Grinding & Classification Circuits

Grinding & Classification Circuits 2017-03-23T09:46:37+00:00
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Spiral classifier or hydrocyclone (7 replies and 1 comment)

Alan Carter
5 months ago
Alan Carter 5 months ago

what is better for classification of copper up to 75 micron size whether to use spiral classifier or hydrocyclone

Marshal Meru
5 months ago
Marshal Meru 5 months ago

Down at 75 um you use cyclones for optimum particle classification.

5 months ago
Modine96069 5 months ago
1 like by David

A hydrocyclone has no moving parts, has a smaller footprint but is less efficient.

a spiral classifier has moving parts, a much larger footprint but is more efficient if correctly set up (feed density) weir height and calming zone.

if you have a spiral classifier, use it, if you do not have one, install hydrocyclones

5 months ago
Romain CADENAT 5 months ago
1 like by Cyanide

If you want to do a classification based on grain size, hydrocyclone is the most appropriate. 

If you want to make a classification based on density (separation of two different minerals) spiral classifier is better. 

4 months ago
AskDerrick 4 months ago

Derrick screen is the best choice for 75 micron cut as it gives you the highest separation (classification) efficiency because it simply separate by physical size.

Sugar Watkins
4 months ago
Sugar Watkins 4 months ago

Hello Mr. Derrick Screen,

would you please complement your "answer" with good reasons and comparisons with spiral classifiers and cyclones? Am looking for technological advantages and capital cost comparisons. You must have supporting data in separation efficiency improvements &  performance of a Derrick screen to carrying it purchase price?

Please do not refer us to your website; write a valuable technical answer here.  

4 months ago
Khosana 4 months ago


Based on my experience, spirals tend to drop in efficiency at below 150microns.


4 months ago

hi, thank you for your reply
do you have any papers or document to support the statement that below 150 microns spiral is not efficient.

4 months ago
David 4 months ago

A friend familiar with this told me the main problem with spiral classifiers is the cut size is directly proportional to retention time (flow rate, Stoke's law, that sort of thing). To get a fine cut size requires flow of almost zero = the finer you want to cut, the lower the flow and density required.

Hitzrot, H. W. wrote a great paper in Society for Mining, Metallurgy & Exploration Mineral Processing Handbook called "Mechanical Classifiers".

The principal use of mechanical classifiers has been in closed circuit wet grinding; however, this application has been widely displaced over the past few decades by the hydrocyclone. The hydrocyclone installation, including its feed pump, offers lower capital costs and requires less floor space.

However, these advantages of the hydrocyclone are being gained at the sacrifice of some of the advantages of the mechanical classifier. The mechanical classifier requires less power and has lower maintenance costs than the hydrocyclone and its feed pump. The underflow product from the mechanical classifier can have a higher solids content and contain less entrapped undersize particles than the comparable product from the hydrocyclone. Consequently, it is capable of operating at a higher classification efficiency. A reduced circulating load results under these conditions in a closed-circuit grinding application.

The proper selection of mechanical classification equipment requires that the properties of the solids and liquid are adequately defined. The following descriptive information regarding the solids is desired: feed rate, chemical and physical composition, density, temperature, size analysis, and desired separation size.

Review in details.

The 2 videos at the bottom are classifiers with 50 TPH of overflow at 140 um and 35-40% solids.

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