2010 – AusIMM Gravity Gold Conference, Ballarat Vic


Gravity gold recovery has been practiced for thousands of years, making it one of the oldest forms
of mineral processing. Gold is 19 times heavier than water although the barren rock is generally
only 2.7 times heavier. Any potential gold ore needs to be characterised to assess its amenability
to a gravity recoverable gold (GRG) process based on well planned and executed test work. Scale
up considerations need to be considered in designing a gravity circuit. The economic impact of
a gravity circuit should be justified based on the installed cost and likely benefits. Maximising
gravity gold recovery results in a faster cash flow, lower operating cost per ounce and higher overall
gold recoveries compared to the several weeks required to recover gold adsorbed onto carbon.
The advent of centrifugal concentrators such as the Knelson and Falcon, coupled with intensive
leaching of concentrates (ILR), has revolutionised gravity gold circuit designs. Considerations
associated with the sizing of the centrifugal machines and the percentage of the circulating
load (bleed) that should be processed is discussed in this paper. The trends with gravity circuit
layout, engineering, as well as optimum dumping cycles, are important areas which require close
consideration. Key aspects of these are presented in this paper.
There are a number of circuit configurations to be considered, including the integration of different
gravity concentrators. Other gravity process design considerations such as fewer modules, the
effect of equipment size and enhancement of process efficiency using preconcentration, together
with factors that affect OPEX and CAPEX are addressed.
Practical considerations of maintenance, security from theft, minimisation of risk and water
balance considerations are discussed using different equipment and circuit configurations. The
trend towards using gravity recovery in flotation plants is also reviewed. A number of examples are
cited and good design aspects highlighted.

Read the paper here