Solid Wastes Management in Sulphide Mines: From Waste Characterisation to Safe Closure of Disposal Sites

Transcription

1 APPLICATION Solid Wastes Management in Sulphide Mines: From Waste Characterisation to Safe Closure of Disposal Sites By Katerina Adam (M. Sc., Ph.D) ECHMES Ltd. 2-3 June, 2003 Wroclaw Poland 1

2 Solid Wastes Management in Sulphide Mines: From Waste Characterisation to Safe Closure of Disposal Sites CONTENTS OF PRESENTATION INTRODUCTION WASTE CHARACTERISATION WASTE MANAGEMENT FACILITIES PREVENTIVE TECHNIQUES CLOSURE & RECLAMATION CONCLUSIONS 2-3 June, 2003 Wroclaw Poland 2

3 Solid Wastes Management in Sulphide Mines: From Waste Characterisation to Safe Closure of Disposal Sites Introduction In EU, Waste from the extractive industry represents 29% of annual waste production Potential environmental risks related with Mine Waste management depends on: Waste properties, and quantities Disposal facilities, and techniques, Environmental status at the disposal sites MINE WASTE MANAGEMENT-BAT PROJECT 3

4 Introduction ENVIRONMENTALLY SOUND MINE WASTE MANAGEMENT STRATEGY Starts from the early stages of a project development, continues in construction, operation and closure stages. Aim : to minimise quantity (volume) & harmfulness of produced wastes Selection- Optimisation mining, processing techniques Maximisation of recycling, recovery The unutilised amount of wastes still has to be safely disposed MINE WASTE MANAGEMENT-BAT PROJECT 4

5 Waste Management Scheme in Sulphide Mines 5

6 Waste Management in Sulphide Mines Sulphide wastes if not properly managed, may turn to Acid Drainage generation sources, potentially active for decades Wastes from non-ferrous polymetallic sulphide mines must be carefully managed to avoid water pollution through acid drainage and to prevent failure of structures built to contain them, BRGM, 2001, COM (2000) 265) 6

7 Waste Management in the Extractive Industry EU Priority Actions to improve Mine Waste Management : (a) Amendment of Seveso II, (b) New Directive on Mine Waste, c) BAT on Tailings and Waste Management 7

8 Mine Waste Management Plan Improved sulphide mine waste management plan: Integrating Protection of water & soil quality, Ensure Stability of WMF Waste Characterisation, Disposal technique & Site Selection, Environmental Base Line studies, Assessment of Environmental Impacts, Mitigation Mesures, Monitoring, Closure Strategy 8

9 Waste Characterisation Wastes and tailings Samples collection and preparation Physical/ Geotechnical Characterization Geochemical characterisation Chemical-mineralogical analysis Chemical analyses of ( Solids(pollutants Ci) Paste ph Ci < Solids Standards YES S < 0.3% YES 5< ph <8 INACTIVE NO NO NO Leachability Tests Measure AMD potential ph < 5 NO ACIDIC Ci< Water Standards NO YES AMD < limit NO YES ph > 8 ALKALINE Leachate with increased contaminants Possible AMD Further Kinetic Tests Geochemical Modelling 9

10 Waste Characterisation Criteria to classify wastes from sulphide mines include: NNP= NP-AP, kg CaCO3/t of waste, NPR=NP/AP Chemical Analysis: Ci in solids vs. Quality Standards Leachability tests: Ci in leachates vs. Standards, e.g TCLP, DIN, EN etc. Waste Characterisation starts at exploration stage, and continues during operation, till closure. On-going Risk Assessment : Waste properties (source) evaluated vs field monitoring data, water/ air/ soil (pathway), and ecology and a human health (target) 10

11 Solid Wastes Management in Sulphide Mines: From Waste Characterisation to Safe Closure of Disposal Sites Waste Management Facilities ENVIRONMENTALLY SOUND MINE WASTE MANAGEMENT STRATEGY Aim : to minimise quantity (volume) & harmfulness of produced wastes Selection- Optimisation mining, processing techniques Maximisation of recycling, recovery The unutilised amount of wastes has to be safely disposed MINE WASTE MANAGEMENT-BAT PROJECT 11

12 Waste Management Facilities SURFACE DISPOSAL Waste Rock Stockpiles Tailings Disposal Filtered cake Paste thickened tailings Slurry (sub-aerial-sub-aqueous) Disposal method Disposal method: f(process,waste characteristics, clima, land take, environmental sensitivity ) MINE WASTE MANAGEMENT-BAT PROJECT 12

13 Waste Management Facilities SURFACE DISPOSAL Waste Rock Stockpiles Tailings Disposal Filtered cake Paste thickened tailings Slurry (sub-aerial-sub-aqueous) Site of Disposal Site of Disposal : f(waste volume &characteristics, morphology, geologyhydrogeology, environmental sensitivity) MINE WASTE MANAGEMENT-BAT PROJECT 13

14 SITE SELECTION OF A NEW TAILINGS MANAGEMENT FACILITY Visual Impact Study Existing Status Start up of Operation After closure and reclamation 14

15 Preventive Techniques To prevent water and soil contamination, from the disposal of sulphide mine wastes, techniques developed & applied to eliminate acid generation at source Objective of control Sulphide Removal/Isolation Water exclusion Oxygen Exclusion ph control Bacterial Action Control Techniques Secondary Treatment/Conditioning Sub-aerial disposal, Covers Sub-aqueous deposition, Covers Alkaline additives(carbonates / phosphates / silicates/ fly ash) Bacteriacides 15

16 Preventive Techniques Case Studies: Waste RockTreatment- Alkaline Additives Stratoni Galena-Sphalerite-Pyrite historic producer in Greece MAP, NP (kg CaCO3/t) D C A B MAP NP/MAP Grain size (mm) NP Segregation of sulphide rich -4mm fraction Amendment with engineered application of limestone, NPR>1 Alternative layers to reduce permeability, enhance neutralisation Laboratory/Field Tests Lycimeters running > 3 years ROLCOSMOS, EC BRPR-CT

17 Preventive Techniques Case Studies: Waste Rock Treatment- Alkaline Additives Pad No 1:Control pad,wr 80 mm, NNP: -18Kg CaCO 3 /t Pad No 2: Control pad, 4 mm WR above +4 mm fraction, NNP: -18Kg CaCO 3 /t Pad No 3: Homog. mixture 4 mm + 14% w/w limestone above +4 mm, NNP: +35 Kg CaCO 3 /t Pad No 4:Successive layers of +4 mm +limestone amended 4 mm WR, NNP: +35 Kg CaCO 3 /t 17

18 Preventive Techniques Case Studies: Waste Rock Treatment- Alkaline Additives ph Oct-99 Mar-00 Aug-00 Jan-01 Jun-01 Nov-01 Apr-02 Pad No 1-Control, waste rock -80mm Pad No 2-Control, -4mm layer above +4mm waste rock Pad No 3-Waste rock (-4mm) and limestone above +4mm layer Temporal variation of ph in the testpads leachates 18

19 Preventive Techniques Case Studies: Waste Rock Treatment- Alkaline Additives Cumulative amount of metals and sulphate, g/m3 of dispose material, dissolved from the field testpads Pad 1. Control, WR- 80mm mm, above +4mm 3. -4mm with CaCO 3, above+4mm Dra/ge mm %, 48-89% Fe 9,3 0,9, -90,2% 0,03-99,6% Mn 30,5 19,9-34,8% 0,3-99% SO ,8% 82-94,8% No leachate from Pad.4, after 3 years monitoring 19

20 Preventive Techniques Case Studies: Waste Rock Treatment- Alkaline Additives Field scale Lycimeter tests over a period of 3 Years Waste rock, 80 mm ( No 1), NNP of kg CaCO3/t, potentially acid generating. Leachates collected:ph : , Zn, Mn, Cd in drainage> limits Separation of the 4 mm fraction and its placement as a lower permeability cover layer above coarse size material (No 2) 50% reduction of drainage. Drainage quality improved; Zn, Mn, Cd in drainage > limits, Reduced metals dissolution Homogeneous blending 4 mm with 14% limestone, above + 4mm ( No 3) further drainage reduction, and metal dissolution. NNP 34.8 kg CaCO3/t, drainage neutral to alkaline Successive layers of homogeneously mixed 44 mm WR with limestone and coarse WR fraction (No 4) the most effective configuration for preventing ng water infiltration. 20

21 Preventive Techniques Case Study : Dry Covers Application of fly-ash and bentonite mixed with sulphide tailings, GEOPEDA, EPET II, 98-BIA BIA-27 Mixtures of Sulphide Tailings with pozolanic alkaline material and/or clays to develop barriers Selection Criteria of additives: AP/NP, Leachability, Grain size Evaluation criteria of tailings additives mixtures: Permeability, k 10-9 m/sec, Metal leachability< limits 21

22 Preventive Techniques Case Study : Dry Covers- Barriers Application of fly-ash and bentonite mixed with sulphide tailings as barriers Συντελεστής υδροπερατότητας, k (cm/sec) 1.0E E E E-08 Ιπτάμενη τέφρα Μπεντονίτης Ποσοστό προσθήκης (%) Applications of these barriers improved leachate quality, Field Tests in progress 22

23 Closure & Reclamation Planning for decommissioning key element for cost effective sulphide waste management Main Closure Design Criteria Physical Stability, structures pose no risk on health, environment Chemical Stability Biological Stability, environment restored to a balance ecosystem Hydrogeology, prevention of contamination of aquatic environment Land Use, rehabilitation ensuring the compatibility with surrounding area, Stability, structures chemically stable, no contaminants release and approved/required land uses 23

24 Closure & Reclamation Case Study: Closure of an old pyrite disposal area Risk Assessment based on pyrite properties, and long term monitoring Pyrite Stockpile to remain active AMD source for decades Objectives for closure &rehabilitation Increase embankement stability Prevent further pyrite oxidation Protect quality of ground & surface water Revegitation 24

25 Closure & Reclamation Case Study: Closure of an old pyrite disposal area Objectives for closure &rehabilitation Improve embankement stability 25

26 Closure & Reclamation Case Study: Closure of an old pyrite disposal area Objectives for closure &rehabilitation Prevent further pyrite oxidation Elevation (m) B ottom of disposal area Groundwater level S tabilising berm D istance (m ) Topography of the area before the reclam ation Topography of the area after the reclam ation HDPE geom em brane G eo tex tile S o il layer 26

27 Closure & Reclamation Case Study: Closure of an old pyrite disposal area Protect quality of ground & surface water Water management 3.0m Constructions of drainage zones and istallation of cement pipes in order to: Collect seepage from the embankment Gravelly drainage zone 0.6m 1.0m 0.8m Cement pipe Collect runoff from the pyrite stockpile surface Constructions of a ditch upstream of the stockpile to divert surface waters 27

28 Closure & Reclamation Case Study: Closure of an old pyrite disposal area Revegitation Objectives for closure &rehabilitation 28

29 Closure & Reclamation Case Study: Closure of an old pyrite disposal area Successfull closure and reclamation evidenced by monitoring data, Cost: 102,00$/Ha 29

30 CONCLUSIONS Design of Environmentally compatible Waste/Tailings Management strategy in sulphide mines, from the early project stages to the closure period. Parameters affecting disposal method and site selection, and overall environmental performance of the Management Facilities : properties of sulphidic waste, climatic conditions, geology and hydrogeology of the disposal site, and environmental sensitivity. Novel techniques developed aim to prevent and control acid drainage formation, and ensure environmentally safe water management and soil protection. 30

31 CONCLUSIONS Regarding closure, a number of alternative low cost geocovers, are developed aiming to exploit wastes and other products of the extractive industry, in the cost-effective reclamation of sites where reactive tailings are disposed. 31

32 Solid Wastes Management in Sulphide Mines: From Waste Characterisation to Safe Closure of Disposal Sites Dziekuje Bardzo MINE WASTE MANAGEMENT-BAT PROJECT 2-3 June, 2003 Wroclaw Poland 32