Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1980-12-09
1983-04-26
Andrews, R. L.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
C25C 118
Patent
active
043812252
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
Background of the Invention
This invention relates to the selective dissolution and recovery of lead from lead sulphides and soluble ores and concentrates containing lead.
In this respect the invention specifically relates to ores and concentrates in which lead may be either a major or minor component.
Description of the Prior Art
Lead is normally produced from its sulphide ore or concentrate by pyrometallurgical treatment involving smelting. In this treatment sulphur which is contained in the aforementioned ore or concentrate is subjected to oxidation and sulphur dioxide results. Sulphur dioxide has been recognized as a pollutant to the atmosphere. Consequently the operations of lead smelting processes are being increasingly curtailed and made less economic by the severity of recent legislation.
To overcome the disadvantages of the pyrometallurgical process, particularly pollution, processes have been developed to oxidize sulphides under pressure in autoclaves using ammonia solution. The plant is expensive, uses large amounts of ammonia, produces large amounts of ammonia sulphate which must be disposed of, and often requires an associated plant for the production of pure oxygen.
An example of the aforementioned process is the hydrometallurgical process disclosed in Australian Pat. No. 282,292 (Sherritt Gordon Mines 1964). The process, in an ammonium sulphate environment, uses oxygen at a partial pressure of 0.34 to 6.8 atmospheres, and oxidizes lead sulphide to lead sulphate which product requires further treatment to produce lead metal. In this respect it has been found that lead cannot be economically recovered by electrolysis from their sulphides in an electrolyte containing substantial sulphate ions or by a process in which sulphate ions are produced in appreciable amounts.
In addition to the above, other processes have been proposed where the lead sulphide concentrate has been compacted into conductive anodes and oxidized electrically in an electrochemical cell. These processes were not successful due to the high cost of preparing the anodes, and poor current and extraction efficiencies.
Considerable research has also been directed at the leaching of lead sulphide ore or concentrate. Reference is made to U.K. Pat. No. 1,478,571 (Societe Miniere et Metallurgique de Penarroya) in which there is disclosed a method of dissolving non-ferrous metals contained in the sulphide ore or concentrate which comprises lixiviating the ore or concentrate with an aqueous cupric chloride solution, and regenerating cupric ions from the cuprous ions formed during the lixiviation reaction, by means of gaseous oxygen together with hydrochloric acid and/or ferrous chloride. This process produces a mixture of chlorides and the method of recovery of the metals was not disclosed.
Another process (described in U.S. Pat. No. 3,673,061) accomplishes the oxidation of sulphides at the anode of an electrochemical cell. This process recovers a range of base metals indiscriminately by using highly oxidizing conditions. Whilst current densities of 12 amperes/ft.sup.2 (130 amps/m.sup.2) are mentioned, it exemplifies density in the range of 54-480 amperes/ft.sup.2 which are very high. These highly oxidizing conditions result in high cell voltages and rapid corrosion of graphite anodes. It is believed the requirement of highly oxidizing conditions is due to the gradual build-up of a film of elemental sulphur on the surface of the mineral which inhibits the dissolution, thereby requiring more intense oxidation. It is significant to note that in this patent it is indicated that if the average grain size is greater than about 60 mesh U.S. Standard the process is inoperable.
There is also a pending Australian Patent Application No. 41938/78 (Broken Hill Proprietary Ltd.), which indicates that particle contact approximate or with the anode is necessary for effective dissolution. In particular it recites at page 7: the frequency of collisions between individual mineral particles and the feeder electrode, which for
REFERENCES:
patent: 556092 (1896-03-01), Frolich
patent: 3673061 (1972-06-01), Kruesi
patent: 3736238 (1973-05-01), Kruesi et al.
Andrews R. L.
Dextec Metallurgical Pty. Ltd.
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