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Gold in Grinding Circuit Liners (5 replies and 1 comment)
Hello Tich,
the plant is over 25 years old. There are no feasibility study data anywhere.
As soon as gold-bearing ore has been crushed or ground, some of the freed metal lodges in comers or behind mill liners and other places. Pulp that is spilled or splashed from launders, tables, and other machines carries gold, which becomes lost temporarily. Pumps, elevator sumps, and boots are other points where precious metal is held up. Gold is also retained in the mortar boxes, copper plates, and riffles of stamp mills, especially those in which amalgamation is a feature. This applies also to concentrating and classifying equipment.
Ball-mill and tube-mill liners retain gold—as much as 1000 oz. if grinding is done in water and a tenth of this if done in solution. Some mills retain as much as $3M in gold until cleaned out. Cyanide solutions that contain gold are absorbed by wood, and the metal is there held.
Wood staves from treatment vats have been known to assay 1 Oz/ton and were burned to save this gold. The precipitation and melting rooms always lose some metal. The dismantling and cleanup of many plants have yielded much gold to the owners or to others who have bought them. This temporary disappearance of gold, particularly in mills, is sometimes embarrassing to assayers and metallurgists, who are at a loss to account for discrepancies. However, after a new plant has been running for several months, a balance is struck, and all gold is accounted for.
Gold finds fewer places in which to lodge in the modern plant with its comparatively small amount of equipment and concrete floors which can be washed frequently.
---YOU SHOULD LOOK AT A GRAVITY CIRCUIT
The process is probably similar to the alluvial concentration of gold by water. The heavier particles of gold work their way to the bottom. In the mill with the impact and vibrations caused by grinding media, the gold and other heavy minerals work into the cracks and joints between the liners. If there is gravity recoverable gold in the ore being treated it will always work into the liners. This gold is usually recovered when the liners are changed. It is fairly common to get an increase in gold recovered from the gravity circuit(if the plant has one) in the days after the liners have been disturbed. Typically the liners are cleaned once they have been removed from the mill. This can be done using a high pressure water cleaner or simply scraping or wire brushing. The concentrate can be left in the milling circuit if there is a gravity circuit or further treated using a small table or even panning. There is usually a significant amount of iron from the grinding media that can be removed with a magnet. Accounting for the amount "locked" up in the mill is difficult as it varies with ore type and amount of gravity recoverable gold it contains. Usually this is not done with a bonus received once the liners are replaced and the gold they contain recovered.
Hi Maya,
As a supplier of mill liners we attend a number of mill relines every year. In many cases the old lining is stored under the mill deck until the reline is complete.
Once complete the old lining is cleaned prior to dumping. This way leftover gold will be recirculated through the mill.
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Hello,
Of the gold produced at some mines, 4 per cent of the total was recovered from the ball mills and classifiers when the mills were relined.
I hear that much gold can get trapping in the grinding mill liners of SAG, Rod mills or even Ball mills? How does that work? How can you tell?