Linear sweep voltammetry as a technique to characterize mining wastes

Transcription

1 Linear sweep voltammetry as a technique to characterize mining wastes Francisco Carranza, Pablo González, Rafael Romero & Nieves Iglesias* Manuel J. García

2 MINING WASTE

3 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.

4 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

5 Na (mg/kg) 1112,9 < 100 < 100 < 100 < 100 < 100 < 100 < 100 < ,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 < ,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 Sample Marl Stockwork Carbonated sulfide Gossan sulfide Massive sulfide Arsenopyrite 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) < ,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

6 Linear sweep voltammetry A V CV-27 Bioanalytical Systems C R W

7 Linear sweep voltammetry A V Three electrodes system: W: working electrode (CPE, PE) R: Reference electrode calomel, V vs. SHE C: counter electrode Pt 1mm C R W

8 Linear sweep voltammetry 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.

9 Linear voltammetry of CPE 2 H 2 O 4 H + + O e -

10 Linear voltammetry of CPE

11 Residues sorted in order of increasing corrosion threshold (I = 1 ma) Residues sorted according intensity of degradation (V =1 V) 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

12 Washing PE Air washing Anoxic washing Metal analysis ICP

13 Evolution of Cu, Fe and Zn concentrations in air-washing Time (min) Sample ppm [Cu] Massive sulfide Low-grade sulfide Copper pyrite Carbonated sulfide [Fe ] [Zn] ,8 0.9 [Cu] [Fe ] [Zn] [Cu] [Fe ] [Zn] [Cu] [Fe ] [Zn]

14 Evolution of Cu, Fe and Zn concentrations in N 2 -washing t (s) t (s) t (s)

15 Linear voltammetry of copper pyrite PE

16 Linear voltammetry of massive sulfide PE

17 Linear voltammetry of low-grade sulfide PE

18 Linear voltammetry of carbonated sulfide PE

19 Electrochemical parameters WASTE Threshold Potencial (V) Potencial required to 0.2 ma (V) I/V Q (0-1.3 V) (C) Massive sulfide Low-grade sulfide Copper pyrite Carbonated sulfide

20 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.

21 Thank you! Linear sweep voltammetry as a technique to characterize mining wastes Francisco Carranza, Pablo González, Rafael Romero & Nieves Iglesias* Manuel J. García