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Effect of Size Distribution on Laboratory Results to Full Pl ... (6 replies)

Carl Jenkins
9 months ago
Carl Jenkins 9 months ago

It is a well-knownphenomenon that every operations metallurgist knows, that the full scale grinding circuit over grinds higher density minerals/elements in a manner that reduces the grade of those minerals/elements in the coarse size fractions and concentrates these to some size fraction/range that is often close to the natural mineral/grain size.

In the gold industry this is so marked that it is common practice to use 2 standard screen sizes coarser than the laboratory results for full scale design, i.e. leaching/flotation processes.

The same phenomena occur for base metals, but typically no credit for these phenomena taken as part of the design process. This being one of the key reasons why the large scale Chilean porphyry operators can push tonnage at coarser grinds without too much reduction in recovery. Typically the large scale SAG/Ball milling circuits generate significantly more fines and these are lost in the flotation circuits due to either inappropriate collectors or the inability of the flotation equipment to recover ultrafine material.

My question is "Does anyone actually evaluate or actively take advantage of this issue at the design phase" or is it an opportunity that is left for operations to take advantage of. Using one standard screen size coarser in design than that obtained from the laboratory results could make a significant difference to project economics!

Helena Russell
9 months ago
Helena Russell 9 months ago

Unfortunately it is mostly left to the operators. The best answer to this I have come across is to install a flotation cell either on the mill discharges on classifier under flow if the desired product is a sulfide. If the product is metallic, i.e. gold, install a gravity recovery unit on the classifier underflow. It is easy enough to check the discharge pump box for gold to determine if a gravity unit is feasible. I have seen pump box material run twenty oz/ton of coarse gold.

Of course leaving it to the operator’s means any additional equipment is jammed in willy-nilly. Frankly I believe that flash flotation cells should be an integral part of the design of sulfide circuits. Judicious operation of these can give a final concentrate, relieve the main circuit of a considerable load and prevent some over grinding losses.

The problem is with the disconnect between designers and operators. Typically the design is completed, equipment purchased and even installed before operators are consulted.

9 months ago
Oberfuhrer 9 months ago

You have raised a good point regarding mill sizing. The topic was discussed in a paper presented at the Geometallurgy Conference in Brisbane in 2013.

Particle Size Distribution Effects that Should be Considered when Performing Flotation Geometallurgical Testing K C Runge, E Tabosa and A Jankovic


The paper is available on the following internet site.


I suspect that most engineers are too cautious to risk any deviation from the traditional approach to mill sizing even if there is a potential economic advantage to the client. The value in a discussion such as this present one is that at least the topic receives some airing.

Zander Barcalow
9 months ago
Zander Barcalow 9 months ago

As mentioned, this is mostly left to the operators.

From a design view point, one would not attempt to "correct" the mineral density/particle size distribution effect for a base metal flotation circuit. Actually, the effect usually allows the operators to push throughput beyond the design capacity with no perceptible negative impact on concentrate grades and/or recoveries. However, the closer the design primary P80 is to the top flotation size of the valuable mineral, the smaller the margin for doing this.

One thing, as the desire for maximizing the reuse/recycle of process water for concentrators, the need of a pilot plant campaign with the intended level of reuse/recycle of process water increases to minimize process risks! The historic approach of flotation testing, whether in the laboratory or in the pilot plant, with fresh water only no longer directly applies for such situations.

Alan Carter
9 months ago
Alan Carter 9 months ago

There was a good paper from Newcrest about how they used this to coarseness up the grind at Ridgeway based on the Cadia experience.

I looked and only found a couple of papers by S. Hart that mention what was done, but did not go into a lot of details. If anyone has more details I'd be interested too. I really think that I had something with more details on a job 11 years ago, but Google Drive and OneMine searches are failing me.

9 months ago
Standartenfurer 9 months ago

How can we get the full paper?

Raje Singh
9 months ago
Raje Singh 9 months ago

Yes this is a good IDEA. Yes we can use data from lab to plant. But it should be a PILOT PLANT with continuous operation for at least 4 to 6 hrs daily. Case study- We developed a flow sheet based on pilot plant for Pb, Zn flotation. 100% Practical during commercial operation.

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