Milling Process

By Becky

Ute Ulay Mill Building

Today we were treated to a tour of the Ute Ulay Mill, guided by Matt Ingram who worked there in the mid-1990s. Matt explained the inner workings of the mill to us in depth.

Matt and Buckeye

‘Buckeye’ the 5 cylinder diesel engine ran all the mill equipment until the manifold blew. It is certainly an imposing and glorious piece of engineering.

Coarse Ore Bin

Once the ore had been mined it was put through a grizzly into the coarse ore bin. If it didn’t fit, it was further crushed (with the help of Steve ‘Doublejack’ Jackson and his 8/16lb hammer) until it did. Doublejack was also a fruit forager, and shared the spoils of raspberries with his co-workers.

The coarse ore was taken along a surge belt (2 steps forward, one step back) into the crusher room to the Jaw Crusher and Cone Crusher, and from there, into an elevator up to the fine ore bin.

Ball Mill

This fine ore was sent along belts to the Ball Mill, where it was mixed with water and further reduced in size, 30 gallons at a time. The Ball Mill used steel balls inside a cylindrical drum to break down the ore, the balls started at 6” diameter but wore down to around 1”.

Classifier

Next the ore fed into the classifier, which, with the addition of more water, turned the ore into slurry that felt slightly sandy to the touch. It was important that the particles were of a consistent size for the following stages, so the screw would take any larger particles back up and into the Ball Mill.

Frother Cells

The slurry was fed into the flotation cells. The froth floatation method mixes pine oil with the slurry and blows water through it to create bubbles. Then Xanthate salts enable the metals to stick to the bubbles, and the skimmers took a little bit of this mix off the top in each cell. By the time the mixture reached the last cell it had a metallic appearance, which would coat your hand if you put it in. I have made this sound simple, thanks to Matt’s excellent explanation, but in reality this process requires constant adjustment, with the addition of tiny amounts of different chemicals (44, 350, 3501) according to the precise make up of the particular ore.

Filter Paddles with Cotton Covers

Once the mixture had been through the floatation cells, it was called concentrate. The next stage was to remove the water. The concentrate sat in a tank and was picked up by disc filters that allowed the sediment to stick to a cotton bag, whilst the water drained down a channel on the inside. This semi-dried material was then subjected to the ‘flame thrower’ to dry it a little more.

Finally the resulting dry concentrate was sent off to the smelter. Phew.

Draughty Walls in the Mill

Thanks to Matt (please let me know if I have got anything wrong...) for the wonderful tour.