Surface of Goethite (FeOOH) in Seawater - American Chemical Society

14 Surface of Goethite (αFeOOH) in Seawater LAURIE BALISTRIERI and JAMES W. MURRAY

Downloaded by UNIV OF NORTH CAROLINA on October 1, 2014 | http://pubs.acs.org Publication Date: March 19, 1979 | doi: 10.1021/bk-1979-0093.ch014

Department of Oceanography, University of Washington, Seattle, WA

98195

The mechanism of a d s o r p t i o n has been e x t e n s i v e l y s t u d i e d i n order to evaluate i t s importance i n the r e g u l a t i o n of the c o n c e n t r a t i o n of c e r t a i n species i n n a t u r a l waters. In p a r t i c u l a r , adsorption on i r o n and manganese oxides has been proposed as the chemical mechanism which c o n t r o l s the c o n c e n t r a t i o n of some t r a c e metals i n the world's oceans ÇL, 2) and the e n r i c h ment of c e r t a i n t r a c e metals i n ferromanganese nodules ( 3 ) . The most commonly reported s o l i d forms of i r o n and manganese oxides i n marine sediments and ferromanganese nodules are g o e t h i t e (aFeOOH) and hydrous manganese d i o x i d e ( b i r n e s s i t e , t o d o r o k i t e and 6Mn0 ) (4, .5, 6). The surface chemistry of hydrous manganese d i o x i d e has been p r e v i o u s l y reported Ç7, j8, 9 ) . As an extension of that work we have i n v e s t i g a t e d the surface p r o p e r t i e s of g o e t h i t e (aFeOOH). The primary concerns of t h i s work are to evaluate the e f f e c t of the major ions of seawater on the t i t r a t a b l e charge of aFeOOH and to q u a n t i t a t i v e l y evaluate the c a p a c i t y of the s o l i d f o r these i o n s . Various t h e o r i e s have been proposed to d e s c r i b e and i n t e r pret the a d s o r p t i o n of metal ions at hydrous oxide i n t e r f a c e s (10). Most models have s t r e s s e d e i t h e r the double l a y e r s t r u c t u r e and i o n - s o l v e n t i n t e r a c t i o n s (11, 12, 13) or surface c o o r d i n a t i o n r e a c t i o n s w i t h amphoteric f u n c t i o n a l groups (14, 15, 16). Recently Davis e_t _al. (17) and Davis and L e c k i e (18, 19) have proposed a comprehensive model that combines both of these approaches. No attempt has been made, however, to model surface i n t e r a c t i o n s or to d e s c r i b e the d i s t r i b u t i o n of surface species i n a complex n a t u r a l water such as seawater. We present here experimentally determined a c i d i t y constants and b i n d i n g constants of Na , K+, C a , M g , C l ~ and SO4 w i t h g o e t h i t e . With these data we can now c a l c u l a t e the d i s t r i b u t i o n of the major species on the surface of g o e t h i t e i n seawater. This approach w i l l form the b a s i s f o r modeling t r a c e metal a d s o r p t i o n i n seawater and determining the competitive e f f e c t s of the major ions w i t h each other and w i t h trace metals. 2

+

+ 2

+2

0-8412-0479-9/79/47-093-275$06.00/0 © 1979 American Chemical Society In Chemical Modeling in Aqueous Systems; Jenne, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

276

CHEMICAL MODELING IN AQUEOUS SYSTEMS


Methods Goethite was synthesized according t o the method of A t k i n s o n et a l . (20). Goethite forms a f t e r the h y d r o l y s i s and aging o f f e r r i c n i t r a t e or p e r c h l o r a t e s o l u t i o n s and c o n s i s t s o f double chains of l i n k e d [Fe(0,0H)e ] octahedra. The double chains a r e f u r t h e r c r o s s l i n k e d to adjacent double chains through corner sharing of oxygen atoms to give orthorhombic symmetry ( 6 ) . The oxide was s t o r e d i n d i s t i l l e d , d e i o n i z e d water around pH 7.5. The oxide was i d e n t i f i e d by the occurrence o f major peaks a t 4.18, 2.69, and 2.44 A (Cu r a d i a t i o n w i t h curved c r y s t a l monochrometer) i n the X-ray d i f f r a c t i o n p a t t e r n ( 6 ) . The surface area was 48.5 + 0.2 m g" as determined by N a d s o r p t i o n by the B.E.T. method (21). SEM p i c t u r e s o f the oxide revealed needleshaped c r y s t a l s approximately 1 micron i n l e n g t h and 0.2 microns wide. The value f o r the t o t a l surface s i t e s (FeOf) was taken from Y a t e s (22) work on aFeOOH. Yates (22) determined FeO^ t o be equal to 27.8 μιηοΐ m by t r i t u m exchange. F u r t h e r d e t a i l s of the s o l i d ' s p r e p a r a t i o n , i d e n t i f i c a t i o n , and b a s i c surface c h a r a c t e r i s t i c s can be found i n B a l i s t r i e r i (23). P o t e n t i o m e t r i c t i t r a t i o n s were done i n v a r i o u s concentra t i o n s of NaCl, KC1, MgCl2, CaCl2, and Na S0i+. I n a d d i t i o n , t i t r a t i o n s were done i n mixed e l e c t r o l y t e s o l u t i o n s o f d i f f e r e n t i o n i c s t r e n g t h c o n t a i n i n g the major ions o f seawater i n t h e i r a p p r o p r i a t e seawater p r o p o r t i o n s (24). P o t e n t i o m e t r i c t i t r a t i o n s i n v o l v e measuring the amount o f a c i d which i s consumed or r e l e a s e d by the s o l i d as a f u n c t i o n o f pH. For a given pH, t h i s i s e x p e r i m e n t a l l y accomplished by determining the e q u i v a l e n t s o f a c i d consumed o r r e l e a s e d by the s o l i d i n a supporting e l e c t r o l y t e and s u b t r a c t i n g from that the e q u i v a l e n t s of a c i d consumed or r e l e a s e d only by the supporting e l e c t r o l y t e s o l u t i o n . Care must be taken t o keep the system f r e e of C 0 . Further d e s c r i p t i o n o f the experimental procedures f o r p o t e n t i o m e t r i c t i t r a t i o n s can be found elsewhere (25, _26, 27_, 28) . The amount of a c i d consumed or r e l e a s e d by the s o l i d v a r i e s w i t h the i o n i c s t r e n g t h of the supporting e l e c t r o l y t e and the pH of the s o l u t i o n . The pH a t which the a d s o r p t i o n d e n s i t y of the s o l i d i s independent o f the i o n i c s t r e n g t h i s termed the pH(PZC) or the pH p o i n t of zero charge (10). The charge as a f u n c t i o n of pH i s c a l c u l a t e d r e l a t i v e to the pH(PZC). 2

1

2

1

2

2

2

I n t e r p r e t a t i o n o f P o t e n t i o m e t r i c T i t r a t i o n s f o r aFeOOH i n a Single Electrolyte Solution The t i t r a t a b l e s u r f a c e charge measurements can be i n t e r preted t o give a q u a n t i t a t i v e assessment o f the i n t e r a c t i o n s between the s o l i d and the supporting e l e c t r o l y t e i o n s . Poten t i o m e t r i c t i t r a t i o n s measure the a d s o r p t i o n or r e l e a s e o f protons and the model developed by Yates e t a l . (29) and Davis et a l . (17) proposes r e a c t i o n s between oxide surface groups and

In Chemical Modeling in Aqueous Systems; Jenne, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

14.

277

Surface of Geothite

B A L i s T R i E R i AND MURRAY

supporting e l e c t r o l y t e ions which account f o r t h i s measured proton change. According to t h e i r model the measured surface charge i s a r e s u l t o f the i o n i z a t i o n of the surface f u n c t i o n a l groups (Equation 1 and 2) κϊ

Ν Τ

Fe-OHo

+

Fe-OH 4- H

z

(1)

s


INT 2 +

Fe-OH

Fe-0 + H

(2) s and the i n t e r a c t i o n o f supporting e l e c t r o l y t e ions w i t h the oxide surface (Equation 3 and 4) ΛΚ

Fe-OH 4- c a t i o n s

ΙΝΤ cation ^

+

Fe-OH + a n i o n

g

+ H

g

* κ

^

F e

_ _ 0

c a t i o r i

+

(3)

H

s

Ι Ν Τ l

o

n

Fe-0H -anion . 2

(4)

The s u b s c r i p t s denotes i s o l a t e d ions on the s u r f a c e . The i n t r i n s i c e q u i l i b r i u m constants ( K ) are determined a t zero charge and p o t e n t i a l c o n d i t i o n s , thereby e l i m i n a t i n g the electrostatic field effects. The i n t e r a c t i o n of a c a t i o n w i t h a n e u t r a l oxide group r e s u l t s i n the r e l e a s e of a proton, w h i l e the a s s o c i a t i o n of an anion r e s u l t s i n the adsorption of a proton. A c c o r d i n g l y , the formation of a negative s i t e from a n e u t r a l s i t e i n v o l v e s the r e l e a s e of a proton and the formation of a p o s i t i v e s i t e i n v o l v e s the a d s o r p t i o n of a proton. Therefore, the t i t r a t a b l e surface charge determined by p o t e n t i o m e t r i c t i t r a t i o n i s a measure of both the formation of s u r f a c e - i o n complexes and the i o n i z a t i o n of surface f u n c t i o n a l groups, and I N

σ

F [{FeOHt} + ΣΧ η

ο

{FeOHt - anion } - {FeO } -

n

n

ΣΥ {FeO~ - c a t i o n }] m m

(5)

m

where O F { X

2

= t i t r a t a b l e surface charge i n ycoul cm" = Faraday's constant } = s u r f a c e species c o n c e n t r a t i o n i n mol cm = number of protons consumed by the formation of an i n d i v i d u a l anion complex Y = number of protons released by the formation of an i n d i v i d u a l c a t i o n complex q

2



278


Σ = summation of a l l anion complexes η Σ = summation o f a l l c a t i o n complexes . m The i n t r i n s i c constants are thermodynamic constants w r i t t e n for r e a c t i o n s o c c u r r i n g a t a h y p o t h e t i c a l i s o l a t e d s i t e on the s u r f a c e . A c t u a l a c t i v i t i e s on the surface cannot be d i r e c t l y determined but Q o r apparent s t a b i l i t y q u o t i e n t s can be c a l c u l a t e d based on measurable bulk c o n c e n t r a t i o n s . The i n t r i n s i c constants and apparent s t a b i l i t y q u o t i e n t s are r e l a t e d by con s i d e r i n g the e l e c t r o s t a t i c c o r r e c t i o n f o r an i o n i n s o l u t i o n near the surface compared t o an i s o l a t e d i o n on the s u r f a c e . I n an i d e a l i z e d planar model, Ψ i s the mean p o t e n t i a l a t the plane of s u r f a c e charge created by the i o n i z a t i o n o f the s u r f a c e f u n c t i o n a l groups and the formation o f surface complexes and Ψ i s the mean p o t e n t i a l a t the plane o f adsorbed counter ions a t a d i s t a n c e $ from the surface (17). The e l e c t r o s t a t i c i n t e r a c t i o n energies a t the surface and a t a d i s t a n c e β are expressed as ex ponentials. Therefore: ο

β

+

+

(H ) [cation] [anion]

s

= (H ) exp (-βΨ /kT) ο

(6)

s

= [ c a t i o n ] exp (-εΨ /Μ) ρ

(7)

s

= [anion] exp (εΨ /Μ) ρ

(8)

0

σ

e = e l e c t r o n i c charge Ψ , Ψβ = mean p o t e n t i a l s k = Boltzmann constant Τ - temperature The e q u i l i b r i u m constants which d e f i n e Equations 3 and 4 may t h e r e f o r e be w r i t t e n as: ο

+

+

_ {Fe-O~cation} (H ) {Fe-cfcation} (H ) ^«IJNl _ s_ cation {Fe-OH} [ c a t i o n ] ^ {Fe-OH} [ c a t i o n ] T M

([

β Ψ β

- Ψ ]/ΚΓ) = * Q β

5

β

p

o

(9)

{Fe-OH^ anion}

Ι Ν Τ

anion

X

exp ([βΨ - eΨ ]/kT)

c a t i o n

{Fe-OH* anion} * κ

e

exp +

{Fe-OH} [anion] (H ) s s ([ ψ

+

{Fe-OH} [ a n i o n ] ( H )

- β Ψ ] / Μ ) = *Q . exp ([βΨ - β Ψ ] / Κ ) (10) ρ anion ο ρ -2 { } = c o n c e n t r a t i o n i n mol cm [ ] = c o n c e n t r a t i o n i n mol Ι" ( ) = a c t i v i t y i n mol l " * INT Κ = i n t r i n s i c e q u i l i b r i u m constant *Q = apparent s t a b i l i t y q u o t i e n t The apparent s t a b i l i t y q u o t i e n t s are determined by u t i l i z ing the p o t e n t i o m e t r i c t i t r a t i o n data and the value f o r the β

ο

β

Λ

β

2

2


Surface

B A L i s T R i E R i AND MURRAY

14.

of

279

Geothite

t o t a l surface s i t e s (FeO ). The procedure w i l l be i l l u s t r a t e d by c o n s i d e r i n g aFeOOH i n NaCl. I n t h i s case, T

a

+

Q

= FfiFeOHÎj + {FeOH^Cl"} - {FeO~} - {FeO~Na }]

(11)

and +

FeO = F[{FeOH2> + { F e O H t c O + {FeOH} + {FeO"} + {FeO""Na }]. (12)


T

At h i g h e r e l e c t r o l y t e concentrations the dominant c o n t r i b u t i o n t o the surface charge i s the formation of surface complexes. For a negative surface (pH > pH(PZC)) and f o r values of pH away from the pH(PZC), the surface charge i s approximated by the formation of c a t i o n complexes, i . e . , +

σ fts - F{FeO~Na }. ο In terms of f r a c t i o n a l i o n i z a t i o n t h i s i s w r i t t e n as:

(13)

Under these c o n d i t i o n s the n e u t r a l s i t e s can be approximated as the t o t a l s i t e s minus the c a t i o n surface complexes, i . e . , F e 0

T

-

+

{FeOH} Λ — j r ^ - {FeO Na }

1 - α

r

.

—

(15)

Using these approximations the apparent s t a b i l i t y q u o t i e n t f o r Na i s : +

(H ) (1 - α ) [Na ]

*%0^ determined as d e s c r i b e d e a r l i e r using the t i t r a t i o n data of g o e t h i t e i n the i n d i v i d u a l e l e c t r o l y t e s a t a given pH and a t the c o n c e n t r a t i o n o f the s p e c i f i c i o n i n seawater, r a t h e r than at the i o n i c s t r e n g t h o f seawater. Thus i n these c a l c u l a t i o n s we neglect the e f f e c t o f i o n i c s t r e n g t h on the constant. We a l s o assume that the a c t i v i t y c o e f f i c i e n t s f o r the surface s i t e s are equal t o one. These appear to us to be s e r i o u s d e f i c i e n c i e s i n the present c a l c u l a t i o n s and i n a f i n a l model they w i l l have to be c o r r e c t e d . As w i l l be shown, however, the agreement between measured and c a l c u l a t e d charge i s q u i t e good i n s p i t e o f these d e f i c i e n c i e s . The concentrations of the f r e e ions i n the mixed e l e c t r o l y t e were c a l c u l a t e d by c o n s i d e r i n g the formation of 2

(

Q

Q

w

2

e

r

e


290


0

0

s o l u t i o n complexes (MgSO^ , CaSOi* , NaS0 ", KSOi*-) (33). The t i t r a t a b l e charge i s mathematically r e l a t e d to the surface species d i s t r i b u t i o n s (Equation 27). 4

a

Q

= F [2{FeOH2 - HSO^}

+

+ {FeOH^Cl"} + {Fe-OH*} - {Fe-0~Na }

+

+

_

+


- {Fe0~K } - 2 {FeO"MgOH } - 2 {Fe0 Ca0H } - {FeO~}]

(27)

Table I I i s a summary of the surface species d i s t r i b u t i o n s w i t h pH. These were used to c a l c u l a t e a t i t r a t a b l e charge. The e f f e c t of the i o n i z e d surface species (FeO~ and FeOHj) on the t i t r a t a b l e charge and surface species d i s t r i b u t i o n s i s l e s s than the e f f e c t of the potassium complexes. A l s o i n c l u d e d i n Table I I are the % c o n t r i b u t i o n s of the i n d i v i d u a l complexes to the t o t a l c a l c u l a t e d charge. In Figure 7 the c a l c u l a t e d charge i s compared w i t h the t i t r a t a b l e charge determined by the p o t e n t i o m e t r i c t i t r a t i o n of aFeOOH i n a major seawater i o n e l e c t r o l y t e . A l s o i n c l u d e d i n F i g u r e 7 i s a c o m p i l a t i o n of the t i t r a t i o n data used i n determining the c a l c u l a t e d charge. Discussion An examination of the p o t e n t i o m e t r i c t i t r a t i o n data of g o e t h i t e i n the i n d i v i d u a l e l e c t r o l y t e s o l u t i o n s permits a q u a l i t a t i v e assessment of the s o l i d s c a p a c i t y f o r the major ions of seawater. In more concentrated e l e c t r o l y t e s o l u t i o n s the charge p r i m a r i l y represents the formation of surface complexes and the magnitude of the charge i s i n d i c a t i v e of the amount or s t r e n g t h of complexation. There are two observations to be made of the p o t e n t i o m e t r i c t i t r a t i o n data of g o e t h i t e . F i r s t , the absolute magnitude of the charged s i t e s i n the pH range of 4 to 9.5 does not exceed 5.7 mol cm" of s o l i d . The t o t a l surface s i t e s are 27.8 mol cm of s o l i d and, t h e r e f o r e , the n e u t r a l Fe-OH s i t e s are the dominant surface s i t e s r a t h e r than the g o e t h i t e - major seawater i o n complex s i t e s . Second, the absolute magnitude of the charges of g o e t h i t e i n the i n d i v i d u a l e l e c t r o l y t e s suggests that Mg and S0i+ b i n d more s t r o n g l y than Na, K, Ca or CI. To gether these observations suggest the f o l l o w i n g order f o r the s t r e n g t h of i o n - b i n d i n g w i t h g o e t h i t e : 2

2

H >> Mg - S0/+ > Ca > C l ~ Na * Κ + 2

+ 2

The sequence of M g > Ca i s the reverse of the normal a f f i n i t y sequence (Hofmeister s e r i e s ) which i s observed on most c l a y s and on Mn0 . The observed sequence on aFeOOH i s that expected when i n t e r a c t i o n s between the adsorbed ions and the surface s i t e s are greater than h y d r a t i o n e f f e c t s (31). In an i d e a l i z e d planar model, o i s the charge at the o x i d e s surface caused by the i o n i z a t i o n of the surface f u n c t i o n a l groups and the formation of the surface complexes. This i s x

Q

!


14. BALisTRiERi

Surface of Geothite

AND MURRAY

TABLE I I


D i s t r i b u t i o n o f Surface Species on Goethite i n Seawater as a Function of pH PH % Sites FeOH

5

6

7

8

97.2

96.7

94.9

92.5

1.8

6.7

8.1

—

—

—

0.7

1.8

—

—

—

—

1.5

—

—

—

—

0.8

2.7

1.6

0.7

0.1

—

14.5

-0.1

FeO" MgOH

—

FeO" CaOH

+

FeO" N a FeO~ K

+

FeOH* HSO^ Calculated"'" Charge (ycoul cm" ) 2

87.7

4.4

+

+

9

-19.9

-38.8

-59.5

PH 2 % Charge FeO~ MgOH FeO~~ CaOH FeO~ N a FeO~" K

5

+

—

+

—

+

+

7

8

52.9

86.1

88.7

73.4

9.3

16.0

—

—

(100)

9

6.8

—

—

FeOH* HSO^

6

—

—

(47.1) (13.9)

—

(2.0)

3.7 —

C a l c u l a t e d (or net) charge i s sum o f negative and p o s i t i v e charge ( ) i n d i c a t e the % c o n t r i b u t i o n o f p o s i t i v e charge to the t o t a l absolute charge




292

0.5M

Ν α

0.5M

CI

0.0 5 4

M

«

M g

0.02 8 M 0.01

M

F e 0 0

Η

- *

S 0

Ο •Wo"

4

Ca

seawater type electrolyte m o d e l prediction

° β

-* Ο

40

+

7 Ρ

Figure trolyte

7. Calculated and measured and compilation of titration

Η

10

charge for goethite in a seawater-type data used to obtain the calculated


elec charge

In Chemical Modeling in Aqueous Systems; Jenne, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979. 2

2

MgCl CaCl

KC1 Mg(N0 ) Ca(N0 ) NaN03 NaCl

aFe203

aFe2Û3

aFe2Û3

am. Fe(0H)3

3Fe00H

Breeuswma e t a l . (37)

Davis e t a l . (18)

Murray (39)

2

Na SO

3

3

2

8.1

pH 9, 0.1 M NaCl

pH 9, 0.1 M NaN0

3

pH 9, 0.05 M C a ( N 0 )

6.5 7.9

2

pH 9, 0.05 M M g ( N 0 ) 3

2

pH 9, 0.1 M KC1

6.5

1+

8.5

2

K2S0n.

KNO3

8.5

M

pH 6, 10" M Na S0

3

10- M

pH 6,

8.1 3

0.1

pH 9,

7.5

3

2

pH 9, 0.05 M C a C l

7.1

NaCl, KC1

aFeOOH

Present work

2

2

pH 9, 0.05 M M g C l

5.0

K^SO^

aFeOOH

Lt

pH 9, 0.1 M NaCl/KCl

7.5

KN0

aFeOOH

Yates e t a l . (34) 3

NaCl

aFeOOH

Hingston e_t aJL. (35)

pH 9, 0.1 M NaCl

pH 9, 0.1 M KC1

9.2

KC1

aFe2Û3 7.7

PH 9, 0.1 M KC1

7.5

KC1

A t k i n s o n ej: a l . (20)

aFeOOH

References

Comparison of Various Forms of I r o n Oxide Condition pH(PZC) Salt S o l i d Phase

TABLE I I I


294


the charge measured by p o t e n t i o m e t r i c t i t r a t i o n . In a d d i t i o n , there i s the plane of adsorbed counter-ions and i s the charge caused by the presence of these i o n s . The ions i n the d i f f u s e part of the double l a y e r "see" the combined e f f e c t of and σ^. Therefore the s h i f t i n the pH(PZC) to 5.5 f o r g o e t h i t e i n sea water and the corresponding high negative charge (-36.2 y c o u l cm ) at pH 8 determined by p o t e n t i o m e t r i c t i t r a t i o n cannot be used to evaluate g o e t h i t e s e l e c t r o s t a t i c i n f l u e n c e on ions i n seawater. A comparison of our r e s u l t s w i t h other i n v e s t i g a t o r s ' work on g o e t h i t e and other forms of i r o n oxides i s shown i n Table I I I . Atkinson et_ a l . (20), Yates et a l . (34) and our work on aFeOOH i n d i c a t e e x c e l l e n t agreement f o r pH(PZC) and charge i n the appropriate e l e c t r o l y t e s o l u t i o n s . Hingston et a l . (35) charge data f o r g o e t h i t e tend to be higher i n magnitude. Davis et_ a l . (17) c a l c u l a t i o n s f o r p K * , p K ^ , v*K^ f o r g o e t h i t e agree very w e l l w i t h our r e s u l t s f o r g o e t h i t e . A comparison of the aFe 03, aFeOOH, 3FeOOH and am. Fe(0H)3 data i n d i c a t e s s i m i l a r i t i e s i n the values of the pH(PZC). This c o n t r a s t s w i t h the r e s u l t s of Healy et a l . (36) f o r manganese oxides where the values f o r the pH(IEP)(pH of the i s o e l e c t r i c p o i n t ) as d e t e r mined by e l e c t r o p h o r e s i s ranged from pH 1.5 f o r σ-Μηθ2, pH 1.8 f o r Mn(II) manganite, pH 4.5 f o r αΜη0 , pH 5.5 f o r γ-Μηθ2, to pH 7.3 f o r 3-Mn0 . Breeuwsma and workers (27, 37, 38) found the reverse Hofmeister s e r i e s f o r aFe 03 and i n a d d i t i o n Mg adsorbed much stronger than Ca. Our data on g o e t h i t e i n d i c a t e the same c o n c l u s i o n s . However, the values of the pH(PZC) f o r aFeOOH i n Mg and Ca s o l u t i o n s were 5.0 and 7.1, r e s p e c t i v e l y , w h i l e f o r a F e 0 pH(PZC) was 6.5 i n both Mg and Ca s o l u t i o n s . 2


1

NT

NT

2

2

2

2

2

3

Conclusions A q u a n t i t a t i v e assessment of i o n - b i n d i n g w i t h g o e t h i t e was obtained from an a p p l i c a t i o n of the Davis et: a l . (17), James ejt a l . (30) and Davis and L e c k i e (19) model to p o t e n t i o m e t r i c t i t r a t i o n data. By comparison w i t h s o l u t i o n complex e q u i l i b r i u m constants, the i n t r i n s i c constants f o r the a s s o c i a t i o n of Na, K, and CI w i t h charged aFeOOH s i t e s (Equations 12, 13 and 17 of Table I) i n d i c a t e p r i m a r i l y e l e c t r o s t a t i c i n t e r a c t i o n s . The a s s o c i a t i o n s of Mg, SO^, and Ca w i t h charged g o e t h i t e s i t e s suggest stronger or more s p e c i f i c bonds. The s i m p l i f i e d mass and proton balance model determined what the surface species d i s t r i b u t i o n of g o e t h i t e would be i n a mixed, seawater type e l e c t r o l y t e . This surface species d i s t r i b u t i o n was used to c a l c u l a t e a surface charge f o r g o e t h i t e . T h i s c a l c u l a t e d surface charge s u c c e s s f u l l y p r e d i c t e d the t i t r a t a b l e surface charge, as determined by p o t e n t i o m e t r i c t i t r a t i o n , of g o e t h i t e i n a seawater major-ion e l e c t r o l y t e (Figure 7 ) . These surface species d i s t r i b u t i o n s i n d i c a t e that Fe-OH s i t e s are the primary s i t e s and that the formation of Mg and SO4


14.

BALisTRiERi AND MURRAY

Surface

of

Geothite

295

complexes w i t h g o e t h i t e account f o r the formation o f the m a j o r i t y of the charge (Table I I ) .

Abstract Potentiometric titrations of goethite (αFeOOH) have been performed in various concentrations of NaCl, KCl, MgCl , CaCl , and a mixed electrolyte containing the major ions of seawater in their seawater proportions. From this data we have calculated apparent stability quotients. A method of double extrapolation has been used to calculate intrinsic acidity and surface complex equilibrium constants. Using these constants we calculate the titratable charge and surface species distribution of goethite in seawater. At pH 8 the calculated charge is -38.8 μcoul cm and 90% of the titratable charge.is due to FeO¯MgOH surface complexes. The calculated charge over the pH range 5-9 is in excellent agreement with the measured charge in the seawater type electrolyte. 2

Na SO


2

4

2

-2

+

Literature Cited 210

226

1. Bacon, M. P., Spencer, D. W., and Brewer, P. G., Pb/ Ra and Po/ Pb disequilibria in seawater and suspended particulate matter. Earth Planet. Sci. Lett. 32, 277-296 (1976). 2. Boyle, Ε. Α., Edmond, J . M., and Sholkovitz, E. R., The mechanism of iron removal in estuaries. Geochim. Cosmochim. Acta 41, 1313-1324 (1977). 3. Murray, J . W. and Brewer, P. G., The mechanisms of removal of iron, manganese, and other trace metals from sea water. p. 291-326 in Glasby, G. P., ed., "Marine Manganese Deposits," Elsevier, Amsterdam, 1977. 4. Dymond, J., Corliss, J . B., Heath, G. R., Field, C. W., Dasch, E. J., and Veeh, H., Origin of metalliferous sediments from the Pacific Ocean. Bull. Geol. Soc. Am. 84, 3355-3372 (1973). 5. Heath, G. R. and Dymond, J., Genesis and transformation of metalliferous sediments from the East Pacific Rise, Bauer Deep, and Central Basin, Northwest Nazca Plate. Bull. Geol. Soc. Am. 88, 723-733 (1977). 6. Burns, R. G. and Burns, V. Μ., Mineralogy of ferromanganese nodules. p. 184-248 in Glasby, G. P., ed., "Marine Manganese Deposits," Elsevier, Amsterdam, 1977. 7. Murray, J . W., "The Interaction of Metal Ions at the Hydrous Manganese Dioxide-Solution Interface." Ph.D. Thesis, Mass. Inst, of Tech.-Woods Hole Ocean. Inst., 1973. 8. Murray, J . W., The interaction of ions at the manganese dioxide-solution interface. Geochim. Cosmochim. Acta 39, 505-519 (1975). 210

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9. Murray, J . W., The interaction of cobalt with hydrous manganese dioxide. Geochim. Cosmochim. Acta 39, 635-647 (1975). 10. Parks, G. Α., Adsorption in the marine environment, p. 241308 in Riley, J . P. and Skirrow, G., ed., "Chemical Oceanography," Vol. 1, Academic Press, New York, 1975. 11. James, R. O. and Healy,T. W., Adsorption of hydrolyzable metal ions at the oxide-water interface. I. Co(II) adsorption on SiO and TiO as model systems. J . Coll. Interface Sci. 40(1), 42-52 (1972). 12. James, R. O. and Healy, T. W., Adsorption of hydrolyzable metal ions at the oxide-water interface. II. Charge reversal of SiO and TiO colloids by adsorbed Co(II), La(III), and Th(IV) as model systems. J . Coll. Interface Sci. 40(1), 53-64 (1972). 13. James, R. O. and Healy, T. W., Adsorption of hydrolyzable metal ions at the oxide-water interface. III. A thermo dynamic model of adsorption. J . Coll. Interface Sci. 40(1), 65-81 (1972). 14. Stumm, W., Huang, C. P. and Jenkins, S. R., Specific chemical interaction affecting the stability of dispersed systems. Croatica Chem. Acta 42, 223-245 (1970). 15. Schindler, P. W., Furst, Β., Dick, R., and Wolf, P. U., Ligand properties of surface silanol groups. I. Surface complex formation with Fe , Cu , Cd , and Pb . J. Coll. Interface Sci. 55(2), 469-475 (1976). 16. Stumm, W., Hohl, H . , and Dalang, F . , Interaction of metal ions with hydrous oxide surfaces. Croatica Chem. Acta 48(4), 491-504 (1976). 17. Davis, J . Α., James, R. O., and Leckie, J . O., Surface ionization and complexation at the oxide-water interface. 1. Computation of electrical double layer properties in simple electrolytes. J . Coll. Interface Sci. 63(3), 480499 (.1978). 18. Davis, J . and Leckie, J . O., Surface ionization and complexa tion at the oxide-water interface. 2. Surface properties of amorphous iron oxyhydroxide and adsorption of metal ions. J . Coll. Interface Sci. (in press) 19. Davis, J . A. and Leckie, J . O., Speciation of adsorbed ions at the oxide/water interface. Adv. Chem. Series, (in press). 20. Atkinson, R. J., Posner, Α. Μ., and Quirk, J . P., Adsorption of potential-determining ions at the ferric oxide-aqueous electrolyte interface. J . Phys. Chem. 71(3), 550-558 (1967). 21. Brunauer, S., Emmett, P. H . , and Teller, E . , Adsorption of gases in multimolecular layers. J . Amer. Chem. Soc. 60, 309-319 (1938). 22. Yates, D. E., "The Structure of the Oxide/Aqueous Electrolyte Interface." Ph.D. Thesis, Univ. of Melbourne, 1975.


2

2

2

2

3+

2

2+

2+



14. BALisTRiERi

Surface of Geothite

AND MURRAY

297

23. Balistrieri, L. S., "The Basic Surface Characteristics of Goethite (αFeOOH)." M.S. Thesis, Univ. of Washington, Seattle, 1977. 24. Wilson, T. R. S., Salinity and the major elements of seawater. p. 365-413 in Riley, J . P. and Skirrow, G., ed., "Chemical Oceanography," Vol. 1 (2nd Ed.), Academic Press, New York, 1975. 25. Parks, G. A. and deBruyn, P. L., The zero point of charge of oxides. J . Phys. Chem. 66, 967-972 (1962). 26. Blok, L. and de Bruyn, P. L., The ionic double layer at the ZnO/solution interface. I. The experimental point of zero charge. J . Coll. Interface Sci. 32(3), 518-526 (1970). 27. Breeuwsma, A. and Lyklema, J., Physical and chemical ad sorption of ions in the electrical double layer on hematite (αFe 0 ). J . Coll. Interface Sci. 43(2), 437448 (1973), 28. Huang, C. P. and Stumm, W., Specific adsorption of cations on hydrous γ - Α l O . J . Coll. Interface Sci. 43(2), 409420 (1973). 2

3

2

3

29. Yates, D. E., Levine, S., and Healy, T. W., Site binding model of the electrical double layer at the oxide/water interface. J . Chem. Soc. London Faraday Trans. 1, 70, 1807-1818 (1974). 30. James, J . O., Davis, J . Α., Leckie, J . O., Computer simulation of the conductometrie and potentiometric titra tions of the surface groups on ionizable latexes. J . Coll. Interface Sci. 65(2), 331-344 (1978). 31. Stumm, W. and Morgan, J . J., "Aquatic Chemistry," 583 pp., Wiley-Interscience, New York, 1970. 32. Westall, J . C., Zachary, J . L., and Morel., F. Μ. Μ., MINEQL, a computer program for the calculation of chemical equilibrium composition of aqueous systems. Water Qual. Lab., Tech. Note No. 18, Dept. of Civil Eng., Mass. Inst, of Tech., Cambridge, 1976, 33. Garrels, R. M. and Thompson, M. E., A chemical model for sea water. Amer. J . Sci. 260, 57-66 (1962). 34. Yates, D. E. and Healy, T. W., Mechanism of anion adsorption at the ferric and chromic oxide/water interfaces. J . Coll. Interface Sci. 52(2), 222-228 (1975). 35. Hingston, F. J., Posner, Α. Μ., and Quirk, J . P., Adsorption of selenite by goethite. Adv. Chem. Series 79, 82-90 (1968). 36. Healy, T. W., Herring, A. P., and Fuerstenau, D. W., The effect of crystal structure on the surface properties of a series of manganese oxides. J . Coll. Interface Sci. 21, 435-444 (1966).


298

CHEMICAL

MODELING

IN AQUEOUS

SYSTEMS

37.

Breeuwsma, A. and Lyklema, J., Interfacial e l e c t r o c h e m i s t r y of hematite ( α - F e O ) . D i s c . Farad. Soc. 52, 324-333 (1971). 38. Breeuwsma, Α., "Adsorption of ions on hematite ( α - F e O ) . " Ph.D. T h e s i s , Agricultural Univ., Wageningen, Netherlands, 1973. 39. Murray, J. W., βFeOOH i n marine sediments. Ε S 59, 411-412 [Abstract] (1978). 2

3

2

November 16,

1978.


RECEIVED


3

Surface of Goethite (FeOOH) in Seawater - American Chemical Society

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