[1]3 1 1 9 , 8 1 7 2 0 Uiiited States Patent Office -Pa@ierited Aug. 3, 1965 3,198,720 METHOD OF DEIININING TEQ-PLATE Gustav Knippers, Au.k dem Snamberg 18, Mulheim an der Ruhr Saarn, Germany, and Johann Christian Gri3ber, P,,iLIheim an der Ruhr, Germany; said GrUber 5 assignor to said Knippers Filezl May 23, 1960, Ser. No. 31,081 Clpims pr-@arity, application Germany, May 23, 1959, K 37,820 9 Clainis. (Cl. 204- 121) 10 The invention reiates to a method for the recovery of the tin contained in tin plate and more particularly to a method for the recovery of the tin containe in scrap tin-plate of any kipd s@,ich as i-7sed cans and the L-ke ivhich may be taken from the refused dust. 15 An obj;Cct of this invention is to prov-'@d-@ an improv.--i ,niethod of an device for recoverin- the tin - contained in scrap tin-plate of any kind, A further object of this invention is to provide an irnproved method for recovering the tin contailled in 9-0 scrap tin-plate of any kind i-@icluding such as used cans providod vi;th a protective coatin.- layer or covered with adhesive material for labels and the like, Another object of this iii-,7.-ntion relates to a method 25 for the recovery of the tin contained in scrap - tin-plate which enables the scrap to be treated direct'.y in the state of pressed blocks, such as blocks having bee@i pressed in order to facilitate pr@-ceding transportation of the scrap. Yet another object of this invention relates to the ' provision of a new and i--inprov-.d rnethod of recoverinthe tin cortained in scrap tin-plate of any ki@nd in a simple and econon-iical manner. In accordance -,vith the main featlres of this inve-Ti- 35 tion there is provided -an improved method of recovering the tin contained in scrap tin-plalp of any kind wherein the scrap tin-plate is treated in an electrolyte wh-"ch co-iitains an aliphat;c alcohol with at most thlree carbon atoms, and the tin deposited on the cathode is 40 n-i--Ited under reducing conditions, and casted if wanted. Another feature resides in the provision of an improved rnethod of recovering the tin contained i-.i scrap tinplate of any kind Nvherein the scrap t-lil-pi-ate is treated in an electrolyte which contains an aliipha@ic alcohol 45 with at mos+l three carbon atow-s, water, and an alkali carbonate, and the tin deposited or. the cathode is melted, under reducin.- conditions, and casted if wanted. Other objects, features and advanta-es of this -@nveiition will mor.- fully appear from the - following detailed r@o descripl-lon taken in connection with the accon-ipanyin.- drawings. Methods are known for the detinning by e'iectrolysis in alkaline solutions, especially in 60' to 70' C. warm 9% caust-le soda solutio-ii with a cell output of 1.5 volts 55 and 1500 amperes. These known electrolytic treatments have been replaced in practice by the chlorine - d,-tinv@g process according to Goldschmidt since they have various d;sad-,,anta,@es. They operate with a rela"ively hi-,h current consumption and also cafoonate formation occurs 60 since the alkali hydro,,@ide present in aqueous solution reacts with the carbon dioxide of the s,.irroundin- a' . ir. The presence of carbonates in the known methods has also provide very disadvantageous so that the baths lose Lheir effect a-'Lter a relatively short time. Moreover, 65 the tin scum which forms on th-. cathode melts with considerable difficulty. It has now been found tnat these disadvantages can be avoided if the scrap tin-plate is treated in an electrolyte which contains organic liquids miscible with water, 70 preferably lo,@,er alcohols with at irost three carbon atoms. 2 It has been found particularly suitable to use methanol as the alcohol and to add this is an amount of 5 to 20% by volume. In order to increase the conductivity of the bath liquid, alkali in an an-iount of about 35 to 45 grams per litre of bath fluid calculated as Na2O is perferably added thereto. Surprisingly it has been folnd that the alkali must be never be added in the for-m of alkali hydroxide as in the previous method; however, it is possible and generally satisfactory to use the cheaper carbonates, e.g., soda or potash. A satisfactory ce'J temperattre would be obtained at about 80' C. and the output oil' th-, c--lls should advantageously have a current strength of at least 2500 amperes and a cell potential of about 2.8 to 3.0 volts. The tin deposited as a spo@-igy mass on the calhode is subsequently melted under reducing conditions and cast in a oxy@en-free atmosphere. In contrast to all previously known detinning methods, the scrap tin-plate can be directly treated as blocks in th@- pressed state. It is no lorg@-r necessary, as was always the case before, to baie ruptured the scrap Nvliieh, in order to facilitate preceding transportation will always be pressed into blocks, which conventional rlpture operation means a. troubl,-;somc separate and additional workin.- step. Moreover it is suitable to subject pressed scrap tin-plate bollor-, electrolysis to a vacuum pretreatment in such a way that it is ;nlroduced into a vacuum container filled with a I-iquid approximately correspondin.- to the electrolyte fliid, preferably subjected to a "O vacLLlm of about 60 mm. Ng and R-.qally the vaucuum discontinued. The air conlained in the small hollow spaces i-iiside the blocks is thus r@- moved therefrom and the spaces are filled with ,he electrolyte flllid. In this way, th@, tin layers on the squashed inner waus are reliably dissolved durin- the suosequent eieclrolysis. The tin deposited on the cathode is melted at a temperature betweeii 1100' and 1150' C., advantageously in a contir-luously operating rotary drum melting oven and in order to avoid oxidation with atmospheric oxygen, it is preferably protect--d from attack of the oxy-en by running off the tin flow from the melting oven with a neutral gas, e.g., by blowing through nitrogen. Accordiri,- to the -niethod @of the invention, in particular The iron residues hav-- a residl'al tin content which used cans vvhich are collected on a reruse tip ar-. detinned amounts to only half that which -,@ias possible with the most careful detinning accordln,- to the chlorine gas method. In the chlorine @as or chlorine detinnin.a method, the dry chl@orine gas acts on the dry scrlp tin-plate in large tightly closed reaction chambers. The tin is -thus converted into fluid tin tetrachloride SnCl4. The iron of the tin-plate remains unaffected if the reaction temperature is -held below abolit 3' C. The value m.-ntioned obtained by the invention holds for all kinds of strongly hydraulically con-ipress@-d can blocks, w@bereas in the known chlorine aas method, it was only possible to detain loose scrap tinplate or cans. Apart from- the fact that the k-@iown chlorine detinnin.a method has an essentially hi,@her techni-.al consumptior. than the r@lethod applied for, it on'@Y -partially detins scrap tin-plate coated with a protective lay--r, since the chlorine can only partly attack the tin layer lyin.- under th@- protective coatir.,g' Moreover' thpSnCI4 formed under the action of the chlorine, since it is obtairied as a water-free liquid, cannot be entirely removed from the inner hohow spaces of the used cans, e.g., from milk cans or fruit juice cans which duriig their consumption are provided generally with only one or two small holes in the cover. There is thus a loss of tin which would otherwise in later foundry tise of the detinned scrap plate operate quite iinsatisfactorily for example as steel scrap in Siemens-Martin furnaces. -ibis proportion of tin
[2]in the steel scrap can cause the properties or the dee,p dr,-,win.@ properti-,s of plate produced fron-i the ti@acontair.ing steel to rise to unacceptable limits. A furth,-r d;sadvanta.-C is that chlorin-. aas residues a@id d;ssociated tin chlo@-ide act to d,siiitegrate the detinned PIPte blocksbyacidforrr@ati@--ti. T@@--blocksci,.r@-.iottheri@for.-be stored and they disiite.@rate aftdr L sho,-t t;me siich as by scalin.@ so that they r-.-@ust be iised up very rapidly. Comparative investigptions on 'che dctin@.iiiig efficiency according to the eblorine detin-iin.- metbod and the riiethod of ti%c inve@ition have bee.@i carried c@at by r.- icais of borin- tests in the 13ressed b'iocks. From the cuttir.,.@s th.- TeSidual tin content from the tests on the pressed pieces of the blocks of d,-t'iiir@ed scrap plate accordin.- to t,he methcd of the ir@veiition arroi-,rits to 0.24%, wliereas the scrap sh-.et de'cinned qs loose scrad -ccordip.- to the chlorin-- d,--tinr,.ing process aid subs--q@iently pr,@ssed into iblocks had a residlial tiii content of O.z@7 to 0.4@@%. By substitutio-i of oil@y li- tly pressed blocks, nanae"y, ,hose which have b--en manufaelured in the press at about 150 atms., in the xrethod of the in@7ent,'.oi,, the -,@s,d-Lial tir. cop.ter.t even sank to 0.18%. FLi-Lherniore, the test pieces trcated acccrrdirig to the chlorii,,@- dttin,-iin- method coilsisted of unpressed- scra,) from can manLifact,-lr--, wher-,,-s the method of the invention was c,-.rr@l@-d o-ct with used cans pressed before d,-tivning, in vvhich the iesiiual tin, even that pr--s.@r@t -@'n 'Lhe soldt,-, would be fixed ii-.ore easily, so that the belter result shoulld be eypec'Led w;th the unpressed scrap. iii tests ip which co-,-InDi,- 'Lely simila,- ma,tp-ria'is @ii,--re use'@, qtiq,- a mr-ire --'varta.-@-ous ration of the detinnin.- efficieiicies of the kriowil method and th@. n-icthod according to 'he invept:on was obtained. The m--thc)d accordill@-, 'Lo tll-- ;.Ive-nLion is P.-Iso tccbnically stiperior to the known electrolytic methods which are less tecbnically advarta.-cous than th-. k-@lowi chlorin-. deiiiining process. In particular, the scrap tii7@-plate covered with protective co,-ttin.-S h,-s rio@, previolisy b,-en d-etinned since the coatings prevented the attack of t@ic el.- ctrolyte. In th,- new m43thod accord'lnl- to 'the inve-@itio,-i, onei-ating ,on an electro'iytic bas-z with the niod'Ified bath liquid as well as with the curreit supply ratio in th.- bath, et,.-'ects are obtained slic,.@ tiat the detinnin- can be carried ol7,t substantially.rr@ore completcly 'Lhan pi7eviodsly. The bath liquid based up, -.-i an aqtieo-,is alr-ohol sollitioi preferably of lower P.Ico,,@ols is respoiisible for increasing the conductivity with alkali hydroxides or alkali carbo-,iates. Methyll --thyl ard Drcnyl -,Icohol aro preferably ,used as lorer alcohols, partic-alarlv methyl alcohol usel in crude technical forrn. - he additior@ amounts, accordin,- to the particular kird of maler;ai to be detin-@i,@d, to approximately 5 to 20%, alkali carbonates are Liscd in the amounts of 5% potash and 10% soda. In their pla,ce, the hydroxides ea-ii also b@@ us--d. Tho Plethanol used has the pro_perty of makip.- Igcqder layers, A@,hich cover the inside of the cans or the scran sheet, movable for removal of the tin. Adhesive mater-ials for lebellir@g the cans are also dissolved so that the da-irrin@ can be reliably catried oi,-t at th-.se places also. The fact that alka@'i carbonates can be used contrasts particul.arly with the stltements which have been made previously in tin chem;stry liter-,itiire. The electro'@ysis of tin coatin-s of iron plate is, acerrdi@-ig to prior literature, so carried out that alkali hydroxides dissolv-- the tin in the form of stapnat.-s and the tii-i is ele,-trolyti-@ally d@-posited from thesc, so that it waS Dreviously considered that carbonates which are of advanta.-e since they are technically cheaper and chomically more stable would disturb the electrolysis of the tin. 1.1 fact, it has iiow surprisin.aly been found that with the use of carbonates, th-. detinnin- according to th.- method of the invention can b-, carried out satisfactorily. The technical conditions are not sufficiently clear. It has be@-n determined that the detinning capacity of the b--th decreases strorigly if the addition of methyl alcohol is too small. Ther,- is a tendency to consider the i)rocess as on-. i@i whieb the carbonates to.@ether with a small hydrolytic action are de-composed by ciirrent, a-Tid Cnat the number of 01-1-ior,6 is i-iicr--ased, 'i.e., that a convers@on of the carboiates into hydroxides is ei-ecled. Analysis of the bith flu;d which is determined for its C02 con,ent cannot confirm this assumiation. T'r-,e clectroiytic det;nnin,@ method previously faile-d in that the alkali hydroxide used lost its effect by taking up C02 '@'rom thp- air. Consequeritly iii the riiethod of the inv-.nt;on, th-, bath liquid las opz@rated @,,,ithout renewal for much Ion.- er than half a y,-ar in day and n;ght operation and shows substantially no alteration in this r---spect in its,datinn:@n.- cat)acity. A ' UrCiier dif,'.cre-,ice co.-@sists in the appearance of thp, deti-@ined pla',e. In the absence of met'@-,anol, the scrap iron Dlate has a blue-gr.-y appeararice as if the iron plate 5 has annealed. it thtis adpears that this plat-. has bee-@l oxidized by the ox3igen occurrin- at the anode. In 'Lhe prt-senc,- of methaiiol in the bath, a sp.-cular steel -loss is -iven to th,- plates so that tliis could be falsely assumed to be stainless steel. Traces of an oxidation of the iron Dlate covering were not observed. The bath liqti-'@d is preferably held constant at about 80' C. In order to maintain as small as possible the d-.iuling and/or vat)orizing losses of the m,-thanol, the bal,hs are advantage'olisly prov,.cled with co@-idensers which are ccoled with water so that the cordensed liquid is retvrned to the bath. The inventive process will now be described by a spec@ific example, it being Liiiderstood, however, that this exanple is g@'.ven by way of illustration and not by way ]- limitation, apd that many chan.-es may be effected without in any way affecti@-i.- t.ie scope and spirit of this i-tiver@tion as recited i.-i the a-o ended ciair@is. p Evainp7e The raw ma@erial for the detiih-iin.- process to be de@-cribed consiste'd of tin plate scrap collected from refuse dumps. '.his scrap was n-iad-. up from uncleaned cans of the usual kind, i.e., the cans were varnish or lacquer coal I ed and had still attached thereto labels, printing legends and the lil- The cans were compacted into parcels or blocks and the thus compacted parcels were inserted iito an anode basket. The ai@ode basket with the scrap parcels therei-@l was thereafter suspended in an electrolytic bath which in tum was contained in a vacuum vess--I. 45 The electrolyte ir@ the bath consisted of an aqueous solution of 5%, '@,0% sodiun-i cartonate apd 15% by volume of methanol, the rer@iainder bein.- water; The temperature of the electrolyt.- was about 70' C. The vacuiim container was then subjected to subatmospheric pressure 50 conditions of about 60 mm. Hg for such time as will result in aii evacuation of the air contained in the spaces or i,@iterslices of the scrap parceis.. so that upon reestablishing iormal pressure conditions in th.- vacuum container, these interstices were filled with electrolyte. Thereafter, 55 the anod-. basket kvith th- scran parc-,Is was placed into an electrolysis container and connec@lions to a direct current solirc,- were established, the anode basket constitutin-. t@ic anod-, while the cleclrolysis container, of course, was provided with a cathode. The electrolyte in the electrol0,0 ysis container was of the same composition as hereinbefore defined. The temperalur-- of the bath was about 70' C. Th,- electrolysis was carried out with a mininium current stren.-th of 2,100 ar-,peres and a cell potential of qoout 3 volts. After completed electrolysis, th.- anode 65 basket w-ith the scrap parcels was again subjected to a vacuum of about 60 mm. Hg for about 10 minutes. This resulted in re@noval of el,-ctrolyte from the interstices of the scrap parcels. TI@e anode basket was thercafter emptied and thC Temainin,@ scrao was subjected to analysis 70 which indicated a tin residue of 0.24%. The tin was removed from the cathode and showed a piirity of 99.2%. It will, of course, be realized that the purity of the recovered ti,-i is dependent on the raw material, that is the coitaminations and other extraneous matter adherin,@ to 75 the car@s, but generally varies between 96% and 99.5%.
[3]3,198,720 Th-- electrolys-s coitainer proper riiay be constructed as a vacuum conta;ner so that &@e pretreatment, i.e. the vacuum treatment prior to electrolysis referred to, may be carried out in the sarne clecirolysis bath. A detiini@-l@ apparatus for carryiii- out the metl,.od accordin@ to the invention can advanta.-Cotisly co-nsist of .@everal pref,-rably two, detimii-@i- baths which for exam'@e a lower curved ce c'iiarnber and an iron ple ha flrna baih container preferably arra-@iged thefcover. Each bath co--,itai@ier conta-@ns a cathode constructed as a drt:m oper@ 10 above ar@d below and an anode -inserted in the cathode drum and consructed as a basket. To re.-Ulate the contact it is particularly advantageous to hold the cathode drum viith three suppo-ting arms displaced at 120' to i@ihich th.- contacts are soldered and which ar-. supported 1,3 on a fla-ii-C welded to the upper edge of the bath con+a; , .;,er with an i-,iternedia+e 'iayer of, for example, hard ppper as an insulatiop,. The basl@@et anode is then provided w-ith 3 rec' angu.ar shaped eyelets likewise space at 120' and a copp-.r disc is soldered to th.- lower edge of 20 each. Catc!i meni bers can en.-age in the eyelets which serv-, i-@l turi ior the current supply to the anode and also for holdi-tig the anode basket. The catch members for this purpose ar.- preferably con?iected to th-. positive pole ol@' the currcnt source and are movably arranged in the 25 insul.atino shell o@i the Lipper edge oll the bath conlainer. The anode basket is prel'erably provided w@ith d@filect;ng p'-ates so that o,,y,-eii evolved is def'iected away ard an atta-.k c-@i the t;-@i derositing at the cathode is avoided. Preferred ,ipparat,@s for car.-ying out the method ac- 0 cording to the inv.-nt-on is d@-scribed below i@l conjunct,.o.1 with the accompanying drawi-.i.- in which: FIG. I sho-ws a plan view of an apparatus wilh current sui)p' y consist,.ng of '@Wo detinr@ing baths; Fl-'G. 2 shows a vertical section throu.-h a bath con- @5 tainer with a cathode druni and basket anode; FIG. 3 shows perspective views o'L two forms of ba-..ket ,n-Tiodo, namely, (a) witho-,it de-,iector plates, (b) wi' h deflector plates in s.-etion. As will be se.-n in FIG. 1, tivo bath coiainers are J-0 provided in the embodirnent @vhic' i are arranged ad-jacent one arother and electrically connect,-d in seri,-s. TI@e bath cor@tainers themselves are constructed siir,.Iarly. Their copstruct,@'on will be first explained ,,iith reference to FIG. 2. Each bath contain-,r consists of a cylindric.il @@ 5 container 17 oi' steel with an inwardly errved base 11- on vib@ch outwardi'y prc@,ecti-,ig heat transfer ribs 6 are welded. Thp- sr)E,,ce 9 between the lower edge of the container 1-7 and the base 11 servps as a furnace space. On the upper edge of the contain,-r 17, a flange I is welded, 50 on which th-- anode 3 and also the cathode 4 are suppor@led. The cathode 4 is construct,-d in the form of an ui) i,vardly and dc)w@iwardly open drum of stee'l plate. At its u-pper erd, it includes three stipport arms 5 Nvhich are displaced by 120'. They preferably consist o' , ri-jd 5,5 iro@i bars and are supported on the contairer flan.-c I by way o,' an interr@iediate layer 7 of hard pa-,)er actiri-. as a.1 insulation. On each support arm 5, a copper bolt 12 is soldered by @neans of silver solder which serves as a currerit con,-Iuctor. 60 The apode 3 is siispended cor@centrically in the inside of th,- drtim-shaded cathode 4. For tlais purpose, each a,lode inclu,-Ies @nree eyelets 8 displaced by 120' which ai7e constructed rectan.-ularly a-nd carry a co-pper bar 10 on their lower ed.-c which is sol,-iered to the whole flange. 65 These eyelets 8 serve for susper@ding the apode basl,,et in the bath aiad also as current conductors for the anod.-. For t-his purpose on the flange 1, three insulati@ig bushings 13 consistin.- of hard paper are secured, in which longitudinally movabl-- support menibers 2 are mounted which 70 are cor@nected with th@ c-Lirrent source. The three insulating b-,jsbin.-s 13 displaced with rcspect to one another by 120' are displac.-d by 60' with respect to the three insulatin.- sbells 7 for the cathode support arms 5. To improv-. the cur-ent @@Piow from the catch members 2 to 7,5 6 the anode basket 3, th-@ copper contacts -,an be amalgamed with mercury. The amalgam layer smooths out any small uneven,-ss in the surface of the copper plate so that a high surface contact is ensured and impurities cail be avoided by simply covering with a coeLi,19. FIG. 3 shows perspectively two possible co.-istructions for the anode. According to FIG. 3a, the anode basket is welded from rings 18 and tars 19 o' bar or roiind iron. The base o-I tl-@e basket is made in tiie form of a <,Yrid from iron rods 20. In order to t)revent passage of oxygen form@.ng on the anode preferably at its inside to the tin layer depositiii.@ on the cathode it is preferab@le to provide th-. cover siirface of the anode baslet, as indicated i@i FIG. 3b, with, i-Unnel-shLped rin.as 1-6 which preferably son-ew!iat overltp. The electrode res;stance oL the baskecs is thus heid si-ifficiently small in com-,)a@-ison with the definrii.- material. FIG. I shows d-@'agram-.natically the electric circlit for tv@,o adjacently arrang--d batli containers o' the Iciid described. The direct current genera+lor 15 driven by a motbr 14 is connected at its positive pole to the three catcn members 2 o@-1 the basket anod-- 3 of th-. first bat.q con'taine@.-. The tl-ro@e support arms 5 of the cathode drum 4 of the f@rst bath co-ritainer are connected by co@.1ductors to ',he three catch rrorqbers 2 of the basket arode of the second bath container, whereas e support a - rms 5 of the second bath container are cbnnected to t-he negative pole of th.- gen-.rator IS. In the embodirnent, th-, container of 'Lhe bath containp-r 17 has a diameter of 1800 millimetres with a b@)fn depth of 2000 rrillilictres. Th-c cathode druril 4 has a diameter of 1700 millitnetres and the basket anode 3 a diameter of 1350 millimetres. Both bath co-litainers can preferably be heated by a commen oil furnace fire. They are inserted for h,,llf their bath depth ben,-at--h the base sL,.rfa-.e a-@id are covered on the outs-id.- with thick fire,lay walls. Bothconta,nerscaiibeheldatthesameteinperature preferably about 80, C. with only s'@i,-hf fl@,ictuqtions. This apparati-is with the dimensions giv@-n operates Nv@ilth a bath content of 3000 litres per container. The rotat:in gen-,rator 15 has a storaae pote-Titial of 6 volts with a current stren.@th of about 2500 amperes. The higher current strergth is advantageol@s. Th-- output of this plant, with a deposited amount of tin bf about 130 kilograms per 24 hours of operatio-@i, correspaiids to approxima,ely th, amolnts theo,:etically available on the basis of @@he Faraday laws if the valenc-- of the tin is asslimed to be 4. The titi is deposited as tin powder which is removed frorn the cathode viith spec,"al scrapers and withdrawn froii the, bath. This tin -pon,-e is then melted in a rotary oven wth ammolaium chloride and borax additions, Nvhich facilitaie the reduction. 11, can be treated with a reducingilame wit!-.out carbon additioa or w@ 'tli a nelitral Ran-e with !he addition of carbon in !he form of I anthracite or small coal. As a coiering for tb-- oven, a ileutral waterial (AI203.SiO2) is chosen. This rqaterial has theadvanta.@e that with contintious da;ly lisc of the oven a duration of about 4 y,- ars is obtained. Fro@m the co.,itinuously operating oven, the liqu;d tin is run off wh-,reby it is protected as far as possible with a iaeutral gas against attack from atmosp@ieric oxygen. The t@,@n is cast from the. casting label i@i block shapes of gr-@y cast iron or chill moulded iro.1 into blocks of about 2000 kilo.@rams weignt. The tin so recovered has a pur'ity of 99.2 to 99.4%. The dimensions and values given in the examt)'Ies serve merely for illustration and should not be taken as lin-iiti@ig the scope of the inv.-ntion. W-'lat we
