Electrolysis of melts and solutions of substances. Electrolytic production of calcium and its alloys

3. Receipt. Calcium is obtained by electrolysis of its molten chloride.

4. Physical properties. Calcium is a silver-white metal, very light (ρ = 1.55 g/cm3), like the alkali metals, but incomparably harder than them and has a much higher melting point, equal to 851 0 C.

5. Chemical properties. Like alkali metals, calcium is a strong reducing agent, which can be schematically represented as follows:

Calcium compounds color the flame brick red. Like alkali metals, calcium metal is usually stored under a layer of kerosene.

6. Application. Due to its high chemical activity, calcium metal is used for the reduction of some refractory metals (titanium, zirconium, etc.) from their oxides. Calcium is also used in the production of steel and cast iron, to purify the latter from oxygen, sulfur and phosphorus, to produce certain alloys, in particular lead-calcium, necessary for the manufacture of bearings.

7. The most important calcium compounds obtained in industry.

Calcium oxide is produced industrially by calcining limestone:

CaCO 3 → CaO + CO 2

Calcium oxide is a refractory white substance (melts at a temperature of 2570 0 C), has chemical properties inherent in the main oxides of active metals (I, Table II, p. 88).

The reaction of calcium oxide with water releases a large amount of heat:

CaO + H 2 O ═ Ca (OH) 2 + Q

Calcium oxide is the main component of quicklime, and calcium hydroxide is the main component of slaked lime.

The reaction of calcium oxide with water is called lime slaking.

Calcium oxide is mainly used to produce slaked lime.

Calcium hydroxide Ca(OH) 2 is of great practical importance. It is used in the form of slaked lime, lime milk and lime water.

Slaked lime is a thin, loose powder, usually gray in color (a component of calcium hydroxide), slightly soluble in water (1.56 g dissolves in 1 liter of water at 20 0 C). A dough-like mixture of slaked lime with cement, water and sand is used in construction. Gradually the mixture hardens:

Ca (OH) 2 + CO 2 → CaCO 3 ↓ + H 2 O

Lime milk is a suspension (suspension) similar to milk. It is formed when excess slaked lime is mixed with water. Lime milk is used to produce bleach, in the production of sugar, to prepare mixtures necessary in the fight against plant diseases, and for whitewashing tree trunks.

Lime water is a clear solution of calcium hydroxide obtained by filtering lime milk. It is used in the laboratory to detect carbon monoxide (IV):

Ca(OH) 2 + CO 2 → CaCO 3 ↓ + H 2 O

With prolonged passage of carbon monoxide (IV), the solution becomes transparent:

CaCO 3 + CO 2 + H 2 O → Ca(HCO 3) 2

If the resulting clear solution of calcium bicarbonate is heated, clouding occurs again:

Similar processes also occur in nature. If water contains dissolved carbon monoxide (IV) and acts on limestone, some of the calcium carbonate is converted to soluble calcium bicarbonate. At the surface, the solution warms up and calcium carbonate precipitates out of it again.

* Bleach is of great practical importance. It is obtained by reacting slaked lime with chlorine:

2 Ca(OH) 2 + 2 Cl 2 → Ca(ClO) 2 + CaCl 2 + 2H 2 O

The active component of bleach is calcium hypochlorite. Hypochlorites undergo hydrolysis. This releases hypochlorous acid. Even carbonic acid can displace hypochlorous acid from its salt:

Ca(ClO) 2 + CO 2 + H 2 O → CaCO 3 ↓+ 2 HClO

2 HClO → 2 HCl + O 2

This property of bleach is widely used for bleaching, disinfection and degassing.

8. Plaster. The following types of gypsum are distinguished: natural - CaSO 4 ∙ 2H 2 O, burnt - (CaSO 4) 2 ∙ H 2 O, anhydrous - CaSO 4.

Burnt (semi-aqueous) gypsum, or alabaster, (CaSO 4) 2 ∙ H 2 O is obtained by heating natural gypsum to 150–180 0 C:

2 → (CaSO 4) 2 ∙ H 2 O + 3H 2 O

If you mix alabaster powder with water, a semi-liquid plastic mass is formed, which quickly hardens. The hardening process is explained by the addition of water:

(CaSO 4) 2 ∙ H 2 O + 3H 2 O → 2

The property of burnt gypsum to harden is used in practice. For example, alabaster mixed with lime, sand and water is used as plaster. Pure alabaster is used to make artistic items, and in medicine it is used to apply plaster casts.

If natural gypsum CaSO 4 ∙ 2H 2 O is heated at a higher temperature, then all the water is released:

CaSO 4 ∙ 2H 2 O → CaSO 4 + 2H 2 O

The resulting anhydrous gypsum CaSO 4 is no longer able to add water, and therefore it was called dead gypsum.

Water hardness and ways to eliminate it.

Everyone knows that soap foams well in rainwater (soft water), but in spring water it usually foams poorly (hard water). Analysis of hard water shows that it contains significant amounts of soluble calcium and magnesium salts. These salts form insoluble compounds with soap. Such water is unsuitable for cooling internal combustion engines and powering steam boilers, since when hard water is heated, scale forms on the walls of cooling systems. Scale does not conduct heat well; therefore, overheating of motors and steam boilers is possible, in addition, their wear is accelerated.

What are the types of hardness?

Carbonate, or temporary, hardness is caused by the presence of calcium and magnesium bicarbonates. It can be fixed in the following ways:

1) boiling:

Ca(HCO 3) 2 → CaCO 3 ↓ + H 2 O + CO 2

Mg(HCO 3) 2 → MgCO 3 ↓ + H 2 O + CO 2

2) the action of lime milk or soda:

Ca(OH) 2 + Ca(HCO 3) 2 → 2CaCO 3 ↓ + 2H 2 O

Ca(HCO 3) 2 + Na 2 CO 3 → CaCO 3 ↓ + 2NaHCO 3

Ca 2+ + 2 HCO 3 - + 2 Na + + CO 3 2- → CaCO 3 ↓ + 2 Na + + 2HCO 3 -

Ca 2+ + CO 3 2- → CaCO 3 ↓

Non-carbonate, or permanent, hardness is due to the presence of sulfates and chlorides of calcium and magnesium.

It is eliminated by the action of soda:

CaSO 4 + Na 2 CO 3 → CaCO 3 ↓ + Na 2 SO 4

MgSO 4 + Na 2 CO 3 → MgCO 3 ↓ + Na 2 SO 4

Mg 2+ + SO 4 2- + 2Na + + CO 3 2- → MgCO 3 ↓ + 2Na + + SO 4 2-

Mg 2+ + CO 3 2- → MgCO 3 ↓

Carbonate and non-carbonate hardness add up to the total water hardness.

IV. Consolidation of knowledge (5 min.)

1. Based on the periodic table and the theory of atomic structure, explain what properties of magnesium and calcium are common. Write down equations for the corresponding reactions.

2. What minerals contain calcium and how are they used?

3. Explain how to distinguish one natural mineral from another.

V. Homework (3 min.)

Answer the questions and complete exercises 1–15, § 48,49, solve exercises 1–4, pp. 132–133.

This is exactly what a lesson plan looks like at school on the topic “Calcium and its compounds.”

Based on the above, the need to fill the school chemistry course with environmental content is obvious. The results of the work done will be presented in the third chapter.

One-time) – 0.01%. 4 Contents Introduction................................................... ........................................................ ....................4 Chapter 1. Interdisciplinary connections in the course of the school subject of chemistry using the example of carbon and its compounds............ ........................................................ .........5 1.1 Using interdisciplinary connections to develop students...

Activity. The search for methods and forms of teaching that contribute to the development of a creative personality has led to the emergence of some specific teaching methods, one of which is game methods. The implementation of game teaching methods in the study of chemistry in compliance with didactic and psychological-pedagogical features increases the level of students' training. The word "game" in Russian...

And hygienic requirements); compliance of educational and physical activity with the age capabilities of the child; necessary, sufficient and rationally organized motor mode. By health-saving educational technology (Petrov) he understands a system that creates the maximum possible conditions for the preservation, strengthening and development of spiritual, emotional, intellectual, ...

Electrolysis is a redox reaction that occurs on electrodes when a direct electric current is passed through a melt or electrolyte solution.

The cathode is a reducing agent and gives electrons to cations.

The anode is an oxidizing agent and accepts electrons from anions.

Activity series of cations:	Na + , Mg 2+ , Al 3+ , Zn 2+ , Ni 2+ , Sn 2+ , Pb 2+ , H+ , Cu 2+ , Ag + _____________________________→ Increased oxidative capacity
Anion activity series:	I - , Br - , Cl - , OH - , NO 3 - , CO 3 2- , SO 4 2- ←__________________________________ Increased recovery ability

Processes occurring on electrodes during electrolysis of melts

(do not depend on the material of the electrodes and the nature of the ions).

1. Anions are discharged at the anode ( A m - ; OH-

A m - - m ē → A °; 4 OH - - 4ē → O 2 + 2 H 2 O (oxidation processes).

2. Cations are discharged at the cathode ( Me n + , H + ), turning into neutral atoms or molecules:

Me n + + n ē → Me ° ; 2 H + + 2ē → H 2 0 (recovery processes).

Processes occurring on electrodes during electrolysis of solutions

CATHODE (-) Does not depend on the cathode material; depend on the position of the metal in the stress series	ANODE (+) Depends on the anode material and the nature of the anions.
	The anode is insoluble (inert), i.e. made from coal, graphite, platinum, gold.	The anode is soluble (active), i.e. made fromCu, Ag, Zn, Ni, Feand other metals (exceptPt, Au)
1.First of all, metal cations are reduced that are in the series of stresses afterH 2 : Me n+ +nē → Me°	1.First of all, the anions of oxygen-free acids are oxidized (exceptF - ): A m- - mē → A°	Anions do not oxidize. The metal atoms of the anode are oxidized: Me° - nē → Me n+ Men + cations go into solution. The anode mass decreases.
2.Metal cations of medium activity, standing betweenAl And H 2 , are restored simultaneously with water: Me n+ + nē →Me° 2H 2 O + 2ē → H 2 + 2OH -	2.Oxoacid anions (SO 4 2- , CO 3 2- ,..) And F - do not oxidize, molecules are oxidizedH 2 O : 2H 2 O - 4ē → O 2 +4H +
3. Cations of active metals fromLi before Al (inclusive) are not reduced, but molecules are reducedH 2 O : 2 H 2 O + 2ē →H 2 + 2OH -	3. During the electrolysis of alkali solutions, ions are oxidizedOH- : 4OH - - 4ē → O 2 +2H 2 O
4. During the electrolysis of acid solutions, cations are reduced H+: 2H + + 2ē → H 2 0

ELECTROLYSIS OF MELTS

Exercise 1. Draw up a scheme for the electrolysis of molten sodium bromide. (Algorithm 1.)

Sequencing	Performing Actions
	NaBr → Na + + Br -
	K- (cathode): Na+, A+ (anode): Br -
	K + : Na + + 1ē → Na 0 (recovery), A + : 2 Br - - 2ē → Br 2 0 (oxidation).
	2NaBr = 2Na +Br 2

Task 2. Draw up a scheme for the electrolysis of molten sodium hydroxide. (Algorithm 2.)

Sequencing	Performing Actions
	NaOH → Na + + OH -
2.Show the movement of ions to the corresponding electrodes	K- (cathode): Na+, A + (anode): OH -.
3.Draw up diagrams of oxidation and reduction processes	K - : Na + + 1ē → Na 0 (recovery), A + : 4 OH - - 4ē → 2 H 2 O + O 2 (oxidation).
4. Create an equation for the electrolysis of molten alkali	4NaOH = 4Na + 2H 2 O + O 2

Task 3.Draw up a scheme for the electrolysis of molten sodium sulfate. (Algorithm 3.)

Sequencing	Performing Actions
1. Create an equation for the dissociation of salt	Na 2 SO 4 → 2Na + + SO 4 2-
2.Show the movement of ions to the corresponding electrodes	K- (cathode): Na+ A+ (anode): SO 4 2-
	K - : Na + + 1ē → Na 0 , A + : 2SO 4 2- - 4ē → 2SO 3 + O 2
4. Create an equation for the electrolysis of molten salt	2Na 2 SO 4 = 4Na + 2SO 3 + O 2

ELECTROLYSIS OF SOLUTIONS

Exercise 1.Draw up a scheme for the electrolysis of an aqueous solution of sodium chloride using inert electrodes. (Algorithm 1.)

Sequencing	Performing Actions
1. Create an equation for the dissociation of salt	NaCl → Na + + Cl -
	Sodium ions in the solution are not reduced, so water is reduced. Chlorine ions are oxidized.
3.Draw up diagrams of the processes of reduction and oxidation	K - : 2H 2 O + 2ē → H 2 + 2OH - A + : 2Cl - - 2ē → Cl 2
	2NaCl + 2H2O = H2 + Cl2 + 2NaOH

Task 2.Draw up a scheme for the electrolysis of an aqueous solution of copper sulfate ( II ) using inert electrodes. (Algorithm 2.)

Sequencing	Performing Actions
1. Create an equation for the dissociation of salt	CuSO 4 → Cu 2+ + SO 4 2-
2. Select the ions that will be discharged at the electrodes	Copper ions are reduced at the cathode. At the anode in an aqueous solution, sulfate ions are not oxidized, so water is oxidized.
3.Draw up diagrams of the processes of reduction and oxidation	K - : Cu 2+ + 2ē → Cu 0 A + : 2H 2 O - 4ē → O 2 +4H +
4. Create an equation for the electrolysis of an aqueous salt solution	2CuSO 4 +2H 2 O = 2Cu + O 2 + 2H 2 SO 4

Task 3.Draw up a scheme for the electrolysis of an aqueous solution of an aqueous solution of sodium hydroxide using inert electrodes. (Algorithm 3.)

Sequencing	Performing Actions
1. Create an equation for the dissociation of alkali	NaOH → Na + + OH -
2. Select the ions that will be discharged at the electrodes	Sodium ions cannot be reduced, so water is reduced at the cathode. Hydroxide ions are oxidized at the anode.
3.Draw up diagrams of the processes of reduction and oxidation	K - : 2 H 2 O + 2ē → H 2 + 2 OH - A + : 4 OH - - 4ē → 2 H 2 O + O 2
4.Draw up an equation for the electrolysis of an aqueous alkali solution	2 H 2 O = 2 H 2 + O 2 , i.e. Electrolysis of an aqueous alkali solution is reduced to the electrolysis of water.

Remember.During electrolysis of oxygen-containing acids (H 2 SO 4, etc.), bases (NaOH, Ca (OH) 2, etc.) , salts of active metals and oxygen-containing acids(K 2 SO 4, etc.) Electrolysis of water occurs on the electrodes: 2 H 2 O = 2 H 2 + O 2

Task 4.Draw up a scheme for the electrolysis of an aqueous solution of silver nitrate using an anode made of silver, i.e. the anode is soluble. (Algorithm 4.)

Sequencing	Performing Actions
1. Create an equation for the dissociation of salt	AgNO 3 → Ag + + NO 3 -
2. Select the ions that will be discharged at the electrodes	Silver ions are reduced at the cathode, and the silver anode dissolves.
3.Draw up diagrams of the processes of reduction and oxidation	K - : Ag + + 1ē→ Ag 0 ; A+: Ag 0 - 1ē→ Ag +
4. Create an equation for the electrolysis of an aqueous salt solution	Ag + + Ag 0 = Ag 0 + Ag + electrolysis boils down to the transfer of silver from the anode to the cathode.

Choose the correct option.

91. From a mixture of cations: Ag + , Cu 2+ , Fe 2+ , Zn 2+ the following cations will be reduced first:

92. To coat metal with nickel, electrolysis is carried out using:

93. During the electrolysis of a sodium chloride solution, the solution environment at the cathode is:

1. neutral

   alkaline

94. Calcium can be obtained from calcium chloride by:

1) electrolysis of solution

2) electrolysis of the melt

3) reduction of hydrogen

4) thermal decomposition.

95. During electrolysis of a solution of copper chloride (copper anode), the following will oxidize at the anode:

2) oxygen

3) hydrogen

96. During the electrolysis of a sodium carbonate solution with graphite electrodes at the anode, the following occurs:

1) release of CO 2

2) release of oxygen

3) hydrogen evolution

4) sodium precipitation.

Part B

Give complete solutions to the tasks.

1. Create an electronic formula for iron atoms, graphically indicate the valence electrons in the normal and excited states. What oxidation states can an iron atom exhibit? Give examples of iron oxides and hydroxides in the corresponding oxidation states, indicate their nature.

kJ/mol y y y (-285.84)

heat of formation of ammonia (N 0 arr.(N.H. 3 )) is equal to:

92.15 kJ/mol;

92.15 kJ/mol;

46.76 kJ/mol;

46.76 kJ/mol.

4. The reaction of reduction of copper (II) oxide with aluminum is possible

G 0 arr.. 3CuO + 2Al = Al 2 O 3 + 3Cu

kJ/mol -129.8 -1582

Gibbs free energy (Gx.r.) is equal to:

5. When 1 mole of orthophosphoric acid reacts with 1 mole of sodium hydroxide, the following is formed:

1) sodium orthophosphate 3) sodium dihydrogen orthophosphate

2) sodium hydrogen phosphate 4) sodium phosphate

Write molecular ionic reaction equations. The sum of all coefficients in the short ionic equation is...

6. Methyl orange turns yellow when each of two salts is dissolved in water:

1) K 2 S and K 3 PO 4 3) LiCl and FeSO 4

2) KNO 3 and K 3 PO 4 4) CH 3 COOK and K 2 SO 4

Write molecular ionic equations for hydrolysis reactions.

7. When aqueous solutions of aluminum sulfate and sodium carbonate salts interact, the sum of the coefficients in the short ionic equation is equal to:

1) 10 2) 12 3) 13 4) 9

An acidic environment is formed when each of two salts is dissolved in water:

1) BaCl 2 and AlCl 3 3) CuCl 2 and LiCl

2) K 2 S and K 3 PO 4 4) NH 4 NO 3 and Zn(NO 3) 2

Compose molecular ionic hydrolysis equations and derive the hydrolysis constant using the first step.

In the reaction equation the diagram of which is:

FeSO 4 + KMnO 4 + H 2 SO 4 Fe 2 (SO 4) 3 + MnSO 4 + K 2 SO 4 + H 2 O

The sum of the coefficients in front of the formulas of the starting substances is equal to:

Give a complete solution to the problem (use the ion-electronic method).

Establish the correct sequence of actions when determining the type of hybridization CA. in particle:

Match:

Hybridization type C.A. Particle

1) sp 2 a) H 2 O

2) sp 3 b) VN 3

3) sp 3 d c) SCl 6

4) sp 3 d 2 d) CO

Using the algorithm, consider those particles in which C.A. in sp 3 and sp 3 d hybridization.

ING. E.: Ag | AgNO 3 | | Fe(NO 3 ) 2 | Fe

Calculate the emf at no.

Give complete solutions to the tasks

Introduction

CHAPTER I. Literature review

1.1. Methods for obtaining and recycling calcium chloride 7

1.1.1 Chemical methods 7

1.1.2. Electrochemical methods 10

1.2. Preparation of calcium saccharates and their use as corrosion inhibitors 12

1.3 Electrochemical synthesis of chlorine gas 13

1.4. Carbon dioxide synthesis 16

1.5. Patterns of electrochemical processes in natural waters containing calcium ions 17

1.5L. Electrolysis of thermal waters 17

1.5.2. Electrolysis of sea water 20

1.6. Conclusions from the literature review 23

CHAPTER II. Experimental procedure 24

2.1. Polarization measurements 24

2.2- Electrochemical syntheses 25

2.3. Methodology for analysis and identification of products 26

2.4. Mathematical processing of the obtained results 33

Chapter III. Experimental data and discussion

3.1. Patterns of electrode reactions in a solution of calcium chloride on various electrode materials 39

3.1.1. Anodic process - kinetics and mechanism of formation of chlorine gas during electrolysis of calcium chloride solution 39

3.1.2. Cathode process - kinetics of formation of hydrogen gas during electrolysis of a calcium chloride solution 45

3.1.3. Preparative aspects of electrolysis of an aqueous solution of calcium chloride 48

3.2. Features of the occurrence of electrode reactions in aqueous solutions (CAC12 + SUCCAROSE) on various electrode materials 50

3.2.1. Cathode process 50

3.2.2. Preparative aspects of electrochemical production of calcium saccharate 58

3.2.3. Patterns of electrode reactions in the system: (CaC12 + sucrose + Ca(OH)2) 61

3.2.3.1 Anodic process 61

3.2.3.2 Cathode process 62

3.3. Patterns of the course of electrode reactions in the system [CaCl2+HN33+Ca(N33)2] 65

3.3.1. Anodic process 65

3.3.2. Cathode process. 68

3.3.3. Preparative aspects of the electrochemical synthesis of calcium nitrate 74

3.3.4. Preparative aspects of the electrochemical production of carbon dioxide 75

3.4 Electrochemical preparation of calcium acetate 78

3.4.1. Features of the cathodic process in the electrosynthesis of calcium acetate on various electrode materials 79

3.4.2. Preparative aspects of calcium acetate electrosynthesis 87

Literature

Introduction to the work

Relevance of the topic. Almost all natural waters contain calcium compounds in varying concentrations. Large quantities of calcium chloride are formed as waste during the production of soda, the hydrolysis of chlorinated organic compounds and in other production processes.

Known chemical and electrochemical methods for processing calcium chloride have significant disadvantages: decomposition of chloride

calcium at a temperature of 950-1000 C requires the use of special construction materials and high energy costs; during the electrolysis of calcium chloride solutions, an insoluble precipitate is deposited on the cathode (tCa(OH)2* iCaCI2) and over time the passage of electric current through the system stops.

The processing of calcium chloride into more valuable products, using it as a new type of raw material for the production of hydrochloric acid, chlorine, chlorosulfonic acids and aluminum chloride in organic and pharmaceutical production, is an urgent problem.

Particularly promising for these purposes are electrochemical methods that allow syntheses of chemical products without the use of reagents, using electro-oxidative and electro-reductive processes.

The choice of research objects in the dissertation work was determined, on the one hand, by the value of the final products, and on the other hand, by the possibility of using calcium chloride as a raw material, a large-tonnage industrial waste, the processing of which helps protect the environment from harmful industrial emissions.

Purpose and objectives of the study. The purpose of the work was to study the law
dimensions of electrode reactions and the production of calcium-containing
liquid compounds from aqueous solutions of calcium chloride.

Achieving this goal required solving the following tasks:

study the anodic reaction of chlorine release from aqueous solutions of calcium chloride on various electrode materials;

establish the kinetics and mechanism of electrode reactions in aqueous solutions of calcium chloride, calcium nitrate, calcium acetate and a mixture of calcium chloride with sucrose;

Determine the optimal parameters for the electrochemical synthesis of calcium
F ci-containing compounds: current density, electrolyte concentrations,

current outputs of target products.

The objects of study were electrochemical processes, prote
penetrating on various electrode materials in aqueous chloride solutions
calcium with various additives. The choice of the research object was determined with
on the one hand, the lack of knowledge and complexity of electrode processes in races
systems under review, and on the other hand, the possibility of using waste
Sh large-scale production of calcium chloride to obtain valuable

products.

Scientific novelty:

A scientific basis for the technology and advanced technological solutions for the electrolysis of aqueous solutions containing calcium ions have been created;

The patterns of occurrence of anodic and cathodic reactions according to
radiation of calcium-containing compounds on various electrode materials

Practical significance works:

For the first time, using calcium chloride as a raw material, such valuable chemical compounds as calcium acetate, calcium sucrose, calcium nitrate, carbon dioxide, chlorine and hydrogen gases were synthesized.

Approbation work. The main results were reported and discussed at the XIV meeting on the electrochemistry of organic compounds "News of the electrochemistry of organic compounds" (Novocherkassk, 1998), at the All-Russian scientific and practical conference "Chemistry in technology and medicine" (Makhachkala, 2002), at the International Scientific -technical conference dedicated to the 70th anniversary of the St. Petersburg State University of Low-Temperature and Food Technologies (St. Petersburg, 2001), the International Conference "Modern problems of organic chemistry, ecology and biotechnology" (Luga, 2001), at the final All-Russian conferences " Ecology and rational use of natural resources" (St. Petersburg, 2001 and 2002).

Scope and structure of the dissertation. The dissertation consists of an introduction, three chapters, conclusions and a list of references, including 111 titles. The work is presented on 100 pages of typewritten text, includes 36 figures and 6 tables.

The work was carried out within the framework of a grant from the Ministry of Education of the Russian Federation under the program "Scientific research of higher education in priority areas of science and technology", subprogram - "Ecology and rational use of natural resources", section - "Problems of man-made formations and the use of industrial and household waste 2001-2002." .

Preparation of calcium saccharates and their use as corrosion inhibitors

Chlorine is used in significant quantities to prepare bleaches (calcium hypochlorite and bleach). By burning chlorine in a hydrogen atmosphere, pure hydrogen chloride is obtained. The corresponding chlorides are used in the production of titanium, niobium and silicon. Iron and aluminum phosphorus chlorides are also used industrially.

Over 60% of all chlorine produced is used for the synthesis of organochlorine compounds. Large consumers of chlorine include the production of carbon tetrachloride, chloroform, methylene chloride, dichloroethane, vinyl chloride, and chlorobenzene. Significant amounts of chlorine are consumed in the synthesis of glycerol and ethylene glycol using chlorine methods, as well as in the synthesis of carbon disulfide.

For water disinfection, chlorine dioxide, obtained through the electrolysis of a sodium chloride solution, is more promising.

According to preliminary estimates, chlorine production in 1987 in the United States amounted to 10.4 million tons. The cost of 1 ton of chlorine is $195. Chlorine is obtained by electrolysis of a NaCl solution. The theoretical foundations and designs of industrial electrolyzers are described in the monograph.

Mastering the technology of electrolysis of NaCl brines using ion-exchange membranes makes it possible to reduce (compared to diaphragm or mercury electrolysis) the cost of equipment (by 15-25%) and energy costs (by 20-35%). The profitability of membrane electrolysis is associated with the possibility of producing alkali with a concentration of 40% with an electricity consumption of 200 kWh/t of product. Double-layer membranes allow operation at current densities of up to 4 kA/m, which ensures more efficient use of cheap electricity at night. These advantages fully compensate for the relatively high cost of new membranes (500-700 $/m2).

The effectiveness of using activated cathodes to reduce the overvoltage of hydrogen evolution is discussed. A further reduction in the cell voltage can be achieved by increasing the operating pressure to 5 bar while simultaneously increasing the temperature. The use of oxygen (air), which depolarizes the cathode, replacing the process of hydrogen evolution with the process of oxygen reduction, reduces energy costs to 1600 kWh/t of alkali (if the lost energy intensity of hydrogen is not taken into account). An alternative route is the electrooxidation of hydrogen in a fuel cell.

The experiments of the Hoechst company with a chlorine membrane electrolyzer with a membrane area of ​​0.1 m2 are described. It was found that the current efficiency, which decreases with increasing alkali concentration, reaches a minimum at a concentration of 30% and then increases to a concentration of 34%, after which it falls again. Various mechanisms for the implementation of the membrane process and the selection of membrane properties and the reasons for their aging are considered. It has been shown that only at a low cost of steam the cost of energy costs in membrane electrolysis can approach that of the mercury method.

The work carried out a systematic study of the process of electrolysis of solutions of chlorides of alkali and alkaline earth metals without a diaphragm. It has been shown that the differences in the course of the anodic process, depending on the nature of the cation of the initial electrolyte, are due to different solubilities of the electrolysis products, mainly the solubility of the hydroxides of the corresponding metals.

In a chloride membrane electrolyzer, at least on one side of the membrane there is a porous gas- and liquid-permeable layer that does not have electrode activity. In the cathode and anode chambers, the pressure is preferably maintained at up to 15 kgf/cm2, which makes it possible to reduce the electrolysis voltage. The method can be applied to the electrolysis of water and hydrochloric acid.

The paper discusses a model of the process of producing chlorine gas in a non-flow electrolyzer.

Electrolysis of thermal waters

Recently, sodium or calcium hypochlorite has been used to purify and especially neutralize water. The increased interest in hypochlorite is largely due to the great possibilities of its use. The use of hypochlorite obtained by electrolysis of sea water for wastewater treatment is environmentally sound.

The electrochemical method for producing hypochlorite solutions by electrolysis of aqueous solutions of table salt or natural waters makes it possible to organize this production directly at the places where the solutions are consumed, and there is no need for long-term storage of hypochlorite solutions.

Currently, two methods of electrochemical production of a disinfectant have been used: electrolysis of concentrated solutions of sodium chloride followed by mixing with treated water and direct electrolysis of disinfected water. The electrolysis process, in both one and the other case, depends on the current density at the electrodes, the concentration of sodium chloride, pH, temperature and the nature of the movement of the electrolyte, the material of the electrodes and their passivation, as well as the method of current supply to the electrodes.

The process of electrochemical synthesis of sodium hypochlorite in a membrane electrolyzer with an ORTA electrode and an inorganic ceramic membrane based on 2x0g was studied. The influence of current density, concentration of sodium chloride solution, rate of supply of sodium chloride solution, rate of supply of solutions to the electrode chambers was studied. It has been shown that, under optimal conditions, the current efficiency of sodium hypochlorite is 77% with a specific electricity consumption of 2.4 kWh/kg and sodium chloride of 3.1 kg/kg. The corrosion ability of the anode was determined under experimental conditions.

A method and device for monitoring chlorine-containing compounds during water treatment is proposed, intended mainly for disinfecting water in swimming pools. The generation of a disinfecting solution of sodium hypochlorite is carried out using the electrolytic method, and it is assumed that the water in the pool contains a sufficient amount of chlorides. Water circulates in a closed circuit, in the outer part of which there is an electrolyzer, as well as a filter for water purification.

To disinfect drinking water, the authors of the patent propose to build a mini-electrolyzer into the side surface of the pipeline, in which hypochlorite is electrochemically produced from a dilute chloride-containing solution.

The features of electrolysis of a dilute (0.89%) sodium chloride solution under flow conditions were studied. It has been established that increasing the flow rate leads to a sharp decrease in the yield of chlorate and can significantly increase the productivity and stability of the electrolyzer. The best results were obtained in an electrolyzer with titanium electrodes coated with dispersed platinum with a roughness factor of at least 200, with periodic cathodic activation of the anodes.

The electrochemical process of synthesis of sodium hypochlorite under pressure has been studied. Electrolysis is carried out in an autoclave made of titanium alloy, reinforced inside with fluoroplastic with stirring. Hydrogen gas formed during the cathodic reaction accumulates in the system, increasing its pressure. The studies were carried out under a pressure of 100-150 atm. Due to the fact that the solution is under high pressure, the solubility of chlorine increases, which leads to higher current yields of sodium hypochlorite. Titanium-based ruthenium dioxide, graphite and platinum were used as cathode materials, and titanium served as the cathode.

The use of sodium hypochlorite, obtained by electrolysis of natural waters, is reported to purify water from the Makhachkala-Ternair field from phenol.

Sea water has high mineralization. The mineralization of sea water in general is 3.5% or 35,000 ppm. "1. Of these, only two components (chlorides and sodium) are present in quantities of more than 1%, while the concentration of the other two: sulfate and magnesium is about OD%; calcium, potassium, bicarbonate and bromine make up about 0.001%.The remaining elements are present in very low concentrations.

According to the ratio of individual salts to their sum, the salinity of the waters of the Caspian Sea differs from the oceanic and Black Sea. The waters of the Caspian Sea are relatively poor, compared to the oceanic ones, in Na and SG ions and rich in Ca and SO4 ions. The average salinity of the waters of the Caspian Sea is 12.8-12.85%, varying from 3% at the mouth of the Volga to 20% in the Balkhan Bay.In winter, the salinity of the waters of the North Caucasus is high, which is explained by ice formation and the weak influx of Volga waters.

In recent years, there has been an increase in the flow of salts into the sea, which is associated with an increase in the ionic flow of rivers.

The largest amount of suspended particles present in sea waters contain the same minerals as the surrounding rocks (kaolinite, talc, quartz, feldspar, etc.). Table 1.1. The main composition of the water of the Caspian Sea is presented.

Electrochemical syntheses

The analysis of chlorine-containing compounds was carried out using the following methods: Determination of HC by the Pontius method. 10 ml of electrolyte (pH = 8) with the addition of a small amount of starch was titrated with an OD solution of potassium iodide. Definition of SG. Bring 1 ml of electrolyte to 100 ml with distilled water. Titrate 10 ml of sample with a 0.1 N solution of silver nitrate in the presence of a few drops of CH3COOH + K2ClO4.

Determination of C1CV. Add 25 ml of Mohr's salt to 10 ml of sample. Heat until bubbles appear and cool sharply. Add 5 ml of Reinhart's mixture and titrate with 0.1 N potassium permanganate solution until a pink color appears.

Definition of SY/. Add 10 ml of saturated potassium chloride solution to 10 ml of electrolyte. If a precipitate does not form, then there are no CO/s in the system. Determination of the amount of released chlorine The gaseous chlorine formed during electrolysis is passed through a solution of potassium iodide and the released iodine is titrated with sodium thiosulfate of a certain concentration. Chlorine is determined by the iodometric titrimetric method.

Reagents: sodium thiosulfate - 0.005 N solution; KI - 10% solution; acetate buffer mixture. Prepare by mixing equal volumes of 1 N solutions of CH3COONa and CH3COOH; freshly prepared starch solution - 1% solution.

Progress of determination. Pipette 100 ml of tap water into a 250 ml conical flask, add 5 ml of 10% KI solution, 5 ml of acetate buffer mixture and 1 ml of starch solution. Titrate the sample with 0.005 N sodium thiosulfate solution until the blue color of the solution disappears.

To determine the calcium content in waters, the trilonometric method is used, which makes it possible to determine Ca in the sample from 0.1 mg and above. This method is based on the use of Trilon B in the presence of the indicator murexide. The essence of the method lies in the fact that Ca2+ ions in an alkaline medium form a complex compound with murexide, which is destroyed during titration with Trilon B as a result of the formation of a more stable sodium complexonate. Murexide (ammonium salt of purple acid at pH 12 interacts with Ca ions, forming pink compounds.

Murexide does not react with Mg ions, but if the latter in the water under study is more than 30 mg/l, a precipitate of Mg(OH)2 will form, adsorbing the indicator on its surface, which makes it difficult to fix the equivalence point. Then the test solution should be diluted 5-6 times to reduce the magnesium concentration.

Reagents: Trilon B - 0.05 N solution. Exact normality is established using a standard 0.05 N solution of MgS04 or prepared from fix-sanal; NaOH - 10% solution; murexide - dry mixture (1 part murexide and 99 parts NaCl).

Progress of the analysis. Pipette 100 ml of the water to be tested into a 250 ml conical flask, add 5 ml of a 10% sodium hydroxide solution, and add a little dry indicator mixture. The solution turns red. The sample is titrated with Trilon B with vigorous stirring until a purple color appears, which is stable for 3-5 minutes. With further addition of Trilon B, the color does not change. A titrated sample can be used as a “witness”, but it should be remembered that a titrated sample retains stable color for a relatively short time. Therefore, it is necessary to prepare a new “witness” if a change in color of the previously prepared one is observed.

Cathode process - kinetics of formation of hydrogen gas during electrolysis of a calcium chloride solution

Considering that platinum is an expensive electrode material, the process of chlorine release was studied using a cheaper material - graphite. Fig. Figure 3.3 shows anodic current-voltage curves on graphite in aqueous solutions of calcium chloride at a concentration of 0.1 - 2.0 M. As in the case of a platinum electrode, with an increase in the concentration of calcium chloride, the potential for chlorine release shifts to the anodic side by an average of 250 - 300 mV.

From the current-voltage curves of chlorine release presented above on electrode materials made of platinum, graphite and ORTA, it follows that with increasing calcium chloride concentration, the process of molecular chlorine release is facilitated due to a decrease in the diffusion component of the process.

To compare the kinetic parameters of chlorine release in Fig. Figure 3.4 shows the corresponding Tafel dependences of overvoltage (n) on the logarithm of current density (lg і) on platinum, graphite electrodes and ORTA.

The corresponding straight line equations, after calculating the coefficients a and b, can be presented in the following form: Using the calculated coefficients a and b, the characteristics of the process were found - exchange current i0 and transfer coefficient a

The parameters for the electrochemical separation of chlorine from a 2M calcium chloride solution are given below:

In Fig. 3.5. For comparative analysis, anodic current-voltage curves for platinum, graphite and ORTA in a 2M calcium chloride solution are presented. As can be seen from the figure, chlorine is released from a calcium chloride solution at the lowest potentials at the ORTA anode, and the current-voltage curve on graphite is shifted by 250 - 300 mV relative to the ORTA curve to the anodic side. Therefore, it is obvious that it is preferable to use ORTA as an anode material in the electrolysis of aqueous solutions of calcium chloride. On graphite, energy consumption will be higher, and the latter is inferior in durability to ORTA, especially at high anodic loads.

Considering that the energy costs during electrolysis also depend on the kinetics of the cathodic process, we studied the patterns of hydrogen evolution from aqueous solutions of calcium chloride on various electrode materials.

In Fig. 3.6. Current-voltage curves of cathodic hydrogen evolution from calcium chloride solutions with a concentration of 0.5 - 2.0 M on a platinum electrode are presented. Analysis of the current-voltage curves shows that with increasing concentration of calcium chloride, the overvoltage of hydrogen evolution increases (by 30-40 mV). A probable explanation may be the formation of a sparingly soluble precipitate of calcium salts, shielding the surface of the platinum electrode and the amount of which increases with increasing concentration of Ca+ ions. In this regard, there is a noticeable increase in the voltage on the electrolyzer, noted earlier in the work during the electrochemical production of calcium hypochlorite.

Cathode current-voltage curves taken on more affordable electrode materials for practical electrolysis - graphite, steel, copper and titanium - are presented in Figures 3.7 and 3.8. Current-voltage curves show that a low overvoltage of hydrogen evolution after platinum is observed on the graphite electrode (Fig. 3.7, curve 2)? while the electroreduction of hydrogen ions on a titanium cathode (Fig. 3.8, curve 2) proceeds with the highest overvoltage. This behavior is typical for metals coated with phase oxides in the range of hydrogen evolution potentials and having an inhibitory effect on the process. Therefore, the most suitable cathode material for the electrolysis of calcium chloride solution is graphite.

Physicochemical properties of the electrolyte

The melting point of calcium chloride is 774°. In some cases, potassium chloride (melting point 768°) and sometimes sodium chloride (melting point 800°) are added to the electrolyte.
The fusibility diagram of the CaCl2-KCl system was studied by O. Menge. The compound CaCl2 KCl is formed in the system and there are two eutectics, at 75% (mol.) CaCl2 with a melting point of 634° and at 25% (mol.) CaCl2 with a melting point of 587°.
The CaCl2-NaCl system gives a eutectic at 53 mol% CaCl2 with a melting point of about 494°.
The state diagram of the CaCl2-KCl-NaCl system was studied by K. Scholich. In it, at 508°, a eutectic with the composition 52% CaCl2, 41% NaCl, 7% KCL is formed
The electrolyte recommended by Ruff and Plato contains 85.8% CaCl2 and 14.2% CaF2 and melts at 660°. The density of calcium chloride, according to Arndt, is expressed by the equation: d = 2.03-0.00040 (t° - 850°) .
According to V.P. Borzakovsky, the density of CaCl2 at 800° is 2.049; at 900° 2.001, at 1000° 1.953 Additions of potassium chloride or sodium chloride reduce the density of the melt. However, even with significant additions of alkali metal chlorides, the difference in the densities of the melt and calcium metal is still sufficient for the metal to easily float to the surface of the electrolyte
The value of viscosity and surface tension of calcium chloride at the boundary with the gas phase, according to V.P. Borzakovsky are given below

Additions of potassium chloride and sodium chloride to calcium chloride reduce the viscosity of the melt and increase the surface tension at the boundary with the gas phase
The electrical conductivity of calcium chloride is, according to Borzakovsky: at 800° 2.02 ohm-1/cm3, at 900° 2.33 ohm-1/cm3; a value close to these data was obtained by Sandonini. Additions of up to 25% (mol.) potassium chloride, or up to 55% (mol.) sodium chloride reduce electrical conductivity; further increase in additives increases the electrical conductivity of the melt
The vapor pressure of calcium chloride is significantly higher than that of KCl, NaCl, MgCl2. The boiling point of calcium chloride is approximately 1900°. The total vapor pressure in a mixture of calcium chloride with the indicated chloride salts was studied by V.A. Ilyichev and K.D. Muzhzhalev.
Calcium chloride decomposition voltage (v), measured by Combi and Devato from e.m.f. polarization in the temperature range 700-1000°, expressed by the formula

E = 3.38 - 1.4*10v-3 (t°-700°)

Below is a comparison of the decomposition voltages of several chloride salts at a temperature of 800°.

In practice, with a current output of 60-85%, the reverse emf on the bath is 2.8-3.2 V. Drossbach points out that the reverse e.g. observed during electrolysis. d.s. responds e.m.f. cells

Ca/CaCl/CaCl2/Cl2.

The decomposition voltage of salts decreases with increasing temperature. Ho, since the temperature coefficients of change in the decomposition voltage for different salts are different, the sequence of separation of a particular metal from a mixture of salts can change with temperature. At the temperatures of electrolysis of calcium chloride, a discharge of magnesium and sodium ions is possible. Therefore, the electrolyte of the calcium bath must be free from impurities of these salts

Electrolysis with touch cathode

Basic theory

During the electrolysis of molten calcium chloride, the calcium released at the cathode, as in the production of magnesium or sodium, is much lighter than the electrolyte and therefore floats to the surface of the bath. However, it is not possible to obtain calcium in liquid form in the same way as magnesium. Magnesium dissolves slightly in the electrolyte and is protected by a film of electrolyte held on the surface of the metal. Magnesium floating on the surface of the electrolyte is periodically scooped out. Calcium is much more active than magnesium and is not protected by an electrolyte film. Its solubility in electrolyte is high; according to Lorenz's research, 13% of the metal is dissolved in calcium chloride. When it dissolves, subchloride CaCl is formed, which, reacting with chlorine, turns into CaCl2. Under the influence of oxygen and atmospheric moisture, subchlorides form a suspension of calcium oxide in the melt. If the molten calcium is allowed to remain in contact with the electrolyte, then, due to the circulation of the latter, the calcium will be carried away into the region of the anode chlorine and will eventually all turn into calcium chloride. In addition to dissolving in the electrolyte, calcium, being on the surface of the bath, actively reacts with the gases surrounding it.
When calcium is released below its melting point, a spongy dendritic metal is formed, permeated with salt, with a large oxidation surface. Melting such metal is very difficult. Therefore, calcium metal with an acceptable current output can only be obtained using the Rathenau and Süter method - electrolysis with a touch cathode. The essence of the method is that the cathode initially touches the molten electrolyte. At the point of contact, a liquid drop of metal is formed that well wets the cathode, which, when the cathode is slowly and evenly raised, is removed from the melt along with it and solidifies. In this case, the solidified drop is covered with a solid film of electrolyte, which protects the metal from oxidation and nitriding. By continuously and carefully lifting the cathode, the calcium is drawn into rods.
The conditions for electrolysis with a touch cathode on an electrolyte of calcium chloride and fluoride were further studied and improved by Goodwin, who developed an apparatus for laboratory experiments, Frery, who paid attention to practical techniques in electrolysis, Brace, who built a 200 A bath, and others.
In Russia, this method was studied and improved in baths with a current from 100 to 600 A (Z.V. Vasiliev, V.P. Mashovets, B.V. Popov and A.Yu. Taits, V.M. Guskov and M.T. Kovalenko , A.Yu. Taits and M.I. Pavlov, Yu.V. Baymakov).
One of the conditions for achieving satisfactory current efficiency is the use of high current density at the cathode. This is necessary so that the amount of metal released per unit time significantly exceeds its dissolution. Depending on the working surface of the cathode, the power of the electrolyzer and other factors, the cathode current density is selected within the range of 50-250 A/cm2. For the normal course of the process, it is important to ensure precise control of the cathode rise. Too rapid rise of the cathode causes a liquid drop of metal to separate and dissolve in the electrolyte. With a slow rise, the calcium overheats and melts away from the rod. Metal separation can also be caused by overheating of the electrolyte. The dissolution of calcium in the electrolyte with the formation of calcium subchloride and calcium oxide causes thickening of the electrolyte and the formation of foam, which disrupts the normal operation of the bath. When the bath runs cold, the metal on the cathode grows in the form of dendrites.
The current density at the anode is selected as low as possible (about 0.7-1.5 A/cm2) in order to avoid the anode effect. The anode effect occurs when the current density on graphite reaches 8 A/cm2, and on the carbon anode 5.6 A/cm2. The temperature of the calcium chloride electrolyte without additives is maintained at 800-810°, but with the addition of other salts it decreases. Around the cathode, due to the high current concentration, a rim of superheated electrolyte is observed, having a temperature of 820-850 °. Due to the need to maintain the temperature of the electrolyte close to the melting point of calcium (851°), additives to lower the melting point of the electrolyte are not significant, but their role is positive in reducing the solubility of calcium in the electrolyte.
The electrolyte used must be as dehydrated as possible and free of harmful impurities. The moisture contained in the electrolyte decomposes with the release of hydrogen at the cathode, which, combining with calcium, forms calcium hydride, which is accompanied by an increase in temperature at the cathode. In addition, moisture promotes the formation of foam in the electrolyte. All this disrupts the normal course of electrolysis. Another harmful impurity in the electrolyte is silica, which, even in small quantities, causes calcium to dissolve in the electrolyte. As a result, subchloride is formed and the electrolyte thickens, which makes it difficult to separate calcium at the cathode. Impurities of magnesium and sodium are undesirable, since they, released during electrolysis, fuse with calcium, lowering the melting point of the cathode metal and making it difficult to draw out.

Electrolysis practice

The industrial production of calcium by electrolysis with a touch cathode began before the First World War in Germany (Bitterfeld) and France (Jarry). Montel and Hardy indicate that electricity consumption ranged from 30,000-50,000 kWh per 1 g of metal, depending on the size of the electrolyser, its design features and the duration of the electrolysis campaign. Calcium chloride consumption was 4.5 kg per 1 kg of metal.

The working chamber of a German bath (Fig. 2) has an octagonal shape with a diameter of 400 mm and a height of 350 mm. It is lined with coal blocks that serve as an anode. The space between the blocks and the bath casing is lined and filled with thermal insulation. An iron cathode with a diameter of 60 mm is fixed above the working chamber of the bath, which moves in the vertical direction and in the horizontal direction to regulate the voltage on the bath. Air cooling is supplied to the cathode and the air, together with the anode gases, is removed through a channel arranged in the wall of the bath. Bath capacity 40 l for 90 kg of melt. Electrolyte composition, %: 35.46 Ca, 63 Cl, 0.35 CaO, 0.03 SiO2 (max.), 0.04 Fe2O3+Al2O3 (max.). In addition, 1-1.5 kg of potassium chloride is added to the bath, and sometimes a small addition of fluoride salt is given. Electrolyte temperature 800-820°, cathode current density 50-100 A/cm2, anodic 1-1.5 A/cm2, bath current 900-2000 A, voltage 20-25 V. The current output fluctuates greatly at different times of the year and depending on air humidity and averages 35-40%. However, the bath gives from 6 to 15 kg of calcium per day. For 1 kg of calcium, about 70 kWh of electricity and 8 kg of salt are consumed. Analysis of impurities in cathode metal, % (wt.): 0.01-0.08 Mg 0.01-0.05 Si, 0.1-0.3 Fe + Al, 0.05-0.07 Mn, 0.008 -0.03 N, 0.7-1.6 Cl.
According to Bagley’s description, in the USA (Michigan) in 1939, a pilot installation of three baths with a current strength of 2000 A was built, which was soon doubled (Fig. 3). The cathode control was automated, while the operations of periodically adding electrolyte and removing calcium rods were performed manually. Subsequently, new series of baths were supplied for 4000 a, then for 5000 a and, finally, for 10,000 a.

The resulting calcium rods have a diameter from 175 to 350 mm and a length of up to 600 mm. The outside of the rod is covered with a crust of electrolyte. The internal metal part of the rod is quite compact.
It should still be noted that, despite the existing technical achievements, electrolysis with a touch cathode has serious disadvantages: low current efficiency, high power consumption, low extraction of calcium from raw materials, the need to use an electrolyte completely free of impurities H2O, SiO2, etc. compounds, the difficulty of constructing a bath of greater power, etc. All this forced in the last decade, when the demand for calcium increased greatly, to look for fundamentally different methods of production. The search was not unsuccessful.

Liquid cathode electrolysis and production of calcium alloys

Basic theory

Obtaining calcium from a liquid metal cathode eliminates the main difficulties encountered in the isolation of pure liquid metal. The fusion of calcium with the cathode metal located at the bottom of the bath under the electrolyte prevents it from dissolving in the electrolyte and recombining with chlorine and makes it impossible for calcium to be oxidized by surrounding gases. This ensures high current output. The possibility of close proximity of electrodes to each other, the absence of a high cathodic current density required for electrolysis with a touch cathode, and depolarization during the release of calcium at the liquid cathode can significantly reduce the voltage on the bath. Achieving high performance depends on the choice of cathode, cathode current density, temperature and other process conditions. The cathode metal must be alloyed with calcium, and the magnitude of the cathode current density must correspond to the rate of diffusion of calcium into the alloy. Therefore, stirring the cathode alloy is useful. The nature of the phase diagram of calcium and cathode metal is of great importance. For example, during the electrolysis of calcium chloride with a liquid lead cathode, it is not possible to obtain rich alloys with good current efficiency due to the fact that during the formation of the alloy, the melting temperature, according to the phase diagram (Fig. 4), increases sharply, reaching 28% Ca 1106°.

V.M. Guskov and V.F. Fedorov obtained a good current efficiency (89.3%) by stirring the Pb-Ca alloy and saturating it with calcium to 4.4%; the electrolysis temperature was 800-810°. As the calcium content in the alloy increases and the temperature rises, the current efficiency decreases sharply.
Before the amount of calcium in the alloy reaches 1-2%, the cathode current density can only be increased to 2 a/cm2. With a further increase in the amount of calcium in the alloy, the current density must be reduced. A similar pattern was established by A.F. Alabyshev.
Due to the different nature of the Ca-Al phase diagram, A. Yu. Taits and A.V. Golynskaya electrolysis of calcium chloride with a liquid aluminum cathode produced alloys containing 62% Ca at a temperature of 840-880° and a cathodic current density of 1.5 A/cm2. To prevent the calcium-rich alloy from floating, 15% potassium chloride was added to the bath, which reduced the density of the electrolyte from 2.03 to 1.84.
According to the Zn-Ca phase diagram (Fig. 5), the electrolytic separation of calcium on the zinc cathode, bringing the Ca content in the alloy to 90%, is possible at temperatures not exceeding 720°. However, it is difficult to obtain very rich alloys on a zinc cathode due to the floating and suspension of alloy particles.

Calcium deposition on the copper cathode works well. According to the Cu-Ca phase diagram (Fig. 6), the melting point of the alloy lies below 750° when it contains from 25 to 70% Ca, the alloy of this composition does not float, its density even with a content of 60% Ca is 4.4 at a density electrolyte 2.2. The electrolytic production of calcium-copper alloys is of exceptional interest for the production of pure calcium. The large difference in the vapor pressure of copper (boiling point 2600°) and calcium (boiling point 1490°) allows pure calcium to be isolated from the alloy by distillation.

Electrolysis practice

In industry, electrolysis is used with lead, zinc and copper cathodes. The production of lead alloys with calcium and barium is organized in the USA at the United Ltd. Company plant. Each bath is an iron crucible placed in brickwork, in which external heating is installed. Approximately 2 tons of pig lead are loaded into the bath. Lead is covered with a layer of melt of pure calcium and barium chlorides 75-100 mm high. In the center of the bath, a graphite anode is immersed with a device for lowering and raising, the movement of which regulates the temperature of the bath. A scallop is formed at the bottom, as well as along the walls of the bath, which prevents current losses that are possible due to its flow from the anode to the walls of the bath, bypassing the liquid lead cathode. Calcium and barium released during electrolysis are absorbed by molten lead. It is noted that the efficiency of the process is reduced due to anodic effects, metal dissolution and the formation of calcium and barium carbides. Electrolysis is carried out until an alloy containing 2% alkaline earth metals is obtained (approximately three days of electrolysis). When the desired concentration is reached, the current is turned off and the alloy is released into a ladle, from which it is poured into a general mixer.
In the GDR, a calcium-zinc alloy was produced at the IGF plant.
The bath (Fig. 7) consists of a cast-iron box measuring 2250x700x540 mm, walled up in brickwork. The anode is six coal blocks with a cross-section of 200X200 mm, suspended on a common shaft with a manual drive for lowering and lifting. Zinc is poured into the bottom of the box, and the alloy accumulates in the bath, from where, with a content of 60-65% Ca, it is periodically scooped out without stopping the bath. The released chlorine is sucked out from above through the cap. Each bath consumes a current of 10,000 A at a voltage of 25 V. The electrolyte is an alloy of calcium chloride with 18% potassium chloride. Electrolysis temperature 750°. The productivity of the bath is 4 kg of calcium in the alloy per hour; the plant produced 10 tons of alloy per month.
In recent years, electrolysis of calcium chloride with a liquid calcium-copper cathode, followed by distillation of calcium from the alloy, has received widespread industrial use.
The electrolyzer for producing calcium-copper alloy (Fig. 8) is a rectangular cast-iron bath. The width of the bath is 0.90 m and the length is 3 m. The outside of the bath is lined with refractory bricks and enclosed in a metal casing for mechanical strength.

The anode is a package of graphite bars, which are attached to a metal crossbeam. Current is supplied to the anode through flexible busbars attached to the traverse. The anode can be raised and lowered using the steering wheel. Chlorine is pumped out through flues located on the side of the bath. A copper-calcium alloy is poured into the bottom of the bath, serving as a cathode. The current strength in such an electrolyzer is 15,000 A. Recently, electrolyzers with high current strength have been created. The voltage on the bath is 7-9 V. The daily productivity of the electrolyzer is 15,000 and approximately 300 kg of calcium in the alloy.
The technological regime is ensured by compliance with the following conditions. Electrolyte temperature 675°-715°. The electrolyte composition is 80-85% calcium chloride and 15-20% potassium chloride. The electrolyte level in the bath is 20-25 cm, the level of the cathode alloy is 5-20 cm. The alloy is saturated with calcium to 60-65%. The return alloy after distillation contains approximately 30% Ca. The distance between the electrodes is 3-5 cm. The temperature of the electrolyte is regulated by changing the interpolar distance.
Cathode current density is 0.4-0.5 a/cm2, anodic current density is 1.0-1.2 a/cm2. There are indications of using almost twice as high current densities.
The bath is fed with small portions of solid calcium chloride (20-30 kg each). Unlike electrolysers with a touch cathode, this bath can be fed with partially dehydrated raw materials containing up to 10% moisture. Its final dehydration occurs on the surface of the bath.
The alloy is removed when the calcium content does not exceed 65%. With a richer alloy there is a danger of it floating. Scoop out the alloy using a vacuum ladle to a level in the bath of ~5 cm. After draining the rich alloy, load the lean alloy and calcium chloride into the bath
In the electrolysis of calcium chloride with a liquid calcium-copper cathode, the current efficiency is 70-75%. Specific energy consumption is 15,000 - 18,000 kW/h per 1 ton of calcium in the alloy, consumption of calcium chloride is 3.5 g, and graphite anodes are 60-70 k per 1 g of calcium in the alloy. Cast iron baths last 10-14 months.