4. Merchant concentrates

Depending on extraction and concentration costs, the cut-off grade for zinc ores is between 3% and 10%. Mining is mainly carried out underground. Ore processing differs from site to site, depending on the mineralogical composition of the ores and the metals to be recovered.

• Once the ore has been extracted, it is crushed and then wet-ground in several stages, before undergoing the flotation separation and concentration phases that lead to the production of the various types of mineral concentrates.

  The mesh size of zinc and lead-bearing minerals is generally quite low. This requires, in most cases, regrinding steps within the flotation circuit itself (d ₈₀ of 40 µm sometimes required in some parts of the process).

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