RU2252201C2 - Portland cement with limited chrome compound content - Google Patents

Abstract

FIELD: building materials, particularly ecologically safe Portland cement.

SUBSTANCE: Portland cement with limited content of water-soluble chrome Cr⁶⁺ is product of clinker component, gypsum component and de-chromatic agent intergrinding. De-chromatic agent includes chromate reducing agent. Clinker component additionally has accelerator for linking water-soluble chrome compounds into insoluble hydration phase in the form of pre-hydrates - AFm/AFt phases. Above de-chromatic agent additionally has chrome promoter for compound linkage into insoluble hydrated phase including substances selected from the following group: calcium ulfoaluminate, aluminum hydroxide, aluminum sulfate or hydroxosulfate of anhydrous type or of crystalline hydrate type, double magnesium-magnesium sulfate of anhydrous type or of crystalline hydrate type, wherein pre-hydrates are taken in amount of 0.3 - 1.5 parts by weight per 100 part by weight of clinker component, reducing agent and accelerator are taken with ratio of 0.3-4:1 in parts by weight. Portland cement components are taken with the following mass ratio: clinker component:gypsum component recalculated to SO₃:de-chromatic agent - 100:(1-3.5):(0.3-8.5). Portland cement includes at least one substance taken from group including ferrous iron sulfate or hydroxosulfate of anhydrous type or of crystalline hydrate type, double sulfate of sodium or potassium and ferrous iron of crystalline hydrate type, calcium sulfide of oldgamite or synthetic semi- amorphous product type, salts of products of oligomerization of sulfonic acids with formaldehyde, lignosulphonates modified with synthetic resins or mixtures of above substances with neutral salts or inert substances, namely mineral additives, wherein above substances are contained in amount of not less than 20% by mixture weight, are used as chromate reducing agent. De-chromatic agent is chemical compound including above reducing agent and accelerator of double sulfate of aluminum and ferrous iron or sulfoaluminate or sulfoalumoferrite or sulfoferrite clinkers including ferric monoxide or product of stoichiometric mixture reaction recalculated to active substances of ferrous iron hydroxosulfate and sulfuric acid of red gypsum and kaolin or kaolin clay taken in amount of 0.5-2 % by weight. Clinker agent includes tetragonal calcium aluminate R₂O·8CaO·3Al₂O₃, where R is K, Na is taken in amount of 0.2 - 1 % by weight when specific surface area of Portland cement is 250-350 m²/kg or in amount of 0.3-2 % by weight when specific surface area of Portland cement is 350-700 m²/kg.

EFFECT: increased ecological safety, possibility to transport thereof without strength reduction.

4 cl, 1 ex, 1 tbl

Description

The invention relates to the technology of building materials, mainly to obtain hydraulic binders, namely, environmentally friendly Portland cement with a low content of water-soluble chromium compounds. The ultimate goal of the invention is the prevention of chromdermatitis or “chromatexemia” arising from regular contact of personnel in the building complex with unhardened cement-based materials containing hexavalent water-soluble chromium ion in the composition of pathogenic chromic acid salts - chromates.

According to the results of a study of domestic industrial Portland cement clinkers and Portland cement [1], the content of water-soluble chromium in them, without the use of special measures to reduce it, is in the range of 0.005-0.2 wt.% In terms of Cr ⁶⁺ , reaching the indicated values in peak samples materials of individual enterprises values of 0.5-0.6 wt.%. In this work, it was found that in the initial ingredients of the cement raw mix, chromium is present only in the form of chromites (Cr ⁵⁺ compounds), which are not pathogenic, since they are not water soluble. About two-thirds of chromium gets into Portland cement clinker from raw materials and one-third from chromium-containing refractories in the lining of rotary kilns, where such refractories have not yet been replaced by much more expensive chromate-free ones. However, the transition to the latter alone does not solve the problem of the pathogenicity of Portland cement, since the normal Cr ⁺⁶ content, at which dermatitis does not occur, is two to three orders of magnitude lower than the average value found in domestic industrial clinkers. In other countries, the situation differs little from the above. So, in Germany, the average content of hexavalent chromium in cements is 0.015 wt.% [2], which is an order of magnitude higher than required.

Currently, it is known from published data on domestic sanitary-hygienic studies that chromdermatitis occurs when the content of water-soluble chromium is more than 0.00005 wt.% In drinking water - in the population and more than 0.002 wt.% (More than 2 mg / kg) in cement and other binders - at construction workers and personnel of enterprises for the production of concrete and reinforced concrete, directly in contact with concrete and mortar mixtures. So, for this Moscow sanitary epidemiological station, chromdermatitis is prevalent in 8% of cases of occupational diseases of workers in the construction complex. Similar results served as the basis for the introduction of sanitary standards in a number of countries, in particular in Denmark (since 1982), Sweden, Norway, Finland (1985-1995), in part of the countries of the British Commonwealth of Nations in the mid-90s and in Germany (from 1.01.2000), according to which it is not allowed to contain in building materials, in particular in cement, water-soluble chromium (Cr ⁶⁺ cation) in an amount of more than 0.0002 wt.%, or more than 2 mg / kg [ 3]. Unfortunately, in Russia until now there were no technologies that could withstand the requirements of the specified standards for the content of water-soluble chromium in cement, which did not allow Russia to join these countries by introducing an identical standard for domestic producers.

; Н₂О=Н; К₂О=К; MgO=M; Na₂O=N; SiO₂=S;

; коэффициент при оксиде в обычной химической формуле клинкерных минералов становится в сокращенной формуле подстрочным индексом. Так, Ca₃SiO₅=3CaO · SiO₂=С₃S и т.д.For a detailed analysis of the chemistry of chromium in cement, here and below, in the description of the invention, the abbreviated notation of oxides adopted in the chemistry of cement is used: Al ₂ O ₃ = A; CaO = C; Fe ₂ O ₃ = F;

; H ₂ O = H; K ₂ O = K; MgO = M; Na ₂ O = N; SiO ₂ = S;

; the oxide coefficient in the usual chemical formula of clinker minerals becomes the subscript in the abbreviated formula. So, Ca ₃ SiO ₅ = 3CaO · SiO ₂ = C ₃ S, etc.

Using thermodynamic analysis and research, the authors of the present invention found that chromates - water-soluble salts of chromic acid Н ₂ CrO ₄ - arise in Portland cement clinker from chromites - salts of chromic acid Н ₃ CrO ₃ , as a result of a set of reactions proceeding in the presence of alkaline oxides metals (potassium, sodium) during clinker firing:

where at 800-1100 ° С the indicated reactions proceed in the direct direction, and at 1250-1400 ° С - in the opposite directions; the presence of alkali metals in the form of sulfates does not change the situation, because instead of the salts of R ₂ Cr ⁶⁺ O ₄ (R = Na, K) - the product of reactions (1, 2) - double salts of R ₂ [(SO ₄ ) _x · ( Cr ⁶⁺ O ₄ ) _y ] at x + y = 2.

The authors of the present invention also found that in the presence of silicate clinker phases, these reactions are cyclic and proceed in the following forms, starting from the indicated temperatures:

here CaO _svob - free calcium oxide.

In the presence of calcium aluminoferrites, the forms and initial temperatures of similar reactions are as follows:

Of these, reactions (3) and (4), (5) and (6) are pairwise cyclic, and a compound with a mixed chromium valence — chromite-chromium calcium — is marked with an asterisk (*).

The oxidizing atmosphere in the clinker kiln during clinker burning, which is considered optimal for its hydraulic activity [4], accelerates the undesirable transition Cr ³⁺ → Cr ⁶⁺ in the presence of R ₂ O, R ₂ SO ₄ due to the following reactions:

moreover, Cr ⁶⁺ gets into more pathogenic, faster water-soluble phases.

Known Portland cement with a limited content of water-soluble chromium compounds, which is the product of the joint grinding of the Portland cement clinker ingredient, calcined in a reducing environment, and gypsum ingredient [5]. However, firing in a reducing environment reduces clinker activity, therefore, the technical properties of the specified Portland cement are significantly inferior to the control obtained from clinker fired in an oxidizing environment. Moreover, the normative Cr ⁶⁺ content in Portland cement obtained from clinker calcined in a reducing medium cannot be achieved: the concentration of Cr ⁶⁺ in cement remains more than an order of magnitude higher than normal.

It is known that the solubility limit of chromium impurities in alite is usually half that of belite [6], therefore, in parallel, the proposal to obtain “chromate-free” belite cement based on belite clinker calcined in oxidizing and reducing media in an oven was experimentally tested in parallel. This proposal also took into account the fact that the decomposition of the chromium-containing refractory lining of clinker kilns with a clinker melt decreases with a decrease in the basicity of the latter and the content of calcium oxide in the calcined material, so that belite clinker could be useful even in the presence of a chrome-containing furnace lining. However, in the studies conducted, no positive results were obtained. The analysis showed that this is due to the lower solubility of chromium in comparison with alite and belite in clinker intermediate; therefore, during crystallization of alite and then belite from a clinker melt, chromium compounds are grouped at the phase boundaries of belite grains. The material located at the phase boundaries after mixing Portland cement with water dissolves approximately twice as fast as the rest of the cement [7]; therefore, low-alumina clinkers and cements based on them can be even more pathogenic compared to others if special measures are not taken. In addition, such cements are characterized by reduced hydraulic activity.

Portland cement with a limited content of water-soluble chromium compounds is also known, which is a joint grinding product of the Portland cement clinker ingredient, gypsum ingredient and a dechromatizing agent, including a chromate reducing agent, with which Cr ⁶⁺ contained in the clinker is reduced to Cr ³⁺ in the mixing water. The term “dechromatizer” in the scientific and technical literature in Russian was introduced in [1]. The specified dechromatizing agent contains a by-product of the production of titanium dioxide (titanium white) from ilmenite (FeTiO ₃ ) by treating the latter with sulfuric acid followed by fractional crystallization, in which ferrous sulfate FeSO ₄ · 7Н ₂ О с is formed as a by-product of red gypsum an admixture of approximately 15% sulfuric acid in terms of monohydrate: Н ₂ SO ₄ · Н ₂ О [8]. A feature of this technical solution is the presence of free sulfuric acid in the dechromatizer, which complicates both the loading and unloading and transportation of this dechromatizer, as well as the work of production personnel at a cement plant. In addition, in this case, the concentration of Cr ⁶⁺ in Portland cement with this dechromatizer remains about an order of magnitude higher than the indicated norm.

The closest analog of the present invention is a Portland cement with a limited content of water-soluble chromium compounds, which is the product of co-grinding Portland cement clinker ingredient gypsum ingredient and dehromatizatora comprising a reducing agent of chromate, characterized in that as dehromatizatora it comprises chetyrehvodny ferrous sulfate FeSO ₄ · nH ₂ O (n≅ 4) [9]. The latter, being a by-product of the processing of ferrous metal products in pickling baths, must be washed and dried before being used as a dechromatizing agent to free it from free sulfuric acid. The mechanism of action of this dechromatizer is determined by the reaction

Abroad, it is supplied to cement plants for the dechromatization of Portland cement in vacuum packaging. Dissolving the dechromatizer in a predetermined amount of water, a solution is obtained which is introduced by spraying into a cement mill, which also achieves the cooling of the cement. The solution is prepared before each working shift (8-12 hours), because after about 1 day, as a result of the conversion of Fe ²⁺ → Fe ³⁺ under the influence of atmospheric oxygen, the solution loses its properties as a reducing agent. In domestic practice, the indicated dechromatizing agent is introduced “dry”, in the form of a curd mass from the input axle side into the cement mill using screw and belt feeders. However, in this case, the concentration of Cr ⁶⁺ in cement remains significantly higher than normal. It is likely that the form of introducing the indicated dechromatizing agent in the form of an aqueous solution is more appropriate, but under domestic conditions the weight dosage of this material to prepare the solution is difficult, and in the solid phase the dechromatizing agent under consideration is more stable and cannot be oxidized for up to 30 days.

The objective of the invention is to obtain a joint grinding with a dechromatizer Portland cement with a standard or lower than normal content of water-soluble chromium compounds.

This problem is solved by the fact that in Portland cement with a limited content of water-soluble chromium compounds, which is a product of the joint grinding of the Portland cement clinker ingredient, gypsum ingredient and a dechromatizing agent, including a chromate reducing agent, the specified clinker ingredient additionally contains a catalyst for the binding of water-soluble chromium compounds into an insoluble, hydrated phase prehydrates - AFm / AFt phases, and the specified dechromatizer additionally includes a promoter for the binding of compounds chromium into an insoluble hydrate phase containing substances from the group: calcium sulfoaluminate, aluminum hydroxide, aluminum sulfate or hydroxyl sulfate anhydrous or in the form of crystalline hydrates, aluminum-magnesium double sulfate anhydrous or in the form of crystalline hydrate, with the content of these prehydrates of 0.3-1.5 wt .h. per 100 parts by weight specified clinker ingredient and the ratio in parts by weight the specified reducing agent and promoter of 0.3-4: 1, in the following wt. the ratio of Portland cement ingredients: the specified clinker ingredient: gypsum ingredient in terms of SO ₃ : the specified dechromatizing agent 100: (1-3.5) :( 0.3-8.5).

In an embodiment of the invention, as a chromate reducing agent, it contains at least one substance from the group: ferrous sulfate or hydroxosulfate anhydrous or in the form of crystalline hydrates, alkali metal double sulfate - sodium or potassium - and ferrous iron in the form of crystalline hydrates, calcium sulfide in the form of oldhamite or synthetic semi-amorphous product, sulfonated coal, salts of products of oligomerization of sulfonic acids with formaldehyde, lignosulfonates modified with synthetic resins, mixtures of these eschestv with neutral salts or inert substances - mineral additives at a content of these substances is not less than 20% by weight of said mixtures.

In another embodiment of the invention, as a dechromatizing agent, it contains a chemical compound of said reducing agent and promoter in the form of aluminum sulphate-ferrous double sulphate or sulphoaluminate or sulphoaluminoferritic or sulphoferritic clinkers, including iron monoxide in an amount of 0.5-2% of the mass, or the product of the interaction of a stoichiometric mixture in terms of the active substances of ferrous hydroxide sulfate and sulfuric acid in the form of red gypsum and kaolin or kaolin clay.

In a further embodiment of the invention, as said clinker ingredient, it contains an ingredient comprising tetragonal calcium aluminate R ₂ O · 8CaO · 3Al ₂ O ₃ , where R-K, Na-0.2-1 wt.% With a specific surface area of cement of 250-350 m ² / kg or 0.3-2 wt.% with a specific cement surface of 350-700 m ² / kg.

The essence of the invention lies in the fact that in order to eliminate the pathogenicity of Portland cement caused by an admixture of Cr ^6+, it is necessary to bind and precipitate a large part or all of this admixture immediately after its dissolution in the liquid phase of the cement-water system in the form of a water-insoluble hydrate phase. It is known that the first of the hydrated phases deposited from the liquid phase of the cement-water system almost immediately after the Portland cement is mixed with water are the so-called AFm / AFt phases, which are hydroaluminates and hydroferrites / hydrosulfaluminates and calcium hydrosulfoferrites, their mixed crystals and solid solutions [10 ]. In cements known from the prior art, after they are mixed with water before the start of the release of AFm / AFt phases in the form of crystals, 3-4 hours pass, although they appear in the form of a gel after 10-12 minutes [11], and the end of their binding to aluminum salts and chromium occurs after about 3-7 days of hardening, often even later, so the AFm / AFt phases practically do not reduce the pathogenicity of cement, known from the prior art. To remove pathogenicity, the presence of Cr ⁶⁺ in the liquid phase of the cement-water system in time should be practically eliminated. In connection with this invention, the following problems should be solved:

1) to achieve the instantaneous formation and deposition of AFm / AFt phases, immediately after mixing the cement with water, from the solution and at the same time leave them gel-like so as not to accelerate the setting of the cement;

2) ensure the entry of the maximum amount or all impurities of chromates in the composition of these phases. In principle, it is known that AFm / AFt phases take impurities, including chromites, into their columnar (AFt phases) or layered (AFm phases) su 6 microstructure [12], but they had to be given the ability to include chromates, and for of this, they should also be able to accept a reducing agent along with chromates in their submicrostructure.

To solve the above problems, in turn, it is necessary and sufficient:

3) catalyze the synthesis of AFm / AFt phases in the liquid phase of the cement-water system immediately after the cement is mixed with water;

4) to promote the specified catalyst to accelerate the synthesis reaction to instantly proceeding; this is enough to exceed the kinetic solubility limit of the AFm / AFt phases in the liquid phase of the cement-water system and achieve their instantaneous precipitation from the solution;

5) to ensure the combination of catalyst, promoter and reducing agent for physico-chemical interaction in the entire volume of ingredients, without which the solution of previous problems is impossible.

All of these problems are new and their technical solutions are elements of the novelty of this patent.

The main ones are:

1. The formation as a catalyst in the clinker ingredient in the process of co-grinding the ingredients of the specified Portland cement prehydrates, mainly in the form of AFm / AFt phases. The term “prehydrates” was introduced in [13] to denote the products of the reactions of hydration of Portland cement in the process of co-grinding its ingredients with drop moisture that condenses in films on the surface of clinker particles. Usually, hydrosilicates and calcium hydroxide predominate in the composition of prehydrates. To solve the problem of the invention, the prehydrates should contain predominantly other calcium compounds - hydroaluminates, including those with an admixture of hydroferrites, and hydrosulfoaluminates, also with an admixture of hydrosulfoferrites - in the form of nuclei of AFm / AFt phases. To achieve the predominance of the AFm / AFt phases among the prehydrates, it is necessary to carry out a number of technological methods: a) to achieve a degree of calcination of the initial Portland cement clinker approaching 100% with a free calcium oxide content of not more than 1% by weight; only in this case a high degree of crystallization of the clinker intermediate is achieved (C ₃ A + C ₄ AF); in this case, most of it is concentrated in a small fraction of cement, more accessible for interaction with drip moisture during joint grinding with a gypsum ingredient, in the films of which prehydrates of AFm / AFt phases are formed; b) the minimum content of marginal phases in the specified clinker is RC ₈ A ₃ , C ₂ F, CF, RF, RA (the concept of marginal phases was introduced in [14]), namely, not more than 3% by weight; otherwise, the latter form gels that block the formation of prehydrates of the AFm / AFt phases; it should be noted that marginal alkaline ferrites and aluminates (RF, RA) are present only in highly alkaline clinkers, including R ₂ O = Na ₂ O + 0,658 K ₂ O in an amount of more than 0.8 wt.%, but additional clinkers require technological methods, in particular, ensuring the fulfillment of the SO ₃ / R ₂ O criterion in the range of 0.8-1.2, which allows us to prevent the sum of the marginal phases from exceeding the level of 3% of clinker mass; c) the level of relative humidity of the air during grinding is not less than 60%, etc. These techniques add up to a whole technology for the dechromatization of Portland cement, which includes naturally introducing the indicated promoter and reducing agent in the composition of the dechromatizer.

In order to exhibit the catalyzing effect of AFm / AFt phase prehydrates on the formation and subsequent precipitation of the same phases, including Cr ⁶⁺ , from the liquid phase of the cement-water system, the number of these prehydrates, as shown by studies of the authors of the present invention, should be within 0.3 -1.5 wt.%. At a lower content, their catalytic effect on these phenomena is absent, and at a higher content, they enhance the aggregation of Portland cement particles and make it difficult to grind. Determination of the content in portland cement of the prehydrates of the AFm / AFt phases is carried out using differential thermal analysis. At a heating rate of 8–12 ° C, cement samples in the form of a 1 g sample are calcined losses in the temperature range 110–135 ° C for AFt prehydrates, and in the temperature range 140–185 ° C, for AFm prehydrates.

, сокращенно - моносульфат (МС), а при отсутствии примесей железа - моносульфат (МС), а при отсутствии примесей железа - моногидросульфоалюминат кальция

и, соответственно, трехсульфатный гидросульфоалюмоферрит кальция

сокращенно - трисульфат, а при отсуствии примесей железа

- эттрингит (Э).The main types of prehydrates of the AFm phases and AFt phases that play a catalytic role in the binding of chromates are calcium monohydrosulfoaluminoferrite

abbreviated as monosulfate (MS), and in the absence of iron impurities, monosulfate (MS), and in the absence of iron impurities, calcium monohydrosulfoaluminate

and, accordingly, trisulfate hydrosulfoaluminoferrite calcium

abbreviated trisulfate, and in the absence of iron impurities

- ettringitis (E).

As is known, during the formation of prehydrates - prehydration of Portland cement - the surface of its particles is “ulcerated” by capillary moisture, which increases their reaction surface in the subsequent interaction with water [15]. AFm prehydrates are most active in this process, which often leads to manifestations of false setting, which is the subject of work [15]. AFt prehydrates are obtained by the interaction of AFm prehydrates of the indicated clinker ingredient with the gypsum ingredient in the process of co-fine grinding of the latter [16]. As experimental practice shows, due to the mentioned “ulceration” of the surface of the particles of the clinker ingredient, the indicated, relatively small amount of prehydrates is sufficient for the formation and instant crystallization of the AFm / AFt phases after mixing Portland cement with water according to the invention.

2. The combination of two components in the composition of the dechromatizer: a) a reducing agent - a known component; in fact, not all substances from the group of reducing agents listed in the embodiment of the invention were previously known, but their very function of reducing the concentration of chromates in cement was known in the early 80s of the last century [2]; b) a promoter of the catalyzed formation of AFm / AFt phases in the liquid phase of the cement-water system; the group of promoters is represented by substances that are the starting reagents for the formation of AFm / AFt phases. But for their entry into the reaction of the formation of these phases, the presence of a catalyst is necessary, which serves as a seed and initiates the decomposition of an intermediate substance of clinker particles with its release from silicate phases to participate in the formation of new portions of AFm / AFt phases in the liquid phase of the cement-water system with immediate removal of parallel to precipitate leaving a solution of the silicate phases impurity Cr ⁶⁺ paradox dehromatizatsii process according to the invention lies in the fact that in the clinker Cr ⁶⁺ contained mainly in silica entering phases in the solution, it is precipitated by the products of hydration of calcium aluminates and aluminoferrites and their interaction with gypsum, and hexavalent chromium in cement stone is already predominantly in non-silicate hydrates, where it is gradually reduced due to cationic vacancies that determine the presence of excess interlayer anions, primarily hydroxyls .

The promoters listed above, activating the action of AFm / AFt prehydrates as a seed for instant crystallization of the same phases from the liquid phase of the cement-water system, are completely or partially (congruent) water-soluble substances that serve together with reducing agents as initial reagents for the synthesis of hydrated AFm / AFt phases, entailing upon crystallization from the liquid phase, all Cr ⁶⁺ dissolved in it in the form of (CrO ₄ ) ^2- , converting it from a water-soluble to an insoluble form, thereby preventing its pathogenicity. This is the main element of the novelty of the present invention, not limited to the simple reduction of (CrO ₄ ) ^2- to (CrO ₃ ) ^3- , known from the prior art, and therefore much more effective.

A promoter such as aluminum-magnesium double sulfate in both anhydrous and hydrated forms, including in the form of hydroxosalt [17], characterized by a binary layered submicrostructure in which a layer of aluminum sulfate is replaced by a layer of magnesium sulfate, deserves special consideration. Magnesium, characterized by a small ionic radius, is most mobile and facilitates the entry of the large and heavy Cr ⁶⁺ ions into the structure of the sulfate phase, and then into the structure of AFm / AFt phases.

Separately, mention should be made of such “indirect” reducing agents, such as the naphthalene and lignosulfonates first used in this capacity (the latter in a modified form), as well as sulfonated coal.

The novelty element in this case is the use of a new mechanism of interaction between the clinker ingredient of Portland cement and the mentioned organic reagents in the process of mechanochemical activation of the clinker ingredient during joint grinding. In a non-ground clinker, the surface layer of alite crystals (tricalcium silicate, C ₃ S) is characterized by a lack of calcium, or rather, a lower atomic ratio Ca / Si compared to the stoichiometric composition, as indicated by X-ray photoelectron spectroscopy (XPS), often called Auger spectroscopy by the name of the French physicist P. Auger (R. Auger) who proposed this method (1925). A lack of calcium in the surface layer is also characteristic of other clinker phases — belite (C ₂ S), tricalcium aluminate (C ₃ A) and aluminoferrite phase [C ₂ (A, F)]. Due to the indicated non-stoichiometry, which manifests itself in the presence of vacancies (Schottky defects) in the cationic sublattice of the crystal lattices of the indicated clinker phases, in the initial states inside the clinker granules, the crystals of these phases are prone to interfacial aggregation, in which the individual phases are “crosslinked” by oxygen “bridges” that increase strength and microhardness of the clinker ingredient and hindering the grinding of cement. After joint grinding of the indicated clinker and gypsum ingredients in the surface layer of alite, which is the main phase of ordinary Portland cement, on the contrary, an excess of calcium, or rather, an increased value of the atomic ratio Ca / Si, is fixed in comparison with the stoichiometric composition. A detailed analysis of the infrared spectrum of the particles of finely ground Portland cement shows that this excess is caused by distortions during grinding of the forms of silicon oxygen tetrahedra (SiO ₄ ^4- ) in the crystal lattice of tricalcium silicate, which facilitate the accelerated migration of Ca-O ion pairs to the surface of the particles of the cement clinker ingredient. In other clinker phases, these phenomena are observed on a smaller scale and, as a result, the composition of their surface layers in the grinding process approaches stoichiometric.

Being essentially plastic deformations of the crystal lattice of alite and other phases at the molecular level, these phenomena, similar to premelting, lead to excessive absorption of the energy of grinding media during grinding and ultimately generate free electronic orbits of superstoichiometric calcium in the interstices of the crystal lattice (Frenkel defects) , which are the basis of dislocation cores on the alite surface, visible under an electron microscope (adsorption tests show that it’s on these the nucleus with excess calcium against stoichiometric composition sorbed acidic surface-active compounds (surfactants) type of higher fatty acids, sulfonic acids, and the like with the group -COOH ^- and accordingly these nuclei are acceptors for electron pairs anionic groups (SO ₄₎ ^{2 -} , (СО ₃ ) ^2- and 2 (ОН) ^- from alkali sulphate, carbonate and hydrosulphate impurities on the surface of clinker particles. These acceptors at the moment of transfer of electron pairs and unpaired impurity electrons to the alite surface form aggregates of cement particles. The latter represent the basis for the initial stage of clumping and other negative phenomena during the grinding of cement mentioned above.

The presence of chromate impurities in the clinker ingredient and the indicated organic reagents as a reducing agent when grinding together the clinker cement ingredient and this organic reducing agent changes the situation. It was established that the organic reagent, penetrating deep into the alite crystal structure of the clinker ingredient during grinding — this follows from a decrease in the intensity of the spectral signal from the aromatic groups of the indicated reagent in the ultraviolet range — and forming bonds of the carbon atom from the specified reagent and the oxygen atom from alite, fixed on spectra in the infrared range, delays the movement of Ca-O ion pairs to the surface of the alite phase, which contributes to the formation of negatively charged vacancies in the crystalline Alita lattice in the process of joint grinding of ingredients. From a mechanical point of view, this phenomenon is embrittlement, and from a chemical point of view, the restoration of alite. Considering the presence on the surface of Portland cement particles of highly ionized anionic groups (SO ₄ ) ^2- , (СО ₃ ) ^2- and 2 (ОН) ^- this phenomenon increases the possibility of reduction of (СrO ₄ ) ^2- in (СrО ₃ ) ^3- in solid phase in the process of plastic deformation. Thus, these organic reagents play the role of reducing agents not directly, but indirectly, enhancing the reducing potential of the clinker ingredient of Portland cement as a result of interaction with it. From this, the influence of these reagents does not become less intense: they are very active reducing agents, since they act on a number of surface layers of the crystal lattice of the clinker ingredient, the first to interact with water and that is why they significantly reduce the concentration of Cr ⁶⁺ in the liquid phase of the cement-water suspension in first minutes after mixing cement with water. Exceptions to this rule are possible only with an explicit burning of the clinker ingredient, as mentioned above. Unburned, including an excess of marginal phases (in excess of 3 wt.%), Portland cement clinkers are not applicable for the manufacture of Portland cement according to the invention.

With a lower content of marginal phases (not more than 2 wt.%), The choice of the optimal specific surface area of cement according to the invention, corresponding to the completeness of the surface coverage with the available amount of organic reagent and other reducing agents, as well as promoters, is essential. The higher the content of marginal phases in the clinker ingredient within the specified limits, the higher the specific surface of the cement must be, in order to ensure that the content of Cr ^{6+ is} limited by the present content of the reducing agent and promoter within the specified limits, eliminating the pathogenicity of the cement according to the invention. The corresponding concentration of these organic reagents in cement can be adjusted by the method of successive approximations (iterative). The above wt. the ratio of clinker, gypsum ingredients and dechromatizer 100: (1-3.5) :( 0.3-8.5) corresponds to the optimums selected by the mentioned iterative way. Deviation from it causes an increase in the content of hexavalent chromium in cement in excess of the specified norm. A deviation from the above wt. the ratio of components in the dechromatizer.

The use of dechromat and congestion in the form of mixtures thereof with neutral or inert materials in redox processes, such as table salt or active mineral additives, is advisable in the case when this simplifies the uniform distribution of dechromatizing agents by weight of cement with a low content of dechromatizing agents in cement (0, 3-0.5 wt.%). Studies have shown that the condition for maintaining the effectiveness of dechromatizers in this case is their content of at least 1/5 of the mass of their composition with a neutral or inert material.

Significantly higher efficiency of a pre-prepared chemical compound or mineral composition, combining the functions of a reducing agent and a promoter, namely, double aluminum sulfate-ferrous iron in the form of crystalline hydrate - a pre-prepared chemical compound, or sulfoaluminate, sulfoaluminoferrite or sulfoferrite clinker - pre-prepared mineral compositions, including 0, 5-2% iron monoxide. The above chemical compound in industry is obtained by processing a secondary product of the production of titanium pigment dioxide (titanium white) - a mixture of ferrous hydroxosulfate Fe ₂ (OH) ₂ (SO ₄ ) ₃ · nH ₂ O and sulfuric acid in the form of red gypsum with kaolin (2SiO ₂ · Al ₂ O ₃ · 2H ₂ O) or kaolin clay, comprising at least 30% kaolin, at a temperature of 70-350 ° C. In the presence of sulfuric acid, kaolin and kaolin clay secrete amorphous Al (OH) ₃ and / or AlOOH. The product of the interaction of these aluminum compounds with ferrous sulfate forms an analogue of the aforementioned aluminum ferrous double sulfate in the form of a crystalline hydrate, initiating, like the mentioned sulfoaluminate, sulfoaluminoferritic and sulfoferrite clinkers with an admixture of iron monoxide in the presence of AFm / AFt phase prehydrates, the formation of the latter in the liquid phase cement mixing with water, which, due to the presence of ferrous iron, entrain Cr ⁶⁺ in the sediment while simultaneously restoring it and preventing the pathogenic effect of the latter in the cement-water system. Additionally, the barrier role of the silica gel released from kaolin decomposed by sulfuric acid improves the situation.

The invention becomes clearer from an example of its implementation.

Example. For the manufacture of Portland cement according to the invention, the following starting materials are used:

clinker ingredient (K):

K1: chemical composition (wt.%): For major oxides: SiO ₂ 21.80; Al ₂ O ₃ 5.29; Fe ₂ O ₃ 5.09; CaO 65.35; MgO 1.1; SO ₃ 0.38; R ₂ O 0.32; including K ₂ O 0.3 and Na ₂ O 0.12; the sum of 99.33, n 2.10; p 1.04; KN according to V.A. Kindu: 0.90; the content of the remaining small components: Li ₂ O≅ 0, BaO 0.07, SrO 0.002, NiO 0.031, CoO 0.02, Mn ₂ O ₃ 0.095, Cr ₂ O ₃ 0.188, MoO 0.054, TiO ₂ 0.02, P ₂ O ₅ 0.19, Cl ₂ 0, F ₂ 0.H.O .: 0.16. The calculated mineralogical composition of the average sample (wt.%): C ₃ S 58, C ₂ S 19, C ₃ A 5.4, C ₄ AF 15.5, RC ₈ A ₃ 0.3, C ₂ F + CF 0, 2, the sum of 98.2, impurities - the rest (i.e. 1.8);

K2: chemical composition (wt.%): For major oxides: SiO ₂ 20.99; Al ₂ O ₃ 5.82; Fe ₂ O ₃ 4.75; CaO 64.25; MgO 1.79; SO ₃ 0.63; R ₂ O 1.08; including K ₂ O 0.84 and Na ₂ O 0.53; amount of 99.31. silicate module n = S / (A + F) = 1.99; alumina module p = A / F = 1.23, lime saturation coefficient (KH) according to V.A. Kindu = (C-1.65A-0.35F) / 2.8S = 0.90; the content of the remaining small components: Li ₂ O≅ 0, BaO 0.049, SrO = 0, NiO 0.025, CoO 0.02, Mn ₂ O ₃ 0.09, Cr ₂ O ₃ 0.12, MoO ₂ 0.015, TO ₂ 0, 18; P ₂ O ₅ 0.19, Cl ₂ 0, F ₂ 0.H.O .: 0.28. The calculated mineralogical composition of the average sample, wt.%: C ₃ S 56, C ₂ S 18, C ₃ A 7.4, C ₄ AF 14.4, RC ₈ A ₃ 1.5, C ₂ F + CF 0.5 , the sum of 97.8, impurities - the rest (2.2).

These clinkers were obtained by firing, before sintering in rotary kilns, of cement raw materials based on limestone, clay and a glandular component, including alkali metal compounds - sodium and potassium, as well as small components that are part of the granular firing product - Portland cement clinker.

Gypsum ingredient (G): gypsum stone, including, in wt.%: Two-water gypsum 98.8; impurities - the rest;

Dechromatizer with its components:

promoter:

98%-ный;A: synthetic calcium sulfoaluminate

98%;

B: sulfoaluminate clinker, comprising 30% by weight of the active substance - calcium sulfoaluminate

B: aluminum hydroxide Al (OH) ₃ - chemical reagent qualification chemically pure;

D: analogue B - the gibbsite mineral - obtained by crystallization of B after heat treatment;

D1: anhydrous aluminum sulfate Al ₂ (SO ₄ ) ₃ - chemical reagent qualification x. hours;

D2: aluminum sulfate 14.5-aqueous Al ₂ (SO ₄ ) ₃ · 14.5H ₂ O - crystalline hydrate (industrial product, 96%, impurities - the rest);

E: aluminum hydroxosulfate synthetic anhydrous Al (OH) (SO ₄ );

G: aluminum hydroxosulfate synthetic four-water Al (OH) (SO ₄ ) · 4H ₂ O - crystalline hydrate;

H: double aluminum-magnesium sulfate synthetic in anhydrous form Al ₂ Mg (SO ₄ ) ₄ ;

And: aluminum-magnesium double sulfate synthetic crystalline hydrate Al ₂ Mg (SO ₄ ) ₄ · 2H ₂ O;

K-1: a mixture of A and D1 in wt. ratio 2: 1;

K-2: a mixture of A, G and D1 in wt. ratio 2: 1: 1;

reducing agents:

BX1: ferrous sulfate anhydrous FeSO ₄ ;

BX2: ferrous hydroxosulphate - crystalline hydrate Fe (OH) ₂ (SO ₄ ) ₂ · 4H ₂ O;

BX3: ferrous sulfate crystalline hydrate FeSCO ₄ • 4H ₂ O;

BX4: sodium sulfate and ferrous iron double crystalline hydrate Na ₂ Fe ₂ (SO ₄ ) ₃ · nH ₂ O;

BX5: potassium and ferrous ferrous sulfate crystalline hydrate K ₂ Fe ₂ (SO ₄ ) ₃ · nH ₂ O;

BX6: oldgamite - a mineral of CaS composition - a product of thermal crystallization of BX7;

BX7: synthetic calcium sulfide, semi-amorphous CaS product;

BX8: sulfonated coal - a product of the processing of coal powder by oleum; conditioned fractions are used as cation exchanger, and the residue used in this case is periodically introduced into cement mills as an intensifier for grinding cement, which removes static electric charges (excess electrons) from the surfaces of cement particles, grinding media and inside mill devices; with regular introduction it reduces the hydraulic activity of cement, like the rest of the reducing agents listed above; not a surfactant; in this case serves as a reducing agent;

ВХ9: sodium salt of products of oligomerization of sulfonic acids with formaldehyde - МЦ-1 according to TU 5743-026-00369171-2001 Cement modifier “МЦ-1”; serves as a plasticizer; weak reducing agent;

BX10: technical lignosulfonates modified with synthetic resin KS-11 - LSTM-12 according to TU 2455-005-00281039-03 Lignosulfonates technical modified - “Plasticizer LSTM-12”; also serves as a plasticizer; weak reducing agent;

BX11: a mixture of BX1 and a neutral or medium salt of calcium acetate in wt. ratio 1: 0.5;

BX12: a mixture of H and an active mineral additive - Volsky flask, previously dried, in wt. ratio 1: 5; the composition of the flask, wt.%: pp 17,36; SiO ₂ 52.03; Al ₂ O ₃ 6.25; Fe ₂ O ₃ 3.54; CaO 17.31; MgO 1.67; SO ₃ 0.05; Na ₂ O 0.25; K ₂ O 1.54. In such a mixture, the reducing agent is better distributed between the particles of cement and its content in Portland cement can be reduced for the sake of cost savings;

BX13: a mixture of H and a neutral, or medium salt - sodium formate in wt. ratio 1: 0.2;

BX14: a mixture of H, the specified flask and BX8 in wt. ratio of 1: 3: 0.5;

L: aluminum sulphate-ferrous double sulfate in the form of stoichiometric crystalline hydrate: Al ₂ Fe (SO ₄ ) ₂ · nH ₂ O;

28, моноксид железа (FeO) 1,3;M: sulfoaluminate clinker calcined in a reducing medium and comprising, wt.%: Calcium sulfoaluminate

28, iron monoxide (FeO) 1.3;

36, моноксид железа (FeO) 1,8;N: sulfoferrite clinker, calcined in a reducing medium and comprising, wt.%: Calcium sulfoferrite

36, iron monoxide (FeO) 1.8;

32, моноксид железа (FeO) 1,5; определение присутствия именно указанного твердого раствора - по межплоскостному расстоянию в кристаллической решетке образующегося из него после затворения водой гидросульфоалюмината/гидросульферрита кальция (ГCAK/ГCФK)_ss в области 8,9-9,6· 10^-10 м на порошковых рентгенограммах; эттрингит (безжелезистый ГСАК), генерируемый

характеризуется значениями этого расстояния 8,9-9,1· 10^-10 м; гидросульфоферрит кальция из

- 9,5-9,7· 10^-10 м; твердый раствор

образует при гидратации смешанные кристаллы (ГCAK/ГCФK)_ss с указанным расстоянием 9,3-9,4· 10^-10 м;MN: sulfoaluminoferrite clinker calcined in a reducing medium and comprising, wt.%: Calcium sulfoaluminoferrite in the form of a solid solution

32, iron monoxide (FeO) 1.5; determination of the presence of this particular solid solution — by the interplanar spacing in the crystal lattice formed from it after mixing with calcium hydrosulfoaluminate / calcium hydrosulferrite (HSC / HFCK) _ss in the range of 8.9–9.6 · 10 ⁻¹⁰ m in powder x-ray diffraction patterns; ettringite (ironless hsac) generated by

characterized by the values of this distance of 8.9-9.1 · 10 ^-10 m; calcium hydrosulfoferrite from

- 9.5-9.7 · 10 ^-10 m; solid solution

during hydration forms mixed crystals (GSAK / GSKK) _ss with a specified distance of 9.3-9.4 · 10 ^-10 m;

in clinkers M, H, MH the rest is white, mayenite, anhydrite, calcium monoaluminate, alkali metal salts;

O1: the product of the interaction of a stoichiometric mixture in terms of the active substances of ferrous hydroxosulfate and sulfuric acid in the form of red gypsum - with kaolin; the interaction temperature is 70-140 ° C for 1.5 hours; the result is the formation in the composition of the product of the interaction of aluminum hydroxosulfate and silica gel, both compounds are in the active state (at the time of nucleation, in statu nascendi), preserved by the surrounding glandular compounds; It is a reducing agent due to the presence of Fe (OH) SO ₄ ;

O2: the product of the interaction of the stoichiometric mixture in terms of the active substances of ferrous hydroxosulfate and sulfuric acid in the form of red gypsum - with kaolin clay - corresponds to O1, but with a lower content of aluminum hydroxosulfate and high - silica gel (more about the composition of O1 and O2 products, called crystallization components — krents — in [18], where it was also shown that the introduction of krents in Portland cement made it possible to increase its strength indices by approximately a brand or class; however, in the time of this work was not found dechromatizing action of these crents on Portland cement);

As the mentioned catalyst, monosulfate (MS) or ettringite (E) was used, corresponding to the AFm or AFt phases, respectively, and formed as prehydrages when co-grinding the clinker and gypsum ingredients of Portland cement. Their content in Portland cement is determined by x-ray phase analysis according to the method [16]. Their formation occurs during the joint grinding of the indicated clinker and gypsum ingredients of Portland cement both in the absence and in the presence of a dechromatizing agent and promoter. In the latter case, the content of Portland cement of both catalyst compounds in the composition of the clinker ingredient significantly increases - at least 1.5-2 times. Both of these compounds result from the interaction of C ₃ A on the surface of the particles of the clinker ingredient with the gypsum ingredient in the capillary moisture films. Which of them arises as the first prehydrate, which determines the final type of catalyst, depends on the initial concentration on the particle surface of the indicated clinker ingredient during the grinding of aluminate phases, lime and gypsum, as well as the presence of gels, which are products of the prehydration of marginal phases. The larger the latter in the clicker ingredient, the greater the likelihood of the prevalence of MS as a catalytic phase. A mixture of catalytic phases (E and MS) is formed only at a high temperature in the mill during grinding, but the effectiveness of E and MS as dechromatization catalysts is, judging by the available data, close. Therefore, both E and MS and the mixture of E and MS are characterized by approximately the same catalytic effect, which is confirmed by the results of the experiments, presented in table form in the present description. The indicated catalyst hydrates, remaining on the particle surface of both Portland cement clinker and gypsum ingredients, are the first to take Cr ⁶⁺ cations released by the surface layer of Portland cement clinker particles after mixing Portland cement with water, delay the latter and then interact with the promoter, reducing agent and hydrolytic lime, the cement-water suspension released from the alite of the clinker ingredient released into the liquid phase forms a structure of hydrated neoplasms of the AFm / AFt type sorption capacity in order to continue to take the entire mass of hexavalent chromium impurities released by clinker particles from the dislocation zones in this structure already prepared by the first portions of chromates. Thus, the ability for a long-term process of binding of harmful impurities slowly released into the liquid phase by emerging neoplasms is due in this case to the already prepared micro-structure of these neoplasms inherited from the prehydrated catalyst.

In the manufacture of Portland cement, known from the prior art — control (without a dechromatizing agent), Portland cement according to the prototype — based on a Portland cement clinker ingredient, a gypsum ingredient and a dechromatizing reducing agent, and finally, Portland cement according to the invention — based on a Portland cement clinker with a catalytic prehydrate catalyst dechromatization, gypsum ingredient and dechromatizer, including reducing agent and promoter, - physical and mechanical characteristics of cements fissioning samples in laboratory grinding which is carried out in a two-mill batch-lined cast iron armor plates, with dimensions of each camera: length 0.28 m, diameter 0.5 m, speed 48 min ^-1, drive power of 1.1 kW, the frequency engine rotation of 930 min ^-1 and the following grinding load on one chamber (with a suspension of cement ingredients of 10 kg in each chamber): balls with a diameter of 60 mm - 6 kg, a diameter of 50 mm - 8 kg, a diameter of 40 mm - 8 kg, a diameter of 30 mm - 8 kg, tsilpebs with a diameter of 20 mm and a length of 32 mm - 25 kg, a total of 55 kg. Before weighing, the clinker ingredient is crushed to a fraction of 1-2 mm in a laboratory jaw crusher. The fineness of the obtained samples of these Portland cements was evaluated by the specific surface, determined by the method of breathability in accordance with [19].

Other equipment, instruments, and devices for assessing the physicomechanical properties of the specified cement are standard ones used for the preparation and testing of control samples from standard cement dough and mortar according to [20].

The determination of the content of Cr ⁶⁺ in clinkers and cements was carried out in accordance with the results of [9] using the European methodology laid down in the draft European standard, in which a water extract is extracted from the cement test by filtration and an analytical determination is started in the filtrate for no more than 5 minutes Cr ⁶⁺ . This technique is described in detail in the Finnish standard [21], which was used in this case. There is no domestic analogue of this methodology yet, since the departmental method for determining Cr ⁶⁺ in cement involves boiling an aqueous suspension of a cement sample with a water-cement ratio (W / C) of 50 to simulate the situation of asbestos-cement production using Gatchek sheet-forming machines and is not suitable for modeling the real situation that exists when mixing cement with water as part of a concrete or mortar mixture with a W / C of 0.3-1.

The test results of these samples of Portland cement, including Portland cement according to the invention, are presented in the table. Two series of data are presented for Portland cement according to the invention: with a dosage of a dechromatizer to achieve a minimum Cr ⁶⁺ content and with a dosage of a dechromatizer to achieve a normative, that is, the maximum allowable Cr ⁶⁺ content. The data presented, as well as the totality of the obtained experimental data, allow us to conclude the following.

1. Portland cement according to the invention, in contrast to the control and Portland cement according to the prototype, is characterized by a normative content of Cr ⁶⁺ in all samples.

2. The consumption of the dechromatizing agent required to achieve this result substantially depends on the initial Cr ⁶⁺ content in the control Portland cement, which is synbatic with the content of marginal phases in the initial clinker ingredient (RC ₈ A ₃ , C ₂ F and CF): when the content is 0 , 5 wt.% In the K1 clinker, the amount of Cr ⁶⁺ is 150 mg / kg, and with an increase in the content of these marginal phases to 2 wt.% In the K2 clinker, the amount of Cr ⁶⁺ increases to 210 mg / kg, which is two orders of magnitude higher than normal . Rows 7-24 of this table provide data indicating that in order to achieve a minimum or standard content of Cr ⁶⁺ in cement according to the invention made from clinker K1, it is necessary to add from 0.3 to 8.5 parts by weight dechromatizer, comprising from 0.15 to 6.5 parts by weight reducing agent, in samples, where the latter is a separate component of the dechromatizing agent (in lines 7-19 of the specified table). As for the required amount of dechromatizer for Portland cement according to the invention from the clinker ingredient K2, as follows from the data given in rows 25-27 of the table, it is doubled or approximately doubled in comparison with the dechromatizer compositions of Portland cement according to the invention compared to the previous clinker ingredient with lower content of marginal phases. Moreover, to achieve the normative content in Portland cement according to lines 25-27 of the table, an average higher fineness of grinding according to the invention is required — specific surface area is on average higher than 400 m ² / kg — compared to a series of Portland cement according to the invention from clinker ingredient K1 — on average less than 370 m ² / kg - according to lines 7-22. It should be noted that Portland cement according to lines 23, 24 with the organic components of the dechromatizing agent is an exception, since the mechanism of the reducing action of the organic components is inextricably linked to the high fineness of grinding of Portland cement, which imparts the properties of a reducing agent to the surface layers of cement particles in the presence of the indicated organics.

From the above data it follows that clinker ingredients with an even higher content of these marginal phases for economic reasons are not suitable for Portland cement according to the invention. However, such a high content of marginal phases is usually associated with the burning of clinker [14]; therefore, this fact does not limit the general industrial value of the invention.

3. Mineral promoter promoters (lines 20-24, 27 of the table) in the composition of the dechromatizing agent for dechromatizing action require higher dosages (4-7 parts by weight) in the composition of Portland cement according to the invention even to achieve the normative content of Cr ⁶⁺ according to compared with oxide-salt two-component dechromatizers (0.8-1.5 parts by weight of a reducing agent, 1-3 parts by weight of a promoter, only 2-3.8 parts by weight) in the cement composition to achieve a minimum Cr ⁶ content ⁺ (lines 9-11 of the specified table). To achieve the normative content of Cr ⁶⁺ in the cement according to the invention, the dosage of the oxide-salt two-component dechromatizing agent is further reduced to 0.3-0.8 parts by weight. (lines 19 and 20 of the specified table). However, it should be borne in mind that cement enterprises can prepare mineral promoters or mineral reducing promoters as part of dechromatizers themselves, while oxide-salt two-component dechromatizers include components purchased at chemical plants with subsequent preparation of a single composition at cement enterprises, and the first dechromatizers can be stored in for almost unlimited time, while the second - only up to 7 days in the open air, and only in plastic containers They can be stored for an unlimited time, and such a package significantly increases the cost ..

4. A significant advantage of Portland cement with a limited content of water-soluble chromium according to the invention is at least no less strength than control cement in both early and late hardening periods: it is sufficient to compare the data in rows 1 and 2 of this table for control cements and lines 12, 14, 20, 25 for Portland cement according to the invention. At the same time, Portland cement according to the prototype — the data in lines 3–6 of the table — is significantly inferior in strength to the control cements (data in lines 1 and 2 of the table), and this is a common phenomenon for dechromated cements known from the prior art.

The more significant element of the novelty of Portland cement with a limited content of water-soluble chromium according to the invention is an increase in their strength compared to control Portland cement (especially significant for Portland cement according to lines 8, 15. 17, 22, 23; moderate - for Northland cement in lines 7, 11, 16, 21, 26, 27; observed only in the early stages of hardening - for Portland cement in line 10, observed only in the late periods of hardening - for Portland cement in lines 9, 13, 19, 24, and in the latter case it is especially significant) . An analysis of the dependence of the strength characteristics of Portland cement on the composition of the dechromatizing agent leads to the conclusion about the advantages of compositions containing more aluminates compared to compositions containing more ferrous compounds.

In this regard, it should be noted the harmful effect, at least on the consumption of the dechromatizing agent, established in the studies of the inventors, provided by an admixture of P ₂ O ₅ in the clinker ingredient. According to the prototype [9], phosphates bind part of ferrous iron to water-insoluble iron phosphate by reaction

This phenomenon also occurs in Portland cement according to the invention, but in this case, unlike the prototype, this does not prevent either the achievement of the normative content of Cr ⁶⁺ in Portland cement according to the invention, or the increase in strength of the latter compared to the control.

в указанном сульфоалюминатном клинкере - компоненте промотора - в пределах 20-60 мас.% - не изменяет основных свойств цемента согласно изобретению, а при увеличении содержания указанного минерала в указанных пределах позволяет несколько уменьшить дозировку промотора в составе дехроматизатора. Попытки выйти за указанные пределы содержания этого минерала экономически нецелесообразны, так как при меньшем его содержании требуется значительно увеличить дозировку промотора для сохранения требуемой эффективности, а при большем его содержании значительно возрастают требования к чистоте и стоимость исходного сырья для изготовления сульфоалюминатного клинкера. Следует отметить примерно равную эффективность в составе дехроматизатора сульфоалюминатного, сульфоалюмоферритного и сульфоферритного клинкеров. Подобно этому сульфоуголь мало отличается по эффективности действия в качестве агента, вызывающего восстановление хроматов, от других, упомянутых выше, органических компонентов дехроматизатора.Similarly, a change in the mineral content of calcium sulfoaluminate

in the specified sulfoaluminate clinker - the component of the promoter - within 20-60 wt.% - does not change the basic properties of the cement according to the invention, and with an increase in the content of the specified mineral in the specified range allows you to slightly reduce the dosage of the promoter in the composition of the dechromatizer. Attempts to go beyond the specified limits of the content of this mineral are not economically feasible, since with a lower content it is necessary to significantly increase the dosage of the promoter to maintain the required efficiency, and with a higher content it significantly increases the purity requirements and the cost of the feedstock for the manufacture of sulfoaluminate clinker. It should be noted that approximately equal effectiveness in the composition of the dechromatizer sulfoaluminate, sulfoaluminoferrite and sulfoferrite clinkers. Similarly, sulfonated coal differs little in its effectiveness as an agent causing the reduction of chromates from the other organic components of the dechromatizing agent mentioned above.

5. Portland cement according to the invention can be made on the basis of almost any normally burnt Portland cement clinker, regardless of their mineralogical composition. This is not prevented by differences in the content of caustic alkali impurities in the Portland cement clinker ingredient, impurities in the gypsum ingredient; cement grinding intensifiers, water for cooling the cement crushed in the mill are acceptable, additional introduction of active mineral additives and fillers, as well as plasticizing additives into the cement composition. However, false setting typically disrupts the action of the dechromatizing agent according to the invention, and before starting to produce Portland cement with a limited content of water-soluble chromium according to the invention, the signs of false setting of cement should be eliminated beforehand. It is also not recommended to use any hydrophobic additives, both in the composition of Portland cement, and in the composition of mortar and concrete mixtures when using Portland cement according to the invention.

Thus, this Portland cement has significant advantages compared to those known from the prior art, characterized by elements of novelty and being multivariate, not requiring tight binding to a narrow raw material base, which is essential to reduce its cost in a market economy. An additional advantage of Portland cement according to the invention is the diversification of its fields of application, that is, the possibility of using both high-strength concrete and low-grade concrete, cellular concrete and other types of concrete and mortar. The present invention completely solves the environmental problem of protecting the health of workers in the construction complex from the pathogenic effects of water-soluble chromium impurities in cement. For the first time, it allows domestic cement enterprises to export Portland cement to industrialized countries without fear of sanctions from trade union organizations and sanitary inspection bodies abroad and creates an opportunity for Russia to accede to the Convention on the Protection of Workers' Health in the Building Complex adopted by the European Union. Portland cement according to the invention has been successfully tested in a production environment. Therefore, the invention is fully prepared for industrial implementation.

Literature

1. Yudovich B.E. Chromium-free Portland cement is an environmental and economic necessity for a construction complex. In the book. Concrete at the turn of the third millennium: Materials of the 1st All-Russian Conference on the problems of concrete and reinforced concrete, September 9-14, 2001, Moscow: Assots. “Reinforced Concrete”, 2001., book 3. Section reports, pp. 1630-1631.

2. Anonym. International Cement Review / London, 1989, No. 6.

3. Anonym. International Cement Review / London, 1991, No. 8.

4. Kravchenko I.V. and others. High-strength and especially quick-hardening Portland cement. M .: Stroyizdat, 1971, 231 p., See p. 90.

5. Research Institute for gas treatment facilities, safety and labor protection in the building materials industry (NIPIOTstrom). Research report No. 1428: “Reducing the chromate content in Portland cement clinker by burning it in a reducing medium with the help of an additional device for burning fuel”. Novorossiysk, 1985.

6. Butt Yu.M. and other Portland cement. M .: Stroyizdat, 1974, 328 p., See p. 64, 107-112, 131, 185 and below.

7. Belov N.V et al. Elucidation of block boundaries as the dissolution channels in hydrated cement. In "Electron Microscopy, 1978" - 9th Internat. Congress of Electron Microscopy. Proceedings, Toronto, 1978, Ed. Microsc. Soc. of Canada, v. 1 "Physics", Toronto, 1978, p. 485-486.

8. Patent GDR No. 275998, 1987.

9. Yudovich B.E. et al. On the technology of chromate-free Portland cement. 9th meeting on chemistry and technology of cement. Abstracts of reports. M .: Publishing. MKHTI them. D.I. Mendeleev et al., 1996 (prototype).

10. Taylor, Hal. Chemistry of cement. Reference Edition. M .: Mir, 1996.560 s., See p.203 and below, 215 and below.

11. Emanuelson A. et al. Ferrite Microstructure in clinker and hydration of synthetic phases in sulphate resisting cements. 10th International Congress on the Chemistry of Cement (ICCC). Gothenburg, Sweden, 2-6 June 1997. Proceedings, ed. by H. Justnes. Amarkai AB and Congrex Göttenborg AB, 1997, vol. 1 (Plenary lectures. Clinker and Cement Production), li060, 8 pp.

12. Allmann R. In Neues Jahrb. Mineral Monatschr., 1968, s. 140 (no AFm phases); see also Dosch W. Ibidem, 1967, s. 200 (for chromium-containing AFm phases); Moore A.E. et al. Nature, 1968, v. 218, p. 1048 (in AFt phases); see, in addition, Buhlert R. et al. Zement-K-alk-Gips, 1971, v.24, s. 83 (for chromium-containing AFt phases).

13.Locher F.W. et al. Erstarren von Zement. 1. Reaktion und Gefügsentwicklung. Zement-Kalk-Gips, B. 29, 1976, s. 435 - 444 (introduced the concept of prehydrates).

14. Entine Z.B. et al. The liquid phase alite generation model in sintering portland cement clinker. 10th International Congress on the Chemistry of Cement. Gothenburg, Sweden, June 2-6, 1997. Proceedings, ed. by H. Justnes, Publ. by “Amarkai”, Gothenburg, 1997, v. 1, li046. 4 pp.

15. Hansen W.C. False set in Portland Cement. IV Intemat. Symposium on the chemistry of cement. Proceedings, v. 1, Washington, 1960, ed. Nat. Bureau Stand. Monograph 43, Washington, 1962, pp. 387-403.

16. Yudovich B.E. et al. Surface phenomena in high-strength cements and false setting. Proceedings of the Research Institute of Cement, 1977, issue 46, pp. 40-56.

17. Litvinov S.D. Aluminum-magnesium double hydroxosulphates: formation conditions in Mg, Al // SO ₄ , OH - H ₂ O systems, properties, physicochemical substantiation of the possibilities of using Portland cement as an additive. Abstract. DNSS. for the competition. student step.kand. Chem. Sciences, Moscow: IONKh im. H.S. Kurnakova, 1985, 30 p.

18. Zapolsky A.K. and others. Krents - a new class of effective additives in cement. Overview information. M .: VNIIESM, Ser. 1. Cement industry, No. 1, 1989. 60 p.

19. GOST 310.2-76 Cements. Methods for determining the fineness of grinding.

20. GOST 310.1-76 Cement. Test methods. General Provisions

GOST 310.3-76 Cements. Methods for determining normal density, setting time and uniformity of volume change. GOST 310.4-81 Cement. Methods for determining the tensile strength in bending and compression.

21. SFS 5183 1986-03-24. Section: Determination of the content of water-soluble chromium in cement materials.

Notes: 1 - wt. the ratio of C ₃ S: C ₂ S: C ₃ A: C ₄ AF is approximate; more accurate in the text; 2 - clinker ingredient includes, according to the data of x-ray phase analysis (XRD) and differential thermal analysis (DTP) according to the procedure [16], the catalyst in the form of prehydrates is ettringite (E) or monosulfate (MS); this is not mentioned in the description of the prototype; 3 - in terms of SO ₃ : 4 - reducing agent; 5 - promoter; 6 - in the experiments described in rows 7-33 of this column, K denotes the sum of the clinker ingredient and the catalyst (prehydrate) contained therein; in the experiments characterized in rows 1 and 2 of this column, there are no prehydrates; in the experiments characterized in rows 3-6 of this column, the prehydrates were not taken into account in advance, therefore, the proportion of clinker ingredient in Portland cement in them in a mass ratio is 99 parts; however, such a small difference in the shares of clinker ingredient in Portland cement in the experiments on the prototype and according to the invention (99 versus 100) allows them to neglect and consider the comparison legitimate; 7 - specific surface by the method of breathability; 8 - [Cr ⁶⁺ ] is determined according to the Finnish standard [21], identical to the projected European standard for methods of chemical analysis of cement and materials of cement production; explanations in the text of the description; 9 - when tested according to GOST 310.4-81 in samples of a specified age.

Claims (4)

1. Portland cement with a limited content of water-soluble chromium compounds, which is the product of the joint grinding of the Portland cement clinker ingredient, gypsum ingredient and a dechromatizing agent, including a chromate reducing agent, characterized in that said clinker ingredient further comprises a catalyst for binding water-soluble chromium compounds to an insoluble hydrated phase in the form of / AFt phases, and said dechromatizing agent further includes a promoter for the binding of chromium compounds to non-growth Orim hydrate phase containing substances from the group of - calcium sulfoaluminate, aluminum hydroxide, aluminum sulfate or gidroksosulfat anhydrous or in the form of crystalline, double-magnesium aluminum sulfate anhydrous or in the form of crystalline, when the content of said predgidratov 0.3-1.5 wt. hours per 100 wt. including the specified clinker ingredient and the ratio in wt. including the indicated reducing agent and promoter 0.3-4: 1 in the following weight ratio of Portland cement ingredients: specified clinker ingredient: gypsum ingredient in terms of SO ₃ : specified dechromatizing agent = 100: (1-3.5) :( 0.3- 8.5). 2. Portland cement according to claim 1, characterized in that it contains at least one substance from the group as chromate reducing agent: ferrous sulfate or hydroxosulfate anhydrous or in the form of crystalline hydrates, alkali metal double sulfate - sodium or potassium - and ferrous iron in in the form of crystalline hydrate, calcium sulfide in the form of oldgamite or synthetic semi-amorphous product, sulfonated coal, salts of products of oligomerization of sulfonic acids with formaldehyde, modified with lignosulfone synthetic resins dates, mixtures of these substances with neutral salts or inert substances - mineral additives when the content of these substances is not less than 20% of the mass of these mixtures. 3. Portland cement according to claim 1 or 2, characterized in that it contains a chemical compound of said reducing agent and promoter in the form of a double aluminum sulfate — ferrous iron or sulfoaluminate, or sulfoaluminoferrite or sulfoferrite clinker, including iron monoxide in an amount of 0, as a dechromatizing agent. 5-2% of the mass, or the product of the interaction of the stoichiometric mixture in terms of the active substances of ferrous hydroxyl sulfate and sulfuric acid in the form of red gypsum and kaolin or kaolin clay. 4. Portland cement according to any one of paragraphs. 1-3, characterized in that as the specified clinker ingredient, it contains an ingredient comprising tetragonal calcium aluminate R ₂ O · 8CaO · 3Al ₂ O ₃ , where R - K, Na - 0.2-1 wt.% With a specific surface Portland cement 250-350 m ² / kg or 0.3-2 wt.% with a specific surface area of Portland cement 350-700 m ² / kg.