Assaying, Microscopy, Mineralogy & XRF/XRD

Assaying, Microscopy, Mineralogy & XRF/XRD 2017-04-04T06:57:57+00:00
  • To participate in the 911Metallurgist Forums, be sure to JOINLOGIN
  • Use Add New Topic to ask a New Question/Discussion about Assaying, Microscopy, Mineralogy & XRF/XRD.
  • OR Select a Topic that Interests you.
  • Use Add Reply = to Reply/Participate in a Topic/Discussion (most frequent).
    Using Add Reply allows you to Attach Images or PDF files and provide a more complete input.
  • Use Add Comment = to comment on someone else’s Reply in an already active Topic/Discussion.

Zinc Analysis with an XRF (13 replies)

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

XRF beads to determine Zn in concentrated mineral: I have problems with the determination of Zn, ore concentrate zn, by preparing fused beads.
value of Zn is between 40 and 60%

JohnnyD
2 years ago
JohnnyD 2 years ago

Did it mean you are not detecting Zn, or was concentration wrong ? Example: too high or low. What calibration program are you using ? Are you able to share spectrum.

Fusing ores with high metal content can be challenging. It would help to know what fusion recipe you were using( flux and dilution) and also what problems you observed( beads crystallizing etc.). Also what was they type of ore ? Sphalerite or some type of zinc oxide.

What is the problem you are having? You could play with dilution if concentration is too high, or, try to add some silicon oxide - it helps to form the glass. What kind of ore do you have? If it's sulphide (as are 95% of all zinc ores), you probably need to oxidize it first, or add oxidizer during fusion. I would go for oxidation before fusion - much safer for platinumware and it's part of production process anyway.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

The formula used is: 10 gr Flux (Li2B4O7, LiBr) + NaNO3, and 0.3 g of sample.   The working sample is zinc concentrate (ZnS) problems observed with the beads are not completely transparent, apparently not smelting entire sample, necessary to oxidize the sample and for this used program with a temperature gradient in the OX Machine.

I'm trying to change the process of determination of zinc, change the classical method by volume for the determination of zinc in concentrate by the determination by XRF, get results but they are not accurate enough, just have to have an error rate of 0.2%.

Example:

  • Result by classical method by volume: 52.82% Zn
  • XRF result: 53.73% Zn
  • difference: +0.91% is outside the range of 0.2%
  • classical : 45.74 % Zn
  • XRF : 44.15 % Zn

Difference: -1.54% is outside the range of 0.2%

JohnnyD
2 years ago
JohnnyD 2 years ago

Are you using EDXRF or WDXRF? Did you try to use Mixed fluxes (with Lithium Metaborate?) And it looks to me that your dilution is too high. Usually 10-12:1 is Ok, even as little as 4:1. In that case, I would recommend pre-oxidation and use flux without oxidizer. Another thing you might try - using LiOH method (but be aware of possible formation of H2S, which is toxic).

David Kano
2 years ago
David Kano 2 years ago

Recipes aside, what you're trying to do is going to be very challenging. First, for a 300 mg sample, 0.2% accuracy in weighing it will require a scale with resolution and accuracy better than 0.6 milligrams. Most lab scales have an accuracy and resolution on this order, so you better be using a scale that can give you good measurements at 0.1 milligram or better. This applies to both the sample and the flux. Second, your standards and samples must not have any systematic bias to that better than 0.2%. This could easily arise from variations in the moisture content, but your method can also introduce loss on ignition that may depend on the fusing time, so you better be managing that too. Also, any change in purity of the flux between the standards and samples can similarly spoil your ability to quantify at this level. Next, random influences are important. Are you measuring the peak intensity and the background such that when you propagate the error for the net intensity, you have a counting statistical error significantly below this level? Your peaks need to have at least 1 million counts to reach this level, even ignoring the background and other factors. At the accuracy you describe, errors are lurking around every corner and your ability to reach this level is limited by whatever factor is the worst. Good luck.

Victor Bergman
2 years ago
Victor Bergman 2 years ago

The accuracy you are looking for could be technically challenging. The spectrum will not help in this case. Hopefully calibration and co-efficient adjustment may get you closer to your target.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

Very good comments Andy. With respect to the recipes: The cloudy beads are most likely due to non-oxidized Sulphide. It is relatively hard to dissolve Sulfur unless it is present as Sulphate. If Sulfur is present in another form, particularly sulphide, then it may form cloudy beads. These beads are not necessarily inhomogeneous, but may well be. Solution in this case may be longer oxidation time. Maybe the amount of oxidant is insufficient to oxidize the Zn and S? Please notice that you are at risk of damaged Pt ware in case the wall is not protected well against the sample. Cloudy beads may also be formed because of improper cooling, when micro-crystals are being formed. If this is the case, then this may be circumvented by increasing the cooling speed. This may, however result in cracking beads in case the cooling speed is too high.

Helena Russell
2 years ago
Helena Russell 2 years ago

I would also agree with your assessment of the possible errors associated with not only this method, but any laboratory assay. I feel fortunate when my monitor ratios fall within +- 5%. But to take the square root of the sum of squares of all the uncertainties involved in your process and expect 0.2% accuracy (or precision) would be heroic, if not futile. If I could consistently demonstrate accuracy or precision within 2%, I would march into my supervisor's office and demand a sizable raise in salary.

JohnnyD
2 years ago
JohnnyD 2 years ago

While I agree with the others on the challenge of marking this analysis work, I would certainly look at the comparison data you have gathered so far to look for systematic biases. The two data points you have in your posit both show XRF shooting low. If there is a systematic bias, often resulting from the calibration, then I would correct this first and see where you are. If your data are randomly distributed, then that's a different story.

Alan Carter
2 years ago
Alan Carter 2 years ago

I guess there is a problem with dissolving sample into bead, first. Have you tried to pre-concentrate sample first and fuse using the same recipe or using flux without oxidizer? In my case generally it eliminates possible errors step by step. I usually pre-concentrate using diluted HNO3 @50-80C overnight.

Do you get similar correlation using known assayed powdered samples and not the fused bead?

You should be able to get close to 0.2% if you use known assayed pressed powder samples for calibration .Is it EDXRF or WDXRF?

Bill Fraser
2 years ago
Bill Fraser 2 years ago

Cloudy beads! I've been doing some fusion recently with zinc concentrate samples myself. It seems that if I fused the sample in a mixture of sodium nitrate and lithium tetraborate that the resulting fused bead were cloudy as you reported. However fusing the same sample in lithium nitrate, lithium metaborate and boric oxide - eutectic composition, gave better results. The compatibility of the sample and flux is the key here regardless of the physical state of the oxidant. Using LiT the more 'acidic' flux will inevitably lead the loss of sulphur as sulphur dioxide.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

I hope you have fixed the problem since that time 😉 If not, I take this opportunity to give you a potential approach that you can try mainly to obtain clear beads and improve your results. In your case, the problem should come from non-effective oxidation process. NaCO3 and/or your temperature program could not be enough to ensure a complete oxidation of your sample (unoxidized sample mean undissolved particles resulting in cloudy bead in some case). Also, the use of 100% LiT (Li2B4O7) is not appropriate to ensure a stable oxidation state of sulfur during fusion. You will lose considerable amount of sulfur (sulfites) during fusion and change your initial amount of sample, then your sample/flux ratio, so a direct incidence on the results. Here is my suggestion that can be use for a lot of unoxidized mineral sample:
* weigh your sample directly in the platinum crucible and oxidize it with acid (HNO3 or HCl) on a hot plate. (Use HNO3 in this case to form Zn(SO4) because you will form H2S (g) with HCl !!! bad compound and loss of sulfur !! )

* After the oxidation reaction, evaporate the excess of acid until dryness (very important because remaining acid can damage your platinum at high temperature and/or create very corrosive vapor for the instrument)

* Add your flux (I propose you 50/50 LiT/LiM in this case to stabilize sulfur into sulfate) and NWA in your crucible on the top of your oxidized sample and run the fusion. (you don't need oxidation step and things like that anymore in your fusion program)

I hope it can help for your ZnS sample or other unoxidized sample in the future 😉
Don't hesitate to contact me if you need more specific information about this technique

Bob Mathias
2 years ago
Bob Mathias 2 years ago

There is no way to accurately calculate wear life on crushing components. On one site a set of jaw liners could last 1000 hours, and on another site 100 hours. There are too many variables; material being crushed, particle size distribution, mPA of rock, LA index, gap setting, feeding habits, fines content, moisture content, pre-screening efficiency, abrasiveness of material, quality of liners, manganese content, good maintenance practices, etc etc.
You could estimate it by taking the above factors into consideration, but never be very accurate.

David
2 years ago
David 2 years ago

Use the Social Share Bar on the Left. Tell everyone you can about https://www.911metallurgist.com/metallurgy/ It's FREE & GOOD.

Please join and login to participate and leave a comment.

 

BUY Laboratory & Small Plant Process Equipment

We have all the laboratory and plant equipment you need to test or build/operate your plant.

ENTER our Mining Equipment' Store

We Sell EQUIPMENT for all types of Mineral Treatment PROCESSES and Laboratory Testing needs

Have a Mineral Processing QUESTION?

Come in, ask your question

911Metallurgist Community Forums

Talk to other metallurgists and be helped.

Need ENGINEERING Services or Plant TROUBLESHOOTING?

We can IMPROVE ALL PLANTS / Mineral Processing Engineering & LABORATORY Ore Testing

911Metallurgy Engineering

Contact us for process engineering, metallurgical investigations, plant optimization, plant troubleshooting, needs. WE “FIX” METALLURGY.