Preparing Cathode Wool for Smelting

The cathode wool is changed weekly or more often if necessary. Electrowin day is however the cut off point. First thing on Monday morning a sample should be taken from the cell for assay and then the eluate solution diverted to the spare cell.

Removing the Wool

1. Dump the solution in the cell by opening the drain valve on the line leading back to the eluate tank.
2. Allow the cathodes to drain for about ten minutes.
3. Remove each cathode from the cell and place it on the unloading table – ensure that there is a large container under the discharge slide,
4. Undo the wing nuts and remove the copper contact bar.
5. Cut away the section of unloaded wool and put the remaining loaded wool into the container.
6. When all of the cathodes are unloaded, weigh the wool.

Acid Digestion of the Wool

1. Put on appropriate safety gear – organic acids mask and rubber gloves.
2. Place the wool in equal amounts into two large containers and place these on the decant platform. (See fig 17)
3. Put a 4:1 mix of HCL and water in each container. Normally two buckets to half a bucket in each container. This quantity ensures good contact with all of the wool. Put lids on the containers.
4. Stir up the wool regularly.
5. When the wool has broken up completely, the acid solution may be decanted off into buckets. Allow this solution to settle before decanting the buckets off into the acid area sump*. Retain any sludge left in the buckets.
6. Fill up each container with raw water, stirring up the wool thoroughly as this is done.
7. Decant off the water into buckets and allow to settle before decanting the water into the gravity sump. Retain any sludge left in the buckets.
8. Repeat the rinse/decant process at least three times – the rinse water should become quite clear.

Drying the Cake

1. Line the large drying tray with newspaper – helps prevent cake from sticking to the metal.
2. Place the tray on the hot plates and switch the controller to the 4′ setting. Do not put on the top setting as it is important that the hot plates don’t get red hot.
3. Place the wool from the final decant in the tray – in an even layer. Put any sludge from the decant on top.
4. Make sure that the fume exhaust fan is operating.
5. Stir the cake up at regular intervals to facilitate drying.
6. Do not over-dry; it is better if the cake is left slightly damp as this helps prevent the loss of fines. When it is dry enough remove the cake from the tray and after weighing it, lock it up in the strongroom. Do not leave it outside of the strongroom. The C.I.L. cake is virtually pure gold/silver the shrinkage during smelting amounts to less than 5% normally.
7. Switch off the hot plates.