The concentrate dewatering circuit, thickeners and filters at a Chilean copper producer were not operating at maximum efficiency. Several areas in the circuit were identified where improvements could be made.
The filter plant was having difficulty keeping up with daily production. The concentrate from the filter plant was near the maximum allowable moisture level.
The overflow of the concentrate thickeners contained excess concentrate. This solution, when combined with the tailings thickener overflow, was wearing out pumps prematurely, requiring frequent maintenance and pump rebuilding.
Also, operational problems with the concentrate thickeners occurred.
The thickeners were often overloaded, and high torque was common, causing excessive wear on the rake mechanisms. Because of the high torque, the automatic rake lift mechanism kept the rakes at very high levels.
Even with three concentrate thickeners in operation, the thickener circuit was often unable to maintain a balance with the milling operation.
To solve the problems with solids in the thickener overflow, the Nalco Representative recommended using a program called FilterMax.
The FilterMax program was recommended instead of the conventional flocculant approach because it had been tested and approved in circuits containing ceramic filters.
The FilterMax program functions by agglomerating the fine copper concentrate with the coarse copper concentrate.
As a result of this agglomeration, foam on the thickeners and solids in the overflow are both reduced.
Plant personnel conducted filtration and sedimentation laboratory tests to determine if the product would have any negative effects in the filter plant.
Ceramic filter performance can be very susceptible to reagent addition. Any reagent that can alter the surface tension of the fluid medium or change the contact angle can potentially have a devastating effect on ceramic filter performance.
Plant personnel fed the FilterMax product to the concentrate thickeners at a rate of two grams per ton. The effects were seen almost immediately as foam on the thickeners began to break up.
With time, the overflow became cleaner. The foam in the overflow sump also disappeared.
Reduction in copper circulation back to the mill:
The amount of copper circulating back to the mill as a result of the copper contained in the concentrate thickener overflow was significantly reduced.
Before implementing the FilterMax program, the line feeding the mill that contains the concentrate thickener overflow and the tailings thickener overflow averaged 92 ppm Cu.
After implementing the FilterMax program, the copper in this line was reduced by 91.3% to an average of 7.97 ppm.
Filter capacity increase:
Adding the FilterMax product to the concentrate thickeners to agglomerate the fines also resulted in a substantial increase in filter capacity.
Without increasing the filter feed density or changing the particle size distribution, the capacity of the filter plant increased.
Before the addition of the FilterMax product, the filter plant had an average production rate of 101.9 tons per hour. After the addition of the FilterMax product, the production rate increased by 21.6% to 123.9 tons per hour. At the same time the filter capacity increased, the moisture of the filter cake was reduced.
Prior to the addition of the FilterMax product, the average filter cake moisture was 9.59%. After the addition of the FilterMax product, the filter cake moisture averaged 9.19% — a 4.2% decrease.
Operation of the concentrate thickeners improved significantly, as torque was reduced with the introduction of the FilterMax program.
The operation was also able to shut down one of the three concentrate thickeners and continue operations using only two thickeners.
As a result of using the FilterMax program at the Chilean copper producer, the following results were achieved:
- Increased filter capacity by 21.6%
- Decreased filter cake moisture by 4.2%
- Decreased filter run time by 23.4%
- Reduced circulation of copper back to the mill by 91.3%
- Reduced the amount of froth on the concentrate thickeners
- Anticipated reduction in overflow pump maintenance
- Plant production rate, tons per hour