WATER MANAGEMENT & TREATMENT
former gold mines, according to
ANDRITZ.
The water line has reached a critically
high level, as determined by the
specialists from the ANDRITZ
subsidiary, ANDRITZ Ritz, in
Schwaebisch Gmuend, Germany,
which was given the first order to
drain the mine water back in 2010.
The execution of the project was
delayed by four years, however, and it was only
in Spring 2014 that two powerful ANDRITZ
submersible motor pumps were installed in the
middle of Johannesburg city centre, in the so-
called ‘Central Basin’. Each pump is capable of
bringing 1,500 m³/h (1.5 million litres per hour) of
water to the surface, according to ANDRITZ; with
60 million litres of water per day pumped, it is a
never-ending task, ANDRITZ said.
“In Johannesburg, however, acid mine water is
an ongoing problem. Rainwater seeps into the
tunnels and reacts chemically with residual
minerals like pyrite, producing corrosive sulphuric
acids. In the worst case scenario, this can result in
a pH value of 2, which is enough to cause lasting
damage to humans and the environment. Because
of this corrosive acid, the Johannesburg pumps
had to be completely redesigned. The design is
based on ANDRITZ’s proven HDM (Heavy Duty
Mining) technology, which uses the concept of a
double-suction pump. The thrusts produced are
offset by the counter-rotating arrangement of the
impellers and the pumps run without axial thrust,
giving a properly maintained pump a service life of
10 to 15 years.”
The pumps for the Johannesburg project are a
tailor-made, customised design built for this
special individual application, according to
ANDRITZ. Part of the new system is an
encapsulation of the submersible motors (see top
photo), which enables the creation of an internal
pressure higher than the external pressure. This
prevents the intrusion of the corrosive water and
the components inside the motor being attacked
and possibly destroyed. “At the same time, the
water being drained is used to cool the motor by
means of a heat exchanger,” ANDRITZ said.
ANDRITZ engineers spent weeks developing the
sophisticated technology needed to encapsulate
the motor so it could withstand the higher internal
pressure. The first two pumps have been running
since June 2014. These 21 t pumps, each 15 m long
with a 1 m diameter, were installed side by side in
March, 5 m apart, but could only be started after
completion of the water treatment plant.
Freely suspended on 430 m long duplex steel
pipes, they transport the acid mine water to the
surface and onwards into an adjacent treatment
plant. Here, through the addition of lime, the pH
value is raised, the acid is neutralised and the
heavy metals dissolved in the water are absorbed
36 International Mining | MARCH 2020
ANDRITZ last year released details of a
project it has been working on to de-
water old mines in Johannesburg,
South Africa
and
precipitated as
hydroxides,
ANDRITZ said.
The South African authorities are planning a
total of three pumping stations, which will each be
developed at the mines’ disused extraction shafts.
In addition to the Central Basin in Johannesburg’s
city centre, invitations to tender for the ‘Eastern
Basin’ and the ‘Western Basin’ are currently in
progress, according to ANDRITZ.
“The long-term goal is to force the water level
in the flooded mines back from its current level of
approximately 200 m to a depth of 1,000 m, and to
keep it there, to then be able to begin mining gold
and gold ore in the drained upper layers of the
mines once again,” the company said.
A record water tanker for Australia
Perhaps water management at its most basic but
water spraying is still vital for haul road
maintenance and the delivery vehicles are a
speciality market in their own right. Austin
Engineering says it has recently commissioned the
first of its high-performance truck-mounted water
tanks which, the manufacturer claims, is the
biggest water truck in Australia. The result of a
significant re-design process, the new Stairway
Access Tank (SAT) includes several features to
improve efficiency, operator safety and truck
stability, Austin said.
Custom-built to suit most haul trucks, the new
SAT starts at 14,000 litre capacity and includes all
spray equipment along with the
company’s “Water Wise”
system. The first tank off the
production line has a 198,000
litre capacity fitted to a Cat
793C haul truck.
The most obvious external
feature of the Austin water tank
is a stairway from the top of the
tank structure down to a large
(137 cm x 259 cm) access port
for easy entry and exit for
personnel and maintenance
equipment to the tank interior.
The fill port is located behind the water dam to
ensure any overflow flows away from the cab and
deck to the rear of the truck, Austin says.
Inside the tank, the design of the new Austin
SAT directly tackles the safety concerns
surrounding the confined workspace in mine site
water tanks, addressed by a recently-completed
10-year study by the US-based National
Institute for Occupational Safety and Health
(NIOSH).
Part of the NIOSH study looked at operator
access to the tank and ease of movement once
inside, according to Austin. “Traditional access
inside the tank has been through a series of semi-
circular portholes in the baffle system which,
although adequate, slowed access and movement,
especially in the case of an emergency,” the
company said. “The diameter of the portholes –
generally 600 mm wide x 740 mm high – also
restricted operator manoeuvrability and the
physical size of any equipment that could be used
inside the tanks.”
The new SAT from Austin features a series of
oversize rectangular access ports – 630 mm wide x
1,550 mm high – throughout a unique baffle
system to replace the traditional portholes and
significantly improve operator safety and comfort
inside the tank, it said.
The engineered corrugated baffle system,
which interlocks the baffles for increased
structural integrity, controls both transverse and
longitudinal water surging and reduces the
overturning forces by 19% to improve truck
stability, according to Austin. Maximum
overturning force is delayed by about one second
– providing an increase in the time to react to any
side force, it explained.
The design of the corrugated baffle system also
allows for a lighter-weight tank, which translates
to additional payload and lower operating costs.
Additionally, the alignment of the oversize access
ports, combined with the horizontal baffle system,
gives unobstructed movement within the tank,
Austin claims. To improve the worksite
environment inside the tank during maintenance
periods an air exchange system has also been
developed for the tank. IM
Austin Engineering says it has recently
commissioned the first of its high-performance
truck-mounted water tanks which, the
manufacturer claims, is the biggest water truck
in Australia