US1591253A - Production of oxides and other compounds of zinc, lead, and the like - Google Patents

Description

Patented July 6,-- 1926.

V UNITED STATES PATENT OFFICE;

LELAND E. wEmrLE, or ST. LOUIS, MISSOURI, assreno 'ro AMERICAN zmc, LEAna smEL'rmG COMPANY, or BOSTON, MASSACHUSETTS, A CORPORATION or MAINE.

. PRODUCTION OE OXIDES AND OTHER oourounns OE ZINC, LEAD, AND THE LIKE.

No Drawing.

tion applies to the pro notion of compounds of zinc, lead and the like in grate furnaces of which the well known Wetherill furnace is a type. 1 Zinc and lead are the metals to which the present invention has its most extended a plication but it will be understood that t e process is applicable to other metals of similar properties particularly as regards volatility and for convenience in the present description all these may be referred to as volatilizable metals as it is believed that no misunderstanding as to the scope of the invention will arise from this term. For the sake of definiteness in the following descrip-- tion reference will be had more particularly to zinc as it is treated to produce zinc oxide for pigment purposes, the invention, however, not bein limited thereto although find- '25 ing a major eld of application in the production of zinc oxide fume, either substantially ure or in combination Withlead.

To facilitate understanding of my invention brief reference will first be made to the common practice of treating zinc bearing materials in grate furnaces of the Wetherill type. These furnaces consist essentially of a series of grate sections having a common arch connecting all the sections along a longitudinal axis and forming a tube through which the products of combustion of the charge pass off. Each section has a bottom or grate consisting of cast iron grate bars laid side by side and perforated with 0 small holes usually about one-eighth of an inch in diameter placed on two-inch centers, these bars forming a complete flooring for a grate section of from 100 to 132 square feet.' In the o eration of the furnace the air blast. 1s force up beneath the grate through the apertures in the grate bars and supports the combustion of the charge resting on the bars.

In the customary operation of a furnace of this type, the walls being heated either by a kindling fire or by the residual heat from a previous operation, a layer of fine kindling coal is thrown in on the ate and, ignitin from the heat of the wal s, reaches a rapi stage of combustion in fifteen or twenty minute There i hen adde th main f rn e Application filed February 17, 1920'. Serial No. 359,241.-

char'ge consisting of a mixture of more or less finely. divided metalliferous material or ore and reduction fuel. troduced either by hoppers or from the side 'doors of the furnace,is levelled to'unifor'm This charge is in-,

thickness, the air blast is turned onthroughv the grate bars and the charge 'smelted, the V metal being volatilized and driven off anda clinker being retained on the grate bars.

A 'difiiculty hitherto attendin this operation has been that the air su p ied through the grate does not pass .uni ormly through the charge, especially when this consists of 1 very finely divided'mate'rial forming .a comparati-vely dense and impervious mass. The air tends to collect at certain points and force an exit through the over-burden at. q

other equipment even smelting of the charge and while the chemical reactions are not fully carried out at some points, at other points where the air escapes there is an intense ,heat,'overheatng the vapors given off and causing the oxide to be of an inferior color and of inferior physical properties. At these points the-fuel rapidly burns out, leaving a orous noncombustible clinker through which .more air escapes without efi'ectingcombustion of the remainder of the charge. The diflicultyhas hitherto been combateol by opening the furnace doors and raking over the charge beds to fill'up these craters'and to force the air to penetrate the charge at another point. This raking is a laborious 1 rocess and is otherwise wasteful since the urnace is con-v siderably cooled during'the raking. Adso during the first part of the raking the zmc va or will be given off in immense volume and, since the draft equilibrium of the furnace has been destroyed. by the rush of outside air through the 0 en doors,.-this cloud through the ports pre ared for it but backs up and escapes throng the charge door and is lost; I

In he use of high grade ores having a 105 .of vapor cannot be carried out of the furnace no a making a relatively impervious bed. Furthermore, in the case of highly leaded ores or metallic zinc the metal is quickly reduced to a' liquid state and trickles down through the charge and coming into contact with the cold air blast through the grate bars solidifies, stops up the openings in these bars, accentuating the channelling action of the air blast as already referred to or even completely stopping further smelting action.

- vide for an even distribution of the air- In accordance with my invention I prothrough the charge of metalliferous material and reducing fuel and a consequent uniform smelting temperature therein by the provision of what I may term a filter bed of relatively coarse particlesof refractory material spread over the grate bars and supporting the charge. Thismaterial may conveniently be introduced at least in part in connection with the charge of kindling fuel and; may consist of siliceous gravel,

limestone, dolomite, crushed clinker residuum obtained from previous charges or refractory ores containing more or less zinc and lead and the like. Conveniently I utilize the crushed clinker from a previous smelting operation asv this is already saturated with the metal and will therefore not take up and waste any of the metal in the charge to be smelted.

In order that my invention may be more clearly understood I will describe in detail a particular example as practically applied to the production of zinc oxide. As already stated, while not limited thereto I prefer to utilize the clinker obtained from a previous smelting operation and this clinker is suitably crushed, preferably in a jaw breaker or other suitable machine, producing a minimum of very fine material. The crushed product is suitably. screened or gradedproviding two products, one consisting of particles ranging in size from one-half inch to seven-eighths of an inch in diameter and the other from one-quarter to one-half inch in diameter. These sizes are approximate to represent what I have found desirable in practice.

In performin the smelting operation I prefer toform t e filter bed first by spreading directly upon the grate bars a layer of the coarser material ranging from a half an inch in diameter to seven-eighths of an inch in such thickness as will just completely cover the bars, The finer clinker product having a size of from one-quarter to onehalf an inch I mix with kindling fuel such as anthracite screenings, coke breeze or the like and add this above the first layer ofrefractory particles to provide a bed from an inch to an inch and a half thick. In the case of a grate section having an area of 120 square feet about 150 to 250 pounds each of clinker and kindling fuel are required.

In the case Of'VGlY rich zinc ore containing approximately zinc or when metallic spelter is used for making zinc oxide or where a large proportion of lead is present the thickness of the filter bed is advantageously increased by -one or two inches. This may be done by increasing the proportion of clinker material fixed with the kindling fuel or by adding a layer of the coarser refractory particles before the mixture of refractory material and' kindling fuel is added. It will be understood that the conditions here may be widely varied and that under certain circumstances the preliminary charge of coarser particles may be omitted and merely the mixture of finer particles and kindling be charged directly 'on the grate bars. The particular example and figures here given are by way of an ex.

ample to indicate more definitely certain practical applications of the basic principles of my invention.

The mixed charge of metalliferous material and reducing fuel, preferably finely divided and intimately mixed, is added in the usual manner to the furnace over the porous bed provided by the refractory particles introduced in whole or in part with the kindling fuel. This porous bed rovides for an even distribution of the air through the charge, resulting in uniform heating and smelting without the formation of craters. Furthermore, in the case of materials carrying a high proportion of metal the liquefied metal is permitted to volatilize and to pass oif in the furnace without reaching the grate bars as liquid and solidifying thereon. While the process herein described is of general application it finds a particular application in the treatment of finely divided ores of high zinc content such as ordinary zinc concentrates having a content of 50 to 70% of zinc. \To effectually treat these ores they must be finely divided and intimately mixed with the reducing fuel and in treat-- ing hese in grate furnaces hitherto they formed a compact mass largely impervious to the air blast and the channellin action of the latter was therefore intensi ed. Fur- 12 thermore, if a high air blast pressure were maintained fine particles were blown out of the charge and carried over into the condensed fume resulting in serious injury to its color and hysical condition. If, on the. other hand, the depth of. the charge in the furnace were reduced in anattemptto'make it less impervious, a uniform sine tingmtzmperature -was not obtained, has a dybeen pointed out were also eabars to ignite the charge. By refractory countered in the case of metalliferous materials of a high metal content on account-of the separation of the metal in liquid form tending to, stop up the apertures in the grate bars and stop the smelting process entirely By the use of the present invention there may be produced from spelter in the grate furnace a' zinc oxide product identical with that commonly known as the French process wherein the metallic zinc is volatilized in vessels out of contact with the fuel used. In the smelting of lead ore a charge can be treated to produce a pigment product ,of lead sulphate, lead oxide and basic lead sulphate, such as hitherto could be produced only in an entirely different type of furnace similar to a blast furnace and having a shaft to receive the metalliferous material and reduction fuel into which the air blast was introduced through twyers entering the. side walls near the bottom of the shaft.

The above description has referred par ticularly to the type of furnace commonly known as the Wethrill furnace in which the grate is stationar The process, however, is'applicable to 0t er types of furnace using a grate bar which, for example, may be ar-- ranged to travel along a lateral axis or may be arranged to tilt to receive anddischarge its burden or ma be arranged to move along a vertical axls or tohave various combinations of these motions.

By the word charge in the above description I have meant the mixture of ore or metalliferous material and reduction fuel prepared in the customary manner by mixing with about 10% water in a cement mixer. This charge is conveniently of a pulverulent nature, being very finely ground and intimately mixed. By metalliferous material I refer to that portion of the charge which carries the metal to be volatilized and such extraneous material as may be associated therewith and this metalliferous material includes ordinary ores, zinc concentrates, flotation concentrates, flue dust, or metal itself as spelter. The fuel may be anthracite, semianthracite, bituminous or coke breeze and by kindling fuel reference is made to that portion commonly used directly on the grate material I have referred to material such as burnt clinker, gravel, siliceous, limey, ferric ores and the like, which is infusible or antifiuxing at the low temperature existin 'just above the grate bars or in the charge itself.

Having described in detail a particular application of my invention, the principles exemplified thereby which I claim as new and desire to secure by Letters Patent I shall express in the following claims.

7 1. The method of smelting-volatilizable metals of the nature of lead or zinc particularly applicable to practice with a grate furnace which comprises providing a bed of refractory particles, said particles being crushed gangue or clinker from a like operation saturated with the volatilizable metal, supporting thereon a charge ofmixed metalliferous material and reduction fuel and supplying air to the char e through the bed to support combustion wlxereby even penetration of the charge and emission of the metal as vapor are assured.

2. The method of smelting volatilizable metals of the nature of lead or zinc particularly applicable to practice with a grate furnace which comprises providing a relatively thin supporting layer of refractory particles and kindling fuel, said particles being crushed gangue or clinker from a like opera-' tion saturated with the volatilizable metal, igniting said bed, added thereover a charge of mixed metalliferous material and reduction fuel and supplying air to the charge throughsaid supporting layer to support combustion.

3. The method of smelting volatilizable metals of the nature of lead or zinc ina grate furnace which comprises providing on the ate a thin layer of coarse refractory partlcles a half inch or greater in diameter forming a highly pervious layer for the dissemination of air supplied through the grate and a superposed layer of vfiner refractory particles, adding thereover a charge of mixed metalliferous material and reduction fuel and supplying air to said charge from beneath the grate to support combustlon.

In testimony whereof, I have signed my name to this specification.

LELAND E. WEMPLE.