1 The Use of AuRIX®100 Resin and Gekko Systems Technology for

Transcription

Gold Symposium – Lima, Peru, May 2004
The Use of AuRIX®100 Resin and Gekko Systems Technology for the
Recovery of Gold
M.J.Virnig -Cognis Corporation
Jurgen Picardo- Cognis Corporation
J.M.W. Mackenzie- Consultant
Nick Katsikaros- Gekko Systems Pty Ltd
Sandy Gray- Gekko Systems Pty Ltd
1
M.J.Virnig, Jurgen Picardo, J.M.W. Mackenzie, Nick Katsikaros, Sandy Gray
The Use of AuRIX®100 Resin and Gekko Systems Technology for the Recovery of Gold
1.0 Introduction
Both Cognis ion exchange technology and Gekko gravity and leaching technology for
the recovery of gold are specialized systems which suit certain types of gold orebodies.
There are some cases where synergy exists between the Gekko and Cognis
technologies. These have already been discussed in a paper by Gray et al (1)
In this paper the application of these technologies will be discussed, both individually
and in combination to develop novel flow sheets for certain gold orebodies.
2.0 Cognis AuRIX® 100 Ion Exchange Technology
NR
RNH
HNR
R = H, Alkyl, Resin
Figure 1. General chemical structure of LIX® 79 and AuRIX® resin
AuRIX® 100 is a cross linked polystyrene resin functionalized with a guanidine group.
The chemistry of the protonation and de protonation of AuRIX®100 resin and the
concomitant extraction and elution of anionic species has been described in a number of
papers ( 2 ) (3 ) ( 4 ).
Loading
RG(org) + H2O
RGH1+OH1-(org) + Au(CN)21-
RGH1+OH1-(org)
RGH1+Au(CN)21-(org)+ OH1-(aq)
Elution
RGH1+Au(CN)21-(org)+ OH1-(aq)
RG(org) + H2O + Au(CN)21-(aq)
G = Guanidine, R = Resin, Alkyl
.
Figure 2. Guanidine chemistry
The appropriate Chemistry for the extraction of aurocyanide by AuRIX®100 is shown in
Figure 2.
2
AuRIX® 100 has undergone extensive pilot testing. Two of these pilot tests have been
reported at a previous International Gold Symposium in Peru and will be referred to only
briefly here.
3.0 Resin in Solution (RIS) Pilot Plant Trials
3.1 Trial at Anglo American’s Isabella Mine- Zimbabwe
The plant had 5 extraction stages and one Zadra elution stage. Each stage contained
120 kg (wet) or 60 Kg (dry) resin. The upflow contactors were 0.8 metre diameter. The
trial results are summarized below:
• PLS upflow at 6.9 m3/hr
• PLS grade 1.13 g/t Au
• Duration of trial 137 days
of elutions
36
This •trialNumber
demonstrated
the robustness
of the technology and the stability of the AuRIX
resin.• Gold recovery 60-80% which was equivalent to a parallel CIP circuit
treating the same PLS
• Total
RIS Pilot
Trial gold
in a Gold
Mine 17
in Mexico
produced
kgs
• Average gold on resin 9900 g/t
Equipment
Description
and Test
Parameters.
• Minimum
supervision
was
required
3.2 Trial at a Mexican Gold Mine
The extraction circuit consisted of five 6.35 cm. diameter by 117 cm tall columns
arranged for downflow mode of operation (See Figure 3). Each column was filled with
1.1 L of wet resin. Wedge-wire screens at the top and bottom of the columns held the
resin in place. The pilot plant was operated in a carousel mode and the lead column was
manually taken out of the extraction circuit and placed in the elution circuit. The resin
remained in the column at all times. PLS solution was taken from a tap in the main PLS
line to the CIS plant. A paddle wheel type digital flowmeter / totalizer was used to
measure and record flowrate, prior to entering the extraction circuit. Extraction was
carried out at 70 BV/hr (1.3 L/min) in downflow flow mode.
The elution circuit consisted of the resin column, electrowinning cell, recirculation tank,
and diaphragm pump in a closed loop. The eluate was maintained at 60oC.
Elution was at 30 BV/hr. The polypropylene electrowinning cell contained 4 stainless
steel cathodes and 4 stainless steel anodes. Operating voltage was 2.8-3.0 and the
current was 25-30 amps.
.
3
immersion heater
Eluate
Recirculation
Tank
rectifier
3
sample valve
4
2
valve
eluate
column
TC
deg C
1
5
Flowmeter
Totalizer
EXTRACTION
Elution Circuit
PLS Line to CIS Plant
Electrowinning
Cell
Diaphram pump
Raffinate to Pond
Figure 3. Pilot Plant Layout
Extraction Test
Extraction was carried out in downflow mode at 70 BV/hr. After a break in period, the
lead column was taken to elution every 24 hours, and the eluted column placed in the
last position. Profiles taken at the 24 hour mark are shown in Figure 4 for a five column
operation. As indicated, average solution concentrations, in ppm Au, were 0.319 (PLS),
0.224 (col#1), 0.125 (col#2), 0.044 (col#3), 0.018 (col#4), and 0.005 (col #5)
Extraction Column Profiles after 24hr
5 column extraction
0.4
mg/L Au in solution
0.35
0.3
PLS
0.25
Col #1
0.2
Col #2
0.15
Col #3
Col #4
0.1
Col #5
0.05
0
Days 1
7 days
13
Figure 4. Extraction column profiles after 24 hours period of operation
4
Extraction profiles at the 24 hr period prior to changing the lead column out to elution for
a four column system are shown in Figure 4. Averaged values for Au solution
concentrations, in ppm, were 0.350 (PLS), 0.255 (col #1), 0.154 (col#2), 0.070 (col#3),
and 0.025 (col#4).
Elution Testwork
Rich Eluate Au (ppm)
Initially, all resin elution was performed with an eluate composition of 40 g/L NaOH,
70 g/L sodium benzoate, and 100 ppm free CN. Total eluate volume in the circuit was
64 liters. Sodium benzoate was found in bench scale testing to accelerate elution
kinetics. Elution was carried out at 60 oC for 6 hours. At termination, the difference
between the gold concentration in the eluate entering and exiting the column was less
than 1 ppm Au. Elution profiles (eluate exiting the column) typical of the sodium
benzoate containing eluate are shown in Figure 5. Loaded and eluted resin analysis for
a sample using this eluate is given in Table 1.
20
18
16
14
12
10
8
6
4
2
0
0
60
120
180
240
time (min)
300
360
Figure 5. Rich Eluate profiles versus time
Sample
Au mg/kg of dry resin
Ag mg/kg of dry resin
loaded
1720
393
eluted
163
83
Table 1. Loaded and eluted resin analysis
5
Elutions were also carried out without sodium benzoate. Figure 6 shows the effect of
sodium benzoate in altering the elution profile. At the end of 6 hours, the same
differential between the eluate entering and exiting the column (less than 1 ppm Au) was
obtained. Therefore, sodium benzoate was not a necessary addition for elution.
Elution Comparison
ppm Au
20
15
10
5
0
0
50
100
150
200
250
300
350
time, minutes
2/3/2000 typical w/ benzoate
3/3/2000 no benzoate
Figure 6. Rich Eluate Profile Comparison
Dore analysis
Dore analysis indicated that selectivity of the AuRIX® resin for gold and silver over
copper (the major base metal present) was favorable compared to the production plant
using CIS at the mine in Mexico. During this campaign, the average head grade was
0.326 ppm Au. A total of 16.1 gm of dore was recovered. Approximately 50,000 L of
solution was processed in this campaign, with each column undergoing 5 cycles of
extraction-elution. The dore produced by the AuRIX® 100 resin analyzed: 90.01 % Au,
9.37 % Ag, and 0.62% Cu compared to 68.7% Au, 25.9% Ag, and 5.5% Cu produced in
the CIS production plant.
4.0 Capital and Operating Cost Comparison of AuRIX® 100 RIS and CIS
Plants Treating Heap Leach Solutions – Case Study Parameters
Based on the success of the Isabella Mine and the Mexican pilot plant trials, it was
decided to make an economic comparison of CIS and RIS for the recovery of gold from
heap leach solutions. The engineering study used in this work was carried out by
Lycopodium Pty. Ltd, Perth Western Australia. (5).
In order to make an economic evaluation between these two technologies, two operating
conditions representing the extremes in solution flow and grade generally experienced in
heap leach operations (See Table 2) were selected as the basis for the CIS and the RIS
circuit designs.
Case
Circuit
T
PLS
G d
PLS
Fl
Annual Au
P d ti
6
Type
Grade
(mg
Au/L)
Flow
(m3/hr)
Production
(oz/yr)
1
CIS
0.5
400
50,000
2
CIS
2.0
100
50,000
3
RIS
0.5
400
50,000
4
RIS
2.0
100
50,000
Table 2. Circuits Selected for Comparison
The parameters used in the RIS circuit designs have been based on the results of
preliminary resin testwork and knowledge of conventional ion exchange circuits. The
parameters used in the CIS circuit designs have been based on industry standard values
and CIS plant operating data.
For the RIS circuit design the following parameters were measured in the laboratory:
Resin hydraulics,
Resin extraction isotherm
Resin extraction kinetics.
Resin elution kinetics
4.1 Resin Bed Hydraulics
The low bulk density of the resin and the regular spherical shape results in a low specific
fluidization velocity limiting the upflow flowrate that can be passed through a resin
contactor. Initial bed fluidization occurred at an approximate specific upflow velocity of
3.5 m3/m2hr. Specific upflow flowrates up to 20 m3/m2/hr can be used if sufficient
provision is made in the contactor design to allow for the resulting bed expansion to
prevent resin carryover.
In a downflow configuration, the pressure drop across the resin bed was very low (< 1.5
kPa/m at 100 BV/hr) allowing the circuit to be designed for a high specific downflow
flowrate with a low pressure drop and minimal bed compaction.
Based on these results, the preliminary RIS circuit design incorporates downflow for
extraction and upflow for elution. The downflow configuration for extraction allows the
RIS circuit to operate over a wide range of flowrates without the concern over bed
expansion limitations. The upflow configuration for elution will permit the flushing of any
trapped particulate material from the resin column and partially expand the bed to
prevent compaction and potential short-circuiting.
4.2 Freundlich Extraction Isotherm
Measured volumes of high grade (200 ml) and low grade (1,000 ml) pregnant leach
solutions (PLS) were contacted with five different masses of pre-conditioned resin for a
period of 48 hours to ensure equilibrium was attained. The resin had been preconditioned with dilute caustic solution and pre-loaded to ~600 g Au/t dry resin to
7
simulate an anticipated plant barren resin. The residual solutions were then assayed for
metal values and free cyanide. For the Mexico mine leach solution, 4 resin masses were
contacted each with 19.0 L of solution pumped through a small column for 40 hours.
Residual solutions were assayed for metal values. The resultant resin and solution data
was then used to determine the equilibrium isotherm, which can be described by the
following Freundlich equation:
[Au]Resin = a [Au]Solnb
The Freundlich constants and loading capacity of the resin for the low grade, high grade
and Mexico mine heap leach solution are summarized in Table 3.
Data
a
b
Loading Capacity
(gAu/t) Dry Resin
1,218
0.456
2,364
0.458
10,097
0.304
16,550
Freundlich Constants
Mexico Mine
solution
(0.42 mg
Au/L)
Low Grade
(1.56 mg
Au/L)
2,858
2,323
High Grade
(7.82 mg
Au/L)
Table 3. Summary of Freundlich Constants
The AuRIX® resin has very good loading characteristics at low gold solution grades (<
1.0 mg/L Au) resulting in high loaded resin grades (up to 7,000 g Au/dry tonne of resin).
4.3 Loading Kinetics
The high grade and low grade PLS were contacted with a measured mass of preconditioned resin in bottle rolls. The solutions were sampled at 0.5, 1, 2, 4, 8 and 12
hours and assayed for Au, Ag, Cu and Zn. Loading kinetics were also done on feed
solution from the heap leach operation in Mexico. The data was then plotted as; ln
[Au]Resin versus ln t, resulting in a straight line from which the Nicol-Fleming rate
constant, k, and the equilibrium loading factor, n, could be derived (Nicol et al, 1984).
The Nicol-Fleming rate equation is commonly used to model carbon circuits. It is:
[Au]Resin = k[Au]Soln tn
where [Au]Resin is the concentration of gold on the resin in g/t and [Au]Soln is the time
weighted average gold concentration in solution in mg/L.
The Nicol-Fleming rate constants for the resin at the two solution grades, actual
measured rate constants for carbon derived from plant data and the typical values used
in the design of CIS circuits are shown in Table 4.
8
Case
AuRIX® @ 1.2 g resin /L (high grade)
AuRIX® @ 0.24g resin/L (low grade)
AuRIX® @ 0.23g resin/L (Mexico Mine)
Fairview CIP Data
Activated C Design
“k” (h-1)
“n”
201
449
645
260
150
0.33
0.37
0.51
0.52
0.6
Table 4. Nicol-Fleming Rate Constants
The low “n” values for the two resin bench scale solution tests indicate that the
adsorption rate of gold onto the resin was limited by the equilibrium loading capacity of
the resin (i.e. insufficient resin was used in the kinetic tests). Without consideration of
any effect that the equilibrium loading capacity may have had on extraction kinetics of
the resin, the results indicate that AuRIX® has significantly faster extraction kinetics than
activated carbon as shown in Figure 7.
4000
g Au/t
3500
3000
Mexico Mine
2500
Carbon Data
2000
Carbon Design
1500
Low grade (1.56 mg Au/L)
1000
500
0
0
5
10
t hr
Figure 7. Resin versus Carbon Rate Curves
4.4 Resin Elution
Loaded resin samples from the continuous RIS testwork were combined, placed in three
Perspex columns and used for the elution testwork. The barren eluant used in the
elution testwork contained 40 g/L NaOH, 70 g/L sodium benzoate and 100 ppm NaCN
spiked to 1 mg Au/L as aurocyanide. The barren eluant was heated to 60oC and pumped
in an upflow direction through each column at target flowrates of 5, 10, and 20 BV/hr.
The results are summarized in Figure 8.
The test results indicated the following:
High pregnant eluant tenors (< 400 mg Au/L) were observed at the lowest
flowrate (5 BV/hr) during the initial 30 minutes of elution.
No significant difference in elution rate was observed between 10 BV/hr and 20
BV/hr flow rates
The elution results show that eluted resin values of below 400 gAu/t can be
obtained in 12 hours and below 150 g Au/t in 24 hours of elution. For a
9
carousal mode RIS plant operating with a 24 hour cycle there would be little
advantage in restricting the elution time to 12 hours
.
9,000
Resin Grade (mg/L Au)
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
0
5
10
15
20
25
Elution Time (hours)
5 BV/hr
10 BV/hr
20 BV/hr
Figure 8 Resin Elution Rate
4.5 Resin Fouling/Poisoning and Mercury Issues.
Resin ‘fouling’ relates to the susceptibility of the resin to load or ‘foul’ with inorganic salts
(calcite or gypsum) or organic compounds (humic acid, diesel) that result in an apparent
loss of loading capacity and extraction kinetics. In all laboratory and pilot testwork to
date no evidence has been seen that the resin is susceptible to fouling of any type. The
potential for fouling of AuRIX® resin by organic compounds is expected to be
significantly less than for carbon. Humic acids and other organic anions may load but
will strip along with the aurocyanide in elution. For the purposes of this evaluation, an
acid wash step was included in the resin elution cycle to address any potential fouling by
inorganic salts. During the actual pilot plant experience, however, no requirement for
acid washing was observed.
Metal cyanide complexes such as Co(CN)63-, Fe(CN)63-, and Cu(CN)32- can potentially
bind to strong base ion exchange resins so strongly that they can not be removed
resulting in poisoning of the resin. Data from the Isabella pilot plant trial indicates that
the base metal cyanides will load to some equilibrium value but also are eluted. During
the first 93 days of the trial (23 elution cycles), no increase in the level of base metals on
the eluted resin was observed. Thiocyanate can also poison strong base resins. With
AuRIX® resin, the thiocyanate is eluted along with the gold.
Mercury cyanide anionic complexes such as Hg(CN)3- ,Hg(CN)42- will be extracted by
AuRIX®100 and will elute with the gold. Because AuRIX® 100, unlike carbon, does not
require thermal reactivation no mercury fume problems will be encountered when using
AuRIX®100. The neutral complex Hg(CN)2 is unlikely to be extracted by AuRIX® 100.
While the co extraction of mercury with gold is a disadvantage, it does open the
10
possibility for the use of AuRIX® 100 to clean up the washing solutions used in the
remediation of depleted heaps which contain mercury as cyanide solution (2).
5.0 AuRIX®100 RIS Versus CIS Cost Study
The key CIS and RIS design criteria used as a basis for the evaluation are summarized
in Table 5. No allowance has been made for:
Mining capital.
Heap leach pad and pond construction.
Power and water supply.
Royalties and license fees.
Owner’s costs.
Parameters
Units
Carbon-in-Solution Circuit
Resin-in-Solution Circuit
Case 1 Low
Grade
Case 2 High
Grade
Case 3 Low
Grade
Case 4 Low
Grade
m /h
m3/h
3
400
500
100
125
400
500
100
125
mg Au/L
mg Ag/L
0.50
0.05
2.00
0.20
0.50
0.05
2.00
0.20
Upflow
Upflow
Downflow
Downflow
50
50
60
60
m /m h
60
60
60
60
Number of Contactors
No.
5
6
4
5
Design Gold Loading
g Au/t
1,250
5,000
4,000
10,000
Pressure Zadra
Pressure Zadra
Atmospheric
Atmospheric
PLS Flowrate
Nominal
Design
PLS Grade
Gold
Silver
PLS Flow Direction
Volumetric Flowrate
BV/h
3
Specific Velocity
2
Elution Type
Elution Batch Size
dry tonnes
wet tonnes
5.0
1.2
2.89
5.95
0.72
1.49
Elution Frequency
days
1.3
1.3
2.3
1.5
Upflow
Upflow
Upflow
Upflow
Eluate Flow Direction
Elution Cycle Time
Hrs
16
16
12
12
Number of Electrowinning Cells
No.
2
3
2
3
Parallel
Parallel
Parallel
Series
800 x 800
800 x 800
800 x 800
800 x 800
12
12
12
Configuration of Cells
Size of Cells
Number of Cathodes
mm
12
Table 5 Capital Cost Estimate Parameters
11
5.1 Capital Cost Estimate
Capital costs were estimated for the adsorption, elution, gold room, regeneration, and
reagent/services areas. The capital cost estimate for each circuit is summarized in
Table.6
Cost Center
CIS Circuits
RIS Circuits
Low High Low High
US$
US$
US$
US$
(000's) (000's) (000's) (000's)
Direct Costs
Adsorption
Elution/Gold room
Regeneration
Reagent/Services
317
629
302
379
229
349
221
284
323
410
0
263
189
287
0
221
1,627
1,083
996
697
Indirect Costs
EPCM
Preproduction
First Fill1
Working Capital
Spares
Insurances
250
71
182
244
45
8
250
71
83
152
30
5
250
68
822
165
30
5
250
68
306
117
20
4
Total Indirect
800
591
1,340
765
Contingency
238
155
210
146
Grand Total
2,665
1,829
2,546
1,608
Total Direct
Note: "Low" refers to low grade PLS (0.5 mg Au/L at 400 m3/hr) and "High" refers to high
grade PLS (2.0 mg Au/L at 100 m3/hr). 1 Resin Cost =$30.00/wet Kg, Carbon Cost =
$2.29/Kg.
Table 6 Capital Cost Estimate Summary
5.2 Operating Cost Estimate
Operating costs were estimated for the adsorption, elution, gold room, regeneration, and
reagent/services area in terms of consumables, maintenance, labor, and power. The
operating cost estimate for each circuit is summarized in Table 7 both as an overall
operating cost and as the total operating cost per ounce of gold produced.
12
CIS Circuits
RIS Circuits
Low
US$/a
High
US$/a
Low
US$/a
High
US$/a
Consumables
330,926
96,848
55,456
26,708
Maintenance
129,240
85,930
73,820
51,590
Labor
343,125
343,125
290,625
290,625
Power
173,467
82,019
156,148
74,331
Total
976,758
607,922
576,049
443,255
19.22
12.16
11.52
8.87
US$/oz A
Table 7 Operating Cost Summary
While only at a preliminary level, the testwork was sufficiently detailed to provide a basis
for the (± 25%) capital and operating costs estimates. The capital and operating cost
estimates are summarized in Table 8
Case Plant
1
2
3
4
CIS
CIS
RIS
RIS
PLS
Grade
Annual
Production
oz Au/a
Capital Cost
US$, 000’s
Operating Cost
US$/oz Au
Low
High
Low
High
50,000
50,000
50,000
50,000
2,665
1,829
2,546
1,608
19.22
12.16
11.52
8.87
Table 8 Summary of Capital and Operating Costs
Both the capital and operating cost estimates indicate a savings for a RIS circuit using
AuRIX® 100 (~ 4% to 12% in capital and 27% to 40% in operating costs) over
conventional CIS circuits.
In addition to the savings in capital and operating costs an RIS plant using AuRIX® 100
offers significant advantages in terms of security. The resin would not be moved from
the extraction and elution columns and there would be no access to the loaded resin.
The only part of the RIS plant which would require special security would be the gold
room.
For installation and operation in remote areas where skilled operators are in short
supply, an AuRIX® 100 RIS plant will offer advantages of simple construction and
operation. The plant could be constructed offshore and transported to site in a modular
form. Once assembled, the main operating activities, excluding maintenance, would be
restricted to switching of valves to operate the carousel and management of the gold
room. For small orebodies, the plant could be readily disassembled and transported to a
new location when the original heap was exhausted.
13
6.0 Gekko Systems’ InLine Leach Reactor and AuRIX®100.
The combination of the InLine Leach Reactor (ILR) and Aurix Resin offers some unique
design advantages and synergies. In particular the intensification and modularization
which Gekko Systems’ InLine Leach Reactor brings to gold processing is matched by
the compactness and simplicity of the Aurix systems for loading and stripping.
Furthermore Aurix provides a unique process route for treating gold concentrates which
are difficult to treat for a number of reasons, including high copper and the presence of
preg-robbers and carbon fouling agents.
In a gravity only or gravity flotation plant Aurix improves the economics of treating the
resulting medium grade concentrates by increasing and simplifying gold recovery from
the pregnant solution without the complication and expense of a dedicated carbon
stripping plant.
6.1 Treating High Grade Gold Copper Concentrates – Brown’s Creek
Recovery of gold bullion from gravity or flotation concentrates produced in a copper
concentrator is very attractive from both a cash flow and total gold revenue perspective.
The vagaries of sampling a gravity concentrate containing free gold also lead to
substantial uncertainties in correct payment terms for contained gold.
A process developed by Gekko Systems and Hargraves Resources for the Brown’s
Creek copper concentrator is described in a paper by Gray et al. in which the economics
were found to be very favorable. Unfortunately the mine has since been shut down due
to flooding.
The process involves intensive cyanidation under controlled conditions followed by gold
recovery onto Aurix®100. The resin selectively recovers gold from the mixed gold
copper leach solution. The loaded resin is stripped with caustic solution in a single step
to provide a solution for electrowinning. From a concentrate containing about
15000 ppm gold and 6% copper, over 95% of the total gold can be recovered into an
80% gold bar.
Process Development
A number of processes were investigated before the final flowsheet shown in figure 11
was decided on. Testwork was undertaken to prove leaching and demonstrate
absorption and resin stripping.
It was found that by using lead nitrate and LeachWell, a proprietary leach accelerant, as
well as oxygen, gold recovery was accelerated and copper recovery reduced as shown
in figure 9.
Resin absorption kinetics and selectivity were demonstrated as shown in figure 10. It
should be noted that very high levels of both gold and copper were present in the
pregnant solution. The selectivity of gold over copper remained high with 95% gold and
5% copper being absorbed. In the worse case where all the loaded gold and copper is
recovered into the final product this will result in a gold bar of 85% fineness.
Aurix improves the electrowinning efficiency of the system in two ways. Firstly it reduces
the heavy metal content and secondly it isolates any negative effects due to LeachWell
which will reduce electrowinning efficiency if present in the cell.
14
100
% recovery
80
Au leaching
60
Cu leaching
40
20
0
0
6
12
18
24
time (hours)
Figure 9 Gold and Copper Leaching Kinetics
metal in solution (mg/L)
12000
10000
8000
Au
6000
Cu
4000
2000
0
0.0
0.5
1.0
1.5
2.0
time (hours)
Figure 10 Gold and Copper Absorption Kinetics and Selectivity.
PLANT DESIGN
The proposed plant flowsheet is shown in figure 11. The design is for an InLine Leach
Reactor, model ILR100, followed by resin columns and a standard electrowinning cell.
In the InLine Leach Reactor the concentrate is de-watered, mixed with fresh reagents
and recycled stripped liquor from the resin columns, then leached in the rotating drum.
15
Leached slurry overflows into the solution recovery section where the solids are
recovered and clarified pregnant solution is pumped to the resin columns. The resin
columns will be operated in split cycle; one column will load while the next is stripped
and electrowon at elevated temperature.
Concentrate
reagents
stripped leach solution
settling cone
solution
bleed
Resin
Columns
solid
tails
pregnant
solution
ILR100
feed
hopper
reactor drum
load
(strip)
strip
(load)
discharge
sump
overflow solution
to mill circuit
to concentrate
thickener
Copper Precipitation
and Detoxification
Electrowinning
Figure 11. Simplified Process Flowsheet.
Economics
The capital cost was estimated at about AUD$300,000 not including the electrowinning
cells which are available on site. Operating costs are estimated at about AUD$3.50/oz.
Operating costs are dominated by reagents. The following economic analyses are
approximate with capital costs and benefits annualised over two years.
At Brown’s Creek gold recovered in flotation was about 40% of mill feed, however
payment terms for the concentrate represent considerable operating and capital costs
for the operation. Gold in concentrate attracts a 2% treatment charge and late payment
which, at AUD$450/oz, (~USD330/oz) represents about AUD$290,000 /y treatment
costs and AUD$1.8M in operating capital. This is a considerable economic incentive to
maximise gravity gold recovery.
The breakeven point for the project was an increase in gravity recovery to 60% of mill
feed, with no increase in overall plant recovery which was very achievable based on
mineralogy and the prevailing tabling practice.
Further economic benefit was expected since it was extremely unlikely that a significant
increase in gravity recovery could have no effect on overall plant recovery. The most
16
likely increase in gold recovery was considered to be between 2% and 7%. A 2%
increase in recovery would give a further benefit of AUD700,000/year at the then
prevailing gold price of USD330/oz.
6.2 Gravity Only and Gravity Flotation Plants
Gekko Systems’ has developed a number of flowsheets to treat high grade and difficult
to treat ore bodies using advanced gravity concentration and flotation combined with
intensive leaching of the resulting concentrates as discussed in a paper by Gray et al.
The intensive leaching of gravity and/or flotation concentrates using high levels of
cyanide and oxygen, when used in the proper application, can result in overall gold
recoveries comparable to or greater to those seen with traditional whole ore leach
circuits. Advantages include:
•
•
•
•
•
•
•
•
•
Maximized return to shareholders with a combined reduction in capital and risk
High security and less gold room labour
Easy installation – modular design
A reduction in equipment lead time,
Smaller plant footprint
Reduced cyanide and carbon consumption
Lower reagent handling
Reduced tailings disposal and environmental costs
Lower energy costs
Aurix resin adds further synergy to this flowsheet by extending its application to lower
grade concentrates, where solution recovery is particularly critical, and difficult to treat
concentrates containing copper, heavy metals or carbon fouling material eg kerosene to
inhibit preg robbing.
RIS Recovery for a Complex Preg Robbing Gravity Flotation Concentrate
A current project at Gekko Systems involves the recovery of gold from a highly complex
orebody containing gold occurring as both free and sulphide associated gold of varying
levels of refractoriness with a carbon rich preg robber.
Past metallurgical test work had shown that gravity concentration could yield both a gold
product suitable for smelting and gravity gold sulphide concentrate containing up to 80
percent of the gold. Flotation of the gravity tailings recovered a further 18 percent of the
gold. Combined gold recoveries were reported to be up to 97 percent. However the
recovery of gold from the concentrates by cyanide leaching in conventional CIP or RIP
systems varied from 75% to 91% depending on oretype. This was identified as being
caused by the presence of preg robbers and worsened by the fine grind sizes required to
leach the gold under conventional leach conditions.
Further testwork, by others, indicated that recovery could be improved through the use
of high intensity gravity separation units, coarser grinds to minimise carbon liberation,
kerosene blinding of the preg robbers and the use of the Gekko Systems ILR. The ILR
allowed the use of a high effective liquid to solid ratio. So gold is made available for
recovery from solution at low gold levels as soon as it is leached. This minimizes the
17
time preg robbers are in contact with high grade gold solution.
Au Leaching
100
90%
90
80%
80
70%
70
60%
% leached
Recovery
Tabling Recovery Yield Curve
100%
50%
40%
60
50
40
30%
30
20%
20
10%
10
0%
0%
0
20%
40%
60%
80%
100%
Yield
Fig 12: Gravity recovery mass yield curve
0
6
12
time (hours)
18
24
Fig 13: Concentrate leach recoveries
From the test work results a simplified flow sheet was developed for the plant. This flow
sheet incorporates InLine Pressure Jigs, Bowl Centrifugal Concentrators and tabling to
produce a high yield gravity concentrate. Gekko Systems’ continuous ILR10000 is then
used to leach the concentrate, producing a clarified pregnant solution.
The choice of the optimal process for gold recovery from the leach solution is not trivial,
and has not been finalised. The solution has significant levels of heavy metals, cyanide
and kerosene which affect the performance of carbon, conventional resins, zinc
precipitation, direct electro-winning and Aurix.
The evaluation of Aurix for this application included a pilot trial of a conventional resin in
solution (RIS) system similar to the RIS systems previously piloted for Heap Leach
operations.
The pilot plant consisted of four columns in a carousel arrangement. The pregnant
solution was passed through the four columns in series for 16 hours to load the resin.
After 16 hours pregnant solution flow was stopped, the first column removed and
stripped, then replaced at the end of the series of columns, becoming the final column in
the sequence. Pregnant solution flow then recommenced and continued for a further 16
hours. A total of five loading and four stripping cycles were performed.
The aim of the trial was to confirm design parameters for gold absorption and check for
any reduction in resin performance due to a build up of silver, which was at high levels in
the solution, or other elements.
The solution used was derived from a bulk leach of the concentrate to be treated. The
resin used was pre loaded to gold levels predicted from earlier test work. This was to
accelerate the approach of the system to steady state and therefore minimize the
number of cycles required.
18
Electro-winning was not practical at the scale of the test so a fresh strip solution was
used throughout.
The column geometry was designed to emulate the expected full scale resin hydraulics.
Therefore the height of the column was as per full scale design and the column area was
proportional to the solution flow to give the same superficial flow velocity and bed
expansion.
The major test parameters and results are summarized in table 9 below. Loading
recoveries are the average over the last three absorption cycles. Stripping recoveries
are for all four strips and are related back to the first four loading cycles.
Column Design
Loading
Design Gold Recovery
97.5
Aurix per Stage
92.5
Stage Diameter
15
Aurix Rest Height
523
Cylinder Height
1047
Solution Flowrate
28
Residence Time per Stage
2.6
Total Residence Time
10.6
Load Cycle time
16
Total Test Loading Time
73
Stripping
Strip Flowrate
4.5
Strip duration
15
Result Summary
%
mL
mm
mm
mm
mL/min
min
min
hours
hours
mL/min
hours
Loading
Final Gold Recovery
Gold Initial Grade
Final Silver Recovery
Silver Initial Grade
98.3
13.4
31
64.3
%
ppm
%
ppm
Stripping
Total Gold Recovery
Average Gold Grade
Total Silver Recovery
Average Silver Grade
97
88
18
77
%
ppm
%
ppm
Table 9 Summary of Pilot Test Design and Results.
Gold recovery was high at over 98% and agreed well between the loading and stripping
performance. Indicating the steady state was reasonably close to the initial conditions
chosen. Silver recovery was lower, as had been expected, and more silver was loaded
than stripped indicating the steady state loading of silver on the columns increased
through the tests. This was to be expected since no pre-loading with silver was
performed.
The loading performance of the four column system over time is shown in Figure 14. It
is seen that the recoveries of gold are high throughout the test and are gradually
improving, indicating the steady state performance was slightly better than predicted in
the design calculations.
19
100%
100%
99%
90%
98%
80%
97%
70%
96%
60%
95%
50%
94%
40%
93%
Gold
30%
92%
Silver
20%
91%
Silver Recovery
Gold Recovery
10%
90%
0%
0
10
20
30
40
50
60
70
80
Total Test Time (hours)
Figure 14 Gold and Silver Recovery in Aurix RIS Pilot Test
The silver recoveries can be seen to drop over the duration of the test as the silver
loading on the columns built up. The silver recoveries also drop sharply over each
loading cycle showing the columns are fully loaded with silver.
Analysis of the final loaded resin showed no significant build up of minor elements and
no signs of poisoning were observed during the test. There was no indication of silver
levels interfering with gold absorption.
The results demonstrated Aurix could be used to recover gold from a complex solution at
design performance.
RIP Recovery for a High Copper Gold Flotation Concentrate
In a second project at Gekko Systems the properties of Aurix have been used in the
design of a leach plant for the recovery of gold from a medium grade gold concentrate.
In this project the aim is to economically recover bullion from a flotation concentrate with
a gold grade of about 60ppm and a copper content of about 2%. Currently the
concentrate is sold to a refinery and substantial refinery charges are suffered.
Leaching tests established high gold recoveries were obtainable at economic cyanide
addition rates and moderate levels of copper leaching, however direct electrowinning of
the resulting pregnant solution was too slow to be effective and copper was recovered at
high levels resulting in a very low gold content bullion. Experimental leach recoveries
are shown in figure 15 and electrowinning results in figures 16a and 16b. Note the
difference in solution concentrations between the two electrowinning curves.
20
100
90
80
% leached
70
60
50
40
Au
30
Cu
20
10
0
0
6
12
time (hours)
18
24
Figure 15 Leach Kinetics of Gold and Copper
300
14
12
250
Cu in Solution (ppm)
Au in Solution (ppm)
Experimental
10
Model
8
6
4
Experimental
Model
200
150
100
50
2
0
0
0
50
100
150
200
250
Time (min)
Figure 16a Gold Electrowinning
300
0
50
100
150
200
250
300
Time (min)
Figure 16b Copper Electrowinning
Aurix was recognized as an ideal solution for this application. Initial test work using
actual leach solutions confirmed the isotherms, kinetics and selectivity of gold over
copper were suitable. These are shown below in figure 17b and figure 17c. It was noted
that between the 4 and 24 hour samples the loading of copper on the Aurix reduced as
the gold “crowded off” some of the copper which had initially loaded. This demonstrates
the strong selectivity of Aurix for gold under these conditions.
Design criteria developed in previous projects were used to determine the contact times
and loadings required. Mass balance calculations confirmed the gold to copper ratios
would remain within established performance parameters.
21
Figure 17a Gold Absorption Isotherms
Figure 17b Copper Absorption Isotherms
1600
1600
1hr; pH 11.5
4hr; pH 11.5
24hr; pH11.5
1200
1hr; pH 11.5
4hr; pH 11.5
24hr; pH 11.5
1400
Cu Aurix Loading mg/wet L
Au Aurix Loading mg/wet L
1400
1000
800
600
400
200
1200
1000
800
600
400
200
0
0
0
1
2
Au Solution assay ppm
3
4
0
20
40
60
80
Cu Solution assay ppm
It was then recognized that significant further simplification of the process could be
achieved by using a Resin in Pump (RIP) absorption system. This greatly simplified
solid liquid separation and reduced solution gold losses.
To accomplish the RIP contacting Gekko Systems has developed a multistage
countercurrent downflow column which allows the direct treatment of fine dilute slurries
without the need for clarification. The dilute slurries, under 10% solids, produced by the
InLine Leach Reactor are more amenable to being treated in an RIP column than more
concentrated slurries.
A simplified flowsheet of the process developed to treat this concentrate in shown in
figure 18. The concentrate is fed to the ILR where it is added to recycled barren solution
and make up reagents. The reacted slurry is then pumped to a safety screen to remove
oversize material before being fed to the RIP column. The Barren slurry is withdrawn
from the bottom of the column and dewatered in a thickener, where the bulk of of the
solution is recycled to the ILR. The solids and a small amount of entrained barren
solution is taken to a detoxification circuit prior to disposal. The resin in the contactor is
advanced up the column counter current to the slurry until the highly loaded resin at the
top of the column is withdrawn and transferred to the stripping circuit where it is stripped
at elevated temperature with caustic and the gold simultaneously recovered by
electrowinning. The stripped resin is returned to the base of the column for reuse.
This flowsheet is currently in the final stages of evaluation for installation at full scale.
Gekko Systems believes Aurix presents many opportunities to extend the application of
the InLine Leach Reactor while significantly simplifying existing treatment routes. By
applying a creative design approach based on solid laboratory results the future of Aurix
in gold recovery is extremely promising.
22
23
final tails
Detox transfer pump
Detox Reaction Tank
detox peroxide
ILR Tails Cone
Safety Screen
RIP Column
KEY
Leach slurry
Eduction solution flow
Resin transfer
Strip and electrowin flow
Gold Product
continuous
batch
batch
batch
batch
Strip Solution Storage
Fresh Resin Holding Tank
Resin Strip Column
Resin Screen
Figure 18 InLine Leach Reactor, Aurix in Pulp and Detox Circuit to Treat a Low Grade, High Copper Flotation Concentrate
Detox Holding Tank 2 off
Feed Surge Tank Feed Pump
barren solution tank
InLine Leach Reactor
leach cyanide
repulp sump pump
water
leach peroxide
existing concentrate filter
gold filtercake
Electrowinning
References.
(1) Gray, AH, Katsikaros, N and Fallon, P. Gold Recovery From Copper Gold
Gravity Concentrates Using The Inline Leach Reactor And Weak Base
Resin. Oretest Copper Gold Symposium, Perth. November 1999
(2) Virnig, M.J., Mackenzie, J.M.W., and Adamson, C. The use of guanidine
based extractants for the recovery of gold. Hidden Wealth, Johannesburg. South
African Institute of Mining and Metallurgy. 1996 pp151-156.
(3) Virnig, M.J. and Mackenzie, J.M.W., Extractants for the Recovery of Gold. III
International Gold Symposium Lima Peru. 1998.
(4) Kordosky,G.K. ,Kotze,M.H. ,Mackenzie,J.M.W., and Virnig,M.J. New solid
and liquid extractants for
gold. Proceedings XVIII, International Mineral
Processing Congress. Sydney 1993, pp 1195-1203.
(5) Cognis AuRIX®100 Resin for Gold Extraction. Fisher, G.T., Lewis, R.G.
Virnig, M.J. Mackenzie,J.M.W. , and Davis, M.R. ALTA 2000 SX/IX Technical
Proceedings, 2000. ALTA Melbourne Australia.
(6) Gray AH ,Abols J, McCallum A, Patrick G, Johansen G., CIP – Who Needs
It? Canadian Mineral Processor’s Conference, Vancouver, January 2003
24

1 The Use of AuRIX®100 Resin and Gekko Systems Technology for

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