Influence of Adsorption Process Parameters on the Removal of Hexavalent Chromium (Cr(VI)) from Wastewater: A Review

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 597-630

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Influence of Adsorption Process Parameters on the

Removal of Hexavalent Chromium (Cr(VI)) from

Wastewater: A Review

Sunil Rajoriya*, Ahlaam Haquiqi, Bhawna Chauhan, Girish Tyagi*, Avdesh Singh Pundir*, Ajay

Kumar Jain

Chemical Engineering Department, Meerut Institute of Engineering and Technology, Meerut-250005, India

Received: 23/12/2019

Accepted: 16/02/2020

Published: 20/05/2020

Abstract

In recent years, the release of heavy metals into the aquatic environment has become a major issue. Numerous socio-economic problems

are caused due to the presence of several heavy metals in wastewater. Hexavalent chromium (Cr (VI)) is one of the major heavy metal present

in the wastewater which comes from various industries such as fertilizers, pesticides, metal cleaning, dyes and pigment, especially in tannery

industry. Numerous methods have been employed for the removal of Cr (VI) from wastewater. Adsorption has been reported as a suitable

method due to its high efficiency, low cost, generation of minimum chemical sludge and reusability of the prepared adsorbents. In this review,

various adsorption process parameters such as solution pH, adsorbent dosage, temperature and initial Cr (VI) concentration have been

reviewed on the removal efficiency of Cr (VI) from wastewater. The percentage removal of Cr (VI) strongly depends upon pH of the solution

and the optimum pH range was found to be 1.0-4.0. The reusability of the used adsorbents has also been discussed. It is comparatively good

for practical applications. It can be concluded that the most of the adsorbents have good regeneration capability. This review paper suggested

that the adsorption process parameters had an important role on the removal efficiency of Cr (VI) from wastewater.

Keywords: Adsorption, Wastewater treatment, Hexavalent chromium, Reusability

Introduction¹

in wastewater so that Cr(VI) could be come in the acceptable

levels before discharge in to aquatic environment (6-10). There

are following four stages of the conventional chromium treatment

processes as (8): (a) Cr(VI)–Cr(III) reduction, (b) at higher pH,

precipitation of Cr(III) as Cr(OH) , (c) settle down of the

insoluble metal hydroxide, and (d) disposal of the dewatered

sludge.

Numerous methods such as ion exchange, electrochemical

reduction, precipitation, adsorption and reverse osmosis have

been reported in literature for the treatment of chromium-laden

wastewater. Between all the above methods, adsorption has been

considered to be an appropriate method for the removal of Cr(VI)

from wastewater (11-15). The some advantages of the adsorption

process are its ease of operation, effectiveness and economic

viability.

In the last two decades, various new materials as adsorbents

such as tea waste (1), modified groundnut hull (4), treated waste

newspaper (6), activated neem leaves (13) and banana peel (15)

efficient adsorbents have developed for the removal of Cr (VI).

Mostly adsorbents have shown their higher adsorption efficiency

towards the treatment of wastewater due to their lesser time. But,

The discharge of heavy metals into the water bodies has

become a major environmental concern over the world (1-2).

Amongst all the heavy metals, hexavalent chromium (Cr(VI)) has

been considered one of the major pollutant which is soluble in

water and has deleterious effects on environment as well as

human health (3-4). The major sources of Cr(VI) in

wastewater/waterbodies are electroplating, textile dyeing and

especially tanning processing industries (5). Hexavalent

chromium is highly toxic substance and mutagenic to the most

organisms and is recognized to cause cancer; it also causes lung

carcinoma in human lives [2]. The Cr(VI) is present in the excess

quantity in water/wastewater beyond a permissible limit which

results in skin irritation, ulcer formation, liver damage and

pulmonary congestion [1]. World Health Organization (WHO)

recommended the maximum permissible limit of hexavalent

chromium concentration is 0.05 mg/L in wastewater [1].

According to United States Environmental Protection Agency

(US EPA), the acceptable level of Cr(VI) is 0.05 mg/L for potable

water and is 0.1 mg/L for inland surface waters. Considering this

limit, it is necessary for industries to control their chromium level

Corresponding authors: (a) Sunil Rajoriya, Chemical Engineering Department, Meerut Institute of Engineering and Technology, Meerut-

50005, India. E-mail: sunilrajoriya@gmail.com. (b) Girish Tyagi, Chemical Engineering Department, Meerut Institute of Engineering and

Technology, Meerut-250005, India. E-mail: girish.tyagi@miet.ac.in. (c) Avdesh Singh Pundir, Chemical Engineering Department, Meerut

India.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 597-630

some adsorbents have limited applications because of their low

adsorption capacity and high contact time. The purpose of this

review article is to investigate the influences of various adsorption

process parameters i.e. solution pH, adsorbent dosage,

temperature and initial Cr(VI) concentration on the removal

efficiency of Cr(VI) from wastewater. A summary on the

reusability of the used materials as efficient adsorbents has also

been presented in this review article.

dosage of 10 g/L was enough to acquire maximum removal of

chromium (92.5%) where initial Cr(VI) concentration was 50

mg/L with temperature of 20°C and agitation speed of 150 rpm

(22). It had been reported that the Cr(VI) removal percentage was

enhanced from 74 to 99% for an increase in dosage from 0.5-

1.5g/L due to the number of available sites of adsorption and

surface area increased (20). Usually, it was understood that

chromium removal efficiency was enhanced with increase in the

adsorbent dosage up to an optimum as the number of vacant sites

available for uptake of heavy metals. Nevertheless, adsorbent

dosage cannot keep increasing to attain higher adsorption because

of cost becomes a limiting factor and therefore adsorbent dosage

is required to optimize for adsorption process.

Influence of various adsorption parameters on

the removal efficiency of Cr (VI)

.1 Influence of solution pH

Literature has reported that solution pH is a major factor

affecting the adsorption efficiency of Cr(VI). The solution pH

dependency of metal adsorption is generally linked to the

functional groups of the adsorbents surface and ionic forms of

metal ions in the solution (6, 16). It had been reported that

maximum Cr(VI) removal efficiency was found under acidic

conditions (1, 6, 9, 10, 17, 18-20). The summary of work done in

the area of adsorption process for the removal of Cr(VI) from

wastewater in recent years has been presented in Table 1. The

reduction of Cr(VI) to Cr(III) may comprise generally two main

mechanisms as: (1) the reduction of Cr(VI) to Cr(III) by electron-

donor groups of the adsorbent surface and the reduced Cr(III)

forms complexes with materials (2) the adsorption-coupled

reduction of Cr(VI) to Cr(III) takes place on the sites of

adsorbents (1, 17, 18). In literature, Cr(VI) is easily reduced to the

Cr(III) due to its high redox potential value (1.3 V at standard

state) under acidic conditions (1). In this regards, Nigam et al. (1)

have studied the effect of pH over a pH range of 2–10 on the

removal of Cr(VI) at an adsorbent dosage of 6 g/L and

temperature of 30°C. Almost 97% removal was obtained at an

optimum solution pH of 3.9 in 240 min of processing time.

Owalude et al. (4) have investigated the removal of hexavalent

chromium from aqueous solutions using modified groundnut hull

as an efficient adsorbent at various pH. It was observed that acidic

conditions are more relevant for the removal of Cr(VI) due to the

presence of HCrO as a dominant species on to easy contact to

the binding sites on the adsorbents so that electric attraction with

H+ ions on the surface of adsorbent can adsorbed higher metal

ions. Therefore, maximum Cr(VI) removal of 96% was found at

a low pH of 2.0. Chen et al. (20) have studied the effect of solution

pH on the Cr(VI) removal from wastewater using modified corn

stalks. They have reported that maximum adsorption of

hexavalent chromium (99.5%) was obtained at pH value of 2.3.

Hence, it is very important to optimize the solution pH for

each and every prepared new material as an adsorbent in order to

achieve the maximum Cr(VI) removal efficiency from the

wastewater.

.3 Influence of temperature

Temperature plays an important role in deciding the removal

efficiency of Cr(VI) in the adsorption process (4, 5, 12, 14). It is

necessary to identify the suitable temperature to get good

adsorbent efficiency. The nature of the adsorption can be assumed

depending on the process responds with variation in employed

temperature. The adsorption of heavy metals increases with an

increase in the temperature therefore a process/reaction is

endothermic in nature (5, 12, 17) whereas adsorption of metals

decreases for an increase in the temperature therefore a

process/reaction is exothermic in nature (8). In addition to this, to

determine the process whether it is endothermic or exothermic;

the thermodynamic parameters such as ΔG°, ΔH° and ΔS° need

to be calculated. It has been reported that the values of change in

entropy (ΔS°) and change in enthalpy (ΔH°) can be calculated

from the intercept and slop of plot lnKeq v/s 1/T (1, 5). The

positive values of ΔH° show that the adsorption process is

endothermic in nature and vice-versa (1). Various researchers

have reported the temperature effect over a range of 10 - 60°C for

the various adsorbents towards the Cr(VI) removal from

wastewater (1-5,12, 14-15, 17). Nigam et al. (1) have studied the

effect of temperature over a range of 20 to 40°C on the removal

of Cr(VI) using tea waste as an adsorbent and observed that the

maximum of 97% removal of chromium was obtained at a

temperature of 30°C. The percentage removal of Cr(VI) was

enhanced for an increase in the temperature from 20 to 40°C,

which may be due to the increase in diffusion rate of the metal

ion. Similar results were also reported by other study that the

percentage removal of chromium was increased with an increase

in the temperature suggesting that the adsorption process is an

endothermic process (3, 5, 12, 14, 17). Apart from these studies,

some studies have reported that the adsorption capacity decreased

for an increase in the temperature advising that the adsorption

process was exothermic process (4, 8). Hence, it is very important

to find the temperature conditions so that process could be

identified that it is either endothermic or exothermic in nature.

.2 Influence of adsorbent dosage

Adsorbent dose is another major important factor in the

.4 Influence of initial Cr (VI) concentration

The initial Cr(VI) concentration in wastewater samples is

adsorption process which regulates the amount of metal ion

removal and the economics of process. In the adsorption,

adsorbent dosage to be used can be considered broadly by

carrying out experiments where the amount of adsorbent is varied

when other conditions are kept constants (20-22). It had been

reported that there are various ranges of the different adsorbents

dosage (shown in Table 1). In a literature study of Cr(VI) removal

using biomass of Agaricus bisporus, it was seen that an adsorbent

another important factor which influences the adsorption capacity

of the metal ions. Previous studies have reported that the

percentage removal efficiency of Cr(VI) is decreased at higher

initial concentration of the Cr(VI) (3, 5, 13, 16, 20).

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 597-630

Table 1: Summary of work done on Hexavalent Chromium Cr(VI) removal from wastewater using different adsorbents

Ranges of Process parameters studied

Treated

Cr(VI)

S. No.

Adsorbent

Volume,

Optimum conditions

removal References

(%)

Adsorbent

dosage

Temperature

(°C)

Initial Cr(VI)

Concentration

pH = 3.9, adsorbent dosage =

g/L, T = 30°C, initial Cr(VI)

concentration = 141 mg/L,

time = 240 min

Tea waste

200

2-11

2-10 g/L

20-40

141-455 mg/L

96.7

Nigam et al. (1)

Synthesized

chitosan from

crab shell

pH = 3, adsorbent dosage =

5g/100mL, T = 60°C, time =

60 min

345±1 mg/L

100

3-8

1-6

1-8

1-5 g/L

10-50 mg

30-60

10-50

10-40

99.9

Hossain et al. (2)

Acharya et al. (3)

Owalude et al. (4)

(real effluent)

pH = 1, adsorbent dosage =

Activated carbon

from Tamarind

wood

g/L, T = 30°C, time = 40

10-50 mg/L

min, , initial Cr(VI)

concentration = 30 mg/L

pH = 2, initial Cr(VI)

concentration = 13 mg/L,

time = 60 min, T = 28°C

Modified

groundnut hull

12.5-18 mg/L

pH = 4; adsorbent dosage =

.5g/L, time = 180 min, T =

5°C, initial Cr(VI)

Paper mill sludge

100

2-6

2-7

1-6

1.5-7 g/L

0.4-4g/100mL

20-45

10-100 mg/L

5-70 mg/L

98.4

Gorzin et al. (5)

concentration = 10mg/L

Treated waste

newspaper

pH = 3, adsorbent dosage =

3g/L, time = 60 min

Dehghani et al. (6)

pH=1.5, adsorbent dosage =

Ocimum

americanum L

seed pods

g/L, time = 120min, initial

Cr (VI) concentration =

0mg/L

Levankumar et al.

(7)

100-200mg/L

100

pH = 2, adsorbent dosage = 4

g/L, T= 30°C, time = 70 min,

initial Cr (VI) concentration =

Fertilizer industry

waste material

1-3

1-10g/L

0.05- 0.6g

4-16g/L

30-50

10-100 mg/L

2 mM

Gupta et al. (8)

Pehlivan et al. (11)

Babu et al. (13)

00 mg/L

pH = 2, adsorbent dosage =

0.2g, time = 120 min, T =

25±1°C, initial Cr(VI)

concentration = 2 mM

pH =1-3, adsorbent dosage =

Oak wood

charcoal

1-7

0 g/L, T = 30°C, initial

0. Neem leaves

1-11

20-700 mg/L

Cr(VI) concentration = 50

mg/L

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 597-630

Ranges of Process parameters studied

Treated

Volume,

Cr(VI)

removal References

(%)

S. No.

Adsorbent

Optimum conditions

Adsorbent

Temperature

Initial Cr(VI)

Concentration

dosage

(°C)

pH= 2, adsorbent dosage = 2

g/L, T = 30°C, initial Cr(VI)

concentration = 150 mg/L;

pH = 2, adsorbent dosage =

1g/50mL, T = 26±1°C, initial

Cr(VI) concentration =

Premkumar et al.

14)

1. Ragi husk

2-4

2-5g/L

25-30

50-150 mg/L

10-70 mg/L

68.6

54.8

(

Pre-boiled

2-7

0.2 -1g

Jain et al. (16)

Altun et al. (17)

Gode et al. (18)

Dahbi et al. (19)

Chen et al. (20)

sunflower stem

0mg/L, time = 180min

pH = 2, time = 120min,

adsorbent dosage = 0.1 g, T =

25±1°C; initial Cr(VI)

concentration = 1 mM

pH = 3, T =25±2°C, adsorbent

dosage = 0.1g, initial Cr(VI)

concentration = 1 mM, time

= 120min

Modified walnut

shell

2-9

0.02-0.20 g

0.1g

25-65

0.1-1.0 mM

5-25 mg/L

Modified red pine

saw dust (tartaric

acid modified saw

dust)

3-10

1-11

1.8-5.2

87.7

pH =1, adsorbent dosage =

gm, initial Cr(VI)

5. Bone charcoal

0.5-2 g

concentration = 10 mg/L,

time = 30min

pH = 2.3, adsorbent dosage =

1.5g/L, initial Cr(VI)

Modified corn

stalks

0.5-4 g/L

25-50

100-400 mg/L

99.5

concentration = 100mg/L, T

25±1°C, time = 60 min

pH = 1, adsorbent dosage =

10g/L, initial Cr(VI)

concentration = 50mg/L, T =

Biomass of

100

1-7

3-15 g/L

1-40 g/L

20-40

25-125 mg/L

10-100 mg/L

92.4

99.9

Ertugay et al. (21)

Ahalya et al. (22)

Agaricus bisporus

0°C

pH = 2, adsorbent dosage =

1g/100mL, initial Cr(VI)

concentration = 10mg/L,

time = 180min

Husk of Bengal

gram

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 597-630

Table 2: Overview on the reusability of the prepared adsorbents by various researchers for the removal efficiency of Cr(VI)

Frequency of

reusability

Cr(VI) Removal

efficiency (%)

S. No.

Adsorbent

Optimum conditions

References

pH = 3.9, adsorbent dosage = 6

g/L, T = 30°C, initial Cr(VI)

concentration = 141 mg/L, time

Tea waste

90.5

Nigam et al. (1)

240 min

pH=3, adsorbent

Treated waste

newspaper

dosage=0.4g/250mL, initial

Cr(VI) concentration =20mg/L,

time= 60min

Dehghani et al. (6)

Gorzin et al. (5)

pH = 4; adsorbent dosage =

.5g/L, time = 180 min, T =

Paper mill sludge

68.34

5°C, initial Cr(VI)

concentration = 50mg/L

pH = 3, adsorbent dosage =

5g/100mL, T = 60°C, time =

Synthesized chitosan

from crab shell

Hossain et al. (2)

Memon et al. (15)

Huang et al. (23)

0 min

pH =2, time = 30min, initial

Cr(VI) concentration = 1.92 x

Banana peel

pH =2.0, adsorbent dosage =

0.5 g/500 mL, T = 30°C, time

Chitosan/MWCNTs-

COOH composite

30min

Chitosan functional

gel including with

multiwall carbon

nanotube and

pH =2.0, adsorbent dosage =

0.5 g/100 mL, initial Cr(VI)

concentration = 6 mg/L

Kim et al. (24)

substituted

polyaniline

pH =4.0, adsorbent dosage =

0.13 g/100 mL, initial Cr(VI)

concentration = 48 mg/L

pH =2.0, adsorbent dosage = 2

g/L, initial Cr(VI)

concentration = 50 mg/L

pH =2.0, adsorbent dosage =

0% Aliquat

36/60% PVC PIM

Gherasim et al.

(25)

30.83

Chitosan grafted GO

nano-composite

Samuel et al. (26)

Sharma et al. (27)

0 mg/L, initial Cr(VI)

AC of Cornulaca

monacantha stem

concentration = 20 mg/L,

contact time = 120 min, T =

5°C

In this context, Acharya et al. (3) have studied the effect of

initial feed concentration of Cr(VI) using adsorption at constant

temperature of 30ºC and pH of 6.5 and found that % removal of

chromium decreased from 88 to 63% (at 3 g/L adsorbent dosage)

with an increase in initial concentration of Cr(VI) from 10 to 50

mg/L. A similar observation was also made by Babu et al. (13),

the initial Cr(VI) concentration was varied from 40 to 700 mg/L

at the adsorbent dosage of 10 g/L. They have found that the

percentage Cr(VI) removal decreased from 99.95% to 89.94%

when Cr(VI) concentration increased from 40 to 700 mg/L.

However, literature have reported that at higher concentration of

the chromium, the adsorption capacity increases (12, 13, 20).

Therefore, it is need to be reported in terms of adsorption

capacity. In this regard, Hasan et al. (12) found that adsorption

capacity increased for an increase in the initial concentration of

Cr(VI). A similar trend was also found by Babu et al. (13). They

have reported that adsorption capacity increases from when initial

Cr(VI) concentration increases. From the above studies, it is clear

that % removal of Cr(VI) gets reduced for an increase in the initial

concentration whereas adsorption capacity was found to be higher

at higher concentration. Therefore, it is required to report the data

in terms of percentage removal as well as adsorption capacity.

Overview on the reusability of used adsorbent

In the area of wastewater treatment, reusability of the

prepared adsorbent is the most significant step because of

untreated amount in excess may led to the disposal problems (1,

, 6). The adsorbent can be recycled. The economy of the

adsorption process depends upon how many times the prepared

adsorbents can be reused without sacrificing its percentage

removal efficiency. Many authors have reported on the reusability

study of the adsorbents for the hexavalent chromium removal in

recent years (1, 23-27). Nigam et al. (1) have studied about the

reusability of the tea waste as an adsorbent and found that the %

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 597-630

removal of Cr(VI) was removed from 96.7% to 90.5% after five

repeated cycles. Samuel et al. (26) have investigated the

reusability test of the chitosan grafted graphene oxide (CS-GO)

nano-composite and reported that the % removal of Cr(VI) was

decreased from 96% to 82% after ten cycles. Sharma et al. (27)

reported that the adsorption efficiency for Cr(VI) removal was

dropped to 89.19% after five consecutive cycles. Kim et al. (24)

have observed that the CS-MWNT-PAA-PADPA/FG showed

nearby 85% removal efficiency of Cr(VI) even after three

consecutive adsorption-desorption cycles. An overview on the

reusability of used adsorbents reported in the literature is

summarized in Table 2. Overall, it can be concluded that the

percentage Cr(VI) removal decreases with an increase in the

regeneration cycles of the used adsorbents.

5. Gorzin F, Abadi MMBR. Adsorption of Cr(VI) from aqueous

solution by adsorbent prepared from paper mill sludge: Kinetics and

thermodynamics studies, Adsorption Science & Technology. 2017;

6(1-2): 149-169.

Dehghani MH, Sanaei D, Ali I, Bhatnagar A. Removal of

chromium(VI) from aqueous solution using treated waste newspaper

as a low-cost adsorbent: Kinetic modeling and isotherm studies,

Journal of Molecular Liquids. 2016; 215: 671-679.

7. Levankumar L, Muthukumaran V, Gobinath MB. Batch adsorption

and kinetics of chromium (VI) removal from aqueous solutions by

Ocimum americanum L. seed pods, Journal of Hazardous Materials.

009; 161: 709-713.

Gupta VK, Rastogi A, Nayak A. Adsorption studies on the removal

of hexavalent chromium from aqueous solution using a low cost

fertilizer industry waste material, Journal of Colloid and Interface

Science. 2010; 342: 135-141.

Tahir SS, Naseem R. Removal of Cr(III) from tannery wastewater by

adsorption onto bentonite clay, Separation and Purification

Technology. 2007; 53: 312-321.

Conclusions

The influences of various adsorption process parameters on

0. Sarin V, Pant KK. Removal of chromium from industrial waste by

using eucalyptus bark, Bioresource Technology. 2006; 97: 15-20.

the removal efficiency of Cr(VI) from wastewater using various

adsorbents have been reviewed. There are some conclusions from

this review as following:

11. Pehlivan E, Kahraman H, Pehlivan E. Sorption equilibrium of Cr(VI)

ions on oak wood charcoal (Carbo Ligni) and charcoal ash as low-

cost adsorbents, Fuel Processing Technology. 2011; 92: 65-70.

•

The percentage removal of Cr(VI) depends upon the solution

pH and maximum removal efficiency of Cr(VI) from

wastewater is found under acidic conditions. The optimum

pH range for all adsorbents used in the current work is 1.0-

2. Hasan SH, Singh KK, Prakash O, Talat M, Ho YS. Removal of

Cr(VI) from aqueous solutions using agricultural waste ‘maize bran’,

Journal of Hazardous Materials. 2008; 152: 356-365.

3. Babu BV, Gupta S. Adsorption of Cr(VI) using activated neem

leaves: kinetic studies, Adsorption. 2008; 14: 85-92.

4. Premkumar M, Abinandan S, Sowmya V, Shanthakumar S. Efficacy

of Eleusine coracana (L.) Gaertn (Ragi) Husk for Adsorption of

Chromium(VI): A Study Using Response Surface Methodology,

Environmental Progress & Sustainable Energy. 2015; 34: 139-145.

5. Memon JR, Memon SQ, Bhanger MI, El-Turki A, Hallamc KR, Allen

GC. Banana peel: A green and economical sorbent for the selective

removal of Cr(VI) from industrial wastewater, Colloids and Surfaces

B: Biointerfaces. 2009; 70: 232-237.

.0.

•

Adsorbent dosage should be optimized for newly developed

materials to achieve the maximum removal efficiency of

Cr(VI) from wastewater because every prepared adsorbent

have different adsorption capacity.

It is needed to study the influence of temperature in the

adsorption process for identifying the nature of

adsorption/reaction (either endothermic or exothermic).

From literature, lower concentration is more favorable for

achieving the higher removal efficiency of Cr(VI) whereas

adsorption capacity is found to be higher at higher initial

Cr(VI) concentration.

•

6. Jaina M, Garg VK, Kadirvelu K. Chromium(VI) removal from

aqueous system using Helianthus annuus (sunflower) stem waste,

Journal of Hazardous Materials. 2009; 162: 365-372.

17. Altun T, Pehlivan E. Removal of Cr(VI) from aqueous solutions by

modified walnut shells, Food Chemistry. 2012; 132: 693-700.

•

It is seen that reusability of the prepared adsorbent helps in

the disposal problems and economy of the adsorption process.

8. Gode F, Atalay ED, Pehlivan E. Removal of Cr(VI) from aqueous

solutions using modified red pine sawdust, Journal of Hazardous

Materials. 2008; 152: 1201-1207.

Competing interests

19. Dahbi S, Azzi M, de la Guardia M. Removal of hexavalent chromium

from wastewaters by bone charcoal, Fresenius Jounal of Analytical

Chemistry. 1999; 363: 404-407.

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

0. Chen S, Yue Q, Gao B, Li Q, Xu X. Removal of Cr(VI) from aqueous

solution using modified corn stalks: Characteristic, equilibrium,

kinetic and thermodynamic study, Chemical Engineering Journal.

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