21 Oct 2014

New minerals processing techniques may offer you increased efficiency or may saddle your project with a white elephant, and finding out ahead of time is not always straight forward.

a multifaceted engineer once contrasted for me the work of an electrical engineer and that of a chemical engineer. the electrical engineer does all of his work on paper, and in the modern setting, on the computer. he can draw a design for an entire substation, and as it is on paper, so will it work once construction is complete. not, so for the chemical engineer; his initial rudimentary designs will be refined and revised as trials progress from lab scale, through pilot scale to commissioning and even during operation. for the extractive metallurgist designing his plant’s flowsheet, data from lab scale testing is critically important to ensure that before massive capital outlays are made, the response of the particular ore body’s minerals to the unit processes is well understood.

with some of the newer technologies to come onto the scene recently, lab scale testing is difficult or impossible to perform. this is particularly true in the field of comminution, where high pressure grinding rollers (hpgr), vertical shaft impact crushers (vsi crushers) and isamills are revolutionizing  the way we go about reducing particle size, while bringing with them a suite of challenging scalability issues.

the hpgr is exactly what it sounds like; two big cylindrical rollers mounted horizontally, axes parallel to one another and almost touching. material is fed into the top and the rollers rotate to grind it up, expelling the product out of the bottom. a critical parameter in the design of a hpgr circuit is the angle at which the material is frictionally held between the rollers and pulled downward against high pressure to actuate breakage. this is known as the nip angle. as you can probably visualize, the nip angle will be dependent on the diameter of the rollers and the size of the ore particle. this leads to obvious scalability issues when trying to test the performance of hpgr on your ore types. at a recent industry exhibition i had the chance to speak to a vendor about the recent advances in hpgr technology. there have been some great steps forward in roller surface materials that provide a gripping texture to improve performance. unfortunately, as far as testing goes, there have been no breakthroughs; they still recommend any potential users to send several tones of unprocessed material to their full scale testing facility.

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