Properties of gold
• Five ten – millionths of the earths outer layer.
• Said to have formed due to a supernova nucleosynthesis.
• Its heavy - 19 x water
2 x lead
if we had enough gold to fill a one litre milk carton, it would weigh 19.3 Kg
• Gold is quite soft – slightly harder than finger nails
• Very malleable and ductile.
• Melting point – 1060 c
• Boiling point – 2660 c
• Atomic mass – 196.97
Aurum – “ glowing dawn “.
Automic number 79
Automic mass 196.97
Tensile strength 120 MPa
Youngs modulous 79 GPa
Why gold ?
• Esthetic beauty – high luster.
• High malleability and ductility.
• Rare and high appreciation value.
• White gold alloys – based on palladium silver
& other white metal.
Impact of gold.
• Environmental Impacts: Poisoned Waters Solid Waste Polluted Air Threatened
• Community Impacts: Endangered Communities Disadvantaged Women Violated
Human Rights Toll on Indigenous Peoples
• Worker Impacts: A Dangerous Profession Undermined Workers' Rights
• Economic Impacts: Economic and Financial Toll
• Comminution is the breaking up of ore to make gold available for
treatment. Conventionally, this process occurs in multi-stage crushing and
milling circuits. Modern technology is based on large mills fed directly with
• Gold ores can typically be classified into:
• refractory ores, where the gold is locked within a sulphide mineral and not
readily available for recovery by the cyanidation process; or
• free milling, where the gold is readily available for recovery by the
• Refractory ore treatment – after fine grinding, the sulphide materials are
floated away from the barren gangue material to produce a high-grade
sulphide concentrate. The sulphide concentrate is oxidised by either
roasting as at AngloGold Ashanti Mineração or bacterial oxidation (BIOX)
as at Obuasi. The oxidation process oxidises the sulphide minerals
liberating the gold particles making them amenable to recovery by the
• Free milling and oxidised refractory ores are processed for gold recovery by
agitator leaching the ore in an alkaline cyanide leach solution followed generally by
adsorption of the gold cyanide complex onto activated carbon-in-pulp (CIP).
• The alternative process is the heap-leach process. Generally considered applicable
to only high-tonnage, low-grade ore deposits, AngloGold Ashanti has successfully
applied this to medium-grade deposits where the ore deposit tonnage cannot
economically justify constructing a process plant. Here, the run-of-mine ore is
crushed and placed on the leach pad. Low strength alkaline cyanide solution is
applied, generally as a drip, to the top of the heap for periods of up to three
months. The dissolved gold bearing solution is collected from the base of the heap
and transferred to the carbon-in-solution (CIS) columns where the gold cyanide
complex is adsorbed onto activated carbon. The stripped solution is recycled back
to the top of the heaps.
• Gold adsorbed onto activated carbon is recovered by a process of re-dissolving the
gold from the activated carbon (elution), followed by precipitation in electro-
winning cells and subsequent smelting of that precipitate into doré bars that are
shipped to the gold refineries.
Making gold jewelry
• Making gold jewelry takes time and craftsmanship. Weather you are making 14k
custom gold jewelry or 24k gold jewelry, the process is the same. You start with
your design and from there a wax model is carved . Many tools and techniques are
used to create a wax: steel wax carvers, files, hand gravers, burs, drills, heat, etc. -
whatever is required to achieve a finished model. Then the wax is ready for
investing. The next step in making gold jewelry is to invest. We first attach a
sprue to the wax. The sprue will serve as a channel for melting wax to escape
during burn-out and later for molten gold to enter during casting. Then the
sprued wax is attached to a round rubber base. An investment flask is placed over
the wax and is attached to the rubber base. The investment flask is a round
cylindrical steel tube, similar to a tin can open at both ends.
• Investment begins as a dry fine white powder similar to plaster-of-paris in feel. It is
• This is done by placing the investment slurry in a vacuum where the air is drawn
out. This is called debubblizing. The slurry is then poured into the flask completely
surrounding the wax. The flask is then placed into the vacuum chamber for a final
debubblizing to make sure there are no air pockets attached to the model that
would corrupt the casting. After the investment hardens the rubber base is
removed and the flask goes into the burn-out oven. The burn-out takes hours at a
high temperature until all the wax is eliminated. Once the burn-out has taken
place only a hollow replica of the original wax carving remains inside the flask.
The mold is ready for casting. The flask is placed in a casting machine and the
gold is melted in a crucible with a torch. At the proper casting temperature the
molten gold is thrown by centrifugal force into the hollow mold and held there
until it solidifies. Now you have a cast replica of your “lost” wax. The investment
is then broken away from the cast piece. What remains is the rough casting. Now
it’s time to clean up and polish the casting. The gold jewelry making process is
• making gold jewelry
• investment casting
• Chain making
The price of gold fluctuates according to the
demand of the buyers and the amount being
sold by the sellers.
The term carat in 24K gold refers to the amount
of base metals mixed in the alloy.. 24K being the