Natural Resources. Presented by Victor Tibane

Transcription

1 Natural Resources Presented by Victor Tibane

2 Mineral Resources Impossible to keep up with consumption over the longterm based on the finite resource principle and the exponential growth in population. Minerals = exhaustible legacy from geological past. Mineral resources are limited. 2

3 Resource: Mineral Resource elements, chemical compounds, minerals or rocks which were concentrated in an extractable form and can be utilized as a useable commodity. concentration is such that it may be possible to economically mine it at present or in the future Reserve: identified part of resource from which material can be mined legally and economically at the time of evaluation. 3

4 Minerals on Land Mining can only occur in places where mineral deposits occur. Environmental choices are therefore restricted to: mining method locality of mine infra structure & waste sites choices of energy source, water & raw materials 4

5 How dependent are we on minerals? 5

6 Countries meeting their needs for a given mineral substance today may need to import it in future after depletion of its. Formation of mineral deposits: own resource hydrothermal metamorphic magmatic sedimentary placers weathering (residual) 6

7 Environmental Impacts of Mining method Mining Nature of the mineral deposit Mine tailings Mine rehabilitation is embedded in the law (EMPR) 7

8 Mining Methods 1. Surface Mining Total disruption of surface. Affects the soil, groundwater, fauna & flora & all types of land-use. Understanding of pre-mining environment necessary to plan rehabilitation and final land-use. 8

9 Opencast Mining Remove & stockpiling soil Drill & blast Remove rock with draglines in long parallel strips Remove coal Replace overburden in spoil piles in preceding strip 9

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12 Rehabilitation Landscape spoil piles to required slopes and shape Bring top soil back. Treat soil in conventional agricultural way (fertilizer, etc.). Main objective in SA is to return the mined areas to productive agricultural land. 12

13 Open-pit mining Massive steeply dipping close to surface ore body or pipe. Mine total ore body with no overburden to back in the void. Severely limits the land-use after closure of the mine. Solutions: waste disposal site recreational (filled with water) fence in as tourist attraction 13

14 Residual impact Completely different land-use Usually no water pollution 14

15 Dredge mining Alluvial deposits and heavy minerals in dune sands. Deposit must be soft, contain minerals throughout its bulk, and be able to hold water. Excavate pit in ore body and fill with water. Dredge & Separation plant float on water. Plant separates heavy minerals and pump tailings to mined out areas. 15

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17 Rehabilitation Transport top soil directly onto landscaped tailings. Introduce organic material, seed & microorganisms. Put up wind erosion protection structures or nurse crop. Establishment of different types of vegetation depends on the climate. 17

18 Most important residual impacts Spoil mound from the first strip - forms a low hill. Final strip forms a depression - forms a lake. Ramps also become low-lying areas. Whole new landscape could be higher than surrounding unmined area. Groundwater table recover to its original level. Overburden determine the quality - ph, TDS. 18

19 Spoil mound from the first strip - forms a low hill 19

20 Rehabilitation of strip mining of a coal seam by replacing the overburden

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22 Residual Impacts Perched water tables due to the silt & clay fraction being deposited first in lower portion of tailings. Consequential ecological changes induced by higher water table. Temporal impact if indigenous forest is chosen as rehabilitation goal. Possible depression remaining at end of dredge path. 22

23 Dump Reclamation Tailings generated in the past may still contain payable values of mineral - especially sand & slime dumps at old gold mines. Reprocessing of material by high pressure water jet into a sluice and pipeline towards treatment plant. Protect environment by: keeping storm water away prevent uncontrolled flow of rainwater from site. prevent dust pollution 23

24 Land-use varies depending on the locality. Upper soil layer polluted (Acid Mine Drainage) Radon emission Residual impact not on site but rather the new slimes dam. 24

25 Subsurface Mining Surface subsidence Dewatering Groundwater pollution 25

26 Surface Subsidence Shallow undermining Coal bord & pillar mining Pillars fail working back to surface Air cause spontaneous combustion further weakening pillars Scattered and unpredictable subsidences Surface aquifers leak into mine openings - acidify Pollution of surface streams 26

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28 Rehabilitation can only start after subsurface fires have burnt out Unsuccessful backfill with fire proof material flooding Address water pollution problem 28

29 Deep Subsurface Mining Absence of roof support after mining Subsidence of surface Fracturing of rock between stope and surface dewatering of shallow aquifers 29

30 Deep Subsurface Mining Residual impacts undulating topography open cracks new swamps recharge of near surface aquifers from closed deeper seated cracks 30

31 Dewatering (subsidence) Dolomite on Far West Rand dewatered by gold mines Lead to sinkholes and dolines 31

32 Disposal of mine water Free State 2 aquifers: shallow (Ecca shale & Beaufort sandstone) m, < 300m small volumes, low yield deep (Wits & Ventersdorp fractured rocks) m high volumes, high yields low quality 32

33 Dewater deep aquifer at m 3 /d Conductivity = ms/m TDS = mg/l Not suitable for domestic use Use in gold processing Dispose of in evaporation pans (5 000 ha) 3,7 mt salts brought to surface over past 40 years Limited groundwater pollution due to impermeable rocks May contaminate surface water 33

34 Witwatersrand Old mine openings filled with water Pyrite in rocks pollute water with Ca & MgSO 4 ph = 2-3, TDS = mg/l High levels of Fe & Mn Treat water with lime (subsurface) Salts remain m 3 /d flow into Klip & Els Rivers (Barrage) t salts/d to Barrage Significant impact (economic & environmental) 34

35 South African Situation Coal - water pollution (pyrite) spontaneous combustion high ash content (high volumes of slag) Gold - water pollution (pyrite) dust pollution Platinum Group Metals - dust pollution, air pollution from coal driven refining processes 35

36 Asbestos proven carcinogene protect tailings dumps Heavy minerals locality create controversy old and resent coastal dunes successfully establish wetlands, grass veld, commercial forestry, Acacia forests and dunes > 50 years to establish coastal forest 36

37 Residual impacts of other material extractions Dimension stone: high volume of discard open quarry 37

38 Iron ore: red dust, open pit Aggregates: open quarries, soil erosion, dust Diamonds: mine dumps, open pit Other metals: varies, site specific and localised impacts 38

39 Acid Mine Drainage Water pollution Pyrite (FeS2) oxidises when exposed to air & water to form sulphuric acid, iron oxides and hydroxides. 2FeS 2 + 2H 2 O + 7O 2 2FeSO 4 + 2H 2 SO 4 2FeSO 4 + 2H 2 SO 4 + O 2 2Fe 2 (SO 4 ) 3 + 2H 2 O 2Fe 2 (SO 4 ) H 2 O 4Fe(OH) 3 + 6H 2 SO 4 39

40 ph gets lowered (down to 4) Oxidation reaction is enhanced by bacteria (Thiobacillus ferrooxidans) ph gets lowered even further down to 1.5 Acid reacts with basis in rock and form salts or mobilise heavy minerals. 40

41 Treatment: Add lime Quick removal of water from mines Install reed beds (Phragmites) & bullrushes (Thypha) 41