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Copper Sulphide Concentrate Drying (6 replies)
1- Stockpiles with very small particles (P80 = 75 microns) have a very slow drying speed. I see that you need up to one week to get the results by spreading out the product stockpiles. If possible and feasible, try to find an old rotary drum dryer with the accessories. You will need to manufacture some missing items. Feeding the drum dryer with concentrate in counter-current of hot airflow will improve significantly the drying speed of the concentrate.
2-Concerning a large scale spending (budget constraint), I suggest the following:
-Calculate how much money you are loosing without an appropriate and efficient system to dry up the concentrate;
-Refresh yourself with the different drying systems to identify the most appropriate ones to your case.
-Get at least three formal quotations for an efficient drying system of the concentrate from established manufacturers;
-Finalize a cost-profit analysis (profitability studies) and see if the investment is profitable.
-If the investment is profitable, bring the file to some banks. Chances are one of them can accept your request because the project is profitable.
-If the investment is not profitable, you'll need to revisit the different systems again to look for a way out.
3-As for the filtration of the concentrate, try to use the diatomite ( diatomaceous earth) to improve the level of dryness. Generally, it improves the filtrability for small particles. Lab tests are always helpful.
Concentrate (fines) drying requires a combination of surface area, thermal energy, moving air and low specific humidity.
Where are you located, what is your local climate like? if warm and sunny then this can be done for fairly low capital invstment. Can you supply PSD and chemistry of the material.
Hello, just saw your questions on final concentrate too wet:
(1) At the Kemess mine in BC Canada, on start up there was a concentrate thickener, with thickener underflow to pressure filters and then to a dryer. The pressure filters were not removing enough water. High molecular weight polyacrylamide was added to the concentrate thickener feed with appropriate conditioning of the flocculant/concentrate from the flotation cells, prior to entering the concenetrate thickener, which then allowed the pressure filters to remove much more water (to about 8%) and resulted in no need to put the concentrate through a dyer (which was removed off site permanently).
(2) Why did the high molecular weight polyacrylamide work so well: flocculants also act as filter aids and the optimum settling/clarification concentration coincides with the optimum filtration aid concentration. The pioneer researches writing papers on this topic (~ mid-1960s, J. A. Kitchener et al) realized that using the filtration rate of the flocculated/settled slurry provided more reproducible results connecting flocculant dosage and clarification.
(3) At a copper mill on the Zambian Copper Belt, flocculant was added to the thickener underflow (into the copper concentrate tank feeding the leaf filter system) which reduced moisture content prior to the dryer, and lowered moisture content of the dried concentrate product to ~ 8%). I'm thinking better utilization of the flocculant occurs using the method in (1) because the flocculant is not uniformly distributed to concentrate particles at the relatively high concentration of the concentrate thickener underflow.
It sounds like an audit make be helpful. Run some tests under a range of conditions to see what variables will make a difference, and give some guidance to cost effectiveness of improvements pathways.
With some concentrates, what is very important is how the cake is formed, that is there is sufficient pressure drop across the cake during cake formation to pack the cake properly. Vs. trying to squeeze a cake at the end.
I understand this is a filter press?
You can apply paint to the filter cloth (in a special pattern) so all air flow is forced through the cake properly and reduce losses through thin parts of the cake.
10 % moisture or less is possible on your filter press given the particle size distribution. However it is imperative that your filter press is sized correctly to achieve the mass throughput rates required within the cycle time that will result in your desired final moistures.
The following questions are important:
- Is your filter equipped with diaphragm plates or recessed plates?
- Do you have an air blow cycle?
- Do you discharge the feed core before the air blow?
- Do you control the feed density?
- Do you feed from a feed tank or do you feed directly from the thickener?
- Where do you add your filter aid?
- Do you have a cloth wash cycle?
- What are the gangue minerals associated with the concentrate?
- What pressure do you achieve at during the dewatering stage?
- Do you achieve a clean cake discharge or is the cake sticky?
- How do you determine the completion of the filter cycle?
- How do you feed the filter?
Cake moisture is sensitive to flocculant addition from the point of view of dosage, type and point of addition. Long chained organic flocculants tend to trap water in the cake lattice. This also applies to dosage. Too much flocculant also traps water in the cake lattice and may "blind" the filter cloth. Surfactants can help but in my experience the effects are too small to be of significant. Fixing the hygiene factors supercedes the benefit and additional operating cost.
TonyE (synthan.services@gmail.com)
We produce a sulphide copper concentrate at moistures ranging from 11-13% on average but require a moisture of no more than 10.6% for shipment (and of course would like to achieve even lower moistures in order to save on shipping costs).
At present, we spread out our product stockpiles in indoor sheds and regularly flip the piles while testing daily until the required moisture is achieved. This can take as long as a week for particularly wet piles. As sheds fill up, less space is available to spread out piles which exacerbates the problem.
I have two questions:
1. Does anybody have any ideas or experience for how to increase the speed at which the concentrate stockpiles dry?
We're using fans and have previously used heaters but these have minimal effect. We cannot currently store piles outside as environmental regulations require a paved and bunded area but this will be built at some stage later in the year. We're also planning to remove panelling from the walls of the storage sheds and replacing it with something like shade cloth to allow greater airflow in the sheds.
Aside from these, we can't seem to think of a way to increase the drying time. We're also quite budget constrained and so anything involving large-scale spending is not really an option.
2. Does anybody have any simple ideas for achieving a drier product begin with?
Ideally, we would like to produce a drier concentrate straight out the filters to avoid the need for lengthy drying times altogether. However, this has proven to be extremely difficult. The problems seem to stem from our JingJin filter press which has never worked properly has inherent flaws about it.
Extensive work has been done to improve its performance and various cycle times etc. have been trilled with mixed results.
We also recently tried adding a coagulant to the slurry during each filter cycle but the effect has been minimal. The chemical vendor recommends also adding a surfactant to increase its effectiveness. Does anyone have experience with this?
We're also investigating the effect of particle size on the moisture and whether increasing our grind size can improve filter performance. Our final product has a p80 of between 70-79micron. It was much smaller than this until we started bypassing our rougher cell 1 concentrate directly to the thickener; our regrind mill cyclone overflow has a p80 of below 38 microns. This suggests that product size has an effect on our product moisture but it is unclear whether any further benefits can be obtained from an even coarser final concentrate. In any case, we are attempting to achieve a coarser ball mill grind through changing of cyclone components.
Any advice at all would be greatly appreciated.