Electrostatic safety during the solvent extraction of copper

On-site studies are reported showing that the solvent extraction of copper can be carried out without risks of electrostatic ignition. Safety against creation of electrostatic conditions that could ignite flammable gas mixtures relied primarily on the fast electrostatic charge decay capabilities of the solvent and organic liquids being processed. Measurements of the charge decay characteristics of the solvent, the extractant and the loaded and unloaded processing fluids showed that the time for charge relaxation in these fluids was sufficiently fast (0.025–0.028 s) that the build up of significant electrostatic voltages was prevented throughout pumping and tank separation operations. The use of highly insulating pipework and process tank liners and operation in a low-humidity environment did not compromise safety—even though traditional earth bonding of isolated metal parts was not implemented or practical. Any consideration to change the supply of solvent or extractant needs to be preceeded by measurements of the charge decay performance of the processing liquids.