The Benefits of Better Classification in Grinding Circuits

© 2016 Derrick Corporation

The Benefits of

Better Classification

in Grinding Circuits

Eng. David Perkins – Derrick Corp

Global Average Concentrator

Energy Consumption

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

1995 2000 2005 2006 2007 2008 2009 2010 2011 2012

Energy/Ton Milled

Energy/Ton Conc

• Grades Decreasing

• Finer Grains

• Harder Ore

• Complex Minerology

• HSE Compliance

Why?

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

1995 2000 2005 2006 2007 2008 2009 2010 2011 2012

Energy/Ton Milled

Energy/Ton Conc

Mill – Cyclone Grinding CircuitThe Most Energy Intensive Unit Operation in Mining Today

Mill

Cyclone

Cyclone is easy to operate and can accommodate flowrate variations

It is inefficient

30-45% of product size returns back to mill

• Material overground

• Decrease flotation Recovery

• Increases power consumption


5

Mill – Cyclone (100 tph)

Every 100 tons of product generates

Remilling 90 tons of material that is already product size

80t of -75um

80%-75um100t

400t

90t of -75um30%-75um 300t

100t

Classification efficiency is only 50%

Circulating load = 300%


6

Mill – Screen (100 tph)

Circulating load = 100%

Classification efficiency 85-95%

Remilling 10 tons of material that is already product size

Every 100 tons of product generates

10t of -75um 100t

100t

10%-75um

200t

80t of -75um

80%-75um

100t

Separation Comparison

P80=70um

Hydrocyclone Derrick ® Stack-Sizer®

P80


8

Under and Overgrinding


9

Overgrinding Effects

Rougher flotation feed


10

Undergrinding Effects%

Ch

alc

op

yri

teRougher flotation tailings

CS MiningCopper Mine in USA

• Supplemented Cyclones with Derrick ® Stack

Sizers® and 100 micron panels

• Recovery Increase by 40% (50% to 70%)

• Maintained Concentrate Grade.

Sociedad Minera El BrocalPb/Zn Mine/Mill in Peru

• Primary Classification with Cyclones

• Circulating Load 350%

• Capacity 145 tph

• Pb Recovery 63%

• Zn Recovery 73%



• Cyclones Replaced by Derrick ® Stack Sizer ®

and 230 micron panels


• Idled 1 of 3 Ball Mills

• Capacity 245 tph

• Pb Recovery 71%

• Zn Recovery 78%


OJSC ApatitPhosphate Mine/Mill in Russia

• Cyclones used as Primary Classifiers

• P80 = 190 microns


OJSC ApatitPhosphate Mine/Mill in Russia

• Replaced Cyclones using Derrick ® Stack Sizer ®

with 390 micron panels

• Capacity increase by 30% - 60,000 tpd (total)

• P80 = 240 microns


• Cost per Ton Down by 20%

KMArudaIron Mine/Mill in Russia

• Replaced Cyclones with Derrick ® Stack Sizers®

and 100 micron panels

• Increased Capacity by 20%

• Reduced Circulating Load from 215 to 130%

• Idled 1 of 2 Ball Mills

• Recovery Increased from 82.2 to 84.6%

• Maintained Concentrate Grade



Plant examples

• Nexa Resources – Vazante

• Hydro – Paragominas

• Taboca – Pitinga

• Nexa Resources – Cerro Lindo

• Esan – Balya

• South India Iron Ore

• Glencore – Iscaycruz

• Penoles – Saucito I & II

• Many many more

A few comments about classification…

• 300 to 400% circulating loads are common with

cyclone classification to minimize overgrinding.

• Even so, overgrinding is a common

characteristic of cyclone circuits.

• Circulating loads of around 100% are common

with screen circuits and overgrinding is

minimized, thus driving efficiencies.

• Today limitations for screens have centered

around capacity.


23

Field trial

completed at

American Silica in

USA


24


25


26

Current 5-deck

Stack Sizer

(1.22 m wide)


27

New 8-deck

SuperStack

(1.42 m wide)


28

SuperStack

compared to

Stack Sizer

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