The mining industry continues to face many challenges due to its potential environmental impacts. These challenges are becoming harder to overcome with growing social awareness, increasing regulatory pressure on suitable disposal options and the scarcity of available spaces for long term waste disposal. In addition there is growing pressure on the application of more sustainable approaches in mining.
Historical mining waste and even process waste from many modern processes has potential to contain hidden “gems” of value that with a little effort could be unlocked. The different types of mine waste can include tailings, waste rock or process residues. During the life cycle of a mining operation, the various waste streams will show large variation both from different areas of the operation and over time and the most applicable methods of management may therefore also change over time. In addition, the re-evaluation of mine waste in light of a “circular economy” also seeks to find new uses for old materials, based on the idea that “mine waste is a commodity without a current use”.
SRK has been involved in several projects that have identified efficient and effective solutions prior to mining commencing in operation and even for closed and abandoned sites. Typically such approaches require cross-disciplinary skills to valorise waste materials into market required resources. Some general information is given below.
A common issue lies with flotation tailings where recovery of fine-grained mineral particles became occluded originally by non-responsive gangue minerals during processing. Consequently, metal value was encapsulated within the waste and lost. A good example is the Wheal Maid tailings impoundment in Cornwall where historical mineral processing has left a legacy of heavily contaminated mine waste with high levels of metals in mine water. Copper, zinc, tin, silver, germanium and antimony as well as problematic metal(loid)s such as arsenic and lead occur in mine waste at concentrations similar to many modern mines (up to 3% copper and 2% zinc). These metals are associated with waste pyrite that could be recovered for sulfuric acid production and as inclusions of sulfide minerals in quartz. Recovery of this material may well involve regrinding the material or using modern sorters to selectively concentrate such phases and then process by conventional methods.
In some cases, the value is a surprise, or historically was not assessed. For example, in South East USA there are literally millions of tons of phosphogypsum mine waste that contain rare earth elements. These can be removed by regrind and leaching with an acidic leach. In other cases, the commodity has only recently been identified, for example the presence of high scandium concentrations in bauxite process residue, red muds (Figure 1).
In all these examples the critical link is achieving a better understanding of chemistry and mineralogy of the material to be processed and using this information to develop more sustainable mineral resourced.
20230912172153174.webp)