Tailings disposal: choosing the right technology

Centrifugal pumping

Generally, tailings that are disposed of by using centrifugal pumps involve installing a series of pumps to achieve the required pressure.

Benefits

• This technology is conventional, proven and the most commonly used.
• Centrifugal pumps provide high volume capacity.
• Mobile pumping stations can be added.

Drawbacks

• Centrifugal pumps have a limited pressure capacity.
• It may be necessary to install several pumps in series depending on the distance and elevation of the tailings storage facility, implying a more complex operation and reducing overall system reliability.
• Remote booster stations may be needed. Each pumping station requires a power supply and gland seal water, in addition to periodic maintenance.
• Dump ponds are required at low points to drain piping during shutdowns.
• Backup pumps installed in parallel are generally required, doubling the quantity of pumps to install. It might also be necessary to install a redundant pipeline up to the tailings facility.
• Pumps generally require a pressurized clean gland seal water supply.

Positive displacement pumping

Generally, tailings that are disposed of by using positive displacement pumps involve a single pumping station located in or near the plant.

Benefits

• Positive displacement pumps have a large pressure capacity; a booster station is usually not required.
• This technology requires a limited number of pumps, which increases system reliability and reduces maintenance.
• Positive displacement pumps can reach 98% availability. As such, only one or two redundant pumps are required, regardless of the number of pumps required for operation (parallel installation).
• Operating and maintenance costs are low.
• These pumps do not require gland seal water.
• Their design poses a reduced risk of sedimentation in the piping.

Drawbacks

• Positive displacement pump capacity is limited in terms of volume flow; it might be necessary to install pumps in parallel.
• Positive displacement pumps are big and require a large pumping building.
• These pumps must be pressurized at their suction, usually using centrifugal pumps.
• Dump ponds are required at low points to drain piping during shutdowns.
• They require a high-pressure piping system at the pumps discharge.
• Positive displacement pumps might require cooling water.
• CAPEX costs are significant.

Thickening and pumping paste tailings

This method involves densifying tailings in a paste thickener and then hauling it with positive displacement pumps to the tailings storage facility. The tailings can be deposited from a single discharge point or from multiple spigots in order to raise the deposition slope. Intermediate cells or dikes might need to be built.

Benefits

• The risk of dike failure is reduced compared to a tailings facility that is filled using conventional hydraulic depositing due to the limited volume of water contained in the tailings.
• A bigger volume of tailings can be stored in the tailings storage facility due to higher deposition slopes than those obtained by conventional pumping.

Drawbacks

• A high and constant solids concentration by weight is required at the thickener underflow.
• This method requires complex modelling to predict the deposition slope.
• It might be difficult to control the process upstream to obtain a high and constant deposition slope.
• Depositing in cells or with multiple spigots is a complex operation.

Filtering, conveying and dry stacking

This technology involves building a filtration plant to dry the tailings to a moisture content of 10% to 15% (confirmation with laboratory analysis), then conveying the “cake” of dried tailings and depositing it using stackers.

Benefits

• This technology eliminates the risk of dam failure associated with depositing conventional hydraulic tailings.
• It allows for faster recovery of process water through the filtration process.
• It may allows for progressive reclamation of the tailings storage facility.

Drawbacks

• Selecting filtration technology is very critical to obtain a cake of constant solids density despite process variations upstream.
• Conveying and stacking are vulnerable to precipitation and freezing.
• There is a risk of tailings liquefaction during conveyor hauling.
• It might necessitate installing a conveyor that is several kilometres long up to the tailings storage facility.
• A flat surface is preferred for dry stacking deposition.
• Both CAPEX and OPEX are high (maintenance of several indoor and outdoor equipment).
• This technology generates dust when depositing.

Criteria to consider when selecting tailings disposal technology

• Constructibility
• Integration with existing infrastructure
• Technological change management
• Water and dust management
• Operational activities
• Maintenance
• Equipment reliability
• Criticality of laboratory analyses and pilot testing
• Technical risks
• Environmental risks and impacts
• Permits

In conclusion

Equipment selection and sizing are essential to ensure proper operation of tailings disposal systems. Rigorous design helps achieve operational objectives while preventing costly production downtime.

Our experts can help you select the best technology tailored to your site and operations.