copper, page-8

re: questions to reduce my ignorance This looks like a question for me.

Firstly, oxides:
Take dirt, make smaller, add acid, dissolve metals.
From here the process involves a solid/liquid separation to separate the metals from the rock. This is usually achieved via CCD (counter-current decantation, where a series of thickeners are used with opposing flows of solids and liquids) or alternatively with a thickener then a filtration/washing stage though this is unusual. The other purpose of this is to reduce the acid content in the material being sent to the tailings storage facility. The liquid with the metals in it is termed pregnant and is often polished through a clarifying filter before being pumped to the metals extraction stage.

The metals extraction usually involves a process called ion exchange, solvent extraction or precipitation.

Solvent extraction, most commonly used for copper involves the intricate mixing of the pregnant liquor with a oil based solvent. The copper has a greater affinity for a lixivant in the solvent and transfers from the liquor to the solvent. The old phrase where you can't mix oil and water comes to play and the two phases separate, concentrating the metal in the solvent. The solvent is then contacted with another phase with different chemical properties(usually higher pH) and the metal transfers back over to the water phase. The metal concentration can be concentrated each time leading to a solution that has sufficient concentration to electrowin the metal to cathode.

The second process is called ion exchange and is most often used for nickel and cobalt. It involves passing the pregnant through a solumn of plastic beads that have a specific affinity for the selected metal leading to the adsorption of the metal to the resin. This process is semi-continuous and involves several colums to allow low enough tailings grades. At regular intervals a column is removed from circuit and a stripping solution is passed through the column to remove the metal and rejuvenate the resin. It is then returned to circuit. This also allows the metal value to be concentrated.

The above two processes do not change the properties of the pregnant solution sufficiently except for the removal of the desired metal. Therefor the two processes can be used repeatedly to remove different metals into different concentrates.

The last process is precipitation. This involves changing the chemical properties of the pregnant solution (usually pH) to have the metal removed from the solution as a solid salt or sometimes as a metal as in the merryll-crowe process. The metal is removed through filtration.

These are the basic concentration and recovery processes for metals in solution. It's all quite easy to do once someone really smart designs it right in the first place.

Sulphides will have to wait till after dinner.