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Non-toxic In Situ Recovery

Non-toxic In Situ Recovery

The generic name for a liquid medium that is able to extract a target metal from ore is known as a lixiviant. The most familiar of these used in the gold sector is Sodium Cyanide (NaCN) which has revolutionised the hydrometallurgy of gold. However, Cyanide has one crucial disadvantage: It is highly toxic. When combined with hydrogen, it forms a deadly gas, hydrogen cyanide, HCN. This significant drawback has led to a plethora of non-toxic lixiviants being produced such as glycine and thiosulphate. However, despite numerous papers claiming the contrary, performance to date has been poor and generally subeconomic.

We are currently trialling a range of FDA approved lixiviants whose performance and leach kinetics have to date been equal or better than cyanide. The development of this lixiviant would allow low cost in situ recovery (ISR) methods to be used. ISR refers to the dissolution and subsequent recovery of subsurface minerals by injection of the lixiviant and extraction of the pregnant solution. Whilst ISR has been used extensively for uranium, potash, salt and copper, it has not been successfully used for gold because of poor lixiviant performance.

A key difference with our holistic approach to previous attempts in this field is combining the non-toxic lixiviant with Hyperjet high shear reactor technology within the recovery process.