Chromium removal from leach liquors produced during high pressure acid leaching of lateritic ores
A method is provided for the removal of chromium from leach liquors produced during high pressure leaching of laterite ores in an autoclave, by addition to the autoclave of carbon in a quantity of about 0.5%-1% by weight with reference to the total dry feed.
1. In a method for producing leach liquors by high pressure acid leaching of laterite ores with acid in an autoclave, the improvement comprising removing chromium from the leach liquors by adding carbon to the autoclave.
2. Method according to claim 1 , in which the acid leaching is carried out by processing in the autoclave a slurry of the ore in sulphuric acid to a temperature in the range of 240 to 270° C. with a retention time of 25 to 105 minutes.
3. Method according to claim 2 , in which the pulp density of the slurry is 25 to 50% solids.
4. Method according to claim 2 , in which the acid is added in sufficient amount to give a residual free acid of 30 to 50 g/L at room temperature before flashing.
5. Method according to claim 1 , in which the amount of carbon added is such as to produce a reduction in redox potential of between about 100 and 300 mV (SHE).
6. Method according to claim 1 , in which the amount of carbon added is about 0.5%-1% by weight with reference to total solids fed to the autoclave.
7. Method according to claim 1 , in which carbon is added in the form of carbon black, metallurgical coke, graphite, activated carbon or a combination thereof.
8. Method according to claim 1 , in which the laterite ore is a limonitic ore.
9. Method according to claim 8 , in which the limonitic ore is a limonite/saprolite ore blend.