December 9, 2023
milling process

Miners extracted a very heavy ore from a mine, and only a very small proportion contained precious metals. Transport was expensive, so miners wanted to get as much valuable material out of the ore as possible before transporting it to a smelter. Prior to smelting, the waste rock must be separated from the metal in a process called milling. The process is known as separating the waste rock from the metal.The following is a basic outline of a milling rocks process, although not all mills were the same.

milling rocks

  1. On the top floor of the milling rocks building was a room where ore was received
  2. Raw ore was crushed by jaw and gyratory crushers. The jaw crusher separated rocks into smaller pieces, then gyratory crushers turned the pieces into sand
  3. Crushing – Rod mills and ball mills grind the ore by turning steel rods or balls inside cylinders while water is added to form a slurry. As the rotating cylinders turn, these steel rods or balls collide and grind the ore to an even finer texture
  4. In the classifier, the slurry was divided into large and small pieces, with the large pieces going back to the grinder while the small pieces went on to concentration
  5. This is why the lowest and largest floors were used for concentration since it was not linear
  • It was then sent to flotation cells where agitators mixed in more water and various reagents. The reagents caused certain metal ore particles to adhere to the froth bubbles. Agitation caused aeration, causing a froth to form. Different reagents could be used to target specific metal ores.
  • In order to separate the froth from the heavier material, paddles were used to sweep off the top of the cell by paddle into a flume.
  • To prepare it for shipment to the smelter, the metal-containing froth is sent to an industrial thickener and drier for rinsing, drying, and packaging.
  • It is possible to send the heavier material to another or even a third flotation cell where the reagents are changed to remove a different metal ore. Vibrating tables could be used to separate the heavier metal ore particles from the lighter wastes. Heavy metal ore concentrated in this manner is then sent to a thickener and a dryer before being sent to the smelter for processing.
  1. In addition to amalgamation, other steps may be necessary depending on the ore being recovered.
  2. To make metal, the ores were sent to the smelter once they had been processed.
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