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pH is a measure of the acidity or alkalinity of water. pH is defined as the negative logarithm of the proton concentration in a solution.



Optimal pH for bioleaching is usually around 1.7. Some minerals affect pH in a direction which reduces the quantity of costly pH-regulators. Other minerals affect pH in such a way that costly neutralisation is needed. Silicates and carbonates are mineral types that increase pH while sulfides reduce pH.

Systems to regulate pH

  • In heaps
    • by sprinklers spraying a suitable amount of acid (or base?).
    • by bleeding portions of the off-solution to a neutralization system. The volume removed is compensated by the addition of fresh water to the system.
    • Addition of pyrite is well suited if it is necessary to lower the pH. For this purpose, also elemental sulfur may be added instead of pyrite, Thiobacilli will then oxidize sulfur to sulfuric acid.

Sulfate-reducing prokaryotes

Sulfate-reducing bacteria (SRB) produce alkalinity when they reduce sulfur oxyanions to sulfide.

See also

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