Nitrate

Nitrate is found naturally in the environment and can act as an important plant nutrient (WHO 2017). Leaching from natural vegetation acts as a source of groundwater contamination by nitrate. The major source of nitrate to humans is through vegetables and drinking water. The guideline value for nitrate is 50 mg/1 as nitrate ions. Nitrate can cause methemoglobinemia (Johnson 2019). An overview of the experimental parameters and optimized conditions from batch adsorption experiments for nitrate is presented in Table 6.2.

Effect of pH

The adsorption of nitrate is achieved at lower pH with chitosan-modified microsphere (Zhao and Feng 2016), quaternized melamine-formaldehyde resin (Banu and Meenakshi 2017b), Fe,O4/ZrO2/chitosan composite (Jiang et al. 2013), MgO-biochar, FeO-biochar (Usman et al. 2016), and potassium carbonate and ammonium chloride activated carbon (Nunell et al. 2015).

The high removal is attributed to the increase in the electrostatic force of attraction and increase in competition from hydroxide ions on increase in pH (Banu and Meenakshi 2017b; Jiang et al. 2013; Usman et al. 2016) and in some cases, lack of ionization of surface groups at higher pH (Zhao and Feng 2016). However, the maximum removal of nitrate was not achieved at the lowest pH as studied in some cases (Zhao and Feng 2016; Banu and Meenakshi 2017a, b). This phenomenon is attributed to the instability of the adsorbent at the lowest pH studied (Zhao and Feng 2016).

In some cases, the adsorption capacity after attaining the maximum adsorption capacity at a certain pH plateaued up to a pH (Banu and Meenakshi 2017a, b; Hu et al. 2015). The adsorption capacity was also not maximum at low pH in the sorption of nitrate with amino-functionalized MCM-41 (Ebrahimi-Gatkash et al. 2017) and graphene (Ganesan et al. 2013). The maximum adsorption was achieved under near-neutral conditions. The reason was attributed to the electrostatic phenomenon as a major factor governing the adsorption process.

Effect of Coexisting Ions

A number of anions such as bicarbonate, carbonate, sulfate, chloride, and fluoride affect the adsorption of nitrate (Srivastav et al. 2014; Banu and Meenakshi 2017b; Wan et al. 2012; Bagherifam et al. 2014). The effect of sulfate was more pronounced in the case of adsorption with hydrous bismuth oxide (Srivastav et al. 2014), chitosan quaternized resin (Banu and Meenakshi 2017a), quaternized form of melamineformaldehyde (Banu and Meenakshi 2017b), and granular chitosan-Fe3+ complex (Hu et al. 2015).

The effect of sulfate is attributed to the lower stability of sulfate (Srivastav et al. 2014) and charge density (Banu and Meenakshi 2017a, b). The effect of bicarbonate in the case of nitrate removal with hydrous bismuth oxide is attributed to increase of the pH, which led to decline of electrostatic attraction (Srivastav et al. 2014).

The effect of chloride and carbonate was more pronounced than sulfate in the case of adsorption with organoclay (Bagherifam et al. 2014) and calcined hydrotalcite (Wan et al. 2012). The more pronounced effect of carbonate than sulfate on nitrate removal with calcined hydrotalcite is attributed to charge density (Wan et al. 2012). The Hofmeister series of anions with respect to their free energy of hydration affected the removal of nitrate with organoclay. Anions with less free energy of hydration were advocated to have the least competitive effect. Therefore, sulfate has less effect as compared to chloride on nitrate removal.

Anions such as chloride, sulfate, and carbonate caused the decline in percentage removal from 93% in control to 72%, 79%, and 88%, respectively, with organoclay (Bagherifam et al. 2014). The results suggested by the author were in the order of

TABLE 6.2

Summary of Parameters and Optimized Conditions for Batch Adsorption of Nitrate

Surface Area

Adsorbent

Adsorbate

(m2/g), Pore Volume (em’/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

Modified chitosan

NOf

7.8-8.0

pH = 2-9

Dose = 0.2-2 g/1

Agitation speed = 120rpm

Concentration = 10-100 mg/1

Contact time = up to 360 min

Temperature = 303.15 K

32.15

Pseudo

second

Older

Linear

Langmuir model Linear

pH = 3

Dose = 1 g/1

Contact time = 90min

Zhao and

Feng (2016)

Hydrous bismuth oxide

NOf

7.8-8.0

pH = 5-10

Dose = 25-100 g/1

Concentration

= 14-56mg N/l

Contact time

= 60-360 min

Temperature

= 293-323 K

0.512 mg N/g

Pseudo-first order model Linear

Langmuir and Freundlich model Linear

Dose = 50 g/1

Concentration = 14 mg

N/l

Contact timc= 180min Temperature = 323 K

Srivastav ct al. (2014)

AhO/bio-TiOj

nanocomposite

NOf

pH = neutral Dose = 1-5 g/1 Agitation speed = 120rpm

Concentration

30.3

Pseudosecond order model Linear

Langmuir model No comparison

Dose = 2 g/1

Contact time = 60 min

Suriyaraj et al. (2015)

= 25-125 mg/1

Contact

lime= 200 min

Temperature

= room temperature

  • 222 Batch Adsorption Process of Metals and Anions
  • (continued)

TABLE 6.2 (Continued)

Summary of Parameters and Optimized Conditions for Batch Adsorption of Nitrate

Surface Area

(m2/g), Pore

Kinetic

Volume

Adsorption

Model and

Isotherm

(em’/g), Pore

Experimental

Capacity

Thermodynamic

Curve

Model and

Maximum Adsorption

Adsorbent

Adsorbate

Size (nm)

pHzpc

Conditions

(mg/g)

Parameters

Fitti ng

Curve Fitting

Conditions

References

Quaternized form of

NOf

6.3

pH =2-11

40.1

AH°

Pseudo -

Freundlich

pH = 4-8

Banu and

melamine

Dose = 0.5 -4 g/1

= -10.77 kJ/mol

second

Contact time = 30min

Meenakshi

formaldehyde

Agitation speed

AS°

order

Temperature =303 K

(2017b)

= 1 20rpm

= 0.02 kJ/mol

Concentration

AG°

= 50-300 mg/1

= negative

Contact time

= 5-40 min

Temperature

= 303-323 K

Chitosan-grafted

NOj-

pH =2-11

34.5

AH0

Pseudo

Freundlich

pH = 4-8

Banu and

quaternized resin

Dose = 0.5-3 g/1

= -29.36 kJ/mol

second

model Linear

Dose = 3 g/1

Meenakshi

Agitation speed

AS°

order

Contact time = 60min

(2017a)

= 1 20rpm

= 0.07 kJ/K mol

model

Temperature =303 K

Concentration

AG°

Linear

= 50-400 mg/1

= negative

Contact time

= 10-80 min

Temperature

= 303-323 K

Fe,()/Zr()2/chitosan

NOj-

pH = 3-8

89.3

Pseudo-

Langmuir model pH = 3

Jiang et al.

Dose = 0.5 g/1

first order

Linear

Contact time = 840min

(2013)

Agitation speed

model

= 150rpm

Linear

Concentration

= 1-1000 mg/1

(isotherm study)

Contact time

= c.a. 1440 min

Temperature = 25°C

Remediation of Anions 223

TABLE 6.2 (Continued)

Summary of Parameters and Optimized Conditions for Batch Adsorption of Nitrate

Adsorbent

Adsorbate

Surface Area

(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

Montmorillonite modified with hexadecylpyridinium chloride

NOf

Dose = 0.5-4 g/1 Concentration

= 0.2-1 mM

(isotherm study)

Contact time=24h

0.67 mmol/g

Pseudosecond order model

Langmuir model Dose = 2 g/1

Linear Contact lime = 120 min

Bagherifam et al. (2014)

De-Acidite FF-1P resin (batch and column study)

NOf

pH = 2-10

Dose = 5 g/1

Agitation speed

= lOOrpm

Concentration = 50-300 mg/1

Contact time

=0-60 min

Temperature = 293-323 K

35 and 30

AH0

= 27.45 to 34.68 kJ/mol

AS°

= 105.27-

131.19J/molK

AG°

= negative

Pseudo-first order model Nonlinear

Freundlich model nonlinear

pH = 2-6

Contact time = 25 min

Temperature = 323 К

Naushadet al.

(2014)

Polyacrylic anion exchange resin (batch and column study)

NOf

Surface

area=3.07

Pore size = 8.14

Dose = 2 g/1 Agitation speed = 140rpm Concentration = 0.805-4.83 mmol/1 (kinetic study)

Contact lime = up to 100 min

2.46 mmol/g

Pseudo first order and second order model

Langmuir and Freundlich model

Contact time = 20 min

Song et al.

  • (2014)
  • (continued)

224 Batch Adsorption Process of Metals and Anions

TABLE 6.2 (Continued)

Summary of Parameters and Optimized Conditions for Batch Adsorption of Nitrate

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

Chemically modified pinewood .sawdust

NOf

Dose = 3 g/1

Concentration

= 10. 30 and

50mgN/I

Contact timc = 2h

Temperature = 278.

296 and 313 K

32.8 mg N/g

AH”

= -6.8 kJ/mol AS°

= 0.11 kJ/moIK AG°

= negative

Redlich-

Peterson model

Linear

Temperature = 278 K

Kerânen et al.

(2015)

Anionic rice husk

NOf

pH = 3-11

Dose = 4 g/1

Agitation speed

= 400rpm

Concentration

= 50 mg/1

Contact time

= up to 110 min

Temperature = 2O°C-5O°C

8.32

AH0

= -19.56 kJ/mol

AS°

= 2.21 kJ/Kmol

AG°

= negative

Pseudosecond order model Linear

Langmuir, Freundlich and Dubinin-Radu shke vic h model

pH=7

Contact time = 90min

Temperatures 20°C

Katal, Baci.

et al. (2012)

Graphene

NOf

Pzc=5.7

pH = 2-12

Dose = 0.67 g/1

Agitation speed = 200rpm

Concentration = 100-500 mg/1

Contact limc= 12h

Température = 303-343 K

202.43

AH0

= 1.6102 kJ/mol AS0

= 5.31 J/Kmol AG°

= negative

Pseudosecond order model Linear

Langmuir model Linear

pH = 6.5-7.5

Contact time = 45 min Temperature = 343 K

Ganesan et al.

(2013)

Remediation of Anions 225

TABLE 6.2 (Continued)

Summary of Parameters and Optimized Conditions for Batch Adsorption of Nitrate

Surface Area

(m2/g), Pore

Kinetic

Volume

Adsorption

Model and

Isotherm

(cm3/g), Pore

Experimental

Capacity

Thermodynamic

Curve

Model and

Maximum Adsorption

Adsorbent

Adsorbate

Size (nm)

pHzpc

Conditions

(mg/g)

Parameters

Fitting

Curve Fitting

Conditions

References

Calcined hydrotalcite

NOf

11.50

pH = not controlled

34.36 mg N/g

Pseudo

Langmuir model

Wan et al.

(Mg/Al)

Dose = 2 g/1

second

Nonlinear

(2012)

Agitation speed

older

= 130rpm

model

Concentration

Linear

= 25 mg N/l

Contact time = 18 h

Temperature = 25°C

Granular chitosan-

NO,-

Surface area

5.4

pH = 3-12

8.35

AH°

Pseudo

Langmuir-

pH = 3-10

Hu et al.

Fe-U complex

= 8.98

Dose = 5-40 g/1

= -5.06 kJ/mol

second

Freundlich

Dose = 40 g/1

(2015)

Pore volume

Agitation speed

AS°

older

model

Contact time = 90 min

= 0.019

= 140rpm

= 27.65 J/mol К

model

Nonlinear

Temperature = 288 K

Pore size

Concentration

AG°

Nonlinear

= 5.69

= 0.9-4.62 mg

= negative

NO3-N/g

Contact time

= 120 min

Temperature = 288-

328 K

MgO-biochar

NO,-

Surface area

pH = 2-8

45.36

Pseudo

Langmuir model

pH=2

Usman et al.

= 391.8

Dose= 10 g/1

mmol/kg

second

Linear

Time = 30-60 min

(2016)

Pore volume

Agitation speed

order

= 0.012

= 250rpm

model

Pore size

Concentration

Linear

= 1.856

= 1-100 mg/1

(isotherm study)

Contact time

= up to 120 min Temperature = 25°C

226 Batch Adsorption Process of Metals and Anions

TABLE 6.2 (Continued)

Summary of Parameters and Optimized Conditions for Batch Adsorption of Nitrate

Surface Area

Adsorbent

Adsorbate

(m2/g), Pore

Volume

(cm3/g), Pore

Size (nm)

Experimental pHzpc Conditions

Adsorption

Capacity (mg/g)

Thermodynamic Parameters

Kinetic

Model and

Curve

Fitting

Isotherm

Model and

Curve Fitting

Maximum Adsorption

Conditions

References

Amino-functionalized

inesoporous MCM-41

NOf

Surface area

= 733

Pore volume

= 0.336

Pore size

= 1.86

pH = 4-8

Dose = 0.5-15 g/l

Agitation speed

= 150rpm

Concentration

= 30-250 mg/1

Contact time = 2h

Temperature = 25°C

38.81

Langmuir

pseudosecond older model

Linear

pH = 6-7

Dose = 10 g/l

Contact

time = equilibrium in 10-15 min and but adsorption process proceeded tor 120 min

Ebrahimi-

Gatkash et al. (2017)

K2CO3-activatcd carbon

NO3"

Surface area = 777cm2/g Pore volume = 0.35

Pore size = 1.81

pH = 2-7

Dose = up to 1.5 g/l

Agitation speed

= 300rpm

Concentration

= 0.1-6 mmol/1

Contact time

= 400 min

Temperature = 25°C

0.34 mmol/g

Pseudosecond order model

Langmuir model pH = 2

Dose =0.5 g/l

Contact time = 300min

Nunell et al.

(2015)

NII^OH-activated carbon

NO3"

Surface area = 58cm2/g Pore volume = 0.03

Pore size

= 1.91

pH =2-7

Dose=up to 1.5 g/l

Agitation speed

=300rpm

Concentration

=0.1-6 mmol/1

0.4 mmol/g

Pseudosecond order model

Freundlich model

pH = 2

Dose =0.5 g/l

Contact time = 30min

Nunell ct al.

(2015)

Contact

time=30 min

Temperature = 25 °C

Remediation of Anions 227

Hofmeister series of anions. Anions with less free energy of hydration have the least competitive effect.

Effect of the Material and Surface Modification

The increase in the Mg/AI ratio in precursor for the formation of calcined hydrocalcite influenced the adsorption capacity of calcined hydrotalcite (Wan et al. 2012). The increase of magnesium to aluminum ratio from 2 to 4 led to increase in adsorption capacity. The increase in the Mg/AI ratio decreased the electric charge density between layers, which led to the increase in the interlayer spacing (Wan et al. 2012). The adsorption of nitrate into the interlayer spacing was favored by the large size of the interlayer space.

The LaCl3 treatment of biochar increased the adsorption capacity by 11.2-fold (Wang, Guo, et al. 2015). This is attributed to the increase in basic functional groups that are positively correlated with nitrate removal efficiency.

The change in the number of amine groups via the surface modifying agent on the surface of MCM-41 led to the change in adsorption capacity (Ebrahimi-Gatkash et al. 2017). The change of the diamine group to the triamine group functionalized on the surface of the adsorbent led to the increase in amine groups. This lead to the increase in the adsorbed nitrate anion.

Mechanism

The mechanism of adsorption of nitrate is estimated by a number of methods. The value of mean adsorption energy was used to estimate the mode of adsorption, i.e. whether physical, chemical, or ion exchange (Srivastav et al. 2014; Banu and Meenakshi 2017a, b). To further support the ion exchange nature of adsorption, the authors used XRD, in which corresponding peaks at two theta 31.91° and 34.09° broadened (Banu and Meenakshi 2017b). The author suggested it to be due to replacement of the chloride ion with the nitrate ion, whereas the same authors in another study used EDX analysis to further prove the ion exchange adsorption process (Banu and Meenakshi 2017a). The role of the surface oxide group was investigated by use of FT-IR (Suriyaraj et al. 2015). The mechanism of adsorption can also be investigated on the basis of adsorption behavior at different pH values. The maximum adsorption of nitrate on graphene occurred at pH above the point of zero charge (PZC) of the adsorbent, i.e. 5.7 (Ganesan et al. 2013). At the point of maximum adsorption, the surface of the adsorbent was negative, and this suggests that the adsorption also occurred through a process other than the electrostatic force of attraction.

The mechanism of adsorption on calcined hydrotalcite occurred through the process of memory effect (Wan et al. 2012). The anion in the interlayer space is vaporized on calcination, and its place is taken by the nitrate anion after the adsorption process. This is supported by the disappearance of XRD peaks at two theta 43° and 62°. The peaks reappeared after adsorption with nitrate. This is also supported by weakening of the FT-IR peak corresponding to hydroxide and carbonate anions after calcination. The FT-IR peak at 1384cm-1 emerges after adsorption of nitrate.

Desorption

Sodium hydroxide (Zhao and Feng 2016; Berkessa et al. 2019), sodium chloride (Banu and Meenakshi 2017b), hydrochloric acid (Banu and Meenakshi 2017a), and alkaline pH (Jiang et al. 2013) have been used for the regeneration of the adsorbent. The adsorption efficiency declined after desorption (Zhao and Feng 2016; Banu and Meenakshi 2017b; Hu et al. 2015). The decline of adsorption capacity after the desorption cycle is attributed to irreversible adsorption sites on the surface of the adsorbent.

 
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