P sorption Characteristics On Co-precipitated Amorphous Al-Fe Hydr(oxides) Omar Richard Harvey

Rationale P sorption capacity strongly correlated with Al and Fe hydr(oxide) content in soils (Freese et al. 1992) and wetlands (Reddy et al. 1995). P sorption capacity strongly correlated with Al and Fe hydr(oxide) content in soils (Freese et al. 1992) and wetlands (Reddy et al. 1995). Mixed hydr(oxides) more common than pure phases in nature. Mixed hydr(oxides) more common than pure phases in nature mol% Al found. >40 mol% Al common in sandy soils mol% Al found. >40 mol% Al common in sandy soils. Co-precipitation, sequential precipitation and agglomeration are expected events in aquatic systems (Anderson et al. 1990). Co-precipitation, sequential precipitation and agglomeration are expected events in aquatic systems (Anderson et al. 1990). Properties depends on formation conditions such as metal conc. in solution and pH. Properties depends on formation conditions such as metal conc. in solution and pH.

Objectives General General To determine the effect of Al content on P sorption in co- precipitated amorphous Al-Fe hydr(oxide) systems. To determine the effect of Al content on P sorption in co- precipitated amorphous Al-Fe hydr(oxide) systems. Task 1. Task 1. - To synthesize and characterize the hydr(oxides) based on chemical and physical properties - To synthesize and characterize the hydr(oxides) based on chemical and physical properties Task 2. Task 2. - To determine P sorption characteristics on all hydr(oxides) including the energetics and sorption as a function of time, pH and Al content - To determine P sorption characteristics on all hydr(oxides) including the energetics and sorption as a function of time, pH and Al content Task 3. Task 3. - Use properties of hydr(oxides) to explain differences in P sorption characteristics - Use properties of hydr(oxides) to explain differences in P sorption characteristics

Task 1. Hydr(oxide) Synthesis and Characterization

Synthesis Al-Fe hydr(oxides) containing 0, 9, 17, 33, 50, 67, 83, 91 and 100 mol% Al. Al-Fe hydr(oxides) containing 0, 9, 17, 33, 50, 67, 83, 91 and 100 mol% Al. Co-precipitation from Al and Fe chloride solution at pH by titration with NaOH Co-precipitation from Al and Fe chloride solution at pH by titration with NaOH Precipitate washed, dried at 70◦C, crushed and sieved (150 μm). Precipitate washed, dried at 70◦C, crushed and sieved (150 μm). mol% Al used interchangeably with Al:Fe molar ratio. mol% Al used interchangeably with Al:Fe molar ratio.

Characterization Chemical composition Chemical composition - Metal content ( Al and total) - Metal content ( Al and total) - Acid digestion /atomic absorption - Acid digestion /atomic absorption Physical properties Physical properties - XRD: structure of hydr(oxides) - XRD: structure of hydr(oxides) - SEM : morphology and distribution of Al and Fe in particles - SEM : morphology and distribution of Al and Fe in particles - PSD (Particle Size Distribution) - PSD (Particle Size Distribution)

Metal Content Method of synthesis was sufficient. Method of synthesis was sufficient. Total metal content (Al+Fe) decreases linearly with increase Al content. Total metal content (Al+Fe) decreases linearly with increase Al content. Due to increase amounts of physisorbed, bound or constitutional water (El- Sharkawy et al., 2000). Due to increase amounts of physisorbed, bound or constitutional water (El- Sharkawy et al., 2000).

XRD Amorphous, higher intensity area in 10:1(90.9%) more likely associated to Al. Amorphous, higher intensity area in 10:1(90.9%) more likely associated to Al. Intermediate transitional stage in crystallization (Carim et al. 1997)Al occupying tetrahedral rather than octahedral position (Wolska et al and Rodic et al. 2001) Intermediate transitional stage in crystallization (Carim et al. 1997)Al occupying tetrahedral rather than octahedral position (Wolska et al and Rodic et al. 2001)

FeAl 1:10 1:5 5:1 10: 1 SEM (morphology)

1:101:2 2:15:1 Al FeAl Fe Al Fe Al Fe Metal distribution

1:21:1 Al Fe Al FeAl Fe Metal distribution with depth

2:15:1

Al Fe Al Fe Phase separation Phase separation Bayerite (Wolska et. al. 1994) or Corundum (Korecz et. al. 1972) for crystalline Al-Fe oxide. Bayerite (Wolska et. al. 1994) or Corundum (Korecz et. al. 1972) for crystalline Al-Fe oxide. Korecz suggested a phase change above 5:1 Al:Fe Korecz suggested a phase change above 5:1 Al:Fe 10:1

Particle Size Distribution

Conclusions Al-Fe hydr(oxides) formed by precipitation of Al on Fe (>10mol%). Thickness increases with Al content above 50 mol%. Al-Fe hydr(oxides) formed by precipitation of Al on Fe (>10mol%). Thickness increases with Al content above 50 mol%. Fe controls the morphology and PSD of hydr(oxide). Fe controls the morphology and PSD of hydr(oxide). Increase structural development with Al content. Increase structural development with Al content.

Task 2. P-sorption Characteristics

Batch Experiment Batch Experiment - P sorption as a function of time, pH, Al content - P sorption as a function of time, pH, Al content Flow calorimetry Flow 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 batch Solid: solution - 1:1000 (10mg/10ml) Solid: solution - 1:1000 (10mg/10ml) P input concentration 100mg/L P input concentration 100mg/L Equilibration on reciprocal stirrer for 24hrs except where stated. Equilibration on reciprocal stirrer for 24hrs except where stated. P-sorption expressed as P-sorption expressed as - μg/mg hydr(oxide) for time - μg/mg hydr(oxide) for time - μg/mg metal otherwise ( to account for the weight contributed by water in the hydr(oxides)). - μg/mg metal otherwise ( to account for the weight contributed by water in the hydr(oxides)).

P sorption as a function of time 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 occurred within 1 st hr of equilibration Similarity in slope – difference in sorption occurred within 1 st hr of equilibration Al 10:1 1:1 Fe

90% of 24 hr sorption max occurs within first 3 hrs irrespective of Al content 90% of 24 hr sorption max occurs within first 3 hrs irrespective of Al content Rate of adsorption similar, decrease asymptotically towards zero Rate of adsorption similar, decrease asymptotically towards zero

P sorption as a function of pH P sorption decrease with increasing pH P 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 and 10:1 samples may be due to greater structural development. No significant decrease between 5 and 7 for 2:1, 5:1 and 10:1 samples may be due to greater structural development.

loss decreases with increasing Al content at fixed pH loss decreases with increasing Al content at fixed pH pH 3-9: 65-80% for Al and low Al containing hydr(oxides). 50 % for higher Al containing mixed hydr(oxides). pH 3-9: 65-80% for Al and low Al containing hydr(oxides). 50 % for higher Al containing mixed hydr(oxides) % loss pH 6-7 for lower Al range and pH 7-9 for higher Al range 25-30% loss pH 6-7 for lower Al range and pH 7-9 for higher Al range Corresponds to pKa values for Fe(6.5) and Al(7.5) (McBride 1994) Corresponds to pKa values for Fe(6.5) and Al(7.5) (McBride 1994)

P sorption as a function of Al content Increase with Al content. Al 4*Fe and 2*50-80mol%. Increase with Al content. Al 4*Fe and 2*50-80mol%. Non-linear, particularly at pH<8 Non-linear, particularly at pH<8 Each local maxima or minima due to change in property of hydr(oxide) Each local maxima or minima due to change in property of hydr(oxide) Solid solution Partial coverage of Fe by Al Complete coverage of Fe by Al Phase separation

Conclusions Al content has no effect on the trend by which P sorption occur nor rate of P sorption. Al content has no effect on the trend by which P sorption occur nor rate of P sorption. Al content affects the degree of change in P sorption with increasing pH. Decreasing with increasing Al content. Al content affects the degree of change in P sorption with increasing pH. Decreasing with increasing Al content. P sorption increases non-linearly with Al content, particularly below pH 8. P sorption increases non-linearly with Al content, particularly below pH 8. Differences in sorption characteristics largely due to changes in hydr(oxide) properties with Al content. Differences in sorption characteristics largely due to changes in hydr(oxide) properties with Al content.

Flow Calorimetry Direct, quantitative heat measure (Rhue et al. 2002) Direct, quantitative heat measure (Rhue et al. 2002) Interaction at liquid/ solid interface Interaction at liquid/ solid interface Calorimeter built by Dr. Rhue Calorimeter built by Dr. Rhue Solution + surface sites = signal, which is related to the heat of the reaction. Solution + surface sites = signal, which is related to the heat of the reaction. Heats + quantity sorbed - reaction mechanism + surface properties. Heats + quantity sorbed - reaction mechanism + surface properties. time signal thermistor column

Flow Calorimetry pH 4.8 pH 4.8 Ion exchange Ion exchange - Cation exchange: K and Ca (50mM and 25mM respectively) - Cation exchange: K and Ca (50mM and 25mM respectively) - Anion exchange: Cl and NO 3 (50mM) - Anion exchange: Cl and NO 3 (50mM) - Pre-P and Post-P - Pre-P and Post-P P adsorption (1 mM P in 50mM KCl) - 20 minutes P adsorption (1 mM P in 50mM KCl) - 20 minutes

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%) Idmol% Alcolumn wt(mg) peak area(v.ml)v.ml/mgP ug/mgmJ/ μmol P Fe : : : : : : : Al Heats of adsorption

Ion exchange NO 3 /Cl exothermic, Cl/NO 3 endothermic and reversible NO 3 /Cl exothermic, Cl/NO 3 endothermic and reversible Reduction in AEC due to P sorption. P sorption and anion exchange occurs on same sites. more likely OH 2 + Reduction in AEC due to P sorption. P sorption and anion exchange occurs on same sites. more likely OH 2 + P sorption is irreversible P sorption is irreversible Magnitude of change varies with Al content Magnitude of change varies with Al content NO 3 Cl pre-P post-P

Energy of anion exchange on Al = 4*Fe. Unclear whether this is due to greater energy or more exchange sites. Energy of anion exchange on Al = 4*Fe. Unclear whether this is due to greater energy or more exchange sites. P sorbed was equal but loss 2*Fe energy units loss on Al. May be due to difference in mechanism of P sorption on Fe vs. Al. P sorbed was equal but loss 2*Fe energy units loss on Al. May be due to difference in mechanism of P sorption on Fe vs. Al. 50% loss in peak area for Fe, 25% for mol% Al. similarity in loss for indicative of surface similarity. 50% loss in peak area for Fe, 25% for mol% Al. similarity in loss for indicative of surface similarity. Pre-P Post-P

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

Acknowledgement Lord God Almighty My lovely wife, Keisha Dr. R.D. Rhue Dr. W.G. Harris Dr. N. Comerford Dr. V. Nair Bill Reve Keith Hollien Gill Brubaker (PERC) Brad Willenberg (MAIC) My family and friends

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