Limestone belongs to the group of monomial rocks. Its main component is the mineral calcite, which is calcium carbonate (CaCO3) as a chemical compound.

In nature, some limestones really consist exclusively of one calcite, while others contain, in addition to it, various amounts of magnesite and other impurities. These impurities most often consist of iron oxides, clay minerals, sand grains, inclusions of amorphous silica, bitumen, etc. In so-called pure limestone, the total content of additives and impurities rarely exceeds 1%, while in highly contaminated limestones it is can reach 15 and more weight percent. Such limestones are called sandy, clayey (marly), siliceous, dolomite, etc. If the non-calcite components reach the upper limit, we can talk about calcareous sandstone, marl, calcareous dolomite, etc.

Additives and impurities have significant influence on the behavior of limestone in corrosion. Therefore, component analysis of limestone can provide very useful information about some of the processes in determining the genesis of karst. It is often necessary to install:

1) the ratio of carbonate and impurities in calcareous rock,

2) the distribution of cations (Ca: Mg ratio) of its carbonate minerals,

3) composition and mineralogical nature of impurities. The carbonate mass of limestone dissolves without residue in dilute hydrochloric acid:

Therefore, for purposes of study, any sediment consisting of non-carbonate impurities can easily be isolated in this simple manner.

Table 6 shows the chemical compositions of some types of limestone, and in particular the ratio of additives and impurities in them.

Perfectly pure limestone (calcite) contains 56% CaO and 44% CO2, but limestone of this composition is extremely rare in nature.

Impurities in limestone, insoluble in dilute hydrochloric acid, as a rule, do not dissolve in both groundwater and karst waters and can therefore accumulate in the form of significant masses of sediments during the evolution of limestone relief, thereby playing a decisive controlling role in the karst process. The various sediments filling the caves are also composed mainly of these insoluble sediments (Boglt, 1963/2; Lais, 1941; Kukla-Lozek, 1958).

The most common foreign inclusions in limestone, as can be seen from the table. 6. is magnesium carbonate, which is to be expected in most limestones. Its amount is very variable, and in nature there is a gradual transition from chemically pure limestone to chemically pure dolomite, in which the molar ratio of CaCO3 to MgCO3 is 1: 1, which corresponds to a ratio of 54.35: 45.65 in weight percent. The next most common components are SiO2, A12O3 and Fe2O3, but their concentrations are lower than those of MgCO3. The rest of the components are found in smaller quantities and less frequently.

The theoretical assumption regarding the influence of the mineral composition on the solubility of limestone gives ambiguous results, as can be seen from the conflicting conclusions of the corresponding calculations (Ganti, 1957; Marko, 1961). The reason, apparently, is that differences in composition are not always accompanied by differences in the features of the crystal structure and lattice structure, which also affect the dynamics of dissolution. That is why it is essential that experimental researchaimed at comparing the rates of dissolution of known types of limestone in similar conditions.

Among Hungarian authors, mention should be made of T. Mandy and his interesting studies on the comparative solubility of limestones of different geological ages and the Upper Triassic "main dolomite" in aqueous solutions saturated with CO2 at partial atmospheric pressure and flowing down the surface of rocks with different slopes. His experimental findings confirmed and shed new light on the ancient dogma of practice and theory that the solubility of dolomite is much less than the solubility of any limestone. In particular, the longer the contact between the rock and the solvent, the greater this discrepancy (Fig. 6).

Dissolution rate of Triassic "main dolomite" and various limestones with tap water saturated with carbon dioxide

Then T. Mundy recorded a large scatter of the solubility indices of dolomites from different places. Unfortunately, he did not publish the geochemical characteristics of the dolomite limestone samples and thus made it difficult to assess causation between solubility and rock composition.

Much more on this issue can be found from the German researchers A. Gerstenhauer and D. Pfeffer (Gerstenhauer - Pfeffer, 1966), who ruled a series of tests in the laboratory of the Institute of Geography at the University of Frankfurt am Main with the aim of finally solving this problem. On 46 samples of limestone of various ages, taken in a large number of places, they for the first time carried out a quantitative analysis of the content of CaCO3 and MgCO3; then, after grinding to a minimum of 2 mm, they held the samples for 28 hours in room temperature water saturated with CO2 from atmospheric air, and then the dissolution rates were determined. The results obtained with exemplary care and using the most modern chemical and technical means are shown in table. 7.

For some samples A. Gershtenhauer and D. Pfeffer also constructed very instructive diagrams of the dissolution rate, covering time intervals over 28 hours; they are shown in Fig. 7.

As from the table. 7 and from Fig. 7 that the contrasts in the value of solubility for different limestones can reach the same order of magnitude. Another interesting observation is that the dissolution process itself is apparently characterized by specific differences, since the inflections on the dissolution rate diagrams for different samples are not correlated.

To clarify the relationship between the composition of the rock and the mode of dissolution, A. Gershtenhower plotted the dependence of the amount of CaCO3 in solution for 28 hours on the percentage of CaCO3 in the rock (Fig. 8). However, the location of the points plotted in this way did not reveal any hidden pattern: Therefore, one of the main conclusions of this series of experiments can be formulated as follows: even if the dissolution rates of limestones of various compositions do show some weak dependence on the CaCO3 content in the rock, this fact by itself is not able to explain the difference in the degree of solubility.

If we consider the above dissolution rates depending on the content of MgCO3 in the rock, and not CaCO3 (Fig. 5), then a much more correct distribution with a relatively narrow dissolution zone covering the overwhelming majority of points will be obtained. This feature is even more clearly visible in the diagram, where the molar ratio of CaCO3 to MgCO3 is plotted along the abscissa. It allows us to formulate the second main conclusion from these experiments: the solubility of limestone is decisively influenced by the content of MgCO3 in it, which is true even at low values \u200b\u200bof the molar ratio.

Figure: 9 also allows us to see another feature, namely, that the solubility is an inverse exponential, and not a linear function of the MgCO3 content. In other words, if, upon dissolving for 28 hours, the concentration of the solution in contact with limestone containing about 1% MgCO3 reached 40 mg / l, then when the content of MgCO3 was from 2 to 5%, the solubility dropped by half this value; higher concentrations of MgCO3 do not cause a further significant drop in solubility.

In order to exclude the influence on the solubility of other widespread chemical components of limestones in the above experiments, or at least explain this effect, in order to unambiguously determine the effect on the solubility of only magnesium carbonate, A. Gerstenhauer and D. Pfeffer (Gerstenhauer - Pfeffer, 1966 ) conducted similar experiments on dissolving various mixtures of chemically pure powders of calcium and magnesium carbonates. Noteworthy results of these experiments are illustrated in Fig. 10 and 11; in fig. 10 covers the range of all possible concentrations of MgCO3, and in Fig. 11 shows in more detail the range from 0 to 10%: this is the amount of MgCO3 that is found in most of the limestone found in nature.

These experiments show with no doubt that the solubility of CaCO3, or, which is almost the same, of limestone, noticeably decreases even with a minimal content of MgCO3, but that a further, more significant increase in the content of MgCO3 causes a disproportionately smaller decrease in solubility.

Comparison of the absolute values \u200b\u200bof solubility shown in Fig. 10 and 11, with those in Fig. 8 and 9 reveals an interesting pattern: the solubility of natural limestones, both pure and those that contain magnesium, is much higher than the solubility of calcium carbonate powder or a mixture of chemically pure powders of calcium and magnesium carbonates. This somewhat unexpected conclusion may be due to one of two reasons: either non-carbonate impurities in natural limestone contribute to solubility, or the results reflect the influence of the crystal structure and texture of natural limestone.

Solubility in water at room temperature and atmospheric рСО2 - CaCO3 and MgCO3

Since we are talking about an objective assessment of karst phenomena, we are strongly interested in solving this problem. Therefore, we used the analytical data of A. Gershtenhauer and D. Pfeffer, given in table. 7, in order to calculate the content of non-carbonate impurities in 46 samples of limestone, they were entered into the corresponding column of the table. 7 and then depicted the dependence of solubility (for 28 hours) on the content of impurities in the form of a diagram (Fig. 12).

A significant scatter of points in Fig. 12 indicates that the dependence of solubility on the concentration of non-carbonate constituents is not decisive. Obviously, any change in solubility or any other characteristic phenomena associated with the dissolution process, not due to the Ca: Mg ratio, must be attributed to another only possible factor - the influence of the specific texture and crystal structure of the rock.

There is another argument in favor of what has been said, at least as an at least approximate explanation of the phenomenon. Samples A. Gershtenhauer and D. Pfeffer Nos. 1, 34, 35 and 45 consist only of CaCO3 and a small amount of MgCO3. Therefore, the dissolution ability of these four samples should be entirely dependent on the Ca: Mg ratio, if we do not take into account the textural differences. In other words, the dependence curves for these samples should in this case coincide with the graph in Fig. 11. The true situation is shown for comparison in fig. 13 by the authors of this book.

The location of the four points in Fig. 13 in no way can be attributed to the chemical composition of rocks, and it can only be repeated that, most likely, the specificity of solubility is due solely to the effects of lithostructure.

Limestone composition

The chemical composition of pure limestones is close to calcite, where CaO 56% and CO 2 44%. Limestone in some cases includes admixtures of clay minerals, dolomite, quartz, less often gypsum, pyrite, and organic residues, which determine the name of limestones. Dolomitized limestone contains from 4 to 17% MgO, marly limestone - from 6 to 21% SiO 2 + R 2 O 3. Sandy and silicified limestone has impurities of quartz, opal and chalcedony. It is customary to reflect in the name of limestones the predominant presence of organogenic residues (bryozoan, algal), or its structure (crystalline, clotted, detritus), or the shape of rock-forming particles (oolitic, brecciated).

Description and types

According to their structure, limestones are distinguished: crystalline, organogenic-detrital, detrital-crystalline (mixed structure) and drip (travertine). Among crystalline limestones, coarse, fine, and cryptocrystalline (aphanitic) are distinguished by grain size, and recrystallized (marbled) and cavernous (travertine) by their luster at the fracture. Crystalline limestone - massive and dense, slightly porous; travertine - cavernous and highly porous. Among organogenic-detrital limestone, depending on the composition and size of particles, there are: reef limestone; shell limestone (), consisting mainly of whole or crushed shells, fastened with carbonate, clay or other natural cement; detritus limestone composed of shell fragments and other organogenic fragments cemented with calcite cement; algal limestone. White (so-called writing) limestone also belongs to organogenic-detrital limestone. Organogenic-detrital limestones are characterized by a large, low bulk mass and are easily processed (sawn and grinded). Clastic-crystalline limestone consists of carbonate limestone of various shapes and sizes (lumps, clots and nodules of fine-grained calcite), with the inclusion of individual grains and fragments of various rocks and minerals, lenses of cherts. Sometimes limestone is composed of oolitic grains, the cores of which are represented by fragments of quartz and flint. They are characterized by small pores of different shapes, variable bulk density, low strength and high water absorption. Flowing limestone (travertine, calcareous tuff) consists of flowing calcite. It is characterized by cellularity, low bulk density, easy to process and saw.

According to the macrotexture and bedding conditions, limestones are distinguished among massive, horizontally and obliquely bedded, thick and thin platy, cavernous, fractured, spotty, lumpy, reef, funicular, styloid, underwater landslide, etc. Organogenic (biogenic,) chemogenic clastic and mixed limestones. Organogenic (biogenic) limestones are accumulations of carbonate residues or entire skeletal forms of marine, less often freshwater organisms, with a small admixture of mainly carbonate cement. Chemogenic limestones arise as a result of lime deposition followed by recrystallization of the carbonate mass of sediments, mainly from seawater (crystalline limestone) or from mineralized sediments (travertine). Clastic limestones are formed as a result of crushing, washing away and redeposition of angularly rounded fragments of carbonate and other rocks and skeletal remains, mainly in sea basins and on the coasts. Limestones of mixed origin are a complex of deposits formed as a result of sequential or parallel superposition of various processes of formation of carbonate sediments.

The color of limestones is predominantly white, light gray, yellowish; the presence of organic, ferruginous, manganese and other impurities causes a dark gray, black, brown, reddish and greenish color.

Limestone is one of the most widespread sedimentary rocks; it composes various forms of the earth's relief. Limestone deposits are found among the deposits of all geological systems - from Precambrian to Quaternary; the most intense limestone formation occurred in the Silurian, Carboniferous, Jurassic and Upper Cretaceous; make up 19-22% of the total mass of sedimentary rocks. The thickness of the limestone strata is extremely variable: from the first centimeters (in separate layers of deposits) to 5000 m.

Limestone properties

The physical and mechanical properties of limestones are extremely heterogeneous, but they are directly dependent on their structure and texture. The density of limestone is 2700-2900 kg / m 3, fluctuates depending on the content of impurities of dolomite, quartz and other minerals. The volumetric mass of limestones varies from 800 kg / m 3 (in shell rock and travertine) to 2800 kg / m 3 (in crystalline limestones). The compressive strength of limestones ranges from 0.4 MPa (for shell rock) to 300 MPa (for crystalline and aphanite limestone). When wet, the strength of limestones often decreases. Most of the deposits are characterized by the presence of limestones that are not uniform in strength. Losses for wear, abrasion and crushing increase, as a rule, with a decrease in the bulk density of limestone. Frost resistance for crystalline limestones reaches 300-400 cycles, but changes sharply in limestones of a different structure and depends on the shape and connection of pores and cracks in it. The processability of limestones is directly related to their structure and texture. Shell rock and porous limestones are easily sawn and trimmed; crystalline limestones are well polished.

Limestone application

Limestone has universal industrial applications, agriculture and construction. In metallurgy, limestone is used as a flux. In the production of lime and cement, limestone is the main component. Limestone is used in the chemical and food industries: as an auxiliary material in the production of soda, calcium carbide, mineral fertilizers, glass, sugar, paper. It is used in the refining of petroleum products, dry distillation of coal, in the manufacture of paints, putties, rubber, plastics, soaps, medicines, mineral wool, for cleaning fabrics and processing leather, liming soils.

Limestone is the most important building material, from which facing

This governing normative document specifies methods for determining the chemical composition of flux limestones.

The methods described in this document apply at the manufacturer's place of shipment and at the customer's place when the product arrives.

1. GENERAL REQUIREMENTS

1.1. All reagents must be at least analytical grade. Distilled water for preparation of reagent solution and analysis - according to GOST 6709-72 and deionized.

1.2. The determination of the mass fraction of elements is carried out in two parallel samples, weighed with a random error of 0.0002 g.

1.3. The value of the total error of the average analysis result is monitored at least once per shift by carrying out the analysis of the standard sample simultaneously with the analysis of the sample and under the same conditions. For control, select a standard sample with a chemical composition that meets the requirements of this document for the method for determining the mass fraction of elements. The average result of the analysis of a standard sample should not differ from the value of the mass fraction of the element to be determined by more than half the value of the allowable difference for the corresponding range of the mass fraction of the element. Otherwise, the determination of the mass fraction of the element of the analyzed sample in the standard sample is repeated. The reanalysis results are considered final.

1.4. For the final analysis result, the arithmetic mean of the results of two parallel measurements is taken, provided that the discrepancy between the results of parallel measurements should not exceed the discrepancies allowed at a confidence level of 0.95, given in table. ...

Table 1

	Mass fraction of the element,%	Permitted discrepancies, abs. %
Calcium oxide	from 40.0 to 50.0
	st. 50.0 "60.0
Magnesium oxide
	st. 2.0 "5.0
Insoluble residue
	st. 0.5 "1.0
	from 0.005 to 0.01
	st. 0.01 "0.02
	from 0.015 to 0.03
	st. 0.03 "0.05
		A solution with a volume fraction of hydrochloric acid of 0.5; 0.06 - according to GOST 3118-77. Porcelain rectangular boats - according to GOST 9147-80 K, low porcelain crucibles - according to GOST 9147-80 E. Ash-free filters "white tape", filter paper with a known ash content or medium density filters. 2.2.3. Algorithm of operations for preparing solutions for analysis A solution with a volume fraction of hydrochloric acid of 0.5 is prepared as follows: one volume part of a solution of hydrochloric acid with a mass concentration of 1.19 g / cm3 is mixed with the same volume of water and shaken thoroughly. A solution with a volume fraction of hydrochloric acid of 0.05 is prepared as follows: five parts by volume of a solution of hydrochloric acid with a mass concentration of 1.19 g / cm3 are mixed with 95 the same volumes of water and stirred. 2.2.4. Measurement Algorithm A weighed portion of an air-dry sample weighing 1 g is placed in a conical flask with a capacity of 100 cm3, previously moistened with water. Carefully poured 15 cm3 of a solution with a volume fraction of hydrochloric acid of 0.5, heated to boiling and boiled for 3 minutes. The precipitate is washed by filtration through an ashless white ribbon filter or filter paper. The walls of the flask are washed twice with a hot solution with a volume fraction of hydrochloric acid of 0.06, wiped with a piece of filter and the precipitate is washed five times with hot water. The filter with an insoluble residue is placed in a weighed porcelain boat or crucible, ashed and pierced at 900 ° C for 20 minutes. The cooled precipitate is weighed. 2.2.5. Analysis results processing The mass fraction of the insoluble residue (X) in percent is calculated by the formula where m is the found mass of the insoluble residue, g; M1 is the mass of the sediment of the control experiment, g; M - sample weight, g. 2.3. Determination of the mass fraction of calcium oxide 2.3.1. Measurement method The method is based on the determination of calcium oxide by complex-metric titration with an acid chromium-dark blue indicator at pH 12. The effect of ferric iron and aluminum is eliminated with a masking mixture or triethylamine, binding them into a fluoride complex. It is allowed to use the indicators fluorexon and murexid. 2.3.2. Measuring instruments, auxiliary devices, reagents GOST 1770-74 E. GOST 25336-82 E. GOST 3760-79. A solution with a volume fraction of hydrochloric acid of 0.33 - according to GOST 3118-77. A solution of potassium oxide hydrate with a mass concentration of 20 g / cm3. Disodium salt of ethylenediaminetetraacetic acid (Trilon B), the molar concentration of Trilon B equivalent is 0.025 mol / dm3 - according to GOST 10652-73. Zinc granular. Triethanolamine - according to TU 6-09-2448-86. Congo paper. It is allowed to use imported reagents and glassware. 2.3.3. Algorithm of operations for preparing solutions for analysis A solution of the molar concentration of a zinc salt equivalent, exactly 0.05 mol / dm3, is prepared as follows: 1.6345 g of metallic zinc is weighed with a random error of ± 0.0002 g, placed in a porcelain cup and dissolved by heating in a water bath in a mixture of 100 cm3 water and 15 cm3 of nitric acid, covering the cup with glass. Then the glass is thoroughly washed off with water, collected in the same cup and the solution is evaporated to 3 - 4 cm3. The remainder of the dish is quantitatively transferred, washing the walls of the dish with water, into a volumetric flask with a capacity of 1 dm3 and the volume is brought up to the mark with water. The solution is suitable for a month. The molar concentration of the Trilon B equivalent, equal to 0.025 mol / dm3, is prepared as follows: 9.31 g of Trilon B is dissolved in water and the volume is brought to 1 dm3 with water. The solution is stored in polyethylene or glass, waxed from the inside, vessels. A buffer solution pH 9.5 ... 10 is prepared as follows: 70 g of ammonium chloride is dissolved in 1000 cm3 of aqueous ammonia, solution 1: 1. The masking mixture is prepared as follows: 15 g of sodium fluoride is dissolved by heating in 1 dm3 of water and 20 cm3 of triethanolamine is added. The indicators are prepared as follows: 0.250 g of the indicator is ground in a mortar with 25 g of sodium chloride or 1 g of the indicator is dissolved in 10 cm3 of a buffer solution of pH 9.5 ... 10 and the volume is adjusted to 100 cm3 with distilled water. The molar concentration of the Trilon B equivalent, equal to 0.5 mol / dm3, is determined by the zinc salt solution as follows: 5 cm3 of the buffer solution is added to 25 cm3 of the zinc salt with a molar concentration of the equivalent of 0.05 mol / dm3, about 0.1 g of the eriochrome indicator black T and 70 cm3 of water. The solution is stirred and titrated with Trilon B solution until the violet-red color turns blue. The molar concentration of the Trilon B equivalent, equal to 0.05 mol / dm3, is calculated by the formula where Y is the volume of Trilon B with a molar concentration equivalent of 0.005 mol / dm3, consumed for titration, cm3. The mass concentration of Trilon B (T) for calcium oxide in g / cm3 is calculated by the formula where N is the molar concentration of the equivalent; 28.04 is the gram equivalent of calcium oxide. In addition to this method, it is allowed to set the mass concentration of Trilon B according to a standard sample. 2.3.4. Measurement Algorithm A weighed portion of an air-dry sample of 0.5 g is dissolved in 30 cm3 of a solution in a volume fraction of hydrochloric acid of 0.33 in a conical flask with a capacity of 250 cm3 with heating and boiled for 3 minutes. The solution is transferred into a volumetric flask with a capacity of 250 cm3, the volume is added up to the mark with water, mixed thoroughly. To determine the mass fraction of calcium oxide, 50 cm3 of the prepared solution is taken into a conical flask with a capacity of 500 cm3, diluted with water to 200 cm3, 5 cm3 of a masking mixture or 5 ... 7 drops of triethanolamine is injected, (15 ... 20) cm3 of Trilon B solution is added , neutralized with a solution of potassium oxide hydrate with a mass concentration of 20 g / cm3 on Congo indicator paper, give an excess of about 10 cm3 of alkali (pH 12-13); 0.10 - 0.15 g or 4 - 6 drops of dark blue acid chromium indicator and continue adding Trilon B until the color changes from crimson to violet. Titration is allowed not only, but also with various kinds of titrators in appropriate vessels. 2.3.5. Processing results The mass fraction of calcium oxide (X) in percent is obtained by the formula where Y is the volume of Trilon B consumed for titration, cm3; T is the mass concentration of Trilon B in terms of calcium oxide, g / cm3; M is a sample portion contained in an aliquot part of the solution, g. 2.4. Determination of the mass fraction of magnesium oxide 2.4.1. Measurement method The method is based on the tetrametric determination of magnesium ions after precipitation of calcium in the form of oxalate. 2.4.2. Measuring instruments, auxiliary devices, reagents Analytical balance with weights. Laboratory glass beakers and flasks - according to GOST 25336-82 E. Laboratory glassware. Cylinders, beakers, flasks - according to GOST 1770-74 E. Laboratory glass measuring instruments. Pipettes, burettes - in accordance with GOST 20292-74E. A solution with a volume fraction of hydrochloric acid of 0.5 - according to GOST 3118-77. Magnesium sulfate - according to TU 6-09-2540-87. A solution of ammonium oxalate with a mass fraction of 4% - according to GOST 5712-78. An ammonia solution with a mass concentration of 25 g / cm3 - in accordance with GOST 3760-79. Methyl orange indicator - according to TU 6-09-5171-84. Eriochrome black T indicator - according to TU 6-09-1760-72. Dark blue acid chromium indicator - according to TU 6-09-3870-84. Ash-free filters "white tape" or filter paper with a known ash content. It is allowed to use imported reagents and glassware. 2.4.3. Algorithm of operations for preparing solutions for analysis An ammonia buffer solution with pH 9.5 is prepared as follows: 70 g of ammonium chloride is dissolved in 1000 cm3 of aqueous ammonia, a 1: 1 solution. The molar concentration of the equivalent of magnesium sulfate, equal to exactly 0.1 mol / dm3, is prepared as follows: the contents of one ampoule of magnesium sulfate fixanal are quantitatively transferred into a volumetric flask with a capacity of 1 dm3 and brought to the mark with water. The molar concentration of the Trilon B equivalent, equal to 0.025 mol / dm3, is prepared as follows: 9.31 g of Trilon B is dissolved in water and brought to 1 dm3. The indicators are prepared as follows: 0.250 g of the indicator is ground in a mortar with 25 g of sodium chloride or 1 g of the indicator is dissolved in 10 cm3 of a buffer solution of pH 9.5-10 and the volume is brought to 100 cm3 with distilled water. The molar concentration of the Trilon B equivalent, equal to 0.5 mol / dm3, is determined by the zinc salt solution as follows: 5 cm3 of the buffer solution is added to 25 cm3 of the zinc salt with a molar concentration of 0.006 mol / dm3, about 0.1 g of the eriochrome black indicator T and 70 cm3 of water. The solution is stirred and titrated with Trilon B solution until the violet-red color turns blue. The molar concentration of the Trilon B equivalent, equal to 0.05 mol / dm3, is calculated by the formula where Y is the volume of Trilon B with a molar concentration equivalent of 0.005 mol / dm3, consumed for titration, cm3. The mass concentration of trilon B (T) for magnesium oxide in g / cm3 is calculated by the formula where N is the molar concentration of the equivalent; 20.16 is the gram equivalent of magnesium oxide. It is also allowed to set the mass concentration of Trilon B according to a standard sample and synthetic resin of standard samples. 2.4.4. Measurement Algorithm A weighed portion of an air-dry sample of 0.5 g is dissolved in 20 cm3 of a solution with a volume fraction of hydrochloric acid of 0.5 in a conical flask with a capacity of 250 cm3 with heating and boiled for 3 minutes. 50 cm3 of hot water, 20 cm3 of a solution of ammonium oxalate with a mass concentration of 4 g / cm3 are poured into the solution, allowed to boil, 1 - 2 drops of methyl orange indicator are introduced and neutralized with an ammonia solution with a mass fraction of 0.5. The precipitate is filtered through a medium-density filter, the walls of the flask and the filter with the precipitate are washed with cold water. The filtrate and water washing are collected in a volumetric flask with a capacity of 250 cm3, brought to the mark with water and mixed thoroughly. In a conical flask with a capacity of 250 cm3, take 50 cm3 of the filtrate, add 50 cm3 of water, 5 cm3 of an ammonia buffer solution, 0.1 - 0.2 g of an indicator mixture of acidic chromium dark blue or 4 - 5 drops of an indicator solution and titrate with a solution of Trilon B to color transition from pink to purple. 2.4.6. Processing results The cash fraction of magnesium oxide (X) in percent is calculated by the formula where Y is the volume of Trilon B consumed for titration, cm3; T is the mass concentration of trilon B in terms of magnesium oxide, g / cm3; M is a sample portion contained in an aliquot part of the solution, g. 2.5. Determination of the mass fraction of sulfur - according to GOST 23581.20-81 or the methods of flux-producing enterprises, approved by ISO TsNIICHM. 2.6. Determination of the mass fraction of phosphorus 2.6.1. Measurement method The method is based on the formation of a phosphorus-anadium molybdenum complex compound in the presence of an acid and photometry of the colored solution. 2.6.2. Measuring instruments, auxiliary devices, reagents Analytical balance with weights Glass laboratory glasses and flasks - according to GOST 25366-82 E. Laboratory glassware. Cylinders, beakers, flasks - according to GOST 1770-74 E. Laboratory glass measuring instruments. Pipettes, burettes - in accordance with GOST 20292-74E. A solution with a volume fraction of nitric acid of 0.33 - according to GOST 4461-77. Potassium phosphate monobasic - in accordance with GOST 4198-75. Ammonium molybdenum - in accordance with GOST 3765-78. Ammonium vanadium acid - according to GOST 9336-75. The use of imported reagents and utensils is allowed. 2.6.3. Algorithm of operations for preparing solutions for analysis A solution of ammonium vanadium molybdate is prepared as follows: 10 g of ammonium molybdate is dissolved in 100 cm3 of hot water, then 2 cm3 of nitric acid is added and filtered if a precipitate forms. Separately dissolve 0.3 g of ammonium vanadium acid in 50 cm3 of water at 50-60 ° C, cool and add 50 cm3 of a solution with a volume fraction of nitric acid of 0.33. The prepared solution of ammonium molybdate is poured with stirring into a solution of ammonium vanadium, then 16 cm3 of nitric acid is added and stirred. Store the solution in a closed bottle in a dark place. A standard phosphorus solution is prepared as follows: 0.1917 g of double-recrystallized monosubstituted potassium phosphate is dissolved in a small amount of water in a 1 dm3 volumetric flask, added with water to the mark and stirred. 1 cm3 of a standard solution corresponds to 0.1 mg of phosphorus pentoxide. The solution of the control experiment is prepared as follows: 15 cm3 of nitric acid heated to 60 - 80 ° C is placed in a volumetric flask with a capacity of 100 cm3, then 10 cm3 of a solution of ammonium vanadium molybdicate is poured in, topped up to the mark with water and stirred. 2.6.4. Measurement Algorithm A weighed portion of an air-dry sample of 1.0 g is moistened with water and placed in a glass with a capacity of 100 cm3, 5 cm3 of aqua regia is poured in and evaporated to dryness. The residue is moistened with 3 cm @ 3 of hydrochloric acid and evaporated to dryness. 5 cm3 of nitric acid is poured in and evaporated to a syrup consistency, at which the liquid is covered with a film. The volume of the solution should be no more than 1 - 1.5 cm3. If at the end of evaporation brown nitrogen oxides continue to evolve, indicating the presence of organic compounds, then 5 cm3 of nitric acid is re-poured and again evaporated to a syrup consistency. To the evaporated solution is poured 15 cm3 of a solution heated to 60 - 80 ° C with a volume fraction of nitric acid of 0.33, heated for several minutes, filtered through a "white tape" filter or a medium density filter into a 100 cm3 volumetric flask. The filter cake is washed 2 - 3 times with cold water. To the reagent in the flask, add 10 cm3 of a solution of ammonium vanadium molybdate, bring to the mark with water and mix. The optical density of the solution is measured on a photochromatograph at 413 nm using a filter No. 3 with a transmission range of 400 - 500 nm and a cuvette with a colorimetric layer thickness of 50 nm relative to a solution that does not contain a standard phosphorus solution. To build a calibration graph, 0, 1, 2, 3, 4 and 5 cm3 of a standard phosphorus solution are taken into a series of volumetric flasks with a capacity of 100 cm3, which corresponds to 0; 0.1; 0.2; 0.3; 0.4 and 0.5 mg of phosphorus oxide. 5 cm3 of nitric acid and 8 cm3 of ammonium vanadium molybdicate are poured into each flask, add water to the mark and mix. After 3 - 4 minutes. measure the optical density of the solution. As a reference solution, a solution of the control experiment prepared simultaneously with the analyzed solution is used. The optical density of the analyzed solution is used to establish the mass fraction of phosphorus pentoxide according to the calibration graph. 2.6.5. Processing results The mass fraction of phosphorus in terms of pentoxide (X) in percent is calculated by the formula where М1 is the mass of phosphorus pentoxide, found according to the calibration graph, mg; M is the mass of the sample, g; U1 - volume of an aliquot of the analyzed solution, cm3; Y is the volume of the entire analyzed solution, cm3. The mass fraction of phosphorus (X1) is determined by the formula where 2.29 is the conversion factor of phosphorus pentoxide to phosphorus. 2.7. It is allowed to conduct a chemical analysis of flux limestones according to other methods and procedures certified by ISO TsNIICHM, which guarantee no less accuracy than this RD. In case of disagreement in assessing the quality of fluxed limestone, the analysis is carried out according to RD 14-16-3-90. 2.8. Determination of conformity of KDU-1 limestone to the technical requirements of NTD for the stability of the content of magnesium oxide (MgO). 2.8.1. This definition produced by a statistical method for each batch of limestone based on the results of chemical analysis. 2.8.2. The main statistical characteristics of the mass fraction of magnesium oxide in a batch of limestone are: xi - mass fraction of magnesium oxide in i-th sample taken from a batch of limestone ( i = 1, 2, ..., n), %; The arithmetic average mass fraction of magnesium oxide in a batch of limestone,% σ - standard deviation of samples from the average value in a batch of limestone,% 2.8.3. A batch of limestone meets the technical requirements of NTD for the mass fraction of magnesium oxide in the case when all samples (X1, X2, ..., Xn) fit into the standard range of 7 - 12%, and the actual standard deviation (σf) does not exceed the maximum allowable standard deviation (σm), given in table. ... 2.8.4. If the actual standard deviation (σf) is more than the maximum permissible deviation (σm), then the limestone of this batch is unaveraged dolomitized limestone. 2.8.5. Reducing the range of fluctuations in the mass fraction of magnesium oxide in a batch of limestone is determined in the case when the actual standard deviation (σf) is less than the standard standard deviation equal to ± 0.5% (σm \u003d 0.5%). Assuming that the results are guaranteed with a probability of 0.95, the decrease in the range of fluctuations in the mass fraction of magnesium oxide in a batch of limestone (D) against the calculated rate (± 1.0%) is equal to table 2 Number of samples taken from a batch of limestone (n) Maximum permissible deviation (σm),% Mining Branch of the All-Union Institute of Refractories (GF VIO) Director Yu.I. Berezhnoy Head of laboratory I.V. Andryushchenko Topic leader, researcher T.A. Booth Donnyichermet Head of laboratory A.I. Ryabenko Agreed Concern "Metallurgprom" of the Ministry of Metallurgy of the USSR Vice-chairman V.T. Poluyekt Letter dated 12.03.90 No. 01-4-90 Concern "Rudprom" of the Ministry of Metallurgy of the USSR Deputy Chief Engineer V.G. Evsin Letter dated 12.03.90 No. 06-3 / 31 Ferroplastic Industry Department of the USSR Ministry of Metallurgy Deputy Chief V.A. Matvienko Letter dated 12.03.90 No. 04-65 / 7 Mining Department of the USSR Ministry of Metallurgy Deputy Chief IN AND. Kolesnikov Letter dated 12.03.90 No. 41-31-06 SCROLL documents referred to in the text RD 14-16-3-90
	Iron ores, concentrates, anglomerates and pellets. Methods for determination of sulfur
TU 6-09-3870-84	Chrome dark blue indicator (acid chromium dark blue), indicator; 2- (5-chloro-2-hydroxyphenyl) -AEO-1,8-dioxynaphthalene-3,6-disulfonic acid disodium salt) pure for analysis
TU 6-09-2448-86	NITILotriethanol
TU 6-09-2540-87	Standard titers (fixed channels, norm doses)
TU 6-09-5171-84	Methyl orange indicator (sodiumnic), pure for analysis

MUNICIPAL EDUCATIONAL INSTITUTION SECONDARY EDUCATIONAL SCHOOL p. OCTOBER

STERLITAMAK DISTRICT OF THE REPUBLIC OF BASHKORTOSTAN

Section: World of Chemistry

Category: The world around us

Performed:Zaydullina Alsou, student of grade 7 MOBU secondary school s. Oktyabrskoe

Scientific adviser: Iskhakova R.U., teacher of chemistry MOBU secondary school p. Oktyabrskoe

2015

Introduction

study the literature on this issue;

study the physical properties of limestone;

study the chemical properties of limestone;

get limestone yourself;

to conclude.

STUDY OF LITERATURE. What is limestone?

Limestone - sedimentary rock of organic origin, consisting mainly of calcium carbonate (CaCO 3 ) in the form of crystals of calcite of various sizes.

Limestone, consisting mainly of the shells of marine animals and their debris, is called shell rock. In addition, there are nummulite, bryozoan and marble-like limestones - massively layered and thinly layered.

According to their structure, limestones are distinguished: crystalline, organogenic-detrital, detrital-crystalline (mixed structure) and drip (travertine). Among crystalline limestones, coarse, fine, and cryptocrystalline (aphanite) are distinguished by grain size, and recrystallized (marbled) and cavernous (travertine) by their luster at the fracture. Crystalline limestone - massive and dense, slightly porous; travertine - cavernous and highly porous.

Among organogenic-detrital limestone, depending on the composition and size of the particles, there are: reef limestone; shell limestone (shell rock), consisting mainly of whole or crushed shells, fastened with carbonate, clay or other natural cement; detritus limestone composed of shell fragments and other organogenic fragments cemented with calcite cement; algal limestone. White (the so-called Writing) chalk also belongs to organogenic-detrital limestones.

Organogenic-detrital limestones are characterized by large porosity by my mass and are easily processed (sawn and polished). Clastic-crystalline limestone consists of carbonate detritus of various shapes and sizes (lumps, clots and nodules of fine-grained calcite), with the inclusion of individual grains and fragments of various rocks and minerals, lenses of cherts. Sometimes limestone is composed of oolitic grains, the cores of which are represented by fragments of quartz and flint. They are characterized by small pores of different shapes, variable volumetric weight, low strength and high water absorption. Flowing limestone (travertine, calcareous tuff) consists of flowing calcite. It is characterized by cellularity, low bulk density, easy to process and saw.

Limestone has universal applications in industry, agriculture and construction:

In metallurgy, limestone is used as a flux.

In the production of lime and cement, limestone is the main component.

Limestone is used in the chemical and food industries: as an auxiliary material in the production of soda, calcium carbide, mineral fertilizers, glass, sugar, paper.

It is used in the purification of petroleum products, dry distillation of coal, in the manufacture of paints, putties, rubber, plastics, soap, medicines, mineral wool, for cleaning fabrics and processing leather, liming soil.

Limestone has been used as a building material since ancient times; and at first it was rather "simple-minded": they found a cave and settled it in accordance with the existing requests.

2.STUDY OF PHYSICAL PROPERTIES.

(Appendix 2).

Each mineral has its own, inherent only to him signs, I considered the following signs:

Shine

matt

Hardness

average

Colour

white-gray

Density

2000-2800kg / m 3

Electrical conductivity

10 ~ 5 to 10 ~~ 4

Thermal conductivity

0.470 m * K

Solubility. (Appendix 3)

Water solubility

Limestone does not dissolve in water

Solubility in acetone (organic solvent)

Limestone does not dissolve in acetone

STUDY OF CHEMICAL PROPERTIES

(Appendix 4)

Experience number 1. Interaction of limestone with acids (hydrochloric, acetic, nitric).

Chemicals and equipment:

Strong acids:HCI (hydrochloric), HNO 3 (nitrogen).

Weak CH 3 COOH (acetic).

Test tube rack, spirit lamp, holder.

Reagent

Observations

Conclusion

HCI (salt),

The reaction is violent

Reacts well with hydrochloric acid

HNO 3 (nitrogen)

Droplets of water appeared on the walls of the test tube and carbon dioxide was released.

The reaction is violent

Reacts well with nitric acid. Better with salt.

CH 3 COOH (acetic)

Droplets of water appeared on the walls of the test tube and carbon dioxide was released.

The reaction is slow, but when heated, the reaction rate increased.

Reacts poorly with acetic acid. Because acid is weak.

CaCO 3 + 2HCl \u003d CO 2  + H 2 O + CaCI 2

CaCO 3 + 2CH 3 COOH \u003d (CH 3 COO) 2 Ca + H 2 O + CO 2 

CaCO 3 + 2HNO 3 \u003d Ca (NO 3 ) 2 + CO 2  + H 2 O

Conclusion: Limestone interacts with acids with the release of carbon dioxide and water. With strong acids, the reaction was violent, and with a weak acid, the reaction began only after heating.

Experience number 2. Interaction with alkalis (water-soluble bases).

(Appendix 4)

Chemicals and equipment:

Sodium hydroxide -NaOH , tripod with test tubes, spirit lamp, holder.

Experience description : A certain amount of limestone was added to the test tube and sodium hydroxide was added. There was no reaction, after 15 minutes more reagent was added and heated. No reaction was observed.

Conclusion: Limestone does not react with alkalis.

Experience number 3. Limestone decomposition.

(Appendix No. 5).

Chemicals and equipment: limestone, tripod, gas pipe, flask, torch, spirit lamp.

Experience description : Limestone was placed in a test tube and closed with a gas outlet tube, the end of which was lowered into a flask. We lit a spirit lamp and started heating. The presence of carbon dioxide was determined using a burning torch.

Observations: Limestone decomposes. The color turned white. Droplets of water appeared on the walls of the test tube and carbon dioxide was released.

CaCO 3 CaO + CO 2

Conclusion: When heated, limestone decomposes to form calcium oxide and water.

Experience number 4. Getting limestone at home.

To complete the experiment you will need:

plastic bucket

plastic cups

dry plaster

gypsum mix

Time for the experiment: 15 minutes to prepare for the experience and 5 days to get limestone.

To get limestone:

1. 1. 1. I poured the resulting mixture into plastic cups.

         I put the cups in a warm place. Left alone for 5 days.

         On the 5th day, I extracted the resulting limestone.

Note:

Shells can be any size, but use smaller shells for the best limestone quality.

Observation: Does the resulting limestone look like natural?

Result:

Limestone is a type of sedimentary rock. When microscopic marine animals die, they fall to the ocean floor, where they are harvested for shells. This is how shells collect these particles over time and limestone is formed..

Objective: determine the activity of lime, the speed and temperature of slaking.

Basic concepts

Building air lime is a product obtained by burning calcium-magnesium rocks to the fullest possible release of carbon dioxide. Lime is used in a mixture with various additives to obtain various binders: lime-quartz, lime-slag, lime-clay, etc. It is used to make silicate bricks, silicate blocks, reinforced large-sized silicate parts and various other building products.

The main process in the production of air lime is calcination, in which limestone is decarbonized and converted and converted to lime by the following reaction:

CaCO 3 + 178.58 kJ →CaO + CO 2

Under laboratory conditions, the dissociation of calcium carbonate occurs at about 900 ° C, in production the firing temperature is 1000-1200 ° C.

Quicklime is lumpy and ground. It is obtained in the form of lumps of light yellow or gray color. It intensively absorbs moisture and therefore it is recommended to store it in a hermetically sealed state. If the raw material contains more than 6% clay impurities, then the fired product exhibits hydraulic properties and is called hydraulic lime.

The quality of the resulting lime is assessed by its activity, which shows the total content of free calcium and magnesium oxides in an active state. In addition to them, lime may contain oxides of MgO and CaO in an inactive state; these are undecomposed carbonate and coarse-crystalline inclusions (burnout).

Depending on the content of active CaO and MgO, lime is produced in three grades (Table 9.1).

Table 9.1

Classification of lime by grade

Air lime can be used slaked.

Slaked lime comes in the form of fluff, dough or milk. The moisture content in the fluff does not exceed 5%, in the dough it is less than 45%. The quenching process proceeds as follows:

CaO + H 2 O ↔ Ca(OH) 2 +65.1 kJ

and is accompanied by the release of heat, which causes a rise in temperature that can ignite the tree. Hydration of calcium oxide is a reversible reaction, its direction depends on the temperature and pressure of water vapor in the environment. The elasticity of dissociation of Ca (OH) 2 into CaO and H 2 O reaches atmospheric pressure at 547 ° C; at a higher temperature, calcium hydroxide can partially decompose. In order for the process to go in the right direction, it is necessary to strive to increase the elasticity of water vapor over Ca (OH) 2 and not to allow too high a temperature. At the same time, overcooling of the slaked lime should be avoided, as this greatly slows down the slaking. More than half of its grains have a size not exceeding 0.01 mm. Vaporization protects the material from excessive temperature rise.

The volume of fluff during lime slaking is 2-3 times higher than the volume of the original quicklime due to an increase in the volume of voids (pores) between individual grains of the resulting material. The density of quicklime is on average 3200, and that of slaked lime is 2200 kg / m 3.

To slake lime, it is theoretically necessary to add 32.13% water by weight to the fluff. Almost depending on the composition of the lime, the degree of its burning and the method of slaking, they take about two and sometimes three times more water, since under the influence of the heat released during slaking, vaporization occurs, and part of the water is removed.

Depending on the temperature developed during quenching, there are high exothermic (t quenching\u003e 50 ° C) and low exothermic (t quenching.<50 °C) известь, а по скорости гашения: быстрогасящуюся (не более 8 мин.), среднегасящуюся (8-25 мин.) и медленногасящуюся (более 25 мин.) известь.

To accelerate the lime slaking process, CaCl 2, NaCl, NaOH additives are used, which interact with calcium oxide to form more soluble compounds in comparison with Ca (OH) 2, and to slow down - the addition of surfactants, salts of sulfuric, phosphoric, oxalic, carbonic acids.