US2092451A - Electrolytic production of lead - Google Patents

Description

Patented Sept. 7, 1937 PATENT OFFICE 7 2,092,451 ELECTROLYTIC PRODUCTION or LEAD Allan Robert Gibson, Redland, Bristol, and Stanley Robson, Shirehampton, Bristol, EnglamL assignors to The National smelting Company Limited, London, England, a limited-liability company oi. England No Drawing. Application October 12, 1935, Serial No. 44,804. In Great Britain November 5, 1934 3 Claims. '(Cl. 204-19) This invention relates to the treatment 'of' metalliferous materials containing lead and sulphur.

It has been proposed hitherto to add a sulphide ore such as lead sulphide to a fused lead chloride bath and by electrolysis to recover the metal and elementary sulphur from the respective electrodes. We have found that in order to obtain a constant production of elementary lead and sulphur with the least consumption of electrical energy, a comparatively low concentration of lead sulphide is generally necessary, but the concentration is dependent upon the temperature of the melt and the current density applied.

According to the present invention lead and sulphur are separated from metalliferous materials containing them (for example, galena) by submitting to electrolysis fused lead chloride containing the said metalliferous material, the process being characterized in that the concentration of lead sulphide in the melt is maintained between 1% and 10% and the current density is so adjusted for this range of concentrations that i as the concentration is increased above 1%, the

the melt of 3% at a temperature of 550 C. and

employing a current density of 600 to 750 amps. per square foot. If the process is conducted at the lower end of the ranges given above, 1. c. with a current density of 500 amps -per square font a temperature of 500 to 600 C. and a galena concentration of 1 to 2%, electrolysis proceeds normally. If, however, with the current density and temperature remaining constant, the galena concentration be progressively increased the ohmic resistance of the melt is decreased until a point is reached in the neighbourhood of 3% galena concentration at which normal electrolysis is suspended and the sulphur is retained by the melt presumably in the form of di-' or poly-sulphide of lead. Beyond this point if the galena concentration is increased the current density must be correspondingly increased until with a be about 750 amps. per square foot. with this increase of current density the temperature of the melt will naturally rise. However, normal electrolysis of the cell maybe restored by cessation of the feed oi lead sulphide. Sulphur will then be liberated at the anode, and PbSreformed at the cathode by electrolytic decomposition of the'complex, until eventually only lead sulphide (PbS) remains in themelt, when normal electrolysis with the formation of the lead at the cathode and sulphur vapour at the anode is resumed.

In one wayof carrying out the process of the invention lead chloride is melted and maintained in the fused condition in any well known type of cell suitable for the electrolysis of fused salts, and galena is added-from time to time to maintain a concentration of about 3-5%. The current density employed for this concentration is .about 750 to 1000 amps. per square foot of electrodes surface. We prefer to employ a column of bi-polar electrodes with a gap of A inch. The voltage drop over each gap is 1.2 to 1.4. The supply of galena to the cell is regulatedaccording to the voltage over the cell, the temperature being constant. At a fixed temperature the voltage over the cell serves as a guide to the concentration of galena in the melt andthis may be maintained approximately constant by additions of galena during operation. If in this way too much galena is added it will also be readily observed by the decrease or cessation of sulphur at the anode owing to the formation of complex sulphides'in the melt, a condition which may be remedied by cessation of the feed or increase of the current density. It is desirable ,to employ mechanical agitation to keep the composition of the electrolyte constant, because the agitation due to thermal convection currents only is insufiicient for this purpose. Under these conditions lead is recovered with a consumption of 750 to 800 kilowatt hours per ton of lead, and the sulphur is recovered in the elementary state.

According to a feature of the invention the mixture may be subjected to a preliminary electrolysis to remove metals electro-negative to lead, in particular silver.

We have found it desirable to make the additions of galena to an inner compartment which can be sealed from the electrolysis proper, In this inner compartment the gangue formed on the addition of galena may be readily skimmed from the melt. The preliminary electrolysis may also be carried out in the inner compartment while it is sealed from electrolysis proper, or

purification may be effected by allowing the mixture to pass through a molten lead seal between the inner compartment and the cell proper.

Using bi-polar electrodes the passage of the current causes separation of molten lead at the cathode surfaces and gaseous sulphur at, or near, the anode. The sulphur is collected by means of a suitable reflux condenser, and the lead is removed in the molten state from the cell by means of a suitably designed syphon.

The gangue removed from the melt will contain some lead chloride, and this may be removed by volatilization of lead chloride and the fume condensed on galena and returned to the cell.

What we claim is:-

1. A process for separating lead and sulphur from metalliferous materials containing lead sulphide which comprises submitting to electrolysis fused lead chloride containing the said metalliferous material with a concentration of lead sulphide in the melt between 1% and 10% and at a current density between 500 and 1000 amps. per square foot, the current density varying proportionately to the lead sulphide concentration.

2. A process for separating lead and sulphur from metalliferous materials containing lead sulphide comprising submitting a solution of 3 to 5% of lead sulphide in lead chloride to electrolysis at a current density between 750 and 1000 amps. per square foot so as to cause sulphur vapour to be given oil at the anode, adding further lead sulphide-containing material to the melt and regulating the rate of addition and the current density so that the flow of sulphur vapour from the neighbourhood of the anode remains substantially constant.

3; A process for separating lead and sulphur from metalliferous materials containing lead sulphide which comprises electrolyzing in a cell employing bi-polar electrodes with a voltage drop of 1.2 to 1.4 over each gap, 9. solution of 3% to 5% of lead sulphide in lead chloride, adjusting the current density between 750 and 1000 amps. per square foot according to the concentration of lead sulphide so that a substantially constant flow of sulphur vapour is maintained from the neighbourhood of the anode.

ALLAN ROBERT GIBSON. STANLEY ROBSON.