BENEFICIATION
PFG has its own lamination plant on site.
PFG also produces mirrors and sealants:
Intruderprufe is a PFG product.
John Lotter, PFG process technology
manager at the Springs facility, anticipates
that the biggest demand in the future is
likely to be that for double-glazed glass,
which is widely used in energy-efficient
‘green’ buildings.
A matrix of raw materials
Recycled glass called cullet is used as one of the raw materials
Lotter describes the process starting with
the raw material feed, “Silica sand, soda
ash, dolomite, limestone, sodium sulphate
and cullet are mixed together to form
the raw material batch. Sand is the main
ingredient accounting for 60% of the
batch.” The plant receives high grade silica
sand (99% SiO 2 ) and this high quality
means the facility’s relationship with a
quarry is one of its trade secrets.
“Silica sand, soda ash,
dolomite, limestone,
sodium sulphate and
cullet are mixed together
to form the raw material
batch. Sand is the main
ingredient accounting for
60% of the batch.”
The raw material mixture that is fed to the furnace being melted as it moves along the furnace.
The furnace is fuelled by gas.
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The other quarry materials play a key
function. “Silica is the main network
forming oxide and gives glass the ability
to allow light to be transmitted through
the glass. It has a melting temperature of
1 720°C and the furnace refractory melts
before the silica, and the addition of soda
ash reduces its melting point. However,
soda ash isn’t durable as it dissolves in
water, so it needs another element and so
we add limestone and dolomite, which adds
calcium and magnesium. The composite
reduces the silica’s melting temperature
(slightly) while improving durability.
“Rouge is added to colour the glass. The
level of iron affects the glasses’ absorption of
light depending on how much iron is added
– the clearer the glass the less rouge is used
(and despite the name it adds a green tint
QUARRY SA | MARCH/APRIL 2019_29