Mining inevitably produces waste materials, often on a massive scale. Billions of tonnes of mineral wastes are produced annually, with some commentators even suggesting, perhaps tongue-in-cheek, that mining companies could equally be considered as waste management companies!
The range of mineral wastes produced includes: waste rock and overburden, tailings, spent heap leach ores, abandoned ore stockpiles, residues from coal and alumina production, refinery discards and sludges, smelter and other furnace slags, ashes, water treatment sludges, dredging materials and soils and soils contaminated by mineral wastes. In terms of volume and tonnage though, waste rock and overburden win hands-down. Often, these are piled high with enormous surface footprints. Some tailings structures are the largest objects ever made and may contain hundreds of millions of tonnes of material.
Mineral wastes are associated with a range of environmental and social issues, such as: providing a source of contaminated dust and water, including AMD, that affects surrounding soils, waters and people; unstable landforms that may cause serious injury and damage; covering expansive areas resulting in losses of biodiversity and/or economically useful land; aesthetic impacts in areas regarded as naturally and/or culturally significant, to name a few.
However, there are many instances were opportunity has been derived from the mineral waste challenge, creating value from a problem – improving environments and people’s lives. Some examples are offered below.
Reworking mineral wastes
Many mineral wastes were produced using older, less efficient techniques, and may still contain economically viable concentrations of metal or coal, etc. Modern techniques re-work the wastes to extract any remaining valuable minerals while re-depositing the wastes in better managed structures. A great examples is South Africa’s ERGO project which, to date, has re-processed over 50 of the old, iconic gold mine waste sites around Johannesburg. It lasted 25 years, and the reworked wastes were deposited in enormous, modern new tailings structures that reduced the overall environmental impact, and made available for use land that had previously been sterilised by the wastes.
Green construction materials
Mineral wastes, particularly waste rock, can be used for construction (depending on the proximity of a viable market). The UK’s Cornish china clay mining industry produces substantial amounts of waste sand that is ideal for construction, including the production of concrete blocks for use in buildings, as well as aggregates for more general use.
Around 60,000 tonnes of china clay sand waste were used for creating 85,000 tonnes of artificial soils by the Eden Project (– itself an iconic example of post-mining regeneration of an old mine site (which will be considered in a later #MineClosurePerspectives blog)).
The permanence, size and shape – and resulting visibility – of waste rock dumps can act as a personal cultural anchor to the “sense of place” of surrounding people. We all want to come from somewhere and that somewhere is usually defined in our minds by visual references, be they buildings, trees, mountains, or mine waste dumps. When these references are gone, it affects who we think we are. Such important cultural considerations are often overlooked during mine closure planning and regeneration projects, to the detriment of local people. An excellent example is provided in the iconic, conical china clay waste tips of Cornwall, UK.
Old mine waste sites are also of interest to geologists and those studying historic mining and processing methods, as well as new reclamation techniques. Old underground mines, for example, are often no longer accessible, but the waste rock, etc., removed from underground when the mine was working can offer valuable clues as to how the mine operated. There are many old mine sites in the UK that are protected as Regionally Important Geological Sites – like a nature reserve for rocks – for just such reasons.
New landforms can also be created from surface mineral waste features in attempts to reduce their impacts and also create something of value for the future. Such new landforms may sometimes court controversy as the old features from which they are created have already become accepted as cultural focal points by local people. Often the old waste dump is crafted into a landform more in keeping with the local topography; however the creation of 3-D land-art is of growing interest in Europe, allowing visitors to the site to physically explore the landform, such as Sultan, the Penallta Pony in South Wales and Northumberlandia in the northeast of England.
Such projects indicate a different perspective to viewing mineral wastes as problematic – a valuable lesson for all those concerned with mine closure planning and delivery.
#MineClosurePerspectives is produced in support of the international conference Mine Closure 2014. Building Understanding is one of four Future Terrains service areas for tackling the challenge of degraded lands.