Everything Science Grade 11

CHAPTER 9. THE LITHOSPHERE 9.5

STEP 1 - The ore is crushed until it is in fine pieces

STEP 2 - A sodium cyanide (NaCN) solution is mixed with the finely ground rock

4 Au + 8NaCN + O 2 + 2H 2 O→ 4 NaAu(CN) 2 + 4NaOH

Gold is oxidised.

STEP 3 - The gold-bearing solution can then be separated from the

remaining solid ore through filtration

STEP 4 - Zinc is added. Zinc replaces the gold in the gold-cyanide solution.

The gold is precipitatedfrom the solution.

This is the reduction part of the reaction.

Figure 9.3: Flow diagramshowing how gold is processed

Characteristics and usesof gold ESBCP

Gold has a number of uses because of its variedand unique characteristics. Below is a list of some of
these characteristics that have made gold such avaluable metal:

• Shiny
  Gold’s beautiful appearance has made it one of the favourite metals for use in jewellery.


• Durable
  Gold does not tarnishor corrode easily, andtherefore does not deteriorate in quality. It is
  sometimes used in dentistry to make the crownsfor teeth.


• Malleable and ductile
  Since gold can be bent and twisted into shape, as well as being flattenedinto very thin sheets, it
  is very useful in fine wires and to produce sheets of gold.


• Good conductor
  Gold is a good conductor of electricity and is therefore used in transistors, computer circuits and
  telephone exchanges.


• Heat ray reflector
  Because gold reflects heat very effectively, it is used in space suits and invehicles. It is also used
  in the protective outer coating of artificial satellites. One of the more unusual applications of
  gold is its use in firefighting, where a thin layerof gold is placed in themasks of the firefighters
  to protect them from theheat.