The hydrocyclone has three pipes: a feed, an overflow, and an underflow pipe. The ore sludge is fed from the feed pipe located on the side at high pressure. The pressure is optimized so that smaller particles circulate around, and heavier ones accumulate against the cyclone wall. Lighter ones spin closer to the center of the device. The strong circulation of the sludge causes a vacuum vortex in the middle of the device. The direction of this vacuum vortex is opposite to the direction of the rotation of the sludge, meaning towards the overflow pipe, so the smaller particles rise up the vortex and exit through the overflow pipe. The larger particles continue to go downwards and exit through the underflow pipe. The grain-size of the classification can be adjusted either by reducing the outlet of the underflow pipe or by changing the pressure at which the sludge is fed to the cyclone.