Minerals from Sequestration in Tailings

Both CO2 and ammonia are waste in the atmosphere we need to remove. The best solution is to include them in the supply chain

Old mines and tailings dams are of significant environmental concern.[1]

In the past mining companies have got away with containment which obviously has not worked well when you take into account breaches, floods and leaching. There have been many deaths including by poisoning.

There are at least 3,500 tailings dams [2] and they are a huge untapped resource as they often contain minerals (including rare earths, graphene etc.) that were not but are now valuable.

They could be made safer profitably by extracting minerals and at the same time cleaning the water which if potable could be release in a controlled manner. By keeping water levels low in tailings dams and berms around heaps they are far less dangerous or environmentally damaging.

There are many ways to recover value from tailings dams and carbonic acid from carbon dioxide (CO2) sources and the air and ammonium hydroxide from ammonia (NH3) in sewage and other wastes are ideal for this purpose. Both are waste gases, toxic and should be removed before entering global commons. Their use in controlled processes makes more sense and is suggested. As acids and bases respectively they can regulate the precipitation of carbonates, hydroxides and other salts depending on anions present.

The following graphs make this clear. The usual base used to precipitate magnesium is sodium hydroxide, but the graphs below and my own work demonstrate that ammonium hydroxide also has real possibilities as a base for this purpose.

Source: Sole, K., Parker, J., Cole, P., Mooiman, M. (2018). Flowsheet options for cobalt recovery in African copper-cobalt hydrometallurgy circuits.

Speciation of Mg and Ca carbonates and hydroxides with pH.[6]

CO2 is easier to use and safer than sulphuric acid for pH regulation.[3] Both ammonia and CO2 have the advantage of introducing no other ions to solution for later removal.

Software, automated remote control and monitoring could be used for the development of highly automated processes to extract valuable minerals particularly from remote now abandoned locations.

Ammonia is increasingly being harvested from animal waste and sewage [4] and by using genetically enhanced bacteria such as Azotobacter vinelandii.[5] Ammonia is ideal as a base for the control of pH is mineral recovery processes and for precipitation as it introduces no anions and can be evaporated and recycled, as I have demonstrated. Unlike sodium hydroxide, ammonium hydroxide has the interesting property of being recoverable as a gas at low temperatures and returned to use as a base again, which could make for a genuinely low-cost recycling loop. I should be upfront that this idea was never robustly proven in the lab — I did not have the money or equipment for proper analysis such as XRD, so it remains a promising possibility rather than a demonstrated result. That said, I am reasonably confident the precipitate was a magnesium carbonate (there are around a dozen possible forms, and ours was probably nesquehonite initially): I don't believe ammonia would have precipitated as an ammonium carbonate under these conditions, and what formed closely resembled magnesium carbonate precipitates I had made and identified previously. Green production is replacing the carbon intensive Born Haber process

Governments have a vested interest in dealing with the mining legacy issues forfeited to them.

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