NICHROMET
CYANIDE-FREE PROCESS
FOR GOLD EXTRACTION
D. Lemieux, B. Dubreuil and J.-M. Lalancette
Nichromet Extraction Inc.
3700 rue du Lac Noir
Thetford Mines, QC Canada
Corporate Information
 Private company founded in 1997
 Controlling shareholder : Dundee Corporation
 30 M$ investment since its foundation in development of
technologies and properties
 Current portfolio of technologies includes :
 Nickel from laterites (high Mg content)
 Production of specialty fertilizers
 Stabilisation of arsenic
 Precious metals extraction by chlorination
Current Global Situation
 Pressure over cyanide is increasing worldwide
 Banned in some area (Eastern Europe, Montana, Wisconsin,
etc.)
 Environmental impact is now a decisional factor in
many new mine projects
 El Morro project, Goldcorp, Chile
 Pasca Lama project, Barrick, Chile
 Rosia Montana project, Gabriel Resources, Romania
Introduction
 Patented process for precious metals extraction using chlorination
instead of cyanidation
 Based on a century old known chemistry using chlorine but
applied with modern techniques
 Using hypohalides, instead of chlorine gas, simplifies operation,
safety and recycling of halogens by electrolysis
 A closed circuit approach with full recycling of reagents
 Base metals, if present, (Cu, Zn) are also recuperated
Chemistry involved
Chlorine, along with a catalytic amount of bromine, used as oxidizing
agents because of the particularly fast reaction of bromine with gold.
2 HOCl + 2 HCl → 2 Cl2 + H2O
2 NaBr + Cl2 → 2 NaCl + Br2
2 Au + 3 Br2 → 2 AuBr3
2 AuBr3 + 3 Cl2 →
2 AuCl3 + 3 Br2
Process Flowsheet Overview
Ore
Sodium
Hypochlorite
Sulfuric
Acid
Slurry Preparation
Reactor
Vat Leaching
Reactor
Rinsing
Water
Electrolysis
Filtration
CaCO3
Polishing
Na2CO3
Pregnant
Brine
Na2SO4
Na2SO4
Crystalisation
Barren Solid
CounterCurrent
Washing
Ca(OH)2
Neutralisation
Fe(OH)3
Barren
Brine
Silica
Absorption
Melting
Au/Ag
Sodium
Sulphite
Some Pictures of the Pilot Plant
General Characteristics
 Mild conditions
– The leaching of precious metals is done in vat leaching at
atmospheric pressure and ambient temperature
 Produce inert tailings
– The barren solid after gold/silver extraction is essentially sulfurfree, inert and stable
 Closed-circuit
– Water is fully recycled leaving no effluent for the process
A Key Step:
Regeneration of Hypohalides
 Chlorine/bromine are uses as the active agents in
the reactor itself
 Chlorine/bromine generated in situ by introducing
hypohalides in the reactor under acidic condition
2 HOCl + 2 HCl → 2 Cl2 + H2O
 Hypohalides are further regenerated by electrolysis
Electrolysis Chemistry
Involved for Regeneration
Halogens are generated in a membrane less
electrolytic cell.
Anode:
2 Cl- → Cl2 + 2e-
Cathode:
2 Na+ + 2e- → 2 Na
2 Na + 2H2O → 2 NaOH + H2
Mixing :
2 NaOH + Cl2
→ NaOCl + NaCl
Pilot Plant System
Gold depleted brine is
circulated through the
electrolysis cell
ELECTROLYSIS CELL
ELEMENTS
INLET
OUTLET
NaCl
57 g/L
56 g/L
NaBr
5 g/L
1,15 g/L
NaOCl
0,00 %
0,71 %
NaOBr
0,03 %
1,93 %
pH
8,62
8,84
Flow rate
20 gph
Regeneration of Hypohalides
Pilot Plant Results
 Electrolysis is producing preferentially sodium
hypobromide before sodium hypochloride
Cl- → Cl2
Br- → Br2
E° = -1,36 V
E° = -1,07 V
 The regenerated this brine was used for leaching
and leads to the >90-95 % gold extraction yield in
1 hour
Application at the Pilot Scale
on a Refractory Concentrate
 Direct cyanidation yielded only 55% recovery
 Gold finely distributed in matrix

Average grain size at 3,9 microns
 Gold associated with pyrite

Concentrate produced with 93 % recovery
Elements
Ore
Concentrate
Au (g/T)
4,21
60,4
As (%)
0,05
0,66
Fe (%)
4,91
33,92
Ssulphides (%)
2,53
35,82
Oxidation of the Concentrate
 Can be either POX or Roasting (with
appropriate gas treatment)
 In this particular case, roasting was used
Elements
Concentrate
Au (g/T)
66,0
As (%)
0,61
Ca (%)
2,82
Fe (%)
39,0
Stotal (%)
2,7
Ssulphides (%)
0,2
Successfully Demonstrated on a
Wide Range of Material
Type
Grade (g/T)
Barren Solid
(g/T)
Yield (%)
1: Canada
(Quebec)
Ore
2,58 g/T
0,07 g/T
97,5 %
2: Canada
(Quebec)
Ore
3,45 g/T
0,34 g/T
93,2 %
3: Canada
(Quebec)
Ore
13,9 g/T
0,79 g/T
95,4 %
4: Canada
(Ontario)*
Conc.
55,3 g/T
4,79 g/T
94,0 %
5 : Eastern
Europe*
Conc.
7,5 g/T
1,48 g/T
91,0 %
6: Canada
(Quebec)*
Conc.
53,5 g/T
3,56 g/T
94,1 %
Sources
*Flotation concentrates requiring pre-treatment by oxydation
Environment
 Closed-loop process with recycling of reagents
and water (no need of costly tailings ponds)
 The barren solids are rinsed with water and meet
easily environmental regulation
Concentration*
(mg/L)
Criteria
(mg/L)
Parameter
Concentration*
(mg/L)
Criteria
(mg/L)
290
1,500
Ni
< 0.1
2
148
-
Co
< 0.1
-
SO4
663
1,500
Cr
< 0.1
5
Ca
335
-
Cd
< 0.1
0.5
Mg
25
-
Pb
< 0.1
5
Mn
< 0.1
50
Zn
< 0.1
250
Fe
< 0.1
-
As
< 0.1
5
Parameter
-
Cl
Better than
regulation
for mining
residues
-
Br
=
* : EPA 889/10
** : Environnement-Québec
Economics of the Process
 Evaluation of operating costs for a 400 TPD plant
REVENUS
Compare
advantageously
to industry
standards
Units
Ore grade
4,38 g/T
Value (1300 $/oz, 95% recovery)
173 $/T
PROCESS COSTS*
Units
Crushing/grinding
10,00 $/T
Gold Extraction
9,15 $/T
Labor
8,05 $/T
Energy
1,85 $/T
G&A
0,95 $/T
TOTAL PROCESS COST
21,95 $/T
156 $/oz Au
*Mining costs not included
Economic Comparison to Cyanide
 Nichromet process operation costs are similar
to cyanidation on a $/oz basis
 Capital costs lower by a factor of about 10-15
% (Canadian installation) due to
 Smaller plant (24-48X shorter process time)
 No need of costly tailings pond as for cyanide
Pilot Plant Summary
 Built in 2010
 Accumulated 2 years of operation
 7 different ore or concentrates processed so far
 Total of about 70 T of ore processed
 Over 800 hours of operation
 Extraction yield
 > 90 % in all cases
 95% in most cases
 Demonstrated on a whole ore and concentrates
First Industrial Plant is
Currently Under Construction
 Construction of a 25 M$ Demonstration Plant is
underway



Capacity of 15 TPD of concentrates
Gold pyrite concentrates as feed material
Includes a 300 TPD concentration plant
 Start-up scheduled for 3rd quarter of 2014
 2 years demonstration program on a continuous
basis 24/7 plant
Conclusions
 Technology successfully demonstrated at pilot
scale (Due diligence by Hatch)
 First industrial implementation underway
 Full support from majority shareholder (Dundee
Corporation) for project financing
 Companies with advanced exploration or prefeasibility stages projects are invited to submit
samples for lab demonstration
 Performed at Nichromet own costs