Mineral Processing Techniques

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INVESTIGATION ON IMPACT OF HYDROGEN PEROXIDE ON GOLD

CYANIDE LEACHING

Hezron Hugo Nzowa

University of Dar es salaam, collage of engineering and technology, mining Eng Dept.

mineral processing.

ABSTRACT

Cyanide leaching of gold ore obtained from Barrick gold mine Kakola-Kahama Tanzania

was investigated. The effect of sodium cyanide (NaCN) concentration, type of PH

adjustment reagent and the hydrogen peroxide (H2O2) addition in relation to the leaching

time on gold recoveries were examined and the optimum cyanide leaching condition

were determined. A 74% of gold were recovered with the addition of 0.8mls of hydrogen

peroxide during a cyanidation carried out for 24 hours. As a result of this investigation it

was proven that the addition of hydrogen peroxide as an oxidant during cyanide leaching

had an increasing effect on the leaching recoveries of gold and reduces the consumption

of cyanide.

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Background

The cyanidation process is based on the conversion of gold into water soluble cyanide. Over a

century ago, it was discovered that beside the complexing cyanide ions, an oxidant must be

available simultaneously to oxidize the element gold. Since that time, oxygen from the air was

used by introducing the compressed air into the pulp or slurry. Researches and industrial

application over the years showed that the dissolution rate of gold are directly related to the

dissolved oxygen.

Considerable effort was put into improvement of the important oxidant supply, mainly by using

advanced techniques for gas dispersion or substituting the compressed air by pure oxygen in 1987

(Loroesch 1990), since the pure oxygen technology is very similar to aeration with compressed air

in the case of viscous and strong oxygen-consuming pulp/slurry, the phase transfer of oxygen gas

into a liquid is difficult as the introduction of air. The idea of controlled addition of an oxidant

liquid could come over this problem. Thus the use of hydrogen peroxide were introduced and

peroxide assisted cyanide leaching process (PAL) in gold mining industry started to be used.

Bulyanhulu gold mine it uses the compressed air as the source of dissolved oxygen which

encounter them on facing a challenge on a gold recovery at both new and old CIL circuits. Due to

this challenge they had requested me to do a testwork as my IPT project in order to investigate if

hydrogen peroxide has an impact on cyanide leaching so as to boost up their recoveries. The result

obtained during this test work will be used to demonstrate if hydrogen peroxide has an impact on

gold recovery.

Main objective

To conduct the metallurgical testwork in order to investigate the impact of hydrogen peroxide on

cyanide leaching of gold if it can boost the recovery.

Specific objectives

It is an object of the project to provide an improved process for the leaching of gold with controlled

addition of hydrogen peroxide. More particularly, to ensure low consumption of H2 O2 as possible

the consumption of sodium cyanide is not higher than in the conventional leaching process where

air is used for gassing. In addition, the improved process according to the project is intended to be

able to be safely controlled.

Methodology

In order to meet the targeted objective (main and specific objectives) of a project a literature review

on gold cyanide leaching and impact of hydrogen peroxide were understood, required equipment

and reagents were prepared and all metallurgical procedure were followed as required. This

investigation included a sample collection, test works, data collection and data discussion

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EXPERIMENTAL TESTWORKS

Sample collection

A representative sample were collected from a new CIL feed (which contain a TSF materials,

rougher scavenger and tail from old CIL). 36 kg of sample were collected for a leaching testwork.

All test work were done in metallurgy laboratories and the assaying was done by SGS.

Sample preparation

a collected samples were filtered, dried in oven and rolled to obtain a fine particles, there after a

sample were sieved and the result obtained were used to determine the P80 of the materials. Then

a sample were taken for leaching testwork.

Metallurgical test work

There are two main metallurgical testwork conducted during this investigation which were sieve

analysis by Cyclosizer, and the second was leaching by bottle rolling. Tests started with sizing,

and then followed by leaching testworks. The details of the testworks that were performed are

outlined below.

Particle size analysis

The aim of this test work was to determine the P80 of the sample, a particle size was determined

by using a cyclosizer. The equipment that used and procedures that were used to conduct particle

size analysis by using Cyclosizer are as follows:

Material and equipment

Beakers (500 mls)

Filter paper

Cyclosizer machine

Buckets

Electronic weighing balance

Oven

Sample tray

CIL feed sample

Funnels

Spatula

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Sieving procedures

The following are the procedures used for Cyclosizer test.

Twenty five grams of sample were weighed and then mixed with water to form slurry, the

slurry was transferred to the sample container.

Sample container was on panel, the pump was started and water was passed through the

cyclosizer to expel air.

Water was flowing at 25% greater than the pre-determined separation flow rate, sample

container was opened then preliminary distribution of solids to the cyclones (five minutes)

was obtained at a pressure of 210 Kpa.

The flow rate was reduced to the pre-determined value and elutriate for 10 minutes at a

pressure of 183 Kpa.

When elutriating was completed, the flow rate was increased and solids were discharged

in each apex chamber in turn through the apex valve. Discharged solids were collected in

separate beakers.

Samples were filtered, dried and weighed for each fraction and particle size distribution

was calculated after putting data in the excel sheet.

Leaching test

During this test work the following are used

3.4.8 Equipment and material used

Measuring cylinder

Conical flask

Separating funnel

pH meter

Bottle roller machine

Filter paper

Prepared sample

Plastic bags for collection of samples

Electronic balance with at least 0.01 sensitivity

bottles

Reagents used

Lime for pH modification

Cyanide (NaCN)

Hydrogen peroxide (H202)

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Procedures for Cyanidation test

A sample of one kilogram (1Kg) was weighted on a beam balance and placed in a bottle.

One liter of water was measured using a 1000ml graduated cylinder and then placed in a

bottle.

Two grams of lime was added in the bottle while stirring until pH was above 11.1

Different weights of NaCN (ranging from 1.4 to 0.8) was added in the bottle to make

concentration of 1400 ppm, 1200ppm, 1000ppm and 800ppm respectively in each bottle.

A bottle was placed on bottle rolling machine rolled at moderate speed for 24 hours.

Upon completion of each test the slurry (mixture in the bottle) was filtered, dried and

samples were submitted SGS Lab for Au, Cu and Ag for assaying.

The same procedures were repeated for the least testworks.

RESULT AND DISCUSSIONS

In the assistance of hydrogen peroxide on cyanide leaching testworks, the effects of hydrogen

peroxide and cyanide concentration at a constant pH a recoveries of gold (Au) and consumption

of sodium cyanide (NaCN) were determined.

Particle size analysis

Particle size analysis was done to determine P80 of materials. The result showed that the P80 of

material was 26micron for new CIL and 30 for old CIL.

Effect of hydrogen peroxide

Four different experiment were done at constant pH, cyanide concentration and leaching time of

24 hours. Table 1 below shows the change of gold recovery with change of hydrogen peroxide

concentration used in the cyanidation. In experiments without hydrogen peroxide the recoveries

was low but when hydrogen peroxide was added the recoveries increased similarly with different

concentration of hydrogen peroxide was observed and showed that as concentration of hydrogen

peroxide increase the recoveries increases.

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NaCN added

(g/tonne)

Recoveries when H2O2 added (mls)

without 0.4 0.5 0.6 0.7 0.8

1.4

Test 1 33 60 47 - 57 -

Test 2 54 61 - 65 - 74

1.2

Test 1 23 54 45 - 46 -

Test 2 60 63 - 57 - 73

1.0

Test 1 18 50 51 - 52 -

Test 2 59 62 - 58 - 73

0.8

Test 1 18 46 52 - 52

Test 2 57 59 - 55 - 73

Table 1: showing a recoveries at different concentration of hydrogen peroxide and sodium cyanide

for test one which was sample from new CIL and test two sample from old CIL

Effect of sodium cyanide concentration

The test work was conducted at different concentration of sodium cyanide concentration which

varied from 1400ppm (1.4g/tonne) to 800ppm (0.8g/tonne) at constant pH and hydrogen peroxide.

The results showed that without hydrogen peroxide addition as the concentration of sodium

cyanide increases the recoveries increased too. But when the hydrogen peroxide added the cyanide

concentration has less effect, result showed that a huge recoveries obtained at a hydrogen peroxide

concentration of 0.4 mls at a different sodium cyanide concentration for test one which was done

with a new CIL feed samples, also result of test two which was done with a feed of old CIL feed

sample showed that the impact of sodium cyanide concentration had a less impact on addition of

hydrogen peroxide since the recoveries increases with increase of hydrogen peroxide concentration

and less consumption of hydrogen peroxide observed as shown in table 1 above.

3.5.3 Effect of pH

In all testworks done the concentration of pH was aimed to be at constant value which was to be

11ppm, due to inabilities of proper control of pH the effect was observed on recoveries variation

when the two testworks done with the same concentration of hydrogen peroxide, sodium cyanide

and the pH which was to be 11ppm.

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Conclusion

As the result of cyanide leaching testworks carried out with CIL feed sample from old and new

CIL showed that the addition of hydrogen peroxide provide a remarkable increase on the leaching

recoveries of gold. With addition of 0.8mls of hydrogen peroxide the 74% of gold were leached.it

was proven that the use of hydrogen peroxide as an oxidant in cyanide leaching result in increase

of gold recovery and decrease cyanide consumption.

Recommendation

It had identified in the testworks done that the hydrogen peroxide has a positive impact on a

cyanide leaching of gold but some of the condition that are required was not specified due to

various inabilities such as experimental instruments, there for it is required to perform a more test

works with all requirements in order to verify the results obtained during these experiments

because under certain condition hydrogen peroxide is capable of oxidizing the cyanide into cyanate

(CNO-) which can result in excessive consumption of cyanide and hydrogen peroxide itself. Also

hydrogen peroxide can inhibit the dissolution process through passivation of gold surface.

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LIST OF ABBREVIATIONS

CIL Carbon in leach Au Gold Cu Copper Ag Silver TSF Tailing Storage facility Ppm Parts Per Million Lab Laboratory Mls Mill liter Gm grams F Mass of feed T Mass of tails f Feed grade t Tails grade g/t Grams per tone NaCN Sodium Cyanide C Mass of Concentrate c Concentrate grade

soln solution

conc concentration

COB crushed ore bin

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REFERENCES

Breuer, P.L. Jeffrey, M.I. & Hewitt, D.M. (2008) Mechanisms of Sulfide Ion

Bulyanhulu gold mine handouts

Consep Pty Ltd. Consep Acacia Innovation in Process Technology. [Brochure]

Crundwell, F.K. & Godorr, S.A. (1997) A Mathematical Model of the Leaching of

Dai, X. & Jeffrey, M.I. (2006).The Effect of Sulfide Minerals on the Leaching of

Engineering, Vol 21, pp. 579-586.

Fahrenwald, A. W., et al., "Some Studies on the Gold-Dissolution Rate in Cyanide

Solutions", Engineering and Mining Journal, vol. 140, pp. 44-46, 1939.

Gold in Aerated Cyanide Solutions. Hydrometallurgy, Vol 82, pp. 118-125.

Gold in Cyanide Solutions. Hydrometallurgy, Vol 44, pp. 147-162.

http://www.consep.com.au/page13604324.aspx.

Julian, H. F., et al., Cyaniding Gold and Silver Ores: A Practical Treatise on the Cyanide

Process, 1904, pp. 73-76.

Oxidation during Cyanidation. Part I: The Effect of Lead (II) Ions. Minerals

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Appendix

Assay tables for gold dissolution of different testworks

CN conc (ppm) Au in soln (mg/l) Au in carbon (ppm) Au in tail (ppm)

1400 0.02 17.5 157

1200 0.01 16.5 151

1000 0.01 14.5 178

800 0.001 16.5 134

Table 2. Assay for test one without hydrogen peroxide


1400 0.04 138 2.67

1200 0.06 148 2.68

1000 0.04 151 2.8

800 0.03 124 2.88

Table 3. Assay for test two without hydrogen peroxide


1400 0.05 163 2.7

1200 0.07 139 2.79

1000 0.06 140 2.92

800 0.03 137 2.92

Table 4. Assay for test three with 0.4mls hydrogen peroxide


1400 0.01 54 0.55

1200 0.001 44 0.56

1000 0.01 43 0.65

800 0.001 39 0.68

Table 5. Assay for test four with 0.4mls hydrogen peroxide

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1400 0.001 18 0.6

1200 0.01 17 0.64

1000 0.01 14 0.59

800 0.001 16 0.67

Table 6. Assay for test five with 0.5mls hydrogen peroxide


1400 0.08 139 2.79

1200 0.01 123 2.81

1000 0.08 125 2.77

800 0.01 117 2.91

Table 7. Assay for test six with 0.6mls hydrogen peroxide


1400 0.02 23 0.54

1200 0.02 18 0.67

1000 0.03 20 0.62

800 0.04 22 0.64

Table 8. Assay for test seven with 0.7mls hydrogen peroxide


1400 0.04 174 1.83

1200 0.04 158 1.77

1000 0.17 154 1.76

800 0.05 160.5 1.81

Table 9. Assay for test eight with 0.8mls hydrogen peroxide

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Tables and charts

Tables and charts of cyanide concentration, recovery, and hydrogen peroxide concentration and

cyanide consumption Table 10

Cyanide concentration

before leaching

(gm/tonne)

H2O2 amount

(mls)

Consumption of


(gm/tonne)

Recovery

1.4 0 1.0 33

1.4 0.4 1.0 60

1.4 0.5 1.2 47

1.4 0.7 1.08 57

A table showing a consumption of cyanide concentration, amount of hydrogen peroxide

used and the recoveries.

0

10

20

30

40

50

60

70

0 0.4 0.5 0.7

REC

OV

ERY

HYDROGEN PEROXIDE (mls)

A CHART OF RECOVERY V/S HYDROGEN PEROXIDE

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.4 0.5 0.7

A CHART OF CN CONSUPTION AND RECOVERY V/S H2O2

CN consumption recovery

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Table 11 Cyanide concentration

before leaching

(gm/tonne)

H2O2 amount

(mls)

Consumption of


(gm/tonne)

recovery

1.2 0 0.63 23

1.2 0.4 0.85 54

1.2 0.5 1.02 45

1.2 0.7 0.99 46



0

10

20

30

40

50

60

0 0.4 0.5 0.7

REC

OV

ERY



0

0.2

0.4

0.6

0.8

1

1.2

0 0.4 0.5 0.7



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before leaching

(gm/tonne)

H2O2 amount

(mls)

Consumption of


(gm/tonne)

Recovery

1 0 0.77 18

1 0.4 0.75 50

1 0.5 0.92 42

1 0.7 0.89 52



0

10

20

30

40

50

60

0 0.4 0.5 0.7

REC

OV

ERY



0

0.2

0.4

0.6

0.8

1

0 0.4 0.5 0.7



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before leaching

(gm/tonne)

H2O2 amount

(mls)


after leaching (ppm)

Recovery

0.8 0 0.65 18

0.8 0.4 0.62 46

0.8 0.5 0.72 42

0.8 0.7 0.72 52



0

10

20

30

40

50

60

0 0.4 0.5 0.7

REC

OV

ERY



0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.4 0.5 0.7



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before leaching

(gm/tonne)

H2O2 amount

(mls)

Consumption of


(gm/tonne)

Recovery

1.4 0 1.33 60

1.4 0.4 1.33 61

1.4 0.6 1.33 65

1.4 0.8 1.31 74



0

10

20

30

40

50

60

70

80

0 0.4 0.6 0.8

REC

OV

ERY



0

0.5

1

1.5

0 0.4 0.6 0.8



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before leaching (ppm)

H2O2 amount

(mls)


after leaching (ppm)

Recovery

1.2 0 60

1.2 0.4 63

1.2 0.6 57

1.2 0.8 73



0

10

20

30

40

50

60

70

80

0 0.4 0.6 0.8

REC

OV

ERY



0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.4 0.6 0.8



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before leaching

(g/tonne)

H2O2 amount

(mls)

Consumed Cyanide

concentration

(gm/tonne)

Recovery

0.8 0 0.77 57

0.8 0.4 0.76 59

0.8 0.6 0.77 55

0.8 0.8 0.77 73



0

10

20

30

40

50

60

70

80

0 0.4 0.6 0.8

REC

OV

ERY



0

0.2

0.4

0.6

0.8

1

0 0.4 0.6 0.8



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before leaching

(gm/tonne)

H2O2 amount

(mls)

Consumption of


(gm/tonne)

Recovery

1 0 0.96 59

1 0.4 0.93 62

1 0.6 0.96 58

1 0.8 0.96 73

A table showing a consumption of cyanide concentration, amount of hydrogen peroxide used and the recoveries.

0

10

20

30

40

50

60

70

80

0 0.4 0.6 0.8

REC

OV

ERY



0

0.2

0.4

0.6

0.8

1

1.2

0 0.4 0.6 0.8



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Some formula which used

Recovery = concentrate/ feed

= 𝐶𝑐

𝐹𝑓∗ 100

but f = grade of gold in solution tail + grade of gold in solid tail + grade of gold in carbon

c = f – t

where t = grade of gold in tail

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Mineral Processing Techniques

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