SHHRR A VOLUMETRIC METHOD FOE THE DETERMINATION OF LITHIUM R. H. Moore Analytical Section Technical Services Division January 9, 1951 HANFORD WORKS RICHLAND. WASHINGTON Operated for the Atomic Energy Commission by the General Electric Company under m ‘ Contract I W-3l-109-eng-52 Photostat **«• $. Microfilm Prlco t ----/ f e d . — .T"*"*» Avolloblo from tho T !* * ' «■*■•». «• i.- Offlco of Tochnlcol Sorvlcos ~ •» b> *1, Department of Commerce 2 C . r r p’s*MrT 4'^ «•«—— — Washington 25, D. C. __ _ M *,. • - 1- 2- a 5 -s- A VOLUMETRIC METHOO FOR THE DETERMINATION OF LITHIUM INTRODUCTION " r r iiiii*T1i I il It has become desirable to develop an alternate method tor the determine- tion of lithium to serve as a stand-by method at tim es when the flame photometer U inoperative, or to supplement the latter in caeee where a doubtful analysis requires further investigation. A method based upon the pre­ cipitation of lithium with potassium ferriperiodate was Investigated because of its expected freedom from interference by aluminum. Potassium periodate is an inorganic complexlng agent which prevents the hydroxide precipitation of many non-oxidiaable me tula. For example* ferric iron reacts quantitatively with potassium periodate to yield s yellow precipitate soluble In an excess of potassium hydroxide, giving an amber -colored solution (1). The precipitation and subsequent solution may be represented by the equations: ' ? ‘ F .+++ 1104‘ * E20 -------> 1^ ♦ 2 H+ (l) r +ZK* * Z0H -------> F « ^ o'>IC^O + 2IC+ + Hz# (S) The ferric iron In the principal valence compound shown as the product in equation (2) is compiexed against precipitation by hydroxide, carbonate, or phosphate ions, This tendency to form the iron-bearing anion Is so strong that ferric hydroxide precipitated from acid solution by an excess of potassium hydr­ oxide goes Into solution upon the addition of potassium periodate. Such a solu­ tio n is of particular interest, for Procke and Usel (2) have shown that an alkaline ferric periodate solution la a very sensitive and selective precipitant for lithium ions. Somewhat later, Procke and Slouf (3) showed that lithium can be estimated quantitatively with the reagent by dissolving the precipitate of LUCfPelOg) in acid and determining the lithium In terms of periodic acid, which is liberated when the »■ precipitate la dissolved, The method « u investigated to detam tae whether It could bo applied to the determination of lithium. WIOOKY 1. Potassium forrlperlodate has bno shown to oltoct quantitative predpl m tatlon of lithium from solutions made strongly aihsUna with potaaatum | | hydroxide. Tho lithium in tho precipitate of lithium potassium ferrlperio- | data U eatimated ta term* of poriodic odd, which forma who* tho pro* cipitato ta dissolved la acid and may bo determined lodometrlcaily. 2. Aluminum dooa not lnttrforo with tho dotorminatioo of lithium. ao tho method U easily adapted to tho aaalyala of lithium‘aluminum alloy a. 3. tho roaulto of aaalyaoa pur for mud on Simula tod lithium -aluminum allop aampiaa ahow that a ralatlvo procialon of i 3.2 % and a relative accuracy of ♦ 0.99% can bo obtained. Tho method gives slightly high rooulU for lithium as a result of interference due to sodium which la proaont in tho reagents. TITRATION OF FKRIOOIC ACID la a few preliminary experiments a lithium‘aluminum alloy containing 1.90% lithium waa diaaolvod In potaaelum hydroxide and the lithium precipitated by tho addition of an oxcoaa of potaaelum forriporiodato. After boiling to complete the precipitation of lithium* the precipitate waa aeparated by filtration mad dried. In nil of aeveral caaes low recoverlaa were obtained and it waa observed that tho precipitate appeared to decompose upon drying, even when drying waa affectad in a vacuum at 50°C. Despite the low recoveries calculated from the weight of tho precipitate, the filtrates failed to give a flame teat for lithium. This behavior precludes the determination of lithium gravlmetricmUy. The precipitate may. however, be aeparated by filtration and diaaolvod in acid to yield a solution containing periodic acid and ferric ion. The lithium may bo determined in terms of either of these substances by a suitable titration procadure. Periodic acid in an acid solution of the complex lithium salt may be titrated iodometrlcaiiy, but an exceaa of fiuorida. or better, phosphate ion, roust be present to prevent interference from ferric ion. The titration la affectad by high concentrations of mold and the solution must either be partially neutralised or diluted after volution of the precipitate. That the simple expedient of diluting the solution suffices to overcome this difficulty is shown by the results recorded in Table 1 where data obtained from the titration of standard samples of pure potassium periodate are t ~ recorded. An appropriate wolgbt of ferri* ton (a* ferric ammonium tdfote) and an acid mixture of 100 ml, of 10% sulfuric acid pin* 16 mL of conod. p in * pboric acid worn added to tin potassium poriodaio > o u to s imulate w ry clcnsly the titration of an acid eolation of Um lithium precipitate. It la evident frwm Um data la Tabi* 1 that Um titration la accural* altar dilution to at laaat 500 mL # and preferably to 400 mi. la mor* concentrated solutions, air oxidation of hydrlodlc ad d proceeds to rapidly that high titrations cannot bo avoided. It la aUo clear that ferric iron la satisfactorily prevented from interfering by Um completing action of phoopborlc add. TABLE I tOPOKETRlC TITRATION OF PKIUOOIC ACtD IN THE PRESENCE OF FERRIC ION Titratloa Wt. **•++♦, Uft. W O., Volume at tim* Vol. Na.S.O**, error, ml. grama gram* of titration. ml. miunAdH* *W» 0 .0 4 0 2 o. lift? 120 10.05 + 0.11 •« ft 120 1 0 .7 0 + 0.U •« II 210 10.01 + 0.02 it II 210 10.60 + 0.07 •i 1* 310 1 0 .6 0 + 0.07 «t II 310 1 0 .5 0 + 0.02 it II 400 10. 4 ft •0.01 $sdf| it II 400 10. 8 ft + 0.04 0.000ft 0. 3314 110 2 1 .8 0 t o i l 11 H n o 2 1 .7 0 + 0. II •1 II 210 21.10 + 0.16 i •1 II ■p 220 2 1 .2 0 + 0.26 •1 tl 320 2 0 . 9 ft + 0.03 It tl 320 2 0 . 9 ft + 0.03 #' It II 400 2 0 . 9 ft + 0.03 8 It II 400 2 0 . 6 ft •0.67 rhe volumes of 0• 5800 N. Na^S^Oj are corrected for a blank which was I A» conatant• blank of 0. Oft ml. was obtained at dilutions of 300 ml. or more and for titrations of from on* to two minutes duration. MK-'. 'iV te^eM ******'*****'* * wr'" “ -T-1-'- -w -'V'-r;: -• . j * ' : ■■ * k . k '■ * • ' Mgm- sfe*A*#! • m m m ***■; *-*i< rV V- • a s s f m g * Z : $ t e r . farrlpariadala m l •ointloo of tfca raaalttag farrlc «04a la lUvfta **, I f * , . ... f with barium dlpturnyUmla. (ulfoaaU. Tho mothod to co|»bll of food r »OoH« U ihow by t t t dot* In Toblo a , which cw ttlM tho n w l h af ooaijoU of Umadird lithium chlorkW ootaOooo. TVo tpittioo stop M il bo 4om w ry M' corwftUy, he wo tor, to pro w l lo«a by (UfUfrotUm of tho proolptteto, • OtOf which boootoi locrooslofty difficult M tho woifht of tho procipitoto lo la- craaaad. Tfca nitkod nKjulw eonaidarabljr a ir t Uom thin that lavohrtaf an lodoaatrlc titration, tod w u not iavattigatad furtbar. % TABLEU UTmATtOH o r UTHUtti W TERMS OF TOT ISOM COWTEWT O f THE UXjWM%) PRECIPITATE Wto U (trot), Wt. Lt (found). Rtcovary miUtirama aaiUlirama par cant M t 100 1U 1015 i i 101 00.1 i» 1U 1010 f H 3.15 106.0 II 115 1010 100 111 11.0 H 111 1 1 1 II 5.01 0 16 II M l 0 10 II 6 . 0 2 06.6 a 1 -7- precipitation o r utwum The reagent uMd for the precipitation of lithium throughout this work It pro* p trtd a* follows: DU sol vs 140 g. of potassium hydroxide la 4 SO ml. of wstor. While the solution is still hot. dissolve 34. 5 g. of potassium periodate is it and then slowly add 30.0 ml. of a ferric chloride solution containing 1 .70 g. of ferric chloride hexahydrato. Beat until a clear solution U obtained. la theory, t. • ml* of thU reegent will precipitate 1.0 sag. of lithium, al­ though experiment shows an excess Is necessary to ensure complete pre­ cipitation*. To determine the effect of reegent volume, a series of standard lithium chloride samples, prepared from pure Lithium carbonate to provide constant lithium concentration, were analysed using various volumes of re­ agent. The final volume waa maintained constant at approximately 130 ml. The results of these analyses are shown in Table 111. from which it would appear that the reagent volume is s critical factor. These data indicate that a Urge excess of reegent is as serious sa Insufficient reagent. TABLE 111 EFFECT OF REAGENT VOLUME — 1 11,1 ■’ ■ • ■, VoL Reagent, WL Li (true), Wt. Li (found), Rato very, milliliters milligrams milligrams per cent 30 0.39 8. 0« 90.8 33 »« 9.95 97.9 40 i» 9. 75 99.8 30 i« 9.93 97.4 73 i» 9.22 93.2 100 i t 8.17 82.6 + This reagent Is somewhat more than four times as concentrated as that usbd by Frocks, e t.a l., to permit precipitation of substantially larger amounts of lithium than those authors attempted.