Scandium

Scandium finds its application in mercury vapor lamps, Russian MIG fighter planes and tracers in the oil industry (RSC 202011). Due to the limited use, there have been hardly any reports of scandium pollution till date. However, the adsorption studies were available mostly for its extraction from rare-earth element solutions.

The percentage removal of scandium increased with increase of pH (Ramasamy et al. 2017; Ma et al. 2014; Zhao et al. 2016). The high competition of the hydronium ion at low pH was held responsible for the low removal at low' pH (Ma et al. 2014).

In the case of scandium adsorption on “silica doped with bifunctional ionic liquid”, the adsorption of the scandium decreased with increasing concentration of the nitric acid (Turanov et al. 2016), and scandium is separated from lanthanides(III) by simply adjusting the pH of the aqueous phase. The adsorption of scandium from the rare-earth element solution with lysine-modified SBA-15 increased with increase of pH, but below pH 5, there was no adsorption of any rare-earth element (Ma et al. 2014).

In some cases, the maximum adsorption capacity was achieved at lower pH, e.g. the percentage removal of scandium from the rare-earth element solution with “PAN immobilized chemically onto APTES-functionalized silica gel” (PAN= l-(2-pyridylazo)-2-napththol and A PTES = 3-A mi nopropyl triethoxy silane) was c.a. 100% at pH 4 and did not change on increase of pH up to 7. However, the immobilized material changes under different conditions, e.g. percentage removal with “acetylacetone immobilized chemically onto APTES-functionalized silica gel” increased on increase of pH from 4 to 7 (Ramasamy et al. 2017). In addition, the percentage removal declined in a natural water solution of rare-earth element with “PAN immobilized chemically onto APTES-functionalized silica gel” at pH 4, and the percentage removal increased on increase of pH under real water conditions (Ramasamy et al. 2017).

The percentage removal of scandium was 93% from the rare-earth element solution with “PAN immobilized chemically onto APTES-functionalized silica gel” in a time period of 15 min (Ramasamy et al. 2017). The faster removal was attributed to the smaller ionic radius of scandium. The rapid adsorption of scandium with lysine-modified SBA-15 is attributed to the -CO group acting as an effective adsorption site (Ma et al. 2014).

The lysine-modified SBA-15 has selective adsorption at pH 5 toward scandium at a low concentration of the rare-earth element solution (Ma et al. 2014). This was due to the presence of interaction strength between the functional groups (-NH2 and -CO) and metal ions and smaller ionic radius of scandium. This led to higher polarizability of the scandium ion. The adsorbent dose also plays a role in selectivity like in the case of adsorption of scandium removal from red mud solution with “tri-butyl phosphate-modified activated carbon”; at an adsorbent dosage of 6.25 g/1, the percentage removal of scandium was higher than the rest of the elements. This helps in choosing the optimum dose in respect of selectivity for scandium in the presence of other ions. The increase of the adsorbent dose leads to escalation in removal efficiency for other elements (Hualei et al. 2008). The desorption of the scandium can be achieved with acidic media, e.g. nitric acid and (Turanov et al. 2016) sulfuric acid (Zhao et al. 2016).

Titanium

Titanium finds its application in a wide number of products like aircraft, golf clubs, laptops, power plant condensers, hulls of ships, submarines, paint, enamels and sunscreens. There is no known biological role of titanium (RSC 2020j). In addition, it is nontoxic in aqueous media. So there are only a few reports for titanium adsorption from water like its nanomaterial removal (Kiser et al. 2009). In addition, there were some theoretical studies for adsorption of titanium on other solid surfaces (Ciszewski et al. 1998; Gale et al. 1999; Kucharczyk et al. 2010). The adsorption of titanium on tungsten leads to decrease in work function (Szczudlo et al. 2001).

Gallium

Gallium has no biological role and is considered as a nontoxic element (RSC 2020e). However, there are studies on recovery of gallium along with arsenic (gallium arsenide) from the semiconductor industry (Sturgill et al. 2000) and from bayer liquor (Zhao et al. 2012). An overview of the experimental parameters and optimized conditions from batch adsorption experiments for gallium is presented in Table 5.2.

TABLE 5.2

Summary of Parameters and Optimized Conditions for Batch Adsorption of Gallium and Germanium

Surface Area

(m2/g), Pore

Volume

(em’/g), Pore

Experimental

Adsorption Capacity

Adsorbent

Adsorbate

Size (nm)

pHzpc

Conditions

(mg/g)

Bentonite

Ga

pH = 1-3

Dose = 5-3 5 g/1

Agitation speed

= 300 rpm

Concentration

=5.74x10-’M

Contact time

= 5-300 min

Temperature

=20°C-70°C

Quaternary

Ga

pH = 1-3

0.48 meq/g

amphoteric

Dosc = 10 g/1

starch

Concentration

=57-570 mg/1

Contact time

=2h

Temperature

= 30°C-60°C

Sodium chloride

concentration

=up to 1 M

Tertiary

Do

0.54 meq/g

amphoteric

starch

Thermodynamic Parameters

Kinetic Model and Curve Fitting

Isotherm Model and Curve Fitting

Maximum

Adsorption

Conditions

pH =2.5

Dose = 35 g/1

Temperature = 20°C

References

Chegrouche and Bcnsmaili (2002)

AH°=7.65 Kcal/ mol

AS” =20.18-20.48 cal/mol

AG° = positive

pH =0 M HCI

Concentration = 57 mg/l

Temperature = 60 °C

Sodium chloride concentration = 0 M

Chan (1993)

AH° = 7.84 Kcal/ mol

AS° =21.12-21.19 cal/mol

AG° = positive

Do

Chan (1993)

Remediation of Miscellaneous Elements 197

TABLE 5.2 (Continued) 05

Summary of Parameters and Optimized Conditions for Batch Adsorption of Gallium and Germanium

Surface Area

Adsorbent

Adsorbate

  • (m2/g), Pore Volume
  • (cm’/g), Pore

Size (nm)

pHzpc

Experimental

Conditions

Adsorption Capacity (mg/g)

Thermodynamic Parameters

Kinetic Model and Curve Fitting

Isotherm Model and Curve Fitting

Maximum

Adsorption

Conditions

References

Nano-TiO,

Nano-SiO, (batch and column study)

Ga

Ga

pH = 1-5

Dose = 10 g/l Concentration =up to 25 mg/l (isotherm study)

Temperature =2°C-40°C

pH = 1-14

Dose = 1 g/l

Concentration

= 10-50 mg/l (isotherm)

Contact lime =upto4min

Temperature =275-323 K

  • 8.92
  • 5.77 and 4.6 in column study

A H°= 18.96-24.03 kJ/mol

AG° negative

A°S= 110.1-

140.2 J/K mol

A°H = 6.18-8.72 kJ/mol

A°S =97-102 J/ mol К

A °G=negative

Pseudo-second Linear Dubininorder linear Radushkevich

isotherm (only DR isotherm is analyzed)

Pseudo-second Langmuir order linear (no Linear (no comparison comparison with

with first other isotherms)

order)

pH =3-5 (pH 3 chosen in the study)

Temperature = 40 °C

pH =3-4 and 8-12

Contact lime = 1 min

Temperature = 323 K

Zhang. Zhu. et al.

(2010)

Zhang ct al.

(2011)

Alum water treatment sludge

Ga

Surface area

= 47.17

5.6

pH =3-10 Dose = 10 g/l Concentration

= 1 mg/l

Contact lime =2h

Temperature

=25°C

28.74

Pseudo-second-order model

Freundlich model

pH =3-4

Huaet al. (2015)

Bauxite

Ga

Surface area

= 28.97

7.9

Do

19.72

Pseudo-second-order model

Freundlich model

Do

Huaet al. (2015)

Batch Adsorption Process of Metals and Anions

TABLE 5.2 (Continued)

Summary of Parameters and Optimized Conditions for Batch Adsorption of Gallium and Germanium

Surface Area

(m2/g), Pore

Adsorbent

Adsorbate

Volume

(cm3/g), Pore

Size (nm)

pHzpc

Experimental Conditions

Adsorption Capacity (mg/g)

Thermodynamic Parameters

Kinetic Model and Curve Fitting

Isotherm Model and Curve Fitting

Maximum

Adsorption

Conditions

Blast furnace

Ga

Surface area

5.8

Do

3.21

Pseudo-second-

Freundlich model

Do

slag

= 3.37

order model

Bauxite

Ga

Surface area

6.6

Do

8.70

Pseudo-second-

Freundlich model

Do

processing

= 17.13

order model

residue sand

Activated

Ge

Surface area

3.8

pH = 5. 8 and 10

4.6

pH = 5

carbon

= 1580

Dose = 4 g/1

Contact time = 60

(catechol-

Pore volume

Concentration

min

functionalized

= 0.64

= 50 mg/l

Ge)

Contact time

= up to 420 min

Temperature

= 23°C

Activated

Surface

7.1

Do

8.7

pH = 5

carbon T

area= 1540

Contact time = 420

(catechol

Pore

min

ftmctionalized

volume =0.62

Ge)

Catechol-

Ge

pH=2-12

6.07

Pseudo-second-

Langmuir model

pH =4.5

functionalized

Dose = 2 gm/1

order model

linear

Contact time = 30

nanosilica

Agitation speed

linear

min

References

Hua et al. (2015)

Hua ct al. (2015)

Marco-Lozar et al. (2007)

Marco-Lozar et al. (2007)

Cui et al. (2016)

= 300 rpm Concentration

= 5-50 mg/l

(isotherm)

contact time = 2 h

Temperature

=25 °C

Remediation of Miscellaneous Elements 199

Effect of pH and Coexisting Ions

The adsorption of gallium increased on raising the pH up to 3 or 4 (Hua et al. 2015; Zhang et al. 2011; Zhang, Zhu, et al. 2010); after that, it starts to precipitate as Ga(OH)3 (Hua et al. 2015). After pH 7, it forms soluble Ga(OH)~4. In some cases, the adsorption of Gallium declined after pH 7 (Hua et al. 2015; Zhang et al. 2011). This was attributed to the isoelectric point of the adsorbent (Zhang et al. 2011). The surface of the adsorbent was positive below the isoelectric point and negative above it. The positively charged gallium species occurred below pH 4. Hence, adsorbents having isoelectric point in the acidic region prefer to adsorb more in the acidic region than in the basic region. The absence of gallium ions in the solution reduced the adsorption of aluminum or vice versa with graphene oxide (Jankovsky et al. 2015).

Effect of Temperature and Desorption

The increase in temperature causes percentage removal to be decreased (Chegrouche and Bensmaili 2002) or increased (Chou et al. 2010) varying from adsorbent to adsorbent. The reason for increase in adsorption with rise in temperature was credited to the increase in rate of diffusion of particles across the external surface and into the interior pores of the adsorbent molecules (Chou et al. 2010). Sodium hydroxide was applied for the desorption of gallium from nano-TiO, (Zhang, Zhu, et al. 2010).

Sodium hydroxide and HC1 were applied for the desorption of gallium from nano-TiO, (Zhang, Zhu, et al. 2010) and polyacrylic acid-functionalized graphene oxide, respectively (Zhang, Liu et al. 2019).

Germanium

Germanium has no known toxicity toward human beings, but being effective against bacteria, it has been utilized in many fields such as electronics and infrared spectroscopy (RSC 2020f; Cui et al. 2016). An overview of the experimental parameters and optimized conditions from batch adsorption experiments for germanium is presented in Table 5.2.

Effect of pH and Desorption

The Ge-catechol complex is not stable at pH = L The adsorption for Ge was performed by previously converting germanium to a complex (Marco-Lozar et al. 2007). The optimum pH was found to be pH 5 (Marco-Lozar et al. 2007) and 4.5 (Cui et al. 2016). The higher adsorption at acidic pH is credited to the positive surface charge on the adsorbent below pHzpc, and after pHzpc, it was negative, and there is repulsion between the adsorbent and the adsorbate (Marco-Lozar et al. 2007). Apart from electrostatic interaction, adsorption of germanium on catechol-modified silica is also attributed to complex formation (Cui et al. 2016). Hydrochloric acid is used for germanium-catechol complex desorption from activated carbon (Marco-Lozar et al. 2007).

 
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