Water recovery and paste technology
Jerold Johnson of WesTech
Engineering, Inc, Salt Lake
City, outlines the water
benefits from using paste
type thickeners
he increase in water recovery with Paste
and Thickened Tailings (P&TT) technology
has provided many benefits in addition to
tailings management. Of particular note is the
benefit of having little or no free water on the
P&TT impoundment. Several studies of slurry
pond failures such as Mt Polley, Canada, and
Samarco, Brazil, attribute much of the damage
downstream to the standing water volumes in
the pond.
Slurry ponds are the major point of the water
loss for a plant. Often there is water recovered
from the pond in the range of 20 to 25% of the
water sent to conventional ponds. Water losses
are due to evaporation, seepage, and water
trapped with the solids, particularly the loosely
compacted fines that are greatly reduced with
P&TT technology.
The P&TT thickener technology generally
traditional high rate thickener. This improved
produces higher underflow wt% by 10-20
efficiency results in fewer CCD stages and/or
percentage points compared to high rate
less wash water needed to meet target
thickeners processing the same stream. This
discharge. The final stage of the CCD is the most
water balance significance of P&TT has
been documented in the Khumani iron
P&TT pilot thickener and
mine in South Africa. This greenfield
deposition study
plant was permitted to be installed due
to the water benefits of P&TT. The
permitting of this site hinged on the
mine demonstrating that the water
consumption could be less than 0.09
m 3 /t of product. The P&TT system uses a
T
two-stage thickening with a high rate
thickener located at the plant (90 m
unit), the underflow from which is
pumped 5 km to the paste-type
thickener (18 m unit) at the disposal site
5 km away. The paste overflow
(approximately 70% of the stage one
underflow water) is then returned to the
plant and the P&TT underflow is surface
stacked in a shallow valley site. The
water recovery at this site is as high as
98%.
P&TT thickeners also have large
benefits for Counter Current Decantation,
CCD circuits. For CCD circuits the greater
underflow density means that less liquor
is following the solid down the circuit.
The P&TT thickener therefore, improves
the stage efficiency compared to a
Baotou Steel P&TT plant and insulated tailings
pipe
critical one and increasing the discharge density
by using a P&TT type thickener
provides dramatic improvements.
The common practice of dewatering
a stream in thickeners prior to feeding
a filter can also benefit by the higher
underflow density of the P&TT
thickeners. Reducing the hydraulic
load on the filter shortens the form
time of the cycle, and because the
P&TT suspension is relatively non-
segregating, a formation of a slimes
layer on the cake is reduced.
Case Study – Baotou Steel,
Inner Mongolia
A case study showing the benefits of
water recovery with P&TT technology
is the Baotou Steel plant in Inner
Mongolia. The climate at Baotou is
arid, and the water for the site and the
surrounding community is pumped in
a 130 km pipeline from the Yellow
River. This pipeline transports 2,500
m 3 /h of wa