Abstract: A method is provided for decomposing free cyanide ion and metallic cyano complex ions in a liquid, comprising the steps of bringing the liquid into contact with ozone gas in a counterflow relation in the condition that the pH of the liquid is at least 10 with the mass flow rate of the ozone in the ozone gas up to 20 mg per minute per liter of liquid, and then bringing the liquid into contact in a counterflow relation with ozone gas having an ozone concentration of at least 150 g/m3 in the condition that the pH of the liquid is 7.0 to 9.5.

Abstract: A method of beneficiation of complex sulfide ores comprises crushing and grinding complex sulfide ore containing sulfides of copper, zinc, iron and other minerals, subjecting the ground ores to differential flotation to obtain a bulk copper-zinc concentrate which is separate from pyrite and gangue, and passing the bulk copper-zinc concentrate through a high-gradient magnetic separator having an open-bore magnetic field filled with a matrix element, so as to recover separately a magnetic copper concentrate and a non-magnetic zinc concentrate. By combining the differential flotation with high-gradient magnetic separation, the present invention enables individual separation of copper and zinc concentrates without using many reagents in high volumes and by a simple process control.