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- 1 Introduction Table of Contents
- 2 Calcium
- 2.1 Properties of Calcium
- 2.2 Uses of Calcium Metal......................................................................................................
- 2.3 Occurrence & Natural Abundance of Calcium
- 3 Methods of Calcium Production
- 3.1 Calcium Production by CaCl2 Electrolysis
- 3.2 CaCl 2 Production...............................................................................................................
- 3.2.1 Limestone Hydrochloric Acid Process
- 3.2.2 Solvay Process
- 3.2.3 Natural Brine Process................................................................................................
- 3.3 Purification of Calcium Chloride.......................................................................................
- 4 Calcium Electro-winning by CaCl 2 +CaO Mixture
- 4.1 Cell Specifications & Parameters
- 4.2 Features & Operation of Cell............................................................................................
- 4.2.1 Dependence of Cell Potential on Calcium Oxide Content
- 5 Electrolysis of CaCl 2 +CaF
- 5.1 Disadvantages of using CaCl 2 & CaF 2 as an Electrolyte
- 6 Use of CaCl 2 + BaCl 2 as Electrolyte
- 6.1 Advantages of using CaCl 2 + BaCl 2 as Electrolyte
- References:
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List of Figures
Figure 1: Flow-sheet of Solvay Process ........................................................................................... 4
Figure 2: Scematic of Cell ................................................................................................................ 5
Figure 3: Dependence of Celle Potential on CaO Content.............................................................. 7
List of Tables
Table 1 : Properties of Calcium ....................................................................................................... 2
Table 2 : Natural Abundance of Calcium ........................................................................................ 3
Table 3: Cell Parameters ................................................................................................................. 6
Table 4: Feed Composition vs Melting Point .................................................................................. 8
Table 5: Operating Conditions of Cell ............................................................................................. 8
2 Calcium
Properties of Calcium Calcium is a soft gray alkaline earth metal with following properties.
Uses of Calcium Metal Following are the uses of calcium metal.
As an alloying agent for metals such as Al, Pb, Cu & Mg
As a reducing agent in preparation of Ni, Cr, Th & U
As a separator for argon & nitrogen
As a deoxidizer for Cu, Fe, Ni alloys
As a desulfurizing agent for petroleum fractions
As a dehydrating agent for alcohol & organic solvents
As a starting material for calcium hydride production
Occurrence & Natural Abundance 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. Calcium is the fifth-most-abundant element by mass in the Earth's crust. Natural abundance table is given below.
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 Table 1 : Properties of Calcium
3 Methods of Calcium Production
The known methods of calcium production are:
Reaction of Calcium chloride with sodium-lead alloy
Aluminothermic production of calcium metal
Electrolysis of molten calcium chloride or a mixture of calcium chloride with calcium fluoride
Calcium Production by CaCl2 Electrolysis Calcium metal is majorly produced by electrolysis of molten:
Calcium Chloride
Calcium Chloride + Calcium Oxide
Calcium Chloride + Calcium Fluoride
Calcium Chloride + Barium Chloride
CaCl 2 Production Calcium chloride is produced by three different processes.
The Limestone-Hydrochloric Acid Process
The Solvay Process
The Natural Brine Process
Element Abundance Oxygen 46.60 % Silicon 27.72 % Aluminum 8.13 % Iron 5 % Calcium 3.63 % Sodium 2.83 % Potassium 2.59 % Magnesium 2.10 % Table 2 : Natural Abundance of Calcium
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 CaCl2 solution when the concentration of calcium chloride is increased during the evaporation of water.
Purification of Calcium Chloride Prior to electrolysis, it is necessary to purify calcium chloride. There are two methods for calcium chloride purification.
Crystallization from aqueous solutions
Joint precipitation of impurities from aqueous solutions onto inorganic collectors (hydrated aluminum or zirconium oxides).
4 Calcium Electro-winning by CaCl 2 +CaO
Mixture A cell for electro-winning of calcium was designed and experiments were performed to obtain calcium metal from CaCl 2 +CaO feed. The dependence of cell potential on calcium oxide content in feed was studied.
Figure 2 : Schematic of Cell
Cell Specifications & Parameters
Features & Operation of Cell The distinctive feature of this cell is the ceramic diaphragm shown around the anode.
This sheath is required to prevent the anodic carbon and the gases from mixing with the catholyte and lowering the cell efficiency.
It is also required to keep the deposited calcium away from the anodic gases.
The dc current was applied to the cell and the anodic gas composition was monitored for the evolution of chlorine.
The current was interrupted once an appreciable level of chlorine was detected in the anodic gas.
The bleaching action of chlorine was used to indicate its presence.
Intermediate and final levels of oxygen were recorded by the titration method as a function of time.
The cell was held at a set temperature.
Table 3 : Cell Parameters
6 Use of CaCl 2 + BaCl 2 as Electrolyte
The patent is about a novel electrolyte consisting of a mixture of calcium chloride & barium chloride.
Operating temperature is 600-650°C.
Following table gives different compositions of electrolyte & the melting point.
A mixture of 100 parts of calcium chloride, 100 parts barium chloride & 20 parts potassium chloride was electrolyzed & it produced calcium deposit 96.9 % purity.
The operating conditions were as follows.
Table 4 : Feed Composition vs Melting Point
Table 5 : Operating Conditions of Cell
Advantages of using CaCl 2 + BaCl 2 as Electrolyte Reduced bath temperature
Convenient recovery of calcium metal
Longer cell life
Low voltage required. i.e. 3.5V
High power efficiency. i.e. 4kW required for 1 lb calcium metal production
