RU2395470C1 - Method of preparing portland cement from dolomite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to building materials and can be used in production of cement, as well as articles based on caustic magnesite. The method of preparing portland cement from dolomite involves crushing dolomite, roasting it at 900-1100°C, slaking with water into a lime suspension, its separation into heavy and light particles through settling for 1-2 hours with separation of light particles - lime milk, thickening of the lime milk into a lime paste through settling for 20-24 hours, adding clay to the lime paste, homogenisation of the obtained raw mixture, its sinter roasting and fine grinding the obtained clinker with gypsum stone.

EFFECT: increased strength of the portland cement.

2 tbl, 2 ex, 1 dwg

Description

The invention relates to the field of building materials and can be used in the production of cements, as well as products based on caustic magnesite.

The known "wet" method for the production of Portland cement (V. S. Kokololnikov and others. "Cement Production", Higher School, M., 1974, p. 34), including the operation of crushing limestone and clay, joint "wet" grinding to obtain raw sludge humidity of about 40%, sludge firing in a rotary kiln, grinding of the resulting clinker with gypsum stone.

The known "dry" method for the production of Portland cement (A.V. Volzhansky and others. "Mineral binders", Stroyizdat, M., 1973, p.198), including the operation of crushing limestone and clay with joint "dry" grinding and homogenization of the raw material charge , which is fired in rotary or shaft furnaces before sintering to produce clinker, which is ground with gypsum.

The disadvantage of the first two methods is the use in the production of cement of high-quality limestone with a maximum amount of CaO with a minimum content of impurities, in particular MgO, which significantly narrows the raw material base of the cement industry, negatively affects the cost of cement.

A known method of producing cement clinker on a sintering grate (SU, 1625842 A1, C04B 7/36), including operations: co-grinding chalk, loam, concentrate, firing the mixture on a sintering grate to produce clinker.

The disadvantage of this method in the use of low-carbonate is chalk, which does not allow to widely introduce the known method.

A known method of production of magnesian Portland cement (Handbook of cement production, edited by II Kholin, Stroyizdat, M., 1963, p. 39), including operations: crushing the lime component, co-grinding the lime component and clay, homogenizing the sludge, firing the raw material charge to clinker, followed by fine grinding of clinker with gypsum stone.

The advantage of the method is that as a calcareous component, not conditioned limestones, which are in high demand by ferrous and non-ferrous metallurgy, but calcareous magnesian rocks are used, which significantly expands the raw material base for the production of Portland cement, increases the strength of Portland cement, reduces its cost.

Disadvantages: since the well-known magnesian Portland cement contains up to 10% MgO (the norm for classic Portland cement is up to 5%), there are phenomena of uneven changes in the volume of cement paste with a delayed increase in strength, lower tensile strength compared to classical Portland cement. Therefore, the use of magnesian Portland cement is limited: it cannot be used for underwater and sanitary installations, for tensile structures. Concretes on magnesian Portland cement cannot be steamed.

The last technical decision was made as a prototype.

The purpose of the invention is the expansion of the raw material base for the production of Portland cement with the replacement of conditioned limestone with dolomites widespread in nature with a slight increase in the quality and properties of the classic lime Portland cement according to GOST 10178-85 “Portland cement and slag Portland cement. Technical conditions. "

The goal is achieved in that the method of producing Portland cement from dolomite, including the operations of crushing dolomite, sanding the clay, homogenizing the obtained raw material mixture, firing it before sintering and fine grinding the resulting clinker with gypsum stone, further comprises operations: firing dolomite at a temperature of 900 ... 1100 ° C quenching with water the lime in the lime suspension; separation of heavy and light particles of milk of lime; thickening of light particles of milk of lime into lime dough.

The drawing shows a scheme for producing magnesian portland cement (prototype) and portland cement from dolomite (invention), by settling for 1-2 hours with the separation of light particles - milk of lime, thickening the milk of lime into lime dough by settling for 20-24 hours, and the grinding of clay is carried out to the obtained lime test.

The technological process of obtaining Portland cement from dolomite proceeds as follows.

Dolomite of any composition is crushed to a fraction of 10 ... 20 mm and sent for firing either in a rotary kiln or in a shaft furnace (depending on the production capacity). Firing is carried out at a temperature of 900 ... 1100 ° C, the temperature is selected depending on the content in the dolomite MgO. The more MgO, the lower the firing temperature in the specified range.

As a result of firing dolomite, quicklime is formed, which belongs to dolomitic according to GOST-9179-77 “Building lime. Technical conditions. "

Dolomite lime is quenched in a 3 ... 5-fold excess of water while grinding. The operation is best carried out in a rotating drum of the core mixer.

The extinguished lime is a suspension consisting of the following particles, differing in size and density (according to the results of our own research):

MgO 10 ... 80 μm 3250 ... 3350 kg / m ³ CaCO ₃ 10 ... 80 microns 700 ... 2790 kg / m ³ Ca (OH) ₂ 0 ... 20 μm 2240 ... 2260 kg / m ³ Other (SiO ₂₎ Al ₂ O ₃ , Fe ₂ O ₃ ) 10 ... 80 microns 2500 ... 2580 kg / m ³

Our own studies have established that during quenching, MgO particles practically do not hydrate, on the contrary, CaO particles turn into Ca (OH) ₂ almost 100%. About 5% of unfired CaCO ₃ remains in suspension. unfired MgCO ₃ particles are not installed.

The suspension in the form of milk of lime merges into sedimentation tanks-precipitators of particles. Heavy particles of MgO, CaCO ₃ and "other" settle for 1 ... 2 hours. Light particles of Ca (OH) ₂ settle in 20 ... 24 hours. Therefore, after the formation of a layer of heavy particles at the bottom of the sump, milk of lime containing mainly light particles of Ca (OH) ₂ is drained into the pool for sedimentation and compaction.

After settling of the particles and reaching a densified layer of moisture of approximately 50% (lime dough), the clarified water is drained and sent for reuse in slaking lime.

The estimated amount of clay is added to the lime test, and the raw material sludge for clinker production is thoroughly homogenized.

Next, the raw material sludge is sent to a rotary kiln to obtain clinker, which at the final stage is crushed into powder together with gypsum stone and sent to the consumer.

Heavy particles from the sump are washed with water (washing water is mixed with milk of lime) and dried. In this way, a magnesia concentrate is obtained in which the MgO content ranges from 60 to 80%, depending on the type of dolomite used.

The cement production method described above refers to “wet”, but cement can be made according to a more progressive semi-dry method, for which raw material sludge with a moisture content of about 40% is dried under natural conditions to a residual moisture content of 20 ... 24%, after which the mass is granulated in perforated rollers and served for firing either in a rotary kiln or in a shaft.

The practical application of the invention will show a number of examples. Table 1 presents the chemical composition of the rocks used in the laboratory production of cements.

To compare the characteristics of cements made from dolomite, samples of Portland cement according to GOST 10178-85 and magnesian Portland cement (prototype) were pre-made.

To produce a sample of classic Portland cement, limestone from the Malaya Kamala deposit and clay from the Zeledeevskoye deposit were used per 1 kg of clinker:

- limestone 1.28 kg;

- clay (dry) 0.301 kg.

The clinker exit coefficient from the raw mix K _Out = 0.632.

Estimated mineralogical composition of Portland cement clinker,% by weight:

C ₃ s 66.9 C ₂ S 16.8 C ₃ A 7.9 C ₄ AF 5.8  MgO 2.1  Other 0.5

From a dry raw material mixture, granules with a size of 5 ... 7 mm were formed on a plate granulator, which were burned in a PVK-1.6-30 electric furnace at a maximum temperature of 1450 ... 1480 ° C. Clinker samples were crushed to a fineness characterized by a residue on a sieve 008 5 ... 7%.

Table 1 Rocks used in the laboratory production of Portland cement Type of rock and field The content of oxides,% by weight SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO other ppp 1. Limestone, Malaya Kamala, Krasnoyarsk Territory 2,4 0.2 0.2 51.8 1,5 - 43.9 2. Magnesia limestone, Stanovushinsky, Krasnoyarsk Territory 2.5 0.7 0.1 45.6 6.8 0.5 43.8 3. Dolomite-1, Matyushinskoe, Republic of Tatarstan 2,3 1.4 0.5 33.8 16,2 0.9 44.9 4. Dolomite-2, Krutokachinsky, Krasnoyarsk Territory 3,5 1,5 0.4 29.0 22.0 0.6 43.0 5. Clay, Zeledeevskoe, Krasnoyarsk Territory 66.0 15,5 6.6 1,6 1,6 2.1 6.6 6. Gypsum stone "Khakassgips", Republic of Khakassia 7.33 3.15 0.95 29.6 0.9 37.57 20.5

For the manufacture of a sample of magnesia cement (prototype) used limestone deposits "Stanovushinskoe" and clay deposits "Zeledeevskoye" per 1 kg of clinker:

 limestone 1,373 kg  clay (dry) 0.275 kg

The clinker exit coefficient from the raw mix K _Out = 0.61. The estimated mineralogical composition of clinker magnesian Portland cement (prototype),% by weight:

C ₃ s 55.8 C ₂ S 16.8 C ₃ A 10.7 C ₄ AF 5.5  MgO 9.8  Other 1.4

Samples were made and fired similarly to samples of classical cement.

Example 1. To make Portland cement from dolomite-1 (table 1).

They took 2 kg of dolomite from the Matyushinsky deposit, crushed to obtain a fraction of 5 ... 10 mm. The crushed stone was fired at a temperature of 1050 ° C for 1 hour. Received 1,128 kg of dolomite lime composition,% by weight:

 MgO 28.7  CaO 56.9 CaCO ₃ 5.3  Other 9.1

Analysis showed that almost all MgCO ₃ underwent dissociation, but CaCO ₃ remained unbaked for about 5% (underburning).

Dolomite lime was hydrated in 5 times the amount of water, i.e. 5.64 liters of water were added to 1.128 kg of lime. The total weight of the suspension was 6.768 kg. The suspension (milk of lime) was poured into a settling tank. After 1 hour, a dense layer of heavy particles formed at the bottom of the sump. The milk of lime above the compacted layer was poured into a second settling tank.

The densified layer had a residual moisture content of about 50%. The dried precipitate had a mass of 0.528 kg and the following composition,% by weight:

 MgO 61,4 Ca (OH) ₂ 8.0 CaCO ₃ 11,4  Other 19.2

The milk of lime in the second settling tank was held for 24 hours. During this time, a layer of lime dough with a moisture content of about 50% was formed in the lower part of the settling tank. The clarified water was drained. The amount of lime test with W = 50% was 1.605 kg, in which Ca (OH) ₂ contained 0.806 kg and CaO 0.606 kg.

0.33 kg of dry clay was added to 1.605 kg of lime dough. The mass was subjected to thorough homogenization. The moisture content of the homogenized feedstock was approximately 41%. The mass was dried to a residual moisture content of 20 ... 25% and granulated into tablets with a diameter of 10 mm and a height of 5 mm. The tablets were finally dried and burned in an electric furnace at a temperature of 1450 ... 1480 ° C. Received 0.9 kg of clinker. The calcined granules were crushed to a fineness characterized by a residue on a sieve 008 5 ... 7%.

The resulting clinker was characterized by the following mineralogical composition,% by weight:

C ₃ s 60.6 C ₂ S 20,0 C ₃ A 10.6 C ₄ AF 6.8  CaO 0.6  MgO 0.6  Other 0.8

The clinker exit coefficient from the raw mix (if one considers Ca (OH) ₂ and clay) To _Ex = 0.79. If the raw mixture is considered 2 source kg of dolomite and 0.33 kg of clay, then K _Out = 0.386.

The activity of the obtained clinker was checked according to the standard method, namely, 6 rolls 40 × 40 × 160 mm in size were prepared from cement: Volsky sand 1: 3, normal density. The samples were tested for compressive and bending strength on day 28 of natural hardening. Cement for the samples was prepared from clinker 97% and gypsum stone 3%.

Example 2. To make Portland cement from dolomite 2.

They took 2 kg of dolomite from the Krutokachinskoye deposit. Crushed and fired similarly to Example 1. Received 1.16 kg of dolomite lime composition,% by weight:

 MgO 36.9 MgCO ₃ 2.2 (underburn)  CaO 47.2 CaCO ₃ 5.0 (underburn)  Other 8.7

Extinguishing was performed in 3 times the volume of water, i.e. 3.48 liters

The separation of heavy and light particles of milk of lime was carried out similarly to Example 1. The result was a dry residue of heavy particles weighing 0.656 kg with the following composition,% by weight:

 MgO 65,2 Ca (OH) ₂ 6.7 MgCO ₃ 4.0 CaCO ₃ 8.8  Other 15.3

The amount of lime test with W = 50% 1.36 kg, in which Ca (OH) ₂ 0.68 kg, and CaO 0.515 kg

0.28 kg of dry clay was added to 1.36 kg of lime test, homogenization, granulation, firing and grinding were carried out similarly to Example 1, clinker was obtained having the following mineralogical composition,% by weight:

C ₃ s 60.6 C ₂ S 20,0 C ₃ A 10.6 C ₄ AF 6.8  CaO 0.6  MgO 0.6  Other 0.8

The composition of the clinker is identical to Example 1, since in both cases one clay was used, however, the clinker yield is less than 0.777 kg.

The clinker exit coefficient from the raw mix (if the raw mix consists of Ca (OH) ₂ and clay) is identical to Example 1. However, if the raw mix is 2 kg of initial dolomite and 0.28 kg of clay, the yield coefficient decreases, K _Yield = 0, 34.

Thus, the above two examples show that regardless of the MgO content in dolomite, it is possible to prepare lime Portland cement from dolomite. The amount of MgO affects the yield of Portland cement. The less MgO is in dolomite, the greater is the yield coefficient of Portland cement clinker from the raw mix.

Table 2 presents the comparative quality characteristics of the resulting cements.

table 2 Comparative characteristics of the quality of the obtained cements Type of cement Setting time, hour-min Strength, MPa Start end bend compression Classical lime Portland cement in accordance with GOST 10187-85 0-45 1-20 5.8 42,2 Magnesian Portland cement (prototype) 0-55 1-45 4.2 39.6 Portland cement from dolomite-1 (invention) 0-40 1-30 5.8 45.5 Portland cement from dolomite-2 (invention) 0-45 1-35 5.9 44.8

Note to table 2.

The fineness of grinding all cement samples was characterized by a residue on sieve 008 of not more than 7%. Cement samples were prepared from clinker 97% and gypsum stone 3%.

The table shows the average results when testing 6 samples.

The results presented in table 2 indicate a significant superiority of the quality of the invention over the prototype, especially in terms of the strength of cement stone in bending.

The quality of cement samples (invention) is noticeably better than samples of classical Portland cement, which is explained by the production method. Classic Portland cement is made from CaCO ₃ and clay, Portland cement from dolomites is made from Ca (OH) ₂ and clay. From the physical chemistry of silicates, it is known that the synthesis of solid solutions from Ca (OH) ₂ and clay is much more efficient than the same synthesis from CaCO ₃ and clay.

Claims (1)

A method of manufacturing portland cement from dolomite, including crushing dolomite, sanding clay, homogenizing the resulting raw material mixture, firing it before sintering and fine grinding the resulting clinker with gypsum stone, characterized in that after dolomite crushing it is fired at a temperature of 900-1100 ° C, quenching water into a lime suspension, its separation into heavy and light particles by settling for 1-2 hours with the separation of light particles - milk of lime, thickening of milk of lime into a lime dough by settling Bani for 20-24 hours and podshihtovku clay performed to the resultant lime test.

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