Leaching of minerals
A method for treating a mineral composition containing iron, arsenic or other Group VA compounds comprises milling the mineral composition to a particle size of P 80 of less than 25 μm and leaching the mineral composition in the presence of lime and/or limestone and a soluble alkali complexing agent and in the presence of an oxygen containing gas at a pH in the range of from 3.5 to 6.
1. A method for treating a mineral composition containing iron, arsenic or other Group VA compounds comprising milling the mineral composition to a particle size of P 80 of less than 25 μm and leaching said mineral composition in the presence of lime and/or limestone and a soluble alkali complexing agent in the presence of an oxygen containing gas at a pH in the range of from 3.5 to 6.
2. A method as claimed in claim 1 wherein a second complexing agent forms a soluble complex with iron, arsenic or other Group VA compounds during the leaching.
3. The method of claim 2 wherein the second complexing agent is selected from the group consisting of soluble alkalis, soluble carbonates, soluble hydroxides, and carbon dioxide gas.
4. A method as claimed in claim 1 wherein the soluble alkali complexing agent forms a soluble complex with iron, arsenic or other Group VA compounds during the leaching.
5. The method of claim 1 wherein limestone is present during the leaching and lime is not added during the leaching.
6. The method of claim 1 wherein the soluble alkali complexing agent comprises a soluble carbonate or soluble hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, magnesium hydroxide, ammonium hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, and ammonium carbonate.
7. The method of claim 1 wherein the mineral composition comprises a refractory material containing precious metals.
8. A method as claimed in claim 7 wherein the refractory material comprises:
(a) refractory sulfides in which precious metals are encapsulated;
(b) ores which contain carbonaceous material and telluride materials; or
(c) ores which contain carbonaceous material and selenide materials.
9. The method of claim 7 wherein the mineral composition also contains one or more of stibnite, tetrahedrite, argentopyrite, calaverite, altaite, gold bearing selenides, tennantite and pentlandite, or the mineral composition comprises a composition including carbonaceous matter, where the carbonaceous matter would otherwise interfere with the precious metals recovery process.
10. The method of claim 9 wherein the refractory material comprises flotation concentrates.
11. The method of claim 1 wherein the composition is finely ground to a particle size range of 80% passing 2-25 μm, or about 80% passing 2-15 μm.
12. The method of claim 1 wherein the method is carried out at ambient pressure.
13. The method of claim 1 wherein the leaching is conducted at a temperature of between about 50° C. up to the boiling point of the mixture.
14. A method as claimed in claim 13 wherein the leaching conducted at a temperature of between about 50° C. up to about 98° C.
15. The method of claim 13 wherein the leaching is carried out in the presence of an oxygen containing gas selected from oxygen, air or oxygen enriched air.
16. The method of claim 1 wherein after the composition has been leached, the mixture is further treated to recover precious metals.
17. The method of claim 1 wherein the soluble alkali complexing agent comprises a soluble alkali compound that forms a complex with arsenic or other group VA elements or compounds, the complex comprising a short-lived complex that subsequently migrates away from particles of the mineral composition and then precipitates.