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Separating.pdf

Shaking Tables.pdf

Separating

mill worker at a pair of shaking tables

Once the tin ore particles were ground to fine sand, the separation process removed any remaining waste from the ore.

Lots of different machinery was used to separate the tin ore, Geevor was at the forefront of development of these machines.

Buddles

A buddle was a device for concentrating tin ore. In the mid-19th century these most usually took the form of an inclined circular pit with rotating brushes; the tin from the stamps was fed into the centre or side of the pit and was graded by gravity, concentrating the heavy ore near the inlet point.

In the mid 19th Century the traditional buddle was mechanized to become the round buddle. Originating as pits in the ground with sloping floors, the job of the buddle was to take the finely crushed rock, and wash away the waste material whilst the ore settled and was dug out periodically. Buddles used the difference is density between the heavier tin particles and the lighter waste material. It was a slow and labour intensive process.

Shaking Tables

Shaking tables are mechanical versions of the prospectors gold pan - a shallow wooden bowl used in early times. Water, a shaking motion and the different densities of particles are used to separate heavier minerals from lighter rock.

The first recorded table was developed by Robert Stagg of Nenthead in the northern Pennines in 1828 for use in separating lead ore. In the 1840s this was refined by the German engineer von Rittinger.

Tables were commonly used in Britain form about 1900 onwards. The modern type of table was developed by Wilfley and used a deck or table driven by steam or later electric power. The head motions most widely used were those produced by the Holman Company of Camborne, Cornwall. The table is fed with ground ore in suspension from a ball mill – called pulp.

The wooden deck is covered with linoleum upon which are ridges or dams called riffles, which trap the heavier particles of cassiterite behind them. The lighter particles are washed over the riffles by the flow of wash water. The shaking motion takes the particles to the end of the table. The concentrate was split into three parts: the heads or high grade concentrates – about 74% tin content, the middlings, which contained about 24% tin and the slimes or tails with about 12% tin. At the bottom of the table, water was caught in a trough.

The heads went for further processing to remove the arsenic and sulphide minerals. The high grade concentrate finally passed through a magnetic separator, which removed tin with iron content. The concentrate picked up by the magnetic separator was sold as medium grade concentrate. The middlings from the shaking table were further milled in a regrind ball mill and put back on to another set of shaking tables, to extract more tin. This regrinding process would be repeated up to three times for efficient recovery of tin concentrate. The slimes were treated in a separate slimes plant and a low grade concentrate was obtained.

 

Photographs  reproduced with the kind permission of the David Wills collection held by the Geevor Archive, the Royal Institution of Cornwal and the T Grevatt Collection held by Cornwall Council

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