Linear sweep voltammetry as a technique to characterize ... · presence of carbon in Carbon Paste...
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Linear sweep voltammetry as a technique to characterize mining wastes
Francisco Carranza, Pablo González, Rafael Romero & Nieves Iglesias* Manuel J. García
MINING WASTE
GOAL
The aim of this study is the development of a methodology for the mining waste
characterization and the prediction of their potential long-term degradation, based on
electrochemical tests of short duration.
Linear sweep voltammetry
The characteristics of the linear sweep voltammogram recorded depend on: • The rate of the electron transfer reaction(s) • The chemical reactivity of the electroactive species • The voltage scan rate
Sample
1 2 3 4 5 6 7 8 9 10
Marl Stockwork Carbonated
sulfide Gossan sulfide
Massive sulfide
Arseno-pyrite
Low-grade sulfide
Copper pyrite
Slate Porphyry
Ag (mg/kg) 29,2 26,6 41,4 127,2 18,2 6,8 25,0 36,7 51,1 5,5 As (mg/kg) < 50 1358,7 1807,6 2109,4 1712,6 1436,5 3300,8 1676,3 679,6 < 50 B (mg/kg) 0,9 0,2 0,2 0,1 0,1 0,0 1,3 0,2 0,0 0,2 Bi (mg/kg) < 20 < 20 89,9 823,4 72,3 < 20 57,1 301,5 436,0 < 20 Ca (%) 10,17 < 0,01 < 0,01 1,49 0,13 0,01 0,12 0,49 < 0,01 7,44 Cd (mg/kg) < 20 < 20 20,0 < 20 < 20 < 20 33,6 80,4 < 20 < 20 Co (mg/kg) 11,4 48,4 127,3 20,3 62,4 15,5 133,1 116,9 25,5 19,5 Cr (mg/kg) 43,0 79,1 50,2 57,6 81,4 67,1 45,0 27,4 84,1 73,7 Cu (%) 0,004 0,071 0,565 0,260 1,608 0,013 0,584 1,066 0,697 0,003 Fe (%) 3,4 28,2 39,9 20,4 16,5 4,0 14,5 15,1 7,6 5,3
Hg (mg/kg) < 5,0 < 5,0 < 5,0 < 5,0 < 5,0 8,9 < 5,0 < 5,0 < 5,0 < 5,0 Li (mg/kg) 22,8 22,9 108,8 < 10 < 10 < 10 45,1 < 10 < 10 < 10
Mn (mg/kg) 875,3 994,9 1182,8 208,8 264,0 516,8 458,3 288,1 21,9 724,8
Mo (mg/kg) < 10 < 10 < 10 59,3 < 10 < 10 < 10 32,1 < 10 < 10
Na (mg/kg) 1112,9 < 100 < 100 < 100 < 100 < 100 < 100 < 100 < 100 75,7 Ni (mg/kg) 36,7 38,7 < 20 < 20 < 20 38,0 < 20 35,6 46,6 < 20 Pb (%) 0,003 0,033 0,426 4,065 0,174 0,000 0,182 0,501 0,132 0,000 Sb (mg/kg) 60,9 66,1 689,3 1170,0 141,2 11,4 563,9 716,5 75,4 143,7 Se (mg/kg) < 50 < 50 < 50 < 50 361,3 < 50 < 50 < 50 57,5 < 50 Sn (mg/kg) 30,9 310,8 485,7 155,1 455,1 39,2 458,8 393,2 72,4 48,4 Tl (mg/kg) < 50 < 50 < 50 < 50 < 50 < 50 < 50 < 50 80,8 < 50 V (mg/kg) < 50 53,5 65,4 < 50 < 50 < 50 < 50 < 50 < 50 < 50 Zn (%) 0,008 0,071 1,299 0,012 0,009 0,010 0,620 0,930 0,018 0,008
C R W
A
V
Linear sweep voltammetry
CV-27 Bioanalytical Systems
Linear sweep voltammetry
C R W
A
V
Three electrodes system: W: working electrode (CPE, PE) R: Reference electrode calomel, +0.2444V vs. SHE C: counter electrode Pt 1mm
Experimental conditions: • Potential applied: from -0.1 V to +2.5 V • Distance between working and reference electrodes: 1-2 mm • Luggin capillary • Sweep rate: 5 mV/s. • Electrolyte: solution of pH 1.5 (sulfuric acid in ultrapure water). • Electrolyte volume: 25 mL • Atmosphere: Nitrogen is bubbled for 1 minute before each test.
Linear sweep voltammetry
Linear voltammetry of CPE 2 H2O → 4 H+ + O2 + 4 e-
Linear voltammetry of CPE
Residues sorted in order of increasing corrosion threshold
(I = 1 mA)
Material Potential (V) Copper pyrite 0.06 Massive sulfide 0.23 Carbonated sulfide 0.32 Gossan/sulfide 0.41 Arsenopyrite 0.46 Low-grade sulfide 0.48 Slate 0.50 Porphyry 0.56 Marl 0.57 Blank 0.91 Stockwork 0.98
Material Intensity (mA) Copper pyrite 70.1 Carbonated sulfide 19.6 Massive sulfide 15.8 Low-grade sulfide 14.7 Gossan/sulfide 10.9 Slate 8.6 Marl 5.8 Arsenopyrite 4.3 Porphyry 3.2 Stockwork 1.2 Blank 1.4
Residues sorted according intensity of degradation
(V =1 V)
Washing
PE Air washing Anoxic washing
Metal analysis ICP
Evolution of Cu, Fe and Zn concentrations in air-washing
Time (min) Sample ppm 30 195 560 1315 1875 2910 4308
[Cu] 582 610 595 645 465 650 635 Massive sulfide
[Fe ] 150 254 332 402 382 417 467
[Zn] 0.6 0.6 0.6 0.7 0.7 0,8 0.9 [Cu] 6.0 9.1 8.4 23 29 40 53 Low-grade
sulfide [Fe ] 219 755 1150 1175 1205 1235 1235
[Zn] 32 50 73 100 125 140 160 [Cu] 26 55 77 100 102 111 121
Copper pyrite
[Fe ] 128 156 187 238 225 258 295
[Zn] 30 47 70 138 150 175 203 [Cu] 1.6 3.0 3.8 21 29 46 59
Carbonated sulfide
[Fe ] 155 618 573 608 543 1040 1080
[Zn] 18 55 50 78 83 200 240
Evolution of Cu, Fe and Zn concentrations in
N2-washing
t (s)
t (s)
t (s)
Linear voltammetry of copper pyrite PE
Linear voltammetry of massive sulfide PE
Linear voltammetry of low-grade sulfide PE
Linear voltammetry of carbonated sulfide PE
Electrochemical parameters
WASTE
Threshold Potencial
(V)
Potencial required to 0.2 mA
(V) I/V
Q
(0- 1.3 V) (C)
Massive sulfide 0.67 0.59 6.1 654
Low-grade sulfide 0.71 0.75 3.6 146
Copper pyrite 0.71 0.72 7.0 551
Carbonated sulfide 0.70 0.81 3.2 156
CONCLUSIONS • A low intensity signal corresponds to relatively insulating materials that are not
susceptible to weathering and therefore do not generate acid mine drainage. • A threshold potential higher than 1.3 V (electrolysis of water potential)
corresponds to non-electroactive materials at ambient conditions that will not generate acid mine drainage.
• The materials which threshold potential below 1.3 V are electroactive materials
that are susceptible to environmental weathering and generation of acid mine drainage. Among them, the most active are the copper pyrite and massive sulfide.
• The use of Press Electrodes prevents the inhomogeneity introduced by the
presence of carbon in Carbon Paste Electrodes, but the electric contact between particles may be inefficient due to the degradation products around the particles. In order to avoid this effect, a washing before voltammetry test is needed.
Linear sweep voltammetry as a technique to characterize mining wastes
Francisco Carranza, Pablo González, Rafael Romero & Nieves Iglesias* Manuel J. García
Thank you!