INSTITUTO POLITECNICO NACIONAL ESCUELA SUPERIOR DE INGENIERIA QUIMICA E INDUSTRIAS EXTRACTIVAS

The basic flowsheet is shown in Fig. 12. The leaching step is carried out with a cupric chloride solution containing about 250 g/1 of sodium chloride to avoid precipitation of cuprous chloride. The leaching takes place at a pH not greater than 1. For chalcopyrite the temperature is kept cise to the boiling point. By leaching in two stages it is reported that more than 98 % of the iron and copper passes into solution, the leaching reaction being:3CuCl2 + CuFeS2 - 4CuCl + FeCl2 + 2SThe loaded solvent may subsequently be stripped by a spent electrolyte solution of sulphuric acid:R2Cu + H2SO4 CuSO4 + 2RHBoth the extraction and the electrolysis steps are closed-loop processes and the copper should be obtained as a high quality product by conventional electrolysis from a sulphate solution.The aqueous raffinate solution I from the solvent extraction, containing re- generated cupric chloride, is returned to the leaching stage, probably via the iron rejection stage for at least partial removal of the appreciable amount of ferrous ions present.

From this equation it vvill be seen that only one quarter of the copper from the leach reaction is to be withdrawn from the circuit as a metal product. To achieve this goal the leach solution containing CuCl, FeCl2 and NaCl s split in two halves, with one half directed to the solvent extraction - electrowinning circuit.The extraction of copper takes place with the copper sclective reagent LIX 65N (RH) which will release H+ during the extraction. By a simultaneous introduction of air to the extraction stage, however, the H+ will be consumed by the oxidation of the cuprous ions to the cupric state. Thus the simplified overall reaction for the simultaneous oxidation and extraction will be:2CuCl +2RH + 1/202 R2Cu + CuCl2 + H20The pH is stabilised at its optimum value of 2-6 and the temperature kept above 80C to ensure that the precipitate has good filterability. It is to be noted that according to equation (31) the simultaneous cuprous chloride oxidation and goethite precipitation will be in balance with two moles of cuprous ions oxidised for each mole of iron rejected. Taking into account that half of the cuprous to cupric oxidation takes place in the solvent extraction step, it will be realized that the overall (Cu/Fe) ration of 4 of the leaching reaction (28) is in balance for the overall process.The Minimet recherche process has been further developed for treatment of complex sulphide ores. It is claimed to be a very flexible process for non-ferrous metals, particularly Zn, Pb and Cu.

This process is carried out by selective leaching with the cupric chloride solution.

Any pyrite present in the sulphide ore will remain unattacked.

The Zinc will be recovered from the leaching solution by a similar oxidation-extraction process as is shown above for copper using an extracting agent selective for Zinc. Its a great adventage of the process that the steps of solvent extraction of copper/Zinc and the rejection of iron as goethite can be balancead by the simultaneous oxidation and regeneration of the cupric chloride leach solution .

Thus avoiding the adittion of any further external source of chemical agents within the processing circuit.

On the other hand, this may have to be paid for by an appreciable coprecipitation and loss of copper in the goethite precipitation.