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Calculation of value of Fe, SiO2 and Al2O3 % in a Flow sheet (2 replies)

7 months ago
anjanisail 7 months ago

Dear All

While preparing Flow Sheet for designing of a flow sheet for beneficiation of Hematite Iron Ore, I came across a Problem. I have considered Jig, Spiral Concentrator and WHIMS in my envisaged flow sheet. Based on the available test test results I have considered yield and respective assay value at any equipment. Problem is that my client wants to change the feed grade of the Iron Ore, hence considering the same yield with same geological characteristics of the Ore how we will calculate new value of Product Fe, SiO2 and Al2O3.

Example, Consider at Jig:

  • Feed: Fe: 62.23, SiO2: 3.12, Al2O3: 3.27
  • Product: Fe: 63.52, SiO2: 2.78, Al2O3: 2.72
  • Yield : 53% 

New Feed Data:

  • Feed: Fe: 60.44, SiO2: 5.66, Al2O3: 6.12
  • Product: Fe:    , SiO2:       , Al2O3: 
  • Yield: 53%

How I will calculate new value of Fe, SiO2 and Al2O3, based on given yield. Whether the methodology  of extrapolating or intrapolating will be applied.

Waiting for comments.

7 months ago
David 7 months ago

Hi, I referred to a friend more familiar with this and he says:

"First off I doubt if the yield would stay the same, the Fe assay in the concentrate would likely stay the same but not the overal yield. The basis being that you have heavy and light particles of some ratio which will give a certain recovery to the cons. 

The change in feed is an increase in the amount of the light particles. Thus you will recovery the same amount of heavies, but this will be a smaller percentage of the feed. 

I would start with the Fe assay in the cons as the same and then using the standard met balance equations calculate the resultant yield. 

A better approach would be to have a sink float analysis of the feed, which can then be adjusted for various grades, and the jig and spiral performance could then be calculated. But this is probably not very likely to be available."


Your client needs to test that new ''imaginary' sample to get the correct answer.

Marshal Dienes
7 months ago
Marshal Dienes 7 months ago

AS YOU MUST KNOW, One of the biggest mistakes in designing a process flowsheet is designing for an "average" ore that will never actually be seen. If Pilot Plant work is done, a range of ores should be run through it to determine the answers to this specific question.

Flowsheets can be constrained by feed end limitations (primary grinding capacity, first separation step capacity and so on) and / or discharge limitations (filtering, final separation, even things like tailings pumping capacity) that will definitely put a constraint on feed changes.

For example, a plant that is feed constrained will suffer a decline in output if incoming weight recovery of the ore decreases because the additional feed needed to compensate for the lower feed recovery can not be force fed into the plant. Higher than "average" recovery ore will only result in higher concentrate output at a given feed rate, generally a good thing.

A plant that is product constrained might be able to tolerate a decrease in incoming weight recovery by increasing the feed rate, but will not produce more if the incoming weight recovery increases above "average".

Then there are mineralogy changes. The above are based on only the incoming weight recovery changing, with product and tails grades staying about the same. If the mineralogy changes and you have to, say, grind finer to make concentrate grade, all bets are off and you have a whole different set of circumstances to determine the operation changes from the ore. Some ores even simply can't be processed with the available flowsheet.

It is very important early on to develop a test protocol that will predict what a given ore will do when it is fed to the plant at the drill core stage, repeated at the bank sample or drill stemming stage. This allows eventual mine planning to keep the key ore parameters fed to the plant within the plant's abilities.

By the way, my experience is that most plants have a tolerable range of feed grade. Any lower grade and they become feed constrained, any higher incoming grade and they are product constrained.

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