Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 2, Pages: 597-630  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link:  
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  
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  
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  
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  
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: (b) Girish Tyagi, Chemical Engineering Department, Meerut Institute of Engineering and  
Technology, Meerut-250005, India. E-mail: (c) Avdesh Singh Pundir, Chemical Engineering Department, Meerut  
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 210 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  
.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  
S. No.  
Optimum conditions  
removal References  
Initial Cr(VI)