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SPECIALIST EQUIPMENT MEANINGFUL PROCESS MINERALOGY U


Simon Isherwood explains why valuable minerals are lost to tails and provides some possible remedies


sing automated scanning electron microscopes in mineralogical investigation is not new. What is innovative is how the data can be used to make the mineralogy


meaningful to the fl otation process. Why are we losing copper, nickel or platinum to tails? T is is a familiar question that has provoked discussion since we were able to do elemental analysis. A-SEM data is now regularly used, to identify where value minerals are lost in the fl otation process and then to focus the metallurgical problem solving. Riaan Grobler, manager of the Betachem


and Nasaco Process Mineralogy Laboratory, explains: “Off ering the right chemical for the application is the basis of what we do. We are regularly sent samples for analysis, by clients and others who are experiencing fl otation problems. We scan these on one of our three A-SEM units (MLA from FEI), measure where the losses are, form an opinion of why the losses are occurring and suggest a remedy based on our process experience and reagent know- how.” Here, we will look at the main reasons why mineral values are lost to tailings, explore the reasons, examine some case studies and look at the suggested remedies. T e Betachem/Nasaco process mineralogy laboratory in South Africa uses a simple fi ve-point approach in identifying the losses to tails.


● Too fi ne to fl oat: the Betachem and Nasaco lab normally assumes a cut off size of 10 micron if the process in not operated for fi ne particle fl otation


● Too coarse to fl oat: the lab normally assumes a cut off size of 150 microns in a non-coal fl otation circuit


● Locked in non-fl oating gangue: the lab assumes 80% locking as a locked mineral for most of its projects


● Not the correct process or reagent suite to fl oat a value mineral


40 www.engineerlive.com


● Other reasons, which may include process effi ciency


Too fi ne to fl oat


Chalopyrite (red) particles in fi nal tails


Combined Rougher Scavenger Tails Calculated Assay (wt. %) Mass Elemental distribution


Cu 0.2 Ni


Chalcopyrite 0.0


Fe 5.0 S 2.7 Total Cu Ni


Wt% 0.4


% 89


% 0


Fe


% 2


S


% 5


In this copper fl otation plant tails, 89% of the copper is lost as chalcopyrite, of which 49% is smaller than 10 micron. T e main reason for copper loss is “too fi ne to fl oat”.


T is client was advised to:


● Install a fl ash fl otation cell in the milling circuit to capture liberated copper before overgrinding


● Perform a milling and classifi cation survey, recommended addition of water to the cyclone feed and not cyclone overfl ow


● Reduce pulp viscosity by adding a suitable rheology modifi er


● Investigate high-energy fl otation cells Too


Summary (wt. %) Well sized


small < 10


micron 49%


10 to 212 micron Lib


34%


Not Lib 16%


Too Big >212 micron


1%


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