Abstract
Periodic mesoporous organosilica (PMO), functionalized with soft lewis base organic
groups were synthesized to be used for gold adsorption from a thiosulfate complex. PMOs were
assembled using a non-ionic surfactant (Pluronic P123) along with an ethylene-bridged
organosilane precursor. Recovery of gold from gold-thiosulfate systems has proven to be a
challenge and inefficient in relation to the current cyanide leaching recovery process. PMOs
with high BET surface areas (over 900 m2/g) and uniform pores sizes of about 70 Å were used to
prevent pore blockage by organic groups – a problem that exists in regular organic-inorganic
mesoporous silica hybrids. Organic functionalization of PMOs was done using thiol, dithiol, and
thiourea nucleophiles, and their use in gold recovery from both thiosulfate and chloride systems
was effective. Adsorption of gold (I) ions from gold-thiosulfate solutions also demonstrated
maximum adsorption at weakly basic pH levels.
i
Acknowledgements
I would first like to give thanks to my family and friends for the tremendous support they
have given me throughout my entire life. I would like to express my sincere gratitude to my
supervisor Dr. Mercier for his support, direction, and supervision of my thesis project and
studies. I also greatly appreciate all the help that my lab partners Mauricio Melo and Babak
Fotoohi have given me this past year, along with all professors and laboratory technicians that
have taught me at Laurentian University. Finally, to Laurentian University, and specifically the
Department of Chemistry and Biochemistry, I thank you for the last four years of my life, for
they have truly been special.
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Table of Contents
List of Figures
v
List of Tables
vii
1.
Introduction
1
1.1
1
1.2
1.3
Gold
1.1.1
Mining
1
1.1.2
Extraction by Cyanide Leaching
1
1.1.3
Recovery from Cyanide Complex
2
1.1.4
Environmental Concerns
2
1.1.5
Chloride Leaching
3
1.1.6
Thiosulfate Leaching
3
1.1.7
Recovery from Thiosulfate Complex
4
Mesoporous Silica
4
1.2.1
Synthesis
6
1.2.2
Organic Functionalization
7
Periodic Mesoporous Organosilica
1.3.1
1.4
2.
Synthesis
8
16
Objective
15
Experimental
15
2.1
Synthesis of Periodic Mesoporous Organosilica
15
2.1.1
Materials
15
2.1.2
Synthesis
15
2.1.3
Characterization
16
iii
2.2
3.
Bromination of PMO
16
2.3
Organic Functionalization
17
2.4
Gold Adsorption
17
2.4.1
Recovery from Thiosulfate Complex
17
2.4.2
The Effect of pH
18
2.4.3
Recovery from Chloride Complex
18
Results and Discussion
22
3.1
Analysis of PMO-EE
22
3.1.1
Nitrogen Adsorption
22
3.1.2
Thermogravimetric Analysis
22
3.2
3.3
3.4
4.
Bromination of PMO-EE
23
3.2.1
Nitrogen Adsorption
23
3.2.2
Thermogravimetric Analysis
23
3.2.3
Calculation of Fraction Brominated
23
Substitution of PMO-Br
24
3.3.1
Nitrogen Adsorption
24
3.3.2
Thermogravimetric Analysis
24
Gold Adsorption
25
3.4.1
Adsorption Capabilities of PMOs
25
3.4.2
The Effect of pH
26
Summary and Conclusions
4.1
5.
41
Future Plans
42
References
43
iv
List of Figures
Figure 1.1
The Influence of pH on Thiosulfate Stability
Figure 1.2
General Synthesis of Mesoporous Silica with Amphiphilic Surfactant and
TEOS Silica Precursor
Figure 1.3
10
11
Functionalization of Mesoporous Silica by (A) Post-Synthesis Grafting
and (B) Co-Condensation
12
Figure 1.4
Synthesis of PMOs using Bridged Organosilane Precursors
13
Figure 2.1
The Structures of BTEE and Pluronic P123
19
Figure 2.2
The Adsorption of Gold to Thiol-Functionalized Periodic Mesoporous
Organosilica (PMO-SH) from Gold Thiosulfate Complex
21
Figure 3.1
Nitrogen Adsorption Isotherm of PMO-EE
28
Figure 3.2
Pore Distribution Curve of PMO-EE
29
Figure 3.3
TGA Weight Loss Data for PMO-EE
30
Figure 3.4
Nitrogen Adsorption Isotherm of PMO-Br
31
Figure 3.5
Pore Distribution Curve of PMO-Br
32
Figure 3.6
TGA Weight Loss Data for PMO-Br
33
Figure 3.7
Nitrogen Adsorption Isotherms of PMO-SH, PMO-TU, and PMO-EDT
34
Figure 3.8
Pore Distribution Curves of PMO-SH, PMO-TU, and PMO-EDT
35
Figure 3.9
TGA Weight Loss Data for PMO-SH, PMO-TU, and PMO-EDT
36
Figure 3.10
Gold Adsorption Isotherms with AuThioS concentrations 1-100 ppm
using PMO-SH, PMO-TU, and PMO-EDT
Figure 3.11
37
The Effect of pH on Gold Adsorption with PMO-SH, PMO-TU, and
PMO-EDT
38
v
Figure 3.12
Gold Adsorption Isotherms with AuCl concentrations 1-200 ppm using
PMO-SH, PMO-TU, and PMO-EDT
vi
40
List of Tables
Table 1.1
Stability Constants of Various Gold Complexes
14
Table 2.1
Nucleophiles for Substitution with PMO-Br
20
Table 3.1
The Effect of pH on Gold Adsorption with PMO-SH, PMO-TU, and
PMO-EDT
39
vii