Laboratory Disc-Stack Centrifuge

A disc-stack centrifuge is the only practical way to clarify a process liquor down to a few mg/L of suspended solids at lab scale and still generate numbers that scale. The bowl spins at 7,700 to 13,500 rpm, which puts 10,000 to 20,000 times gravity on the feed, and the disc stack turns that bowl into the equivalent of several thousand square metres of settling area. That equivalence is the point: the machine is not a faster version of a settling tank, it is a settling tank folded into a box.

Where the capacity comes from

Separation in a disc stack is described by the equivalent settling area, usually written Σ. For a stack of conical discs the value is roughly proportional to the number of discs, the outer radius cubed and the disc angle, and it is quoted in square metres — a 260 mm lab bowl lands in the thousands, a production bowl with a 510 mm bowl and a taller stack lands near 80,000 m². Throughput then follows the classical relation between flow, Σ and the settling velocity of the particle you are trying to capture.

That relation explains the trade every operator makes. Run at the top of the capacity range and you capture only the coarser solids; run at half the rated flow and the same bowl cuts a much finer particle. Published figures for this class of machine quote 50–200 L/h with water and a clarified liquid at around 2 mg/kg with a 0.2 µm cut on benchmark duty — those two numbers belong to different tests, and no single pass delivers both at once.

What it will and will not take

Disc stacks are clarifiers, not dewatering machines. Feed solids above roughly 3% by volume turn the bowl into a sludge conveyor and the discharge interval into the bottleneck; above that, a decanter is the correct machine. The solids holding volume on a lab bowl is 0.6 to 1.5 L, so the operating question is not whether it fills but how often it has to be emptied, and whether that is by manual bowl opening or by a sliding-piston partial discharge on the larger frames.

Where the machine earns its place in a hydrometallurgical flowsheet is the dirty duties: crud and entrained organic from a solvent-extraction stage, fine gypsum that survived the thickener, graphite or carbon fines from a leach, and the colloidal clay that blinds a filter press. In each case the disc stack produces a clarified liquor clean enough for the next unit operation — ion exchange resin, electrowinning cell or membrane — without the filter aid that a plate-and-frame would need.

What a lab campaign should measure

• Solids capture against flow: run at least four flow rates and assay both streams. The curve, not the single point, is what the scale-up uses.
• The cut size at each flow, from a particle size distribution of the overflow solids — this is what tells you whether the production machine needs a bigger Σ or a different machine.
• Discharge interval at the intended feed solids, measured, not estimated from the holding volume.
• Whether the solids are abrasive or sticky. Gypsum and jarosite behave very differently on the bowl wall, and the difference decides the bowl material and the maintenance interval.

What to send for a quotation

Feed solids concentration and particle size distribution, the target clarity in mg/L, the liquor chemistry (pH, chloride, organic content), the temperature, and whether the machine will run batch or continuous. If the duty is crud treatment, say so — the wetted-material and seal specification changes.