The determination of aluminum, nickel, cobalt, copper, and iron in alnico

I-.

372

VOL.

XEITES

18

(rg$)

and the analysts consists of measuring the quantity of ckXtrIclty CXJXWUXTfCd In tllrs oxldatlon. the elements commonly assoctatcd wrth chromium, only vanacltum (ad, when it IS present In largc nmoitnts, mofybtfcnum) intcrferc In this proccciurc.

strrtc, Of

Iiccclvrtl

THE

DETERMINATION COPPER,

OF AND

ALUMINUM, NICKIX, IRON IN ALNICO

June

a~st,

1957

C013ALT,

by

The dctcrmination of the major constituents of Alnico type magnetic materials by classical methods now in WC is quite tedious. For cxamplc, the determination of nick4 with dimetl~ylglyoximc rccluires a double prccipitntion and the volumetric cobalt dctermination requires the time-consuming plotting of the potontiametric titration curve. It appeared that a mot-c simplified procedure coulcl be dcvelol~ccl by using an ion cxchangc separation and a volumetric dctcrmination of all the major constituents of Alnico. Kraus and coworkers have d~t~r~~~i~~ccl the absorption characteristics of aluminuml, nickel”, cobalt213, copper” and iron(I 11)” ions on a strongly basic anion exchange resin from hydrochloric acid solutions of various concentrations. Aluminum and nickel chloriclcs are not absorbed over the acid concentration rangc of o to rz.11 hydrochloric acid, Cobalt has a masimum absorption in about ~$2 l~yc~ro~l~loric acid and dccreascs to xcro at about 3.5~111. Coppcr(I1) shows a masimurn absorption at about G:\l hydrochloric acid which clecrcases to zero at about 3.11. Iron{ I I I) has an absorption maximum at about rortr hydrochloric acicl which decreases to zero in about 0.5.1f. If a mixture of the five major constituents of Alnico is added in gJf hydrochloric acid to an anion eschangc column in the chloride form, the ~~lurnin~lrnand nickel pass through the column while the copper, cobalt and iron are absorbed on the resin. This, Jiefcrertrrs

p. 375

VOL. 18 (1958)

DETERMINATION

OF

Al, Ni, Co, Cu ANL, Fe

373

of course, is due to the presence of chloride complexes of these elements. The iron is absorbed most strongly and is at the top of the column followed by the cobalt and finally by the copper. The aluminum and nickel cannot bc separated in the column since neither are absorbed from a chloride solution. However, after a back titration of an excess of EDTA (cthylcnediaminetetraacetic acid) with standard copper to determine the total equivalents of aluminum plus nickel, the EDTA can bc displaced from the aluminum complex by the addition of fluoride. The EDTA released is titrated with standard copper solution and the pcrccnt of aluminum and *nickel are easily calculated from the data of t lie two titrations. If the solvent in the column is now changed to +lf hydrochloric acid, the cobalt is clutcd but unfortunately the separation from copper is not very good. For tllis reason the copper was rcmovcd electrolytically prior to adding the sample solution to the column. The absorption of ,iron(III) m 4.11 hydrochloric acid is still high enough to (Inable the cobalt to be elutctl complctcly while tllc iron moves only a short distance clown the column. After the cobalt is elutcd, the iron may be removed from the column lvith o.5.V hydrochloric acid. The separation of the constituents of Alnico by ion exchange appcarcci feasible and the analyses of each constituent was complctcd volumetrically by a back titration of an c.xccss of ISDTA with a standard copper solution.

4 convcnlcnt

divitlccl cell may 1)~ constructed t>y setetinfi a frrttctl glass scaling: tube which will insitlc ;L platinum gniix nndc from commcrcinlly nv;ul;~blc clcctronnnlysrs appratus The glass IS cut off a+ close to the frrt aci poss~l~lc ant1 the portion with the fret 15 lnscrtccl in tlic ccntcr of ttic platinum clcctrotlc ant1 fillccl with il lo?<, sodium srllfntc solution Insert il platinum wIrc tu hcrve as an illlOCtC XllCt lllIlTlCl-?rc ttlC ctcct.r~JttC! LlSSClllt,t)lllh ttlc hOtlltlOIl t,iJ tJC cl~ctroly02d Cc,iincct the gdci~c clcctroclc: to ttic ncg:Ltivc tc*rrninnl iLlIt ttic platinum wire to ttic posltlvc tcrininal of R t1.c power s~ipply capntdc Of tlcllvcring nbout 25 V Rcrmovc the txakcr from the clcctrotlc as\cmldy and rinse the clcctrorlc with water into Ihc bcakcr contrrming ti1c.iron. cobalt, nlckcl, ant1 alummum inert the clectrotlc x~scmbly Into n 250 ml lwcnkcr contulnlng IO ml of buffer (20 pcrccnt SH,hc) nncl 5ufflcicnt water to cover the copper tlcposit Xevcrsc tha ciirrcnt flow in ttic clcctrrdc n+c*mtAy and stnp the colqxr into the buffer solution. .\tttl iln vsccss of CJ 01 .%f iel‘~\. q-5 drops of l’l\x (r-(r-l~yri’iylszo)-z-naplltittl~)l) and buck titrate wlttl ;l St~~llCli~CXl copper solutlorl

cc~nvcnicntly

fit

.\tltl 3 ml of Joy<, tiytlrogc*n pcros~clc tc> ttic solution from the* clcctrolyscs ant1 CVilpOKltC to .*-s acid from ;L polycthylcnc ~;isti bottle to an ion ml. Transfer tt8c snmplc witti g11f tlyclroctiloric chloritlc form) wtilcll cxchangc column (x cm tli;imctcr Y 35 cm long, t)owcu i ,* .I*, I oo- 150 mesh, tlilS cntcratl ttlc resin. has lxcvmusly bon wnshctl with gdI hytlrochlor~c oc~tl ,\ftcr ;\I1 the sxmplc clutc the nlumlnum ant1 nickel with two column volumes of r_~If hyclrochlorlc acttl into a 250 ml ~111 move down bcakcr XOW bcgln the clubon of the cc,lxdt wllh .+A1 hyrlrod~torlc ac~rl. ‘1‘11~ cobalt Ltic column in a blue bontl ant1 when it 14 within zbtx)iit .j cm from ttlc bottom of ttic column rcmovc the bcakcr containing the ;ltumln~lm ant1 nickel anct rcccIvc the cobalt in :mothcr 250 ml bcnkcr When the cobalt 15 rcmovctl from the column, clutc the iron with o _5N hydrochloric ac~cl into nnothcr rgo ml bcakcr + Dow k-/CYClJCCS

Chemical p.

375

Coriilx~ny,

Midland,

Michigan.

JZvqxxatc the solutwn contalnlng the nrckel nnd rrlnmrntrm to &out IO ml. Transfer the to a 250 ml volumctrx flask and dllutc to volnme wth wrtur ‘Cmnsfcr a 25 ml rrlquot ml bcnkcr, a&I IO ml of buffer (JIM ,I 8) and ;1 mcasurctl amount of EJXA sufftcicnt to the alummum and mckel uncl prov~cJe a small CXCL’SS. I-lcat the solution to in 1~~11,add 4-5 l*A,l arid back fxtrxtc tfw cxccbb JCDTA wxth o 031M stanclad Crt soltit~on unttl the rndxator frc,m yellow to puqde. ‘I’hl\ end-point g~vcs the sum of the nickel ,lntJ nlumtnum A(Jd ~UW gram of ;lmmonium fluor~clc to the hot solutton ant1 back tltr;ltc the ELYJYA from the d111111nllI7i wlth the 0.031VI stnntlarcl cqqxr solution lhrs cntl-Jx~nt g~vcs the c>f ;duminum prcwnt. illIt\ the nickel 1%calculatctl by rliffcrcnce

solution to a 250 complex drops of changes

rclcw~~J amount

'f‘lic two sctfutions contatmng tlit: rrlm wxl the coLxtIt ;irc trcatccl m iln ttlcnttcaf miltirwr ah foltows. JCvn~xn+,rtc tlw wtutwn to about 10 ml, trnwifcr to a 250 rr11 vtrliinwtr:c flask ~Ux.1titlutc tu \VJiUKW xltl il _j to 10 ml cxccs5 of stanclnrd EJ>‘l’A, with wntcl ‘I’txrislcr il 35 ml :dquot to a 250 ml IJcirkcr, f 0 ml cJf Imffcr (pII ,} 8) ;lncl Ixrclc tltratc tllo cxcc5% 151 )‘I’h with il standard crqqwr solution using xn npprqwl:rte cncl-point Inthcntton. ‘I’l~c rcwlts g8vcn rn ‘Tilblc I were obtnlncd usmg an autom;itlc trtratorC rlcvclopctl In thb labor;,tory. ‘1’1~ trtratctr’h rtpcrntlon IS bascrl cm an Inct-cLtsc in cttrrcnt when a pIi~tIIllIn1 clccttrrctc is clcJx~lar~~cd.

l31bCUSS10N

l’llc copper separution can bc nccomplishccl by ion eschango also, howctler, when the nickel ancl aluminum arc clutccl with qdf hydrochloric acid the cobalt is more strongly absorbed titan copper and as a result the copper is below the cobalt in the column. When the cluting agent is changed to .@I hyc1rochloric acid the cobalt is moved down the column faster than the copper and as a rcstrlt the cobalt bancl must pass the copper band ant1 leave the column bcforc the coppcc reaches the bottom of the column. With very slow flow rates and juclicious care in changing solvents this can lx accomplished. If the sample is introclucccl into the column in 7Jf hydrochloric acid with all five clements present ant1 the nickel and alumin~lm elutccl with 7:lf l~yclrocllloric acid, then the copper ancl cobalt have about the same absorption. Under these conditions a separation of the cobalt bnncl from the copper band on elution with +Jf hyclrochloric acid is somewhat easier. However, the flow rate still must bc quite slow, For this reason the copper was removed electrolytically prior to the ion exchange separation. The prcscncc of iron in the sample neccssitatcs the USCof a divided cell for the copper deposition in order to obtain a copper clcposit without the use of a depolarizer which would intcrferc with the subsequent column separation. With the copper removed, the separation of the four remaining elements into three groups, namely aluminum and nickel, cobalt, and iron, proceeds in a routine manner. Neither the flow rate nor the time when the elutiori of cobalt is started is critical. The copper ~lct~rn~ination of course could bc concluded by weighing the copper dcposit. In this work the copper was strip@ off the cathode and titrated complexiometrically for two reasons. (A) With the method used, no attempt is made to obtain a weighable deposit. The only criterion is that the copper cleposit must stick to the electrode. As a result, a high current clcnsity may be used which will give a burnt deposit and satisfactory result3 for copper arc still obtained. (13) With small amounts of copper, the titration is as accurate as weighing the deposit, and is more convenient with the clectrodc assembly used. The clctcrmination of aluminum and nickel must bc clone in a hot solution. The aluminum reaction with EDTA requires that the solution bc hcatcd to a boil for a few minutes0 and also the reaction of the aluminum EDTA complex with fluoride is rapid Refetzrrces

p. 375

DETKRhlISATIOIG

18 (1958)

VOL.

OF Al,

xi,

CO,

CU

ANU

375

l;e

and complete in a hot solution. If the titration of the sample is begun as soon as the solution is removed from the hot plate, no reheating is necessary between the t\vo titrations. The dctcrmination of cobalt or iron by various techniques using EDTA has been All of the methods using visual indicators limit the describd in many publications. is used, an amount of cobalt or iron \vhich may bcOIxesent ‘1”. If a Visual intllcator appropriate aliquot slioulcl bc taken bo as not to csccctl the pcrniissible concentrations of cobalt or iron. ‘fhcrc arc, of course, many procedures available for the direct titration of aluminum, nickel, copper, cobalt, and iron with ISD’I‘A as well as other back titrations of these elcmcnts. In this work, roll of the elcmcnts were dctcrnlinctl by a back titration with a standard copper solution because it is convcnicnt to llavc a single standard solution and proccclurc for clctcrtnining a number of diffcrcnt clcmcrits on a routine basis and the back titration with copper is ideally suited for automatic titrxtionsfi. ‘I’l~c results on the analysis of some _Mnico sillnples arc sl~own in Table I. ‘l’.\l~l,l3

_--

--_-

_

_.---

_.

__._ -_.. II

.I1

Somt ml

‘VI

I -wd -. __._

SO I I

8

0

I I

i

----._-

* Nominal

.\ o,,, I !I,* I -_-___. lj

I

7.0 H I

H0 70

7.0

I*

7.’ 7.1 7.1 7.2

-1 *4 8

I

i

-. -. _ ----._-

vnlucs tlctcrm~nctl by classical

___-.--.

_----__

.--

---

. .._--

wet nnalys~s

A mctlwd hs been tlcvc1opctl for the tlctcrmlnntion of the ni.Ljor coiatltucnts of Alnico bnsctl on an anion cxchngc separation of the clihrltlc complcxcs ant1 tllc subscqucnt rlctcrminiltion of nlurnlnum, nlckcl. copper, cohlt ‘anrl Iron wrtil EIJTA. ‘I’lic nictllod is more convcntent than convcntional ClR%lCill 1llCtllOdS.

Hcccivctl

August

zotli,

1957