Finn from Ecuador
Member
Re: Further things which may be of interest to members
Table optimising
Many years ago I was involved with a project to maximise gold recovery from a milled ore by using a small (3') wilfley table to clean up concentrates and middlings from a bank of larger tables.
Due to environmental constraints chemical processing was not allowed on site.
A short period of operation revealed that running the table in its standard format was leading to losses of fine gold where the particle size was less than 50 micron screen size.
The gold particles were flattened from the milling and appreciable quantities were also lost from the plus 100 micron screen sizes.
Despite doing all of the standard optimisings of adjusting feed size screening, feed rate onto the table, table side tilt and water flow I could not get a major recovery improvement.
I went into the literature and found that the largest number and most useful papers were those from the British tin industry.
Basically they said that keeping a tight sizing on the feed was vital, I was already doing that so OK there.
Making sure that the table was level on the longitudinal axis was a fundamental which I was also doing.
Feed rate was best when a loose bed was set up along the table, don't put too little feed on the table nor try to put too much feed on the table.
Keeping the feed rate constant was also very important, I was feeding from a wet sump with a screw feeder so OK there also.
Side tilt was to be such that clay fraction particles were washed over the side of the table but the tilt was to be little enough that a middlings product could be readily separated at the end of the table.
Even when I had the table set up to cover all of the above parameters I was still losing fine gold.
The only area where I did not have full control was the side water coming onto the table, no matter how much I tried I could not get a perfectly even flow across the table.
I decided that I needed to improve the delivery of water to the table.
I did so by running a length of 3/4" copper pipe suspended about 4" above the side of the table where the water exited the original flow boxes.
The pipe was blanked off at the table exit end and was connected to a hose and ball valve at the feed supply end.
Ever 1" along the pipe was drilled a 1/8" hole.
When the water was turned on a curtain of water sprayed down onto the top edge of the table and delivered an even flow of water which could be easily adjusted for flow rate with the ball valve.
Even this change only partly improved the recovery, it was evident that there needed to be a difference in the water flow rate supplied to various parts of the table.
After a lot of testwork I settled on having the water delivery pipe as two pipes.
The holes remained the same size and spacing but the delivery was split into two parts.
The first part was as above but only extended 2/3 of the table.
The second part covered the last 1/3 of the table, each part was as a separate length of pipe so that adjustments could be made to either part without affecting the other part's flow rate.
In order to keep the water holes at the 1" spacing the pipe for the last 1/3 of the table was fed from the bottom of the table and the pipe ends almost touched.
Each pipe length had its own ball valve for separate flow adjustment.
The side wash water pipes were fed from an overflow overhead tank so that a constant head was maintained.
This was important on a mine site where valves were being opened and closed in other parts of the circuit, this would affect the pressure to the wash pipes.
This setup allowed recovery of free gold down to 25 microns, the disappointing part was the low weight of the 25 to 50 micron gold recovered, it looked a lot as a sheet like paint on the table but weighed far less.
On the plus side there was a substantial improvement in the plus 50 micron gold which did weigh well.
If run from a municipal water supply the overhead header tank may not be necessary depending on the vagaries of the particular supply.
Deano
This article was written by Deano in "Chemical Proses" section of this forum. I wanted to put it also here in mining section because i found it very educative.
Salud
Finn
Table optimising
Many years ago I was involved with a project to maximise gold recovery from a milled ore by using a small (3') wilfley table to clean up concentrates and middlings from a bank of larger tables.
Due to environmental constraints chemical processing was not allowed on site.
A short period of operation revealed that running the table in its standard format was leading to losses of fine gold where the particle size was less than 50 micron screen size.
The gold particles were flattened from the milling and appreciable quantities were also lost from the plus 100 micron screen sizes.
Despite doing all of the standard optimisings of adjusting feed size screening, feed rate onto the table, table side tilt and water flow I could not get a major recovery improvement.
I went into the literature and found that the largest number and most useful papers were those from the British tin industry.
Basically they said that keeping a tight sizing on the feed was vital, I was already doing that so OK there.
Making sure that the table was level on the longitudinal axis was a fundamental which I was also doing.
Feed rate was best when a loose bed was set up along the table, don't put too little feed on the table nor try to put too much feed on the table.
Keeping the feed rate constant was also very important, I was feeding from a wet sump with a screw feeder so OK there also.
Side tilt was to be such that clay fraction particles were washed over the side of the table but the tilt was to be little enough that a middlings product could be readily separated at the end of the table.
Even when I had the table set up to cover all of the above parameters I was still losing fine gold.
The only area where I did not have full control was the side water coming onto the table, no matter how much I tried I could not get a perfectly even flow across the table.
I decided that I needed to improve the delivery of water to the table.
I did so by running a length of 3/4" copper pipe suspended about 4" above the side of the table where the water exited the original flow boxes.
The pipe was blanked off at the table exit end and was connected to a hose and ball valve at the feed supply end.
Ever 1" along the pipe was drilled a 1/8" hole.
When the water was turned on a curtain of water sprayed down onto the top edge of the table and delivered an even flow of water which could be easily adjusted for flow rate with the ball valve.
Even this change only partly improved the recovery, it was evident that there needed to be a difference in the water flow rate supplied to various parts of the table.
After a lot of testwork I settled on having the water delivery pipe as two pipes.
The holes remained the same size and spacing but the delivery was split into two parts.
The first part was as above but only extended 2/3 of the table.
The second part covered the last 1/3 of the table, each part was as a separate length of pipe so that adjustments could be made to either part without affecting the other part's flow rate.
In order to keep the water holes at the 1" spacing the pipe for the last 1/3 of the table was fed from the bottom of the table and the pipe ends almost touched.
Each pipe length had its own ball valve for separate flow adjustment.
The side wash water pipes were fed from an overflow overhead tank so that a constant head was maintained.
This was important on a mine site where valves were being opened and closed in other parts of the circuit, this would affect the pressure to the wash pipes.
This setup allowed recovery of free gold down to 25 microns, the disappointing part was the low weight of the 25 to 50 micron gold recovered, it looked a lot as a sheet like paint on the table but weighed far less.
On the plus side there was a substantial improvement in the plus 50 micron gold which did weigh well.
If run from a municipal water supply the overhead header tank may not be necessary depending on the vagaries of the particular supply.
Deano
This article was written by Deano in "Chemical Proses" section of this forum. I wanted to put it also here in mining section because i found it very educative.
Salud
Finn
