# Laboratory Testing & General Mineral Processing Engineering

Laboratory Testing & General Mineral Processing Engineering 2017-04-04T06:57:51+00:00
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## Using a Pycnometer to Determine the SG of rock (7 replies)

Bill Fraser
2 years ago
Bill Fraser 2 years ago

Can you assist me with a method that I can use to determine the Specific gravity of a gold ore other than the Pcynometer method. I have the Pycnometer specific gravity test procedure and how to use a pycnometer but am looking for more methods used to determine the density of a solid.

Victor Bergman
2 years ago
Victor Bergman 2 years ago

What's the issue with pycnometers? A very simple test as long as you have the right grind, weights to 4-decimals and accurate meniscus volume measurement...if the flask volume is too small, switch to 25 ml or 50 ml.

You can use a Le Chatelier flask this method is very simple.

Specific Gravity Flask (Le Chatelier): For determining the specific gravity of hydraulic cement, dust, sand and other fine materials. The body holds approximately 250ml. The oval bulb in the neck holds 17ml. Volume below the bulb is graduated from 0 to 1.0ml in 0.1ml subdivisions, with an additional 0.1 subdivision below the 0 and above the 1.0ml mark. The neck is graduated from 18 to 24ml in 0.1ml subdivisions above the bulb (white graduations). The stopper is a number 13.

Maya Rothman
2 years ago
Maya Rothman 2 years ago

What sensitivity do you want? Using a graduated cylinder, a balance and water is a simple method to determine the specific gravity. You determine the weight of water displaced by a known weight of solid. Solid weight divided by water displaced weight is the specific gravity. Please look up Archimedes to better understand this process. https://en.wikipedia.org/wiki/Archimedes

JohnnyD
2 years ago
JohnnyD 2 years ago

Can you say your concern about using a pycnometer? You may have to use a little wetting agent (back in the day we used methylated spirits) to ensure you could get full submersion of the sample, otherwise it is a good method provided your sample is fine enough to get into the vessel.

Alan Carter
2 years ago
Alan Carter 2 years ago

A pyknometer is good for wettable finely ground samples but getting a representative sample of a few grammes can be hard. For gold ores the nugget effect is a large potential problem. The measuring cylinder is fine for most ores and can be used on fairly coarse ores. Typically, you would run a number of determinations and average them to reduce variations. If porous, you need to either evacuate the air so the water is forced into the pores, or grind the sample to reduce the effect of the pores. If not sure, measure coarse and then ground, if higher when ground, you have porosity.

You can get results to 2 decimal places fairly easily with a measuring cylinder, providing you are careful. I have yet to find a reason why density need to be known any more precisely. All projects should undertake periodic SG determinations of the ore body as it will change throughout a deposit. However, most projects don’t.

Bill Fraser
2 years ago
Bill Fraser 2 years ago

My concern with the pycnometer is the form of my material its not grounded and wanted to avoid challenges associated with finely ground ore as highlighted. So a method which utilizes ore which is not grounded will be ideal and also looking for the methods that can be applied highlighting the porosity acceptable.

JohnnyD
2 years ago
JohnnyD 2 years ago

Ok, I thought that might have been the reason. The measuring cylinder method should work out ok for you. You probably should do duplicates or triplicates just to make sure you have a handle on your precision.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

Pycnometers work well if there is zero porosity, either as pores in the rock, or as open spaced fractures. Bulk Density is the term used for measurement that includes the open spaces, whether its a crushed product or in Situ rock. For a finely crushed product I would do some kind of bucket test, getting the best possible volume of a bucket full, and ensuring it was completely dry before weighing. The larger the sample you can use, the lower the error, so for larger sized products, I'd go even bigger. There has been a lot written about Bulk Density measurement, and I'd look into the literature about it.

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