Chemistry · Ch 1 — Metallurgy
SUMMARY
SUMMARY
- Metallurgy relates to the science and technology of metals.
- A naturally occurring substance obtained by mining, containing a metal free or combined (e.g. as oxides, sulphides), is called a mineral; a mineral containing a high enough percentage of metal to be extracted conveniently and economically is called an ore -- so all ores are minerals, but not all minerals are ores.
- Extracting a metal of interest from its ore consists of three metallurgical processes, in order: (i) concentration of the ore, (ii) extraction of the crude metal, and (iii) refining of the crude metal.
- Concentration removes gangue by gravity separation, froth flotation, leaching (cyanide/ammonia/alkali/acid) or magnetic separation, depending on the ore.
- Extraction of crude metal from the concentrated ore is carried out in two steps: (i) conversion of the ore into an oxide of the metal (by roasting or calcination), and (ii) reduction of that oxide to the elemental metal (by smelting/carbon/hydrogen/a reactive metal/auto-reduction).
- The graphical representation of how the standard Gibbs free energy of reaction for the formation of various metal oxides varies with temperature is called the Ellingham diagram.
- The Ellingham diagram helps select a suitable reducing agent and appropriate temperature range for a given reduction, by comparing the relative stability (position on the diagram) of competing oxides.
- Electrochemical principles, alongside thermodynamic ones, also find application in metallurgical processes -- most importantly for the most reactive metals, whose oxides cannot be reduced by carbon. …