Metallurgical development
OF
alluvial diamond
processing
By Arthur Phosiwa
Rockwell Diamonds, Douglas, Northern Cape
[email protected]
Introduction
Material volume
• Diamond concentration processes in alluvial
have historically been either inefficient,
manpower intensive, have a large footprint
and been based on many years of operator
experience
• To achieve required maximum plant throughput it is important to keep the plant volume
constant and allow direct proportions material
density and mass flow rate to influence one
another
• A recent advance in the concentration
technology in Southern Africa is the
introduction of the Russian high throughput
X-ray technology, manufactured by
Bourevestnik
• Any change in material type, i.e. change in
material density can have a significant impact
upon efficient treatment of ore if the change in
density is not monitored appropriately
Figure 2: Clay bedrock contained in feed at MOR SHC mine
• The BV machines specifically treat volumes of
material rather than tonnages
• Presently Rockwell Diamonds employs this
advanced technology in two of its MOR
operations namely Nuwejaarskraal and
Saxendrift hill complex
Metallurgy of high tonnage X-ray
sorters
• The BV machines are similar to any other
particular diamond concentration technology,
attention must be given to ore types and
characteristics inherent in the ore
• The technology is described in more detail
including benefits associated with its
application in alluvial diamonds processing
Background
• Alluvial diamonds are recovered from deposits
of sand, gravel and clay/calcrete in river beds
and sea
• The metallurgical development of alluvial
diamonds dates back to ancient times, and
has brought about changes in alluvial diamond
mining
• Metallurgical developments lead to formation of
agreement initiatives such as the DDI, PDA and
Mwaduli community diamond initiative which
were established to develop practical solutions
to assist small-scale diggers in cooperation
with NGOs and De Beers group
• The initiatives constantly seek for continual
improvement and creating a challenge to
metallurgical development of advanced, cost
effective and process effective technology to
mine alluvial diamonds
Process Metallurgical Test Work
Material hardness
• Figure 1, 2 and 3 show different feed types
treated at MOR SHC plant
Figure 3: Wet Rooikoppie gravel from MOR SHC mine
• Hardness is a measure of how resistant or
easily solid materials are to change in shape,
understanding hardness is important this
influenced by differential rock types in the feed,
i.e. calcrete, clay content and bended iron
formation rocks
Figure 5: Example of air record graph shown on the
BV control machines
• It is very important to understand the impact
these material fines have when they enter the
recovery stage of the plant from the point of
washing or scrubbing, slurred fines tends to
cause blinding of X-rays lenses regardless of
overfeeding the machines
• Machine sensitivity is a function of the machine
parameter settings such as detection rise and
decay times of luminescent signal
Material shape and size
• Investigation into creating a stable machine
operating environment led to the formula
detection wavelength (D) is a function of = Air
wavelength + Luminescent material wavelength
• The shape of the material influences the type of
panels to be used when sizing the material and
this is a point of loss or recovery of valuables in
the plant
• Screens are fed to a capacity of 75% for
effectiveness and to obtain 80-90% efficiency
• Material size and shape has an effect on screen
efficiency and grain size distribution because
it determines the retention capability of screen
panel which also affects the bulk X-rays in
terms of throughput-particle size relationship
(figure 4)
• The settings determine the percentage of
concentrate recovered, i.e. higher sensitivity
results in recovery of material, and thus,
increases the yield
• Material adsorb different amount of radiation
(FC) fast component or rise of inner excitation
state of protons at different rate and emit
radiation at different rates (SC) slow component
or decay of radiation from the proton
• The sensitivity is set in order to deliberate
capture those particles that could be
diamondiferous
Conclusion
The introduction of the Bourevestnik high
throughput X-ray technology to alluvial diamond
processing has provided the means to specifically
“hunt” for diamonds, whilst lowering the footprint
of the concentration processing step. Currently, it
has proven to be effective, considering efficiency
and ease of application to a production
environment.
Figure 1: MOR feed type containing high calcrete content
Figure 4: 5x25mm size bottom deck
panel the de-sanding screen at MOR SHC plant
Uncovering the facets of our potential…
420 x 594 PHOSIWA N.A.indd 1
REREFENCE
Wills B.A and Napier-Munn T.J,2006,mineral processing technology; an introduction to the practical aspects
of ore treatment and mineral recovery.
http://www.bouvestnik.co./eng/catalogue/item/.14htmAccesed 23/07/2014.
Alluvial diamond mining fact sheet article, world diamond council. Accessed 23 July 2014.
ACKNOWLEDGEMENT
A special thanks to Dr K Petersen, A Malivha, A Mabilu, K Selolo, J Kroukamp and M Nenzhelele.
2014/09/02 4:12 AM