Development of a Quantitative Accelerated Sulphate Attack Test for Mine Backfill

218 Pages·2009·4.85 MB·English

Development of a Quantitative Accelerated Sulphate
Attack Test for Mine Backfill

By

Shahé Shnorhokian

Department of Mining and Materials Engineering
McGill University, Montreal

May 2009

A thesis submitted to McGill University in partial fulfillment of the
requirements of the degree of Doctorate of Philosophy

© Shahé Shnorhokian, 2009
i
ABSTRACT
Mining operations produce large amounts of tailings that are either disposed of in
surface impoundments or used in the production of backfill to be placed underground.
Their mineralogy is determined by the local geology, and it is not uncommon to come
across tailings with a relatively high sulphide mineral content, including pyrite and
pyrrhotite. Sulphides oxidize in the presence of oxygen and water to produce sulphate
and acidity. In the concrete industry, sulphate is known to produce detrimental effects by
reacting with the cement paste to produce the minerals ettringite and gypsum. Because
mine backfill uses tailings and binders – including cement – it is therefore prone to
sulphate attack where the required conditions are met. Currently, laboratory tests on mine
backfill mostly measure mechanical properties such as strength parameters, and the study
of the chemical aspects is restricted to the impact of tailings on the environment. The
potential of sulphate attack in mine backfill has not been studied at length, and no tests
are conducted on binders used in backfill for their resistance to attack.
Current ASTM guidelines for sulphate attack tests have been deemed inadequate by
several authors due to their measurement of only expansion as an indicator of attack.
Furthermore, the tests take too long to perform or are restricted to cement mortars only,
and not to mixed binders that include pozzolans. Based on these, an accelerated test for
sulphate attack was developed in this work through modifying and compiling procedures
that had been suggested by different authors. Small cubes of two different binders were
fully immersed in daily-monitored sodium sulphate and sulphuric acid solutions for a
total of 28 days, after 7 days of accelerated curing at 50ºC. In addition, four binders were
partially immersed in the same solutions for 8 days for an accelerated attack process. The
two procedures were conducted in tandem with leach tests using a mixed solution of
ethylene glycol and methanol solution, which enabled the quantification of ettringite and
gypsum that had formed due to the attack.
Combining the partial immersion technique with the dissolution of ettringite and
gypsum in the organic solutions, a new quantitative accelerated test for sulphate attack
was developed.
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RÉSUMÉ
Les opérations minières produisent de grandes quantités de rejets miniers qui sont
soit stockés en surface dans des haldes, soit réutilisés comme remblais sous terre. La
minéralogie de ces déchets est dictée par la géologie des lieux, et il est commun de
trouver des rejets qui ont une teneur élevée en minéraux sulfurés comme la pyrite et la
pyrrhotite. Les sulfures sont oxydés en présence d’eau et d’oxygène et produisent une eau
acide et riche en sulfates. Dans l’industrie du béton, un des grands problèmes provient de
la réaction des sulfates de sources externes avec le ciment du béton pour former de
l’ettringite et du gypse. Étant donné que les remblais dans les mines se servent des rejets
et d’agents de liaison comme le ciment, ils sont sensibles aux attaques des sulfates si les
conditions sont propices. En ce moment dans les laboratoires, on s’intéresse surtout aux
paramètres mécaniques comme la résistance en compression et l’impact chimique que les
rejets miniers ont sur l’environnement. Aucune recherche concrète n’a été faite sur les
dangers de l’attaque des sulfates sur les remblais dans les mines et sur les différents
agents de liaisons, afin de déterminer leurs résistances à de telles attaques.
Les directives actuelles de l’ASTM pour tester l’attaque des sulfates se sont avérées
inadéquates. En effet, ces tests sont seulement basés sur l’expansion, ce qui ne se produit
pas forcément lors de l’attaque par des sulfates. De plus, ces tests sont trop longs et ne
peuvent s’appliquer qu’à certains mélanges spécifiques de ciment et pas à d’autres
comme la pouzzolane. Sur ces faits, un test accéléré a été mis en place par certains
chercheurs. Après un séchage accéléré dans un four à 50ºC, des échantillons sont
immergés dans des solutions de sulfate de sodium et d’acide sulfurique pendant 28 jours
d’une part. D’autre part, d’autres échantillons sont immergés à moitié dans ces mêmes
solutions pendant 8 jours pour une attaque accélérée. Ces deux procédures sont suivies
par un filtrage des échantillons qui sont séchés par une solution 3:1 d’éthylène glycol et
de méthanol, un mélange qui permet de déterminer la quantité d’ettringite formée. Ainsi,
non seulement nous avons pu étudier des échantillons qui ont subi une attaque accélérée
de sulfates, mais aussi nous avons pu évaluer l’ampleur de l’attaque en mesurant la
quantité d’ettringite formée dans les échantillons.
iii
TABLE OF CONTENTS
ABSTRACT........................................................................................................................I
RÉSUMÉ...........................................................................................................................II
TABLE OF CONTENTS...............................................................................................III
LIST OF TABLES..........................................................................................................VI
LIST OF FIGURES.....................................................................................................VIII
LIST OF ABBREVIATIONS..........................................................................................X
ACKNOWLEDGEMENTS..........................................................................................XII
CHAPTER : 1 INTRODUCTION..................................................................................13
1.1. Tailings geochemistry................................................................................13
1.2. Sulphate attack in mine backfill.................................................................13
1.3. Sulphate attack tests...................................................................................14
1.4. Problem definition......................................................................................16
1.5. Objectives and scope of the research project.............................................17
1.6. Thesis outline.............................................................................................18
CHAPTER : 2 THE GEOCHEMISTRY OF SULPHIDE-RICH MINE TAILINGS ...............19
2.1. Introduction................................................................................................19
2.2. Tailings production....................................................................................19
2.3. Quebec sulphide deposits...........................................................................20
2.4. Sulphide oxidation......................................................................................22
2.4.1. Mechanisms of sulphide oxidation........................................................23
2.4.2. Factors affecting sulphide oxidation......................................................24
2.4.3. Rates of sulphide oxidation....................................................................27
2.5. Acid mine drainage....................................................................................28
2.5.1. Definition and scope..............................................................................28
2.5.2. Effects and examples.............................................................................29
2.5.3. Neutralization.........................................................................................29
2.5.4. Prediction...............................................................................................31
2.5.5. Classification and testing.......................................................................32
2.5.6. Prevention..............................................................................................33
2.5.7. Treatment...............................................................................................36
2.6. Secondary minerals....................................................................................38
2.6.1. Categories..............................................................................................38
2.6.2. Hardpan layer.........................................................................................39
2.6.3. Iron oxides.............................................................................................40
2.6.4. Testing and analysis...............................................................................41
2.7. Conclusions................................................................................................44
CHAPTER : 3 SULPHATE ATTACK............................................................................45
3.1. Introduction................................................................................................45
3.2. Cement and concrete..................................................................................45
3.2.1. Cement components...............................................................................46
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3.2.2. Cement hydration...................................................................................46
3.2.3. Components of concrete........................................................................47
3.3. Definition of sulphate attack......................................................................50
3.4. Types of sulphate attack.............................................................................50
3.4.1. Chemical and physical attack.................................................................51
3.4.2. Internal attack.........................................................................................51
3.4.3. External attack.......................................................................................53
3.5. Characteristics of sulphate attack...............................................................57
3.5.1. Formation of ettringite...........................................................................57
3.5.2. Formation of gypsum.............................................................................59
3.5.3. Physical consequences...........................................................................60
3.6. Prevention of sulphate attack.....................................................................62
3.7. Testing for sulphate attack.........................................................................63
3.8. Assessment of tests for sulphate attack......................................................64
3.9. Conclusions................................................................................................65
CHAPTER : 4 SULPHIDE MINERALS IN MINE BACKFILL..........................................66
4.1. Introduction................................................................................................66
4.2. Mechanical properties................................................................................66
4.2.1. Compressive strength.............................................................................67
4.2.2. Permeability...........................................................................................68
4.2.3. Particle size distribution.........................................................................69
4.2.4. Forms of failure......................................................................................69
4.2.5. Strength gaining methods......................................................................70
4.3. Mineralogical properties............................................................................71
4.4. Components of mine backfill.....................................................................73
4.4.1. Tailings..................................................................................................73
4.4.2. Natural sands..........................................................................................75
4.4.3. Rock and aggregate................................................................................75
4.4.4. Cement...................................................................................................75
4.4.5. Pozzolans...............................................................................................76
4.4.6. Admixtures.............................................................................................78
4.4.7. Cost of binders.......................................................................................78
4.5. Types of backfill.........................................................................................79
4.5.1. Slurry or hydraulic backfill....................................................................79
4.5.2. Paste backfill..........................................................................................81
4.5.3. Rock fill.................................................................................................82
4.6. Sulphide-rich tailings in backfill................................................................83
4.7. Conclusions................................................................................................85
CHAPTER : 5 EXPERIMENTAL PROCEDURE............................................................86
5.1. Introduction................................................................................................86
5.2. Materials.....................................................................................................86
5.2.1. Chemicals and solutions........................................................................86
5.2.2. Cementitious binders.............................................................................89
5.2.3. Laboratory hardware..............................................................................89
5.3. Instrumentation...........................................................................................90
5.3.1. X-ray diffraction....................................................................................90
v
5.3.2. Atomic absorption..................................................................................91
5.3.3. Ion chromatography...............................................................................91
5.3.4. ICP-OES................................................................................................91
5.4. Methodology..............................................................................................91
5.4.1. Washing procedure................................................................................92
5.4.2. Weighing and volume measurement......................................................93
5.4.3. Quality assurance – Quality control.......................................................93
5.4.4. Sample acidification and storage...........................................................93
5.4.5. Fumehood..............................................................................................94
5.4.6. pH measurement....................................................................................94
5.5. Phase I – Tests on minerals........................................................................94
5.5.1. Gypsum leaching...................................................................................95
5.5.2. Ettringite formation................................................................................99
5.5.3. Ettringite leaching................................................................................101
5.5.4. Leaching of other materials.................................................................111
5.6. Phase II – Tests on binders.......................................................................113
5.6.1. Preparation of binders..........................................................................113
5.6.2. Curing process.....................................................................................114
5.6.3. Sulphate and acid attack tests..............................................................115
5.6.4. Qualitative analysis – XRD.................................................................120
5.6.5. Quantitative analysis – EGM 31..........................................................121
5.7. Conclusion................................................................................................122
CHAPTER : 6 RESULTS AND DISCUSSION...............................................................123
6.1. Introduction..............................................................................................123
6.2. Phase I results – Minerals.........................................................................123
6.2.1. Gypsum characterization.....................................................................123
6.2.2. Ettringite 2 characterization.................................................................131
6.2.3. Ettringite 3 characterization.................................................................147
6.3. Phase II results – Binders.........................................................................159
6.3.1. Curing process.....................................................................................160
6.3.2. Full immersion tests.............................................................................166
6.3.3. Partial immersion tests.........................................................................180
6.3.4. Full and partial immersion tests - Comparisons..................................190
6.3.5. Conclusions..........................................................................................196
CHAPTER : 7 CONCLUSIONS AND RECOMMENDATIONS.......................................198
7.1. Introduction..............................................................................................198
7.2. Conclusions..............................................................................................198
7.3. Statement of originality............................................................................199
7.4. Recommendations for future work...........................................................200
REFERENCES...............................................................................................................203
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LIST OF TABLES
Table 3-1 – Typical compositions of clinker and admixtures (mass %)...........................48
Table 3-2 – Age required for pore discontinuity (Powers et al 1959)..............................49
Table 4-1 – Comparison of binder costs (DeGagné 1996)...............................................79
Table 5-1 – Chemical composition of cementitious binders (in %).................................89
Table 5-2 – Details of Batch 1 tests on gypsum...............................................................96
Table 5-3 – Details of Batch 2 tests on gypsum...............................................................96
Table 5-4 – Details of Batch 3 tests on gypsum...............................................................97
Table 5-5 – Details of Batch 4 tests on gypsum...............................................................97
Table 5-6 – Details of Batch 5 tests on gypsum...............................................................98
Table 5-7 – Details of Batch 6 tests on gypsum...............................................................99
Table 5-8 – Details of Batch 1 tests on ettringite............................................................102
Table 5-9 – Details of Batch 2 tests on ettringite............................................................103
Table 5-10 – Details of Batch 3 tests on ettringite..........................................................104
Table 5-11 – Details of Batch 4 tests on ettringite..........................................................105
Table 5-12 – Details of Batch 5 tests on ettringite..........................................................106
Table 5-13 – Details of Batch 6 tests on ettringite..........................................................107
Table 5-14 - Details of Batch 7 tests on ettringite..........................................................108
Table 5-15 - Details of Batch 8 tests on ettringite..........................................................109
Table 5-16 - Details of Batch 9 tests on ettringite..........................................................110
Table 5-17 – Details of batch tests on chemicals............................................................112
Table 5-18 – Details of batch tests on cementitious binders..........................................112
Table 5-19 – Binders used in several Canadian mines (Mining Sourcebook 2003).......113
Table 5-20 –Phase II binders and their proportions........................................................114
Table 6-1 – Results of Batch 1 tests on gypsum – IC/centrifuge....................................125
Table 6-2 – Results of Batch 2 tests on gypsum – IC/centrifuge....................................125
Table 6-3 – Results of Batch 3 tests on gypsum – ICP/centrifuge.................................126
Table 6-4 – Results of Batch 4 tests on gypsum – ICP/centrifuge.................................126
Table 6-5 – Results of Batch 5 tests on gypsum – ICP/filter..........................................127
Table 6-6 – Results of Batch 6 tests on gypsum – ICP/filter..........................................128
Table 6-7 – Aluminum and ettringite extraction (from Uchikawa and Uchida 1974)....134
Table 6-8 – Results of Batch 1 tests on Ettringite 2B – AAIC/centrifuge......................135
Table 6-9 – Results of Batch 2 tests on Ettringite 2A – AAIC/centrifuge.....................135
Table 6-10 – Results of Batch 3 tests on Ettringite 2C – AAIC/centrifuge....................136
Table 6-11 – Results of Batch 3 tests on Ettringite 2C – ICP/centrifuge.......................136
Table 6-12 – Results of Batch 4 tests on Ettringite 2B – ICP/centrifuge.......................137
Table 6-13 – Results of Batch 5 tests on Ettringite 2A, 2B, and 2C – ICP/centrifuge...138
Table 6-14 – Results of Batch 6 tests on Ettringite 2B – ICP/filter................................139
Table 6-15 – Results of Batch 7 tests on Ettringite 2A and 2B – ICP/filter...................140
Table 6-16 – Results of Batch 9 tests on Ettringite 2B – ICP/filter................................141
Table 6-17 – Results of Batch 1 tests on Ettringite 3B – AAIC/centrifuge....................148
Table 6-18 – Results of Batch 2 tests on Ettringite 3A – AAIC/centrifuge...................148
Table 6-19 – Results of Batch 3 tests on Ettringite 3C – AAIC/centrifuge....................149
Table 6-20 – Results of Batch 3 tests on Ettringite 3C – ICP/centrifuge.......................149
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Table 6-21 – Results of Batch 4 tests on Ettringite 3B – ICP/centrifuge.......................150
Table 6-22 – Results of Batch 5 tests on Ettringite 3A, 3B, and 3C – ICP/centrifuge...151
Table 6-23 – Results of Batch 6 tests on Ettringite 3B – ICP/filter................................152
Table 6-24 – Results of Batch 7 tests on Ettringite 3A and 3B – ICP/filter...................153
Table 6-25 – Results of Batch 8 tests on Ettringite 3B – ICP/filter................................153
Table 6-26 – Results of leach tests on PS binder – 3 days of curing..............................163
Table 6-27 – Results of leach tests on PS binder – 7 days of curing..............................163
Table 6-28 – Results of leach tests on PF binder – 3 days of curing..............................164
Table 6-29 – Results of leach tests on PF binder – 7 days of curing..............................164
Table 6-30 – Results of leach tests on PS binder - fully immersed in NS – 14d............173
Table 6-31 – Results of leach tests on PS binder - fully immersed in NS – 28d............173
Table 6-32 – Results of leach tests on PF binder - fully immersed in NS – 14d............174
Table 6-33 – Results of leach tests on PF binder - fully immersed in NS – 28d............174
Table 6-34 – Results of leach tests on PS binder - fully immersed in HS – 14d............177
Table 6-35 – Results of leach tests on PS binder - fully immersed in HS – 28d............177
Table 6-36 – Results of leach tests on PF binder - fully immersed in HS – 14d............178
Table 6-37 – Results of leach tests on PF binder - fully immersed in HS – 28d............178
Table 6-38 – Results of leach tests on PS binder - partially immersed in NS – 8d........186
Table 6-39 – Results of leach tests on PF binder - partially immersed in NS – 8d........186
Table 6-40 – Results of leach tests on PC binder - partially immersed in NS – 8d........186
Table 6-41 – Results of leach tests on PSF binder - partially immersed in NS – 8d......186
Table 6-42 – Results of leach tests on PS binder - partially immersed in HS – 8d........187
Table 6-43 – Results of leach tests on PF binder - partially immersed in HS – 8d........187
Table 6-44 – Results of leach tests on PC binder - partially immersed in HS – 8d........187
Table 6-45 – Results of leach tests on PSF binder - partially immersed in HS – 8d......187
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LIST OF FIGURES
Figure 2-1 – Map of operating mines in Quebec..............................................................21
Figure 4-1 – Typical size distributions of mine backfill (Henderson and Revell 2005)...74
Figure 5-1 – Ettringite formation on the horizontal shaker............................................100
Figure 5-2 – Direct filtration into 50 ml tube.................................................................109
Figure 5-3 – Extraction of ettringite samples in 60 ml Nalgene bottles on shaker.........111
Figure 5-4 – Oven curing of cubes wrapped in wet towels............................................115
Figure 5-5 – Full immersion of binder cubes in sulphate and acid attack solutions.......116
Figure 5-6 – Monitoring of pH for samples fully immersed in NS................................117
Figure 5-7 – Partial immersion of binder cubes in stainless steel trays..........................118
Figure 5-8 – Grinding a cube in excess acetone.............................................................120
Figure 6-1 – XRD plot for gypsum.................................................................................124
Figure 6-2 – Gypsum dissolution (g/l) in water and EGM 31........................................129
Figure 6-3 – Gypsum dissolved in water and EGM 31 (%)...........................................130
Figure 6-4 – Gypsum dissolved in water and EGM 31 (% sulphur)..............................130
Figure 6-5 – XRD plot for Ettringite 2A and 2B............................................................132
Figure 6-6 – Ettringite 2 solubility in water....................................................................142
Figure 6-7 – Ettringite 2 solubility in EGM 31...............................................................142
Figure 6-8 – Ettringite 2 solubility in water (W:V 0.1 to 1.5)........................................144
Figure 6-9 – Ettringite 2 percentage in water.................................................................145
Figure 6-10 – Ettringite 2 percentage in EGM 31..........................................................145
Figure 6-11 – Ettringite 2 sulphur percentage in EGM 31.............................................146
Figure 6-12 – XRD plot for Ettringite 3A and 3B..........................................................148
Figure 6-13 – Ettringite 3 solubility in water..................................................................155
Figure 6-14 – Ettringite 3 solubility in EGM 31.............................................................155
Figure 6-15 – Ettringite 3 solubility in water (W:V 0.1 to 1.5)......................................156
Figure 6-16 – Ettringite 3 percentage in water...............................................................157
Figure 6-17 – Ettringite 3 percentage in EGM 31..........................................................157
Figure 6-18 – Ettringite 3 sulphur percentage in EGM 31.............................................159
Figure 6-19 – XRD analysis of binder components........................................................160
Figure 6-20 – XRD analysis of the four binders – 3 days of curing...............................161
Figure 6-21 – XRD analysis of the four binders – 7 days of curing...............................162
Figure 6-22 – Ettringite percentage in PS binder............................................................165
Figure 6-23 – Ettringite percentage in PF binder............................................................166
Figure 6-24 – PS binder cubes fully immersed in NS (left) and HS (right) – 14d.........167
Figure 6-25 – PS binder cube showing reaction rim – fully immersed in HS – 14d......167
Figure 6-26 – PF binder cubes fully immersed in NS (left) and HS (right) – 14d.........168
Figure 6-27 – PF binder cube showing reaction rim – fully immersed in HS – 14d......168
Figure 6-28 – PS binder cubes fully immersed in NS (left) and HS (right) – 28d.........169
Figure 6-29 – PS binder cube transformed into gypsum – fully immersed in HS – 28d 169
Figure 6-30 – PF binder cubes fully immersed in NS (left) and HS (right) – 28d.........169
Figure 6-31 – PF binder cube showing reaction rim – fully immersed in HS – 28d......170
Figure 6-32 – XRD analysis of PS and PF binders fully immersed in NS – 14d...........170
Figure 6-33 – XRD analysis of PS and PF binders fully immersed in HS – 14d...........171
ix
Figure 6-34 – XRD analysis of PS and PF binders fully immersed in NS – 28d...........172
Figure 6-35 – XRD analysis of PS and PF binders fully immersed in HS – 28d...........172
Figure 6-36 – Ettringite percentage in fully immersed PS binder – 14 and 28 days......175
Figure 6-37 – Ettringite percentage in fully immersed PF binder – 14 and 28 days......176
Figure 6-38 – Gypsum percentage in fully immersed PS binder – 14 and 28 days........179
Figure 6-39 – Gypsum percentage in fully immersed PF binder – 14 and 28 days........180
Figure 6-40 – PS and PF binders partially immersed in NS – 2d...................................181
Figure 6-41 – PC and PSF binders partially immersed in NS – 2d................................182
Figure 6-42 – PS and PF binders partially immersed in HS – 2d...................................182
Figure 6-43 – PC and PSF binders partially immersed in HS – 2d................................183
Figure 6-44 – PS and PF binders partially immersed in HS – 8d...................................183
Figure 6-45 – PC and PSF binders partially immersed in HS – 8d................................183
Figure 6-46 – All binders partially immersed in NS – 8d...............................................184
Figure 6-47 – All binders partially immersed in HS – 8d...............................................185
Figure 6-48 – Ettringite percentage in partially immersed binders – 8 days..................188
Figure 6-49 – Gypsum percentage in partially immersed binders – 8 days....................189
Figure 6-50 – XRD of PS binder immersed in NS – 8d partial and 28d full..................190
Figure 6-51 – XRD of PF binder immersed in NS – 8d partial and 28d full..................191
Figure 6-52 – XRD of PS binder immersed in HS – 8d partial and 28d full..................192
Figure 6-53 – XRD of PF binder immersed in HS – 8d partial and 28d full..................192
Figure 6-54 – Ettringite percentage in PS binder – 8d partial and 28d full....................193
Figure 6-55 – Ettringite percentage in PF binder – 8d partial and 28d full....................194
Figure 6-56 – Gypsum percentage in PS binder – 8d partial and 28d full......................195
Figure 6-57 – Gypsum percentage in PF binder – 8d partial and 28d full......................196