Laboratory Testing & General Mineral Processing Engineering

Laboratory Testing & General Mineral Processing Engineering

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Total digestion of nickel laterite (2 replies)

J
jyang
6 years ago
jyang 6 years ago

I am looking for any suggestions/input on methods to more completely digest a nickel laterite sample. Currently, my lab is using an aqua regia digestion using 5 g of pulverized sample (-200 mesh) with 25 mL of aqua regia on a hotplate. We have been having difficulties in mass balancing the nickel amounts in our head assay size fractions relative to the nickel measured in our composite, 'bulk' sample. Specifically, we note that the calculated head value based on our size fraction analyses are approximately 70% of the value measured in our composite sample. After confirming the accuracy of our analytical numbers from flame AAS, we have begun to suspect that this discrepancy may be due to an incomplete digestion of our sample material by aqua regia. Performing a second aqua regia digest on the residual material from the first digestion extracts more nickel, but still not enough to bring the mass accounting into balance.

Any suggestions or insight would be most welcome! I will say that we are not currently set up to use HF or perchloric acid in our digestions, so that's why we have not opted for a more complete '4-acid' digestion.

 

Mike
6 years ago
Mike 6 years ago
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Comparing a 5g sample to a composite bulk sample will always show some differences, in fact if they agreed I would be surprised.  Getting results that are within 70% of the composite is actually pretty good.  Lab sampling errors, basic variations in material content and generally procedural variations can cause bigger swings than that.  Have you run several 5g samples, and do they all have the same result?  They probably shouldn't.

T
Todd H
6 years ago
Todd H 6 years ago
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When you complete the aqua regia digestion how much solids are left from the original 5 grams?  You should be filtering the digestion prior to dilution and running on the AAS - I am sure you are.

There are two methods that I would examine - after looking at the statistics of the sample reproducibility.  The issue could be totally related to sampling methods.  However, lets assume that is not the case.

  1. Take the residual solids and digest them with HF to solubilize the quartz, then add aqua regia to dissolve any liberated metals - be careful with HF.
  2. Conduct a fusion before digestion - borate flux is one method - google assay fluxes

Regards

 

Todd Harvey - Global Resource Engineering http://www.global-resource-eng.com

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