Financial restraints being experienced by the South African gold
industry have sparked renewed interest in the use of pure oxygen as
a cost reducer in the gold leaching process, reports Air Products
chemical processes development engineer Robert Holmes.
Oxygen has been used in the recovery of gold since the 1980s, but
new developments in this technology by the company have increased
its potential in the industry as studies have shown that oxygen
reduces the consumption of reagents, particularly cyanide, which
can be a significant cost in gold recovery, he explains.
“With the gold industry being unstable, everyone should be
looking at ways to improve production without increasing
costs,” says Holmes.
The oxygen can be suprussia tin ore crushing plantplied as bulk liquid in cryogenic tankers to a
storage facility on the customer’s site where it is then
vaporised, or it can be manufactured on site depending on the needs
of the customer.
A reduction in the consumption of reagents, such as cyanide, is
achieved by oxidising the cyanocides in the slurry prior to the
leach reaction, explains Holmes.
“Other reagents such as lead nitrate and lime can also be
reduced but cyanide savingsstone crushers for hire south africa are the main benefit,” he
says.
The margins are so fine in gold recovery that a fraction of a
percent improvement could mean a significant increase in
revenue.
Oxygen can provide this improvement, particularly when treating
refractory ores or ores with high levels of pyrite, chalcopyrite or
organic materials and it is also beneficial when treating slimes or
dumps, explains Holmes.
The requirement for compressed aiworlds largest crushersr is reduced, if not eliminated,
and some recovery plants have justified the simple conversion to
pure oxygen for this reason alone.
Often with high tonnages a small improvement in recovery means a
large increase in gold.
This is achieved through improved leach kinetics, higher dissolved
oxygen levels, a more stable, consistent leach and reduced
residence time.
There are various methods of getting oxygen dissolved in the slurry
and, in the past, oxygen has been bubbled into leach tanks,
injected into venturis and introduced under pressure into slurry
pipes, all of which provide better results than compressed
air.
Now filblast gas shear reactor technology, developed by Australian
company Atomaer, is able to offer the best results by optimising
production and recoveries at a minimum cost to the client as it is
retrofitted to the existing plant, explains manager in Africa
Pieter Jansen.
The gas shear reactor is not only able to improve gold recoveries
but also increases throughput and reduces the existing reagent
costs in the extraction of gold, he adds.
“A net benefit is achieved after all costs for the addition
and changes made to the plant to accommodate the gas shear reactor
are recouped within a relatively short period,” says
Jansen.
Security aspects were also considered in the development of the gas
shear reactor and it has been designed to use less labour than
conventional systems.
“An important aspect in any project is that it remains of
zero concern to the customer,” explains Jansen.
The system requires low maintenance and inspections can be
preplanned to minimise the security risk, he reveals. The two
companies also provide training on the use of the equipment to all
operators in the plant.
A reliable supply of oxygen is essential to the running of the
plant since it will be the only source of oxygen for the leach,
replacing the compressed air.
Air Products, one of South Africa’s largest gas suppliers,
has five large air-separation units in Vanderbijlpark, close to the
main mining areas of the West Rand and Free State.
The company also supplies telemetry equipment, which is a remote
tank pressure and level monitoring system to ensure a consistent
and reliable supply.
Both companies are working together to achieve substantial results
through reliable supply, practical experience and well-proved
technology.