Sustainable and efficient – Filtration of tailings with BoVac Disc filters
Tailings are the unavoidable by-product of extracting minerals and metals, and they are becoming an increasingly challenging issue for the mining industry. This is due to the decreasing concentrations of valuable materials in mining products, which results in more waste being produced. Safe and sustainable storage of this waste is a major concern. The question, then, is what to do with tailings.
Traditionally, tailings slurries are stored in large-scale tailings storage facilities. However, this method has several disadvantages. Firstly, the contained process water, which is becoming increasingly important for mining companies, evaporates. Secondly, tailings ponds can pose a considerable safety risk: a dam failure can lead to catastrophic consequences (including loss of life or destruction of ecosystems). In combination with increasing pressure from investors, mining companies are now more than ever required to find innovative solutions for dealing with tailings. This is precisely where filtration comes into play.
On this page, we aim to answer many of the current questions about tailings and present the advantages of tailings filtration. Our expert team is always happy to answer any questions you may have about tailings filtration.
Dry stacking & Paste backfill
One approach that uses filtration processes is dry stacking. In this process, the tailings are dehumidified mechanically to such an extent that the remaining residue can be transported without risking reliqueficaction, and can be stacked and driven over with heavy machinery (e.g. bulldozers).
Some mining companies also use tailings to backfill underground tunnels in a process known as paste backfill. In this process, after filtration of the tailings, cement is added before the mixture is then pumped back into the pit. This procedure provides sufficient stability for the tunnel throughout its service life, while also reducing the amount of residue that needs to be stored above ground.
In addition to treating new tailings, many mine operators are also interested in reprocessing historical tailings ponds. In the past, it was often impractical to fully digest the minerals and ores, partly due to the significantly higher concentration of valuable materials in mining products and partly due to the lower efficiency of the processing equipment. Consequently, many of these ponds still contain tailings with a significant amount of valuable material. As well as the economic benefits, this approach has another positive side effect: properly removing contaminated sites significantly reduces the risk of dam failures. This is an important step towards greater sustainability and responsibility towards the environment and society.
BOKELA – The filtration people
Thanks to its many years of experience in a wide variety of dewatering tasks and an extensive portfolio of filter units, BOKELA is able to offer tailored solutions for almost all tailings sludge tasks. These solutions are often the best answer to the respective filtration challenge, both technically and commercially.
Filtration of concentrates and tailings
With BoVac disc filters from BOKELA, you can maximise the yield of your mine. Our vacuum disc filters are revolutionising tailings filtration. They have a significantly higher immersion depth in the suspension, using far more of the filter surface for production (cake formation) than conventional disc filters. They are also characterised by high filtration speed and complete cake discharge. The result is high specific filtration performance, a reduced number of filters and the recovery of large quantities of process water, all with lower energy consumption and the elimination of the risk of dam breakage. Our innovative filtration technology enables you to achieve your tailings targets with significantly lower operating and investment costs.
Tailings FAQ (Frequently Asked Questions)
What are tailings, and what types are there?
Tailing is the part of the ore or the mineral (ROM – run of mine) that remains after extracting the valuable part through an ore or mineral processing plant. Depending on the geological ore formation, the level of the ore seam below surface and the degree of liberation (grinding and milling) required to produce a high grade of concentrate, there are tailings like waste rock, overburden, coarse and fine tailings from processing plant. And they may contain more or less amounts of clays which are a challenge for dewatering. Furthermore, if in contact with water they dissolve ions resulting in extreme pH values and/or liberate hazardous heavy metals.
What is done with tailings? Today and in the future.
At the moment tailings are mainly deposited in tailings dams. These dams are covering huge areas of land, often require regular increase of dam height and bear a constant risk of dam failure for the communities living downstream of these dams. And dam breaks happen almost every year with often many fatalities. In several underground mines the tailings are used for mine backfill. In this case the tailings are mixed with cement, pumped into the stopes of the underground mine and after solidification the valuable ore next to these backfilled stopes can be mined. Some old tailings dams are reclaimed and reprocessed, as processing technology and efficiency has improved over time.
How are tailings related to filtration?
Most tailings are the rejects of a wet processing of the valuable ore and therefore appear as a slurry containing up to 80 % water. The more water, the bigger the tailings dam. Thickening the tailings prior to deposition has become common practice in the past, but still bears the risk of dam breakage. Therefore, some countries have already legislative requirements for tailings filtration. This results in basically zero risk, but also improves the water balance, the land consumption and make rehabilitation after mine closure much less costly. And in mine backfill the filtration of the thickened tailings is a must anyway, to ensure proper water content for mixing with cement and pumping to the underground.
Tailings filtration using the innovative BoVac Disc XL352 filter.
BOKELA has developed the "high performance disc filter" technology which is based on:
- Maximizing cake formation
- Minimizing internal filter system pressure losses
This is achieved by:
- 50% slurry level in the filter trough/bath
- Trapezoidal filtrate pipes
- Pre-separation control head
- > 50% perforation of filter segments
- Online cloth wash
The new BoVac Disc XL352 is the pinnacle of continuous vacuum disc filter development and combines all these requirements. With up to 1.000 t/h and convincing arguments in favour of CAPEX & OPEX it is the perfect match for tailings filtration.
Which technology is suitable for tailings filtration: disc filters, belt filters or filter presses?
In mine backfill applications the competitors are other vacuum filters because the moisture target is relaxed (typically >20 %w/w) as the filtered tailings are mixed with cement and pumped back to underground. However, standard vacuum disc filters have less than half of the capacity per m² of filtration area and horizontal belt filters require 5 time the footprint in the tailings filtration building.
In filtered tailings storage applications, the main competitors are filter presses. They have up to 8 times filtration area, run at pressures of up to 25 bar with and without membrane and allow for air blow through the cake. And therefore, filter presses achieve moistures of <15 %w/w in most cases which is possible with vacuum filters only for coarse tailings (d50 >50–75 micron). But they run discontinuously, have a high consumption of filter fabrics, require much bigger and stronger buildings and infrastructure and a higher qualification of operational and maintenance staff.
Advantages of high-performance vacuum disc filters for operators.
If the target moisture can be reach with the BOKELA high performance vacuum disc filters, the customer benefits from:
- Simplicity of the filter design and operation (no high quality staff required)
- High availability of >97%
- Less number of filters in operation
- Very little maintenance required
- Water consumption only 1 m³/h per filter
- Less CAPEX
What about CAPEX & OPEX? What are the advantages of high-performance vacuum disc filters?
The benefits listed above finally accumulate in the calculation of operational expenditures (OPEX) and capital expenditures (CAPEX). The OPEX of a filtration project are the sum of the following main factors:
- Energy consumption
- Filter aid consumption
- Fresh water consumption
- Consumables (mainly filter cloths)
- Operational and maintenance staff
- Spare parts
In most cases the OPEX of the BOKELA high performance vacuum disc filters is only 35–45% of the filter press OPEX mainly driven by the consumables.
The difference in CAPEX is only 20–30% of the filter press CAPEX. A detailed comparison is given in the paper "How tailings characteristics affect CAPEX and OPEX in filtration – two case studies" presented at the Paste Conference in Melbourne in April 2024 by Jurgen Hahn. You can download this whitepaper below on this website.
Sounds good! What happens next? (Data analysis & sample investigation)
BOKELA has a huge filtration data base from both reference operations as well as lab testing. We are frequently using this data base to do preliminary sizing and pricing for filtration applications in a conceptual of pre-feasibility stage. All we need is the following data:
- Elevation of plant
- Type of ore mined (copper, gold, ...)
- Total solids throughput (on dry basis)
- Feed solids content
- Medium particle size in feed
- Any other data to the particle size (if available)
- Feed temperature
- Feed pH (if available)
- Clay content (if available)
- Moisture target
And you will get your sizing and budget pricing within 48 hours.
BOKELA lab is located at the headquarters in Karlsruhe, Germany. It is specialized in testing the filtration properties of slurries for mining and chemical applications. Typically, testing starts with a basic program targeting on identifying the most suitable filtration technology or filter type to reach the target figures (moisture, washing target, ...). If the most suitable technology or filter type is determined, then the filter sizing tests start which finishes with the formulation of the process guaranty. A good overview of the stepwise approach in the laboratory is given in the paper "From a 10 kg Tailings Sample to Over 10 Years of Disc Filter Operation in a Backfill Plant" presented at the MineFill Conference in Vancouver in May 2024 by Jurgen Hahn. If you are interested in this paper, just send us an email at sales@bokela.com
Are you facing any particular challenges with tailings? Put us to the test!
Store residues safely and protect water
Water plays a crucial role in processing metal ores and minerals. After the valuable components have been extracted, a tailings sludge containing up to 80 %w/w water is usually left behind and stored in huge ponds. This method is associated with considerable risks (e.g. dam breakage) and high costs (e.g. handling enormous volumes and consuming large amounts of land). A far more economical and sustainable approach is to thicken and dewater the tailings sludge. A key technology for this is filtration, provided it can be implemented quickly, reliably and easily. The BoVac Disc XL352 high-performance filter was developed to meet these requirements precisely.
Holistic: Keeping an eye on the costs
BOKELA offers reliable, cost-effective solutions for tailings filtration. BoVac Disc filters are renowned for their high performance, reliability and cost-effectiveness across a range of industries and applications. Operating engineers around the world appreciate their simple operation and ease of maintenance. When reporting on their experiences with BoVac Disc filters, they usually just say: "Switch on and forget." In his detailed investigation, Jurgen Hahn – experienced senior product manager at BOKELA and an expert in tailings treatment – presents the investment and operating costs in two case studies.
BoVac Disc XL352 – The world's largest vacuum disc filter
The BoVac Disc XL352 is the world's largest vacuum disc filter. With a filtration area of 352 m², it boasts an impressive capacity for filtering up to 1,000 tons of tailings per hour, while maintaining particularly low residual moisture levels. It only requires around 10% more floor space than our previous largest model, the L176, meaning that throughput can be doubled with just one replacement and only minor adjustments to the building and transition to the conveyor belt. The unique BoVac Disc XL352 thus sets new standards in tailings filtration.
Disc filters vs filter presses
Case 1: Tailings treatment for backfill applications
Conventional standard vacuum filters (belt, disc and drum filters) used for backfilling mines with residual moisture content of over 20 %w/w have less than half of the filtration area in comparison to the advanced BoVac Disc filters. Furthermore, horizontal belt filters require around five times as much installation space for the same output.
The advantages of modern BOKELA high-performance vacuum disc filters are clear: BoVac Disc filters have minimal pressure loss due to their special design. The effective pressure difference at the filter cloth is up to 100% higher than with conventional disc filters. All components (e.g. filter segments, shaft, filtrate tubes, control head, drive unit and filter trough) have been systematically developed and successively optimised by our experts, who have decades of experience. The results speak for themselves: high specific throughputs, intensive cake dehumidification, long-term operational safety and reliability.
Case 2: Tailings treatment for dry stacking applications
Chamber filter presses are generally used for tailings treatment if the aim is to store the residues. They have a filter surface area eight times larger than that of the BoVac Disc XL352, can operate at pressures of up to 25 bar, and can achieve residual moisture levels of less than 15 %w/w. However, they are operating discontinuously, which results in high wear of the filter cloth, and they also need substantial buildings and infrastructure. Highly qualified maintenance and operating personnel are also required.
A comparison of investment (CAPEX) and operating (OPEX) costs quickly reveals the advantage of BoVac Disc technology: OPEX amounts to only 35-45% of the operating costs of filter presses, primarily due to the significantly lower cost of filter cloths. CAPEX in this comparison is only 20-30%. Additionally, maintenance costs for the BOKELA disc filter are significantly lower and no specially trained personnel are required.
The table below provides a detailed comparison of CAPEX and OPEX for BoVac Disc filters and filter presses. Alternatively, you can download our free white paper on this topic.
»The new filters have shown us that efficiency and sustainability can go hand in hand. Our high-performance vacuum disc filters are the answer to the challenges of tailings management for our customers. They are simple to use and demonstrate how effortless sustainable management can be«
JURGEN HAHN, SENIOR MANAGER PRODUCT AND BUSINESS DEVELOPMENT
Capex vs Opex
The advantages of BoVac Disc vacuum disc filters become clear very quickly when the investment costs (CAPEX) are compared with the operating costs (OPEX). Take a look at the detailed comparison in the table below to see for yourself how cost-efficient BoVac Disc filters are.
BOKELA high-performance vacuum disc filters usually have operating costs that are only 35-45% of those of filter presses. This is mainly because filter cloth consumption is considerably higher with filter presses.
With investment costs of only 20-30% compared to filter presses, entry into tailings filtration is considerably easier.
The following factors must be taken into account when calculating operating costs:
• Energy consumption
• Consumption of filtration aids
• Water consumption
• Consumables (filter cloths)
• Deployment of operating and maintenance personnel
• Consumption of spare parts
Good to know: Maintenance and operating costs are significantly lower with the BOKELA high-performance vacuum disc filter. Furthermore, no specially trained personnel are required.
|
Parameter |
Category |
Unit |
BoVac Disc Filter | Filter Press |
|
Total solids throughout |
General |
[t/d] |
150,000 |
150,000 |
|
Moisture target / Moisture reached |
General |
[%-w/w] |
15.0 / 14.5 |
15.0 / 12.0 |
|
Total filtration area per filter |
General |
[m2] |
352 |
2,800 |
|
Solids throughout per filter |
General |
[t/d] |
6,140 |
12,230 |
|
Filters operating / installed |
General |
[–] |
25 / 28 |
13 / 15 |
| Energy requirement per filter |
Energy |
[kW] |
572 |
900 |
| Total energy requirement per year |
Energy |
[MW/y] |
125,160 |
102,500 |
| Total energy cost per year |
Energy |
[€/y] |
10,012,700 |
8,199,360 |
| Flocculant dosage |
Filter Aid |
[g/t] |
0 |
0 |
| Total filter aid cost per year |
Filter Aid |
[€/y] |
0 |
0 |
| Number of cloth changes per year |
Consumables |
[–] |
6 |
8 |
| Quantity of cloths per filter |
Consumables |
[–] |
180 |
560 |
| Cost per filter cloth |
Consumables |
[€] |
50 |
300 |
| Cost per filter per year |
Consumables |
[€/y] |
54,000 |
1,344,000 |
| Total cost of cloths per year |
Consumables |
[€/y] |
1,350,000 |
17,472,000 |
| Cost per filter with auxiliaries |
Spare Parts |
[€] |
40,000 |
260,000 |
| Total cost of spares per year |
Spare Parts |
[€/y] |
1,000,000 |
3,380,000 |
| Total OPEX |
– |
[€/y] |
12,362,700 |
29,051,360 |
CONCLUSION: Using BoVac Disc filters for dewatering tailings results in total OPEX costs that are around 60% lower.
You can find the full data set here:
BoVac Disc filters vs the competition
The advantages of BoVac Disc filters from BOKELA over other technologies, such as filter presses, are clear:
✓ Continuous operation
Unlike filter presses, BoVac Disc filters allow for continuous dewatering.
✓ Smaller footprint
The filter area is eight times smaller with BoVac Disc vacuum disc filters compared to competitor filter presses with the same daily throughput.
✓ More productive
BoVac Disc filters allow you to achieve higher throughput in less time.
✓ Lower energy costs
50% lower energy requirement with almost twice as many filters in use.
✓ Lower consumption costs
Significantly less filter fleece/filter media is required per filter.
Would you like to know more?
Our filtration experts are here to help! Send us a message detailing your challenge, and we will get back to you with a solution!