This document summarizes the results of a study analyzing gold content in minerals containing tellurium using cupellation. Various flux mixtures were tested on pure substances and industrial minerals with and without prior roasting. Higher gold recoveries were achieved with roasted minerals compared to unroasted. Future work will evaluate different roasting times and temperatures and perform material balances and assays on slags from unroasted ore.

1. “GOLD ANALYSIS BY CUPELLATION IN
MINERALS CONTAINING TELLURIUM”
V.M. Rodríguez-Chávez*, P.C. Santos-Munguía, J.C. Fuentes-Aceituno,
F. Nava-Alonso
*manuel.rodriguez@cinvestav.edu.mx
Zacatecas, Zacatecas. April 25, 2018
XXVII INTERNATIONAL CONGRESS OF EXTRACTIVE
METALLURGY
CINVESTAV
Unidad Saltillo
1

2. 4.92 5.29 5.79
1.3
0.88
0
5
10
15
20
25
30
700 800 900 1000 1100 1200
Gold
loss
(%)
Temperature (°C)
Con Teluro Sin Teluro
Gold losses in cupellation as a function of temperature, for minerals with
and without tellurium (Easley & Keniston, 1909).
Introduction
with tellurium without tellurium
2

3. • Preliminary assays
• Assays with pure
substances
• Assays with industrial
mineral
• Assay with flux mixtures for
sulfur matrix minerals.
• Assay with flux mixtures for
oxidized matrix minerals.
• SiO2 + Au
• SiO2 + AuTe2
• SiO2 + Cu2Te + Au
• SiO2 + Te + Au
• Roasting the ore at
650°C for 24 hours
• Oxidation
pretreatment
(roasting)
Methodology
3

4. 1st Stage: Fusion
Homogenization of
the ore by means of
quartering.
Preparation of flux
mixture.
Mixing of the ore and
fluxes inside the clay
crucible.
Bórax-glass addition on
the mineral and flux
mixture.
Fusion of the mineral and
fluxes mixture at 1'000°C
for 1 hour.
Emptying the molten
mineral in the crucible
mold.
Solidification
and cooling
to room
temperature.
Separation of the lead,
gold and silver by
gravity.
By hammering, the lead is
separated from the slag.
4

5. 2nd Stage: Cupellation
Preheating of cups
at 850 °C.
Placement of leads
on top of the cups
at 850°C.
Cooling the dore
to room
temperature.
Weighing of
the dore.
5

6. 3rd Stage: Parting
Preheating
HNO3 (25%) at
90°C in a
water bath.
Placement of
doré in the
preheated
HNO3.
Separation of solid gold by
decantation with
preheated deionized
water.
Calcination of
solid gold
(elimination of
HNO3 residues)
at 600 °C for 5
minutes.
Weighing the gold.
6

7. Results of the fire assay (cupellation) ...
Preliminary assays mixtures of fluxes:
Mixtures for minerals with
sulfur matrix
Mixtures for minerals with
oxidized matrix
M1 M2 M3 M4 M5 M6 M7 M8
C
o
m
p
o
n
e
n
t
s
Mineral (g) 10 10 10 10 3 10 10 10
Na2CO3 (g) 17.44 13.03 14.4 20.57 10 10.29 14.736 22.984
PbO (g) 40.57 33.71 40.57 13.71 46 72.5 50 45.6
KNO3 (g) 23.81 3.43 15.78 0 0 0 0 0
SiO2 (g) 6.17 3.43 4.12 1.37 3 0 6.312 2.368
Na2B4O7 (g) 3.43 0 6.86 6.86 1 3.43 4.736 8.208
C (g) 0 0 0 0 0 18 7 0.84
AgNO3 (g) 0 0 0 0 0 0.5 0.5 0
Fe (g) 0 0 0 31 0 0 0.5 0
K2CO3 (g) 0 0 0 0 0 0 4.208 0
Results
and
discussion
7

8. Results…
Weight of lead buttons obtained (g)
0
62.18
40.65
0.21
0
62.339
42.954
0
0
10
20
30
40
50
60
70
5 6 7 8
Weight
(g)
Mixtures of fluxes
Prueba de fund. para mineral
con matriz oxidada
Réplica
Flux mixtures for
minerals with
oxidized matrix
Replica
Results
and
discussion
8

9. Results…
Weight of the doré obtained (g)
0
0.1193
0.3252
0.0016
0
0.1802
0.3044
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
5 6 7 8
Weight
(g)
Mixtures of fluxes
Prueba de fund. para mineral con
matriz oxidada
Réplica
Replica
Flux mixtures for minerals
with oxidized matrix
Results
and
discussion
9

10. Results…
0
0.338
1.036
0
0
0.61
1.077
0
0
0.2
0.4
0.6
0.8
1
1.2
5 6 7 8
Weight
(mg)
Mixtures of fluxes
Prueba de fund. Para
mineral con matriz oxidada
Réplica
Weight of the solid gold (mg)
Flux mixtures for
minerals with oxidized
matrix
Replica
Results
and
discussion
10

11. Results
and
discussion
Mixtures of fluxes
Chemical
reagents
Mineral (g)
Results…
11

12. Temperature Time of permanence Heating rate
1000°C 60 min 10°C/min
Temperature Time of permanence Heating rate
850°C 60 min 10°C/min
1000°C 30 min 10°C/min
Temperature Time of permanence Heating rate
850°C 10 min 10°C/min
Fusion
Cupellation
Preheating of cups
Temperature Time of permanence
90°C Aprox. 5 min
Preheating HNO3 (Al 25%)
Conditions for each stage of the assay:
Results
and
discussion
Results…
12

13. 0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
0.002
1 2 3
Weight
of
gold
(g)
Mixtures of fluxes
Gold recovery (SiO2 + Au)
Au0
Au
Recovery of gold in assays with pure substances (SiO2 + Au)
Results
and
discussion
Results…
Au0
Au1
13

14. 0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
0.002
1 2 3
Weight
of
gold
(g)
Mixtures of fluxes
Gold recovery (SiO2 + AuTe2)
Au0
Au
Recovery of gold in assays with pure substances (SiO2 + AuTe2)
Results
and
discussion
Results…
Au0
Au1
14

15. 0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
0.002
1 2 3
Weight
of
gold
(g)
Mixtures of fluxes
Gold recovery (SiO2 + Cu2Te + Au)
Au0
Au
Recovery of gold in assays with pure substances (SiO2 + Cu2Te + Au)
Results
and
discussion
Results…
Au0
Au1
15

16. 0
0.0005
0.001
0.0015
1 2 3
Weight
of
gold
(g)
Mixtures of fluxes
Gold recovery (SiO2 + Te + Au)
Au0
Au
Recovery of gold in assays with pure substances (SiO2 + Te + Au)
Results
and
discussion
Results…
Au0
Au1
16

17. Temperature Time of permanence Heating rate
650°C 1440 min (24 hrs) 10°C/min
Roasting conditions
AuAgTe4 + 4 O2  Au + Ag + 4 TeO2
Proposed reaction:
References:
• Lu Z, Lawson F. Metallurgical properties of synthetic sylvanite, 1994. AusIMM Proceed.
299(2):89–93.
• Padmanaban V, Lawson F. Metallurgical properties of synthetic calaverite, 1991. AusIMM Proceed.
296(1):31–37.
Results
and
discussion
Results…
17

18. 18
3.6 3.5 3.4
4.802
4.214 4.214
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
1 2 3
Concentration
(g/ton.)
Mixtures of fluxes
Mineral sin tostar
mineral tostado
Unroasted ore
Roasted ore
Recovery of gold in ore with and without previous roasting treatment.
Results
and
discussion
Results…

19. Diffractogram of the ore before being roasted.
3.1 Characterization of mineral before roasting treatment:
Results
and
discussion
Results…
19

20. Diffractogram of the ore after being roasted.
3.1 Characterization of mineral after roasting treatment:
Results
and
discussion
Results…
20

21. Thermal analysis of the unroasted mineral
Results
and
discussion
Results…
21

22. • Assays with industrial
minerals
• Evaluation of the effect of
roasting time (24 and 72
hours)
• Evaluation of the effect of
roasting temperature (550,
600, 650, 700 and 750°C)
• Oxidation
pretreatment
(roasting)
Future
• Material balance
• Assaying of unroasted
ore slags
22