Calcium Metal Production via Electrolysis of Calcium Chloride: Cell Parameter Analysis, Study Guides, Projects, Research of Process Engineering

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In the name of Allah,

the most beneficent,

the most merciful.

Synopsis

 Objectives

 Calcium & Ores of Calcium

 Calcium in Pakistan

 Production of Calcium Metal

 Electrolytic Cell

 Tasks Ahead

Calcium

Calcium is a soft gray alkaline earth metal

with following properties.

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Atomic number 20 a.m.u. Atomic Weight 40 a.m.u. Phase (at room Temp.) Solid Melting point 842 C° Boiling point 1484 C° Density 1.55 g/cm^3 Heat Capacity 25.929 J/mol.K Heat of Fusion 8.54 k.J/mol Heat of Vaporization 154.7 k.J/mol (^) Pure Calcium Metal

Reference: Metals Handbook, Joseph R. Davis, Ed. 2, 1998

Uses of Calcium

Calcium is used in the production of aluminum, beryllium, copper, lead and magnesium alloys.

It is also used in making cements and mortar that are used in buildings.

Calcium carbonate is used in the purification of iron from iron ore in a blast furnace.

Calcium is an important nutrient that we need in our bodies. It helps develop strong bones and teeth and is involved in blood clotting and muscle contractions. (^) Calcium Foods 5

Occurrence of Calcium

 Calcium naturally occurs in the form of carbonate, sulphate, fluoride, silicate and borate compounds.

 Calcium carbonate occurs in marble, chalk, limestone and calcite.

 Fluorspar, gypsum, phosphorite and asbestos are the other notable minerals of calcium.

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Lime-stone Gypsum

Calcium Ores in Pakistan

The important deposits of calcium are located in

Kohat D.I.Khan Daud-khel Rakhi-Munh & Zinda Pir in Suleman Range of D.G. Khan Jehlum district at Khewra gorge Dandot Kot Diji Kalabagh Hills

The average annual production of limestone is 8697 million tons used mainly in the manufacture of cement.

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Reference: Geological Survey of Pakistan (www.gsp.gov.pk/)

1- The Limestone-Hydrochloric Acid Process

Limestone is treated with hydrochloric acid to form

white flakes of calcium chloride.

CaCO 3 + 2HCl CaCl 2 + CO 2 + H 2 O

 Extremely pure calcium chloride products can be

obtained using this process if the purity of the

hydrochloric acid is sufficient. Hence, the process is well

suited for producing food grade products.

 It is also an environment friendly method to utilize

by-product hydrochloric acid.

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Reference: Electrochemistry in Mineral and Metal Processing VI, F. M. Doyle, G. H. Kelsall, and R. Woods, Editors, PV 2003-18, The Electrochemical Society Proceedings Series, Pennington, NJ (2003).

2- Solvay Process

The most common method to produce calcium chloride is Solvay process. The basic raw materials are limestone and sodium

chloride brine and the reaction is:

2NaCl + CaCO 3 Na 2 CO 3 + CaCl 2

 It should be noted that the purpose of the Solvay process is to produce soda ash, Na 2 CO 3 , rather than calcium chloride.

 The calcium chloride obtained is a 10-15% solution that also contains a percentage of sodium chloride.

 This stream is purified and concentrated before putting it into electrolytic cell.

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Reference: Calcium Chloride Handbook (www.dowcalciumchloride.com)

3- Natural Brine Process

 In some countries including U.S.A., production is utilized by the concentration and purification of naturally occurring brines from salt lakes and salt deposits.

 Magnesium is removed by adding milk of lime, Ca(OH) 2 , which causes magnesium to precipitate in the form of magnesium hydroxide, Mg(OH) 2. Sodium chloride, NaCl, is removed by precipitation. Ca(OH) 2 + Mg2+^ Mg(OH) 2 + Ca2+

 Sodium chloride precipitates from the CaCl 2 solution when the concentration of calcium chloride is increased during the evaporation of water.

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Reference: Pozin, M.E., Technology of Mineral Salts, Leningrad: Khimiya, 2001

Electrolysis

 Electrolysis is the method of separating a compound

into its constituent elements by passing an electrical

current through it when in a molten or aqueous state.

 The basic principle is that if you melt or dissolve an

ionic compound (such as NaCl or Cacl 2 ), then the ions

become free to move around – and carry electrical

current.

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Molecule of CaCl 2

Chloride ion

Calcium ion

Free ions of Ca & Cl after melting down Cacl 2 Reference: Volume 1, Modern Electrochemistry, Second edition, Ionics

Feed to Electrolytic Cell

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% CaCl 2 % BaCl 2 KCl^ CaF 2 Melting Point (C°) 50 50 0 0 595 42 42 8 8 570 38 57 5 0 524 59 31 6 4 491

Calcium chloride is fed to electrolytic cell with different feed

compositions. The temperature of electrolytic operation is

dictated by the input feed composition.

Parameters and Problems of Electrolytic Cell

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The most important cell parameters are:

 Cell Voltage

 Current Density

Problems in electrolytic cell include:

 Ohmic Resistance of electrolyte

 Polarization of electrolyte

 Over potential due to organic additives

 Anode Passivity

 Voltage Loss in circuit

Electrolysis Equations

 At the positive electrode, the negative ions lose electrons to become neutral chlorine molecules. The half equation is:

2Cl-^ Cl 2 + 2e-

 At the negative electrode, the positive ions gain electrons to become neutral calcium atoms. The half equation is:

Ca2+^ + 2e-^ Ca

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Reference: Modern Electrochemistry, Second edition, Volume 1, Ionics

Objectives & Tasks Ahead

1. To understand different cell and process parameters.

 Voltage  Purity of Calcium Chloride  Current Density  Distance between electrodes  Electrodes material  Modifications in electrode

2. To study and observe the effect of these parameters

on the production of calcium metal.