Post Lab Discussion

Bond Ball Mill Work Index

Procedure

Work Indices

• Measures of the energy necessary to break a particular type of ore

• Relates the power input and the reduction ratio in comminuting ore

• Generally dependent on material; but some equipment factors should be considered when using different methods for determining WI

Bond’s Energy Equation• Derived from FC Bond’s 3rd theory of

Comminution

• Generally used for all equipment!

EFFP

WE i

1110

E = energy input, in KWh/MT or HP F = Feed size in microns P = Product size in microns EF = Efficiency Factor

Bond Ball Mill Grindability Index

• This parameter controls the calculation of the basic energy requirements of the comminution circuit

• It can be used to determine the grinding power required for a given throughput of material under ball mill grinding conditions

• It is the most important parameter

Bond Ball Mill Grindability Index

• 12-in diameter by 12-in long (internal dimensions) horizontal axis mill with rounded corners and a smooth lining. There are no lifters. The mill rotates at 70 rpm

Bond Ball Mill Grindability Index• BWI Equipment

• Data obtained: Grindability

Grindability

• A material property• Defined as the ease at which a mineral particle

is reduced to a prescribed size, given the amount of energy input

• For BMWI test, grindability is the net grams of undersize product per revolution of mill

Bond Ball Mill Grindability Index• Equation is given as:

FPGp

W

bpi

i 11

45.4

82.023.0

pi = test sieve size in microns Gbp = grindability P = product size in microns F = Feed size in microns

Procedure

1. Set the test sieve size (100 mesh = 150μm)2. Prepare 10 kg of 100% passing -6 mesh of

sample (the FEED)3. Obtain an initial particle size distribution

– Should be representative!

4. Determine % of undersize of the FEED

Procedure

5. Pack fill a 1000-mL plastic graduated cylinder to 700mL level,

– This fraction shall be the constant charge weight

6. Set aside the remaining sample for replenishment

7. Determine the weight and bulk density

Procedure

8. Determine the intended product passing (IPP) by dividing the 700mL material weight by 3.5

Intended Product Passing

• The target weight of material as 100% PRODUCT UNDERSIZE with 250% circulating load

• Illustrative example:– Feed weight of 700mL sample = 1050 grams

Intended Product Passing

– 300 grams is the 100% (target undersize weight)– 750 grams is the 250% (target circulating load)– 300 + 750 = 1050– 100% + 250% = 350% = 3.5!

gramsIPP

gramsIPP

3005.3

1050

3.5

700mL Weight,Feed

Procedure

9. Run in the ball mill for 100 revolutions (initial, arbitrary)

10. remove the charge from the ball mill, ensuring that all material is recovered

11.Screen the material using test screen for oversize and undersize

12.Fill-in the table

Bond Work Index TablePeriod Weight, grams # of

revsWeight, Grams Net Under

size per Rev

% Circu-lating Load

Fresh Feed Undersize, fresh feed

Over size Under size

Net Undersize

1

2

3

4

5

6

7

8

9

10

Example

• Sample: 10 kg of Calcite (Limestone) from Camp 6, Benguet

Example

• PSA of feed Calcite (100% Passing 6 mesh)

Example

• PSA of feed Calcite (100% Passing 6 mesh)

Formulae

• Fresh feed = weight of fresh feed = weight of 700mL material

(for period 1 only!)

• Weight of 700 mL sample = 1,285 grams



size per Rev

% Circu-lating Load



Net Undersize

1 1,285

2

3

4

5

6

7

8

9

10

Formulae

• Undersize Fresh Feed

* Based on PSA of feed, 15.28%

35.196

1528.0285,1

*Undersize%FeedFresh ofWeight



size per Rev

% Circu-lating Load



Net Undersize

1 1,285 196.35

2

3

4

5

6

7

8

9

10

Formulae

• # of Revolutions = 100– Arbitrary, for the 1st period only!



size per Rev

% Circu-lating Load



Net Undersize

1 1,285 196.35 100

2

3

4

5

6

7

8

9

10

Formulae

• Weight Oversize– Weight of material retained on test screen

• Weight Undersize– Weight of material passing the test screen

• Screening is done AFTER the prescribed revolutions are applied!



size per Rev

% Circu-lating Load



Net Undersize

1 1,285 196.35 100 850 435

2

3

4

5

6

7

8

9

10

Formulae

• Net Undersize

65.238

35.196435

FeedFresh ersize,Weight UndersizeWeight Und



size per Rev

% Circu-lating Load



Net Undersize

1 1,285 196.35 100 850 435 238.65

2

3

4

5

6

7

8

9

10

Formulae

• Net Undersize per Revolution

39.2100

65.238

sRevolution of #

izeNet Unders



size per Rev

% Circu-lating Load



Net Undersize

1 1,285 196.35 100 850 435 238.65 2.39

2

3

4

5

6

7

8

9

10

Formulae

• % Circulating Load

40.195435

850

ersizeWeight Und

OversizeWeight



size per Rev

% Circu-lating LoadFresh Feed Undersize,

fresh feedOver size

Under size

Net Undersize

1 1,285 196.35 100 850 435 238.65 2.39 195.40

2

3

4

5

6

7

8

9

10

Procedure

13. Discard ALL the screened undersize14. Replenish the oversize from the set-aside

sample, with the SAME AMOUNT discarded* to maintain the total weight of charge (1285 grams)

*ensure that proper representative sampling is performed to obtain replenishment mass!



size per Rev


fresh feedOver size

Under size

Net Undersize

1 1,285 196.35 100 850 435 238.65 2.39 195.40

2 435 66.47

3

4

5

6

7

8

9

10

Procedure

15. Determine the # of Rev for Period 2 using the formula:

*IPP is computed as 367.14 grams (1285/3.5)

Revper izeNet Unders previous

feedfresh Undersize,-*IPP Rev of #

Procedure

126 Rev of #2.39

66.47-367.14 Rev of #

Revper izeNet Unders previous

FeedFresh Undersize,-*IPP Rev of #



size per Rev


fresh feedOver size

Under size

Net Undersize

1 1,285 196.35 100 850 435 238.65 2.39 195.40

2 435 66.47 126

3

4

5

6

7

8

9

10

Procedure

16. return the replenished charge (previous oversize + replenishment = 1285 grams) to the ball mill

17. run the mill based on the computed # of revolutions

18. repeat steps 10-17, until convergence is reached!



size per Rev


fresh feedOver size

Under size

Net Undersize

1 1,285 196.35 100 850 435 238.65 2.39 195.40

2 435 66.47 126 870 415 348.53 2.77 209.64

3 415 63.41 110 915 370 306.59 2.79 247.30

4 370 56.54 111 915 370 313.46 2.82 247.30

5 370 56.54 110 915 370 313.46 2.84 247.30

6 370 56.54 109

7

8

9

10

Procedure

• Convergence is reached when:– The last three (3) entries for % Circulating Load is

at 250 ± 5%– The Weight Undersize approaches the IPP value

(367.14 grams)



size per Rev


fresh feedOver size

Under size

Net Undersize

1 1,285 196.35 100 850 435 238.65 2.39 195.40

2 435 66.47 126 870 415 348.53 2.77 209.64

3 415 63.41 110 915 370 306.59 2.79 247.30

4 370 56.54 111 915 370 313.46 2.82 247.30

5 370 56.54 110 915 370 313.46 2.84 247.30

6 370 56.54 109

7

8

9

10

Procedure

19. When convergence is reached, DO NOT DISCARD the last screened Undersize

20. Determine the particle size distribution of the last screened Undersize

Example

• PSA of the last screened Undersize

Example

• PSA of the last screened Undersize

Procedure

21. Compute the average of the last three (3) entries for the Net Undersize per Revolution

22. this value is taken as the GRINDABILITY of the sample!



size per Rev


fresh feedOver size

Under size

Net Undersize

1 1,285 196.35 100 850 435 238.65 2.39 195.40

2 435 66.47 126 870 415 348.53 2.77 209.64

3 415 63.41 110 915 370 306.59 2.79 247.30

4 370 56.54 111 915 370 313.46 2.82 247.30

5 370 56.54 110 915 370 313.46 2.84 247.30

6 370 56.54 109

7

8

9

10

Example

• Test sieve = 100 mesh = 150 μm• Grindability = 2.818 grams/rev• 80% Passing size of feed = 1,654.40 μm • 80% Passing size of product = 97.89 μm

Example

• Equation is given as:

FPGp

W

bpi

i 11

45.4

82.023.0

pi = test sieve size in microns Gbp = grindability P = product size in microns F = Feed size in microns

Example

• Substituting the values:

Mt

kWhr 86.7

40.654,1

1

89.97

1818.2150

45.4

82.023.0

i

i

W

W

Mesh of Grind

Procedure

1. Obtain 1-kg of 100% passing 6-mesh sample2. Determine the ball loading of the ball mill3. Grind the sample for 5 minutes4. Perform particle size analysis of the sample5. Determine the cumulative 80% passing6. Repeat steps 3-5 for an additional 5, 5, 5, 10,

15, and 15 minutes

Data Processing

0 2000 4000 6000 8000 10000 12000 140000.00

20.00

40.00

60.00

80.00

100.00

15 mins

30 mins

45 mins

60 mins

Microns

Cu

mu

lati

ve

% P

as

sin

g

Data Processing

1.5000 2.0000 2.5000 3.0000 3.5000 4.0000 4.50000.0000

0.5000

1.0000

1.5000

2.0000

2.5000

f(x) = 0.320920332811502 x + 0.649853133588051f(x) = 0.35934139282703 x + 0.464774812086754f(x) = 0.362065725088539 x + 0.415169569378266f(x) = 0.437253546602284 x + 0.0475020990195434

Log Size, microns

Lo

g C

um

ula

tiv

e %

Pa

ss

Data Processing

Time, min Log 80% Pass, um

Initial

15 17,510.09

30 12,854.59

45 10,332.51

60 8,039.61

Data Processing

1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 3.0000

3.5000

4.0000

4.5000

f(x) = − 0.329264725751256 x + 4.64083772097153

Log10 (Time, minutes),

Lo

g1

0(C

um

80

%P

as

s,

um

)

Dense Medium Separation

Dense Media Separation

• Prepare SG 1.3 and 1.7 solutions of ZnCl2

• Obtain 10-g of powdered coal sample• Place solution in 500-mL graduated cylinders• Place sample in solution• Scoop out the “float” samples• Filter out the “sink” samples• Burn the samples in the muffle furnace for 1

hour @ 9000C

Findings

• Separation by density– Separate coal by grade– Higher grade, higher density– Separate other minerals

• Determination of ash content– Verify coal grade by ash residue after burning

Hand Panning

Hand Panning

• Prepare 100 grams chromite @ 100% passing 30 mesh, 100% retained 50 mesh

• Prepare 100 grams silica @ 100% passing 10 mesh, 100% retained 20 mesh

• Mix the two minerals• Separate by hand panning• Collect the concentrate and tails and screen to

separate the two minerals

Findings

• Determine separation of minerals by gravity and particle size

Findings

• Behavior of minerals:

Bubble Pick-up

Bubble Pick-up

1. Obtain 1-gram of ore sample2. Place in 100-mL beaker 3. Fill with water4. Ultra-sonicate for 3 minutes5. Discard water6. Repeat steps 3-5 until water is clear7. Condition pH8. Add collector

Bubble Pick-up

9. Condition pH10. Add frother11. Lower the glass tube into the pulp12. Press the rubber plunger13. Without releasing the plunger, raise the glass tube

and apply the bubble into a glass slide14. Repeat steps 11-13 until 10 droplets were recovered15. Dry and perform particle counting using the

microscope

Findings

• Simulate flotation response using a single bubble

• Determine best dosage parameters before froth flotation test

Froth Flotation

Froth Flotation

1. Obtain 1-kg sample2. Grind, at the grinding time determined in the

MOG experiment3. Place sample in flotation cell4. Add enough water to cover5. Pulp for 5 minutes6. Add pH modifier7. Condition for 5 minutes8. Repeat steps 6-7 until proper pH is achieved

Froth Flotation

9. Add collector10.Condition for 10 minutes11.Check the pH, make adjustments if necessary12.Add frother13.Condition for 10-30 seconds14.Scrape froth15.After flotation, scoop out tailings solids16.Perform assay of concentrate and tailings

Findings

• Determine the proper steps in performing flotation– Art vs. science

• Determine the effects of dosage parameters to recovery

Flocculation

Flocculation

1. Prepare a 1000 mL 20:1 water-ore pulp using 100% passing 200-mesh ore from BWI undersize

2. Prepare 10 dosages of flocculant3. Agitate pulp for 5 minutes4. Determine the settling rate without flocculant5. Mark the lowest settling level of solids6. Add 1 dose of flocculant and agitate for 5 minutes

Flocculation

7. Determine settling rate8. Mark the lowest settling level of solids9. Repeat steps 6-8 until no change in settling

rate is observed10.Graph the settling rates vs. time

Findings

• Determine the minimum dosage of flocculation

• Observe stearic stabilization• Observe “swelling” of flocculated solids

Sedimentation

Sedimentation

1. Prepare 1000 mL of 5, 10, 15, and 20% solids pulp using 100% passing 200-mesh from BWI undersize

2. Agitate for 5 minutes3. Mark the level of the solids-water interface at

specified intervals4. Mark the lowest settling level of solids

Findings

H1

H2

H3

Findings

• Determine thickener area using Kynch’s formula:

00CH

tA u

A = thickener areatu = settling timeH0 = initial pulp heightC0 = pulp consistency

Findings

• Determine thickener retention time using Robert’s formula

cu ttt t = retention timetu = settling timetc = time to compression zone

Findings

• Determine the depth of compression zone:

A

xtd

24

1

d = depth of compression zonetu = retention timex = average dilution of pulp at compression zonex = average dilution of pulp between the compression zone and final underflow is reachedA = thickener area

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Post Lab Discussion