In-situ leaching

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In Situ leaching by courtesy of Anna Bauer
In Situ leaching by courtesy of Anna Bauer

In-situ leaching is one of several leaching methods. In-situ or in-place leaching means that the metal values are leached directly from the ore without excavating the ore prior to leaching. Leaching reagents that dissolve the desired metals are pumped into the deposit through injection wells. The leachate is collected in a central underground dump or wells and later pumped to the surface through recovery wells for further processing aboveground. Permeability of the ore body is important and if the ore does not have sufficient natural porosity it has to be fractured by explosives so that the injected solution may flow through the deposit.

Ores suitable for in-situ leaching are usually located below the aquifer and the technique has been used to extract copper, uranium and soluble salts like halite, potash, boron and magnesium minerals.

Advantages:

  • Possibility to mine inaccessible sites
  • Shorter mine development time
  • No excavating costs
  • Lower mining and infrastructure costs
  • Reduces visual impact of mining operation
  • Personnel stays isolated from broken ore and other radiation hazards

Disadvantages:

  • Permeability problems
    • If ore body is impermeable it must be cracked by explosions
    • Precipitation of secondary minerals might cause permeability problems
    • The leaching liquid may stream downwards without percolating the ore body entirely
  • Risk of contamination of ground water (compare acid rock generation) because of poor solution control

Comments on In-situ bioleaching

"In the 1960s, it was discovered that uranium could be recovered by bioleaching, and industrial-scale uranium bioleaching was carried out by spraying stope walls with acid mine drainage and by the in situ irrigation of fractured underground ore deposits. This same process has also been applied to certain copper and other ore deposits. In situ bioleaching has the advantage that the ore does not need to be removed from the ground and is usually carried out on the haloes of the low-grade ore that are left behind after the high-grade ores have been removed. It is most economic when old mine workings can be used to access the low-grade deposits." {Rawlings, 2004 #38}

Examples of in-situ bioleaching operations

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