Document OJMqYwoJVGpKbnKD19kRdzVme

t ' \ Manufacture of Zinc Oxide - By fl If Curry, Chief Chemist/- 6offeyrilla (Taken from June-July, 1919 issue Chameleon) "<as*ar/( ; Commercially, Zinc Oxide or Zinc Ifhite, Is manufacture^Sfetwo processes,which may be termed direct and indirect. The indirect processj^j^Jgih^a been.in^common ,, use in Europe, since the middle of the eighteenth century^jconsiste inheating re torts containing molten sine or spelter. The metal pesses^^^^fee/iformnf-''airapor : . which is oxidised by a current of air in an adjoining.cha'mbeigbf/sine oxide nhich is in turn carried by the draught from a high chimney to:colleciihgfchamber*. The oxide then undergoes a finishing treatment to rid it of impurities which naturally distill over with it. Traces of arsenic, cadmium and lead if-present .in .the metal will be found in the oxide. /X '' ' ' 'V' The color of the oxide if properly made is s purs and brilliant:whit* and abeo- - lutely permanent. It is,yellow when heated, but upon cooling returns,to its original white color. It Is obvious that, in order to produce a pure grade" ofi sino oxide, a pure zinc metal must be used at the Initial stage of the process. A.zinc oxide pro- . duced from the distillation of electrolytic spelter would, in sy opinion, be the purest of all sine oxides. , 1 The chief objection to the indirect method, and the reason that it has never met - with favor in t'ds country ii.-apparent when costs are considered. The metal used in the process must first be extracted from zinc ores which is quite a process in . itself. /' The direct process for manufacturing zinc oxide,, known as.the Wetherill process, and in which the oxide is made directly from tbe ore, - sprang into use soon after the, famous zinc mines at'Franklin, M.J. were opened. Col, Samuel ffetberlil las the / first to manufacture zinc oxide on a commercial ecale,in 1S66. Although many lo- . provements have been made since, the process today is? essentiaJly the same. . . Since that date, however, an abundance of zinc,--lead and leeded zinc ores have - been produced by mines throughout the Suited States. ': The KiSBouri-Cansas-Oklehoma district produces more zinc and lead ores at the present time-than any other dist rict in the world. However, owing to the great ease with which'ores-from this dist rict, are concentrated, the high grade concentrates produced .therefrom command a price, which is, In normal times, prohibitive to the manufacturers of zinc oxide, and consequently these concentrates are used by the manufacturers of spelter. The lower grade disseminated ores of the Western States and Sew Mexico ere the chief ores used in the manufacture of zinc oxide in the middle west. These should contain at least SO percent combined zinc and lead, and should be free.from arsenic,'cad mium, antimony, bismuth and any other objectionable elements which might find their- way later into the pigment and discolor or otherwise injure-its quality. i-These ores are quite variable In composition, but may be carefully blinded ao as;to insure a resultant pigment of the finest quality and of almost .any composition-desired,-whe- - ther it be a zinc oxide or a leaded zinc pigment. ' ' W As may-be inferred from the above, the HetheriH' procese.-a^ibet'.appiied- to the' , manufacture of either zinc oxide or leaded zinc ; pigment, tbe^onl^'iiffe^en^esAbeing in the selection and blending of the ores to-meet thej;requijremen^M9.^^hsS.Sffip-tntr' ' pigment. The ore is usually shipped in open-top or.coal carsje^luhbi^tsjarrivial. at the smelter is sampled by an automatic sampler and^crosh^l^Kfineaess'Tsuch'-that '' . ' the largest piece is only S/16 in. in diamater.t The crushad ibritXsJ-iconveyed"by?an elevator to the top of the crusher where, by aemk-nf gauge tracks, it is put in bins of about 60 tons capacity,^ times' the''chemical , analysis of the ores in the different bias -is. knows. iSthssm^mH^y'^Atherr a * carbonate, slicate or sulfide. The first two mentioned ores,are'-now readyfor'use, J A0 2 Si*- bug the sulfide ores must be roasted to eliminate their original sulphur content !' and in so doing, the ore is rendered fit for furance operations, since by this treatment it has become oxidzed and made more reducible, it .! ' . ' Various types of roasters may be used, (Where the Tsulfur-frou the ora is utilised in the manufacture of sulfuric acid, the ;Hegeler/or.^aaencle7er muffle furnaces are used). Splendid success has been mevwith!liy^|t^iuse.tof: a Cappeau Kiln which is amodified form of the Ropp Stralght-Idne lSa^ceV T^ is a rever- beratory kiln about ISO fast long and 14 fset wide, equipped with two stirring ploughs or rabbles and fired with- foir stokers which ccrisumj&is-.'tons' of coal per day. It is capable of roasting S8 tons of leaded sinc ore !every twanty-four hours. Only enough sulfur is left in the ore to combine with the-lead.in the formation of lead sulphate. The roasted ores are graded and placed in different bins ac cording to their sulfur and metallic contents- The sine in the ora ls now in the form of zinc oxide and the Lead aa load sulphate. The ore is now ready for. the - pigment furnaces. .y'y:.. At the Coffeyville Oxide Works of The Ossrlc, Smelting and Mining Company there ere three bloeka of furnaeee. A block conaists of 16 furnaoes built of . fire brick with a combustion chamber in the canter, making 8 furnaces on each side of the combustion cliamber, a long, arched roof covering the entire block.; - ' , .* .... - The roasted ore is mixed with coal (the particles belng'shout'''one-quarter In.: diam) in the proportion of about one ton of ore to one toniofyc5el'i!end, e''lightly greater quantity of silicious material for anti-flux (the|pai^olMibeing|approxl-. - mately one-half in. diam) also a quantity of water is eided^^|^sswholsftioroughly. mixed. Two eutomatic mixers are .sufficient for the threetblocks'.^lfbi^mixture is. put in bins by the furnaces and charged into tha ^umaess^^^^^^^! The grates are first covered with a thin layer of aemi'-^mthrac'its*-ooal which immediately ignites from the furnace heat of tha pfevlohh^f^iirga^In'a^few'ainutaa about 3600 pounds of tha mixture of coal, ore and ;fluxing?matarial <aracharged into the fumece, one-half on each side of thefurneoe.". A oartalnamount of'blast is turned on at the start and increased as it is found necessary.. About-four.hours are required to burn out the charge which is occasionally raked. 4 The coal serves a double purpose, that of furnishing'the necessary, heat end ' - also as the principal reducing agent. As the charge burns,scarbonmonoxide (evolved from the coal) reduces the zinc and lead in the ore to a ,metellio-;'state from which condition they almost instantly vaporize. The zinc vapor'is lmmedlately oxidized by the carbon dioxide and air present in the furnaoes to sinc oxide acd the lead : * vapor to lead oxide which, in turn combines with sufficient sulfur-trioxide to form lead sulphate. Thus we see how the sine and lead in the form of pure;compounds are separated from the result of the charge which constitutes tho alag or cinder.'. The fume, consisting of solid particles of zinc oxide and leadsulphateao fine ly divided and intimately mixed that they practically form" a compound together with the gases from the combustion of the coal and other impurities, ia drawnfoff-ofthe furnaces by large suction fans. It, of course, first passes through .the-'combustion chamber where particles of carbon and other impurities erevbarned'out>!and then it is carried on through a sheet iron pipe line which is about 6'feet ila idiaa.'and about T 4 age/ 5 ?00 feet long and which aerrea to cool the fume and also to^colleot-any impure or disolored pigment Battling out along the way. The pipeVline is equipped';./ with cleanout doora at regular interrala and the impure pigment taken:from it is returned to the mixers where it is mixed with the.chaxge/and!reburaed. 'The sing or residue'remaining upon the grate after thai.;metal.has been volet- , ilized and drawn off, la taken from the furnaces to a crusher|jrtiere lt ie;roduced' ; in aize and loaded into cars for use by the railroads as ballast. ~ - u- ;'X. . By the time the fume reaches the end of the pipe-line leading to theJ?tag room," it has cooled considerably and it is discharged by the fen into-a hopper V line in thie room. The beg room is in m very large, well Yentilated trick building, it dimeneions being about 100 feet, by ISO feet, by 86 feet. ' The hopper-line ex tends entirely around the room end then branches out into a large number of rows. - Muslin bags SO feet in length are suspended from a runway about and fit ower the openings in the hoppers.. When under pressure, these hags are about 5 in. diam. The pigmen or fume, under pressure from the discharge fan, passes through: the system of hopper lines up into these bags which stop the solid particles but'' - allow the gaaes from the eombustion to escape through the poresof the bags. The bags are frequently shaken and the pigment removed from, the hoppers daily. By.- means of trucks it is conveyed to the pecker where it is usually packed ln barrala - of 350 pounds each, or. in paper bags which hold 75 pounds. Tha daily_output-of. this plant is 36 tons. X ' / -/-/"I .... \53if/,;i: : for the past seven years, however^ most of the pigment produced here baa been subjected to an additional refining process. The idea being to eliminate any're- . maining impurities. - The barrels and bags containing the pigoent-arenow weighed / and properly stenciled ready for shipment to the trade<or stored ln a large ware-/ house. /-S'// The production of zinc oxide is the United States increased from 10,000 tons: in 1680 to 72,000 tons in 1907 and since that time there has doubtless been an ..: enormous increase. According to C. 0. Holley, 61 analysis of ths leading brands of mixed paints sold in this country showed an average ratio of-lead pigments to : zinc oxide of 46.55. Considering the comparatively short period of years during;, which zinc oxide hae been manufactured in this country,lies well as its steady in crease in consumption, it is very apparent that paint manufacturers recognize its'; value as a pigment. Zinc oxide forms a considerable percent of the/.composition of high grade rubber goods, giving them resiliency and durability. . Also it is used in the production of linoleum, and for many other purposes.4 As a pigment, . it he not : the covering power of.white lead but has the double advantage of being; non-poisonous and of not becoming discolored by hydrogen sulfide. Zinc oxide mixed with-chloride form oxychlorides which are used by-dentists for filling teeth. '* Most of the paints made today contain in part sine oxide and leadedlsino-pigments; -A - pigment containing about 65 percent zinc oxide and 55 .percent Ibad/'eulphata/la''an:,/'.ideal one for paints providing touchness, luster and constancy of.coiorinqualities which are essential in this age of conservation. The leaded Binb;::^gmen^lseems/to:; embody only the finest qualities of. other individual of paint it is necessary for`sine oxide to be maohanioelly idxedwi^/the.iprbperproportions of lead eulphate or carbonate of lead (whita lead) whila the^lewied ^aino pigoent, as mads here, is all ready for use, and ona could not hopa to-obiainamore intimate mixture of the particles of xino oxide end lad eulphata..