arsenic removal by iron oxides sonia aredes a thesis submitted in partial fulfillment of requirements

122 Pages·2009·5.3 MB·English

ARSENIC REMOVAL BY IRON OXIDES
BY
SONIA AREDES
B.A.Sc. Chemical Engineering. Universidad Nacional de Salta. Argentina. 1981
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
In
THE FACULTY OF GRADUATE STUDENTS
(Mining Engineering)
THE UNIVERSITY OF BRITISH COLUMBIA
December, 2005
©Sonia Aredes, 2005
ABSTRACT
Arsenic has long been recognized as a toxin and carcinogen. Arsenic contaminated
drinking water probably poses the greatest threat to human health. A successful treatment
for removing arsenic from drinking water requires an understanding of arsenic chemistry
and the physical-chemical processes that occur during each treatment step. Iron oxide
(Fe-Ox) minerals showed good efficiency for arsenic removal (Simeonova 2000, Matis
et.al., 1999). Additionally, naturally occurring iron oxides are more attractive for arsenic
removal from contaminated water than the synthetic oxides because they are more cost
effective. However, few studies have been carried out on the feasibility of their use as
adsorbents for arsenic removal.
Hematite, magnetite, goethite and laterite have been studied in their role as arsenic
adsorbents. Results showed that all of them are suitable as arsenic adsorbents.
Electroacoustic Tests (ET) tests showed that arsenic adsorption occurs over the whole pH
range considered (4-11) and also that the Fe-Ox have IEP at pH between 6.5 and 8.5.
Their surface charge is negative at pH<pzc and positive at pH >pzc. The presence of
inner sphere complex, which implies stability of the arsenic adsorbed onto Fe-Ox because
of covalent bonding, was shown by ET and leaching tests. Leaching tests by MgCL; were
performed to study the stability of the adsorption products and results expressed on a
weight percentage basis showed that hematite had 60.2%, magnetite 75.4%, goethite
78.0% and laterite 86.2% of arsenic strongly fixed. While these results expressed on a
2 * 2
surface area basis showed that hematite had 0.16mg/m , magnetite O.llmg/m , goethite
0.065 mg/m and laterite 0.011 mg/m of arsenic strongly fixed.
ii
In addition, this study presents a simple method developed to remove arsenic from water
using natural iron oxides (Fe-Ox) minerals. The method involves mixing natural iron
mineral bearing soils (lateritic soils) with arsenic contaminated water for ten minutes and
then filtering (coffee filter). The aadsorption capacity of laterite was estimated at
0.1 lmg/m . After addition, arsenic levels in the treated water were below drinking water
standards. The treatment method is inexpensive and simple, making it suitable for house
hold use.
iii
TABLE OF CONTENTS
ABSTRACT
ii
TABLE OF CONTENTS
iv
LIST OF TABLES viii
LIST OF FIGURES x
ACKNOWLEDGEMENTS xii
1. INTRODUCTION 1
1.1 STATEMENT OF THE PROBLEM 1
1.2 THESIS OBJECTIVE AND SIGNIFICANCE 4
1.2.1 Objective 4
1.2.2 Significance and Contribution of the Work 4
2. LITERATURE REVIEW 6
2.1 ARSENIC IN THE ENVIRONMENT 6
2.1.1 Arsenic in Drinking Water 6
2.1.1.1 National and International Standards for Drinking Water 6
2.1.1.2 World Distribution of Groundwater Arsenic Problems 6
2.1.1.3 Arsenic in B. C. 7
2.1.1.4 Health Effects Associated with Arsenic in Drinking Water 8
2.1.2 Sources of Arsenic in the Environment 11
2.1.2.1 Natural Sources of Arsenic 11
2.1.2.2 Anthropogenic Sources of Arsenic 13
iv
2.1.3 Environmental Transfer of Arsenic 14
2.1.3.1. Arsenic Transport between Media 14
2.1.3.2 Arsenic in Soils 16
2.1.3.3 Arsenic in Water 18
2.1.3.4 Arsenic in Sediments 22
2.1.3.5 The Role of Bacteria in Arsenic Mobilization 26
2.1.4 Arsenic Removal Summary of Existing Technologies 27
2.1.4.1 Precipitation - Coprecipitation 28
2.1.4.2 Membrane Filtration 28
2.1.4.3 Adsorption Treatment 29
2.1.4.4 Ion Exchange 29
2.2 IRON OXIDES 29
2.2.1 Natural Iron Oxide Occurrence and Description 29
2.2 A A Introduction 29
2.2.1.2 Iron Oxides in Rocks and Ores 31
2.2.1.3 Iron Oxides in Soils 35
2.2.2 Iron - Arsenic Compounds Interaction in the Environment 36
2.2.3 The Solubility of Fe-Oxides 37
2.2.4 The Adsorption Process and Iron Oxides 39
2.2.4.1 Surface Chemistry 39
2.2.4. 2 Arsenic (V) Adsorption onto Iron Oxides 44
2.2.5 Conclusions 48
v
3. EXPERIMENTAL PROCEDURES 49
3.1 MATERIALS 49
3.1.1 Solids 49
3.1.2 Solutions 49
3.2 PROCEDURES 50
3.2.1 Preliminary Tests 50
3.2.2 Scoping Tests 50
3.2.3 Electroacoustic Tests 52
3.2.4 Adsorption & Leaching Tests 56
3.2.5 Adsorption Isotherms 60
3.2.6 Evaluation of a Simple Water Treatment Process 62
4. RESULTS AND DISCUSSION 63
4.1 SCOPING TESTS 63
4.2 ELECTROACOUSTIC TESTS 64
4.2.1 Magnetite 64
4.2.2 Hematite 65
4.2.3 Goethite 69
4.2.4 Laterite 70
4.3 ADSORPTION & LEACHING TESTS 72
4.3.1 Adsorption Test 72
4.3.2 Leaching Test 72
4.4 ADSORPTION ISOTHERMS 75
4.5 EVALUATION OF A SIMPLE WATER TREATMENT PROCESS 78
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4.6 DISCUSSION OF RESULTS
4.6.1 Electro acoustic Measurements
4.6.2 Adsorption Tests
4.6.3 Leaching Test
4.6.4 Adsorption Isotherms
4.6.5 Evaluation of Simple Water Treatment Process
4.6.6 Comparison between Fe-Ox
5. CONCLUSIONS & RECOMMENDATIONS
5.1 CONCLUSIONS
5.2 RECOMMENDATIONS
REFERENCES
APPENDIX
LIST OF TABLES
Table 2.1 Arsenic Regulatory Limits 6
Table 2.2 Arsenic Concentrations in Environmental media 11
Table 2.3 Most Common Minerals that Contain Arsenic 12
Table 2.4 Summary of Current and Past Uses of Arsenic 13
Table 2.5 Most Common Iron Oxides 30
Table 2.6 Most Common Iron Oxides-Hydroxides and Hydroxides 30
Table 2.7 Dominant Occurrences of the Fe-Ox in Geological Formations 31
Table 2.8 Summary of the Occurrence of Iron Oxides in Various Soils 35
Table 3.1 Solid Particle Size & Surface Area Analysis 50
Table 3.2 Mineralogical Composition of Samples 51
Table 3.3 Test Conditions for Hematite Titrated at Constant pH with As (V)
Solution 55
Table 3.4 Test Conditions for Titration of Fe-Ox Slurries in the Whole pH Range 55
Table 3.5 Tests Conditions for Titration of Fe-Ox Slurries Loaded with As (V) 55
Table 3.6 Sequential Extraction Conditions 57
Table 3.7 Adsorption Tests at Constant pH = 5.2 60
Table 3.8 Adsorption Tests at Constant pH = 9.2 61
Table 3.9 Test Conditions for the Evaluation of a Simple Water Treatment
Process 62
Vlll
Table 4.1 Scoping Tests. As Adsorbed from Different Fe-Ox Slurries at
pH 5.0 63
Table 4.2 Adsorption Test Results 73
Table 4.3 Leaching Test Results 75
Table 4.4 Leaching Test Results in a Surface Area Basis 75
Table 4.5 Adsorption Isotherm at pH 5.2 76
Table 4.6 Adsorption Isotherm at pH 9.2 77
Table 4.7 Evaluation of a Simple Water Treatment Process 79
ix
LIST OF FIGURES
Figure 2.1 Distributions of Documented World Problems with As in Groundwater 7
Figure 2.2 Sources of Human Exposure to Arsenic and Various Modes of Arsenic
Toxicity 10
Figure 2.3 As Cycle. Environmental Transfer of Arsenic 15
Figure 2.4 Chemical Forms of Arsenic and their Transformation in Soils 17
Figure 2.5 Eh- pH Diagram for the System As-O-H-S 20
Figure 2.6 Eh - pH Diagram for the Systme As - S - Fe - H2O 37
Figure 2.7 Solubilities of Goethite, Ferrihydrite and "Soil-Fe" as a Function of pH 38
Figure 2.8 Surface Complex Formation of an Ion (e.g. Cation) on the Hydrous
Oxide Surface 42
Figure 3.1 Sequential Extraction Procedure 59
Figure 4.1 ESA vs. pH of Magnetite Slurries 65
Figure 4.2 ESA vs. pH of Hematite Slurries 66
Figure 4.3 ESA vs. pH of Hematite Slurries, Back and Forward Titration 67
Figure 4.4 Titration of Hematite Slurry with Arsenic (V) Solution 68
Figure 4.5 ESA vs. pH of Goethite Slurries 69
Figure 4.6 ESA vs. pH of Laterite#l Slurries 70
Figure 4.7 ESA vs. pH of Laterite#2 Slurries 71
Figure 4.8 Adsorption Isotherm at pH 5.2 76
Figure 4.9 Adsorption Isotherm at pH 9.2 for Laterite #2 77