MUNICIPAL EDUCATIONAL INSTITUTION SECONDARY EDUCATIONAL SCHOOL with. OCTOBER
STERLITAMAK DISTRICT OF THE REPUBLIC OF BASHKORTOSTAN
Section: World of Chemistry
Category: The world around us
Performed:Zaidullina Alsu, a 7th grade student of the MOBU secondary school with. October
Scientific adviser: Iskhakova R.U., teacher of chemistry, MOBU secondary school s. October
2015
Introduction
study the literature on this issue;
study the physical properties of limestone;
explore Chemical properties limestone;
get limestone on your own;
to conclude.
LITERATURE STUDY. What is limestone?
Limestone -sedimentary rock of organic origin, consisting mainly of calcium carbonate ( CaCO3 ) in the form of calcite crystals of various sizes.
Limestone, consisting mainly of the shells of marine animals and their fragments, is called shell rock. In addition, there are nummulite, bryozoan and marble-like limestones - massively layered and thinly layered.
According to the structure, limestones are crystalline, organogenic-detrital, detrital-crystalline (mixed structure) and sinter (travertine). Among crystalline limestones, coarse-grained, fine-crystalline and cryptocrystalline (aphanite) are distinguished by grain size, recrystallized (marble-like) and cavernous (travertine) by brilliance at a 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, the following are distinguished: reef limestone; shell limestone (shell rock), consisting mainly of whole or crushed shells, bonded 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) chalk also belongs to organogenic-detrital limestones.
Organogenic-clastic limestones are characterized by large porosity and mass and are easily processed (sawn and polished). Detrital-crystalline limestone consists of carbonate detritus different shapes and size (lumps, clots and nodules of fine-grained calcite), with the inclusion of individual grains and fragments of various rocks and minerals, flint lenses. Sometimes limestone is composed of oolitic grains, the cores of which are represented by fragments of quartz and flint. Characterized by small pores of various shapes, variable bulk density, low strength and high water absorption. Sintered limestone (travertine, calcareous tuff) consists of sintered calcite. It is characterized by cellularity, low bulk density, easy processing and sawing.
Limestone has a universal application in industry, agriculture and construction:
In metallurgy, limestone serves as a flux.
In the production of lime and cement, limestone is the main ingredient.
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, soaps, medicines, mineral wool, for cleaning fabrics and processing leather, liming soils.
Limestone has been used as a building material since ancient times; and at first it was rather “simple-hearted”: 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 characteristics, inherent only to it, I considered the following signs:
Shine
matte
Hardness
average
Color
white-grey
Density
2000-2800kg / m 3
Electrical conductivity
10~5 to 10~~4
Thermal conductivity
0.470 m*K
Solubility. (Annex 3)
Solubility in water
Limestone does not dissolve in water
Solubility in acetone (organic solvent)
Limestone does not dissolve in acetone
STUDY OF CHEMICAL PROPERTIES
(Annex 4)
Experience number 1. Interaction of limestone with acids (hydrochloric, acetic, nitric).
Chemicals and equipment:
Strong acids: HCI (salt), HNO 3 (nitrogen).
Weak CH 3 COOH (acetic).
Stand with test tubes, spirit lamp, holder.
Reagent
Observations
Conclusion
HCI(salt),
The reaction is violent
Interacts well with hydrochloric acid
HNO 3 (nitrogen)
Water droplets appeared on the walls of the test tube and carbon dioxide was released.
The reaction is violent
It interacts well with nitric acid. Better with salt.
CH 3 COOH(vinegar)
Water droplets appeared on the walls of the test tube and carbon dioxide was released.
The reaction is slow, but when heated, the reaction rate increased.
Does not interact well with acetic acid. Because weak acid.
CaCO 3 +2HCl=CO 2 +H 2 O+CaCI 2
CaCO 3 +2CH 3 COOH=(CH 3 COO) 2 Ca + H 2 O+ CO 2
CaCO 3 + 2HNO 3 =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).
(Annex 4)
Chemicals and equipment:
Sodium hydroxide - NaOH , rack 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 another reagent was added and heated. No reaction was observed.
Conclusion: Limestone does not react with alkalis.
Experience number 3. The decomposition of limestone.
(Appendix No. 5).
Chemicals and equipment: limestone, tripod, vent tube, 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 the flask. They lit the stove and started to heat it up. The presence of carbon dioxide was determined using a burning splinter.
Observations: Limestone is decomposing. The color turned white. Water droplets appeared on the walls of the test tube and carbon dioxide was released.
CaCO3 CaO+CO2
Conclusion: When heated, limestone decomposes to form calcium oxide and water.
Experience number 4. Getting limestone at home.
To complete the experience you will need:
plastic bucket
plastic cups
dry plaster
gypsum mixture
Time for the experiment: 15 minutes to prepare for the experience and 5 days to get limestone.
To get limestone:
Pour the resulting mixture into plastic cups.
I placed the cups in a warm place. Left alone for 5 days.
On the 5th day, the resulting limestone was removed.
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 one of the types of sedimentary rocks. When microscopic marine animals die, they fall to the bottom of the ocean, where they are collected by barnacles. This is how shells collect these particles over time, and limestone is formed..
Limestone- This is a soft sedimentary rock of organo-chemical or organic origin, consisting mainly of calcite (calcium carbonate) and often containing impurities of quartz, silicon, phosphate, sand and clay particles, as well as the remains of calcareous skeletons of microorganisms. Most often it has a white, yellowish, light gray or light beige color, less often it is pinkish. White-yellow and white-pink limestone is considered the most valuable. According to their structure, limestones are divided into marble-like, dense and porous. Considering that limestone is one of the most budgetary options when choosing natural stone, ordering products from it is an excellent solution to a commercial issue.
Marble rocks are an intermediate link between limestone and marble, and are used in the construction of buildings and the creation of sculptures.
dense rocks are widely used for the manufacture of facing slabs (used for exterior and interior cladding of buildings). Such a stone has been popular since ancient times; even the ancient Egyptian pyramids are covered with a thick layer of limestone. In our country, it was often used for the construction of temples. Often there are also frost-resistant varieties of durable rock, which allowed ancient structures to survive to our times, retaining their appearance almost unchanged.
Porous limestones have several types, differing from each other in the degree and nature of granularity: oolitic, pizolitic, shelly, calcareous tuff and others. Oolitic rocks consist of small balls, in the center of each of which there is a grain of sand, a fragment of a shell, or other foreign material. Larger balls are called pisolite limestone. Shell rock is a collection of small fragments of shells. Some varieties of shells are considered a decorative material, they can be easily processed and even polished. Shell rock, consisting of microscopic shells, is called chalk. Porous rocks are used as a building material for the construction of walls, as well as for internal and external cladding of buildings. Very porous deposits are called calcareous tuff.
Chemical composition limestone: Chem. the composition of pure limestone is close to that of calcite (CaO 56%, CO2 44.0%). The composition of the carbonate part of limestone also includes dolomite CaMg (CO3) 2, FeCO3 and MnCO3 (less than 1%), non-carbonate impurities - clay aluminosilicates and silica minerals (opal, chalcedony, quartz), in small quantities oxides, hydroxides and sulfides of Fe , Ca3(PO4)2, CaSO4, org. in-in. Prom. the classification of limestones is based on the ratios of the contents of calcite and the main impurities, dolomite and clayey matter, the number of which can vary continuously up to complete predominance. Limestones are commonly referred to as rocks with a calcite content of at least 50%.
Physical properties of limestone: Main physical properties limestone are plasticity, which allows to give products from it any shape, durability, purity of color, strength, uniformity of structure, as well as high thermal insulation properties. It can be sawn, cut and pricked in any direction, processed on a lathe or manually, embodying any architectural idea. This material reacts violently to acidic compounds and dissolves in water. As a result of its decomposition, carbon dioxide is formed.
Density 2700-2900 kg/m3,
Bulk weight:
For shells - about 800 kg / m3
For crystalline limestones up to 2800 kg/m3
Compressive Strength:
For shell rock 0.4 MPa
For crystalline and aphanitic limestone 300 MPa
Water absorption - from 0.1% to 2.1%
Porosity - from 0.5% to 35%
Hardness on the Mohs scale - about 3
Frost resistance for crystalline limestones, 300-400 cycles
Features of limestone formation: The vast majority of these rocks were formed in shallow marine basins (although some of them were also formed in land freshwater reservoirs) and occur in the form of layers and sediments. According to their origin, limestones are divided into organogenic (from organic residues), chemogenic (as a result of calcite precipitation) and detrital (a product of the destruction of other limestones).
Limestone mining: Mining natural stone limestone is carried out in an open way, with the help of special crowbars and hammers that break the top layer of rock, and excavators that lift stone blocks. In Russia, career mining of this natural stone is carried out in the Leningrad, Arkhangelsk, Vologda, Tula, Belgorod, Voronezh regions, in the Moscow region, in the Urals, the Volga region, the Krasnodar Territory, in the North Caucasus, in the Urals, in several regions of Eastern Siberia. The limestones of the Myachkovsky horizon (Ryazan region) and Vladimirsky limestone became one of the most common.
Scope of limestone: For 28 centuries BC, the greatest architectural structure of all time was erected on the Left Bank of the Nile - the pyramid of Cheops, for the construction of which 2.5 million m3 of limestone blocks were mined. The pyramid is admired for its colossal size, strict proportions and the high perfection of the work of the ancient builders. It has a height of 147 m.
In Europe, white stone (limestone and sandstone) began to be used for the construction of religious and civil structures by the ancient Greeks and Romans, starting from the 5th-7th centuries BC (the first Athenian Acropolis was built in the 6th century BC).
Products made from natural facing stone limestone is used for the construction of buildings and structures and their cladding, used in the manufacture of architraves, columns, fireplace portals and other decorative elements, indispensable for interior decoration floors and walls, doors and window openings, including in rooms with high humidity (bathrooms, swimming pools). Such products are used in landscape design in the design of paths, fountains, patios, decorative walls and other garden objects, as well as for the design of fences and the construction of alpine slides (retains heat, passes water and air, normalizes the soil composition). Shell rock and tiles from it are used for exterior and interior decoration of premises (apartments, restaurants, offices, saunas), as well as for the manufacture of decorative architectural elements, lining of fireplaces and stoves. It is the only material that has 100% radiation protection. Limestone is one of the most durable flooring solutions and is ideal for use in kitchens and bathrooms as it is waterproof and does not become slippery when wet. In recent years, the use of limestone floor tiles has grown in popularity. In addition to floors, limestone can also be used for many other surfaces. Limestone is commonly used as a work surface for kitchen worktops, bar counters, window sills, facade cladding, interior wall decoration, in landscaping, for swimming pools and to create stunning stairs.
Calcium carbonate is a sedimentary rock of organic, rarely chemogenic origin, consisting of almost 100% CaCO3 (limestone) in the form of calcite crystals of various sizes.
Limestones are sedimentary rocks composed mainly of calcite. Limestones may contain various impurities (clastic particles, organic compounds, etc.). The name of limestone is given depending on the characteristics of its constituent components.
Limestones are widely used in construction (as a facing stone, for the production of lime, etc.), the glass industry, and metallurgy (fluxes).
Pure limestones are white or light gray in color, organic impurities color calcium carbonate black and dark gray, and iron oxides yellow, brown and red.
Description of the object
Calcium carbonate
- Salt; white crystals
- ρ= 2.74 g/cm³, t p l = 825°C,
- Hygroscopic
- Solubility in water 0.00015 g/100 ml
- K 0 s = 3.8 10⁻⁹
It is used as a white food coloring, for writing on boards, in everyday life, in construction.
Electronic theory (donor-acceptor) Lewis 1926
CaCO₃↔ Ca 2 ⁺ + CO₃ 2-
Ca 2 ⁺ - is an acid
CO₃ 2- - is a base
From the point of view of this theory:
Ca 2 ⁺ is an electron pair acceptor for the formation of a common covalent pair.
CO₃ 2- is an electron pair donor for the formation of a common covalent pair.
Choice of methods of analysis
Because K 0 s< 10⁻⁸ титрование CaCO₃ кислотой
or alkali is impossible.
Gravimetric analysis
Gravimetric analysis is based on the accurate measurement of the mass of a substance of known composition, chemically associated with the component being determined and isolated as a compound or as a simple substance. The classical name of the method is weight analysis. Gravimetric analysis is based on the law of conservation of the mass of a substance during chemical transformations and is the most accurate of the chemical methods of analysis: the detection limit is 0.10%; correctness (relative error) - 0.2%.
Distillation methods. the substance to be determined is transferred to a volatile state, distilled off and absorbed by some absorbent, the increase in the mass of which is used to calculate the content of the component.
- Hinge dissolution.
- Create a precipitation condition.
- Washing the sediment.
- Calculation of analysis results
The besieged form should be:
1. Sufficiently soluble to ensure almost complete isolation of the analyte from the solution.
2. The resulting precipitate must be clean and easily filterable.
3. The precipitated form should easily pass into the gravimetric one.
Basic requirements for the gravimetric form:
1. The exact correspondence of its composition to a certain chemical formula.
2. Chemical stability in a fairly wide temperature range, lack of hygroscopicity.
3. The largest possible molecular weight with the lowest content of the determined component in it, in order to reduce the influence of weighing errors on the result of the analysis.
Complete precipitation is achieved if K s 0<10 -8 .
Titrimetric analysis
1. Titrimetric (volume) analysis is one of the sections of quantitative analysis based on the precise measurement of the volume of a reagent solution (titrant) that has entered into a chemical reaction with the substance being determined. The concentration of the solution must be precisely known. A solution of a reagent (titrant) with a precisely known concentration is called a standard or titrated working solution.
2. The most important operation of titrimetric analysis is titration - the process of gradual addition of a titrated working solution to the substance to be determined. Titration is continued until the amount of titrant becomes equivalent to the amount of analyte reacting with it.
Choice of methods of analysis
gravimetric method
CaCO₃ solid can be applied:
- Stripping method
- Precipitation method by first transferring the sample into the solution with hydrochloric acid.
Titrimetric analysis
permanganatometry
- The objects of permanganatometry are alcohols, saccharides, oxidizing agents and ions that do not have reducing activity, therefore, the method of permanganometric titration is suitable for the analysis of calcium carbonate.
- The essence of the method: the substance to be determined is titrated with a solution of potassium permanganate.
MnO₄⁻ + 8H⁺ + 5 = Mn 2⁺ + 4H₂O
Because the constant is high, we can use this method to analyze
- Complexometric titration
Based on the reaction of formation of complexes of metal ions with aminopolycarboxylic acids (complexons).
Of the numerous aminopolycarboxylic acids, ethylenediaminetetraacetic acid is most commonly used.
HOOC H₂C CH₂ COOH
NH⁺ CH₂ CH₂ NH⁺
‾OOC H₂C CH₂COO‾
Sample analysis
- gravimetric method
- Calculation of the weight of the sample of the analyzed substance and its weighing.
- Hinge dissolution.
- Create a precipitation condition.
- Precipitation (obtaining a precipitated form).
- Separation of the precipitate by filtration.
- Washing the sediment.
- Obtaining a gravimetric form
- Weighing gravimetric form.
- Calculation of analysis results
gravimetric method
CaCO₃ is a solid substance insoluble in water. To convert it into a solution, we use HCl.
СaCO₃ + 2HCl = CaCl₂ + CO₂ + H₂O
- gravimetric method
Method of distillation
The substance to be determined is transferred into a volatile state, distilled off and absorbed by some absorbent, the increase in the mass of which is used to calculate the content of the component.
Analysis progress:
When determining calcium carbonate in limestone, CO 2 is isolated (by the action of acid on CaCO 3 or by calcination), it is passed through a gas absorption tube with soda lime or ascarite, the mass of absorbed carbon dioxide is determined by increasing the mass of the tube and the mass and mass fraction of calcium carbonate in the analyzed sample are calculated .
CaCO₃ CaO + CO₂
CO₂ + NaOH Na 2 CO 3 + H 2 O
m(CO₂) = m(pipe end) – m(pipe start)
According to the reaction equation
n(CO₂) = n(CaCO₃)
m (CaCO₃) = n (CaCO₃) * M (CaCO₃)
- gravimetric method
- Essence of the method: СaCO₃ + 2HCl = CaCl₂ + CO₂ + H₂O
Ca 2 ⁺ + C₂O₄ 2 ⁻ + H₂O = CaC₂O₄ * H₂O ↓
The analyzed compound (CaCO₃) is insoluble in water. Before proceeding with the analysis, it is necessary to dissolve a sample of it in acid:
СaCO₃ + 2HCl = CaCl₂ + CO₂ + H₂O
For quantitative determination of Ca 2+, it is precipitated in the form of calcium oxalate CaC 2 0 4 * H 2 0 (oxalic acid salt H 2 C 2 0 4). Precipitation is carried out with a solution of (NH₄)₂C 2 O₄, reacting with CaC1 2:
The tendency of CaC 2 O₄*H 2 0 to precipitate as a finely crystalline precipitate capable of passing through the filter is a very difficult property. Therefore, observance of the main condition for the formation of sufficiently coarse-grained precipitates - conducting precipitation from a slightly supersaturated solution - acquires very great importance here. This goal is achieved by precipitation of CaC 2 O₄ not from a neutral, but from an acid solution
Oxalic acid ionizes according to the equations:
Its ionization constants are equal, respectively:
Ions C 2 O₄⁻ appear as a result of the second stage of ionization, which, as the value of the corresponding constant (K₂) shows, is relatively weak. It follows from this that when the solution is acidified, most of the C₂O₄⁻ ions introduced into it with (NH 4) 2 C 2 O₄ will bind into HC₂O₄⁻ anions and then into free H₂C 2 O 4:
As a result, their concentration will decrease, and, moreover, the stronger, the more H + is introduced into the solution. With a sufficiently strong acidification of the solution, the concentration of C 2 O 4 ⁻ will decrease so much that the product of the solubility of CaC 2 0 4, equal to
will not be reached, and the precipitate will not fall out.
If, however, NH 4 OH is added dropwise to such a strongly acidic solution, then the concentration of H + will gradually decrease, and the concentration of C₂O₄⁻ will increase.
Eventually the concentration product [Ca 2+ ] [C₂O₄⁻] will exceed the solubility product and the precipitate will begin to precipitate. But since ammonia is added dropwise, the concentration of C₂0 4 ⁻ in the solution rises very slowly and gradually. As a result, precipitation occurs all the time from a solution that is slightly supersaturated with respect to CaC₂0 4, and its crystals can become sufficiently coarse.
As the concentration of H⁺ in the solution decreases, the precipitation of Ca 2+ will become more and more complete.
Almost complete precipitation becomes already at pH = 3.3.
Further addition of NH 4 OH is pointless. The moment when the pH of the solution becomes equal to 4 can be detected by carrying out the precipitation in the presence of the methyl orange indicator, which changes its pink color to yellow at about this pH value.
The CaC₂0 4 precipitate is quite soluble in water, washing with clean water would cause a noticeable loss of it. Therefore, C₂O₄⁻-ions, which reduce the solubility of the precipitate, must be introduced into the washing liquid.
Removing Cl⁻ by washing prevents loss on ignition of the precipitate due to the formation of volatile CaCl 2 .
As a weight form, in the definition under consideration, calcium oxide CaO is usually obtained, which is formed from CaC₂0 4 -H 2 0 at 900-1200 ° C; the reaction proceeds according to the equation
The disadvantage of CaO as a weight form is its hygroscopicity and the ability to absorb CO₂ from the air, so a number of precautions must be observed when weighing. In addition, the percentage of Ca in CaO (and hence the conversion factor) is high, which is also disadvantageous.
Due to these disadvantages of CaO as a weight form, it is sometimes preferred to convert CaC₂0 4 * H 2 0 into CaCO 3 by calcination at a temperature of about 500 ° C or into CaS0 4 by treatment with a solution of H 2 S0 4, followed by removal of excess acid by careful evaporation and calcination of the dry residue.
Pemanaganatometric method
Method features:
- Availability
- Cheapness
- High redox potential
- Substance non-standard, requires standardization
- In hydrochloric acid solutions, a side reaction occurs, therefore, a Reinhard-Zimmermann mixture is used
Pemanaganatometric method
The essence of the method is the method of quantitative determination of substances using a titrant - a solution of potassium permanganate KMnO 4 .
Composition of limestone
The chemical composition of pure limestones is close to calcite, where CaO is 56% and CO 2 is 44%. Limestone in some cases includes impurities 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, marl limestone - from 6 to 21% SiO 2 +R 2 O 3. Limestone is sandy and silicified and has impurities of quartz, opal and chalcedony. It is customary to reflect in the name of limestone also the predominant presence of organogenic remains (bryozoan, algal), or its structure (crystalline, clotted, detritus), or the shape of rock-forming particles (oolitic, brecciated).
Description and types
According to the structure, limestones are crystalline, organogenic-detrital, detrital-crystalline (mixed structure) and sinter (travertine). Among crystalline limestones, according to the size of the grains, coarse-grained, fine-crystalline and cryptocrystalline (aphanite) are distinguished, according to the brilliance at the break - recrystallized (marble-like) and cavernous (travertine). 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, the following are distinguished: reef limestone; shell limestone (), consisting mainly of whole or crushed shells, bonded 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) also belongs to organogenic-clastic limestones. Organogenic-detrital limestones are characterized by a large, low volumetric mass and are easily processed (sawed and polished). Detrital-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, flint lenses. 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 various shapes, variable bulk density, low strength and high water absorption. Sintered limestone (travertine, calcareous tuff) consists of sintered calcite. It is characterized by cellularity, low bulk density, easy processing and sawing.
According to the macrotexture and conditions of occurrence among limestones, massive, horizontally and obliquely layered, thick and thin platy, cavernous, fissured, spotty, lumpy, reef, fungal, stylolite, underwater landslide, etc. are distinguished. Organogenic (biogenic), chemogenic, clastic and mixed limestones. Organogenic (biogenic) limestones are accumulations of carbonate remains or entire skeletal forms of marine, less often freshwater organisms, with a small admixture of predominantly carbonate cement. Chemogenic limestones arise as a result of lime precipitation followed by recrystallization of the carbonate mass of sediments, mainly from sea water (crystalline limestone) or from mineralized deposits (travertine). Clastic limestones are formed as a result of fragmentation, washout and redeposition of angularly rounded fragments of carbonate and other rocks and skeletal remains, mainly in marine basins and on coasts. Limestones of mixed origin are a complex of deposits resulting from the successive or parallel superposition of various carbonate sedimentation processes.
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 landforms of the Earth. Limestone deposits are found among deposits of all geological systems - from Precambrian to Quaternary; the most intensive formation of limestones occurred in the Silurian, Carboniferous, Jurassic and Upper Cretaceous; make up 19-22% of the total mass of sedimentary rocks. The thickness of limestone strata is extremely variable: from a few centimeters (in separate layers of sediments) to 5000 m.
Limestone properties
The physical and mechanical properties of limestones are extremely heterogeneous, but are directly dependent on their structure and texture. The density of limestones is 2700-2900 kg/m 3 and varies depending on the content of impurities of dolomite, quartz and other minerals. The bulk mass of limestones varies from 800 kg/m 3 (for shell rocks and travertine) to 2800 kg/m 3 (for crystalline limestones). The compressive strength of limestones ranges from 0.4 MPa (for shell rock) to 300 MPa (for crystalline and aphanitic limestone). When wet, the strength of limestones often decreases. Most of the deposits are characterized by the presence of limestone, not uniform in strength. Losses for wear, abrasion and crushability increase, as a rule, with a decrease in the volumetric mass of limestones. Frost resistance for crystalline limestones reaches 300-400 cycles, but it changes dramatically in limestones of a different structure and depends on the shape and connection of pores and cracks in it. The workability of limestones is directly related to their structure and texture. Shell rock and porous limestones are easily sawn and hewn; crystalline limestones are well polished.
Application of limestone
Limestone has a universal application in industry, agriculture and construction. In metallurgy, limestone serves 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, soaps, medicines, mineral wool, for cleaning fabrics and treating leather, liming soils.
Limestone is the most important building material, it is used to make facing
Various lime fertilizers are used for liming: lime flour (obtained by grinding limestone, dolomitic limestone and dolomite, marl), loose lime rocks, burnt or slaked lime, lime waste from industry, etc. All these materials contain large amounts of carbon dioxide or caustic calcium or magnesium (sometimes calcium silicate), small amounts of iron carbonate, manganese (about 0.3%), P2O5 (0.01 - 0.2%), alkali, as well as impurities insoluble in acids of quartz, clay, organic substances and pyrite.
An approximate idea of the composition of limestone can be given by a qualitative sample with diluted HCl (1: 4): pure limestones boil violently and quickly dissolve in the cold in weak hydrochloric acid, and dolomites, dolomitic limestones and iron carbonate dissolve under these conditions relatively slowly, without noticeable boiling. . Lime tuffs and marls, if they do not contain large amounts of magnesium carbonate and iron, also pass into solution with significant effervescence, but when HCl is exposed to marls, quite a lot of insoluble impurities remain.
When using calcareous rocks as fertilizers, a chemical determination of carbon dioxide, neutralizing ability, insoluble residue, sesquioxides, calcium, magnesium, loss from ignition is carried out. These data are in most cases quite sufficient to characterize the calcareous rock.
To determine the degree of solubility of different limestones, Popp and Kontzen proposed to take into account the degree of solubility of lime fertilizers in 0.025 and. CH3COOH solution using the following procedure.
5 g of an average limestone sample is triturated until it passes through a No. 100 sieve (0.17 mm). A sample portion of 0.25 g is treated with 400 ml of 0.025 N. CH3COOH solution for 1 hour and quickly filtered. After removal of carbon dioxide by boiling and cooling, 100 ml of the filtrate are titrated with 0.05 N. NaOH solution for phenolphthalein. Based on the results of titration, the percentage of carbonates dissolved in the studied limestone samples is determined. In the experiments of the authors of the method, it was dissolved: from dolomite - 23%, from dolomitic limestone with 7.5% MgCO3 - 87%, from limestone with a lower content of MgCO3 - 100%.
The method, according to the authors, characterizes the relative speed and degree of neutralizing effect of lime fertilizers of different quality on the soil, which can be essential when dosing different limestones or when deciding on the desired degree of their grinding before applying to the soil (grinding fineness).
The quality of the lime fertilizer used as a material for neutralizing soil acidity is determined, in addition to the chemical composition, by a number of other properties: rock hardness, fineness of grinding, roasting, and others that affect the solubility and, consequently, the effectiveness of the lime fertilizers used.
The mass liming of soddy-podzolic and podzolic soils has revealed the need to develop simpler, faster and, at the same time, sufficiently accurate methods for the analysis of limestones that do not require specially equipped laboratories for their implementation.
In the analysis of limestones as a material for liming soils, the number of the above determinations can be significantly reduced (Blinova, 1931), while the content of carbonates in limestone can be established significantly. Of the existing methods for determining CO2, we describe three variants of the titration method as the simplest, fastest, and fairly accurate. Let us also point out the well-known gas volumetric method based on the determination of the total amount of CO2 carbonates in limestone fertilizers using a calcimeter.
Determination of the content of CO2 carbonates in lime carbonate by titration.
1st method (Treadwell). Taken on a technical scale, a weighed sample of limestone in 2 g is placed in a 500 ml volumetric flask, poured over with 50 ml of 1.0 N. HCl solution and diluted to 500 ml with water.
The flask, together with the contents, is heated first over low heat, and then gradually over a stronger one, bringing the solution to a boil. A weak boiling of the solution (on the grid) is maintained until the complete decomposition of the limestone (cessation of the release of CO2 bubbles, which takes 15-20 minutes); then the flask is allowed to cool, the contents are diluted to the line with water, shaken and allowed to settle. From the settled liquid in the flask, take 100 ml of a solution corresponding to 10 ml or 1/5 of the initially added 1.0 N. HCl solution, and titrated with 0.1 i. NaOH solution in the presence of methyl orange or bromthymol blue. The amount of HCl consumed for the decomposition of limestone is used to calculate the amount of carbon dioxide and, consequently, calcium (and magnesium) carbonates in a given sample of limestone.
2nd method (according to Förster, in the description of N.I. Alyamovsky, 1963). After grinding, a 5 g sample of lime fertilizer is placed in a 500 ml flask, moistened with water; after that, 250 ml of 1 N. HCl, heated for 30 min. in a boiling water bath with occasional shaking; after cooling, the contents of the flask are brought to the line with water, mixed and filtered through a dry filter into a dry dish. From the filtrate, take 100 ml (corresponding to 50 ml of 1 N HCl or 100 ml of 0.5 N HCl) into a 250-300 ml conical flask or beaker, add 2-3 drops of phenolphthalein and unbound HCl, titrate with 0.5 N. NaOH solution until pink, which does not disappear within 1 min. (1st titration).
Then proceed in two ways:
a. If the precipitate is insignificant, then 2 ml of 1 N hydrochloric acid are added to an almost transparent solution. HCl (or 4 ml 0.5 N HCl) and placed for 30 min. on a boiling water bath to remove the residual CO2 (since CO2 is titrated in the presence of phenolphthalein). After that, without cooling, the solution is finally titrated (2nd titration).
b. If the lime is of poor quality, then after the first titration, a brown precipitate of Fe (OH) 3 usually precipitates, masking the color of phenolphthalein. In this case, the solution is filtered into a 200 ml volumetric flask and the filter cake is washed with hot distilled water. Then, exactly 2 ml of 1N hydrochloric acid are added to the filter flask. HCl and distilled water up to the mark. From a thoroughly mixed flask, 100 ml are taken with a pipette and transferred to a conical flask - a glass of 250-300 ml. The flask-glass is placed in a boiling water bath, after which the hot solution is titrated against phenolphthalein 0.5 N. NaOH solution. The alkali consumption is multiplied by 2, since half the volume of the solution was titrated.
The sum of oxide, hydroxide and carbonate of calcium and magnesium is calculated by the formula:
For the purposes of liming, it is important to know at least approximately the magnesium content of limestone; for this, it is possible not to do a complete analysis of limestone, but it is enough, by establishing the total content of carbonates by titration, to additionally determine calcium in the same solution and then, by recalculation, find the percentage of calcium carbonate in the rock. Knowing the total percentage of carbonates and the content of calcium carbonate, it is easy to calculate the amount of magnesium carbonate in dolomitic limestone from the difference.
When analyzing limestones themselves, it is possible not to produce a two-fold precipitation of calcium, which is necessary in the analysis of dolomites and dolomitic limestones, where a significant amount of magnesium is present, which can be adsorbed by a precipitate of calcium oxalate.
In order to avoid magnesium precipitation together with calcium oxalate, Wiessman recommends conducting a Richards analysis.
To precipitate calcium according to Richards, the solution is heated on a grid to boiling, a few drops of methyl orange and hydrochloric acid solution are added until a distinct pink color appears. Then add a hot solution containing 0.5 g of oxalic acid in 10 ml of 10% HCl (sp. weight 1.05); the solution is slowly neutralized by boiling with 1% ammonia (this neutralization lasts about half an hour). The end of neutralization is recognized by the transition from red to yellow, then 50 ml of a hot 5% solution of (NH4)2C2O4 are added, the flame is removed and left to stand for 4 hours. After that, it is filtered, the precipitate is washed with a 1% solution of ammonium oxalate until the reaction to Cl disappears.
Analysis of burnt and slaked lime. In addition to carbonic lime, when liming soils, burnt and slaked lime (fluff) and other fertilizers containing these forms of lime are also used. Burnt lime, obtained by firing limestone at a temperature of 800-900 °, has, due to the loss of CO2, half as much weight as carbonic lime. Burnt lime, when slaked, easily breaks down into a fine powder, which makes it very convenient to distribute it in the soil. The less impurities were contained in the original limestone, the better the product obtained after firing is quenched. In case of insufficient burning of limestone, when not all CaCO3 has decomposed, burnt lime does not disintegrate into powder during slaking, but remains in the form of pieces.
Burnt lime, when stored in air in pieces, changes in surface, absorbing water and CO2; therefore, for analysis, it is necessary to take pieces cleaned from above from loose mass; weighing is carried out in a glass with a ground stopper.
Determination by titration of the sum of CaO, Ca(OH)2 and CaCO3. Burnt and slaked lime differs from limestone in a more soluble form of calcium. It contains CaO or Ca(OH)2 and only minor amounts of CaCO3. Conventional chemical analysis establishes only the total amount of calcium (and other components) in lime, but does not determine its form. To determine the content of CaO, Ca(OH)2 and CaCO3 in lime, the Treadwell volumetric method is used.
A weighing of 10 g of lime is placed in a porcelain cup, calcium oxide is quenched with a triple weight of boiled distilled water, all the pieces are thoroughly rubbed with a glass rod with an extension at the end and transferred through a funnel into a 500 ml volumetric flask, rinse the cup and funnel, then add the contents flask to the mark with carbon dioxide-free water. After thorough shaking, take 50 ml of a cloudy solution (suspension) into another half-liter flask, add boiled water to the mark, and take part of the titration solution from there.
To determine the amount of CaO + Ca (OH) 2 + CaCO 3 by titration, take 50 ml of the prepared suspension, which corresponds to 0.1 g of lime, into a conical flask. To the suspension is added 50 ml of 0.1 N. HCl solution and boil for 10-15 minutes. Upon cooling, 2-3 drops of methyl orange are added and the excess acid is titrated to 0.1 m.u. NaOH solution. Thus, CaO, Ca(OH)2 and CaCO3 are taken into account in total.
The calculation of the percentage of the amount of alkaline forms of calcium is carried out according to the following formula:
To determine the amount of CaO and Ca(OH2) by titration, take a new portion of 50 ml (corresponding to 0.1 g of lime) of a previously thoroughly mixed suspension, add 1-2 drops of phenolphthalein and titrate with hydrochloric acid in the cold while shaking; titrated acid is added dropwise until the solution becomes colorless. When titrated with phenolphthalein, only CaO and Ca(OH)2 are determined. The percentage of lime is calculated in CaO equivalents.
The total amount of CaO and Ca(OH)2 is equivalent to the consumption of hydrochloric acid during titration of the analyzed suspension with phenolphthalein.
The percentage of calcium is calculated using the following formula:
where c is the amount of 0.1 n. HCl solution used for suspension with phenolphthalein, ml;
d - weighed lime corresponding to the amount of suspension taken for titration, g.
The amount of calcium carbonate corresponds to the difference between the sum of all forms of calcium - CaO, Ca (OH) 2 and CaCO 3 (see the results of the back titration of a suspension with methyl orange) - and the sum of CaO + Ca (OH) 2 (see the results of the back titration of a suspension with phenolphthalein) .
The calculation of the amount of calcium carbonate contained in lime is carried out according to the following formula (in Cao equivalent);
