IM 2017 June 17 | Page 40

High performing disc filters

Andre Egger and Jürgen Hahn of BOKELA outline how their throughput, dewatering performance, and reliability have made high performance disc filters a success in this market
View of four filter discs at
Chelopech mine

For recovery of water from ore processing – typically filter presses, belt filters and rotary vacuum disc filters are used. Among these technologies, in approximately 80 % of all applications, the vacuum disc filter type is assumed to be the most economical solution with reference to both CAPEX and OPEX. In recent years, the BOKELA Boozer disc filter has established itself in applications of tailings dewatering. The reasons for the successful operation of this high performance disc filter in tailings dewatering are the high throughput and dewatering performance, the excellent operational reliability even in the case of varying feed conditions, the simple and robust design, the ease of maintenance and last but not least the small footprint.

Dewatering of gold / copper tailings
The first Boozer disc filter for tailings dewatering started operation in 2010 at the Chelopech mine in Bulgaria where the tailings are used for mine backfill. For this application, two Boozer L4 disc filters with 176 m ² filter area and 5.6 m disc diameter are operated. Their implementation was part of the mine upgrading and modernisation project when Chelopech switched the mining method away from environmentally challenging caving to a drill and fill method( D. Liston) to increase both rate, reliability and sustainability of production. The achieved filter performance is 110 t / h for solids throughput rates and residual cake moisture ranges to 19-22 wt %. After nearly six years of operation, the filters are in excellent condition thanks to the plant’ s preventive maintenance concept. A more detailed description of this application is given by Hatzenbühler.
Dewatering of zinc tailings
For dewatering of zinc tailings from a copper and zinc mine in Australia( Queensland), two Boozer ME8 disc filters were installed which started operation in 2014. Each filter has a filter area of 141 m ² and consists of eight filter discs with a diameter of 4.1 m. It was essential that
small footprint for reducing building cost and
logistical efforts to get all the parts to the remote
area of the plant site. Accordingly, the option of
four large vacuum belt filters was not a viable
solution and the option of pressure filtration
came to the fore. A second mandatory condition
was that the filtration equipment must have low
the two filters should fit into the existing filter floor space with a minimum of modification work. The tailings slurry mainly consists of silicates. Product characteristics of the feed slurry and target values are as follows: n feed solids: 60-65 wt % solids n particle size distribution i. e. mean particle diameter d50: 50 μm n target solids throughput on dry solids basis:
350 t / h( 175 t / h per filter) n target cake moisture content: 20-22 wt %
operation cost as electricity supply is limited and the overall OPEX should be as low as possible.
This disqualified the pressure filtration option. As a final result the high performance Boozer disc filter fulfilled both requirements in the best way and was chosen to be the most suitable dewatering technology for this application.
Product characteristics of the feed slurry( pHvalue 11) are as follows: feed solids is 60 wt % solids, particle size distribution d20 / d50 / d80 ranges to 6.7 μm / 22 μm / 52 μm. The filter layout
has been made to ensure
Expected and achieved operational values of solids
following performance:
throughput and cake moisture
n solids throughput on dry
Dewatering of
Predicted value
Operational value
solids basis: 88 t / h, or 44 t / h
zinc tailings
per filter
per filter
per filter
Solids throughput
n cake moisture content: < 20
normal [ t / h ]
175
> 175
wt %
peek( max.) [ t / h ]
200
210
n flocculent dosage: 10-50
Filter speed [ rpm ]
1.5
< 1
g / t dry solids
Cake moisture [ wt %]
20- 22
17- 20
The two disc filters are
Flocculent dosage [ g / t DS ]
depending on
0- 50
operated in a fully automatic
feed charge
way ie filter start up, filter
operation and filter shut down
The two disc filters are operated fully automatic ie filter start up, operation and shut down are carried out automatically. The operation
are carried out automatically. Operation proved that the filter ran within the required and predicted performance range.
control system follows a specific philosophy for
improved filter operation without continuous
slurry overflow. Accordingly, the filter performance
is adapted automatically to changing slurry and
process conditions to avoid emergencies.
Depending on the slurry feed charge it may occur
that the filter cake is too dry for downstream processing in the mixer. This can be prevented by reducing ie throttling the pressure difference in the dewatering vacuum line which effects higher moisture content values of the filter cake.
Two Boozer disc filter ME8( 141 m 2 filter area each) for zinc tailings dewatering in the filter building( left); discharged filter cake( right)
Conclusion
Vacuum disc filters are an economical solution
for tailings dewatering with reference to both
CAPEX and OPEX where the following conditions
and targets apply:
n low clay content in the solids
n mine backfill is processed
n the tonnage is > 50 t / h
n cake moisture of > 18 wt % is accepted
n energy efficiency is important
n if there is a space constraint
n in developing countries where little know
how for operation has to be assumed
n amount of flocculant shall be limited
n operation cost shall be minimised. IM
Dewatering of tailings from a gold / silver mine at 4,800 m above sea level
For dewatering of tailings from a gold / silver mine in Peru, two Boozer L4 disc filters were installed. Each filter has a filter area of 176 m ² and four filter discs of 5.6 m disc diameter. The dewatered tailings are mixed with cement and backfilled into the exploited mine areas. A worldwide operating engineering company was looking for filtration equipment to dewater these tailings coming from a gold / silver mine which is located 4,800 m above sea level( MSL). This was a big challenge as the client was looking for a cost efficient filtration solution. It was required that the equipment had to have a
A full reference list is available from Franz Meck at fmeck @ bokela. com
P10 International Mining | JUNE 2017 Supplement