A Resin-In-pulp Process for the Recovery of Copper From Bioleach Ccd Underflows

8/12/2019 A Resin-In-pulp Process for the Recovery of Copper From Bioleach Ccd Underflows

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A RESIN-IN-PULP PROCESS FOR THE RECOVERY OFCOPPER FROM BIOLEACH CCD UNDERFLOWS

by

I.P. Greager *, J.P. Wyethe *, M.H. Kotze *, D.Dew and D. Miller

* Mintek Billiton Process Research

Private bag X3015 Private Bag X10014

Randburg Randburg

South Africa 2125 South Africa 2125

ABSTRACT

The resin-in-pulp (RIP) process was developed primarily for the recovery of metals

from high volumes of low-grade pulps, as is the case in the gold processing industry.

However, this technology can also be applied to the recovery of soluble metals from

solid residues on base metal plants. Applications for the RIP process include the

scavenging of valuable metals from leach and precipitation residues, especially where

the solids have poor filterability or settling characteristics. The RIP process will

improve overall plant recoveries, and it may be possible to decrease the filter duties or

the degree of washing on the filters. In addition, the barren stream from the RIP

operation may reduce any environmental impact significantly.

Billiton Process Research (BPR) commissioned Mintek to investigate the

metallurgical and economic feasibility of a resin-in-pulp process for the recovery of

copper from bioleach counter-current decantation (CCD) underflows. Batch

laboratory testwork and a continuous mini-plant campaign was conducted in order to

optimise the process parameters. The results were used to conduct a preliminary

sizing and costing study, in order to evaluate the economic viability of the RIPtechnology for this application.


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A RIP process for the recovery of copper from bioleach CCD underflows.

1

1. INTRODUCTIONThe development of the resin-in-pulp (RIP) process at Mintek was initially targeted

primarily at the recovery of metals from large volumes of low-grade leach pulps, as is

the case in the gold processing industry. Minteks RIP expertise culminated in thedevelopment of a resin-in-pulp process, MINRIP TM , for the recovery of gold from

leached slurries. Mintek has subsequently evaluated the applicability of this

technology to the in-pulp extraction of copper, zinc, nickel, cobalt, vanadium and

manganese [1,2].

The main application of the RIP process in the base metal industry will be the

scavenging of soluble metals from leach residues, precipitation residues and other

solid wastes that have poor filterability or settling characteristics. However, this

technology can also be applied to the recovery of metals from the leach slurry when

low-grade materials are treated.

A schematic layout of the resin-in-pulp process configuration is given in Figure 1.

FEED SLURRY

REPULP TANK

ADSORPTION

RESIN-PULP SEPARATION

ELUTION

WASH

S1 PULPRECYCLED ATTRANSFER

ELUANT

H 2 O

RECYCLE

RECYCLE RESIN

BARREN PULP

denotes RESIN FLOW

denotes PULP/SOLUTION FLOW

Figure 1 : Schematic representation of the resin-in-pulp circuit


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During the adsorption stage, the feed pulp is contacted with resin in a multi-stage,

counter-current plant. After the resin has been passed counter-currently through the

adsorption plant, the resin will be loaded predominantly with the valuable metal

together with lower concentrations of other metals. The barren pulp from the last

stage could be discarded to the slimes dam, after a pH adjustment, or alternatively the

barren pulp could be thickened, and the thickener overflow could be returned to the

plant for use as process water.

The loaded resin exiting the adsorption circuit is separated from the pulp by means of

a linear belt, sieve bend or vibrating screen, and the pulp is returned to the feed. The

loaded resin is then rinsed with water to remove any particulates, after which the resin

is transferred into an elution column. During elution, the metals are stripped from the

resin with sulphuric acid (this could be fresh acid or an acid-bearing stream),

producing a concentrated metal sulphate eluate. The excess acid is then washed from

the resin bed with water, and the eluate, and possibly the wash water, are returned to

the relevant unit operation in the process flowsheet. The eluted, washed resin is

transferred back to the adsorption circuit for the next transfer.

The major advantages of the resin-in-pulp process include :

It is effective for the recovery of soluble metals from pulps with poor filterability

or settling characteristics. The fact that the process operates in a pulp medium

means that the solid-liquid requirements may be reduced or possibly eliminated.

In addition, it may be possible to significantly reduce wash water requirements ;

The RIP process may be able to achieve lower discharge metal concentrations

than those achieved with the more conventional filtration or solid-liquid

separation systems, hence reducing the problems associated with the disposal of

wastes containing soluble metals ;

The overall metal recoveries on the plant can be improved ; and

Co-precipitated and adsorbed metal species may be recovered with the RIP

process, which will further improve the overall metal recovery.

Billiton Process Research (BPR) commissioned Mintek to evaluate the feasibility of a

RIP process for the recovery of soluble copper from a bioleach thickener underflow.


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This paper outlines the process development, from the batch laboratory testwork to

the continuous mini-plant campaign. Based on the results of this testwork, a full-scale

plant was sized and a preliminary techno-economic study was conducted.

2. LABORATORY TESTWORK PROGRAMMEThe resin that was selected for the purposes of this investigation was a commercially

available chelating resin. The resin selectivity, for metals in the feed solution under

consideration over sodium, is given by the following selectivity series :

H+ > Fe 3+ > Cu 2+ > Fe 2+ > Ca 2+ > Mg 2+ > Na +

A number of potential commercial resins were compared, on a techno-economic

basis, during an earlier study at Mintek. The chelating resin that was used during this

study was found to be the most cost-effective resin option.

2.1 Effect of pH

The effect of pH on the copper loading of the resin was investigated to determine the

minimum pH at which maximum copper loading could be achieved. Results are

shown in Figure 2.

0

20

40

60

80

100

0.0 1.0 2.0 3.0 4.0

pH

C o p p e r

l o a

d i n g

( g / L )

* Final copper concentration > 0.01M

Figure 2 : Effect of pH on copper loading.


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ions at a pH of 3.0, an elevated temperature and a strong oxidant, such as oxygen-

enriched air, will be required in order to increase the oxidation rate. Any attempt to

increase the rate of ferrous oxidation by increasing the pulp pH will result in increased

copper losses. Consequently the quantitative oxidation and removal of ferrous ions, at

relatively low pH, will result in increased CAPEX and OPEX. A techno-economic

analysis will have to be conducted, however, to ascertain whether there is an

economic incentive to implement a ferrous oxidation step.

2.3 Ion exchange equilibrium isotherm

An ion exchange equilibrium isotherm was measured at a pH value of 2.5 and at a

solids concentration of 30%. The composition of the feed pulp used for the

measurement of the ion exchange equilibrium isotherm is given in Table 2.

Table 2 : Composition of feed pulp for the ion exchange equilibrium isotherm.

Metal in solution (g/L)

Copper Total iron Calcium Magnesium Aluminium

5.7 0.31 0.55 0.03 0.03

The ion exchange equilibrium isotherm obtained is shown in Figure 3.

0

10

20

30

40

50

60

0 1 2 3 4 5

Copper in aqueous phase (g/L)

C o p p e r

l o a

d i n g o n r e s

i n ( g / L )

DataFreundlich model

Figure 3 : Ion exchange equilibrium isotherm for copper loading.


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The Freundlich isotherm model was fitted to the experimental data. The fitting

parameters and correlation coefficients are shown Table 3.

Table 3 : Freundlich isotherm model fitting parameters.

Parameter pH 2.5

a 12.09

b 0.18

r 2 0.95

Copper and iron were the main species loaded onto the resin. The resin loading, in

equilibrium with 2g/L copper in solution, is given in Table 4. The resin capacity

utilisation under these conditions was 75%.

Table 4 : Equilibrium resin loading.

Metal on resin (g/L)

Copper Total iron Calcium Magnesium Aluminium

47 6.1 1.3 < 0.1 < 0.1

3. CONTINUOUS MINI-PLANT CAMPAIGNThe intention of the RIP plant is to recover copper from a CCD thickener underflow.

However, the feed to the RIP plant may be drawn from any of the CCD underflows in

the CCD train. Hence, the metallurgical response of the resin to three different feeds,

namely 0.5, 1.0 and 4.0g/L copper, was evaluated. These three concentrations span

the entire expected concentration range of the various CCD underflows, for this

specific operation. The optimum plant configuration, however, has to be based on

detailed metallurgical and techno-economic considerations.

During the design of a RIP plant, the selection of the mode of operation is important.

The plant could either be operated in a carousel counter-current mode where resin

handling can be limited and the resin inventory is more accurately controlled in each

stage, or in a continuous counter-current mode. Although inventory control might


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prove more difficult during continuous operation, a substantial CAPEX saving is

possible. However, since relatively low upgrading ratios can be expected, inaccurate

control of the resin volume in each stage might lead to large fluctuations in the barren

stream exiting the plant. Consequently, a carousel mode of operation was chosen for

the mini-plant evaluation. The counter-current flow of resin and pulp in a multistage

carousel adsorption circuit is shown in Figure 4. Feed slurry is pumped into the first

contacting stage. At transfer, the feed is re-directed to the second stage and the resin

and pulp from the first contacting stage is separated. The loaded resin is then sent to

the elution column. After elution, the stripped resin is fed back into the last stage of

the adsorption circuit, hence completing the resin cycle.

S 2 S 3 S 4

S 1 S 2 S 3 S 4 S 5

F E E D

S 5

B A R R E N

F E E D

B A R R E N

S 1

T R A N S F E R

Figure 4 : Schematic diagram of the counter-current flow of pulp and resin in a

carousel RIP cascade.

The mini-plant consisted of a four-stage cascade of contactors, each with an active

volume of 960mL. The resin-pulp mixing in each stage was achieved with mechanical

overhead stirrers. Resin was retained in the contactor by means of a 200 m peripheral

screen, and pulp gravitated through the screens from one stage to the next. During

adsorption, the pH was controlled at the desired set-point in all the stages. Lime

slurry, limestone slurry or any other alkali may be used for pH control.


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After preparation of the feed pulps, ferric ions were neutralised by the addition of

100g/L limestone slurry, at ambient temperature. The pH was adjusted to 2.9. No

attempt was made to oxidise the residual ferrous ions to ferric. The feed pulp

compositions evaluated during this study, after iron precipitation, are shown in Table

5.

Table 5 : Average feed pulp compositions for the mini-plant campaign (after iron

removal).

Parameter 4.0g/L Cu 1.0g/L Cu 0.5g/L Cu

Solids (%) 20 27 25

pH 2.9 2.9 2.9

Copper (g/L) 4.4 0.98 0.49

Zinc (g/L) 0.14 0.16 0.01

Nickel (g/L) < 0.01 < 0.01 < 0.01

Cobalt (g/L) < 0.01 < 0.01 < 0.01

Total iron (g/L) 0.70 0.35 0.12

Manganese (g/L) 0.01 < 0.01 0.03

Aluminium (g/L) 0.02 < 0.01 < 0.01

Calcium (g/L) 0.46 0.50 0.53

Magnesium (g/L) 0.03 0.01 0.05

During the mini-plant campaign the following parameters were evaluated :

Copper feed concentration ;

Pulp residence time ; and

Pulp pH.

3.1 Effect of copper feed tenor

The effect of the copper feed concentration on the process performance was

investigated. For these tests, the pulp residence time per stage was maintained at 1

hour, the resin residence time per stage was 3.1 hours, and the pH was controlled at

3.0. The operating parameters evaluated are presented in Table 6.


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Table 6 : Operating parameters to evaluate the effect of copper feed tenor.

Copper in feed

(g/L)

Resin concentration

(vol. %)

4.4 20

1.0 5.0

0.5 3.2

As the resin residence time was maintained constant, it was necessary to vary the

resin concentration per stage, in order to process the various feeds. The average metal

loadings of the major metals onto the resin removed from the first adsorption stage at

transfer are presented in Table 7.

Table 7 : Average metal loadings and resin capacity utilisation.

Copper in feed (g/L) 4.4 1.0 0.5

Resin loading (g/L)

Copper 49.5 39.8 32.2

Calcium 0.39 1.32 2.56

Total iron 4.95 7.50 5.20

Resin capacity utilisation (%)

Stage 1 86.5 80.8 63.5

Results indicated that with a decrease in the copper feed tenor, the copper loading on

the resin also decreased, whilst the calcium co-loading increased. The average copper

solution profiles across the mini-plant cascade, at transfer, for all three copper feed

concentrations are presented in Figure 5.


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4400

2570

48737 11 4

0500

100015002000250030003500400045005000

Feed S1 S2 S3 S4 Comp.Barren

C o p p e r

i n s o

l u t i o n

( m g

/ L )

(i) Copper feed tenor ~ 4.0g/L

980

670

305

8510 8

0

200

400

600

800

1000

1200


C o p p e r

i n s o

l u t i o n

( m g

/ L )

(ii) Copper feed tenor ~ 1.0g/L

490

325

152

499 7

0

100

200

300

400

500

600


C o p p

e r

i n s o

l u t i o n

( m g

/ L )

(iii) Copper feed tenor ~ 0.5g/L

Figure 5 : Average copper solution profile across the RIP mini-plant cascade


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The average copper concentration in the composite barren stream for all three feed

concentrations was less than 0.01g/L.

It is evident from Figure 5(i) and Table 7 that it is possible to reduce the copper

concentration from 4g/L to below 0.05g/L in three adsorption stages, whilst

maintaining a high resin loading in stage 1. The operating parameters employed

resulted in a relatively large extraction efficiency of 42% across the first stage.

However, as the feed concentration was relatively high, a high resin loading of

49.5g/L could still be attained.

At the lower feed concentrations, the extraction efficiencies across stage 1 were

decreased to approximately 30%, to allow a higher copper tenor in the stage 1

effluent, hence maximising the copper loading on the resin within the equilibrium and

kinetic constraints. Consequently four stages were required in order to reduce the

composite barren to less than 0.05g/L (see Figure 5(ii) and (iii)).

The effect of the number of stages on the overall copper recovery, under the operating

parameters employed, is shown in Table 8.

Table 8 : Effect of number of stages on overall copper recovery.

Copper in feed (g/L) Recovery 3 stages (%) Recovery 4 stages (%)

4.4 > 99 > 99

1.0 > 91 ~ 99

0.5 ~ 90 > 98

3.2 Effect of pulp residence time

Tests were conducted at varying pulp residence times in order to ascertain whether a

reduced pulp residence time had a detrimental effect on the process performance.

Provided the reduced residence time results in a negligible impact on the process

performance, it may be possible to reduce the volume of the adsorption vessels, which

translates into a CAPEX saving.


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The important operating parameters for the investigation into the effect of pulp

residence time ( pulp ) per stage on process performance, for the 1.0g/L copper feed,

are given in Table 9. For these tests, resin residence time per stage was 3.2 hours, and

the pH was controlled at 3.0.

Table 9 : Operating parameters to evaluate the effect of pulp residence time.

Test pulp

(minutes)

Resin concentration

(vol. %)

1 60 5.0

2 30 11.7

3 20 17.9

It was possible to maintain a constant resin transfer time by altering the resin

concentration per stage according to changes in the mass of copper introduced with

the feed.

The average resin loading and capacity utilisation achieved on the stage 1 resin, at the

different residence times, are summarised in Table 10.


Parameter Test 1 Test 2 Test 3

Experimental conditions

pulp (minutes) 60 30 20

Resin loading (g/L)

Copper 39.8 42.3 39.4

Calcium 1.32 1.18 1.15

Total iron 7.50 6.10 6.20


Stage 1 80.8 81.7 77.9


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From the data in Table 10 there seems to be no significant difference in the copper

loading or total resin capacity utilisation for the pulp residence times evaluated. The

behaviour of the iron loadings during the mini-plant trial was somewhat erratic, and

will have to be confirmed during a more extensive mini or pilot-plant campaign.

The normalised average aqueous phase copper profiles across the CCIX cascade, for

the different pulp residence times at a copper feed concentration of 1.0g/L, are

presented in Figure 6. The data was normalised with respect to the feed concentration

in order to eliminate small variations in the copper feed analysis for the three tests.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.91


[ C u

] / [ C u

] f e e

d

Test 1 - 60 minutes

Test 2 - 30 minutes

Test 3 - 20 minutes

Figure 6 : Comparison of the normalised average copper solution profiles.

It is evident that the solution profiles for the three tests are similar. Four adsorption

stages were required to reduce the copper concentration in the aqueous phase to less

than 0.05g/L for all pulp residence time tests.

3.3 Effect of pulp pH

The sensitivity of the process to relatively small variations in pH was tested. The

motivation behind conducting a mini-plant trial at a lower pH was that both the level

of copper loss during iron precipitation and the level of impurity co-loading may be

reduced at a lower pH set-point.


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The important operating parameters for the investigation into the effect of pulp pH on

process performance, for the 1.0g/L copper feed, are given in Table 11.

Table 11 : Operating parameters to evaluate the effect of pulp pH.

Test pH Resin concentration

(vol. %)

1 3.0 5.0

4 2.5 5.0

In order to elucidate the effect of reduced pulp pH, the pulp and resin residence times

were kept constant, at 1 hour and 3.2 hours respectively.

The average resin loading and capacity utilisation achieved on the stage 1 resin, at the

different pH values, are summarised in Table 12.


Parameter Test 1 Test 4

Experimental conditions

Pulp pH 3.0 2.5

Resin loading (g/L)

Copper 39.8 37.5

Calcium 1.32 0.67

Total iron 7.52 7.03


Stage 1 80.8 72.1

From the data in Table 12 it would appear that the lower pH of 2.5 resulted in a

slightly lower copper loading. The change in the co-loading of the impurities was

minimal. The normalised average copper solution profiles across the CCIX mini-plant

cascade, for the different pH values at a copper feed tenor of 1.0g/L, are shown in

Figure 7.


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00.10.20.30.40.50.6

0.70.80.9

1


[ C u

] / [ C u ] f e e

d

Test 1 - pH 3.0Test 4 - pH 2.5

Figure 7 : Comparison of the average copper solution profiles.

It is evident from Figure 7 that the copper solution profile is somewhat higher for test

4 (pH 2.5) than test 1 (pH 3.0). The reason is that the reduced pH set-point in test 4

resulted in a slightly reduced copper loading, compared to the copper loading

achieved in test 1. Hence, the concentration profile shifted, resulting in a slight

increase in the composite barren copper concentration from 0.01g/L (pH 3.0) to

0.016g/L (pH 2.5). However it was still possible to reduce the copper concentration to

less than 0.02g/L in the composite barren using four stages.

These results indicate that pH variations between pH 2.5 and 3.0 should not have a

major impact on the overall plant performance.

4. PLANT SIZING & PRELIMINARY ECONOMIC ANALYSIS4.1 Plant sizing

Slurry flowrates of 100m 3/h were chosen for the economic comparison of streams

containing a solution phase concentration of 0.5, 1.0 and 4.0g/L copper respectively.

The resin concentration was maintained below 25% to limit resin loss through

attrition. A four hour resin transfer time was used to allow adequate time for resin

handling and elution.

The total resin inventory comprised :


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The required resin volume in each adsorption stage to allow for adsorption of the

total load of copper in the feed; and

Two equivalent resin volumes in the elution circuit to allow sufficient time for

resin handling, and the elution and wash steps, so that fluctuations in the copperfeed tenor can be handled, within the design limits.

Although only four active adsorption stages were required for the effective recovery

of copper, a fifth adsorption stage had to be incorporated during the design of the

carousel RIP plant to make provision for resin handling.

The principal results of the plant sizing are shown in Table 13.

Table 13 : Summary of important sizing parameters for a copper RIP plant treating

100m 3 /h pulp, at different copper feed tenors.

Feed:

Cu

Flowrate

% solids

g/L

tonne/annum

m3/h

A

0.5

330

100

35

B

1.0

700

100

35

C

4.0

2 900

100

35

RIP:

Pulp residence time per stage

Number of stages

Active volume

Resin volume

h

m3

m3/stage

0.5

5

70

5

0.5

5

70

8

1.0

5

160

27

4.2 CAPEX calculation

A CAPEX estimate was prepared (to within 15% accuracy) by LTA Process

Engineering, Minteks partners in resin-in-pulp technology, during February/March

2001, for a RIP plant employing adsorption tanks with an active volume of 80m 3. This

CAPEX was scaled using the six-tenths factor rule, using the adsorption tank active

volumes as a basis, in order to obtain an indication of the CAPEX requirement for the

current RIP application.


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It is evident from Table 13, that the LTA CAPEX estimate was conducted for a plant

that is similar in size to options A and B. Option C, however, is significantly larger

than the plant costed by LTA plant. Consequently it is anticipated that the error due to

the scaled calculation of the CAPEX calculation will be larger for option C, than for

options A and B. The resin inventory requirement was based on the resin loadings

obtained during the mini-plant campaign. The scaled CAPEX figures for the three

design scenarios are presented in Table 14.

Table 14 : Scaled CAPEX for the three proposed copper RIP plants.

CAPEX item A

0.5g/L Cu

330 tpa

B

1.0g/L Cu

700 tpa

C

4.0g/L Cu

2900 tpa

Scaled plant CAPEX (Rands, million) 18.4 18.4 31.4

Actual resin CAPEX (Rands, million) 2.0 3.2 9.7

TOTAL CAPEX (Rands, million) 20.4 21.6 41.1

4.3 OPEX calculation

The following components were considered for the OPEX calculations :

Eluant consumption

Resin could be eluted with fresh H 2SO 4, spent electrolyte or solvent extraction

raffinate. For this evaluation a consumption of 1.2 moles of fresh sulphuric acid per

litre of resin was used at a cost of R360/tonne (as 98% sulphuric acid).

However, it may be argued that acid consumption for copper elution may not be

considered an operating expense, owing to the fact that each mole of copper returned

to a solvent extractionelectrowinning plant would produce an equivalent amount of

acid. Thus in this case, the sulphuric acid cost is that associated with the stripping of

co-loaded impurities only.


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Limestone consumption

The limestone consumption for neutralisation during adsorption was taken to be 1.2

moles/L resin at a price of R110/tonne. It can also be argued that the neutralising

agent may be omitted as an OPEX, owing to the fact that the CCD underflow,

assuming that no resin-in-pulp plant was installed, would have to be neutralised and

the metals precipitated prior to disposal.

Labour

It is envisaged that the complex valve and flow sequencing that is required for a RIP

operation will result in a reasonably high level of automation. The labour component

of the OPEX, assuming three eight hour shifts per day, was based on a staff of eight

operators (R90 000/annum/operator) and 2 shift supervisors (R190 000/annum/

supervisor).

Resin replacement

During the operation of the RIP plant, resin will be lost due to degradation and

handling. Resin losses should be determined on a relatively large scale for a specific

application. A replacement figure of 50% of the inventory per annum was used for the

purposes of the OPEX calculations.

Copper losses

A copper loss of 0.05g/L in the barren stream exiting the adsorption cascade was

assumed. A copper price of R13 624.98/tonne was used for calculations [3].

The OPEX associated with the RIP operation is shown in Table 15. It is evident from

Table 15 that the OPEX is highly dependent on the amount of copper produced. The

labour component is dependent on the production level. The OPEX associated with

the eluant, limestone and resin replacement is a function of the level of resin loading,

which in turn is dependent on the feed concentration.


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Table 15 : OPEX breakdown for proposed copper RIP plants

Parameter OPEX (Rand/tonne copper)

A

0.5g/L Cu330 tonne/annum

B


C


Eluant

Limestone

Labour

Resin replacement

Copper loss (barren)

TOTAL OPEX

1 520

460

3 310

3 000

1 510

9 800

1 160

350

1 570

2 280

720

6 080

900

270

380

1 770

170

3 490

4.4 Revenue

The revenue was calculated using a copper price of R13 624.98/tonne [3]. It was

decided that, because the copper eluate produced by the resin-in-pulp circuit must

undergo further treatment before a saleable copper product is formed, the copper

revenue should be discounted. The total copper revenue was thus discounted by 10%.

The revenue, after discounting, was calculated to be R12 262.48/tonne of recovered

copper.

4.5 Cash flow analysis

Cash flow analysis was conducted in order to get an indication of the payback periods

and the internal rates of return of the proposed RIP plants. For the purposes of the

cash flow analysis, the scaled CAPEX was broken down into three categories,

namely:

1. Buildings ;

2. Productive plant ; and

3. Permanent works.


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The composition of the breakdown of the total CAPEX, as well as the associated

depreciation schedule, is shown in Table 16.

Table 16

CAPEX composition and depreciation schedule

CAPEX item Percentage of total Depreciation schedule

Buildings 10% Not depreciated

Productive plant 80% Written off at 20% per annum over 5 years

Permanent works 10% Written off at 5% per year over 20 years

In addition, the cash flow analysis was subject to the following assumptions :

The tax rate was taken as 35% ;

Discount factor was taken as 10% ;

Life of plant was taken as 10 years ;

No variation in the metal and reagents prices was taken into account ; and

Working capital was calculated as 10% of the total CAPEX [4].

The results of the cash flow analysis, carried out for each feed scenario, based on the

OPEX figures from section 4.3, are presented in Table 17. In addition, a cash flow

analysis was conducted for the case in which the OPEX was modified as follows :

Sulphuric acid : Although it may be argued that the cost associated with the

stripping of copper is not an operating expense (owing to the production of a

stoichiometric quantity of acid during copper electrowinning), elution of co-

loaded impurities from the resin remains an operating cost. Thus the sulphuric

acid consumption component of the OPEX was modified to include the cost of

stripping off the impurities only, which translates to 20% of the operating capacity

of the resin ; and

Limestone : The limestone was excluded entirely from the OPEX calculation, for

reasons discussed in section 4.3.


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Table 17 : Cash flow analysis of the proposed copper RIP plants.

Parameter A

0.5g/L Cu

330 tonne/annum

B

1.0g/L Cu

700 tonne/annum

C

4.0g/L Cu

2900 tonne/annum

Sulphuric acid and limestone consumption @ 1.2mol/L resin

Payback period (years) > 10.0 9.7 2.8

IRR (%) -9 11 42

Sulphuric acid consumption @ 20% operating capacity; no limestone consumption

Payback period (years) > 10.0 7.4 2.5

IRR (%) -7 14 47

It is evident from the data in Table 17 that the payback period and IRR are highly

dependent on the mass of copper recovered in the RIP unit operation.

For a greenfield application, the RIP plant may result in a reduction in the number of

CCD stages required. Consequently a techno-economic study comparing the process

economics of the CCD circuit versus the RIP circuit would have to be conducted for

each application, in order to determine the economically optimum process

configuration.

In addition, the environmental benefits of the RIP process have not been factored into

the process economics.

5. CONCLUSIONSDuring the laboratory testwork, the effect of pH on copper loading and capacity

utilisation was determined, and an ion exchange equilibrium isotherm was measured

at a pH value of 2.5. Maximum copper loading was achieved at pH values of 2.5 and

higher and at copper concentrations greater than 0.7g/L (at pH 2.5).

Based on the laboratory testwork, the metallurgical response of the resin to the

bioleach slurry was evaluated on a continuous mini-plant scale, at three different

copper concentrations, namely 4.0, 1.0 and 0.5g/L copper.


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For the 4.0g/L copper feed, a pulp residence time per stage of 60 minutes and a pulp

pH of 3.0 were tested. A copper composite barren tenor of less than 0.05g/L was

attained using three adsorption stages. A copper loading of ~ 50g/L was attained in

the first stage, with an iron co-loading of ~ 5.0g/L.

For the 1.0 and 0.5g/L copper feeds, the sensitivity of the process performance to

changes in the pulp residence time and pulp pH was evaluated. Pulp residence times

were varied in order to ascertain the degree to which the reduced residence time

would impact on the process performance. As the pulp residence time per stage was

reduced from 60 minutes to 20 minutes, no significant changes in the copper loading

or composite barren were observed. Consequently it is evident that the adsorption

vessels may be sized for a 20 minutes pulp residence time, depending on the

flexibility required. Variations in the pulp pH between 2.5 and 3.0 had negligible

impact on copper loading and impurity co-loading.

Mini-plant data was used to conduct a preliminary techno-economic evaluation for

three feed concentrations, based on an assumed pulp flowrate of 100m 3/h. It was

evident that the process economics are extremely sensitive the copper tonnage, but it

is possible for the process to realise a high internal rate of return (IRR). No

environmental benefits were factored into the process economics.

This paper has illustrated that RIP can be an attractive technology for the recovery of

valuable metals from low-grade leach slurries or waste streams. However its potential

has to be evaluated for each individual application.

6. ACKNOWLEDGEMENTSThis paper is published by permission of Mintek and Billiton Process Research

(BPR).


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7. REFERENCES1. Green B.R., Kotze M.H., and Engelbrecht J..P. (1998) Resin-in-pulp - After gold,

where next? EPD Congress, San Antonio, Texas. B. Mishra (ed.). The Minerals,

Metals and Materials Society, Warrendale, Pennsylvania . (Pages 119-136) 2. Taylor M.J.C., Green B.R., Wyethe J.P., Padayachee D.P. and Mdlalose K.E.

(2000) Recovery of vanadium from waste solids and solutions using an ion

exchange process. MINPREX 2000, Melbourne, Victoria.

3. Standard Bank Daily Base Metals Report (22 May 2001)

4. Peters M.S. and Timmerhaus K.D. (1991) Plant design and economics for

chemical engineers. Mc-Graw-Hill Book Company. Fourth edition.

A Resin-In-pulp Process for the Recovery of Copper From Bioleach Ccd Underflows

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