Extractive Metallurgy_Dr TSG_Electrolysis.pptx

A comprehensive notes on Hydrometallurgy

1. Extractive Metallurgy Lecture 5: Electrometallurgy Dr T. Gabasiane

2. Electrometallurgy Electrometallurgy, is a section/branch of extractive metallurgy, which utilizes electrical energy to extract and refine metals It involves the application of electrochemical principles to extract metals from their ores or compounds The process involves transfer of electrons between electrode and a particular metal ion.

3. Electrometallurgy EM plays an integral role in extractive metallurgy, it provides an efficient and environmentally friendly method for extracting metals from their ores and compounds. It mostly useful in extracting metals such as aluminum, copper and zinc (WHY?) EM is also used in the refining of metals, to produce high purity metals

4. Electro winning and refining Electro winning is the commercial deposition of a metal from its solution onto an inert electrode Electro refining is the refining of the metal from its anode to obtain the cathode metal in the purest form under certain conditions

5. Electrometallurgy

6. Electrolysis Electrolysis is the process whereby a molten ionic compound is broken down by an electric current This process also occurs in aqueous solutions Ionic compounds in the solid state cannot conduct electricity either since they have no free ions that can carry charge

7. Electrolysis Electrolyte: a substance that conducts electricity when dissolved in (solution) or molten NB: it contains free moving ions that are essential for carrying the electric current Electrode: is a rod (usually graphite) that conducts electricity into or out of an electrolyte Anode: is the positive electrode of an electrolysis cell Cathode: is the negative electrode of an electrolysis cell Anion: is a negative charged ion which is attracted to the anode Cation: is a positive charged ion which attracted to the cathode

8. Electrolysis During electrolysis, current flows around the circuit, causing movement of ions and electrons Electrons flow from the negative terminal of the power supply to the cathode (this gives the cathode its negative charge) The electrons do not pass the solution

9. Electrolysis cont …. At the cathode, cations gain electrons to form atoms Anions move to the anode and lose electrons The electrons then flow through the external circuit back to the power supply’s positive terminal hence completing the circuit NB: electrons are the charge carries in the external circuit , while ions are the charge carriers in the electrolyte

10. Electrolysis cont …. Electrolysis involves a redox reactions Positive ions (cations) in the electrolyte move towards the cathode (reduction occurs at the cathode – gain of electrons) Negative ions (anions) in the electrolyte move towards the anode (oxidation occurs at the anode – loss of electrons)

11. Electrolysis cont ….

12. Electrolysis Cont …. When Na + ions collide with the negative electrode, the battery carries a large enough potential to force these ions to pick up electrons to form sodium metal Cl - ions that collide with the positive electrode are oxidized to Cl 2 gas, which bubbles off at this electrode. The net effect of passing an electric current through the molten salt in this cell is to decompose sodium chloride into its elements, sodium metal and chloride gas.

13. Electrolysis Cont ……. The potential required to oxidize Cl - ions to Cl 2 is -1.36 volts and the potential needed to reduce Na + ions to sodium metal .

14. Electrolysis Factors Affecting Electrolysis Nature/Type of electrolyte The electrochemical series Molarity/Concentration of Solution Type of Electrodes

15. Electrolysis Cont …… Molten Solution Pure Impure Ionic compound Mixture of ionic Liquid form  

16. Electrolysis Cont …… Electrochemical Series This is a list of elements in order of their ability to be reduced For cations, the higher the element n the series, the lesslikely it is that this will gain electrons (that is be reduced) For anions, the higher it is on the series the less likely will it lose electrons (that is be oxidized

17. Electrolysis Cont ….

18. Electrolysis Cont … What affects the ability to be reduced Reduction Potential Some ions have a greater ability to be reduced than others

19. Electrolysis Cont ….. Concentration of electrolyte Concentration entails the amount of solute in a given volume of a solvent The higher concentration means that the given solute: solvent ratio is high, that is, there is a high level of solute to a given volume of solvent Low concentration means that the given solute: solvent ratio is low, that is, there is a low level of solute to a given volume of solvent

20. Electrolysis Cont …… This is utilized in both extraction and refining of metals Desired properties of electrolyte Must have sufficient high ionic conductivity and conduction must be entirely due to ions Chemically inert towards the electrode Must be stable at the operational temperature

21. Electrolysis Cont ….. Electrolysis of fused salts Used primarily for reactive metals Most metals can be obtained by direct electrolysis of its slats (Halides) It is more advantageous to dissolve a compound such as a halide into a mixture of more stable halides such as sodium chloride and potassium.

22. Electro - winning EW is a metal extraction process that utilizes electrolysis to recover metals from their solutions It is mostly used in mineral processing for metal refining to generate pure metals from metal bearing solutions