Geomicrobiological leaching of tin minerals by Thiobacillus ferro-oxidans and organic agents.

Laboratory investigations confirm that it is possible to leach tin from synthetic minerals like stannite, kesterite, stannoidite, herzenbergite, ottemannite and berndtite, and from natural tin minerals which include stannite, cassiterite and varlamoffite, in the presence of Thiobacillus ferrooxidans, and with organic agents of biological origin, especially oxalic acid and oxalic-citric acids mixture. Over a leaching period of 35 days with 0.5% pulp density, initial pH of 2.5, using minus 0.16 mm size fraction at 32 degree C, as much as 54.45, 72.66, 97.13, and 31.30% Sn were extracted from synthetic stannite, kesterite, stannoidite and natural stannite, respectively. Varlamoffite, found in the dried, leached residues of the tin sulphides, provides evidence that bacterial action can be responsible for the genesis of supergene varlamoffite.