The application of flotation test work to plant design and ... · PDF file• Marula...
Transcript of The application of flotation test work to plant design and ... · PDF file• Marula...
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The application of flotation test work to plant design and
operationMichael Valenta
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Mintek Test Work 1987-1994• Laboratory Test Work
• Pilot Plant Test Work
• Full scale plant operation
• Development of a scale-up procedure
• Introduction of Unit Cells on Mill discharge
• Modelling of the Flotation Process
• Development of a flotation simulator
• Development of the “Mintek 2-concentrate process”
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Optimisation Methodology• Establish a relationship with operations team
• Have monthly FIXCO meetings
• Conduct sampling campaigns
• Mineralogical analyses
• Fractional analysis
• Hot floats of pertinent streams
• Implementation and monitoring of agreed strategies
• Data analysis and feedback
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Case Study 1
Effect of Pulp Rheology
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Project Description• Marula Platinum initiated project in conjunction with Metallicon Process
Consulting to determine process bottlenecks and characterise plant performance
• Surveys identified rougher concentrate thickeners as operational bottlenecks
• Surveys also pointed to low cleaner efficiencies
• Second survey initiated to determine potential cause of low cleaner efficiencies
• Results from both reported here.
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Process Description• Nameplate capacity of 165 ktpm treating UG2 ore on Eastern Limb
of Bushveld Complex
• MF2 type circuit (mill-float-mill-float) with two stage upfront crushing and SAG ball mills.
• Rougher concentrate thickened and attritioned (at SG >1.6) before density reduced (SG = 1.35 – 1.45) and fed to cleaner circuit.
• Cleaner circuit flexible to operate as 2/3/4 stage cleaners.
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Process Flow DiagramMilling
Thickener
Rougher float
Re-cleaners (2/3 stage)
Cleaner float
Attritioners
To secondary float
Final concentrate
Tailings
Tailings
Dilution water
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Preliminary Test Work• Initial campaign very generalised and included hot batch floats in lab
cell on major streams
• Initial campaign included mass balance sample campaigns, screening analyses and down the bank samples.
• Results from mass balance survey and routine plant data indicated high rougher efficiencies but poor cleaner efficiencies
• Data was confirmed by hot batch floats results.
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Grade Recovery CurvesRougher Conc
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Grade Recovery CurvesAttritioner Discharge
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Discussion• Three potential causes identified
– Lack of reagents (specifically collectors) due to thickening and attritioning– Effect of “ageing” (or oxidisation) in thickeners (not confirmed)– Effect of increased density in cleaner feed compared to rougher concentrate.
• Reagent addition to cleaners increased significantly with no improvement noticed.
• Test work through hot floats and plant trials were initiated to evaluate density effect.
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Effect of changing density
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Recovery Density relationship
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Case Study 2
Tackling the chromite problem in UG2 flotation
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Characteristics of UG-2 Ore
• Major Source of PGM’s• Two major gangue phases
– Chromite (25% to 40%)– Siliceous gangue phase
• Specific gravity circa 3.8• PGM’s occur in a variety of minerals• Mode of occurrence of PGM’s varies• Low base metal sulphide content
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Challenges in Processing UG-2
• Mode of occurrence of PGM’s• Two predominant gangue phases
– Different physical properties– Different chemical properties
• Concentrate mass pull limitation• Stringent chromite specification in
concentrate grade to smelter
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Typical Results on UG-2 ore
• Concentrate PGM+Au Grades– Range from 80 g/t to 350 g/t
• Concentrate Chromite Grades– Range from 2.5% to +6%
• Recoveries– Range from 75% to +90%
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PGM+Au Grade vs Chromite Grade
0
50
100
150
200
250
300
350
400
450
0 1 2 3 4 5 6
Chromite Grade [% Cr2O3]
PGM
+Au
Gra
de [g
/t 4e
]
.The grades in the industry
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Various Strategies
• Reagent optimisation• Circuit configuration• Application of alternative technology• Compromising recovery to meet
specifications
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Sub-Processes in Flotation
Froth Phase
Pulp Phase
Flotation EntrainmentDrainage
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Sub-processes in UG-2• Flotation
– PGM+Au (primary)– Copper and Nickel Sulphides (primary)– Siliceous Gangue (secondary)– Chromite (negligible)
• Entrainment– PGM+Au (secondary)– Copper and Nickel Sulphides (secondary)– Siliceous Gangue (primary)– Chromite (primary)
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Strategy
• Maximise PGM+Au recovery through flotation
• Minimise chromite recovery through entrainment
• Judiciously add depressant to reduce silicates recovered by flotation
• …. without increasing chromite grade
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Laboratory study
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Laboratory Testwork• Batch testwork in Denver D12 machine• Grind : 80% -75 micron• Reagents
– Copper Sulphate– SIBX– Depressant (CMC)– Frother (Dow 200)
• Test parameters– Solids Concentration– Frother Concentration– Depressant Concentration
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Effect of Solids Concentration on Solids Recovery
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2
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7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Solids Concentration [g/cc]
Solid
s Rec
over
y[%
]
Ore A Ore B Linear (Ore A) Linear (Ore B)
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Effect of Solids Concentration on PGM+Au Grade
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40
60
80
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140
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Solids Concentration [g/cc]
PGM
+Au
Gra
de [g
/t]
Ore A Ore B Linear (Ore A) Linear (Ore B)
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Effect of Frother Concentration on Solids Recovery
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2
4
6
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14
0 20 40 60 80 100 120
Frother dosage [g/t]
Solid
s Rec
over
y [%
]
Ore A Ore B Linear (Ore B) Linear (Ore A)
NB !!!!
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Effect of Frother Concentration on PGM+Au Grade
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10
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40
0 20 40 60 80 100 120
Frother dosage [g/t]
PGM
+Au
Gra
de [g
/t]
Ore A Ore B Linear (Ore B) Linear (Ore A)
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Effect of Depressant Concentration on Solids Recovery
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0 50 100 150 200 250 300
Depressant dosage [g/t]
Solid
s Rec
over
y [%
]
Ore A Ore B Linear (Ore B) Linear (Ore A)
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Effect of Depressant Dosage on PGM+Au Grade
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5.00
10.00
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20.00
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30.00
35.00
0 50 100 150 200 250
Depressant dosage [g/t]
PGM
+Au
Gra
de [g
/t]
Ore A Ore B Linear (Ore B) Linear (Ore A)
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Effect of Depressant on Chromite Grade
0
5
10
15
20
25
0 50 100 150 200 250
Depressant dosage [g/t]
Cr 2
O3 G
rade
[%]
Ore A Ore B Linear (Ore B) Linear (Ore A)
NB !!!!
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Observations on Plants
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Plant Observations• Depressant is successful in improving PGM+Au
grade• Depressant may result in an increase in
chromite grade• Selection of depressant dosage points is
important
• Frother and solids concentration have a significant effect on entrained solids to concentrate
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Effect of High Depressant Dosage on Fast Floating Fraction
Effect of High Depressant Dosage on High Grade Concentrate
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0 200 400 600 800 1000 1200 1400 1600
PGM+Au Grade [g/t]
PG
M+A
u R
ecov
ery
[%]
.
500 g/t700 g/t900 g/t
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Application of findings
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Successful reduction in final concentrate chromite grade
0
0.51
1.52
2.53
3.54
4.5
0 5 10 15 20 25 30 35 40
Frother dosage [g/t]
Fina
l Cr 2
O3 G
rade
[%]
Western Ore Eastern OreLinear (Western Ore) Linear (Eastern Ore)
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Conclusions and Recommendations
• Chromite and PGM+Au grade targets can be successfully achieved through reagent optimisation
• Effect of solids and frother concentration on entrained mass is significant
• Increased depressant may result in an increase in chromite grade
• Selection of depressant dosage points is important
• Optimisation of reagent suite by starting from scratch• Greater understanding of entrainment required
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PGM+Au Grade
• Been able to increase grades from circa 100g/t to over 200g/t
• No decrease in PGM+Au recovery• No increase in chromite grade
• Major reduction in tonnage to the smelter
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Challenges
• Interrupting the comfort zone• Lack of buy-in• Inappropriate flotation cell sizing• Skills shortage• Unstable feed characteristics• Poor plant control