Zirconium oxide, hafnium and ytterbium doped

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

Experimental determination of ytterbium sorption to silica surfaces:
Silica (silica gel 60H Merck):
- Mean particle size: 15 mm
- No impurities (checked by XPS)
- Specific surface area (confirmed by BET nitrogen adsorption): 384 m²/g
- pH of silica in water: 6.5.
Adsorption was measured in 20 batch experiments with mixes of solid, cation (Yb3+), and solution. Different volumes of HNO3 (10^-2 mol/L) or NaOH (10^-2 mol/L were added in each suspension to achieve a pH range between 4 and 8. The total volume of solution per batch is 50 cm³. Ionic strength in the batch experimentswas constant at 0.1. Measurements were conducted after an equilibrium phase of 7 days. The pH was recorded and solutions were 0.45 µm filtered prior to determination of Yb in solution by means of absorption spectrometry.

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

other: silica

Specific details on test material used for the study:

Yb3+. No specific details reported.

Radiolabelling:

no

Test temperature:

Not reported

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 2x10^-5 mol/L
- Sampling interval: after 7 days of equilibration
- Sample storage before analysis: not reported

Matrix no.:

#1

Matrix type:

other: Silica

% Clay:

0

% Silt:

0

% Sand:

0

% Org. carbon:

0

pH:

6.5

Details on matrix:

Silica used in this work is a commercial product (silica gel 60H Merck). The mean particle size is equal to 15 mm. The raw silica has been checked for impurities by XPS. No impurities have been detected. Its specific area, measured by the BET nitrogen adsorption method, is equal to 384 m²/g. The pH of immersion given by Merck for this silica in water is 6.5.
This result has been confirmed in the lab.

Details on test conditions:

TEST CONDITIONS
- Buffer: none
- pH: 6.5
- Amount of silica: 100 and 10 mg
- NaNO3 concentrations: 0.10 and 0.05 mol/L
- silica solution ratio: 0.1 to 50 and 0.01 to 50
- concentration of Yb3+: 2*10^-5 mol/L added to different amounts of silica; corresponding to 173.05 µg added, corresponding to 1730.5 mg a.i./kg silica and 173.05 mg a.i./kg silica

Sample No.:

#1

Duration:

7 d

Initial conc. measured:

1 730.5 other: mg/kg silica; nominal concentration

Remarks:

Temperature not reported; pH values in the experiment range between 4 and 8. 173.05 µg Yb in 100 mg silica

Sample No.:

#2

Duration:

7 d

Initial conc. measured:

17 305 other: mg/kg silica; nominal concentration

Remarks:

Temperature not reported; pH values in the experiment range between 4 and 8; 173.05 µg Yb in 10 mg silica

Sample No.:

#1

Type:

Kd

Value:

ca. 35 L/kg

pH:

5.9

Matrix:

Silica, 100 mg in 50 mL solution.

% Org. carbon:

0

Remarks on result:

other: Temperature not reported.

Sample No.:

#2

Type:

Kd

Value:

ca. 2 278 L/kg

pH:

6.5

Matrix:

Silica, 100 mg in 50 mL solution

% Org. carbon:

0

Remarks on result:

other: Temperature not reported.

Sample No.:

#3

Type:

Kd

Value:

ca. 559 L/kg

pH:

6.5

Matrix:

Silica, 10 mg in 50 mL solution

% Org. carbon:

0

Remarks on result:

other: Temperature not reported.

Sample No.:

#4

Type:

Kd

Value:

ca. 11 667 L/kg

pH:

7

Matrix:

Silica, 10 mg in 50 mL solution

% Org. carbon:

0

Remarks on result:

other: Temperature not reported.

Adsorption and desorption constants:

Stoichiometries and formation constants of the surface complexes are extracted from sorption experiments. Neither specific capacitance nor surface acidity constants or surface site concentration have been adjusted. The best fits of the data are obtained with the following reaction:
2 H2O + SOH + Yb3+ <-> SOYb(OH)2 + 3H+; log K = -16.2 +/- 0.3
(SOH = surface hydroxides)

Transformation products:

no

Regarding adsorption of Yb³⁺ to silica surfaces, the competitive action of sodium is insignificant.

 

At pH values < 5.5 no adsorption of Yb³⁺on silica could be observed. Slight increases of pH from ca. 5.9 to ca. 6.6 considerably increased the amount of sorbed Yb³⁺ from ca. 6 % to ca. 82 %, corresponding to Kd values of ca. 35 L/kg at pH 5.9 and ca. 2278 L/kg at pH 6.6, when 100 mg of silica were added.

When only 10 mg silica were applied no adsorption of Yb³⁺ was reported at a pH of 5.9. At a pH of 6.5 ca. 10 % were adsorbed and at pH 7 ca 70 %, corresponding to Kd values of 559 L/kg and 11667 L/kg, respectively.

The adsorption coefficient of Yb³⁺ were calculated according to the following equation from OECD guideline 106:

Formula: Distribution coefficient Kd = (Aeq/(100-Aeq)) * (V0/msoil)

Where:

V0:= initial volume of the aqueous phase in contact with the soil (cm³); here: 50 cm³

msoil:= quantity of the soil phase, expressed in dry mass of soil (g); here: 0.1 and 0.01 g silica

Aeq := percentage of adsorption of Yb³⁺ at adsorption equilibrium (%); here: derived from Figure 4.

 

Table 1: Parameter used for the calculation of Kd values and the corresponding Kd values.

	Sample	Aeq in %	V0 in mL	m silica in g	Kd in L/kg
1	silica pH 5.9	6.6	50	0.10	35.33
2	silica pH 6.5	82.0	50	0.10	2277.78
3	silica pH 6.5	10.1	50	0.01	558.64
4	silica pH 7	70	50	0.01	11666.67

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficient for Yb3+ on silica varies from log Kd = 1.5 to 4.1 depending on the pH and the ratio of Yb3+ added to silica.

Executive summary:

The present study investigates the adsorption characteristics of Yb³⁺ on silica surfaces [pH 4 to 8, organic carbon 0 %] from Merck [silica gel 60 H] in a batch equilibrium experiment.  The adsorption phase of the study was carried out in 20 batches by equilibrating silica with Yb³⁺ at 1730.5 mg Yb³⁺/kg and 17305 mg Yb³⁺/kg silica for 7 days. 

Different volumes of HNO3 (10-2 mol/L) or NaOH (10-2 mol/L) were added in each suspension to achieve a pH range between 4 and 8. The total volume of solution per batch was 50 cm³. Ionic strength in the batch experiments was constant at 0.1. Measurements were conducted after an equilibrium phase of 7 days. The pH was recorded and solutions were 0.45 µm filtered prior to determination of Yb in solution by means of absorption spectrometry.

At pH values < 5.5 no adsorption of Yb³⁺on silica could be observed. Slight increases of pH from ca. 5.9 to ca. 6.6 considerably increased the amount of sorbed Yb³⁺ from ca. 6 % to ca. 82 %, corresponding to Kd values of ca.

35 L/kg at pH 5.9 and ca. 2278 L/kg at pH 6.6, when 100 mg of silica were added (see Table 2 below).

When only 10 mg/L silica were applied no adsorption of Yb³⁺ was reported at a pH of 5.9. At a pH of 6.5 ca. 10 % were adsorbed and at pH 7 ca 70 %, corresponding to Kd values of 559 L/kg and 11667 L/kg, respectively.

 

Results Synopsis:

 

Table 2: Kd values and corresponding pH values and amounts of silica.

	soil sample	m silica in g	Kd in L/kg	log Kd
1	silica pH 5.9	0.10	35.33	1.5
2	silica pH 6.5	0.10	2277.78	3.4
3	silica pH 6.5	0.01	558.64	2.7
4	silica pH 7	0.01	11666.67	4.1

Reference 2

Endpoint:

adsorption / desorption, other

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

Due to the low water solubility of the metal components contained in the test substance (zirconium oxide, hafnium and ytterbium doped), a full transformation/dissolution protocol was carried out to study the potential release of these metals to the environment.
After 7 and 28 days (nominal loading of 100 mg/L, pH 8), only ytterbium(III) was found in solution with a maximum concentration of 0.069 µg/L. Zirconium and hafnium were both below the detection limit of 0.07 and 0.02 µg/L, respectively. Therefore, information on ytterbium(III) is relevant for the assessment of environmental fate properties of zirconium oxide, hafnium and ytterbium doped and adsorption studies with ytterbium are used in a read-across approach to fulfil the REACH requirements for endpoint 9.3.1 “Adsorption/desorption screening”.

Reason / purpose for cross-reference:

read-across source

Key result

Sample No.:

#1

Type:

Kd

Value:

24.2 other: cm³/g

Temp.:

18.5 °C

Matrix:

Sand

Remarks on result:

other: no data on organic content of sand available

Adsorption and desorption constants:

For adsorption constant see table 1 above. Desorption was not investigated.

Transformation products:

no

Details on results (Batch equilibrium method):

The adsorption of ytterbium on sand surface has also been studied in the 18-37 °C range. Other conditions, i.e. the amount of adsorbate and adsorbent, the shaking time and the electrolyte concentration, were kept constant at the values previously optimized (> 100 mg of sand sample, 10 min shaking time, [Yb] = 3.8xE-06 M and om M HNO3 for 4 cm³ of the solution).
The results obtained from this study are listed in Table 1 above. The value of the equilibrium constant Kc, was evaluated from the equation (Hasany and Saeed, 1992):
Kc = CBe/CAe
where CBe is the equilibrium concentration of ytterbium on sand and CAe is the equilibrium concentration of Yb in solution.
It can be seen from Table 1 that both Kd and Kc, increase with increasing temperature.

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficient of ytterbium increases with increasing temperature, ranging between 24.3 and 337.5 cm³/g at 18 to 37 °C.

Executive summary:

Adsorption experiments were carried out by shaking known amounts of adsorbent (100 mg sand) with 3.8xE-06 M Yb concentrations for 10 min in a 0.01 M HNO₃ solution. The adsorption coefficient Kd and the sorption equilibrium constant, Kc have been calculated at different temperatures between 18 and 37 °C:

Table 1: Adsorption of Ytterbium at Different Temperatures

Temp. (K) / °C	KD(cm³/g)	Kc
291.2 / 18.05	24.2	0.61
295.7 / 22.55	44.7	1.12
300.2 / 27.05	86.4	2.31
305.0 / 31.85	133.4	4.33
310.6 / 37.45	337.5	8.44

It can be seen from Table 1 that both Kd and Kc, increase with increasing temperature.

This information is used in a read-across approach in the assessment of the target substance. Due to the low water solubility of the metal components contained in the test substance (zirconium oxide, hafnium and ytterbium doped), a full transformation/dissolution protocol was carried out to study the potential release of these metals to the environment.

After 7 and 28 days (nominal loading of 100 mg/L, pH 8), only ytterbium(III) was found in solution with a maximum concentration of 0.069 µg/L. Zirconium and hafnium were both below the detection limit of 0.07 and 0.02 µg/L, respectively. Therefore, information on ytterbium(III) is relevant for the assessment of environmental fate properties of zirconium oxide, hafnium and ytterbium doped and adsorption studies with ytterbium are used in a read-across approach to fulfil the REACH requirements for endpoint 9.3.1 “Adsorption/desorption screening”.

Reference 3

Endpoint:

adsorption / desorption, other

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

The effects of pH, ionic strength and fulvic acid (FA) on the sorption of Yb(III) on alumina were investigated by using batch technique and radiotracer (169Yb) in 0.01–2.0 mol/L NaNO3.

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

other: aluminium (chromatographic Al2O3, 200-300 mesh)

Specific details on test material used for the study:

MATERIALS

Ytterbium
- 169Yb(III)
- Radionuclide purity: 99.00%
- Radiochemical purity: 99.00&
- Source: as oxides from Chinese Institute of Atomic Energy

Aluminum
- Name: Chromatographic Al2O3 (200-300 mesh)
- Source: Wu-Xi Chemical Reagent Factory (Shanghai, China)
- Preparation: Al2O3 was washed with double-deionized water until a constant electric conductivity was reached in the washing water. The washed Al2O3 was dried at 105°C for 2 h and then it was put on a shallow glass dish placed inside a desiccator containing a saturated NaCl solution. The desiccator was placed in a thermostat (25+/- 2°C). The alumina was characterized by potentiometric titration and its pHZPC (zero point of charge) was found to be 7.5.

Fulvic acid:
- Name: fulvic acid (FA)
- Source: weathered coal in the area of Gongxian (Henan Province)
- Concentration determined by spectrophotometric analysis at 465 nm and pH 8.3 in the presence of 0.1 mol/L NaHCO3

Radiolabelling:

yes

Remarks:

169Yb

Test temperature:

25 °C

Analytical monitoring:

yes

Details on sampling:

No details reported.

Matrix no.:

#1

Matrix type:

other: Aluminium

% Clay:

0

% Silt:

0

% Sand:

0

% Org. carbon:

0

pH:

>= 3 - <= 10.5

Details on matrix:

- Chromatographic Al2O3 (200–300 mesh)
- Batch sorption experiments were performed with 0.100 g Al2O3 and 10.0 mL aqueous solution in polyethylene test tubes.

Details on test conditions:

Sorption
Batch sorption experiments were typically performed with 0.100 g Al2O3 and 10.0 mL aqueous solution in polyethylene test tubes. Sodium nitrate, radiotracer, HNO3 or NaOH and FA were added to achieve the desired background electrolyte concentration, FA concentration and pH of aqueous solutions.

Desorption
For desorption experiments, the suspension of alumina was centrifuged (4000 rpm, 15 min) at the end of the sorption experiments, half the supernatant was pipetted and an equal volume of background electrolyte solution was added. Then the mixture was shaken and centrifuged at the same conditions as in the sorption experiments. The concentration of Yb in the solid phase was deduced from the dfference between the amounts of Yb added (C0V) and those remaining in solution after equilibrium (CV) and the weight of alumina (S). The equilibration time was suggested by preliminary kinetic experiments and no attempts were made to exclude atmospheric CO2.

Influence of FA on adsorption and investigation of the effect of the sequence of additions of radiotracer 169Yb and FA:
After adding the radiotracer (or the FA), the test tubes were shaken for 1 h, then the FA (or the radiotracer) was added and the test tubes were shaken for 30 h.

Sample No.:

#1

Duration:

30 h

Initial conc. measured:

0 other: mol Yb/L

Temp.:

25 °C

Remarks:

Investigations in the pH range of 3 - 10.5; c(NaNO3) = 0.01 - 2.0 mol/L; without FA

Sample No.:

#2

Duration:

30 h

Initial conc. measured:

0 other: mol Yb/L

Temp.:

25 °C

Remarks:

Investigations in the pH range 3 - 10.5; c(NaNO3) = 0.1 mol/L; with FA (c=25 mg/L)

Sample No.:

#3

Duration:

30 h

Initial conc. measured:

0 other: mol Yb/L

Temp.:

25 °C

Remarks:

Investigations in the pH range 3 - 10.5; c(NaNO3) = 0.1 mol/L; without FA

Sample No.:

#4

Duration:

30 h

Initial conc. measured:

0 other: mol Yb/L

Temp.:

25 °C

Remarks:

Investigations in pH range ca. 2.2-9; c(NaNO3)=0.1 mol/L; c(FA) = 50 mg/L

Sample No.:

#5

Duration:

30 h

Initial conc. measured:

0 other: mol Yb/L

Temp.:

25 °C

Remarks:

Investigations in pH range ca. 3-10; c(NaNO3)=0.1 mol/L; c(FA) = 200 mg/L

Key result

Sample No.:

#1

Type:

log Kd

Value:

>= 0.5 - <= 5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium (without FA)

% Org. carbon:

0

Remarks on result:

other: log Kd increases with increasing pH (range pH 3 - 8)

Remarks:

Log Kd values were independent of ionic strength.

Sample No.:

#1

Type:

log Kd

Value:

>= 3.5 - <= 5.5 dimensionless

Temp.:

25 °C

Matrix:

Aluminia (without FA)

% Org. carbon:

0

Remarks on result:

other: At pH > 9 the log Kd values decrease with increasing pH up to ca. 10.5

Remarks:

Log Kd values were independent of ionic strength.

Sample No.:

#2

Type:

log Kd

Value:

ca. 1.7 - ca. 4.7 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (25 mg/L)

% Org. carbon:

0

Remarks on result:

other: pH range 3 - 7; c(FA) = 25 mg/L

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#2

Type:

log Kd

Value:

ca. 3.4 - ca. 4.7 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (25 mg/L)

% Org. carbon:

0

Remarks on result:

other: pH range 7-11; c(FA)= 25 mg/L

Remarks:

Decrease of log Kd with increasing pH

Sample No.:

#3

Type:

log Kd

Value:

ca. 1.6 - ca. 4.4 dimensionless

Temp.:

25 °C

Matrix:

Aluminium (without FA)

Remarks on result:

other: pH range 3-7; no FA

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#3

Type:

log Kd

Value:

ca. 4.4 - ca. 4.6 dimensionless

Temp.:

25 °C

Matrix:

Aluminium (without FA)

% Org. carbon:

0

Remarks on result:

other: pH range 7-11; no FA

Remarks:

Slightly decreasing log Kd with increasing pH

Sample No.:

#4

Type:

log Kd

Value:

ca. 1.5 - ca. 5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (50 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 2.2-7.3; c(NaNO3)=0.1 mol/L; c(FA) = 50 mg/L

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#4

Type:

log Kd

Value:

ca. 3.4 - ca. 5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (50 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 7.3-9; c(NaNO3)=0.1 mol/L; c(FA) = 50 mg/L

Remarks:

Decreasing log Kd with increasing pH

Sample No.:

#5

Type:

log Kd

Value:

ca. 1.9 - ca. 5.5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (200 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 3-6.6; c(NaNO3)=0.1 mol/L; c(FA) = 200 mg/L

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#5

Type:

log Kd

Value:

ca. 2.8 - ca. 5.5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (200 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 6.6-10.2; c(NaNO3)=0.1 mol/L; c(FA) = 200 mg/L

Remarks:

Decreasing log Kd with increasing pH

Adsorption and desorption constants:

See "Adsorption coefficient" table above

Transformation products:

no

Sorption on bare alumina

A steep increase in log Kd and the independence of log Kd on ionic strength were observed from 0.5 at pH 3 to 5 at pH 8. The steep increase in sorption is a typical behavior for the sorption of hydrolysable transition metal ions on hydrous oxides.

At pH > 9, log Kd values decreased with increasing pH, and this decrease in log Kd can be attributed mainly to a decrease in ≡SOH concentration and to an increase in concentrations of hydrolysis species and carbonate complexes of Yb(III) in aqueous media.

Obviously, the sorption-desorption hysteresis and the sorption of a positively charged species onto a positively charged surface are direct evidence for the formation of coordination bonds between the surface of bare alumina and Yb(III).

 

Sorption on coated alumina

It was found that in the pH range 3-7, the log Kd values at an initial FA concentration of 25 mg/L were slightly higher than that in the absence of FA, and that in the pH range 3-7, FA was almost exhausted from the aqueous solution and the coating of FA was formed at the bare alumina surface.

In the pH range 8-11, the concentration of FA at equilibrium increased with increasing pH, and in the pH range 7-11, the log Kd values in the presence of FA were lower than those in the absence of FA. The log Kd of Yb(III) vs. pH plots at the initial concentrations 50 and 200 mg/L, show the dependence of FA concentration at equilibrium on the pH. In the pH range 2-7, when the FA initial concentration was increased, the log Kd values obviously increased, i.e. the log Kdv s. pH plots shifted towards lower pH, and that even if the FA initial concentration was 200 mg/L, the FA was almost exhausted from aqueous solution in the pH range 2-7. The FA concentration at equilibrium increased with increasing pH in the pH range 8-11, at pH >8 the log Kd values decreased with increasing pH and the values were even less than those in the absence of FA.

When FA was added, the fact that the log Kd values increased in the pH range 2-7 can be explained by the fact that the complexation of the rare earth elements with the functional groups of FA sorbed on the alumina is stronger than the complexation with the surface hydroxyls of the bare alumina.

Conversely, if the complexation of rare earth elements with the functional groups of FA sorbed on the sorbent is weaker than the complexation with the surface hydroxyls of the bare adsorbent, a negative effect of FA would be observed. The dependence of log Kd on pH in the pH range 2-7 can be attributed to an increase in the dissociation of the functional groups of FA sorbed on the alumina with increasing pH. The dependence of log Kd on pH in the pH range 8-11 can be attributed to a decrease in the extent of surface coverage of FA and to the increase in complexation with soluble FA in aqueous solution.

The sequence of Yb(III) and FA additions to the alumina-NaNO3-Yb-FA-water system was changed to check for reversibility of the sorption process, in these experiments Yb(III) or FA was allowed to react with alumina early on in the presence of NaNO3 for one hour. The log Kd vs. pH plot for adding FA early is slightly higher than that for adding Yb early, and though these results indicate a similar sorption-desorption hysteresis under the conditions of this work, there was not really much difference. This weak hysteresis may be partially explained by the fact that because of the heterogeneous nature of FA, those FA molecules sorbed on alumina are different from those remaining in solution and the FA molecules sorbed early on alumina with high affinity for alumina are not readily reversible.

Validity criteria fulfilled:

not applicable

Conclusions:

Yb(III) sorption on aluminium is strongly dependent on pH. In the pH range of ca. 3 to 8, log Kd values increase with increasing pH. Thereafter a decrease of log Kd values could be observed.

Executive summary:

The present experimental work studied the effects of pH, ionic strength and dissolved fulvic acid (FA) on sorption of Yb(III) on alumina under aerobic conditions. The sorption of Yb(III) onto a bare alumina surface was shown to be dependent on pH, but independent of ionic strength. The sorption mechanism of the hydrolysable rare earth element Yb(III) appears not to be pure ion exchange and the surface hydrolysis model can qualitatively and satisfactorily explain the observations on bare alumina.

The presence of FA significantly affected the sorption of Yb(III) onto alumina, the surface of alumina was coated by FA and the coating of FA had a significant effect on the surface properties of alumina. However, the effect of FA was dependent on pH and concentration of FA, the sorption of Yb(III) was seen to be either enhanced or decreased at different pH ranges as compared with FA free systems. The competition between the complexations of sorbed FA and dissolved FA with rare earth elements can explain the observations on coated alumina.

Reference 4

Endpoint:

adsorption / desorption, other

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

documentation insufficient for assessment

Principles of method if other than guideline:

Adsorption experiments were carried out by shaking known amounts of adsorbent (100 mg) with 3.8 X 10-6 M Yb concentrations for 10 min in a 0.01 M HNO3 solution. A vibrating temperature-controlled (±0.1 °C) Gallenkamp Thennostirrer-100, model BKL 235, water bath was used for temperature studies. The shaking vials were kept in the water bath for at least 1 h to attain constant temperature before sorption measurements were undertaken. After predetermined intervals, the contents of the shaking vials were centrifuged. An aliquot (1 cm³) of supernatant was analyzed radiometrically using a counting technique. The amount of ytterbium adsorbed at any given time was calculated from the difference in the activities of aliquots withdrawn before and after adsorption. All experiments were undertaken at least three times and the results were reproducible to within an experimental error of ± 2-5 %.

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

other: sand

Radiolabelling:

yes

Test temperature:

Determinations of the Kd values were carried out at five different temperatures: 291.2, 295.7, 300.2, 310.6 K

Analytical monitoring:

yes

Remarks:

Centrifuge supernatant was analyzed radiometrically using a counting technique.

Details on sampling:

No details reported

Details on matrix:

Sand samples from Pakistan. No details reported.

Details on test conditions:

No details available.

Key result

Sample No.:

#1

Type:

Kd

Value:

24.2 other: cm³/g

Temp.:

18.5 °C

Matrix:

Sand

Remarks on result:

other: no data on organic content of sand available

Adsorption and desorption constants:

For adsorption constant see table 1 above. Desorption was not investigated.

Transformation products:

no

Details on results (Batch equilibrium method):

The adsorption of ytterbium on sand surface has also been studied in the 18-37 °C range. Other conditions, i.e. the amount of adsorbate and adsorbent, the shaking time and the electrolyte concentration, were kept constant at the values previously optimized (> 100 mg of sand sample, 10 min shaking time, [Yb] = 3.8xE-06 M and om M HNO3 for 4 cm³ of the solution).
The results obtained from this study are listed in Table 1 above. The value of the equilibrium constant Kc, was evaluated from the equation (Hasany and Saeed, 1992):
Kc = CBe/CAe
where CBe is the equilibrium concentration of ytterbium on sand and CAe is the equilibrium concentration of Yb in solution.
It can be seen from Table 1 that both Kd and Kc, increase with increasing temperature.

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficient of ytterbium increases with increasing temperature, ranging between 24.2 and 337.5 cm³/g at 18 to 37 °C.

Executive summary:

Adsorption experiments were carried out by shaking known amounts of adsorbent (100 mg sand) with 3.8xE-06 M Yb concentrations for 10 min in a 0.01 M HNO₃ solution. The adsorption coefficient Kd and the sorption equilibrium constant, Kc have been calculated at different temperatures between 18 and 37 °C:

Table 1: Adsorption of Ytterbium at Different Temperatures

Temp. (K) / °C	KD(cm³/g)	Kc
291.2 / 18.05	24.2	0.61
295.7 / 22.55	44.7	1.12
300.2 / 27.05	86.4	2.31
305.0 / 31.85	133.4	4.33
310.6 / 37.45	337.5	8.44

It can be seen from Table 1 that both Kd and Kc, increase with increasing temperature.

Reference 5

Endpoint:

adsorption / desorption: screening

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

Due to the low water solubility of the metal components contained in the test substance (zirconium oxide, hafnium and ytterbium doped), a full transformation/dissolution protocol was carried out to study the potential release of these metals to the environment.
After 7 and 28 days (nominal loading of 100 mg/L, pH 8), only ytterbium(III) was found in solution with a maximum concentration of 0.069 µg/L. Zirconium and hafnium were both below the detection limit of 0.07 and 0.02 µg/L, respectively. Therefore, information on ytterbium(III) is relevant for the assessment of environmental fate properties of zirconium oxide, hafnium and ytterbium doped and adsorption studies with ytterbium are used in a read-across approach to fulfil the REACH requirements for endpoint 9.3.1 “Adsorption/desorption screening”.

Reason / purpose for cross-reference:

read-across source

Sample No.:

#1

Type:

Kd

Value:

ca. 35 L/kg

pH:

5.9

Matrix:

Silica, 100 mg in 50 mL solution.

% Org. carbon:

0

Remarks on result:

other: Temperature not reported.

Sample No.:

#2

Type:

Kd

Value:

ca. 2 278 L/kg

pH:

6.5

Matrix:

Silica, 100 mg in 50 mL solution

% Org. carbon:

0

Remarks on result:

other: Temperature not reported.

Sample No.:

#3

Type:

Kd

Value:

ca. 559 L/kg

pH:

6.5

Matrix:

Silica, 10 mg in 50 mL solution

% Org. carbon:

0

Remarks on result:

other: Temperature nnot reported.

Sample No.:

#4

Type:

Kd

Value:

ca. 11 667 L/kg

pH:

7

Matrix:

Silica, 10 mg in 50 mL solution

% Org. carbon:

0

Remarks on result:

other: Temperature not reported.

Adsorption and desorption constants:

Stoichiometries and formation constants of the surface complexes are extracted from sorption experiments. Neither specific capacitance nor surface acidity constants or surface site concentration have been adjusted. The best fits of the data are obtained with the following reaction:
2 H2O + SOH + Yb3+ <-> SOYb(OH)2 + 3H+; log K = -16.2 +/- 0.3
(SOH = surface hydroxides)

Transformation products:

no

Regarding adsorption of Yb³⁺ to silica surfaces, the competitive action of sodium is insignificant.

 

At pH values < 5.5 no adsorption of Yb³⁺on silica could be observed. Slight increases of pH from ca. 5.9 to ca. 6.6 considerably increased the amount of sorbed Yb³⁺ from ca. 6 % to ca. 82 %, corresponding to Kd values of ca. 35 L/kg at pH 5.9 and ca. 2278 L/kg at pH 6.6, when 100 mg of silica were added.

When only 10 mg silica were applied no adsorption of Yb³⁺ was reported at a pH of 5.9. At a pH of 6.5 ca. 10 % were adsorbed and at pH 7 ca 70 %, corresponding to Kd values of 559 L/kg and 11667 L/kg, respectively.

The adsorption coefficient of Yb³⁺ were calculated according to the following equation from OECD guideline 106:

Formula: Distribution coefficient Kd = (Aeq/(100-Aeq)) * (V0/msoil)

Where:

V0:= initial volume of the aqueous phase in contact with the soil (cm³); here: 50 cm³

msoil:= quantity of the soil phase. expressed in dry mass of soil (g); here: 0.1 and 0.01 g silica

Aeq := percentage of adsorption of Yb³⁺ at adsorption equilibrium (%); here: derived from Figure 4.

 

Table 1: Parameter used for the calculation of Kd values and the corresponding Kd values.

	Sample	Aeq in %	V0 in mL	m silica in g	Kd in L/kg
1	silica pH 5.9	6.6	50	0.10	35.33
2	silica pH 6.5	82.0	50	0.10	2277.78
3	silica pH 6.5	10.1	50	0.01	558.64
4	silica pH 7	70	50	0.01	11666.67

Validity criteria fulfilled:

not applicable

Conclusions:

The adsorption coefficient for Yb3+ on silica varies from log Kd = 1.5 to 4.1 depending on the pH and the ratio of Yb3+ added to silica.

Executive summary:

The present study investigates theadsorption characteristics of Yb³⁺ on silica surfaces [pH 4 to 8, organic carbon 0 %] from Merck [silica gel 60 H] in a batch equilibrium experiment.  The adsorption phase of the study was carried out in 20 batches by equilibrating silica with Yb³⁺ at 1730.5 mg Yb³⁺/kg and 17305 mg Yb³⁺/kg silica for 7 days. 

Different volumes of HNO3 (10-2 mol/L) or NaOH (10-2 mol/L) were added in each suspension to achieve a pH range between 4 and 8. The total volume of solution per batch was 50 cm³. Ionic strength in the batch experiments was constant at 0.1. Measurements were conducted after an equilibrium phase of 7 days. The pH was recorded and solutions were 0.45 µm filtered prior to determination of Yb in solution by means of absorption spectrometry.

At pH values < 5.5 no adsorption of Yb³⁺on silica could be observed. Slight increases of pH from ca. 5.9 to ca. 6.6 considerably increased the amount of sorbed Yb³⁺ from ca. 6 % to ca. 82 %, corresponding to Kd values of ca.

35 L/kg at pH 5.9 and ca. 2278 L/kg at pH 6.6, when 100 mg of silica were added (see Table 2 below).

When only 10 mg/L silica were applied no adsorption of Yb³⁺ was reported at a pH of 5.9. At a pH of 6.5 ca. 10 % were adsorbed and at pH 7 ca 70 %, corresponding to Kd values of 559 L/kg and 11667 L/kg, respectively.

 

Results Synopsis:

 

Table 2: Kd values and corresponding pH values and amounts of silica.

	soil sample	m silica in g	Kd in L/kg	log Kd
1	silica pH 5.9	0.10	35.33	1.5
2	silica pH 6.5	0.10	2277.78	3.4
3	silica pH 6.5	0.01	558.64	2.7
4	silica pH 7	0.01	11666.67	4.1

This information is used in a read-across approach in the assessment of the target substance. Due to the low water solubility of the metal components contained in the test substance (zirconium oxide, hafnium and ytterbium doped), a full transformation/dissolution protocol was carried out to study the potential release of these metals to the environment.

After 7 and 28 days (nominal loading of 100 mg/L, pH 8), only ytterbium(III) was found in solution with a maximum concentration of 0.069 µg/L. Zirconium and hafnium were both below the detection limit of 0.07 and 0.02 µg/L, respectively. Therefore, information on ytterbium(III) is relevant for the assessment of environmental fate properties of zirconium oxide, hafnium and ytterbium doped and adsorption studies with ytterbium are used in a read-across approach to fulfil the REACH requirements for endpoint 9.3.1 “Adsorption/desorption screening”.

Reference 6

Endpoint:

adsorption / desorption, other

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

Due to the low water solubility of the metal components contained in the test substance (zirconium oxide, hafnium and ytterbium doped), a full transformation/dissolution protocol was carried out to study the potential release of these metals to the environment.
After 7 and 28 days (nominal loading of 100 mg/L, pH 8), only ytterbium(III) was found in solution with a maximum concentration of 0.069 µg/L. Zirconium and hafnium were both below the detection limit of 0.07 and 0.02 µg/L, respectively. Therefore, information on ytterbium(III) is relevant for the assessment of environmental fate properties of zirconium oxide, hafnium and ytterbium doped and adsorption studies with ytterbium are used in a read-across approach to fulfil the REACH requirements for endpoint 9.3.1 “Adsorption/desorption screening”.

Reason / purpose for cross-reference:

read-across source

Key result

Sample No.:

#1

Type:

log Kd

Value:

>= 0.5 - <= 5.5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium (without FA)

% Org. carbon:

0

Remarks on result:

other: log Kd increases with increasing pH (range pH 3 - 8)

Remarks:

Log Kd values were independent of ionic strength.

Sample No.:

#1

Type:

log Kd

Value:

>= 3.5 - <= 4.5 dimensionless

Temp.:

25 °C

Matrix:

Aluminia (without FA)

% Org. carbon:

0

Remarks on result:

other: At pH > 9 the log Kd values decrease with increasing pH up to ca. 10.5

Remarks:

Log Kd values were independent of ionic strength.

Sample No.:

#2

Type:

log Kd

Value:

ca. 1.7 - ca. 4.7 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (25 mg/L)

% Org. carbon:

0

Remarks on result:

other: pH range 3 - 7; c(FA) = 25 mg/L

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#2

Type:

log Kd

Value:

ca. 3.4 - ca. 4.7 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (25 mg/L)

% Org. carbon:

0

Remarks on result:

other: pH range 7-11; c(FA)= 25 mg/L

Remarks:

Decrease of log Kd with increasing pH

Sample No.:

#3

Type:

log Kd

Value:

ca. 1.6 - ca. 4.4 dimensionless

Temp.:

25 °C

Matrix:

Aluminium (without FA)

Remarks on result:

other: pH range 3-7; no FA

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#3

Type:

log Kd

Value:

ca. 4.4 - ca. 4.6 dimensionless

Temp.:

25 °C

Matrix:

Aluminium (without FA)

% Org. carbon:

0

Remarks on result:

other: pH range 7-11; no FA

Remarks:

Slightly decreasing log Kd with increasing pH

Sample No.:

#4

Type:

log Kd

Value:

ca. 1.5 - ca. 5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (50 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 2.2-7.3; c(NaNO3)=0.1 mol/L; c(FA) = 50 mg/L

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#4

Type:

log Kd

Value:

ca. 3.4 - ca. 5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (50 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 7.3-9; c(NaNO3)=0.1 mol/L; c(FA) = 50 mg/L

Remarks:

Decreasing log Kd with increasing pH

Sample No.:

#5

Type:

log Kd

Value:

ca. 1.9 - ca. 5.5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (200 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 3-6.6; c(NaNO3)=0.1 mol/L; c(FA) = 200 mg/L

Remarks:

Increasing log Kd with increasing pH

Sample No.:

#5

Type:

log Kd

Value:

ca. 2.8 - ca. 5.5 dimensionless

Temp.:

25 °C

Matrix:

Aluminium with FA (200 mg/L)

% Org. carbon:

0

Remarks on result:

other: Investigations in pH range ca. 6.6-10.2; c(NaNO3)=0.1 mol/L; c(FA) = 200 mg/L

Remarks:

Decreasing log Kd with increasing pH

Adsorption and desorption constants:

See "Adsorption coefficient" table above

Transformation products:

no

Sorption on bare alumina

A steep increase in log Kd and the independence of log Kd on ionic strength were observed from 0.5 at pH 3 to 5 at pH 8. The steep increase in sorption is a typical behavior for the sorption of hydrolysable transition metal ions on hydrous oxides.

At pH > 9, log Kd values decreased with increasing pH, and this decrease in log Kd can be attributed mainly to a decrease in ≡SOH concentration and to an increase in concentrations of hydrolysis species and carbonate complexes of Yb(III) in aqueous media.

Obviously, the sorption-desorption hysteresis and the sorption of a positively charged species onto a positively charged surface are direct evidence for the formation of coordination bonds between the surface of bare alumina and Yb(III).

 

Sorption on coated alumina

It was found that in the pH range 3-7, the log Kd values at an initial FA concentration of 25 mg/L were slightly higher than that in the absence of FA, and that in the pH range 3-7, FA was almost exhausted from the aqueous solution and the coating of FA was formed at the bare alumina surface.

In the pH range 8-11, the concentration of FA at equilibrium increased with increasing pH, and in the pH range 7-11, the log Kd values in the presence of FA were lower than those in the absence of FA. The log Kd of Yb(III) vs. pH plots at the initial concentrations 50 and 200 mg/L, show the dependence of FA concentration at equilibrium on the pH. In the pH range 2-7, when the FA initial concentration was increased, the log Kd values obviously increased, i.e. the log Kdv s. pH plots shifted towards lower pH, and that even if the FA initial concentration was 200 mg/L, the FA was almost exhausted from aqueous solution in the pH range 2-7. The FA concentration at equilibrium increased with increasing pH in the pH range 8-11, at pH >8 the log Kd values decreased with increasing pH and the values were even less than those in the absence of FA.

When FA was added, the fact that the log Kd values increased in the pH range 2-7 can be explained by the fact that the complexation of the rare earth elements with the functional groups of FA sorbed on the alumina is stronger than the complexation with the surface hydroxyls of the bare alumina.

Conversely, if the complexation of rare earth elements with the functional groups of FA sorbed on the sorbent is weaker than the complexation with the surface hydroxyls of the bare adsorbent, a negative effect of FA would be observed. The dependence of log Kd on pH in the pH range 2-7 can be attributed to an increase in the dissociation of the functional groups of FA sorbed on the alumina with increasing pH. The dependence of log Kd on pH in the pH range 8-11 can be attributed to a decrease in the extent of surface coverage of FA and to the increase in complexation with soluble FA in aqueous solution.

The sequence of Yb(III) and FA additions to the alumina-NaNO3-Yb-FA-water system was changed to check for reversibility of the sorption process, in these experiments Yb(III) or FA was allowed to react with alumina early on in the presence of NaNO3 for one hour. The log Kd vs. pH plot for adding FA early is slightly higher than that for adding Yb early, and though these results indicate a similar sorption-desorption hysteresis under the conditions of this work, there was not really much difference. This weak hysteresis may be partially explained by the fact that because of the heterogeneous nature of FA, those FA molecules sorbed on alumina are different from those remaining in solution and the FA molecules sorbed early on alumina with high affinity for alumina are not readily reversible.

Validity criteria fulfilled:

not applicable

Conclusions:

Yb(III) sorption on aluminium is strongly dependent on pH. In the pH range of ca. 3 to 8, log Kd values increase with increasing pH. Thereafter a decrease of log Kd values could be observed.

Executive summary:

The present experimental work studied the effects of pH, ionic strength and dissolved fulvic acid (FA) on sorption of Yb(III) on alumina under aerobic conditions. The sorption of Yb(III) onto a bare alumina surface was shown to be dependent on pH, but independent of ionic strength. The sorption mechanism of the hydrolysable rare earth element Yb(III) appears not to be pure ion exchange and the surface hydrolysis model can qualitatively and satisfactorily explain the observations on bare alumina.

The presence of FA significantly affected the sorption of Yb(III) onto alumina, the surface of alumina was coated by FA and the coating of FA had a significant effect on the surface properties of alumina. However, the effect of FA was dependent on pH and concentration of FA, the sorption of Yb(III) was seen to be either enhanced or decreased at different pH ranges as compared with FA free systems. The competition between the complexations of sorbed FA and dissolved FA with rare earth elements can explain the observations on coated alumina.

This information is used in a read-across approach in the assessment of the target substance.

Due to the low water solubility of the metal components contained in the test substance (zirconium oxide, hafnium and ytterbium doped), a full transformation/dissolution protocol was carried out to study the potential release of these metals to the environment.

After 7 and 28 days (nominal loading of 100 mg/L, pH 8), only ytterbium(III) was found in solution with a maximum concentration of 0.069 µg/L. Zirconium and hafnium were both below the detection limit of 0.07 and 0.02 µg/L, respectively. Therefore, information on ytterbium(III) is relevant for the assessment of environmental fate properties of zirconium oxide, hafnium and ytterbium doped and adsorption studies with ytterbium are used in a read-across approach to fulfil the REACH requirements for endpoint 9.3.1 “Adsorption/desorption screening”.

Description of key information

The adsorption of Yb(III) on silica and aluminium is strongly dependent on pH. While adsorption at acidic pH values in negligible, Kd values at the pH range of ca. 6.6 to 8 range between 2,300 and 12,000.

Key value for chemical safety assessment

Other adsorption coefficients

Type:

other: Kd (silica surfaces)

Value in L/kg:

2 278

Additional information

Rauf et al. (1996) investigated the adsorption of Yb (3.8 x E-06 M) on sand after equilibration of 10 min. The adsorption coefficient Kd has been calculated at different temperatures between 18 and 37 °C. The Kd value increases with increasing temperature. At the temperature of 18 °C the Kd value is 24.2 cm³/g. The pH value at which the study was conducted is, however, not reported.

 

Marmier et al. (1999) conducted experiments to investigate the adsorption of Yb(III) on silica surfaces at a pH range between 4 and 8. Ionic strength in the batch experiments was constant at 0.1. Measurements were conducted after an equilibrium phase of 7 days. At pH values < 5.5 no adsorption of Yb3+on silica could be observed. Slight increases of pH from ca. 5.9 to ca. 6.6 considerably increased the amount of sorbed Yb3+ from ca. 6 % to ca. 82 %, corresponding to Kd values of ca. 35 L/kg at pH 5.9 and ca. 2278 L/kg at pH 6.6, when 100 mg of silica were added. When only 10 mg/L silica were applied no adsorption of Yb3+ was reported at a pH of 5.9. At a pH of 6.5 ca. 10 % were adsorbed and at pH 7 ca 70 %, corresponding to Kd values of 559 L/kg and 11667 L/kg, respectively.

 

The sorption of Yb(III) on aluminium was investigated by Wang et al., 2000. The effects of pH, ionic strength and dissolved fulvic acid on sorption of Yb(III) on alumina under aerobic conditions were studied. The sorption of Yb(III) onto a bare alumina surface was shown to be dependent on pH, but independent of ionic strength. At pH 3-8, Kd values increased with increasing pH from 3.16 to 10,000 (log Kd range from 0.5 to 5). At pH values > 9 the Kd values decreased to ca. 3,200 at pH 10.5. 

The presence of fulvic acid (FA) significantly affected the sorption of Yb(III) onto alumina, the surface of alumina was coated by FA and the coating of FA had a significant effect on the surface properties of alumina. However, the effect of FA was dependent on pH and concentration of FA, the sorption of Yb(III) was seen to be either enhanced or decreased at different pH ranges as compared with FA free systems. The competition between the complexations of sorbed FA and dissolved FA with rare earth elements can explain the observations on coated alumina.

This information is used in a read-across approach in the assessment of the target substance.

Due to the low water solubility of the metal components contained in the test substance (zirconium oxide, hafnium and ytterbium doped), a full transformation/dissolution protocol was carried out to study the potential release of these metals to the environment.

After 7 and 28 days (nominal loading of 100 mg/L, pH 8), only ytterbium(III) was found in solution with a maximum concentration of 0.069 µg/L. Zirconium and hafnium were both below the detection limit of 0.07 and 0.02 µg/L, respectively. Therefore, information on ytterbium(III) is relevant for the assessment of environmental fate properties of zirconium oxide, hafnium and ytterbium doped and adsorption studies with ytterbium are used in a read-across approach to fulfil the REACH requirements for endpoint 9.3.1 “Adsorption/desorption screening”.