Tailings intake – safely solving a sticky problem

Canadian miner Xstrata-Nickel has installed two heavy-duty „sub-surface” B&W Samson^TM Feeders to intake mine tailings at its Nickel Rim South mine site in the Sudbury Basin located in Northern Ontario. This is the first Canadian installation for the UK based B&W Mechanical Handling Ltd. The sub-surface concept has been extensively developed for under rail applications and designated type SUR. As a track-hopper-feeder the benefits that make the Samson concept attractive are equally valid. But it is in particular the shallow pit depth that is highly desirable in any areas where the ground conditions are challenging.

Tailings, or leach residues, are the materials left over after the process of separating the valuable fraction from the worthless fraction of an ore. The material may be recovered from tailings dams and has a typical density range of 1.4 to 1.8 t/m³ with a moisture content ranging from 2 to 18 % depending upon location and weather. Mostly the moisture content is at the high end of the spectrum and as a result the material is extremely cohesive and does not flow well and is very prone to bridging and blockage during handling, particularly in transfer chutes and tapered hoppers.

Classified tailings are brought from the Strathcona Mill, 85 km distant or legacy tailings from the nearby Nickel Rim North Site in various tipping and self-discharging 40 t capacity trucks to the new processing plant which is part of Xstrata’s ongoing sustainability initiatives. The tailings are screened and processed for backfill into the mine shafts. One of the specialised road trucks is fitted with a movable body for effective weight distribution over the eight carrying axles and a system to move the body to the end of the trailer for discharge. These are not tipping vehicles but feature a moving bulkhead within the tubular body which is forced back towards the end of the trailer to discharge the load. These vehicles are very difficult to manoeuvre in a confined space. For this reason Xstrata preferred the “drive-over-tip” intake arrangement. In this design the truck moves forward over the feeder such that only when the truck is in the discharge position is the feeder intake revealed (Fig. 1 and Fig. 2).

For handling wet and sticky materials the Samson^TM is the ideal solution with a belt width greater than the stored material depth and with near vertical hopper sides there is no risk of bridging or blockage. This design principle combined with the deflected chassis arrangement permits a shallow excavation depth, reducing civil works costs and complications, and a simplified transfer to the following belt conveyors. To control the volumetric discharge rate from the Samson^TM a levelling blade at the discharge controls, the material bed depth and a variable speed (VFD) drive system permits adjustment of the final output rate by varying the belt speed and therefore the output, in line with the process demands. Considering the material characteristics a rotating Picker shaft is provided at the discharge to break up agglomerated slabs and ensure a continuous output.

For the Xstrata project two sub-floor feeders were supplied installed in parallel and each arranged to discharge to a separate belt conveyor. The Samson^TM 1600 Series have an entry capacity of 30 m³ to receive the entire truck contents. The length of the feeders is staggered at 7 m and 9 m allowing the units to discharge onto two parallel conveyors running at 90° and thus allowing near vertical transfer chutes to minimise risk of blockage between the Samson^TM and the conveyor feed boot. Each Samson^TM is designed for a discharge rate of 200 m³/h and at this rate either unit can satisfy the plant demand offering 100 % redundancy in operation.

The plant is designed to run continuously day and night and the feeders are required to receive all types of tailings under all ope­rating conditions with an ambient temperature of +30 °C in the summer months and down to -30 °C in the winter. As a result of the wide belt technology the free fall distance from the truck body to the belt is minimised. With that the velocity of the displaced air is significantly reduced. Therefore for dry materials dust generation is mitigated also and very often no dust plant is required. This new project for Xstrata-Nickel demonstrates the clear benefits of the Samson^TM concept handling this most difficult of bulk materials in a pro­fessional environment where reliability and availability are paramount.


AUMUND Group, Rheinberg (D), www.aumund.com