Zinc is produced from ores by two general methods, distillation and electrolysis.
The general principles involved in the electrolytic zinc process of today were known as far back as 1880. Difficulties encountered in purifying the solution for electrolysis and lack of suitable mechanical apparatus were the main reasons that such a long time elapsed before the process was used to produce zinc in commercial quantities

Bovee, Authur Jewett, Jr.

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Montana Tech LibraryDigital Commons @ Montana TechBachelors Theses and Reports, 1928 - 1970 Student Scholarship5-15-1934Ammoniacal Sulphate Leach of Ananconda ZincCalcine Recovery of the Zinc by Electrolysis.Authur Jewett Bovee Jr.Follow this and additional works at: http://digitalcommons.mtech.edu/bach_thesesPart of the Environmental Engineering Commons, Geology Commons, Geophysics andSeismology Commons, Metallurgy Commons, Other Engineering Commons, and the OtherMaterials Science and Engineering CommonsThis Bachelors Thesis is brought to you for free and open access by the Student Scholarship at Digital Commons @ Montana Tech. It has been acceptedfor inclusion in Bachelors Theses and Reports, 1928 - 1970 by an authorized administrator of Digital Commons @ Montana Tech. For moreinformation, please contact astclair@mtech.edu.Recommended CitationBovee, Authur Jewett Jr., "Ammoniacal Sulphate Leach of Ananconda Zinc Calcine Recovery of the Zinc by Electrolysis." (1934).Bachelors Theses and Reports, 1928 - 1970. Paper 35.Ammoniacul Sulphate Leach of Anaconda Zinc CalcineandRecovery of the Zinc by ~lectro~ysisByArthur Jewett Bovee Jr.of Butte, HontanaA ThesisSubmitted to the Department of lIeta11urgyin Partial Fulfillment of theJequirements for the Degree ofBachelor of Science in l.Ietal1urgicalEngineeringliiontanaSchool of MinesButte, UontannHay 15, 1934Aomoniaca! Sulphate .Leach of Anaconda Zinc Calcineane.Recovery of the Zinc by ElectrolysisByArthur Jewett Bovf)t)Jr.of Butte, llonta:LaCOpy 2MONTANA SCHOO~ OF r.:n ES LIBRARYBUTTEA ThooiaSt!belitted to the Dopar-traentof I:Ietallul'g7in Partial Flllfl11PlG'lt of theRequire~ents fq~ tbe Daf-r~e ofBachelor of Science in ,etallurgi~al &ngineeringuontcac. School of HinesButte, Montanatiny 15, 193.~·.42843o F=TAB L ECOS TEN T S---000-":"'-Introdaction • • • •Ammoniaca.l Leach1.ng.Leaching • . . . . .Purifica.tion • • • •Electrolysis • . .StunCla.ry• • • • • • •Acknowledgment • • •• • • • • •• •• •• •• • • •· . . .• •. . .· . . . . ... ..• •Pa.ge,1259111315• •Ammoniacal tiu.lphate.Leach of Anaconda ~inc Calcineandi{ecovery of the ~inc by .ElectrolysisZinc is produced from ores by two general methods,diBtillation and electrolysis.That produ.ced by distillation, which amou ts to abo utseventy-five percent of t he world's productn on , is cnrriedon by treating zinc ores to yield zinc oxide, by roastingits sulphides, calcining its carbonates, or reducing thezinc of its silioates at a temperature above the boilingpoint allowing the zinc to r-ecombi ne with oxygen. ~hiszinc oxide is then treated with exceae carbon in a retort,the volatilized metal being condensed by suitable means.l:Slectrolytlczinc is produced altogether from sulphideores which are roasted to the o.xide form, the zinc oxidebej.ng dissolved in spent electrolyte containing freesulphuric aeLd, the solution treated to re ove all harmfuLimpurities and the zinc recovered by electrolysis.the general principles involved in the electrolyticzinc process of today were known as far back as 1880.uifficulties encountered in purifying the soilltlon forelect!'olysis und lack of suitable mechanical apparatuswere the main reasons that such a long time elapsed beforethe process was used to produce zinc in commercialquantities.In 1913 the vonsolidated Mining and ~melting uompanyat Trail, Jjritish coLumbf,a began investigation of thisprocess as a possible means of treating cooplex ores;end in 1014 the ':'1.ncc'clldacopper Hi~lng CO[.YjJuQYat l..neconca , ·lOnto.nc ulso bGgc.a work on the process.Both invootigations led to tho eroction of test plantswhich ftl.rtherpxoven th&.t this o t hod could be used toproduce electrolytic zinc froQ cocplox orec. Carefuland thor-ough r-esourch has int~'odn(HH~1r.lprovements whichpernit tho production of very PG.I'Szinc.These methods are, not entirely satisfaotory. Thechie-f objections to the distillation cethod ere thatit is not a continuous operation Dnd no high grade !1inccnn be p?oduced without refining- However, the NewJersey Zinc cOClpuny io producing zinc in a continuousretort, but ~othinG io ,ublished on the 1rocess. ~hereis also the noitzheir.l-Re~y continuous retort process.In the olcc<:;rol;/ticproeece t he aoid disGolves manyiop~rities necocnitnting elaborate purification. Allores of zinc cannot be treated stlccesc>full;,r by this rae thod ,Ziac ferrite, ZnO.Fe203' o_ten foros during =onsting. Thiscorapoand ie inc;olt-:blo in warn dilute sulphuric acid andcO!:Jplioatedt::-eatl:lentis necessa:-y to recover thezinc in the ~errite. S11ticcOUS coterial, "being slightlyaoLub'Le in acids, yiOl.dc a geL ~hich if! ;;ery t zoubLoeomein randling Golutlcl1D eopoclal.LY in ~iltcring.A~ooniaonl ~eachii~Several plants ~ere, at ono tiue, in existence manu--2-facturing ~llOby an ammoniacal carbonate leach process.~he solution, after being purified, was evaporatedleaving a residue of basic zinc ear-bona.te which wascalcined to produce ~nO. 5:hls product was tlnsuitable forthe rubber or pigment indu.stries becallse it was crystalline;so thE plants did not continu.e in operation.Although no commercially sllccessfu.lprocess for leach-ing zinc calcines with ammoniacal soll1tions to producemetallic zinc has been worked out, the problem has beenstudied and several patents have been issued. A largeproportion of the investIgators used ammonium carbonateleach solutions and most of them used pure' ZnQ. l.Ieach-ing of a commercial calCine with ammonium carbonatel}solution has been investigated recently • rlecoveryof the zinc was accomplished by electrolysis in mostcases.Ammoniacal leaching should largely do away withthe troubles encountered in acid leaching: iron doesnot dissolve and therefore does not require precipitation,no silicic acid gels are formed, aud solutions can bepu.rified more eaSily.Theory: When ammonia. is added to a solution contain-ing ions of zinc, enough hydroxyl 10ns are usu.ally present1) J.G.Grunenfeld r-, "Ar:unoniaClllcarbona.te leach ofAnaconda zinc calcine nnd recovery of the zincby electrolysioTl t Montana School of 11.1ne8.to cause the precipitation of the metal hydroxide. As moreammonia is added, IlH3 molecules form faster than thehydroX'Jl ions and a complex ion of the metal and ammoniais formed. Zinc i6 one of the metals vihlch is cap bleof forming a ccmpLex ion in this way. lJ.'he reaction isillustrated below:Zn( OR) o ~ Zn( OR) 2 ~ Zn H1- 20H~ dissolved.,.. -4NH4 + 40H ~ 4NH40H -- 4NH~ t- 2H201~ +-1-Zn(NH, }4According to the law of mass aotion as more ar.monia isadded the reaction goes more near1y to coopletion tarwardthe £ormation of the complex ion. The format.ion of thision is able to make a metallic salt more solu.ble. Asammonia is added the 'Positive coc.plex ion forms and cOClbineswith the negative ion of the solution.ZnS04 ~ ZnS04 ~ Znt-1-1- 3°4--dissolvedT _ffi4t-OH --=:;-. 4NHq,OH ~ 4NH3 1- 2H~01~ ff __ZnC 1H3) 4 +- 304 ~ Zn(NH3) 48°4This idea cay be applied usefully to leaching. Thezinc in a calcine nill f'orrn a complex ion with the aomonia.of a Leach oLutLon, The pos i t tve comp Lex io will combinewith the negative ion in th leach solution, and the zincwill be extracted us soluble amraonfumzinc sulphate.ssuoing that ~n(.Jrrj)4S04 is the wo'pollnd formed,the reaction taking pLaoe when a calci e is leached ~ithammoniun sulphate solution is:-4-LeachingPreparation: 1:1order to find how an &lInonia saltsolution would louc~ a ccomercial ore in preference toa synthetic ore of ZnO, SCr-l8 zinc calcine fron theroasters of the Anaconda Copper Mining vompany wasobtained. The analysis Lc shown below:SulphurInsolublo60.0%1.53.00.90.45.73.3ZincCacoiucLeudCopperMangcneseIron2.2.A.ssUI!ling that tho zinc ooupound forn€ct tc Zn(HHD)4S04'the rolative auoun ts of zLnc , arsmonf e , and sulphate Claybe calculated. Thus it is soen that ~or overy 65..38 gransof z1nc t be ro are required 68 grana of aramonLa and 96grars of sulphate. According to the eq~ation of the reactiontakinG pIcce in the leaching process. holf of the anmoniacomes from the NH4,0H antl·ha1f ..':'r9ut.10 (UH4)2804. Therefore,one graCJ.of celcine conte-ining 0.6 graDs of zinc reluires:0.628 grams nHD0.314 grums as NH40H0.314 grans aet ~m4) 28040.809 gruus rot!"" -5-This gives a relation of 0.646 graCls of NM40H to1.222 grarae of OlH4)2S04.Exp-eriments: AlI leaching \?as done in clonedbottles Doanted oa c wheel w~1ch RBS tn?~od by aneToct::-i.c notor. The ml:z:ture o~ calcine and loech solutionwas agi~atcd for a.bout an hour after which the colutionwas iL.1lllodlatol.1 filt~red and washce1.. V'aohing witt. watercaused ar.lconia salts to be prlcipitatt (l; so a. c..11ute amaonfurahv;dro::rldesolution wos used to \'Jushthe residues thorou.ghlyill oz-doz to reco'Va all the 2inc which hud been dissolved.Results have been chocked by duplicute dete~inations.\ \lro'ntof the zino occur-a as ZnQ in the colo tne , butsane is presont in the £'erm of ZnS04• A t en-gr-am sompleof the calcin.e nus a~i t a.tcc;fo r an hour wj_ th 1.00 oc ofwater. Tho zinc contont of the filtered solution was'. )found by the pot aee tuu ~'errocyanide method It wasfound that 3.32 percent of the zinc in the calcine wae watersoluble. rr!'liois dt:;:.eto t he ZnSC4 content.Zinc oxt d.e,ic slig:!ltl,:,rsoluble in anmon tuu hoidroxidethe roaction product being n zincate. A ~ifteen~grams~ple of calcine ~as leached ~ith NH40H containing 28percent NH::s., The co Lutt on was filtored end the residuewas washed thorough Ly , Zinc eontoat of the oonbt.ned ao Lu t t ons2) Soott. Standard Hethods of Ohomf caL Anal~"sia, ~the~ition, Vol. 1, 600.-6-was found by the potc.seium ferrocyanide titrution method.Fifteen percont of the e.inc in the calcine was extruo ted ,A Dolation ooctntmng (UH4)2804 and NH40H in theproper proportions was prepared. Total ammonia content. 3)was fou.ndby the Kjolduhl method , free anmont a wasdeter::linedby titr~~t1ng tho solution with a standardacid us::.ng::loth:;lorange no an indicator. The solutioncontninod 16.3 p~rcent NH3 by weight. Calcula~ions showthat theoretically 50ce of this solution will dissolveall the zinc in 1":'.9gz-ans of calcine.~wo more Gol~tionc wore made containing 11.3 percentammonia and 8.7 pE)rcent reepectivcly. A sample of calcinef1US lCG.chedpith each of these solutions, m&intaining theaane amount of total :IH3pc r ul:1.itof eaLoi ne , to d.etorE-linethe effect of concontration on ext~nction. Results aresho~n in Table 1.Table l.The effeot of Concentration of ]~xtractionConcent:-ution ~erceilt Extraction10.3 % . 87.28.788.883.7ll.3According to tha Inw of uase ac t t on , a excess of lHI33) Scott, Standard M~thodc of cheru cs 1 liualysis, 4tho~ition, 70:. ~. 451.MONTANA 5CI-L~~L OF MLU: I~ A YBUTTE-7-is necessary to £'orm the corap.Iex ion Zn(l1H3}4. Resultsof an excess NR3 as (NH4)2S04 in leach solutions ofvarious concentrations are shown above. The effect of anexcess 0-1>l'jlI~ in leach solutions as NH40H was also investigated.A. eo lu t t on of (.NH4)gS04 and NH403 in the proper proportionsWHO nade up as before. As the, 16.3 % NH, solution was.3so fiCinl' c. sc.turatec. solution tha t anmo nf a salts werepreCipitated if tho solution was allowed to stand in anopen container :for any Leag t h of tiele. the second leachsolation was ~ade core dilute. Di~tillation with NaOH show-ed t.h~t "-ho ....·I."<tn ...' ~r.'-'t"'onl.·cr-O"..,L,..,r,..L was -. ,.,('1, "u. ",J, . "" "'" .... ....... ,'_ ••, ,lA L. v,,"," "i;1 _ ..... i jOo llitty .....ubiccO:J.ticctorn ot tl:in COJ.ut:t0U 10 capable of diBDolving 6.9grur.lS 0:: s Lno o~' thut ~;lount of zinc contained in 11.5 gra,of ca.Lci no, ?a;,rt o:.t the 12.7 per.cont. amraont a eoLutn on wasdl1utec. to 8.8 porcent Ilnd part to 6.7 pel"Gont UH~. Eaoh oft~e thze e so 1u.tl one was uae d to Leach a s ampLo of calciuekee:;>i:lg the G. aaoaf.c cont en t fJG r un i t of calc), ne the aamein each. Results are cho~~ in Table 2.Table 2Excess MHo as NH40HConcentration Percent Extraction12.7 ;{, 89.588.28.86.7 84.4All solutions t'Jere filtered i lraed1l:1toly;:;..fter leachingfor an h ur. Ho di~ficulty was enoountered as is the casein acid :ecches c~uced b~ ailiclc ~cld gola.Tr.o z ino ext:=-o.otion tina f.)und b;- titrating en aliqu.ot-8-I..f ' I,fi!part and calculating the total zlnc~ ~ome extraotlo11e w'erecalclllated by determining the amol.lnt of zinc left in theleach rssldtles by the r,egular af.nc determination 4). ~hedifference between the weight of the zinc in the originalsample and the weight· of the zinc in. theresidlle was oonsider-ed as the weight of zinc dissolved by the leach solution.Treating the sola.tions proved to be milchmore satisfa.otory •.ttesidueo run about 4..0 perc'Gut zina. ~his was due tothe sme.ll amount of residue left from the leached cs.Lotne ;the weight was red~oeda.bollt 50 peroent dllring leaching.:1:h18residu.ematerinl hJ' too high grade to throwaway.No secondary leaches were tried,; but a system of count erOllrrent leaching wOl.lldprobably prove satisfaotory in treat-ing t·he material Wlt~.l the zinc content wouId be 10 enough8-0 that the residue could be disoarded.Fl'1.rif'icationIt should be impossible to deposit Zn in the presenceof hydrogen i'ons because hydrogen is more eleotropos1 ti vethan zina. However it can be deposited on aocounb of the,high voltage necessary to liberate hydrogen on zin(" !l!his iscalled ovorvoltage. If other metals are present which willeauae the disoharge of hydrogen a.t lower voltages. no zincwill be deposited; but hydrogen will be evolved.Unfortunately t during the leaoh1ng pr-oeoas smallI1;'4} Loe. srs:-9- \ \i \, . \ \\"IIamount e of other metals are c.iss,)lvGcl frOf:l the cc..loineand I~U8t be r-enoved co that the zinc Day be deposited.The process of pari.:>ication is v(~ry if:lllortant for this ::-eason.Acong the oetuls which may be in the calcine, copper anci cadmiumare most t ro ltbleGOrle because they form complex ions wi thB.I!ID10llia and. conseq uent Ly 0. ...e very so LubLe . ~inc is no r ee Lec t z-one ga t Lve t han eithnr of these r:]'':talc~ so they oust ber omoved . Nickel .• cobalt .. arsenic. and ant iClony are also moreeLee t.r opce i.ti"<Ie tr:a.n zinc. but do not cause so ouch troublebecause they are Lesc soluble. l:anganese in the electrolyte doesnot il;~peurto be llar.L:1:fG.l in zinc deposition.Zino is ~ore electronegative than the other octalsoatio::l. Jine. l!ddcd to c. eo lCiit1.n:1co t at nt ng Gore eLec t ro-positive uc~clc ~ill replace ~hc~ C~USiDg their precipitation.t-r t"Zl1 1- eu ~ :~n + OuThis principle was used in purifying solGtio~s before electrolys-ing.~, i prfiCU3.u-:, 2.e G.c!1 so IIIti O::LS '.vero tlue in color showing-..l,.;;i.,,,,,,,",tb.at copper was present. Zino Qust in exe ee s of tho 8.uountnecess~l"y to replace ., -:1 iDpuriti s \?8:S addec. to the olutions.,~..... .-!~o action oocune d -:;l:ich wcc vi olent 0,.10 tgh to e e ; u"'i sa tinewent on, t he OClll~ion grac !c.ll~7 b C!lOC light~~!' l)}.n.e in colorand finally becaee colorlons. Agitation ope ded up the reactionso th: t uch _cee tice aa8 ~eednd to obtain c colorless solution.-10-Filtering ~emoved the excee s zinc nu0. pr6c:J.pitntodimpurities. leaving n pure co Lu t i on f:i."omwhich thezinc could be r ecovo rcc by electrolysis.EleotrolyeisAs e xpLat ns d pr ovt oue Iy the suocessful depositionof zinc c.eper..ds upon maintaining the value of the hyd!'ogenovervoltcgc greater than the potential required to depositzinc at tho eethode thug preventing the evolution ofhydrogen and giV.lllC a high current efficiency. All oonditionswhich tene. to raiee this overvoltege a.re desired an~ thosewhich 10\"1erit a::-celiminated ae much as possible. Someof the .factors \~hich tend. to raise hydroge!1 overvo Lt ageane AO are necessary for a bOoc deposit are:,J... High zinc concentration::{igh current density (30-100 amperes per sq. ft.)c:..3. Good o i r ouLat.t on of eleotrolyte~ow temperature (20o-500~)4.5. ~bsonce of morc e:cctropo~itive metals6. LOw hydrogen ion concentration'7•• Prosence of glue or other colloid.Theory: lluring :he eIect~olysis oxygen io liberated at theano de ~ Z;1 io de:)osi ted a t the cathode, and t he leachsoluti on tc regenerated. In t he elect rolyte the L~n(NH3)4S0 4ionizes to pceitivo Znf?:lH~)4 ions and ne~ative 304 ions:The positivo ion is attracted to the cathode hore twoeLec t rons ur o picl~ec. up ae shown by the react ion:-11-tt-~n( HH3) 4 t- £e -- Zn +- 4NH33inc is deposited and mi./. is l:iberatud wllioh ::-e~ctsOJwith .c.tor to form Nn40H ..Tho negat i VB ion gooe to t he a ode vJhore t wo electronsaro ::"ostHS shown by the re actf on:S04 +: 20 -- 804Tbe S04 recote with water to form H2S04 end lib0~ateoxygen.One-hulf of the enmonauu hy.droxide :foroed in t hesolution at the cathode recctc with al' the sulfuricao Ld :fo:- ott ut the anode to f'orra auoon iurasulphate toregonerate the leach ~olution.Heaction:E!J>critlonto.l: .!..cud t.L.odec cud zinc 0:': thodes spaced t eocentioetc::'sapar-t vmre usod in nIl electrolytic testa.D\U"illg the de t e rmt nat ions the eo Luti on beccme \'JUrr.1er,but t ho length of tine for ouch vms not long enough toeauoe e~oeG81"'10 ,~1eeting. Tile e:ec-:;ro:!..yte was circula.tedoontinually by agitction.An electrolyte ~ae cade by leaching the calcine andpu.rifying the pregnant ec Lutnon ~dding zIno dust. l1.nalysisof the Golu~ion ohowed thct it conttiined 113.5 eruos ofzinc per liter. The Golntion was olectrolysed for about onehour at a ou~rent ~en~ity of 30 amps. pe~ equare foot. Atthe O=:id of that tiLle an {)f~icie cy det .rcination was l:!1adeby oecnc of u copper coulometer 'hich wac in seriee withthe cell. l..nothor hour's electrolys ing of the sane-12-Golntion was oarried on be.fore the next efficisilcy WCoSeaLcu.lrrt ed , Thin ;n'occdure 'iVfi.S car1"i cd on fo I1.rt Los:results ar e shown in TobIe 3.Teble 3Efficlenc ies a. t V[~l'i ous co:lGl::n tri1t iOilS:concentration of Electrolyte E:fficieilCYgo Zn / 1.11;).595.284.370.697.3 )'091.406.703.1Voltflge incroa.sod from 2•.7 to 3 volts duringelectrolys_is due to tnor-eae ed rocistnnce of the solution.':l:.e dopcs:t _:romth-o noLut Lon co! ta.inlng 113.5grane of zinc per liter was a snooth adh~rcat deposit;but deposits froe tho other solutlone showed treeingaround the ed.gee, No collo:lds such as glue wer o addedto prevent treeing. Besides this ~ethod the cathode issOr.:letiosG made larger than the anode a.nd. wood stripsplaced uroQ!1d.tho sides and bottoras of the cathodesto prevent treeing.St:::.rnm.ery_~ncccnd.~~zi.nc cu LcLno lenched with n solution ofaumonf.ura cu Lpha t e az..d anmonf.nn hydroxide w i t h a raaxtrnuraext~&ction of 80.5 percont 3n. The pregnant leach solutionwas pu..rified by adding zinc dust to precip':' tete ilptlri t i ea ,Zinc 'has rcco'VereCl fron the oo:!..utionas a Er.Jcoth adherentdepo s L tat c cr;.r.r0 t dc nc i ty of 30 UO}lerOS per cquar e ro otwith a naxt nun efficiency o~ 97.3 ;,1crcent , Leach noLu ti ons~e~e Tcgenerctcd ready to use on Zresh calcino ••I wif)h to tc:i:O thie opportl'ni ty to thank Dr. Wilsonand Pro~oono!' 1fu.eIi:wc.nof the Montana School of Minesfa.culty for their aGOi8tance in this investiga.tion •..1.180 the Anaconda. Copper Hining Ooupuny. who donatedthe ou::!..cinefor tho probler:l.42843

Ammoniacal Sulphate Leach of Ananconda Zinc Calcine Recovery of the Zinc by Electrolysis.

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Ammoniacal Sulphate Leach of Ananconda Zinc Calcine Recovery of the Zinc by Electrolysis.

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