A study of heterogeneous equilibria in aqueous solutions of the nickel-selenates at 30 degrees C

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A STUDY OF HETEROGENEOUS EQUILIBRIA IN AQUEOUS SOLUTIONS OF THE NICKEL SELENATES AT 30 ° C.

By "H" R o b e r t F r o n i n g

ck

S u b m itte d to the F a c u l t y of th e G rad u ate School in p a r t i a l f u l f i l l m e n t o f the re q u ire m e n ts f o r the d e g re e , D octor o f P h ilo so p h y , in th e D epartm ent o f C h em istry , In d ian a U n iv e rs ity J u n e 1949

ProQuest Number: 10295189

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uest ProQ uest 10295189 Published by ProQ uest LLC (2016). Copyright o f th e Dissertation is held by th e Author. All rights reserved. This work is p ro te c te d ag ain st unauthorized copying u n d er Title 17, United States C o d e Microform Edition © ProQ uest LLC. ProQ uest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346

AC KNOWLEDGEMENT

The a u t h o r w i s h e s t o e x p r e s s h i s s i n c e r e a p p r e c i a t i o n to D r. C h a rle s S. R ohrer whose p a r t i c i p a t i o n i n t h i s i n v e s t i g a t i o n i n t h e r o l e o f c r i t i c a l g u i d e and h e l p f u l counselor has been of in e stim a b le v a lu e . The a u t h o r a l s o w i s h e s t o e x o r e s s h i s s i n c e r e a p p r e c i a t i o n t o D r . B r i a n H. M ason a n d t o D r . R o b e r t B, F i s c h e r f o r t h e i r counsel.

The w o r k d e s c r i b e d i n t h i s t h e s i s was p e r f o r m e d in the L a b o ra to ry of P h y s ic a l C hem istry a t In d ia n a U n i v e r s i t y u n d e r the d i r e c t i o n o f Dr. C h a r le s S. R ohrer

TABLE OF CONTENTS

Page I. II.

III.

In tro d u ctio n

• • .

• .........................................................

P re p a ra tio n of M aterials

. . . . .

....................

4

S e l e n i c A c i d ....................................................................

4

Sodium T h i o s u l f a t e

6

. . . .

................................

D i m e t h y l G l y o x i m e .........................................

6

P o t a s s i u m I o d i d e ..........................................................

6

N i c k e l S e l e n a t e ..............................................................

7

A n a l y t i c a l D e t e r m i n a t i o n s .................................................... 10 N ickel

. . . . .

.........................................................

S e l e n a t e .................................... IV.

1

A pparatus.

10 10

..............................

12

C o n s t a n t T e m p e r a t u r e B a t h ...........................................12 ................................................................12

Pycnom eter s .

.

C ontainers

..........................................................................12

A n a l y t i c a l ............................................................................... 13 V. V I.

E x p e r i m e n t a l P r o c e d t i r e ......................................................... 14 C alculations

and E x n e r i m e n t a l R e s u l t s .

C alcu latio n s

...................................................................

E xperim ental R e s u lts V II.

. . .

. . . . . . . . . .

18 18 21

D i s c u s s i o n o f E r r o r s .............................................................. 28 T e m p e r a t u r e C o n t r o l ...........................................................28 P r e c i s i o n of E x t r a p o l a t i o n

...............................

28

X - R a y D i f f r a c t i o n D a t a ................................................ 33 P r e c i s i o n and A c c u r a c y o f t h e C a l c u l a t e d C o m p o s i t i o n s ................................................ 33

V III.

D i s c u s s i o n o f R e s u l t s ..................................................................... 35 S o l u b i l i t y C u r v e ABC f o r t h e S o l i d P h a s e N i S e 0 4 .6H 2 0 ..................................................................... 36 S o l u b i l i t y C u r v e CD f o r t h e S o l i d P h a s e N i S e 0 4 .4H 20 .....................................................................37 The S o l u b i l i t y C u r v e BE f o r t h e S o l i d P h a s e N i S e 0 4 ................................................................39

IX.

S u m m a r y .................................................................................................... 42

X.

B i b l i o g r a p h y ..........................................................................................43

INTRODUCTION Many s i m i l a r i t i e s p ro p erties

of

the

i n b o t h c h e m i c a l and. p h y s i c a l

su lfates

an d s e l e n a t e s h a v e b e e n

r e c o g n i z e d f o r o v e r one h u n d re d y e a r s , o f th e com m ercial su lfates

im portance

As a r e s u l t

and a v a i l a b i l i t y o f t h e

a tre m e n d o u s number of p a p e r s In c o n tr a s t,

published

on them .

sele n ates

have r e c e iv e d only v e ry l i m i t e d

A s e a r c h o f the l i t e r a t u r e

the

have been

rev ealed

corresponding atten tio n .

t h a t o n ly a sm all

number o f th e e q u i l i b r i u m h y d r a t e s o f th e m e ta l s e l e n a t e s had been d e f i n i t e l y i d e n t i f i e d ,

and t h a t

was a v a i l a b l e o n t h e s o l u b i l i t i e s A s tu d y o f th e system n ic k e l acid ,

of

several

sponding s u l f a t e n ick el su lfa te

in v estig ato rs

1 p

s y s t e m - 1- ?^

as

rz

data

these h y d ra te s.

sele n ate,

and w a t e r h a s n o t b e e n r e p o r t e d

However,

little

selen ic

in th e

literatu re.

have s t u d i e d th e

, a n d Me 11 o r

4

corre-

has lis te d

th e m ost im p o rta n t n i c k e l s a l t .

The

h e x a h y d r a t e o f n i c k e l s e l e n a t e was p r e p a r e d b y E . M itc h e rlic h ^ by e v a p o ra tio n of s o lu tio n s in th e

tem perature

r a n g e f r o m 4° C.

Hauer^ o b t a i n e d t h e tu res,

and s t a t e d

of the

t o 8 0 ° C.

sa lt Von

same h e x a h y d r a t e a t o r d i n a r y t e m p e r a ­

th a t th e

sa lt

w ater.

Topsoe^ r e p o r t e d t h a t

had th e

ax ial ra tio

is very

solub le

the t e tr a g o n a l

a :c = 1 :1 .8 3 6 4 ,

isom orphous w ith th e c o rre s p o n d in g

in

cry stals

and t h a t t h e y were su lfate.

W yrouboff

8

-2-

said th a t th e su lfate, as

sa lt

dim orphous

f o r h e wa s a b l e

tetrag o n al c ry s ta ls .

an i n v e s t i g a t i o n sele n ate of

is

to o b ta in m o n o c lin ic ,

8 2.2°

He f o u n d t h a t

d ih y d ra te

satu rated

from I t s

so lu tio n s

eu tectic

The t e t r a h y d r a t e was s t a b l e

C. a n d t h e b o i l i n g

a t 1 0 3 . 6 ° C.

as w e ll

two c o m p o n e n t s y s t e m n i c k e l

th e h e x a h y d r a te were s t a b l e

- 3 ° G. t o 8 2 . 2 ° C.

corresponding

I n 1 9 4 0 , A n d r e f K lein® p u b l i s h e d

of the

an d w a t e r .

lik e the

po in t of i t s

at betw een

satu rated so lu tio n

D e h y d r a tio n c u rv e s gave b r e a k s f o r th e

a t 105° C .,

and f o r t h e m o n o h y d ra te a t 170° ^ .

The a n h y d r o u s

s a l t was n o t o b t a i n e d due t o d e c o m p o s i t i o n

of

selen ate

the n ic k e l

at higher te m p e ra tu re s.

Demassieux-*-® p u b l i s h e d

a paper

t i o n of th e double s e le n a t e In the d e te rm in a tio n of

i n 194 5 on t h e d e h y d r a ­

o f n ic k e l and p o ta s s iu m .

the d e h y d r a tio n te m p e ra tu re

c u r v e f o r N iS e O 4 . 6 H.2 O, s h e d i d n o t o b s e r v e for

the t e t r a - ,

stated

th at

d i-,

Mme.

o r m o n ohydrates.

any b re a k s

However, she

a b o v e 4 0 0 ° C. t h e a n h y d r o u s s a l t a p p e a r e d .

T his la c k o f d a ta i s n o t p e c u l i a r to th e n i c k e l s e le n a te system . of th ese gated .

th ree

T h is c a n be o b s e r v e d fro m t h e number

component sy stem s t h a t have b een i n v e s t i -

In 1928,

Meyer a n d A u l i c h

11

p u blished th e r e s u l t s

o f some o f t h e s e s y s t e m s c o m p o s e d o f s o d i u m , p o t a s s i u m , calcium , sa lt,

and m agnesium s e l e n a t e s

acid ,

and w a t e r

g a t e d was c o p p e r

in w ater.

equilibrium

sele n ate,

sele n ic

The f i r s t

system to b e i n v e s t i acid ,

1p

a n d w a t e r - Lx _ / 1 0 . 6

_ -2.1

is

a b 1

apparent

is d e s ire a b le

th e h i g h e s t d e g r e e o f a c c u r a c y i n t h e N iSe04

d eterm in a tio n s

w h i c h was

the case

The s e c o n d c o n s i d e r a t i o n , p o in ts fo r th e

e x p e rim e n ta lly be into

fo r th is

th at

com position of the

s o l i d p h ase be as f a r

resid u e

th at i t

the e x p e r i m e n t a l

s o l u t i o n and m o is t

a p a r t as p o s s i b l e ,

scooping

in v estig atio n .

the d e s ir e d

a sin tered -g lass f i l t e r ,

was h e e d e d

amount o f m o is t and t h e n a p p l y ­

i n g s u c t i o n f o r a few s e c o n d s to remove t h e e x c e s s so lu tio n before

tra n sferrin g

A l t h o u g h some o f t h e h y d r a t e s s c o p i c , no n o t i c e a b l e of th is

ch o ice

in the

to

alg eb raic there

is

a re to be used in

advantageous

to

the d iffe re n c e s

the

atm osphere.

a choice

as

( a T - a)

A lthough

For exam ple,

t o w h i c h compo­

the c a l c u l a t i o n .

and

a resu lt

t h e r e was a f u r t h e r

ex trap o latio n .

choose t h a t p a i r o f

d i f f e r e n c e s betw een the so lu tio n s

and s o l u t i o n s w ere h y d r o ­

e x p e r im e n ta l m ethod,

in equation 4, n ents

to a w eighing b o t t l e .

e r r o r was o b s e r v e d a s

s h o r t exposure

l i m i t e d by th e

it

It

Is u s u a lly

com ponents f o r w h ich

(b1 - b),

rep resen tin g

c o m p o sitio n s o f r e s id u e and

i n r e s p e c t to co m p o n en ts A and B,

are

g reatest.

-32-

W ith r e g a r d of

to one o f the

so lu tio n ,

v a ria tio n .

resid u e,

com ponents,

and p u r e

T h erefo re, values

n o t be used in th e

the com p o sitio n s

s o l i d may s h o w l i t t l e for th is

calcu latio n .

comoonent s h o u ld

P o i n t 13 o f f e r s

a

nu m erical i l l u s t r a t i o n . P o i n t N o . 13

% N iSe04

S o lu tio n

8.65

M oist s o l i d

5 7 . 0 0 (=

S o lid phase

x

As i s

% HgSe04

( = a) a T)

5 5 .5 7 ( = b)

35.77

1 4 . 9 1 ( - b 1)

28.10

y

100 - x - y

e v i d e n t fro m the above d a t a and from th e

g eo m etric al p o s itio n s

in the

w ater co m p o sitio n f o r the n o t v a r y to

the

com positions. for

% ,H 0

the

rela tiv e

is o th e rm a l diagram ,

the

s o l u t i o n and m o ist s o l i d does

same d e g r e e a s

t h e N i S e 0 4 a n d KgSeO^

T h e r e f o r e , W iS e 0 4 a n d H g S e 0 4 w e r e c h o s e n

calcu latio n .

T h i s p r a c t i c e was f o l l o w e d I n a l l

sim ilar cases. The t h i r d betw een

facto r,

tie-lin es,

was p a r t i c u l a r l y

the l e s s

im portant

in te rse c tio n p o in t for for

the

th at

tetra h y d rate

t h e mean c a l c u l a t e d

the

t h e more a c u t e the a c c u r a c y o f

tetra h y d rate.

were v e r y c l o s e

ang les.

o f the

The t i e - l i n e s

to g eth er;

com position of th e s o lid p a ir s having

angle

in tersectio n ,

in the d e te rm in a tio n

d e te rm in e d by u se o f t i e - l i n e p o ssib le

the

therefore

p h a s e was

the g r e a t e s t

-33-

X -ray D i f f r a c t io n D a ta : the d /n v a lu e s ,

the e r r o r

In th e d e te r m in a tio n of

i n c r e a s e s from /

3 . 0 A° t o ^ 0 . 2 0 A° a t 16 A ° . a t 1 6 . 0 A° i s d u e t o

the

The g r e a t e r

in accu racies

ment o f th e d i s t a n c e b etw een th e w ould c a u s e a l a r g e r At l a r g e r a n g l e s Increases,

error

in

and s m a l l e r

because as

the

fla tte n s

and t h e r e f o r e

of

s in e 9 c o r r e s p o n d to l a r g e

Inaccuracy

in the m easure­

a r c s on t h e f i l m ,

w hich

t h e d e t e r m i n a t i o n o f JQ. spacings

sin e

it

0 . 0 4 A0 a t

the a c c u ra c y

curve approaches 90°,

sm all changes changes

in

the v a lu e

i n -0 .

P r e c i s i o n and A c c u r a c y o f th e C a l c u l a t e d Com posi­ t i o ns ;

The e r r o r s

o f the v a r io u s

errors

ev alu atio n

com position are l i s t e d

a r e an a c c u m u la tio n o f

from a l l

sources c a rrie d

are

listed

of th e given h y d ra te .

In T able I I I .

the e x p e rim e n ta l

over in to th e f i n a l

v a lu e o f th e co m p o sitio n of th e pure mean d e v i a t i o n s

of the co m p o sitio n s

compounds t o g e t h e r w i t h t h e i r d e v i a t i o n

from t h e o r e t i c a l These e r r o r s

i n the

compounds.

The

f o r e a c h o f th e com ponents

-34-

TABLE I I I

N iSe04

H2 S e 0 4

H2 °

N i S e 0 4 .6H2 0 M ost p r o b a b le c u la te d value T h eo retical sitio n

cal­ 0.09 ^ 1 .0 0

3 4 . 5 9 ^ 0.20

65.10

0.00

34.90

/ 0 .21

/ 0 .09

-0 .3 1

65.32 f

0.72

co m po­

D e v ia tio n from th e t h e o r e t i c a l value

N I S e 0 4 .4 H 2 0 Mean c a l c u l a t e d v alue

73.42 ^

T h eo retical sitio n

0.10 f 1.19

26.48 ^ 1 .4 1

73.67

0.00

26.33

-0 .2 5

/0 .1 0

/ 0 .15

0.90

compo­

D e v ia tio n from t h e th e o re tic a l valu e

N iSe04 . l H 20 M ost p r o b a b l e c u la te d value T heo retical sitio n

cal­ 90.52 ^

0 .58

1.21 ^ 0 .4 3

8.27

91.80

0 .0 0

8 .2 0

-1 .2 8

/ l . 21

/ 0 .07

compo­

D ev iatio n from th e t h e o r e t i c a l value

^ 0.97

-35-

DISCUSSION OP RESULTS F igure d eterm in ed

I rep resen ts com positions

a p l o t of as l i s t e d

the

ex p erim en tally

i n T able

i s o t h e r m a l d i a g r a m shows t h e e x i s t a n c e o f phases:

phases.

T h e r e w as no e v i d e n c e o f t h e a d ih y d ra te

From th e

o r the

anhydrous

d ih y d ra te

o a t 30 C.

salt

K lein

1 0 5 ° C.

9

in se le n ic

acid

d ih y d ra te ,

in h is

curve

so lu tio n s to

the

d e h y d ra tio n curves

concentrations

of se le n ic

acid

in v e s tig a tio n because

ex p erim en tal d i f f i c u l t i e s

of prep arin g

ing w ith s o lu tio n s h av in g a h ig h e r s e le n ic

and w ork­

acid

com p o­

t h a n EgSeC^.HgO.

The d e n s i t y v a l u e s in F igure

II

as l i s t e d

i n T able I and p l o t t e d

showed good s h a r p b r e a k s

p o i n t s B a n d C a s was t o b e e x p e c t e d . v a l u e s may b e h e l p f u l as e x p re sse d g atio n ,

acid .

o b ta in e d a b re a k corresponding

No h i g h e r

of

i t w ould a p p e a r u n l i k e l y t h a t a

t h a n 8 6 , 2 2 % were u s e d f o r t h i s

sitio n

so lid

in the con­

to 86,22% s e l e n i c

could e x i s t

com position of the

of the

ex istan ce

s h a p e and c o m p o s i t i o n o f th e s o l u b i l i t y

f o r th e m on o h y d rate,

at

th ree

th e ir resp ectiv e u n iv arie n t liq u id

c e n t r a t i o n ra n g e from w ater

sta b le

The

N iS e 0 4 .6 H g 0 , N iSe04 .4H g0, and N iS e O ^ .lH 0 ,

in e q u ilib riu m w ith

eith er

I.

in converting

at

in v aria n t

These d e n s i t y

the c o m p o s itio n s ,

in w eight p e rc e n ta g e d u r in g

to a volum e b a s i s .

the

th is

in v esti­

-36-

T h e S ol u b i l i t y C u r v e ABC f o r N iS e 0 4 .6H g0:

The s o l u b i l i t y

wa s f o l l o w e d t h r o u g h i t s m etastab le re g io n . A-B h a s

curve o f the h e x ah y d rate

s ta b le range

of

and on i n t o

The s t a b l e p o r t i o n o f t h e

a r a n g e from p u re w ater

The s o l u b i l i t y

t h e S o l i d _Phase

curve,

t o 4 7 .2 0 /6 s e l e n i c

the h e x a h y d r a te o v e r t h i s

f r o m 2 8 . 8 7 % a t A t o 8 . 0 5 % a t B.

range v a rie s

p ractically

i d e n t i c a l w ith th e c o m p o s itio n as d e te rm in e d f o r I t was i n t e r e s t i n g

p o in t occurred f o r the su lfu ric

to n o te

th at

a t a b o u t 47% s e l e n i c

co rresponding

su lfates

acid .

The I n v a r i a n t p o i n t B

was d e t e r m i n e d b y i n t e r s e c t i o n a n d i s

14.

its

th is

Point

tran sitio n

acid ,

w hile

th at

o c c u r r e d a t a b o u t 45%

acid"*" a t 2 5 ° C.

The p o r t i o n B-C i s t h e m e t a s t a b l e r a n g e o f t h e hexah ydrate.

The i n v a r i a n t

d ire c t an aly sis

p o in t

of a so lu tio n

C was d e t e r m i n e d b y

a t e q u ilib r iu m w ith the

two s o l i d p h a s e s N iS e O ^ . b lig O a n d NISeO

.4HgO.

s o l u b i l i t y o f the m etastab le hexahydrate

The

increased

f r o m - i t s m inim um v a l u e o f 8 . 0 5 % a t B t o 9 .3 6 % a t p o i n t C where th e

sele n ic

acid

The c o l o r o f t h e

c o n c e n t r a t i o n was 5 1 . 1 8 % .

eq u ilib riu m

em erald g re e n show ing a v a r i a t i o n c o lo r w ith n ic k e l s e le n a te p ro p erties

so lu tio n s in

in ten sity

con cen tratio n .

o f th e se w ell-form ed te tr a g o n a l

b e e n l o n g known.

No e v i d e n c e o f t h e

d i m o r p h i s m was o b s e r v e d .

was of

The o p t i c a l c r y s t a l s have

existan ce

of

T h i s same c o n c l u s i o n was

-37-

reached by K lein In h is sele n ate

and w a te r*

s tu d y of th e system n ic k e l

F igure

I shows t h a t

the

w ere r e a d i l y d r a in e d o f ex c e ss m o th er l i q u o r the

co m p o sitio n of th e m oist

clo se

to

fic a n t

e f f e c t upon th e

m ost p r o b a b le v a lu e o f th e I t was n o t p o s s i b l e the ru le

th at

th an the

corresponding

is

the

stab le

p a riso n of th e

the

T h i s f a c t was s i g n i ­

accuracy in d ic a te d f o r th e

so lid phase.

t o make a n y c o r r e l a t i o n w i t h

selen ates

a r e more s o l u b l e

su lfates

sin ce the

s u lfa te under th ese

v a lu e f o r th e com position of th e

h y d rate.

first

cry stallo g rap h ic A search of th e

th eo retic al

in

r e v e a l e d no

of the d d is ta n c e s

listed fo r

Table I I gave

I n f o r m a t io n on t h e h e x a ­

literatu re

I t was i n t e r e s t i n g

seven l i n e s

A com­

III.

p revious d e te rm in a tio n h y d rate.

heotahydrate

e q u ilib riu m hydrate

The X - r a y d i f f r a c t i o n d a t a l i s t e d ad d itio n al

in w ater

co n d itio n s.

c a lc u la te d v alue w ith the

i s g i v e n i n T able

so t h a t

s o l i d p h a s e was g e n e r a l l y

t h a t of th e pure s o l i d .

in i t s

cry stals

for th is

to n o te t h a t

fiv e

th is

agreed w ith in

ex p erim en tal e r r o r w ith v alues

hydrate

recorded^

of th e

fo r n ick el

s u lf a te hexahydrate. The S o l u b i l i t y Cur v e C-D f o r t h e S o l i d P h a s e N iSe04 .4E2 0 : en tire

T h i s h y d r a t e was m e t a s t a b l e

s o lu b ility range.

The i n v a r i a n t

over i t s

po in t C is

the

-38-

poin t of in te rs e c tio n m etastab le of

of th e

so lu b ility

te tr a h y d r a te w ith th e m e ta sta b le p o rtio n

th e h e x a h y d r a te c u rv e as p r e v i o u s l y

The s o l u b i l i t y o f t h i s

in d icated .

h y d rate d ecreased from i t s

o f 9.36% a t p o i n t C t o a b o u t

8

.6 % at a sele n ic

c o n c e n t r a t i o n o f 55.6% and t h e n a value

curve f o r th e

o f 8 . 9 1 % a t p o i n t D.

value

acid

in creased s l i g h t l y

The c o l o r o f t h e

to

so lu tio n s

was e m e r a l d g r e e n a s o b s e r v e d f o r t h e h e x a h y d r a t e . I t was n o t n e c e s s a r y t o s e e d t h e s e the fo rm atio n of

the t e t r a h y d r a t e .

were r e q u i r e d f o r

these so lu tio n s

The c r y s t a l l i n e

so lu tio n s

to

induce

Less th a n te n days to re a c h e q u ilib r iu m .

p h a s e was c o m p o s e d o f s m a l l l i g h t

g r e e n c r y s t a l s w hich s e t t l e d

read ily .

E xam in atio n of

th e s e c r y s t a l s u n d e r a p o l a r i z i n g m icroscope r e v e a le d th at

the

c r y s t a l s had d e f i n i t e

low b i r e f r i n g e n c e .

o b l i q u e e x t i n c t i o n and

The c r y s t a l s

w e r e e u h e d r a l w i t h an

alm ost e q u id im e n sio n a l r e c ta n g u la r fo rm . th a t w ith in

ten o r f i f t e e n

m in u te s a f t e r m ounting th e

c r y s ta l f o r m icro sco p ic exam ination, th e cry stals

began to

change fro m th e was a l s o on t h e

slid e ,

form t h a t

become o p a q u e ,

te tra h y d ra te to

noted t h a t

if

surface

o f the

a p p a r e n t l y due to t h e the h e x a h y d r a te .

It

a n y m o t h e r l i q u o r was p r e s e n t

a f t e r a few m in u te s c r y s t a l s b e g a n t o

could be i d e n t i f i e d as

These f a c t s

made i t d i f f i c u l t

the

p lanes fo r

lattice

I t was o b s e r v e d

those of th e h ex ah y d rate.

to determ ine

th is h y d rate.

spacing

of

-39-

K lein^ p u b lis h e d

a s e m i- q u a n tita tiv e diagram f o r

th e d /n v a lu e s of th is appeared

h y d rate.

His m ost i n t e n s e

t o b e t h e 4 , 2 9 A0 l i n e

observed in t h i s

f o r th e hexahydrate o th e r v alu es tran sitio n

also

lin e stu d y

appeared to be

due to

the

stu d y ,

a b o u t tw en ty p i c t u r e s were ta k e n u s in g v a r i o u s

p recau tio n s

to th e h e x a h y d ra te .

t o make s u r e

th at

In t h i s

th e l i n e s r e p o r t e d were

th o s e due to t h e

tetrah y d rate.

d iscu ssed

s e c t i o n on e x p e r i m e n t a l p r o c e d u r e .

The v a l u e s

in the

obtained are

listed

A ddlestone^- r e p o r t e d of the

corresponding

th a t other

a m etastab le T able

III

calcu lated

of the e q u ilib riu m

have re p o rte d acid

over

M e llo r^ rep o rts it

s o lid are

to e x i s t

so lu tio n s.

and t h e o r e t i c a l

as

In

com position

com pared.

The S o l u b i l i t y C u r v e B - E f o r N iSeO ^.lH gO :

II.

a t 2 5 ° G.

phase in s u lf u r ic

the

in Table

some e v i d e n c e o f t h e p r e s e n c e

su lfate

in v estig ato rs

These t e c h n i q u e s were

th e S o l i d Phase

N i c k e l s e l e n a t e m o n o h y d r a t e was s t a b l e

the e n t i r e

range from i t s

i n v a r ia n t p o in t w ith

t h e h e x a h y d r a t e a t B to p o i n t E where th e

selen ic

acid

c o n c e n t r a t i o n was 8 6 . 2 2 % .

At p o i n t E o n l y 0.03% o f

n ickel

liq u id

of

selen ate

the' c u r v e

though the

wa s i n t h e

in th is

so lu b ility

co n cen tratio n s

concentrated of n ic k e l

of sele n ic

show a f u r t h e r d e c r e a s e .

acid

phase. range

sele n ate

Prom t h e it

shape

a o e e a r e d as

in s t i l l

h ig h er

could be e x o ected to

-40-

The c o l o r o f

t h e s e s o l u t i o n s ra n g e d from em erald

g r e e n in th e r e g i o n of p o i n t B to

a pale green

in the in te rm e d ia te

curve,

tically

co lo rle ss

range of

so lu tio n s

th is

th en to p r a c ­

i n th e r e g i o n o f p o i n t E.

E q u i l i b r i u m was r e a c h e d m uch m o r e s l o w l y f o r o f th e m onohydrate tetrah y d rates. viscous acid ;

those of th e hexa-

i n the r e g i o n fro m 7 0 t to

and

86

the

% sele n ic

in approaching e q u ilib riu m w ith s o lu tio n s

having a m e ta s ta b le wa s n e c e s s a r y t o

co m position along th e

seed th e se

m onths were r e q u i r e d f o r the hexa-

so lu tio n s

A b o u t o n e m o n t h was r e q u i r e d f o r

so lu tio n s

w hile

than f o r

so lu tio n

to

so lu tio n s

c u r v e BC , i t

ard over

two

th e c o m p lete c o n v e r s io n from

th e m onohydrate

to ta k e p la c e .

The m o n o h y d r a t e d i s s o l v e s v e r y s l o w l y i n w a t e r . was o b s e r v e d i n

the p r o c e s s

gram s o f t h e m o is t s o l i d w ith o c c a sio n a l for

the

so lid

sh ak in g , t h a t

to d i s s o l v e

scope s lid e

o r upon a g la s s

h y drate

o p tical is

less

a b o u t 24 h o u r s was r e q u i r e d

co m pletely.

could b e l e f t

w ithout d e te c tin g

to t e n

in a l i t e r v o lu m etric f la s k

m oist s o l i d

eith er

of d isso lv in g s ix

It

Sam ples o f t h i s

f o r s e v e r a l h o u r s on a m i c r o ­ fib re fo r

s e v e r a l hours

th e f o r m a tio n o f a h ig h e r h y d r a te by

or X -ray d i f f r a c t i o n so lu b le

to E th a n i s

n ick el

ing s u l f u r i c

acid

stu d ies.

over the e n t i r e

su lfa te

m onohydrate

con cen tratio n s.

T his

range from B In i t s

correspond­

-41-

As c a n b e s e e n f r o m F i g u r e

I, th e

c o m p o s itio n of

th e m o ist s o l i d phase did n o t c lo s e ly app ro ach t h a t the pure tio n

so lid .

T his

c o n trib u te d to th e

of the c a lc u la te d

from th e

th e o r e tic a l v alue as

W ith t h e more v i s c o u s was r e q u i r e d b e f o r e cien tly passed

com position fo r

for

I n some c a s e s

through a course pore

K lein^ re p o rte d t h a t

hours

in

^able

III.

a week o f s e t t l i n g

t h e two p h a s e s h ad s e p a r a t e d

sam pling.

I s f o r m e d when t h e

larg er d ev ia­

th is hyd rate

In d icated

s o l u t i o n s up t o

of

the

sin tered

su ffi­

p artic le s

g lass f i l t e r .

th e l i g h t g r e e n m onohydrate

s o lid hexahydrate

is

heated f o r f iv e

in

t h e a t m o s p h e r e a t a t e m p e r a t u r e o f 1 7 0 ° G. 10 D em assieux f o u n d no e v i d e n c e f o r i t s e x i s t e n c e i n

her h eatin g literatu re In t h i s ex ist

curve

of the h e x a h y d ra te .

r e v e a l e d no f u r t h e r

in v e stig a tio n th e

A search o f the

i n f o r m a t i o n on t h e h y d r a t e .

cry stals

were o b s e rv e d

in ag g reg ates of fin e g ra n u la r p a r tic le s

v aried

to

w hich

i n c o l o r from a p a le g r e e n to a lm o s t w h ite

in

th e c o n c e n tr a te d r e g io n s depending upon th e p a r t i c l e size .

L ittle

sharp,

c o n s i s t e n t X - ra y d i f f r a c t i o n powder p h o to g ra p h s

of th is

d ifficu lty

h yd rate.

T able

III.

those

recorded

The v a l u e s

These v a l u e s 31

w as e n c o u n t e r e d i n o b t a i n i n g

for

the

obtained

are lis te d

show a m arked

sim ilarity

corresponding

su lfa te .

in to

-42-

SUMMARY S o lu b ility system n ic k e l

and d e n s i t y m easurem ents f o r th e

sele n ate,

C. h a v e b e e n g i v e n .

sele n ic acid ,

tern ary

and w a t e r a t 3 0 °

1'he I s o t h e r m a l d i a g r a m was c o n ­

stru c te d • Over th e ran g e of sele n ic

acid ,

n ick el

were t h e o n ly s t a b l e e q u ilib riu m w ith

s o l u b i l i t y fro m w a t e r to 86.22%

s e le n a te hexahydrate s o li d p h ases found

th eir

so lu tio n s.

and m o n o h y d ra te

to e x i s t

in

The t e t r a h y d r a t e

was f o u n d to b e m e t a s t a b l e o v e r I t s

en tire

so lu b ility

range. X -ray d i f f r a c t i o n s tu d ie s determ in e to p ro v id e

the

la ttice

graphlc p ro p e rtie s

the d is tin c t

In a d d i t i o n

certain

en tity

p rep aratio n

of a h ig h p u r i t y

s e l e n a t e from n i c k e l n i t r a t e

and of

cry stallo -

were g iv e n .

A m ethod f o r t h e n ick el

to

plan e sp acin g s, d /n v alu es,

f u r t h e r p r o o f as to

th e r e p o r te d h y d r a te s .

were co n d u c te d

was g i v e n .

-43-

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