Antimony in the New Zealand environment Antimony minerals and Sb environmental mobility
Dave Craw Geology Department University of Otago Dunedin, New Zealand in collaboration with: Nat Wilson, MSc Otago (PhD Auckland) Assoc Prof Paul Ashley, Armidale, NSW
Principal topics • • • • •
Introduction to Sb Point sources: geothermal and mines Sb minerals and solubility Sb mobility in the environment Arising Sb environmental issues
Antimony: the new bogey-man?
1 H 3 Li
4 B e
1 1 N a
12 M g
1 9 K
20 2 C 1 a S c
22 Ti
23 V
3 7 R b
38 Sr
3 9 Y
40 Zr
41 42 43 Nb Mo Tc
5 5 C s
56 B a
*
72 Hf
73 Ta
Metalloids:
24 25 26 27 Cr Mn Fe Co
74 W
5 B
6 C
7 N
8 O
9 F
10 Ne
13 Al
14 Si
15 P
16 S
17 Cl
18 Ar
29 Cu
30 Zn
31 32 Ga Ge
33 As
34 Se
35 Br
36 Kr
44 45 46 47 Ru Rh Pd Ag
48 Cd
49 In
50 Sn
51 Sb
52 Te
53 I
54 Xe
80 Hg
81 Tl
82 Pb
83 Bi
84 Po
85 At
86 Rn
75 76 Re Os
77 Ir
28 Ni
2 He
78 Pt
79 Au
Chemical behaviour • • • • •
Antimony Sb3+, Sb5+ Forms oxyanions Widely used historically No nutritional use in humans Highly toxic to humans (mimics P)
• • • • •
Arsenic As3+, As5+ Forms oxyanions Widely used historically No nutritional use in humans Highly toxic to humans (mimics P)
Historic usage • Water containers in Ancient Egypt • Cosmetics, especially eye-shadow Ancient Egyptians, Queen of Sheba, Jezebel Still used in Middle East (=“kohl”, Pb-rich)
• Black pigment for paint (cf As in wallpaper pigments) • Medical, e.g., Tartar emetic (K-Sb tartrate) (cf As widely used for skin conditions etc) • Alchemy (As was a more common reagent)
Current usage • Flame retardants in plastics etc: Sb2O3 (2-3%) with halogens (about 50% of total Sb production) • Catalysts in plastic production (e.g., Sb-triacetate for PET) • Alloys, especially with Pb: hardens metals (e.g., batteries; solder) • Electronics (pure Sb metal)
Sb in global human environment • Drinking water limit set very low: WHO and NZ: 20 ppb US EPA: 6 ppb (As = 10 ppb) • Mining areas: up to 100 ppb • Leach Sb, Pb from plumbing: MoH recommends running off first 500 mls • PET bottles: leach up to 1 ppb Sb • Stibine (SbH3) from mattresses implicated in cot deaths (controversial)
Principal topics • • • • •
Introduction to Sb Point sources: geothermal and mines Sb minerals and solubility Sb mobility in the environment Arising Sb environmental issues
Volcanic-hydrothermal zones
Gold Mercury
Northland
Hg, As, Sb pH: 1-7
Cu, Pb, Zn Coromandel Sb, As, Cd, Peninsula pH: 1-7 Waihi Te Aroha
Taupo Volcanic Zone
N 100 km
Hot spring precipitate with elevated Sb, As, Champagne Pool, Wai-O-Tapu
Quartz-rich spring precipitate with elevated Sb, As, Hg Puhipuhi, Northland
Hot spring depositing Hg,Sb,As in sediments, Ngawha, Northland
Dissolved Sb, ppb
Dissolved Sb through Ngawha geothermal power station
Supersaturated
Flow through power station Wilson, Webster-Brown & Brown 2007
New Zealand mesothermal Sb deposits, some mined historically Sb accompanies Au at most sites pH = 7
Principal topics • • • • •
Introduction to Sb Point sources: geothermal and mines Sb minerals and solubility Sb mobility in the environment Arising Sb environmental issues
1 cm
Stibnite (Sb2S3) in quartz veins
100 km Hillgrove antimony (gold) mine, northern New South Wales:
Great Dividing Range
Modern and historic workings Rainfall 800 mm/year Evaporation 1200 mm/year
Natural and historic mine debris is traceable over 300 km downstream
Hillgrove
Pacific Ocean
Downstream of Hillgrove mine site: elevated Sb in sediments and waters
Sediments Mine water
10
Stream water
0.1
Estuary
Sb, ppm
1000 Rock
River junction
100000
Precipitate
Ore
background
drinking water
0.001 0.01Mine site 0.1
1
10 100 1000 Distance downstream, kilometres Ashley, Craw, Graham & Chappell 2003
Macraes gold mine, Otago, New Zealand Rainfall c. 600mm/year Evaporation c. 700 mm/year
1 cm
Arsenopyrite FeAsS
PIXE image of Macraes arsenopyrite with 2000 ppm Sb
Petrie, Craw & Ryan 2005
Macraes mine: high evaporation in mine pits Boulangerite
100000
Pb5Sb4S11(rare)
Arsenopyrite FeAsS
1000 Sb, ppm
Ore
10 Mine waters
0.1 Mine discharge waters
0.001 0.001
0.1
10 As, ppm
1000
100000
Craw, Ashley, Wilson & Hunter 2004
arsenopyrite
Oxidised arsenopyrite forms scorodite (FeAsO4.2H2O), scorodite
Oxidation of sulphide minerals Stibnite (Sb2S3): oxidises to various Sb oxides, which are very soluble (up to 50 mg/L) Stibnite in quartz vein
valentinite on surface
pH = 7
Oxide coating develops on stibnite. Coating dissolves readily to form Sb(V) oxyanion SbO3- or Sb(OH)6(cf HAsvO42-)
(cf FeAs(V)O4 .nH2O)
(cf As(III)2O3)
Ashley, Craw, Graham & Chappell 2003
Sb
As
1 mm Hillgrove mine tailings, c. 1 month old Dry, high evaporation conditions Layering is bedded stibnite and arsenopyrite Incipient antimony oxide formation and cementation Ashley, Craw, Graham & Chappell 2003
800
Antimony oxide: soluble to c. 50 ppm Sb in environment
Re dox pote ntia l,Eh, millivolts
700 -
SbO 3 (a que ous )
600 500 Expe rime nta l s olutions
400
100 ppm
300
0.1
10
200 Sb 2O 3 (a ntimony oxide ) 100 0
Theoretical Sb redox phase diagram
Stibnite , Sb 2S 3
-100
logξ S = -3
-200 3
4
5
6
7
8
9
pH Ashley, Craw, Graham & Chappell 2003
Principal topics • • • • •
Introduction to Sb Point sources: geothermal and mines Sb minerals and solubility Sb mobility in the environment Arising Sb environmental issues
Reefton gold mine, New Zealand: rainfall c. 3000 mm/year Arsenopyrite, pyrite, stibnite; discharges have HFO precipitates
Reefton adit discharge waters and iron oxyhydroxide precipitates 10000 1000 Precipitates
1 0.1 0.01
River junction
Stream junction
10 Adit entrance
Sb, ppm
100
Water
0.001 0.0001 0.1
1
10
100
Distance downstream, metres Craw, Wilson & Ashley 2004
1000
10000
Bulk distribution constants for arsenic and antimony in Reefton iron oxyhydroxide/water 10000000
Sb Kd (L/kg)
Metalloid in solid Kd = Metalloid in water
1:1
100000
1000
10 10
1000
100000 As Kd (L/kg)
Craw, Wilson & Ashley 2004
10000000
Infrared absorbance of adsorbed Sb
Antimony adsorption/desorption on iron oxyhydroxide
pH = 3 pH = 3 pH = 6.5 pH = 10 Adsorption
Desorption
Time, minutes McComb, Craw & McQuillan 2007
Electron backscatter images: pale zones = As-rich
Fuchsia excorticata shoots/leaves As: 30 mg/kg Sb: 0.05 mg/kg
Iron oxyhydroxide As: 10-20 wt% Sb: 100-1000 mg/kg 15 cm
K2FeIII4[AsVO4]3[OH]5.6H2O (pharmacosiderite) Hewlett, Craw & Black 2005
Craw, Rufaut, Haffert & Paterson 2007
Moss, Pohlia wahlenbergii secondary electron images with As X-ray emission
Moss As: 0.8-3 wt%
Moss Sb: 90-200 mg/kg
Substrate As: 3-16 wt% Sb: 10-1000 mg/kg Craw, Rufaut, Haffert & Paterson 2007
As/Sb ratio of plants reflects As/Sb ratio of substrates
1000 Substrate
Sb, mg/kg
100
P. wahlenbergii shrubs
10
grasses
1 plants
0.1 0.01 1
100
10000
1000000
As, mg/kg Craw, Rufaut, Haffert & Paterson 2007
Endeavour Inlet Sb mine (closed 1907)
Mines Smelter
1 cm
Queen Charlotte walkway Sb metal in slag
100 µm
Endeavour Inlet, Marlborough, historic mine tailings: Arsenic up to 5 wt% in stibnite Minor arsenopyrite, pyrite Antimony adsorbed on to iron oxyhydroxides from oxidation of iron minerals; more mobile than As Wilson, Craw & Hunter 2004
Endeavour Inlet, Marlborough, historic antimony mines No iron oxyhydroxide at adits c. 1000 mm rainfall/year Ground and surface water carries Sb for kilometres Sb: 3 grams/day As: 0.5 grams/day
Sb: 1200 grams/day As: 400 grams/day Wilson, Craw & Hunter 2004
Flux of Sb from mine sites at neutral pH 100 Sb flux, mg/second
10
Marlborough, NZ Hillgrove, Aust
1 0.1 0.01 0.001
Reefton, NZ
0.0001 0.00001 0.000001 0.001
0.01
0.1
1
10
100
1000
distance from source, km
Ashley, Craw, Tighe & Wilson 2006
Principal topics • • • • •
Introduction to Sb Point sources: geothermal and mines Sb minerals and solubility Sb mobility in the environment Arising Sb environmental issues
Metalloids in rocks and soils Antimony • Background rocks: 0.01- 0.1 ppm • Background soils:
