P sorption P sorption Characteristics On Co-Characteristics On Co-

precipitated precipitated Amorphous Amorphous

Al-Fe Hydr(oxides)Al-Fe Hydr(oxides)

Omar Richard HarveyOmar Richard Harvey

RationaleRationale

P sorption capacity strongly correlated with P sorption capacity strongly correlated with Al and Fe hydr(oxide) contentAl and Fe hydr(oxide) content in soils (Freese in soils (Freese et al. 1992) and wetlands (Reddy et al. 1995).et al. 1992) and wetlands (Reddy et al. 1995).

Mixed hydr(oxides)Mixed hydr(oxides) more common than pure more common than pure phases in nature.phases in nature.

0-100 mol% Al0-100 mol% Al found. >40 mol% Al common in found. >40 mol% Al common in sandy soils.sandy soils.

Co-precipitationCo-precipitation, sequential precipitation and , sequential precipitation and agglomeration are expected events in aquatic agglomeration are expected events in aquatic systems (Anderson et al. 1990).systems (Anderson et al. 1990).

Properties depends on formation conditions such Properties depends on formation conditions such as metal conc. in solution and pH. as metal conc. in solution and pH.

ObjectivesObjectives GeneralGeneral To determine the effect of Al content on P To determine the effect of Al content on P

sorption in co-precipitated amorphous Al-Fe sorption in co-precipitated amorphous Al-Fe hydr(oxide) systems.hydr(oxide) systems.

Task 1.Task 1. - To synthesize and characterize the hydr(oxides) - To synthesize and characterize the hydr(oxides)

based on chemical and physical propertiesbased on chemical and physical properties Task 2.Task 2. - To determine P sorption characteristics on all - To determine P sorption characteristics on all

hydr(oxides) including the energetics and hydr(oxides) including the energetics and sorption as a function of time, pH and Al content sorption as a function of time, pH and Al content

Task 3.Task 3. - Use properties of hydr(oxides) to explain - Use properties of hydr(oxides) to explain

differences in P sorption characteristics differences in P sorption characteristics

Task 1.Task 1.

Hydr(oxide) Synthesis and Hydr(oxide) Synthesis and CharacterizationCharacterization

SynthesisSynthesis Al-Fe hydr(oxides) Al-Fe hydr(oxides)

containing 0, 9, 17, containing 0, 9, 17, 33, 50, 67, 83, 91 and 33, 50, 67, 83, 91 and 100 mol% Al.100 mol% Al.

Co-precipitation from Co-precipitation from Al and Fe chloride Al and Fe chloride solution at pH 6.5-7.0 solution at pH 6.5-7.0 by titration with by titration with NaOHNaOH

Precipitate washed, Precipitate washed, dried at 70◦C, crushed dried at 70◦C, crushed and sieved (150 and sieved (150 μμm).m).

mol% Al used mol% Al used interchangeably with interchangeably with Al:Fe molar ratio.Al:Fe molar ratio.

CharacterizationCharacterization Chemical compositionChemical composition - Metal content ( Al and total)- Metal content ( Al and total) - Acid digestion /atomic absorption- Acid digestion /atomic absorption

Physical propertiesPhysical properties - XRD: structure of hydr(oxides)- XRD: structure of hydr(oxides) - SEM : morphology and distribution of Al and - SEM : morphology and distribution of Al and

Fe in particlesFe in particles - PSD (Particle Size Distribution)- PSD (Particle Size Distribution)

R2 = 0.8995

010

2030

4050

6070

8090

0 10 20 30 40 50 60 70 80 90 100

Al (mol%)

met

al c

onte

nt(%

)

Metal ContentMetal Content Method of synthesis Method of synthesis

was sufficient.was sufficient.

Total metal content Total metal content (Al+Fe) decreases (Al+Fe) decreases linearly with increase linearly with increase Al content. Al content.

Due to increase Due to increase amounts of amounts of physisorbed, bound or physisorbed, bound or constitutional water constitutional water (El-Sharkawy et al., (El-Sharkawy et al., 2000).2000).

R2 = 0.9993

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

target Al (mol%)

mea

sure

d A

l (m

ol%

)

XRDXRD

Amorphous, higher intensity area in 10:1(90.9%) more likely Amorphous, higher intensity area in 10:1(90.9%) more likely associated to Al.associated to Al.

Intermediate transitional stage in crystallization (Carim et al. Intermediate transitional stage in crystallization (Carim et al. 1997)Al occupying tetrahedral rather than octahedral position 1997)Al occupying tetrahedral rather than octahedral position (Wolska et al. 1994 and Rodic et al. 2001)(Wolska et al. 1994 and Rodic et al. 2001)

Fe Al

1:101:5

5:1 10: 1

SEM (morphology)SEM (morphology)

1:10 1:2

2:1 5:1

Al

Fe AlFe

Al

Fe

Al

Fe

Metal distributionMetal distribution

1:2 1:1

Al

Fe

AlFe Al

Fe

Al

Fe

@10kV @10kV @20kV@20kV

Metal distribution with depthMetal distribution with depth

2:1 5:1

@10kV @20kV @10kV @20kV

Al

Fe

Al

Fe

Phase separationPhase separation Bayerite (Wolska et. al. 1994) or Corundum Bayerite (Wolska et. al. 1994) or Corundum

(Korecz et. al. 1972) for crystalline Al-Fe oxide.(Korecz et. al. 1972) for crystalline Al-Fe oxide. Korecz suggested a phase change above 5:1 Korecz suggested a phase change above 5:1

Al:FeAl:Fe

10:1

Fe (0%)

0

5

10

15

20

25

30

35

40

20 40 60 80 100 120 140 >140particle size (um)

volu

me

%

Al(100%)

010

2030

4050

6070

8090

100

20 40 60 80 100 120 140 >140particle size (um)

volu

me

%

1:5(16.7%)

0

5

10

15

20

25

30

35

40

20 40 60 80 100 120 140 >140particle size (um)

volu

me

%

5:1(83.3%)

0

5

10

15

20

25

30

35

40

20 40 60 80 100 120 140 >140particle size (um)

volu

me

%

Particle Size DistributionParticle Size Distribution

ConclusionsConclusions

Al-Fe hydr(oxides) formed by precipitation Al-Fe hydr(oxides) formed by precipitation of Al on Fe (>10mol%). Thickness of Al on Fe (>10mol%). Thickness increases with Al content above 50 mol%.increases with Al content above 50 mol%.

Fe controls the morphology and PSD of Fe controls the morphology and PSD of hydr(oxide).hydr(oxide).

Increase structural development with Al Increase structural development with Al content.content.

Task 2.Task 2.

P-sorption CharacteristicsP-sorption Characteristics

Batch ExperimentBatch Experiment

- P sorption as a function of time , pH, Al - P sorption as a function of time , pH, Al content content

Flow calorimetryFlow calorimetry

- Heats of P adsorption- Heats of P adsorption

- Effect of P sorption on surface charge- Effect of P sorption on surface charge

P sorption by batchP sorption by batch

Solid: solution - 1:1000 (10mg/10ml)Solid: solution - 1:1000 (10mg/10ml)

P input concentration 100mg/LP input concentration 100mg/L

Equilibration on reciprocal stirrer for 24hrs except Equilibration on reciprocal stirrer for 24hrs except where stated.where stated.

P-sorption expressed asP-sorption expressed as - - μμg/mg hydr(oxide) for time g/mg hydr(oxide) for time - - μμg/mg metal otherwise ( to account for the g/mg metal otherwise ( to account for the

weight contributed by water in the hydr(oxides)). weight contributed by water in the hydr(oxides)).

P sorption as a function of P sorption as a function of timetime

Increase in sorption with Al content and time. Increase in sorption with Al content and time. Fast phase and slow phase thereafter. Fast phase and slow phase thereafter. Similarity in slope – difference in sorption Similarity in slope – difference in sorption

occurred within 1occurred within 1stst hr of equilibration hr of equilibration

R2 = 0.9608

R2 = 0.9269

0

10

20

30

40

50

60

0 3 6 9 12 15 18 21 24

Time (hrs)

P s

orbe

d (u

g/m

g )

Al

10:1

1:1

Fe

0

0.2

0.4

0.6

0.8

1

1.2

0 3 6 9 12 15 18 21 24Time (hrs)

Fra

ctio

nal s

orpt

ion

R2 = 0.8274

0

5

10

15

20

25

30

35

40

45

50

0 3 6 9 12 15 18 21 24

Time (hrs)

rate

of so

rptio

n (u

g/hr

) 90% of 24 hr sorption max occurs within first 3 90% of 24 hr sorption max occurs within first 3

hrs irrespective of Al contenthrs irrespective of Al content Rate of adsorption similar , decrease Rate of adsorption similar , decrease

asymptotically towards zeroasymptotically towards zero

0

20

40

60

80

100

3 4 5 6 7 8 9

pH

P so

rbed

(ug/

mg

of m

etal)

Fe(0%)

1:10(9.1%)

1:5(16.7%)

1:2(33.3%)

1:1(50.0%)

40

60

80

100

120

140

160

180

200

3 4 5 6 7 8 9

pH

P so

rbed

(ug/

mg

of m

etal)

2:1(66.7%)

5:1(80.1%)

10:1(90.1%)

Al(100%)

P sorption as a function of pHP sorption as a function of pH

P sorption decrease with increasing pHP sorption decrease with increasing pH Inflection points at 6 and 7 .Inflection points at 6 and 7 . No significant decrease between 5 and 7 for 2:1, 5:1 No significant decrease between 5 and 7 for 2:1, 5:1

and 10:1 samples may be due to greater structural and 10:1 samples may be due to greater structural development.development.

loss decreases with increasing Al content at fixed pHloss decreases with increasing Al content at fixed pH pH 3-9: 65-80% for Al and low Al containing hydr(oxides). pH 3-9: 65-80% for Al and low Al containing hydr(oxides).

50 % for higher Al containing mixed hydr(oxides).50 % for higher Al containing mixed hydr(oxides). 25-30% loss pH 6-7 for lower Al range and pH 7-9 for 25-30% loss pH 6-7 for lower Al range and pH 7-9 for

higher Al rangehigher Al range Corresponds to pKa values for Fe(6.5) and Al(7.5) Corresponds to pKa values for Fe(6.5) and Al(7.5)

(McBride 1994)(McBride 1994)

R2 = 0.8441

R2 = 0.9451

R2 = 0.859

R2 = 0.7628

010

2030

4050

6070

8090

100

0 20 40 60 80 100 120Al content (mol%)

loss

of

sorp

tion(

%)

4.836.087.178.53Poly. (8.53)Poly. (7.17)Poly. (4.83)Poly. (6.08)

P sorption as a function of Al P sorption as a function of Al contentcontent

Increase with Al content. Al 4*Fe and 2*50-80molIncrease with Al content. Al 4*Fe and 2*50-80mol%. %.

Non-linear, particularly at pH<8Non-linear, particularly at pH<8 Each local maxima or minima due to change in Each local maxima or minima due to change in

property of hydr(oxide)property of hydr(oxide)

R2 = 0.9594

R2 = 0.9721

020

4060

80100

120140

160180

200

0 20 40 60 80 100 120Al content (mol%)

sorp

tion(

ug/m

g of

met

al)3.28

4.83

Poly.(4.83)Poly.(3.28)

R2 = 0.9768

R2 = 0.9591

R2 = 0.9537

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120Al content (mol%)

sorp

tion(

ug/m

g of

met

al)

6.08

7.17

8.53

Poly.(8.53)Poly.(7.17)Poly.(6.08)

Solid solution

Partial coverage of Fe by Al

Complete coverage of Fe by Al

Phase separation

ConclusionsConclusions Al content has no effect on the trend by which P Al content has no effect on the trend by which P

sorption occur nor rate of P sorption. sorption occur nor rate of P sorption.

Al content affects the degree of change in P Al content affects the degree of change in P sorption with increasing pH. Decreasing with sorption with increasing pH. Decreasing with increasing Al content.increasing Al content.

P sorption increases non-linearly with Al content, P sorption increases non-linearly with Al content, particularly below pH 8. particularly below pH 8.

Differences in sorption characteristics largely Differences in sorption characteristics largely due to changes in hydr(oxide) properties with Al due to changes in hydr(oxide) properties with Al content. content.

Flow CalorimetryFlow Calorimetry

Direct, quantitative heat Direct, quantitative heat measure (Rhue et al. measure (Rhue et al. 2002)2002)

Interaction at liquid/ Interaction at liquid/ solid interfacesolid interface

Calorimeter built by Dr. Calorimeter built by Dr. Rhue Rhue

Solution + surface sites Solution + surface sites = signal, which is = signal, which is related to the heat of related to the heat of the reaction.the reaction.

Heats + quantity sorbed Heats + quantity sorbed - reaction mechanism + - reaction mechanism + surface properties.surface properties.

time

sig

nal

thermistor

thermistor

column

Flow CalorimetryFlow Calorimetry

pH 4.8pH 4.8

Ion exchangeIon exchange - Cation exchange: K and Ca (50mM and - Cation exchange: K and Ca (50mM and

25mM respectively)25mM respectively)

- Anion exchange: Cl and NO- Anion exchange: Cl and NO33 (50mM) (50mM) - Pre-P and Post-P- Pre-P and Post-P

P adsorption (1 mM P in 50mM KCl) - 20 P adsorption (1 mM P in 50mM KCl) - 20 minutesminutes

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20 25 30 35 40 45 50

time(min)

sign

al (v

olts

)

0.8

1

1.2

1.4

1.6

1.8

2

2.2

0 5 10 15 20 25 30 35 40 45 50

time (min)

sign

al(v

olts

)

Fe(0%)

1:10(9.1%)

1:5(16.7%)

1:2(33.3%)

1:1(50%)

2:1(66.7%)

5:1(83.3%)

10:1(90.9%)

Al(100%)

Id mol% Al column wt(mg)peak

area(v.ml) v.ml/mg P ug/mg mJ/ μmol P

Fe 0.00 16.1 256 15.9 5.53 35.4

1:10 10.2 15.1 232 15.4 5.03 39.4

1:5 17.9 19.8 156 7.9 3.06 35.4

1:2 33.8 16.9 255 15.1 6.49 30.0

1:1 49.8 17.3 275 15.9 6.82 27.4

2:1 65.8 16.6 157 9.7 5.21 24.9

5:1 81.8 14.9 128 8.6 3.75 33.4

10:1 89.7 14.7 273 18.6 8.31 31.2

Al 100.0 10.2 152 14.9 5.18 37.9

Heats of adsorptionHeats of adsorption

Ion exchangeIon exchange

NONO33/Cl exothermic, Cl/NO/Cl exothermic, Cl/NO33 endothermic and reversible endothermic and reversible Reduction in AEC due to P sorption. P sorption and anion Reduction in AEC due to P sorption. P sorption and anion

exchange occurs on same sites. more likely OHexchange occurs on same sites. more likely OH22++

P sorption is irreversible P sorption is irreversible Magnitude of change varies with Al contentMagnitude of change varies with Al content

Fe (0%)

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 5 10 15 20 25time(min)

signa

l (vo

lts)

1:1(50%)

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

0 5 10 15 20 25 30 35time (min)

signa

l (vo

lts)

10:1(90.9%)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

0 5 10 15 20 25 30

time (min)

signa

l (vo

lts)

NO3

Cl

pre-P

post-P

Energy of anion exchange on Al = 4*Fe. Unclear Energy of anion exchange on Al = 4*Fe. Unclear whether this is due to greater energy or more whether this is due to greater energy or more exchange sites. exchange sites.

P sorbed was equal but loss 2*Fe energy units loss on P sorbed was equal but loss 2*Fe energy units loss on Al. May be due to difference in mechanism of P Al. May be due to difference in mechanism of P sorption on Fe vs. Al.sorption on Fe vs. Al.

50% loss in peak area for Fe, 25% for 50-100mol% Al. 50% loss in peak area for Fe, 25% for 50-100mol% Al. similarity in loss for indicative of surface similarity.similarity in loss for indicative of surface similarity.

R2 = 0.9122

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100 Al content (mol%)

pea

k ar

ea c

hang

e (%

)

R2 = 0.9815

R2 = 0.9841

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60 70 80 90 100Al content (mol%)

v.m

l/mg

Pre-P

Post-P

ConclusionConclusion

Al content did not have any effect on P Al content did not have any effect on P sorption mechanism nor energetics but sorption mechanism nor energetics but reduced anion exchange with no apparent reduced anion exchange with no apparent change in cation exchange.change in cation exchange.

AcknowledgementAcknowledgement

Lord God AlmightyLord God AlmightyMy lovely wife, Keisha My lovely wife, Keisha

Dr. R.D. Rhue Dr. R.D. Rhue Dr. W.G. HarrisDr. W.G. Harris

Dr. N. ComerfordDr. N. ComerfordDr. V. Nair Dr. V. Nair

Bill ReveBill ReveKeith HollienKeith Hollien

Gill Brubaker (PERC)Gill Brubaker (PERC)Brad Willenberg (MAIC) Brad Willenberg (MAIC)

My family and friendsMy family and friends

Questions ?Questions ?