Separation of rhenium from molybdenum, tungsten, chromium, vanadium, selenium, tellurium and osmium by extraction with acetylacetone from alkaline solution

468

SHORT

COi%MUNICATIONS

Separation of rhenium from molybdenum, tungsten, chromium, vanadium, selenium, tellurium and osmium by extraction with acetylacetone from alkaline solution The extraction of rhenium from alkaline solution offers the following advantages: (a) &ments such as copper, chromium, nickel, cobalt, bismuth, etc., wllich interfereL in the clctermination of rhenium are scparatccl along with otllers that form insoluble hydroxides, without loss of rllcnium2; and (b) silica and otlier acidic asides remain in solution. Few methods are available for the extraction of rhenium from alkaline solution and its separation from molybdenum and otller elements. Extractions with t~tra]~hCU~~larSOniUIll ClllOride in chloroform above pi 83, methyl ethyl ketone from 5 N sodium hydrosiclc~, pyricline from 4-G N sodium hydrosicles ancl cluinoline from 4 N sodium hyclroxidefi have been suggested. Rllcnium(VII) estracted by acetylacetone from acicl solutions7 cannot be back estractcd by water from neutral or alkaline medium. Accordingly, the possibility of extracting rhenium from neutral or alkaline solution was stucliccl.

Standard stock solutions at the mg/ml level exactly weighed amounts of potassium perrhenatc Ltcl, London) in water; test solutions were preparccl of the other elements were prepared from sodium or cluality) and stanclardisecl by conventional methocls. Acetylacetone (L. IX., B.D.H.) was purificcl”, (L.R., B.D.I-I.) were used directly.

were prepared by dissolving (Specpure, Johnson-Matthey, by suitable dilution. Solutions potassium salts (C.1’. or A.R. but benzene

and chloroform

Sa~trt$de solzdions Sym!hetic flue dust. A solution in the minimum quantity of sulfuric acid was prepared from ,ug amounts of rhenium and other elements in the following proportions: Zn 80, As 30, Fe 60, Cu IO, l3i 7, MO IOO, V 20, Mg I, Ca 4, Al 06, Cd 3. The solution was made just alkaline, the hyclroxide precipitate was filtered and w,asbed, and the filtrate was analysed. Natzcral sawz$des. A flue clust (500 mg) from copper manufacture, containing no rhenium, was mixed with a solution of known rhenium content ancl dried in an oven. After fusion of the dust in a nickel crucible with a 3 : 2 sodium peroxide-sodium carbonate mixture, the leach was neutralisecl with concentrated sulfuric acid and again made slightly alkaline. After boiling, the hydroxide precipitate was filtered and washecl, the filtrate was adjusted to contain 0.5 N sodium hydroxiclc, and rhenium was separated as described below. A Mexican molybdenite (200 mg) was treatecl with concentrated nitric acid and then the solution was made slightly alkaline with 5 N sodium hydroxide and boiled. The hydroxide precipitate was filtered and washed, the filtrate was adjusted to contain 0.5 N sodium hydroxide and the rhenium was extracted. Extraction with acetylacetogae Solutions containing varying pug-amounts of rhenium and mg-amounts of other elements, or the solutions from synthetic flue dust or natural samples, were -4mal.Ckinz. Acta,

44

(1969)

468-471

SHORT

COrtlhlUNICAl’IONS

40

adjusted to contain 0.5 N sodium hydroxide in 20 ml of solution. The solutions were estractccl with four 25-ml portions of acetylacctone, being shaken for 3 min with from the combined each portion. The solvent was then distilled off completely organic ph,zses. The residue was warmed with 20 ml of I: I benzene-water and shaken. The aclueous layer was drawn off and shaken again ‘with I0 ml of benzene to rcmovc organic matter. Any reduced valcncy states in the aqueous phase were oxiclisecl with bromine, excess of bromine was boiled off, and the elements were cleterminctl. The aqueous layer obtainecl from the residue may contain traces of molybdenum (about IOO pg from IOO mg MO in the original sample). l~henium was clctermined after the removal of this residual molybclcnunl by the santllatc method”.

Rhenium was detcrmincd colorimctrically by the cs-furilcliosimc method”; the volume rccommcnded was dccrcased to 25 ml with proportional clecrcases in the amounts of reagents aclclccl. Beer’s law was obcyccl from 10 to 150 ~6 of rhenium. Other elements were dctcrmincd or shown to be absent by standard calorimetric methods*. Mcasurcmcnts wcrc made with a Spckker Absorptiomcter in I-cm cells.

The percentage cstraction of rhcnium(VI1) at different alkalinities in the aqueous solution is shown in Table I ; alkalinitics above 1.5 N sodium hydroxide lcacl to higher miscibility of acetylacctone with the c~queous phase, longer times for phase separation, and turbidity, without any increase in the perccntagc extraction.

ACISTYLACBTONIS

ISSTRhCTION

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0.3

0.5

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fig.5

72.4

74.5

SOLIJTION r”)

I.5

76.6

The extraction is only slightly affected by the time of shaking and the temperature; shaking for 1-3 min at 20~ extracts 70.3:4 of rhenium(VII) from 0.5 N socliuni hydroxide whereas shaking for 30 min extracts 72.4%. The extraction increases to 75.2% at 10~ and decreases to 62.5O/o at 40”. i.e. a 0.3-0.5O/~ decrease for each degree rise. The estraction of molybdenutn(V1) is 0.33% from neutral solution, and 0.0214 and 0.01 “I0 from 0.5 N and I .o .iV sodium hydroxide, respectively. Consideration of the above data lecl to a choice of 0.5 N sodium hydroxide medium and a 3-min contact time for the estraction of rhenium(VII) with acetylacetone. Under the conditions given in the extraction procedure, there was no extraction of chromium(VI), selcnium(VI), tellurium(V1) or osmium(VIII) ; the percentage extractions of silicon(W), vanadium(V), tungsten(V1) ,and molybdenum(V1) were found to be 0.05, o.orS, 0.004 and 0.023%, respectively. In practical cases, only molybdenum needs to be removed before rhenium can be determined by existing calorimetric methodslo; it is best removed by the thiocyanate method11

SHORT

470

COhfblUNICATlONS

when rhenium(VII) is dctermiried by the thiocynnate-tin(I1) metllod or by the xanthate methodn , as in the present work. The results of emalyses (Table II) of several synthetic samples and a molybclcnite by the present method SlIO\Y that the accuracy is limitccl only by the method of determination. However, the cstimatccl loss of rhenium(VI1) in the extraction is about I’%,. l’hc solvent which is clistillcd off to recover the rhenium, can bc reused directly. The time taken for a single separation is about 30 min excluding the time .for distillation of the solvent.

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Thus, the difficult separation of rhenium from molybdenum, which interferes in almost all methods for its determination, can be achieved by simple extraction followed by removal of the cowith acctylacetone from slightly alkaline solution, The present method also estractccl molybclenum traces by the santliate method. separates rhenium .from V(V), Cr(VI), W(W), Se(VI), Tc(VI), Os(VIII), which interfere in many methods for its cletermination1.. dibenzoylmethane (IO y. solution in Other @-diketones, benzoylacetone, benzene from 0.5 N soclium hyclroxicle) and thenoyltrifluoroacetone (I o/o in chloroform from 2 N sodium hyclroside) clo not extract rhenium. The authors wish to thank the Council of Scientific and Industrial Research, New Delhi, for financial support, Dr. S. M. MUKHER~I for laboratory facilities, Prof. Dr. IL NEEB, Gutenberg University, Main& for the- mclybclenite sample, and the Indian Copper Corporation for the reverberatory flue dust.

.dl?ral. Ckint.

Ada,

44

(rgGg)

468-471

V.

YATIRAJA~I

L.

R.

I
SHORT

The

471

CO~IRlUNICA’I’IOKS

extraction

of gallium

with

cupferron

The armnonium salt of hT-nitrosopl~en~~ll~ydrosylnmi~7c (cupfcrron) is one of the most widely used extraction agents. Such estrnctions have been reviewed by STARY~, and by %-ARY ASD S~II%ANSI SLIIZASSKA~ were rcpcated. A ;h;haratfrs and

reagents

Ricdel). An aqueous 6% (w/v) solution of the reagent 1va.s prepared immediately before use. Sodi~r?. jwvchlorate was prepared from sodium carbonate ‘and percllloric acid and was twice recrystallizecl from deionized water ; it was tested for chloride ions. C/tlovofovnz(~.a., I&anal) was treated with concentrated sulplmric acid, washed and clistillecl from sodium hydroxide immediately before use; it was finally preequilibrated with 0.1 M sodium perchlorate. Gallimn ;hevcitZorate was prepared from gallium oxide (pss., GaaOn content min. gg%, Reanal) by dissolution in 2 Al perchloric acid. After filtration, thestocksolution was standardized complesimetrically. After tile extraction equilibrium had been reaclled the hydrogen ion conccntrations of the solutions were determined by means of an OP-205 PH meter (Radelkisz) and an Ol? 711-x-A glass electrocle and saturated calomel electrode; PH standards were 0.05 M potassium hydrogen phthalate and 0.05 n/rsodium tctraborate. Czs+fervofr(j.a.,