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Assessment of the Performance of Grinding Circuit for Buzwagi Gold Mine

Alphonce Wikedzi


It  had  been  reported  by  the  managementof  Buzwagi  Gold  Mine  (BGM)thatgrinding  circuit  was  designed  to  produce  final  product  size  of  125  μm,  which  hadnot been achieved for a long period of time under both, low to normal (i.e. 450-600t/h)  and  high  (i.e.  >  650  t/h)  throughputs.Also,  the  performancebehaviourof  thecircuit  had  not  been  reviewed  after  long  time  of  operation.  Hence,  an  evaluationstudy  was  conductedin  order  to  recommendimprovementin  mine  operations.  Thestudy   was   realized   through   threecircuit   survey   campaigns   and   laboratoryexperimentations.  From  the  surveys,  size  distributions  and  solids  contents  of  thesamples were determined for all selected circuit streams. Furthermore,grindabilityand  work  indices  of  the  ores  were  determined  through  standard  Bond  tests.  Thestandard Bond tests data revealed increased Bond work indices for currently treatedores  vs.  those  during  design,  indicating  change  in  ore  hardness  over  the  years.Consequently,  a  periodic  review  of  the  ore  blends  was  recommended  as  hardermaterial requires more energy,which increases operationcosts. Such reviews couldhelp  in  establishing  better  ore  blending  and  optimum  throughput  for  existing  plantdesign.  Furthermore,  the  SAG  mill  circuit  indicated  varying  feed  sizes  (i.e.xF,80=102 to 185 mm) which could be rectified by closer monitoring and control of ratiosfor  theSemi-Autogenous  Grinding  (SAG)mill  feeders  drawing  the  ore  from  thestockpile.  The  ball  mill  performance  was  poorasindicated  by  only  5-9  %  of<125μ m   (target   product)   in   the   discharge.   This   had   a   direct   impact   onhydrocyclones,  where  significantly  poor  performance  indicators  were  observed;coarser  overflow  xP,80:  >200  μ m  as  well  as  cutsize,  xT:  >200  μ m.  Also,  the  Bondefficiency  factors  in  the  range  of  48-61  %  were  obtained,  indicating  an  inefficientoperation  that  could  only  achieve  targets  by  lowering  the  current  throughput.Hence, an optimization study of the existing design through computer modelling andsimulation   isrecommended.Through   simulation   ofmulti-effects,   a   deeperunderstanding  of  the  efficiency  problems  for  the  BGM  grinding  will  be  facilitatedand also may provide possible solutions.

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eISSN: 2619-8789
print ISSN: 1821-536X