US2267698A - Method of recovering and refining metal - Google Patents

Description

T. R. JANES METHOD OF RECOVERING- AND REFINING METAL Dec. 23, 1941.-

Filed Oct. 11, 19:59

INVENT OR. Tkamas 21?. c/Eznes Patented Dec. 23, 1941 METHOD OF BECOVERING AND BEFINING METAL Thomas R. lanes, Langliorne, Pa... assignor to Superior Zinc Corporation, Bristol, Pa., a corporation of Pennsylvania Application October 11, 1939, Serial No. 299,008

Claims.

The present invention relates to a process for smelting and refining metals and ores thereof, and it relates more particularly to smelting and refining metals which may be recovered or refined by vaporization or distillation, and it relates more particularly to the recovery and refining of zinc and other metals having relatively low boiling points,

One of the objects of the present invention is to improve the smelting of zinc ores, as well as the recovery and purification of zinc from secondary sources such as zinc skimmings, zinc alloys and other zinc-bearing or zinciferrous materials.

A further object of the present invention is to permit a greater and more ready separation of the several metals which may be present, that is, to permit the greater and more ready elimination of cadmium and lead from the zinc, thereby to recover and purify zinc more nearly free of cadmium, lead and other metals.

A further object of the present invention is generally to increase the efllciency of the smelting, recovery and refining of zinc and other metals.

One of the common and most widely used methods of smelting zinciferrous material is to use multiple retort furnaces in which such material is then heated.

Such furnaces are operated by skilled workmen and produce satisfactory results but are expensive to construct and maintain. Labor is arduous and losses are heavy. Each retort is a sectional view, generally on line l-I of Figure 2,

separate unit, delivering but a small amount of vapor and condensation is not uniform because of the difliculty of regulating numerous condensers.

Also heating cannot be uniform and hence both efliciency and recovery usually suffer.

Various attempts have been made to enlarge the size of retorts but these have been unsuccessful due to limitations of refractories.

In smelting zinciferrous materials, it is necessary to heat the zinc-bearing material with reducing material which causes reduction of the zinc to metallic vapor. This also produces an equivalent amount of carbon monoxide and some carbon dioxide. Carbon dioxide is undesirable since since it tends to reoxidize some of the zinc vapor and interferes with condensation of the vapor in meallic state. Prevention of formation of carbon dioxide in the smelting zone and in the of a furnace suitable for the practice of the present invention, shown more or less schematically, with the elimination of those details of construction which are merely conventional means generally known and used in the art.

Figure 2 represents a longitudinally, vertical cross-sectional view, generally on line 2-2 of Figure 1 Figure 3 represents a horizontal cross-sectional view, generally on line 3-3 of Figure2.

Figure represents a fragmentary perspective view of the lower smelting surface of the furnace shown in Figures 1, 2 and 3.

A smelting furnace suitable for the practice of the present invention generally includes a bottom designated generally by the numeral 5, side walls 6 and I, end walls 8 and 9, which together form a shallow. receptacle-like chamber having substantial horizontal dimensions, which is covered by an upper heating roof 9" which together with the bottom and sides and end walls formsa generally closed and substantially gastight smelting chamber I 0 having only one or more charging openings such as the end charging opening II and the side charging trough l2 and having a discharge opening II, at the other end thereof through which the metallic vapors are discharged into condensers, (not shown).

Above the heating roof 9', a combustion chamber l l is disposed having side walls i5 and I6, end walls i1 and I8 and an arched heat-reflector roof I! for reflecting the heat or concentrating the heat onto the heating roof 9" which also constitutes the bottom of the combustion chamber it.

One or more inlet openings 20 are preferably provided in one of the end walls (or in one of the side walls) of the combustion chamber it, through which the fuel and air may be injected under pressure or sprayed into the combustion chamber, as for instance, by any suitable oil burner or other fuel burner or injector. A stack 21 through the roof I! at the opposite end of the combustion chamber it serves to conduct or carry away the products of combustion.

In the bottom 5 of the furnace, a series of heating tubes 23 are provided of suitable refractory material such as silicon carbide or graphite or other refractory ceramic materials, said heating tubes 23 extending horizontally across and through the furnace in the manner indicated generally in Figure l and having their ends at one side of the furnace all terminating in a stack manifold pipe 2Q having a stack pipe 25 extending to the common stack 20 through which the products of combustion can be carried away. The opposite ends 26 of the heating tubes 23 are adapted to receive fuel injectors similar to that indicated for the opening at of the upper combustion chamber it, but of smaller size or capacity commensurate with the size of the combustion chamber constituted by the interior of the heating tube.

The heating tubes 23 are preferably arranged with their uppermost portions more or less flush with the horizontal bottom surfaces 2d of the smelting chamber it, so as to more directly transmit the heat into the molten mass of metal in said chamber when it is desired to apply the heat through the tubes 23.

The bottom of the furnace is preferably formed of a series of staggered refractory-dike blocks 29 of suitable size having inwardly enlarged recesses St in the upper portions thereof as indicated in Figure 4, the location of said recesses being ofi center so that by staggering the'ultimate blocks the recesses can be brought into alignment in a manner generally indicated in Figures 3 and 4. The distance across the opening or mouth of the recess is preferably slightly greater than the outer diameter of the tube 23, so that the tube can be inserted therein. The clearance between the tube 23 and the recess at is then filled with suitable refractory cement or aggregate at which is then permitted to set or harden, in situ, so as firmly to set the tube 23 in the blocks as and also to form a firm heat-conducting contact around the entire outer be encased in a sheet metal outer sheathing 36 to give support to the furnace and also to make it more nearly gas-tight. The entire furnace may further be supported on pairs of channei irons iii, to the outer ends of which vertical buckstays 38 are secured as at 39, to give lateral support to the furnace, particularly the lateral walls including the walls I5 and i6 thereof and the fire brick arch it; these buckstays being in turn fastened at their upper ends by adjustable stay rods or tie rods 40 provided with suitable turn buckles H for adjusting the tension.

Between the blocks 29 and in the juncture of all refractory bricks and slabs constituting the chamber l0, high temperature cement is provided for filling and sealing the joints or junctures.

A drain tap 42 may also be provided for drawing out all the molten metal when it is desired to shut down the furnace.

The molten metal may be fed in through the charging trough H from time to time, or more or less continuously, so as to maintain the level aaevgeee of the molten metal to a suitable point which is generally below the lowermost point of the discharge pipe it. The metal is melted in any suitable melting pot preferably at a point somewhat higher than the charging trough i2 so as to permit the molten metal to be charged into and through the trough if by gravity.

The furnace may be first heated to a suitable temperature by combustion of fuel in the combustion chamber it and, if desired, also by the combustion fuel in the heating tube Thereafter, the molten metal may be fed in through the trough H2 at a suitable level and the molten metal heated gradually to vaporize the several component parts thereof.

If desired, cold metal and solid metal pieces or zinc-bearing solid masses may be initially fed into the chamber iii through the charging opening lieither while the furnace is comparatively cold or after it has been heated, thereby constituting an initial charge for the furnace. Thereafter, the opening i i is preferably closed up with a fire brick or other suitable closure and after the initial charge of solid material has been molten, the level of the molten metal can be maintained by charging further molten metal into the trough i2.

By applying or withholding heat at the bottom (that is, through the heating tubes 23), the fractional distillation of the component parts of zinc-bearing materials may be more efficiently effected.

Thus, by applying bottom heat of sufiicient extent, there will be an ebullition in the mass of molten metal with the result that the cadmium content of the molten metal will be vaporized more quickly and will be driven off from the molten metal as a vapor in greater proportion than what would be the case if the heat were merely applied from the top. Thus, by applying heat of sufiicient magnitude at the bottom (while also heating from the top) the first vapors which come off are more concentrated in cadmium vapor.

Thereafter, the bottom heat is shut oif or considerably reduced and the molten mass heated entirely from above through the heating roof a Further vaporization of the molten mass takes place and the vapor thus driven off will contain less cadmium than the initial vapor first above described, and by so heating only from above, the zinc is then vaporized thereby leaving behind the lead content of the initial molten mass. In this manner, the lead may be concentrated in the molten mass. As the concentration of the lead gradually increases, it passes the point of maximum solubility of the lead in the zinc, so that the lead will further be concentrated by precipitation at the bottom. If desired, the molten metal containing the higher lead concentration may be drawn ofl from the furnace periodically through the trough block 62 and then the operation is continued by the further addition of molten zinc bearing metals through the charging trough 12 or by the addition of solid zinc-bearing metals through the charging opening H.

Vapors discharged through the outlet tube it are conveyed to condensers where the vapors are condensed to metallic zinc;--with the first condensates more rich in cadmium as hereinabove indicated.

By the foregoing process, the vapors drawn off after the initial removal of cadmium as hereinabove indicated will be substantially pure zinc free of cadmium or other impurities.

By the process or method of the present invention, zinc ores and zinc skimmings may be smelted and refined efiiciently to produce a substantial pure metallic zinc.

Instead of burning fuel such as oil, gas or powder coal in the heating tubes 23, electrical heating units may be disposed within the heating tubes such as electric glow bars. Likewise, the upper heat may be obtained by similar electric heating units disposed directly beneath the roof 9 of the chamber 10, which may be used entirely to replace the upper heating chamber 14 or may be used to augment the same for more ready temperature control.

Thus, it will be seen that by alternately applying and withholding heat at the bottom for suitable periods, first the cadmium may be sepaated from the zinc by vaporization and then the lead content and the copper content of the zincbearing material may be held back and concentrated while the zinc is being driven off in the form of metallic zinc vapor.

When using heating tubes similar to the heating tubes 23 for upper heat, these tubes can either be incorporated in the roof in a manner similar to that shownin the bottom or they can replace the roof 9 entirely.

When using electrical heat instead of heat of combustion, the flue or stacks can be eliminated. Thus, if electric heat is used in the heating tubes 23, the manifold 24 and pipe 25 are eliminated and the tubes 23 are plugged at both ends by refractory, so as to retain the heat and indeed are shortened so as not to extend substantially beyond the width of the metal-vaporizing chamber ID (the electrical conductors extending through the furnace wall to the opposite ends of the tubes 23).

It is to be understood that the zinc vapor discharged through the discharge |3 may also be converted into zinc oxide and any other zinc products which can be made from zinc vapor.

By imbedding the heating tubes 23 in the manner indicated particularly in Figures 2, 3 and 4, the tendency of the tubes to float in the comparatively heavier molten metal, is overcome and the tubes maintained firmly in place.

The blocks 29 are preferably of a fire clay tile having relatively poor or relatively low heat conducting capacity, while the tubes 23 are preferably silicon carbide or carborundum or graphite having somewhat greater heating conducting capacity so as to promote the flow of the heat from the tubes upwardly into the bath of molten metal. So, too, the cement or aggregate filling 3| may contain carborundum or other refractory had to the appended claims rather than to the foregoing description to indicate the scope of the invention. a

Having thus described the invention, what is hereby claimed as new and desired to be secured by Letters Patent, is:

l. The process of recovering zinc which conists in maintaining a relatively shallow pool 'of molten zinc-bearing materials generally isolated from free air and from products of combustion, heating said pool of molten material from beneath the pool by heat applied beneath the pool to a degree and for a time sufficient to boil off a large part of the cadmium content of said molten mass and thereafter withholding the heat in the bottom and thereafter heating said molten mass from the top at a temperature sufficient to vaporize the zinc thereby to concentrate in the residue the lead and other impurities.

2. The process of recovering zinc which comprises maintaining a relatively shallow pool of molten zinc-bearing materials generally isolated from free air and from products of combustion, initially heating said pool of molten material/by applying heat beneath the pool to a degree and for a time suflicient to boil off a large part of the cadmium content of said molten mass while initially withholding heat from the top of said pool and thereafter heating said molten mass from the top at a temperature sufiicient to vaporize the zinc thereby to concentrate in the residue the lead and other relatively higher-boiling impurities.

3. The process of recovering zinc which comprises maintaining a relatively shallow pool of molten zinc-bearing materials generally isolated from free air and from products of combustion, initially heating said pool of molten material only from the bottom while withholding heat from the top thereby to remove most of the cadmium and other low-boiling impurities in the form of an initial distillate having a relatively high percentage of said cadmium and other low-boiling impurities, thereafter applying heat to the top of said pool thereby to remove relatively pure zinc as a subsequent distillate and finally drawing off the molten residue in which lead and other high-boiling impurities have been concentrated.

4. The process of refining zinc-bearing materials which comprises maintaining a molten mass of said materials in the relativeabsence ofair,initially heating said moltenmassonlyfrombeneath for a time and to an extent necessary to remove most of the cadmium and other low-boiling impurities in the form of an initial distillate having a relatively high percentage of said cadmium and other low-boiling impurities, subsequently heating said molten mass from above thereby to remove relatively pure zinc in the form of a subsequent distillate and finally drawing oi! the molten residue having a relatively high percentage of lead and other high-boiling impurities.

5. In the process of refining zinc-bearing materials by distillation, the step of applying indirect heat initially only from beneath the molten materials while withholding heat from above themolten materials;-said indirect heat being applied initially from beneath to a degree and for a time sufficient to remove most of the cadmium and other high-boiling impurities in the form of an initial distillate having a relatively highpercentage 01' said cadmium and other low-boiling impurities.

' THOMAS R. JANES.

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