Pyrometallurgy is a metallurgical process that uses heat to extract and refine metals from ores. It involves roasting ores at high temperatures to remove volatile materials without melting, smelting to separate impurities from precious metals like gold and silver through heating to form alloys and slags, and cupellation to further purify precious metals using their resistance to oxidation at high heat compared to base metals. Key steps include roasting ores from 1200-1800°C, smelting for two hours to separate gold and silver alloys from slag, and refining gold purity to 99% through carbon ashing, borax mixing, aqua regia purification, and final furnace refining.

1. Extraction and Recovery
of Gold using Pyrometallurgy

2. What is pyrometallurgy?
Metallurgy involved in winning and refining metals
in which heat is used, as in roasting and smelting.
Practically all iron and steel, nickel, and tin, most
copper, and large proportion of zinc, gold, and
silver, as well as many of the minor metals, are won
from their ores and concentrates by
pyrometallurgical methods.
It is mostly important and oldest class of the
extractive process.

3. Roasting
Roasting of ores and concentrates can be
defined as the heating of a material to cause
reaction and the expelling of volatile matter
without causing fusion.
Gold or silver are fused at high temperatures,
forming spherical beads which are difficult to
dissolve.
The temperature of the ore should be in the
range of 1200-1800°C.

4. Smelting
This operation is performed for around two
hours to ensure complete separation of
impurities from the precious metals. Gold
and silver form from an alloy heavier than
the slag and sicks t o the bottom of the
furnace.
Once the smelting is completed, the slag is
removed and the precious metals are casted
in inglots. the slag contains gold and silver
and must be reprocessed in order to
minimize the loss of precious metals.

5. Fire Assay
Basically the ore is mixed with a mixture of
fluxes and during the smelting process
precious metals are liberated and most of
heavy metals are trapped by the fluxes.
However, lead is the key element due to
collect precious metals. The latter product is
reprocessed by a cupellation stage so that the
gold-silver alloy that will be leached selectively
to calculate the gold content.

6. Cupellation
The process is based on the principle
that precious metals do not oxidise or
react chemically, unlike the base
metals.
When they are heated at high
temperatures, the precious metals
remain apart and the others react
forming slags or other compounds.

7. Carbon Ashing
It takes up to 15-20 hours to burn out
100 kg activated carbon.
After burning, mix the residual with
borax and silver to be refined then
followed by aqua regia purification to
produce sponge gold and finally
refinery in furnace.
The final product gives 99% gold
purity.