William Champion's zinc process (1825)
Producing metallic zinc
This is the first known description of William Champion's zinc process. It appeared in the Annales des Mines, Tome X, 1825. The present edition was translated directly from the original French.
Figure 1 - general description
The furnace is round and covered with a cone which acts as a chimney. The cone surrounding the furnace has as many openings as there are pots.
- a-a small walls which are removed at will to put in or take out the pots. They are made of bricks, with a hole through which an iron bar can be inserted so the pots can be moved whilst still hot.
- b firedoor, closed with a brick.
- c ashpit in which the workman enters to clean the fire bars.
- d-d holes, formed in the upper part of the furnace dome, to permit entrance of the flames into the chimney. The pots are also charged through these holes. They are never closed all at the same time. The workmen can, by closing some of them, direct the fire to any part of the furnace.
- e-e, e-e passages in the foundation corresponding to the pots.
- g-g containers, in sheet-iron, for the zinc.
- h cylindrical sheet-iron tube to be fitted to the condenser, conducting the zinc into the container. <>i condenser. This a slightly conical sheet-iron tube, with a flange at its upper end by which it is attached to the pot. To secure it, a ring of fireclay is placed on the flange and it is then pressed strongly against the pot. To maintain it in this position, two iron rods k-k are fixed to the lower part of the condenser by a collar. These pass through little pieces of iron m, mounted into the wall. The rods are then locked with the clamp screws n.
- 1-2 level of the upper floor
- 3-4 level of the lower ceiling
- 5-6 level of the lower floor
Figure 2 - Half-plan on the level 1-2.
Figure 3 - Vertical section of a pot and the equipment which is used to secure the condenser against the pot.
Figure 4 - Wheeled tongs for transporting the hot pots.
Figure 5 - Half-plan on the level 3-4.
Note that the passages in the foundation are in double-cross form, to accommodate condensers and containers for six pots.
Locations
Most of the works where [metallic] zinc is manufactured are situated in the neighbourhoods of Birmingham and Bristol. This presumably is caused by the fact that the [much older] direct manufacture of brass [from copper and calamine], has for a long time been concentrated in these two towns. So it is perhaps not strange that, at the time when they began to make brass by alloying [copper] with metallic zinc instead of calamine, the new industry was also located at these places. There are some zinc furnaces in the neighbourhood of Sheffield, too, on the nearby coal-fields.
The works at Bristol and Birmingham are principally supplied [with ore] from workings at Mendip and in Flintshire. The Sheffield furnaces draw their calamine from Alston-Moor in Cumberland.
Roasting of calamine
The calamine, from which any galena has first been separated by sorting, is roasted before being put in a reduction furnace. Roasting is done in a reverberatory furnace of about 10 ft long by 8 ft wide. The ore, coarsely crushed, is placed on the sole of the furnace in a bed about 6 inches thick.
In some works, the ore is not roasted and the calamine, broken to the size of pigeon-eggs, is mixed with an equal volume of small coal.
The reduction process
The reduction furnaces are rectangular or round. They hold 6 or 8 pots. Round furnaces are the most advantageous for working. They usually contain only 6 pots, as is shown on the Plate, in the Figures 1 and 2. The pots are inserted in the furnace after removing the small walls a-a. When the pots are replaced whilst the furnace is (still) hot, they are pre-heated in a special furnace. This has a sole on which the pot is placed and on each side it has a small fire-place. The heated pot is taken out, moved and positioned in the zinc furnace by means of tongs mounted on two iron wheels, as shown in Figure 4. The pots are made of fireclay. They have a hole in the bottom, through which the zinc runs into the condenser. Prior to charging the pots, this bottom hole is closed by means of a suitable piece of wood. During smelting, the wood will be converted to charcoal. This stop prevents the mixture, charged from above, from flowing out of the pot.
Operation
The hole in the lid of the pot, see Figure 3, is left open for about two hours after charging, until the blue colour of the flame indicates the beginning of the reduction. At this point the hole is closed with a plaque of fireclay. Next, the sheet-iron tubes are fastened to the ends of the condensers and into the sheet-iron containers which will receive the molten zinc. Sometimes, these containers are filled with water to prevent the falling zinc from splashing everywhere.
During the time a charge is being worked, the only task of the workmen is to feed the fire and to keep clear the condensers. These are sometimes blocked with zinc, which collects in great abundance. Opening up the condensers is done by means of a red-hot bent iron bar, inserted into the condenser from below.
The zinc collected during smelting is in the form of droplets and fine powder, and mixed with zinc oxide. This mixture is remelted in an iron pot, placed on a special hearth. The oxide floats as a dross on top, it is skimmed from the surface to be placed in the pots again. The metal is cast into ingots.
To empty the pots at the end of each reduction operation, the condenser is removed, the stop of charcoal in the bottom hole of the pot is then broken away completely with a clinker bar and the ore residue falls out when it is stirred from above. When replacing the condenser, they put a little ring of damp fireclay on its flange, see Figure 3, and press it against the bottom of the pot. It is kept in position by means of small rods.
Workforce, output and costs
Three men are employed to work a furnace, a foreman and two labourers. They themselves make the pots. A mixture is used of equal parts of fresh fireclay and of calcined clay, the latter from the debris of old pots. The average life of pots in the reduction furnace is four months.
Five charges are made in fifteen days. In these five charges 6-10 [metric] tons of calamine and 22 - 24 [metric] tons of coal are used. About 2 [metric] tons of zinc are produced.
One can roughly calculate the cost of a [metric] ton of zinc at Bristol, as follows.
| £ | s. | |
| 3 tons of calamine @ £ 6 | 18 | - |
| 24 tons of coal @ 5 s. | 6 | - |
| a foreman @ 6 s. a day, for 7 days | 2 | 2 |
| two labourers @ 4 s. | 2 | 16 |
| various costs | 1 | |
| cost of a ton of zinc at Bristol | 29 | 18 |
The calamine from Alston-Moor, used at Sheffield, is less rich. At most it produces 25% zinc. The coal there costs 5s. 8d. per ton and the calamine, delivered at the works, costs £ 5 [a ton]. From this, Sheffield zinc costs £ 32 14s. per ton.
These are of course cost prices, the zinc actually is sold to the customer for £ 40 to £ 44.
Imported zinc is sold at the London docks for £ 20 to £ 24. This enormous difference is caused partly by the high price of calamine. One is not surprised to learn that this metal has an import duty of 20%.
Use of blende instead of calamine
In England zinc is also made from blende. This mineral, washed and crushed to nut-size is sold at Holywell, at the mine, for £ 3 per ton, or about half the price of calamine.
It is roasted, without any other preparation, in a reverberatory furnace. These furnaces are about 8 ft wide by 10 ft long. The height of the vault from the sole is 30 inches. The height of the fire bridge [over the sole] is 18 inches.
The bed of blende is about 4 - 5 inches thick. It is stirred almost continuously.
The consumption of coal is 4 tons for each ton of roasted blende. The loss [in metal] is 20%. The operation lasts 10 or 12 hours.
The mixture to be smelted is made up of a quarter roasted blende, a quarter roasted calamine and a half of coal. It commonly gives 30% zinc.