Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1986-05-06
1987-08-04
Andrews, R. L.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
75109, C25C 114
Patent
active
046844503
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
The invention relates to the hydrometallurgical production of zinc from zinc bearing ores and concentrates. The sulphide is the more common form of zinc which creates a problem of atmospheric pollution with sulphur dioxide, but zinc in the form of carbonates and oxides may also be treated by this method and can be treated more efficiently in some cases than the sulphides.
DESCRIPTION OF THE PRIOR ART
The conventional method of treating zinc sulphides is by roasting to produce zinc oxide and sulphur dioxide. This sulphuric dioxide may or may not be converted to sulphuric acid. Thereafter the produce is subject to dissolution in sulphuric acid and electrolysis of the purified solution takes place to produce zinc at the cathode and oxygen at the anode. Because of the generation of acid at the anode and the tendency to evolve hydrogen at the cathode rather than zinc, extremely pure solutions must be used and careful control of the current density must be exercised. This requires the addition of reagents to the electrolyte to produce a smooth plate rather than a rough plate or powder, which, under those cell conditions would encourage evolution of hydrogen.
In U.S. Pat. No. 4,148,698 Everett, there is disclosed an alternate method of extracting a base metal from a base metal bearing ore which relies on a cyclic process. It entails the formation of a slurry of the ore with a chloride leaching agent in the presence of ionic copper catalyst. Oxygen is used to enhance the dissolution of the base metal.
Because of the very small amounts of zinc which could be leached per volume of low acid anolyte from the plating cell, large circulation rates were required resulting in expensive solid liquid separation steps. The acid anolyte made plating of zinc in the catholyte difficult due to the ease of migration of hydrogen ions through the diaphragm, even when ion selective membranes such as Nafion (Dupont trade mark) were used.
Zinc has also been produced from chloride solutions with evolution of chlorine at the anode. This requires a high anode potential, expensive anodes (platinum or ruthenium coated titanium) and results in material handling difficulties due to the potential for zinc and chlorine to react explosively. The anolyte is also acidic providing a source of hydrogen ions, normally the main cause of inefficient zinc plating.
The process of this invention overcomes the disadvantages of the above processes and allows the leaching and plating of zinc in a low hydrogen ion environment. This increases the efficiency of plating of the zinc and allows the plating of a powder rather than an adherant plate which would require the addition of plating additives which may have a deleterious effect on the leaching reactions. The anolyte and catholyte are separated by an ion selective membrance (such as Nafion) and the current is passed by the passage through the membrane of ions such as sodium which do not interfere with zinc plating. Hydrogen ions will also pass through these diaphragms and interfere with zinc plating, and it is a particular object of this invention to leach the mineral in a low acid environment to avoid the high cost of low zinc plating efficiency.
SUMMARY OF THE INVENTION
This invention provides a process for recovering zinc from a zinc bearing ore or concentrate in an electrolytic cell, the cell including a cathode compartment containing a cathode, and an anode compartment containing an anode, the cathode and anode compartments defined by interposing an ion selective membrane therebetween, which membrane is characterized as capable of preventing migration of ions which may interfere with zinc plating from the anode compartment to the cathode compartment, the process including forming in the anode compartment, a slurry of the ore or concentrate with a solution containing chloride ions and copper ions, intimately mixing oxygen bearing gas with the slurry, maintaining the mixture substantially at atmospheric pressure and at a temperature up to the
REFERENCES:
patent: 3772003 (1973-11-01), Gordy
patent: 4148698 (1979-04-01), Everett
patent: 4288304 (1981-09-01), De Marthe et al.
patent: 4465569 (1984-08-01), Bjune et al.
patent: 4536214 (1985-08-01), Ochs et al.
Andrews R. L.
Dextec Metallurgical Pty. Ltd.
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