Introduction

Metals are ubiquitous in the environment because of their wide application (Ajmani et al. 2019b). They are present in the solid phase and solution, as free ions, or adsorbed to colloidal soil particles. From these metals, hexavalent chromium has no known vital or beneficial effect on organisms, even for bacterial cells, and its accumulation over time in organisms can cause serious illness even at low concentration. According to World Health Organization (WHO) guidelines, the allowable concentration of Cr (VI) in drinking water is 50 ppb (Jiang et al. 2013). However, humans could be exposed to higher-level chromium contamination through food or drinking water. Industries such as leather tanning, steel fabrication, metal finishing, and other industrial sources related to wood preservation are the major causes of this contamination (Eliku and Leta 2018). The human health effects of hexavalent chromium exposure are respiratory irritation, dermatitis, lung cancer, kidney, and liver damage (Ofudje et al. 2014; Jiang et al. 2013). Therefore, the removal of Cr would be necessary to improve the quality of water and the life of humanity. In line with minimizing the adverse effect on human health nowadays, there are several Cr removal mechanisms. For the removal of chromium from wastewater, adsorption is highly effective compared to other conventional methods (Pranay et al. 2015; Shahnaz et al. 2020b). Adsorption is a process that occurs when a gas or liquid or solute (called adsorbate) accumulates on the surface of a solid or more rarely a liquid (adsorbent), forming a molecular or atomic film. Adsorption process can be influenced by a number of factors such as pH, adsorbate concentration, adsorbent dosage, and other factors (Costanzo et al. 2012).

Most clay can soak up electrically charged atoms and molecules from the solution. Clays’ mineral composition, crystal structural characteristics, and their crystalline size make them potentially sound absorbers (Hoidy et al. 2009). Besides, because of their availability and cost-effectiveness, clay minerals become the most critical industrial resource. As a result, clays have received considerable attention, especially as potential adsorbents for environmental research. In line with the adsorption potential of clay mineral, in the eastern part of Ethiopia, specifically in Saketa district, there is a clay locally named Odaracha. In most of the rural areas of West Hararghe zone of Oromia, regional state peoples depend on this particular kind of clay (Odaracha clay) to remove turbidity of water in their day-to-day life and commercially exchanged in the market for this particular purpose in some woredas. Odaracha soil is a novel adsorbent material and has not been reported in the literature. Therefore, the principal aim of this study was to investigate the effectiveness of Odaracha clay in the removal of Cr from synthetic wastewater. The effect of various parameters such as contact time, pH, adsorbent dose, and initial concentration of adsorbate on adsorption efficiency of Odaracha was considered.

Materials and methods

Chemicals and analytical methods

The chemicals consumed in these set of experimental activities were all of analytical grade. The standard stock solution of chromium (1000 mg/L) was prepared by dissolving 2.828 g of 99.9% analytical-grade K2Cr2O7 in 1000 mL of distilled water. All the required solutions are made ready with analytical-grade reagents and double-distilled water. Synthetic samples of different concentrations of chromium are prepared from this stock solution by appropriate dilutions. The functional groups involved in the adsorption process were identified by Fourier transform infrared (FTIR) spectroscopy (Model 65 spectrometer, USA). X-ray powder diffraction analysis was performed using the XRD spectrometer (PAN analytical X’Pert Pro) with recorded 2θ XRD patterns of 5° to 60°. The surface morphology of Odaracha adsorbent was characterized using INSPECT F50 field emission scanning electron microscope (SEM).

Adsorbent preparation

In this study, a locally available soil type, known by the local community as Odaracha clay, was used as an adsorbent. This natural coagulant is abundantly available in Saketa District West Hararghe zone of Oromia Regional State, Ethiopia. It is also commercially exchanged in the market of Boke Tiko woreda, and the rural communities have been using this clay material to remove water turbidity. In this research, the soil sample was taken from Saketa district (N: 08° 44′ 41.3″ E: 040° 45′ 15.1″, altitude 1470). After air-dried, the soil has been crushed into the desired size and sieved using 125-µm laboratory sieve. Finally, Odaracha powder was dried in the oven with a 120 °C temperature level for 6 h and kept inside the desiccator until the adsorption experiment.

Batch adsorption experiments

The batch adsorption studies were conducted at room temperature by agitating measured quantities of the Odaracha adsorbent in 50 ml of synthetic wastewater at the rate of 150 rpm with the required pH, contact time, dose of the adsorbent and initial concentration of the adsorbate. The timing was started upon the addition of adsorbent. These experiments were run in different Erlenmeyer flasks having a capacity of 150 ml. After shaking, the sample was taken and filtered by the Whatman membrane filter paper of pore size 0.45 µm. Finally, the sample was analyzed by FAAS (Flame Atomic Absorption Spectrophotometer, Model 210 VGP) for the remaining chromium ion in the solution. The experiments were undertaken in triplicate, and the average results are presented. The removal efficiencies of Odaracha adsorbent were investigated based on the following equations. The percentage of chromium removal is obtained using Eq. 1, while the adsorption capacity \({q}_{e}\) is calculated using Eq. 2.

$$\% {\text{removal}} = \frac{{\left( {C_{{\text{o}}} - C_{{\text{e}}} } \right)}}{{C_{{\text{o}}} }} \times 100$$
(1)

where Co = initial adsorbate concentration (mg/L); Ce = final equilibrium adsorbate concentration (mg/L).

$${q}_{e}= \frac{\left({C}_{\mathrm{o}}- {C}_{\mathrm{e}}\right)V}{w}$$
(2)

where Co and Ce are the initial and equilibrium liquid-phase concentrations of the Cr ions in mgL−1, respectively, V is the volume of the solution in L, w is the amount of adsorbent used in g, and \({q}_{\mathrm{e}}\) is the removal efficiency of adsorbent in mg/g.

Isotherm and kinetic studies

To study the adsorption isotherms, the optimum conditions found in optimization experiments were applied only by varying adsorbent doses. These experiments were carried out using adsorbent dose in the range of 1, 3, 5, 7, 10, 15, and 20 g/L. For each adsorbent dosage, 50 ml of the sample was taken and agitated at 150 rpm. The data from the experiment were fitted into Langmuir and Freundlich adsorption isotherm models (Gulipalli et al. 2011). It is essential to know the rate at which the process takes place, factors that control the rate of the process; for this reason, the kinetics of the processes were assessed. These experiments were conducted by setting heavy metal concentration, pH, adsorbent dosage, and agitation speed constant. Then, the sample was withdrawn at 30, 60, 90, 120, 150, 180, and 210 min for the determination of residual heavy metals in the solution. Then, data from the experiment were introduced into the pseudo-first-order model of Lagergren and pseudo-second-order models of Ho and McKey (Dagmawi and Mekibib 2013; Gulipalli et al. 2011).

Results and discussion

Characterization of Odaracha adsorbent

Scanning electron microscope (SEM) studies

The scanning electron microscope (SEM) images shown in Fig. 1 revealed the surface morphology of Odaracha adsorbent before and after adsorption. As shown in Fig. 1a, b Odaracha adsorbent appears rough and porous before adsorption. However, as depicted in Fig. 1c, d, the morphology of Odaracha adsorbent after Cr adsorption appears different where the pores are filled and much smoother. This is an indication of the adsorption of Cr onto the surface of Odaracha adsorbent.

Fig. 1
figure 1

SEM images of Odaracha adsorbent before adsorption (a, b) and after adsorption (c, d)

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FTIR studies

The FTIR spectra of Odaracha clay are shown in Fig. 2. The spectra in the region 3200–3650 cm−1 and the maximum peak 3408 cm−1 were due to –OH stretching vibration. The strong peaks at 2519, 1432, and 1038 cm−1 were due to O–H (carboxylic acid) stretching, C–O, and Si–O–Si (organic siloxane or silicone) bond, respectively (Ghoneim et al. 2014; Kyziol-Komosinska et al. 2014). The spectra viewed below 1000 cm−1 are more comparable to the mineral features of the material. To identify the possible functional groups on Odaracha adsorbent involved in the binding of Cr, FTIR spectra were obtained before and after adsorption. If a ligand coordinates to a metal, the ligand material’s energy will most likely be disturbed, leading ultimately to shifts in the absorption peaks in the FTIR spectra. These FTIR adsorption bands are ordinarily shifted to lower or upper frequencies. In this regard, there are small shifts of vibration from 873, 1038, 2131, 2519, 2874, and 3408 cm−1 in Odaracha adsorbent to 872, 1027, 2127, 2518, 2870, 3408 cm−1 for chromium-loaded adsorbent, respectively. The disappearance of intensities and shifting of peaks to new values signify the involvement of functional groups in the adsorption process.

Fig. 2
figure 2

FTIR spectrum (400–4000 cm−1 (I) and 400–1000 cm−1 (II)) of raw (a) and chrome-loaded (b) Odaracha powder

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XRD studies

X-ray diffraction (XRD) analysis was commenced using Cu Kα1 radiation on a computer-controlled XRD machine model of X’ pert pro-PANalytical. XRD patterns were recorded from 5° to 60° 2θ. The XRD peaks and analysis for raw Odaracha clay before adsorption are shown in Fig. 3. The XRD analysis of powder Odaracha clay revealed the presence of gypsum, alumina, quartz, calcite, dolomite, and magnetite. The characteristic peaks at 23.34, 29.5, 39.6, and 43.36 for the raw Odaracha sample indicated calcite (CaCO3) as the main constituent. Some characteristic peaks at 10.62, 11.74, and 36.1 show the presence of gypsum (CaSO4.2H2O); the peaks at 20.82 and 26.64 show the presence of quartz (SiO2); the peak at 14.6 shows the presence of alumina (Al2O3); the peaks at 32 and 48.64 show the presence of dolomite (CaMg(CO3)2) and magnetite (Fe3O4), respectively.

Fig. 3
figure 3

X-ray diffraction patterns of raw Odaracha clay. Mineral assignments: gypsum (■), alumina (Δ), quartz (▼), calcite (□), dolomite (●) and magnetite (○)

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Effect of various parameters on adsorption of chromium

Effect of contact time

Effect of contact time between the adsorbate and adsorbent particles is one of the important factors in the adsorption studies. To realize the effect of contact time on Cr adsorption on Odaracha adsorbent and to discern the optimum contact time between the adsorbate and adsorbent, the experiment was carried out at room temperature and led within the time range of 60–240 min in 60-min interval using 15 g/L adsorbent dose and by tuning pH of the solution at 3. Other parameters such as agitation speed and adsorbate concentration were retained constant to 150 rpm and 110 mg/L, respectively.

The result of the effect of contact time revealed in Table 1 shows that with an increase in contact time there is also an increase in percent adsorption of Cr. There was very rapid adsorption at the initial period up to 60 min, and after that, the increase in the adsorption rate was gradual. The adsorption process attained equilibrium in 180 min, which was 94.68%. Then, no significant change in Cr removal was observed after 180 min. This is attributed to a large number of vacant surface sites which are available for adsorption during the initial stage of adsorption. As it is shown in Table 1, percentage of removal efficiency of chromium and adsorption of chromium in mg/g showed the same type of increasing trend since there was no variation of adsorbent dose in this set of experiments.

Table 1 Effect of contact time on Cr removal efficiency (Co = 110 mg/L, agitation speed = 150 rpm)
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Effect of pH

The pH is a principal parameter in adsorption process because of its effect on the adsorption efficiency (Attia et al. 2010; Shahnaz et al. 2020a). The functional groups responsible for the binding of metal ions in the adsorbent surface are profoundly affected by pH. There is also a competition between ions that are present in the solution for the adsorbent’s active sites. This competition is affected by the pH of the solution (Reddy et al. 2014). The effect of pH on the adsorption process was examined by undertaking the batch procedure at 120-min contact time, under room temperature, constant agitation speed which is 150 rpm, and 15 g/L of adsorbent dosage. The investigation results on the effect of pH on chromium removal by Odaracha adsorbent are revealed in Table 2. As illustrated in Table 2, it was found that the uptake of Cr increases with decreasing pH. Accordingly, the optimum pH for the maximum uptake of chromium was pH 3. In this regard, Odaracha adsorbent gave the highest removal percentage at pH 3, which is 76.31%.

Table 2 Effect of pH on Cr removal efficiency (Co = 110 mg/L, agitation speed = 150 rpm)
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Conversely, the minimum adsorption capacity was observed at pH 6, which is 74.15%. In this experimental condition, since the adsorbent dose and initial concentration of the adsorbate had been kept constant, both adsorption percent and removal in mg/g show similar increasing trends with decreasing pH of the solution (Ajmani et al. 2019b). As per the result, the maximum chromium uptake in mg/g was detected at pH 3, which is 5.596 mg/g. At acidic pH, the dominant form of hexavalent chromium is HCrO4−, and at higher pH, other forms CrO42− or Cr2O72− predominate. Therefore, the higher adsorption capacity observed at lower pH is due to the strong electrostatic attraction between surface groups and HCrO4− (Singha and Das 2011; Zhu and Han 2013).

The interaction between HCrO4−, CrO42− and Cr2O72− ion and adsorbent surface decreases at higher pH because the adsorbent surface becomes negatively charged, and also there is an abundance of OH− in aqueous solution, which can be attributed to the competitive adsorption of Cr2O72− and OH−. Other previous studies have also reported similar situations (Hsua et al. 2009; Owlad et al. 2010; Rangabhashiyam and Selvaraju 2015). In another way, at lower pH, the degree of surface protonation is high, so that the surface offers a maximum positive charge for adsorption of HCrO4−, which is predominant at lower pH. Therefore, at lower pH, the predominant hydrogen chromate ion (HCrO4−) requires one exchange site from Odaracha adsorbent to be adsorbed, while at higher pH, it requires two exchange sites from Odaracha adsorbent for one chromate ion (CrO42−) adsorption (Nizam Nik Malek 2007). Generally, adsorption of chromium is higher in acidic media because at lower pH, the degree of surface protonation is very high, which plays a vital role in capturing hydrogen chromate ion (HCrO4−) in the solution.

Effect of adsorbent dose

As pointed out in Table 3, the effect of the dosage of Odaracha adsorbent on the removal efficiency of chromium was determined with varied adsorbent doses, which are 1 g/L, 5 g/L, 10 g/L, and 15 g/L under different experimental conditions.

Table 3 Effect of adsorbent dose on Cr removal efficiency (Co = 110 mg/L, agitation speed = 150 rpm)
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As shown in Table 3, the adsorption percentage of chromium increased from 60.04 to 94.68% as the adsorbent dose increased from 1 to 15 g/L, whereas the uptake of Cr in mg/g falls from 66.042 mg/g to 6.943 mg/g when the adsorbent dose increases from 1 to 15 g/L. Higher chromium adsorption percentage with the increase in the adsorbent dose can be attributed to increasing in surface area and the availability of more binding sites for adsorption (Karthik et al. 2018; Rao et al. 2002; Reddy et al. 2014; Umoren et al. 2013). The decrease in uptake of Cr in mg/g with increased adsorbent dose may be due to the unchanged initial concentration of metal ion and the substantial adsorption capacity of the smallest adsorbent dose or less availability of surface area per unit weight (Ajmani et al. 2019a). Similar trends have also been reported by other authors relating to the effect of adsorbent doses on adsorption efficiency of Cr (Garg et al. 2007; Ghorbani et al. 2008).

Effect of initial concentration of adsorbate

The rate of adsorption is a function of the initial concentration of adsorbate, making it a substantial factor to be considered for the optimum experimental conditions of adsorption. The effect of the various initial concentrations of chromium (30, 50, 70, 90, 110, 130, and 150 mg/L) on Cr removal efficiency at constant experimental conditions like pH 3, 180-min contact time, 150 rpm agitation speed and 15 g/L adsorbent dose is presented in Table 4.

Table 4 Effect of initial concentration of adsorbate on Cr removal efficiency
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The adsorption percentage of chromium with the various initial concentrations of adsorbate in different constant experimental conditions such as pH, contact time, agitation speed, and the adsorbent dose is presented in Table 4. According to the result exemplified in Table 4, the effect of initial concentration of Cr on the adsorption percentage shows a decreasing trend, which is 95.69, 95.33, 95.09, 94.70, 94.68, 86.88 and 83.94% with 30, 50, 70, 90, 110, 130 and 150 mg/L of adsorbate concentration, respectively. This can be explained by the fact that all adsorbents have a limited number of active sites, and at a specific concentration, the active sites become saturated (Banat et al. 2000; Tsai and Chen 2010). In another way, the reverse trend is observed in the case of Cr uptake in mg/g, which shows the increasing trend of Cr uptake, which is 1.91, 3.18, 4.44, 5.68, 6.94, 7.53, and 8.39 mg/g with increasing initial concentration of adsorbate from 30 to 150 mg/L by 20 mg/L interval. This is maybe because, at constant adsorbent dose, the number of active sites to accommodate the chromium ions remains unchanged while with rising adsorbate concentrations, the chromium ions to be accommodated increased. Therefore, the loading was faster, with a higher initial concentration of adsorbate.

Kinetic study for adsorption of chromium

To understand the rate and type of adsorption that takes place, the study applies pseudo-first-order and pseudo-second-order kinetic models.

Pseudo-first-order kinetic model

The pseudo-first-order model is expressed by Eq. (3):

$${\mathrm{log}(q}_{\mathrm{e}}- {q}_{t})= {logq}_{e}- \frac{{k}_{1}t}{2.303}$$
(3)

where \({q}_{\mathrm{e}}\) and \({q}_{t}\) \({(\mathrm{mgg}}^{-1})\) represent the amount of Cr ions adsorbed per unit weight of the adsorbents at equilibrium and time t (min), respectively, and k1 is the rate constant of the pseudo-first-order kinetic model.

The pseudo-first-order kinetics is applicable if the plot of log \({(q}_{\mathrm{e}}-{q}_{t})\) against time (t) shows a linear relationship. In addition, the straight-line plot of log \({(q}_{\mathrm{e}}-{q}_{t})\) versus t was used to determine the rate constant (k1), \({q}_{e}\) (cal) and the correlation coefficient (R2). The values of k1 and \({q}_{\mathrm{e}}\) (cal) in mg/g of Cr predicted from the plot shown in Fig. 4 are 4.836 × 10–2 and 49.162 mg/g, respectively. As the result presented in Table 5, the correlation coefficient (R2 = 0.5552) indicates that the experimental data of the adsorption kinetics of chromium are not accurately supported by the pseudo-first-order model.

Fig. 4
figure 4

Pseudo-first-order kinetics plots for the adsorption of Cr ions onto Odaracha adsorbent

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Table 5 Line-fit model of pseudo-first- and second-order kinetics for Cr
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In a second way, the plot of log \({(q}_{\mathrm{e}}-{q}_{t})\) against time (t), which is shown in Fig. 4, does not display a linear relationship, which again communicates the unsuitability of the pseudo-first-order model. Furthermore, the experimental adsorption result (\({q}_{\mathrm{e}}\) (exp)) was not closer to \({q}_{\mathrm{e}}\) (cal). Therefore, the pseudo-first-order model is not suitable to explain the adsorption kinetics of Cr ions on Odaracha adsorbent (Arshadi et al. 2014; Sag and Aktay 2002).

Pseudo-second-order kinetic model

The pseudo-second-order model is expressed by Eq. (4):

$$\frac{t}{{q}_{t}}= \frac{1}{{K}_{2}{q}_{e}{.}^{2}} +\frac{t}{{q}_{e}}$$
(4)

where \({q}_{e}\) and \({q}_{t}\) (mg g−1) represent the amount of Cr ions adsorbed per unit weight of the adsorbents at equilibrium and time t (min), respectively, and k2 is the rate constant of the pseudo-second-order kinetic model. The rate constant (k2) and calculated equilibrium adsorption capacity (\({q}_{\mathrm{e}}\) (cal)) can be determined from the slope and intercept of the plot \(t/{q}_{t}\) versus t, which is shown in Fig. 5. The plot \(t/{q}_{t}\) versus t should give a straight line to apply the pseudo-second-order kinetic model. The plot of \(t/{q}_{t}\) versus t for pseudo-second-order yields a good straight line with the highest correlation coefficient result approaching 1 (R2 = 0.971). In addition, as presented in Table 5, the experimental adsorption equilibrium value (\({q}_{\mathrm{e}}\) (exp.) = 6.943 mg g−1) was well matched with the calculated adsorption equilibrium value (\({q}_{\mathrm{e}}\) (cal.) = 7.745 mg g−1). Therefore, the experimental data of the adsorption kinetics of chromium are accurately supported by a pseudo-second-order model. Thus, this finding suggests that the rate-limiting factor in the adsorption of chromium by Odaracha adsorbent is chemisorption involving the exchange of Cr ions with functional groups in the adsorbent (Rahman and Sathasivam 2015; Senthil and Gayothri, 2013).

Fig. 5
figure 5

Pseudo-second-order kinetics plots for the adsorption of Cr ions onto Odaracha adsorbent

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Isotherm model for adsorption of chromium

In this study, the evaluation of the equilibrium of the adsorption process was carried out by introducing the experimental results into Langmuir and Freundlich isotherm models.

Langmuir adsorption isotherm model for chromium

Equilibrium study for the removal of chromium was performed on the Odaracha adsorbent powder by Langmuir adsorption model. According to the Langmuir isotherm model, the adsorption sites are uniformly equal and no attraction occurs between the adsorbed molecules; hence, monolayers of the molecules are deposited on the Odaracha powder (Langmuir 1916).

The linearized form of this model is presented in Eq. (5) and was used in the determination of its parameters in accordance with Fig. 6.

$$\frac{1}{{q_{{\text{e}}} }} = \frac{1}{{q_{{\text{m}}} }} + \frac{1}{{q_{{\text{m}}} K_{{\text{L}}} }} .\frac{1}{{C_{{\text{e}}} }}$$
(5)

where qe represents the amount of adsorbed Cr in mg/g of the adsorbent, and Ce is the concentration of Cr at equilibrium in mg/L. KL and qm represent Langmuir adsorption constant and the maximum amount of adsorbate that can be adsorbed on Odaracha adsorbent (Langmuir 1918). The values of KL and qm for this study were determined from the slope and intercept shown in Fig. 6. One of the essential features of this model is its ability to determine RL as shown in Eq. (6), which is a dimensionless parameter known as equilibrium parameter or separation factor (Webber and Chakravarti 1974).

$$R_{{\text{L}}} = \frac{1}{{1 + (1 + K_{{\text{L}}} + C_{{\text{o}}} )}}$$
(6)
Fig. 6
figure 6

Langmuir adsorption isotherm model for chromium

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The adsorption process can be described as unfavorable if RL > 1, linear if RL = 1, favorable if 0 < RL < 1 and irreversible if RL = 0. The value of RL obtained in this study as presented in Table 6 is between 0 and 1, which suggests the Langmuir isotherm model is favorable in this study. The maximum monolayer coverage capacity (qm) obtained was 200 mg g−1. This result indicates that the maximum adsorption potential of 1 g of Odaracha adsorbent.

Table 6 Langmuir and Freundlich isotherm model constants for adsorption of Cr
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Freundlich adsorption isotherm model for Cr

The Freundlich isotherm model is an empirical equation employed to describe heterogeneous systems. In this model, it is described that during the adsorption process different sites of the adsorbent are involved with several adsorption energy (Kumar and Kirthika 2009). The linearized form of the Freundlich isotherm model is shown in Eq. (7).

$$\log q_{{\text{e}}} = \log K_{f} + \left( {1/n} \right)\log C_{{\text{e}}}$$
(7)

where qe is the metal uptake (mg g−1) at equilibrium, Kf is the measure of the adsorption capacity, 1/n is the adsorption intensity, and Ce is the final concentration of Cr in solution, or equilibrium concentration (mg L−1). The Freundlich isotherm constants Kf and 1/n are evaluated from the intercept and the slope, respectively, of the linear plot of log qe versus log Ce shown in Fig. 7.

Fig. 7
figure 7

Freundlich adsorption isotherm model for chromium

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If n is between 1 and 10, it indicates favorable adsorption (Goldberg 2005). However, if 1/n is < 1 it indicates normal adsorption, but if it is > 1, it implies cooperative adsorption (Mohan and Karthikeyan 1997). The numerical value of 1/n presented in Table 6 is 0.998, indicating a favorable adsorption process (Kannan et al. 2013).

Comparison of Odaracha and other natural adsorbents

A comparison results between the maximum adsorption capacity of Cr ions onto Odaracha adsorbent and other adsorbents are presented in Table 7. Table 7 shows that the maximum adsorption capacity obtained in this study was higher than other natural adsorbents illustrated in Table 7. Therefore, Odaracha soil can be used as effective and an alternative low-cost adsorbent for chromium.

Table 7 Comparison between the adsorption capacities of various natural adsorbents and Odaracha soil
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Conclusions

In the exploration result of this study, Odaracha soil sourced from Saketa district of Ethiopia was used for the removal of chromium from synthetic wastewater. The characterization results of Fourier transform infrared, X-ray powder diffraction analysis, and the surface morphology of Odaracha adsorbent, which shows the pores of the surface of the adsorbent before and after adsorption, were an indicator for its adsorption capacity. The adsorption capacity of Odaracha adsorbent was influenced by a number of factors such as contact time, pH, adsorbent dosage, and initial concentration of adsorbate. The optimum range of contact time, pH, Odaracha dose, and initial concentration of chromium obtained by the batch experiment was 180 min, pH 3, 15 g/L, and 30 mg/L, respectively. With optimum experimental conditions and at room temperature, Odaracha adsorbent removed 94.68% Cr from the wastewater. The adsorption kinetics of chromium is accurately supported with a pseudo-second-order model. The isotherm data were analyzed by Langmuir and Freundlich isotherms. The maximum monolayer coverage adsorption capacity from the Langmuir adsorption isotherm model was 200 mg g−1. Generally, the ability of Odaracha adsorbent in removing Cr from aqueous solutions has the potential to solve the problem of chromium-containing industrial effluents, which continue to pose increasing risks to human health and environment.