black tin

Black tin is cassiterite (tin dioxide, SnO2) that has been mechanically processed to remove waste rock and concentrate the ore into a fine, dark powder suitable for smelting. The name comes directly from its appearance: after stamping, washing, and separation, the mineral forms a black sand-like material, typically grading 65 to 75 percent tin by weight, though quality varies by source and processing method.

The production of black tin begins in the dressing plant after initial ore extraction. Mined cassiterite is crushed, then stamped (pounded) to break apart the ore from surrounding gangue material. This crushed material is washed and passed through a series of gravity separation stages, often using sluices, jigs, or shaking tables that exploit cassiterite's high density (relative density around 6.9) to separate it from lighter waste. Water agitation and settling allow the finer tin mineral particles to concentrate while lighter materials are discarded.

Black tin from different deposits carries different contaminants. Cornish and Bolivian black tin often contains tungsten and iron oxides; Malaysian material typically carries more silica. Some black tin destined for secondary smelters may be deliberately blended with lower-grade concentrates or recycled tin fines to adjust grade and reduce smelting costs. The powder is usually bagged in 50 kg or 100 kg sacks for transport to the smelting works.

Black tin itself cannot be used directly; it must be smelted to produce metallic tin. The powder is fed into a reverberatory furnace or electric furnace where it is heated above 1200 degrees Celsius in a reducing atmosphere. Carbon monoxide from coked coal or injected natural gas reduces the tin oxide to molten metal, which settles below the slag layer and is cast into ingots or pigs. A typical smelting loss of 2 to 5 percent is normal, so the tin content of black tin directly drives recovery and furnace economics.

The term black tin has been standard in tin mining for at least two centuries, particularly in the Cornwall-Devon mining region where the language became established. It distinguishes the intermediate product (concentrated ore powder) from both crude ore (unwashed rock straight from the mine) and from white tin (refined metal). In modern times, some producers use the term concentrate interchangeably, but black tin remains the conventional name in trading and smelting contexts, especially where historical supply chains and contracts use the older terminology.