waste materials gathered in extraction process
acid based
mainly shales and clays (find out where some red shale spoil tips are around somerset)
From the early 1980’s, and certainly as far as the public funding of reclamation schemes is concerned, there has been a preference for redevelopment of ‘hard’ end-uses, such as commercial, industrial and residential, as opposed to ‘soft’ end-uses such as parks, amenity areas and gardens.
The ecology of such sites is also important. Growing awareness of conservation, habitat creation and protection suggests that reclaimed sites can make a positive contribution of ecological value, particularly where the presence of redundant infrastructure can act as wildlife corridors. Reclamation of contaminated land should therefore be looked upon as a valuable opportunity.
Derelict and contaminated land may be reclaimed to either ‘hard’ or ‘soft’ end uses. ‘Hard’ end uses are considered less sensitive, and involve developing the site for new building or associated hard surfaces, such as car parking facilities. There is little, if any, landscaping of such sites and the risk of contact with the contaminated material has generally been considered confined to building foundations and services which can be protected by engineering design. Developments to hard end uses are generally found in urban environments where land attracts a premium value. Reclamation of contaminated, urban sites has been based on the amount of work required to ensure the risk to man or animal life is low. Guidance on acceptable levels of contamination in soils is given in ICRCL 59/83, which addresses the risk of contamination in relation to threshold and action levels, for specific contaminants and the sensitivity of the proposed end use.
Pre-treatment of metal-contaminated soils with bacteria of genus Thiobacillus in order to remove metal ions by leaching (Olson et al. 1990) is an area of development in the future of soil metal decontamination.
the reclamation of former coal mines – JOURNAL
Freshly exposed colliery spoil often has a pH of 7 or more and may have a high electrical conductivity level. The high conductivity levels are often associated with high concentrations of sodium, calcium and magnesium and indicate elevated concentrations of dissolved salts. The most common salts of these elements are carbonates, sulphates and chlorides of which the carbonates are the most easily leached.
from spoil tip / environmental damage paper
2.5 Conclusions
Ground and water contamination arising from the presence of colliery spoil heaps can present a considerable environmental problem in areas of past, and in some instances present, coal extraction. The physical and chemical characteristics of the material make spoil heaps susceptible to combustion, instability and a potential source of heavy metalsPre-treatment of metal-contaminated soils with bacteria of genus Thiobacillus in order to remove metal ions by leaching (Olson et al. 1990) is an area of development in the future of soil metal decontamination.
2.2.1 Acid production due to pyrite oxidation
The most influential chemical characteristic of many colliery spoils in terms of both pollution generation and preventing effective reclamation using vegetative techniques is the presence of pyrite (iron sulphide). Pyrite was precipitated as the result of coal and shale formation under highly reducing conditions. Sulphur is converted to sulphide (S2_) and the iron present is in the reduced, ferrous form (Fe2+). Pyrite is stable until exposed to air and water, when it is oxidised to produce amongst other products, acid. Seasonality will affect the rate of the oxidation reaction. Pyrite in colliery spoil can be oxidised by er oxygen or ferric ions. The reaction with oxygen is slow, whereas with ferric ions it is fast and catalysed by the bacterium Thiobacillus ferrooxidans.The consequences of un-neutralised acidity on colliery spoil can be severe for plant growth. Cation exchange sites will become dominated by hydrogen ions with the resultant loss of bases previously occupying the sites. At low pH iron, aluminium, manganese, copper and zinc will come into solution creating toxic conditions. Aluminium and manganese can be very toxic in low concentrations in acid conditions (Berg & Vogel 1968, 1973). Low pH can also affect the availability of major nutrients. Phosphate can be fixed and made unavailable to plants at low pH (Doubleday 1972, Pulford & Duncan 1975) and potassium may be made unavailable by the formation of jarosite (Palmer 1978). Even moderately low pH can cause aluminium and manganese toxicity and inhibition of microbial activity resulting in a build up of un decomposed organic matter and inhibition of nitrogen mineralisation (Williams 1975).
playing with mineral imagery – pyrite and cubic crystals
Williams and Chadwick (1977) addressed the problems of seasonal fluctuations of plant available nutrients in acid spoil material, where macronutrients may be low and toxicity levels high. They state that such ations may have considerable significance in the establishment and survival of vegetation, and that the effects of these fluctuations may be even greater in the surface layers of the spoil because of the variation in spoil temperature and moisture. Their study of Mitchell’s Main colliery spoil heap in south Yorkshire showed significant seasonal variations in the levels of several elements in acidic colliery spoil and that addition of limestone reduced both the concentration of these elements and the seasonal variation. It was concluded that the solubility of aluminium, manganese, copper, zinc and iron are closely controlled by soil pH. The decline of pH during the summer months was considered to be the result of more favourable conditions for pyrite oxidation due to high soil temperatures. Accumulation of the reaction products then occurred due to the lower rates of leaching.
Control of pyrite oxidation and the generation of acid has, most commonly, been addressed by the addition of lime (CaC03 or Ca(0H)2) to the colliery spoil, thus neutralising the existing acidity and controlling potential acidity by inhibiting the bacterial oxidation of pyrite.
heap names
- Shilbottle spoil heap (PASSIVE TREATMENT OF SEVERELY CONTAMINATED COLLIERY SPOIL LEACHATE USING A PERMEABLE REACTIVE BARRIER – paper)
- Brodsworth Tip (earthworm remediation – paper)
- Like other South Yorkshire colliery tips, at Brodsworth pH is almost certainly limiting and needs amelioration if the vegetation is to be typical of the area. Such a proposition would mean an immense engineering project to change the whole tip from an acidic clayey shale to a soil rich in Magnesian Limestone. p 39pg 40 has succession of materials that formed geological layerspg 72 – 4.8. Summary. The limitations to plant life in spoil on the main tip are; 1. The very low pH.
- 2. Conductivity beyond the range which will support growth.
- 3. Higher sulphate levels than can normally be tolerated by plants, and.
- 4. In acid conditions, phosphorus becomes fixed by combining with iron forming FePO^, and aluminium from the clay minerals forming AIPO4 .
9.1.1. The tip at Brodsworth.
The ecology of the tip under investigation has been studied, and it shows many similarities with those examined by other researchers, both in regard to spoil and vegetation growing on the main part.
Sufficient history, from map studies chiefly, has been found to indicate that the contrasting vegetation at the west end of the tip is probably due to local soil, rich in Magnesian Limestone, being dumped there at the building of the A1(M), trunk road. Historical studies also indicate that the tip material consists mainly of rocks produced by sinking the shaft, together with waste produced during the first few years of production only. Tipping on the site probably ceased by 1920 or shortly after that date and the tip was shortened by the intrusion of the A1 (M).
Soil studies indicate that the rocks, mainly shales, have weathered on the surface to clays. These clays are not rich in plant nutrients, and due to the presence of oxidising Pyrite, have low pH.
Studies of the spoil and plant life on Brodsworth tip indicate that there is slow succession taking place. Over the greater part of the tip, Betula sp. were dominant, and associated species typical of coal measures vegetation are present. There was successful colonisation of local plant species, including calcicoles, at the west end of the tip where it appears that topsoil had been added. However on other local sites, topsoil was eroding, so that topsoiling is not a universal panacea.
Several areas of the tip are devoid of vascular plants. These areas had lower pH than the vegetated parts
Cofnod Conference 2020 – Spectacular Spoil: An Overlooked Wildlife Habitat – Liam Olds (SOUTH WALSE)
Liam Olds of Colliery Spoil Biodiversity Initiative presents how coal spoil can form a wonderfully rich habitat for plants and animals. He looks at how these habitats
THINKING RESEARCH 