Karowe Comminution Circuit Upgrade

P. Morgan1, L. van Niekerk1, M. Duddy1 , G. Underwood2 and A. Paz3

1. DRA Global, Johannesburg, No. 3 Inyanga Close, Sunninghill, 2157, South Africa, paul.morgan@DRAglobal.com, lehman.vanNiekerk@DRAglobal.com, matthew.duddy@DRAglobal.com

2. Minopex, 7 Pinswood Office Park, 33 Riley Rd, Woodmead, 2196, gavin.underwood@minopex.co.za

3. Outotec Australia, 40 Kings Park Road, 6005 WA West Perth, Australia, andres.paz@outotec.com

Boteti are due to begin treating the significantly more competent (Unit13) kimberlites at their Karowe Diamond plant, Botswana &

wish to continue with AG milling as the “heart” of their process flow sheet.

Aim: – Assess current performance of the AG mill;

– Assess impact of treating harder kimberlites & increased throughput in the new/modified flowsheet;

– A Turbo-Pulp Lifter (TPLTM) system is anticipated to improve upon the original mill grate/pan lifter operation.

Interpreted Abrasion Factor, ta

Interpreted ta13

FK

S2

S1

y = 2.4x-1

Ap

pare

nt

Dw

i(k

W/m

3)

Observed Relative Grinding Rates

Relative Grinding Rates &DWi Relationship

Relative Hardness(Energy Basis)13

S1

S2

FK

U1

SL

New Circuit Design

• Outotec will provide their innovative

Turbo Pulp Lifter (TPLTM) system to

improve the discharge & grate efficiency;

• Two TPL™ designs will be incorporated:

• 90mm pebble ports for treatment of fragmented kimberlites (FK);

• 115mm pebble ports for hard kimberlites (Unit 13), early 2015.

Turbo-Pulp

Lifter (TPL™)

• DRA used an ‘in-house’ modelling tool to compare

against Outotec’s JKSimMet to assess the proposed circuit;

• Two surveys (S1 & S2) indicated that grate ports were ‘clogging

up’ & pan lifters were ‘retaining material’ that should escape the mill;

• Minerals being processed:

• Unusually hard for a kimberlite;

• Very abrasive, high DMS yields;

• Have high crushing strength;

• Low amenability to scrubbing;

• Large degree of variability (soft

sandstones & weathered kimberlites,

to more competent kimberlites,

mudstones & basalts).

• Using this relationship it was possible to

simulate the mill-crusher circuit

performance when ‘treating’ the

harder ores;

• Initial design trial simulations

indicated that partial pre-crushing,

modified grate design & bypass

screening was necessary to control the

mill overloading;

• Less fines were going to be produced,

potentially overloading the existing DMS circuit;

• High DMS yields are also anticipated on harder ores.

Simulation

Results

Circuit

Benefits

Back-

ground

Weathered

& soft

Bulk

Sample

Milling plant

sampling

audit 2

Milling plant

sampling

audit 1

Fragmented

Kimberlite

Unit 13 Hard

Kimberlite

Deeper material is

more competent

• The fully-

autogenous mill:

offers flexibility for high

variability in the ore;

combines crushing &

scrubbing steps;

• A secondary gyratory crusher will crush a

proportion of jaw crusher product for a consistent

feed to the AG mill;

• Mill discharge screen recycles +60mm directly & combines

with -60mm+32mm LDR tails to the existing pebble crusher;

• Pebble crusher product can be partially split to

bypass mill recycle;

• XRT bulk sorting for Large Diamond

Recovery (LDR);

• -8mm+1.5mm fraction will be

treated in the existing DMS;

• TPL™ for improved

mill capacity &

efficiency.

Benchmarking

showed that the mill

would receive material

significantly harder in the

future (Unit 13) than

seen in the past

(S1 & S2).

Good

Attrition

Good Impact

Slurry

Pool

Poor Impact

Improper

Attrition Turbo

Pulp

Lifter™

Radial

Pulp

Lifter

Sam

ple

Po

pu

lati

on

Dwi(kW/m3)

Karowe Drop Weight Testwork

SMC Karowe Data

PopulationDistributionModel

FK

13

S2

S1

A significant degree of hardness

variation is shown, that prescribes

virtually the complete spectrum

of DWi values.

Published DWidatabase

distribution superimposed

PEBBLE CRUSHER

MILL FEED STOCKPILE

MILL FEED PRE-CRUSHER

EXISTING MILL

+60mm

+1.5x60mm

FINES DMS

JAW CRUSHER

-1.5mm

LARGE DIAMOND RECOVERY

(LDR)

LARGE DIAMOND RECOVERY

(LDR)

CONCENTRATE

PEBBLE BLEED SPLITTER

- 32mm

+32x60mm

+20x32mm

LARGE DIAMOND RECOVERY

(LDR)

MIDDLES BULK

SORTERLARGE DIAMOND

RECOVERY (LDR)

FINES BULK

SORTER

-20mm

+1.5x8mm

TERTIARY CRUSHER and DEWATERING

+8x14mm

+14x32mm

1

7

8

14

15

16

17

12

20

18

+8x60mm

19

42

56

9 10

11

13

ROM FEED

THICKENER FEED

GRITS

TAILS

RECOVERY FEED

CONCENTRATE

Current

Circuit

Constraints

(-8mm)

Legend:

T = Tails

C = Concentrate

T

T

C

C

+32mm

+1.25x8mm

-1.25mm

+1.25x8mm

BLEED

SCREENING

T C