjustment; uses simple and readily available equipment such as a tumbling mixer or a pugmill); and produces a pH-neutral product, thus enabling safe and easy handling even for users who do not have the facilities to store and handle FSA.

[0016] It is therefore an object of this invention to disclose a method for preparing a cement flux / mineralizer, comprising: combining an aqueous solution of fluorosilicic acid (FSA) with a carbonate-containing material; and, reacting said FSA with said carbonate-containing material, thereby forming said cement flux / mineralizer; wherein said method does not comprise any step of separating silica or any step of purification of a product of said step of reacting said FSA with said carbonate-containing material. [0017] It is a further object of this invention to disclose such a method, wherein said step of combining comprises combining 15 - 50% of said aqueous solution of FSA by weight relative to said carbonate-containing material.

[0018] It is a further object of this invention to disclose the method as defined in any of the above, wherein said aqueous solution of FSA is 18 - 23% FSA by weight.

[0019] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of combining comprises combining an aqueous solution of FSA with a carbonate-containing material in amounts characterized by a molar ratio of fluorine in said FSA to calcium in said carbonate-containing material of less than 2:1.

[0020] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of combining comprises adding said FSA to said carbonate-containing material over a period of 5 - 30 minutes.

[0021] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of combining comprises stirring said FSA and said carbonate- containing material continuously.

[0022] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of combining comprises mixing said FSA and said carbonate- containing material continuously. In some preferred embodiments of the invention, said mixing is performed in a tumbling mixer. In some especially preferred embodiments of the invention, said tumbling mixer comprises a top, and said step of combining is performed such that product of said reaction freely tumbles before it reaches said top of said tumbling mixer.

[0023] In some preferred embodiments of the invention in which said step of combining comprises mixing said FSA and said carbonate-containing material continuously, said mixing is performed until gas evolution ceases.

[0024] In some preferred embodiments of the invention in which said step of combining comprises mixing said FSA and said carbonate-containing material continuously, said mixing is performed for an additional 10 - 30 minutes after said aqueous solution of FSA and said carbonate-containing material have been combined.

[0025] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of combining comprises: spraying said aqueous solution of FSA on a powder of said carbonate-containing material; and, mixing during chemical reaction between said solution and said powder.

[0026] It is a further object of this invention to disclose the method as defined in any of the above, wherein said carbonate-containing material is selected from the group consisting of limestone and varieties; marl and varieties; chalk and varieties; dolomite and varieties; oil shale; and mixtures and combinations thereof.

[0027] It is a further object of this invention to disclose the method as defined in any of the above, comprising a step of drying following said step of reacting.

[0028] It is a further object of this invention to disclose the method as defined in any of the above, wherein said method does not include any step of pH adjustment.

[0029] It is a further object of this invention to disclose the method as defined in any of the above, wherein all steps of said method are performed at ambient temperature.

[0030] It is a further object of this invention to disclose a cement flux / mineralizer, produced by the method as defined in any of the above.

[0031] It is a further object of this invention to disclose such a cement flux / mineralizer, wherein said cement flux / mineralizer comprises less than 10% fluorine by weight.

[0032] It is a further object of this invention to disclose a cement flux / mineralizer as defined in any of the above, wherein said cement flux / mineralizer is pH-neutral.

[0033] It is a further object of this invention to disclose a method of producing a clinker, comprising: heating a mixture of a carbonate-containing material, an aluminosilicate material, and the flux as defined in any of the above.

[0034] It is a further object of this invention to disclose such a method for producing a clinker, wherein said carbonate-containing material is limestone.

[0035] It is a further object of this invention to disclose the method for producing a clinker as defined in any of the above, wherein said step of heating comprises heating to a temperature not exceeding 1300 °C.

[0036] It is a further object of this invention to disclose the method for producing a clinker as defined in any of the above, wherein said step of heating comprises heating to a temperature not exceeding 1200 °C. [0037] It is a further object of this invention to disclose the method for producing a clinker as defined in any of the above, wherein said step of heating comprises heating to a temperature not exceeding 1100 °C.

[0038] It is a further object of this invention to disclose the method for producing a clinker as defined in any of the above, wherein said mixture comprises between 0.1% and 5% by weight of said flux.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The invention will now be described with reference to the drawings, wherein:

[0040] FIG. 1 is a photograph of a sample of a flux prepared according to the method disclosed herein;

[0041] FIGs. 2A and 2B are photographs of a sample of a second flux prepared according to the method disclosed herein, before and after drying, respectively; and,

[0042] FIG. 3 is a photograph of a sample of a third flux prepared according to the method disclosed herein.

DETAIFED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0043] In the following description, various aspects of the invention will be described. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent to one skilled in the art that there are other embodiments of the invention that differ in details without affecting the essential nature thereof. Therefore, the invention is not limited by that which is illustrated in the figures and described in the specification, but only as indicated in the accompanying claims, with the proper scope determined only by the broadest interpretation of said claims. In some cases, for clarity or conciseness, individual elements of the invention are discussed separately. Nonetheless, any combination of elements of the invention that is not self-contradictory is considered by the inventors to be within the scope of the invention.

[0044] As used herein, the term "comprising" is used to describe embodiments of the invention that include at least the listed elements or method steps, but may include others that are not explicitly listed, while the term "consisting of" is used to describe embodiments of the invention that include the listed elements or method steps but no others. In all cases in which the term "comprising" or "comprises" is used, unless explicitly stated otherwise, the scope of the invention includes those embodiments that "consist of" the listed elements or method steps. [0045] As used herein, with reference to numerical quantities, the term "about" refers to a range of ±20% about the nominal value.

[0046] As used herein, the abbreviation "FSA" stands for the substance assigned CAS Registry number 16961-83-4 and commonly known as "fluorosilicic acid" or "hexafluorosilicic acid."

[0047] Disclosed herein is a method for preparing a flux. In preferred embodiments of the method disclosed herein, an aqueous FSA solution and a carbonate-containing material or mixture of carbonate-containing materials are used as the starting materials. In some preferred embodiments of the invention, the FSA solution is 18% - 23% FSA by weight. In other embodiments, FSA solutions of higher (e.g. 35% or 40% by weight) or lower concentrations are used. Non-limiting examples of carbonate-containing materials that can be used in the instant method include limestone and varieties; marl and varieties; chalk and varieties; dolomite and varieties; oil shale, particularly carbonate-rich shale; and mixtures and combinations thereof.

[0048] In the inventive method, the starting materials are combined, preferably with continuous stirring or mixing. While in some embodiments, the FSA solution and carbonate-containing material are simply mixed, in preferred embodiments of the invention, the starting materials are combined by spraying the FSA solution on a powder of the carbonate-containing material and then mixed, preferably continuously, during the course of the ensuing chemical reaction. In preferred embodiments of the invention, 15 - 50% by weight of the FSA solution is added to the carbonate powder. The inventors have found that the weight ratio of FSA to feed can be varied beyond these limits and the reaction product will still be fully usable as a cement flux / mineralizer, although if higher weight ratios of FSA to powder are used, the product is more likely to be wet and sticky and thus less suitable for use as a flux without an additional step of drying; thus, in preferred embodiments of the invention, the amount of FSA added to the carbonate-containing material is kept sufficiently low that the product does not stick to the rotary drum in which it is mixed, and can pass freely through a sieve. In some particularly preferred embodiments of the invention, the mixing is performed in a tumbling mixer. In other preferred embodiments of the invention, the mixing is performed in a pugmill. In preferred embodiments of the invention, the stirring or mixing is continued until gas evolution ceases. The method can be used to produce the flux on scales ranging from the benchtop (tens to hundreds of grams) to industrial (tons to thousands of tons). A person of ordinary skill in the art will readily understand that the rate of the addition of the FSA to the carbonate material will depend on the scale of the production; in typical embodiments of the invention, the addition of the FSA to the carbonate material is performed over a period of 5 - 30 minutes, and the mixing performed for 10 - 30 additional minutes following the completion of the addition of the FSA to the carbonate material. In preferred embodiments of the invention, the addition and mixing steps are performed such that the product powder freely tumbles before it reaches the top of the mixer.

[0049] The reaction between the FSA solution and the carbonate powder is spontaneous and slightly exothermic. The reaction produces primarily CaF2, AIF3, FeF3, S1O2, and possibly other fluoride salts, depending on the specific starting materials used. The granules obtained as the product of the reaction are collected and can be used as a flux without any further treatment, or if the user prefers, the reaction product can be dried and the dry product used as a flux. As is shown in the examples given below, the flux is typically less than 10% fluorine by weight; for comparison, CaF2 is 48.67% fluorine by weight.

[0050] It is also within the scope of the invention to disclose a novel flux produced by the inventive method. The flux tends to be a complex mixture that is not easily amenable to structural analysis.

[0051] The flux disclosed herein has many advantages over those known in the art. For example, the product of the reaction of FSA with the carbonate material can be used directly as a flux without any need for further purification, separation, or pH adjustment. In addition, the reaction product is pH-neutral and thus easier to handle and store than acidic fluxes known in the art. The flux is also more efficient than other fluxes known in the art such as CaF2, and therefore enables production of clinker at lower temperatures than are typically used in clinker production; for typical embodiments of the flux, clinker can be produced at a kiln temperatures.

[0052] The flux disclosed herein can be used with any Portland or Portland type cement, typically at a concentration of 0.1% - 5% by weight; the specific amount of flux used in a particular application will depend, for example, on the kiln's feed specifications.

[0053] The following examples are provided to enable a person of ordinary skill in the art to make and use the invention disclosed herein, and are not intended to be limiting in any way. In the examples, eight different raw feeds were used for various runs. Raw feed #1 comprised marl, while raw feeds #2 - #8 were obtained from cement industry mines and were used without further preparation except for grinding. Raw feed #1 comprised 14.27 wt% Si (as S1O2, determined by ICP) and 0.42 wt% F (determined by AA). Raw feeds #2 - #8 comprised 12.30 - 14.70 wt% Si (as S1O2, determined by ICP) and 0.01 - 0.04 wt% F (determined by AA). The numbering of the raw feeds is maintained throughout the examples.

Example 1

Flux preparation - method 1

[0054] 23wt% FSA was added over a period of 10 - 20 minutes to a plastic beaker containing 200 g raw feed; in various runs, samples of feeds 1, 2, and 8 were used, and the feed : FSA weight ratio varied between 1.5 and 3. The mixture was stirred continuously with a glass rod. The material began to bubble immediately on mixing, indicating evolution of CO2. The beaker heated slightly during the reaction.

Example 2

Flux preparation - method 2

[0055] 23wt% FSA was gently sprayed over a period of 5 - 20 minutes onto 200 g raw feed in a small benchtop cement mixer; in various runs, samples of feeds 1, 2, and 8 were used, and the feed : FSA weight ratio varied between 1.5 and 3. Granules were obtained after 10 - 30 minutes of continuous mixing. The as-obtained granules were suitable for use as a cement flux. For lab burnability tests, the granules were sieved on a 1.7 mm sieve, dried for 6 h at 105 °C and sieved again on a 0.5 mm sieve to obtain a homogeneous mixture.

Example 3

Preparation of a mineralized pre-clinker

[0056] Fluxes were prepared as described in the previous example. In separate runs, all eight feeds summarized in Table 1 were used. The fluxes were dried at 105 °C for 12 h. 5 g dry flux powder or 1.6 g CaF2 were added to 100 g of feed and mixed thoroughly in a benchtop rotating mixer for 30 m. The mix was spread on a flat plate, wetted with ethanol, and worked by hand to obtain spheres of ~8 mm diameter. The samples were then dried for an additional 12 h at 105 °C. This second drying was performed for the sake of laboratory tests to enable comparison of the different fluxes. In practice, no drying is required, and the flux can be fed wet directly to the kiln.

Example 4

Preparation of clinker

[0057] Three dried mineralized pre-clinker spheres prepared as described in the preceding example were placed on a graphite plate inside a sintered magnesia cup. The sample was placed into an electric furnace preheated to 700 °C. The temperature then was increased to 1350 °C at a rate of 10 °C/m and maintained at the maximum temperature for 30 m. The sample was taken out of the furnace while still at the maximum temperature, and cooled in air until reaching 300 °C. When the sample had cooled to 300 °C, the sample was placed in a thick-walled desiccator charged with silica gel and allowed to cool to room temperature.

Example 5

Determination of free lime content of clinker

[0058] The following procedure, based on methods well-known in the art, was used to determine the free lime content of clinker.

[0059] The clinker is ground to a homogeneous powder and sieved at 200 mesh. 1 g of the powder is mixed with 25 - 30 g ethylene glycol inside a round-bottom flask (RBF). The RBF is closed and heated to 60 °C with constant shaking for 30 m. The mixture is then filtered by using a #40 Whatman paper filter. The filtrate is collected and titrated with 0.1N HC1 using Bromocresol Green as an indicator until the indicator's color has changed from green to yellow. The free lime content is then calculated according to eq (2),

% Free lime = 0.28V_HCI (2) where V_HCI represents the volume in cm³ of the HC1 used in the titration.

Example 6

Preparation of flux #1

[0060] A flux was prepared according to method 2. 55 g of 23wt% FSA was sprayed onto 100 g of feed material 1. The reactants were mixed in a benchtop tumbling mixer for 30 min. A sample of the powder obtained by this method was placed in distilled water for 30 min. The pH of the supernatant liquid was then measured and determined to be 7. Reference is now made to FIG. 1, which shows a photograph of the flux material as prepared (i.e. without drying).

[0061] The wet powder obtained from the reaction of the FSA and the feed material is suitable for use as a flux and can be added directly to the kiln without further treatment. For use in burnability tests, the powder was dried at 105 °C for 8 h. 102 g of dry flux powder was obtained. The results of an analysis of the flux are summarized in Table 1 below. Example 7

Preparation of flux #2

[0062] A flux was prepared according to method 2. 104 g of 23wt% FSA was sprayed onto 200 g of feed material 2. The reactants were mixed in a benchtop tumbling mixer for 30 m. A sample of the powder obtained by this method was placed in distilled water for 30 m. The pH of the supernatant liquid was then measured and determined to be 7. Reference is now made to FIG. 2, which shows a photograph of the flux material as prepared (FIG. 2A) and after drying (FIG. 2B).

[0063] The wet powder obtained from the reaction of the FSA and the feed material is suitable for use as a flux and can be added directly to the kiln without further treatment. For use in bumability tests, the powder was dried at 105 °C for 8 h. 189 g of dry flux powder was obtained. The results of an analysis of the flux are summarized in Table 1 below.

Example 8

Preparation of flux #3

[0064] A flux was prepared according to method 2. 200 g of 23wt% FSA was sprayed onto 500 g of feed material 8. The reactants were mixed in a benchtop tumbling mixer for 30 m. A sample of the powder obtained by this method was placed in distilled water for 30 m. The pH of the supernatant liquid was then measured and determined to be 7. Reference is now made to FIG. 3, which shows a photograph of the flux material as prepared (i.e. without drying). The results of analyses of the fluxes are summarized in Table 1.

_ TABFE 1 _

Flux 1 (Ex. 6) 2 (Ex. 7) 3 (Ex. 8)

Feed # 1 2 8

FSA:Feed weight ratio 1:2 1:2 1:2.5

Component Analysis (percent by weight)

S1O₂ (oxide basis)^a 14.9 14.8 12.6

C0₂ ^b 6.7 -^d 27.3

F ^c 7.6 7.9 5.5 determined by ICP; determined from the change in pressure in a closed vessel following reaction with HNO₃ to form CO₂; determined by AA; ^dno analysis was performed Example 9

Free lime in preparations with and without flux (1)

[0065] 2.63 g of the dry flux powder (-500 pm diameter particles) prepared as described in Example 7 (flux #2) was added to 50 g of powdered dry feed 2 (-500 pm diameter particles) and mixed in a benchtop tumbling mixer for 30 min. The homogeneous mix was spread on a flat plate, wetted with enough ethanol to be workable, and worked by hand to obtain spheres of 8 - 10 mm diameter. The spheres were dried at 105 °C for 12 h.

[0066] Two independent runs were performed in which the dried material (10.76 g in one run and 11.78 g in a second independent run) was placed on a graphite plate inside a sintered magnesia cup and then placed into an electric furnace that had been preheated to 700 °C. The temperature was then increased to 1100 °C at a rate of 10 °C/min and held at 1100 °C for 30 min. The sample was removed from the furnace and then cooled in air until the temperature reached 300 °C. The sample was then placed in a thick-walled desiccator charged with silica gel and cooled to room temperature. The weight of the spheres after drying was 7.3 g in the first run and 8.52 g in the second run. The spheres were hard and could be crushed by a mortar, but not by hand.

[0067] In a separate set of experiments, spheres of raw feed were prepared as described above (6.76 g in one run 9.88 g in a second independent run) except that no flux was added to the raw feed. The weight after heating was 6.5 g in the first run and 6.8 g in the second run. The spheres obtained after heating were not hard and could be crushed by hand.

[0068] The free lime content of the materials was determined by the procedure described in Example 5 above. The results are summarized in Table 2.

TABLE 2

Feed # Flux # Flux wt% Free lime, percent

2 0.20

2 2 5 0.03

[0069] It is clear from the results summarized in the table that addition of the flux significantly lowers the free lime in the clinker. The increased hardness observed in the clinker containing the flux indicates that the flux also affects the phase or phases obtained. Example 10

Free lime in preparations with and without flux (2)

[0070] In order to demonstrate the effectiveness of the flux disclosed herein, a comparison was made of the properties of different feeds described above prepared with and without the flux disclosed herein.

[0071] Six different compositions were prepared (feed numbers as described above, flux numbers according to Table 1):

[0072] Composition la: Feed #3 with no added flux;

[0073] Composition lb: Feed #3 containing 5wt% flux #1;

[0074] Composition 2a: Feed #5 with no added flux;

[0075] Composition 2b: Feed #5 containing 5wt% flux #1;

[0076] Composition 3a: Feed #2 with no added flux; and,

[0077] Composition 3b: Feed #2 containing 5wt% flux #2.

[0078] In all cases, the flux was added to the feed in a manner similar to that described in Example 9 above. The spheres were then burned at 1200 °C. In a separate set of runs, samples of feeds #2, #3, and #5 were burned at 1200 °C without addition of flux. The free lime content was then determined according to the method described in Example 5 above. The results are summarized in Table 3.

TABLE 3

Composition Free lime, percent la 27 lb 14.3

2a 22.6

2b 11.9

3a 0.07

3b 0.03

[0079] In all cases, addition of flux yielded a product with less free lime than the product produced under identical conditions except for the addition of the flux.

[0080] Feeds #3 and #5 were more difficult to burn than feed #2, as can be seen from the higher amounts of free lime obtained in the absence of flux upon burning at 1200 °C. Addition of 5wt% of flux #1 reduced the free lime content by nearly half in both cases, indicating that the flux produced by the method disclosed herein can be used with a variety of different raw feeds without being deactivated. The quantitative effect of the flux in practice is influenced by the composition of the feed. A person of ordinary skill in the art will well understand that this behavior is expected.

Example 11

Comparison of the invention to CaF2

[0081] A series of tests was performed to compare the performance of the flux produced by the method disclosed herein with the performance of CaF2. Fluxes were prepared as described above, and samples for the burning tests prepared as described in Example 9 above. Fluxes were added to the raw feeds as described above. The compositions were molded into spheres and burned at 1350 °C in a process analogous to those described above. The free lime was then determined according to the method given above. The results are summarized in Table 4.

TABFE 4

Feed # Flux Flux wt% F wt% Free lime, %

2 none - - 0.04

2 2 5 0.39 0.03

3 none - - 7.5

3 1 5 0.38 4.7

3 CaF₂ 1.6 0.78 6.1

4 none - - 9.1

4 1 5 0.38 9.7

4 CaF₂ 1.6 0.78 8.8

5 none - - 5.9

5 1 5 0.38 2.9

5 CaF₂ 1.6 0.78 3.9

6 none - - 7.3

6 1 5 0.38 5.6

6 CaF₂ 1.6 0.78 5.6

7 none - - 6.7

7 1 5 0.38 3.9

7 CaF₂ 1.6 0.78 4.2

8 none - - 17.6 8 1 5 0.38 7.2

8 3 5 0.27 6.1

8 CaF₂ 1.6 0.78 8.1

[0082] The results show that in general, fluxes produced by the method disclosed herein are more efficient than CaF2, as they were at least as effective in the reduction of free lime relative to the burning of feed without flux despite having only about half the fluoride concentration.

[0083] Comparison of the results summarized in Tables 2 - 4 shows that the reduction in the amount of free lime in Feed #2 upon addition of flux was much more significant when the burning was performed at 1100 °C (0.03% with flux vs. 0.20% without) than when the burning was performed at 1200 °C (0.03% with flux vs. 0.07% without), while burning at 1350 °C was essentially equally effective at reducing the free lime whether or not flux was added (0.03% with flux vs. 0.04% without). Apparently, the contribution of the flux to the formation of the desired cement phases becomes less significant when the burning is performed at a temperature of 1200 °C or above. These results indicate that adding 5 wt% of the flux produced by the method disclosed herein enables the reduction of the kiln temperature from 1350 °C to 1100 °C without any reduction in quality of the cement produced.

Claims

CLAIMS We claim:

1. A method for preparing a cement flux / mineralizer, comprising: combining an aqueous solution of fluorosilicic acid (FSA) with a carbonate-containing material; and, reacting said FSA with said carbonate-containing material, thereby forming said cement flux / mineralizer; wherein said method does not comprise any step of separating silica or any step of purification of a product of said step of reacting said FSA with said carbonate-containing material.

2. The method according to claim 1, wherein said step of combining comprises combining 15 - 50% of said aqueous solution of FSA by weight relative to said carbonate-containing material.

3. The method according to claim 1, wherein said aqueous solution of FSA is 18 - 23% FSA by weight.

4. The method according to claim 1, wherein said step of combining comprises combining an aqueous solution of FSA with a carbonate-containing material in amounts characterized by a molar ratio of fluorine in said FSA to calcium in said carbonate-containing material of less than 2:1.

5. The method according to claim 1, wherein said step of combining comprises adding said FSA to said carbonate-containing material over a period of 5 - 30 minutes.

6. The method according to claim 1, wherein said step of combining comprises stirring said FSA and said carbonate-containing material continuously.

7. The method according to claim 1, wherein said step of combining comprises mixing said FSA and said carbonate-containing material continuously.

8. The method according to claim 7, wherein said mixing is performed in a tumbling mixer.

9. The method according to claim 8, wherein said tumbling mixer comprises a top, and said step of combining is performed such that product of said reaction freely tumbles before it reaches said top of said tumbling mixer.

10. The method according to claim 6, wherein said mixing is performed until gas evolution ceases.

11. The method according to claim 6, wherein said mixing is performed for an additional 10 - 30 minutes after said aqueous solution of FSA and said carbonate-containing material have been combined.

12. The method according to claim 1, wherein said step of combining comprises: spraying said aqueous solution of FSA on a powder of said carbonate-containing material; and, mixing during chemical reaction between said solution and said powder.

13. The method according to claim 1, wherein said carbonate-containing material is selected from the group consisting of limestone and varieties; marl and varieties; chalk and varieties; dolomite and varieties; oil shale; and mixtures and combinations thereof.

14. The method according to claim 1, comprising a step of drying following said step of reacting.

15. The method according to claim 1, wherein said method does not include any step of pH adjustment.

16. The method according to claim 1, wherein all steps of said method are performed at ambient temperature.

17. A cement flux / mineralizer, produced by the method according to any one of claims 1 - 16.

18. The cement flux / mineralizer according to claim 17, wherein said cement flux / mineralizer comprises less than 10% fluorine by weight.

19. The cement flux / mineralizer according to claim 17, wherein said cement flux / mineralizer is pH-neutral.

20. A method of producing a clinker, comprising: heating a mixture of a carbonate-containing material, an aluminosilicate material, and the flux according to claim 17.

21. The method according to claim 20, wherein said carbonate-containing material is limestone.

22. The method according to claim 20, wherein said step of heating comprises heating to a temperature not exceeding 1300 °C.

23. The method according to claim 20, wherein said step of heating comprises heating to a temperature not exceeding 1200 °C.

24. The method according to claim 20, wherein said step of heating comprises heating to a temperature not exceeding 1100 °C.

25. The method according to claim 20, wherein said mixture comprises between 0.1% and 5% by weight of said flux.