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Laser Particle Size Analyzer and Wet Sizing (8 replies)
Given the variation in measurement principles for different approaches, it probably should not be surprising the correlations vary and are often weak.
In the past some of those I've looked at include:
- * laser (different systems) vs. sieves
- * ultrasonic vs. sieve
- * feeler gauge (Outokumpu) vs. sieve
- * etc. vs. sieve
The relationships varied depending on the system (mineral / ore and measuring device).
Further, for particularly fine (ultrafine) particles a controlling factor was the dispersion regime.
In any physical sizing process or test you will have some oversize in the undesrs and some underzie in the overs as physical test are not 100% accurate. Achieving a 95% accuracy is actually very good.
This comes from the fact that a particle that a particle that has 1 dimension greater than your opening, and two dimensions smaller can pass the wet screening opening, but can report as oversize on the laser scan.
If you need to have a product that is absolutely 100% minus 75 microns, classify at 70 microns and you will achieve probably 99% on the laser.
If you run the test multiply times you can probably derive a factor for your lab and material, but you should repeat this periodically to re-verify.
%(-xi) = %(-xi)MastreSizer * [%(-38 microns)sieve / %(-38 microns)MasterSizer]
%(-xi)= reconstructed % passing size xi (xi < 38 microns)
%(-xi) MasterSizer = % passing size xi obtained by MasterSizer
%(-38 microns)sieve = % passing 38 microns obtained by sieving
%(-38 microns) MasterSizer = % passing 38 microns obtained by MasterSizer
+ You could also contact Outotec they have the PSI 500 and they are experts in these calculations.
There isn't a general adjustment factor. Every ore will have a different one. You will need to do some screening, take the products of the screening and do an analyse in the laser. When you get the results from the laser you will need to do a graphic (dispersion) and the R2 of the equation of this graphic will be the adjustment factor for this ore. You need a good number of screening to have enough information for getting a good statistical analysis. I did it in the past with iron ore and worked very dell.
I used the Malvern and a slurry with low % solids, as Malvern procedure.
The suggestion by Bill is a good one. This is the method we used years ago at the Noranda Technology Centre for comparing grinding technologies. Typically the laser method will yield a larger diameter (the individual particles are rotating in the fluid medium so appear larger), hence they will appear as a coarser size distribution as well. The closer the particles are to a round shape (e.g a cube of galena) the smaller the difference. As Bill suggests, there should be a decent correlation when plotted against each other if you want to compare data obtained by the different methods. Since different minerals will fracture into different general shapes there will be a different correlation for each mineral although in practice many break into similar shapes.
There is no one-size-fits-all factor to correlate particle size information from one measuring technique to another. The particle shape affects the techniques differently. If your particles are spherical the results will not likely vary significantly. On the other end of the spectrum, highly acicular particles will give very different results. For example, a particle 75 micron diameter with 750 micron length can still pass a 75 micron screen, but the laser analyses the largest cross sectional area (10X more) and calculates a size >200 microns. A sedimentation sub sieve analyser will give a result somewhere in between.
As suggested by others, it would be imperative to derive an empirical correction factor for your specific application.
You indicate that you are producing a product of your client. In this situation, using a different measuring technique is very dangerous. If your correction factor is not exactly correct, or there is a minor change in the ore mineralogy leading to a shift in particle shape, you may ship material that does not met the customers specification (based on their measurement) or worse it may not meet the customer requirements and cause downstream problems.
I had a similar problem awhile ago, I found this reference had some useful information:
https://pure.ltu.se/portal/files/5204942/Tobias_Andersson_Doc2010.pdf
http://docslide.us/documents/chapter-2-particle-size-estimation-and-distributions.html
Anyone can share of any factor or adjustment of the Laser Particle Size Analyzer (LPSA) to wet sizing? We have a sample that 100% pass 75 micron. The problem is the LPSA still identify 5% particle of larger than 75 micron. Triplicate sample still showed similar result. The objective is to evaluate two different grinding methods. The previous application was to produce a magnetite product of one of our client. We are currently working with The Malvern Tech Representative for several types of sample. This is a Manganese ore, the application is set of metallurgical test. This also happen for our magnetite sample. which end application is heavy media separation.