COMMINUTION AND CRUSHING
measurable results that help our customers improve their revenue .”
Collahuasi is a mine with three open-pit ore deposits located in Chile . Collahuasi has been working with ME Elecmetal ’ s FIT System for several years . “ Operationally , we have made huge progress working with ME Elecmetal , and not just because we have improved our grinding efficiency . Formerly , grate plugging events occurred frequently and were difficult to troubleshoot since there were two vendors involved , one for liners and another for the media . By implementing the FIT System , we were able to control one of the key variables , which is the grinding media ”, explains Claudio Muñoz , Superintendent of Process Engineering at Doña Inés de Collahuasi mining company . Regarding grinding media consumption , Collahuasi has also had a positive development . “ We achieved a 22 % reduction in the wear rate of grinding balls in the 40 ft SAG mill and just finished the analysis on another of our mills with a 24 % reduction in terms of reduced wear rate . So , there is a net economic advancement ”, says Muñoz .
Outotec ’ s GrindForce - back to basics
Stirred milling and attrition type grinding , Outotec says , “ has overtaken traditional tumbling mills and impact grinding to become the comminution benchmark for regrinding circuits in flotation plants and fine grinding in leaching operations , due largely to energy efficiency gains .”
This major shift towards stirred milling has predominately been driven by the decreasing mineral particle liberation sizes of today ’ s mined ore deposits , where finer grinding requires significantly more comminution power . In addition , ore head grades are decreasing , resulting in the need to crush and grind more rock to produce the same amount of valuable metal .
“ With the current drop in commodity prices , the mining industry requires innovative technologies and solutions that can reduce operating costs and a key area for improvement is energy savings . Outside the mining sector , there are technologies that can have valuable crossover applications . Of particular note are opportunities for technology and know-how crossover arising from the similarities between the hard rock mining and industrial minerals industries .” One such crossover technology from industrial minerals is the Outotec HIGmill™ , which was developed over many years with the primary design motivation being significant energy savings for the grinding of fine particles .
The HIGmill itself is a vertical , fine grinding , stirred mill comprising a drive train attached to a rotating shaft within a stationary grinding chamber shell . Attached to the shaft are GrindForce rotating grinding rotors , not flat discs like in traditional stirred mills . These grinding rotors agitate and mix the bed of fine ( 2 to 6 mm ) ceramic grinding media producing a highly efficient , attrition grinding environment . Attached to the shell are GrindForce counter stator rings , again unique to the HIGmill design . Feed slurry moves upwards and passes into the grinding zones between these stator rings and the wall lining . Due to the vertical arrangement of the HIGmill , classification is conducted simultaneously throughout the grinding process with larger particles remaining longer at the peripheral where there is a high concentration of media particles , while smaller particles move upwards . The stator rings create separate grinding zones around each rotor , and the HIGmill has between 15 and 20 of these zones , more than any other stirred mill on the market . In addition , these distinct stator rings force slurry and media to each grinding zone , eliminating any possibility of particle short-circuit or dead zones within the grinding volume of media which occupies between 60-70 % of the total mill volume .
“ Ideas in physics can explain fundamental mechanisms of stirred milling , in particular the HIGmill which was developed over many years
The keys to the new Outotec HIGmill design are the agitator ( grinding rotors ) and grinding chamber stator rings themselves , just like the rotor and stator in a mechanical flotation cell
with the design motivation of power savings . The HIGmill ’ s unique tubular vessel design with grinding rotors and stator rings operating in plugtype flow is ideally suited for efficient , stirred mill grinding of mineral particles in slurry streams .”
From a particulate technology point of view , the product quality and grindability in a HIGmill is determined by three main factors , namely ; 1 . shear and compression stress mechanisms generated by the grinding media ; 2 . frequency a feed particle is stressed ; 3 . intensity of each stress event .
GrindForce is the trade name for Outotec ' s new profiled grinding rotor for use in stirred milling , taking its name from the very successful FloatForce ® technology , which like GrindForce , is
International Mining | MARCH 2017