Frue vanner
A kind of conveyor belt on which ore is concentrated by a current of water; a kind of buddle.
Frue vanner: water-fed belt that sorts ore by density
A Frue vanner is a shallow, sloped conveyor belt running through a stream of water, used to separate dense ore particles from lighter waste material. The belt moves slowly across an incline while water flows perpendicular to its direction of travel, washing lighter gangue (worthless rock) away while heavier ore particles settle and travel with the belt to the collection end. It is a gravity and water-based concentrator, fundamentally simpler than mechanical jigs or spirals, but effective for primary ore sorting in small to medium operations.
The machine takes its name from the Frue company, which refined the design in the late 19th century. It operates on the principle that water current exerts drag proportional to particle size and density, so a carefully controlled flow rate will move fine waste material while allowing coarser, heavier ore to remain on the belt surface. The belt itself is typically rubber or canvas, 1 to 3 meters wide, with a gentle slope of 5 to 15 degrees.
Frue vanners work best on ore that has already been crushed to moderate fineness, typically minus 2 to 10 millimeters. Feed rate and water volume must be balanced precisely: too little water leaves fine ore mixed with waste; too much washes away valuable material. In practice, operators monitor the density cut by observing the color and composition of the discharge stream and adjust flow on the fly.
Common problems include clogging when feed material contains clay or slime that binds particles together, and uneven water distribution across the belt width, which creates zones of poor separation. Wear on the belt itself is steady, particularly at the feed point and discharge end where particle impact is highest.
The Frue vanner occupies a middle position in ore dressing technology: cheaper and less power-hungry than spiral separators or dense-media plants, but less precise than modern flotation cells. It remains in use in artisanal and small-scale gold, tin, and heavy-mineral operations, especially in regions where water is plentiful and capital for complex equipment is limited. In larger mills it has largely been displaced by jigs and spirals, though some operations run vanners as a roughing stage before more expensive concentration steps.