US2110445A - Process for purifying impure lead - Google Patents

Description

Patented Mar. 8, 1938 PATENT GFFKIE PROCESS FOR PUBIFYING IMPURE LEAD Ferdinand Leferrer, Paris, France, assignorto Societe Miniere et Metallurgiqne de Penarroya, Paris, France, a corporation of France No Drawing. Application October 25, 1935, Se-

rial No. 46,826. In France November 2, 1934 g 1 Claims. It is well known that most of the molten alloys give when slowly cooled a series of solid products the composition of which varies in a continuous manner from the beginning to the end of the solidification.

Only eutectic. alloys do not follow this rule.

It is thus often possible to modify the composition ofan alloy and to obtain a more or less complete separation of its constituents through a partial solidification with 'a separation of the solid and liquid phases which are in presence, in well determined conditions.

This property has been used for a long time in metallurgical processes for the refining of metals.

It has already been proposed to amplify this phenomenon and to render more eflicient the separation of the constituents by adding to the molten alloy, prior to the partial solidification. certain elements conveniently selected.

Thus, by adding a suiiicient quantity of zinc to molten argentiferous lead it has been possible to obtain, by cooling in the neighbourhood of the temperature of solidification of the lead, a floating solid crust which it is easy to separate and which carries with itselfthe totality of the silver pre-existing in the lead. I

More recently it has been tried, by using additions of alkaline or earth-alkaline metals, to

separate thelead from its alloys and especially from copper, tin, antimony, arsenic and bismuth with which it was possibly alloyed.

i It has therefore been indicated that only additions of earth-alkaline metals (calcium, magnesium or barium) made it possible to eliminate the copper, whileit was preferable to use additions of sodium for separating arsenic, antimony and bismuth.

But the experiments which have been made in this way have not alwaysgiven-the anticipated results. It has been found that sodium had'no action on bismuth which could be separated-only through the earth-alkaline metals (which has precisely given rise to a commercial process for debismuthizing lead).

Lastly, antimony couldbe separated from lead by means of sodium only in alloys having a large content of antimony.

Then it has been found, according to this invention, that additions of sodium alone to impure leads in a molten condition,--containing no or only a very small proportion of zinc, but containing copper, with as the case may be, tin

and/or arsenic, and/or antimony and/or precious,

metals-'-, made it possible to separate by cooling and in the same'fioating crust almost the totality of the copper and as the case may be, of the tin, of the arsenic, and also eventually part of the antimony (according to the proportion of sodium used); precious metals, if any, being not eliminated.

Thus, if a liquid working lead known as lead base bullion (having been freed from inclusions of matts and slags by melting and skimming at a low temperature) is treated through metallic sodium, the arsenic and the copper and the tin will be eliminated in the form of a crust which will float on the upper sin-face of the bath.

The-antimony will remain in the lead orit will be partly eliminated according to the quantity of sodium which has been added to the,

working lead.

Gold and silver will remain in the lead.

For carrying the process into practice metallic sodium or sodium" alloys may be used.

The excess of sodium remaining in the lead after treatment can be eliminated by a treat-v composition containing 0.3% of arsenic, 0.08% of tin, 0.3% of antimony, 0.05% of copper and. a

0.1% of silver, metallic sodium in the proportion of 5 kg. of sodium for a ton of lead, there will be obtained, after skimming at a temperature of about 330 C. (626 F.) a lead containing less than 0.01% of arsenic, less than 0.005% tin and less than 0.005% of copper. s The content of antimony will remain of about 0.3% and the content of silver will remain of about 0.1%- a By adding to the same molten working lead'a greater proportion of sodium, for instance 15 kg. of sodium for a ton of lead, the arsenic content of the lead obtained afterskimming will be less than 0.005%, thetin less than 0.002%, the copper content will be less than 0.002% and the antimonycontentwillbelessthanorequal to 0.1%. The silver will remain in the lead, with a silver content of about 0.1%.

This process allows also-by adding a quantity of sodium which is sufficient for eliminating the impurities but which is not suflicient for eliminating the antimony"-of purifying any lead-antimony alloy for freeing it from the impurities which it contains (arsenic, copper for instance) It has been thus possible, for instance, to purlfy'a lead-antimony alloy having the following composition: arsenic 0.1%, tin 0.05%, copper 0.05% and antimony 10%, by adding to the same 0.4% of sodium. After the known treatment,

for instance with water or steam, in order toarsenic, about 0.3% antimony, about 0.05% cop-' per, and about 0.1% silver, adding metallic sodium intheproportionot5kg.ofsodiumpertonoi lead, skimming the dross at a temperature of about 330 C, thereby obtaining a lead containing less than 0.01% arsenic, and less than 0.005%

copper, the antimony and silver remaining substantially unchanged.

2. In a process for purifying impure leads and especially work leads containing about 0.3% ar-. senlc, about 0.3% antimony, about 0.05% copper, and about 0.1% silver, adding metallic sodium in the proportion of 15 kg. of sodium per ton of lead.

skimming the dross at a temperature of about.

330 0., thereby obtaining a lead havingless than 0.005% arsenic, less than 0.002% copper, less than 0.1% antimony, the silver remainingsubstantially unchanged.

3. A process for purifying lead base bullion containing a small amount of tin, from trace to about 1% arsenic, from trace to about 0.15% copper, from trace to about 1% antimony, bismuth and noble metals which consists in adding a small amount of sodium to a molten bath of said bullion, allowing the bath to cool and removing simultaneously in the crust formed on the upper part of the bath all the copper, tin and arsenic present;

.- the antimony, bismuth and noble metals remaining in the bath. 4. A process for purifying lead base bullio containing a small amount oftin, from trace to I mony, bismuth and noble metals about 1% arsenic, from trace to about 0.15% copper, from trace to about 1% antimony,bismuth and noble metals which consists in adding to a molten bath of said bullion an amount oi sodium greater than that necessary for eliminating arsenic, tin and copper,-allowing the bath to cool and removing simultaneously in the crust formed on the upper part or the bath all the copper. tin andarsenic, with a part oi the antimonyin relation-to the excess of sodium added, the bismuth and noble metals and the restoi' antimony remaining in the bath.

5. The process of purifying a hard lead containing a. small amount of tin, an amount 01 antimony oi the order oil-about 10% and one or more of the group comprising arsenic of the order of about 0.1 copper oi the order 01' about 0.05%,

which consists in to a molten bath 0! said lead a small amount of sodium, allowing the bath to cool and removing simultaneously in the crust formed on the bath all the copper, tin and arsenic present, the antimony remaining in-the hath.

. 6. A process for purifying lead base bullion containing the-usual small mounts of arsenic, copper, tin, antimony, bismuth and noble metals. which consists in adding a small amount oi sodium to a molten-bath of said bullion, allowing the bath towel and removing simultaneously in the crust formed on the upper part of the bath all the copper, tin andarsenic present; the antiremaining .in the bath.

7. A process for-purifying lead base'bullion containing the usual small. amounts of arsenic,

.copper, tin, antimony, bismuth and noble metals,

.which c'onsists in adding to a molten bath of said bullion an amount or sodium greater than that necessary for eliminating arsenic, tin and copper,

, allowing the bath. to cool and removing simultaneously in the crust formed on the upper part of the bath an the copper, tin and arsenic, with a part oi the antimony in relation to the excess of sodium added, the bismuth and noble metals and the rest of antimony remaining in the bath.

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