Adsorption of Cr(VI) in Aqueous Solution Using a Surfactant-Modified Bentonite

Castro-Castro, Johnatan D.; Macías-Quiroga, Iván F.; Giraldo-Gómez, Gloria I.; Sanabria-González, Nancy R.

doi:https://doi.org/10.1155/2020/3628163

The Scientific World Journal

On this page

Abstract Introduction Experimental Results and Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2020 | Article ID 3628163 | https://doi.org/10.1155/2020/3628163

Adsorption of Cr(VI) in Aqueous Solution Using a Surfactant-Modified Bentonite

Johnatan D. Castro-Castro,¹Iván F. Macías-Quiroga,²Gloria I. Giraldo-Gómez,¹and Nancy R. Sanabria-González²

Academic Editor: Claudio Cameselle

Received20 Jan 2020

Accepted27 Feb 2020

Published21 Mar 2020

Abstract

Clay minerals can be modified organically by a cationic surfactant resulting in materials known as organoclays. The organoclays have been used as adsorbents of most of the organic contaminants in the aqueous solution and oxyanions of the heavy metal. In this study, a Colombian bentonite was modified with hexadecyltrimethylammonium bromide to obtain an organobentonite, and its capacity to adsorb Cr(VI) oxyanions in the aqueous solution was evaluated. The effect of pH, stirring speed, adsorbent amount, contact time, and ionic strength were investigated at 25°C. Stirring speeds above 200 rpm, contact times greater than 120 min, and the addition of NaCl (0.1 to 2.0 mM) did not have a significant effect on Cr(VI) removal. The influence of the adsorbent amount and pH on Cr(VI) adsorption was studied by the response surface methodology (RSM) approach based on a complete factorial design 3². Results proved that the Cr(VI) adsorption follows a quadratic model with high values of coefficient of determination (R² = 95.1% and adjusted R² = 93.9%). The optimal conditions for removal of Cr(VI) from an aqueous solution of 50 mg/L were pH of 3.4 and 0.44 g amount of the adsorbent. The adsorption isotherm data were fitted to the Langmuir and Freundlich adsorption isotherm models, and the model parameters were evaluated. The maximum adsorption capacity of Cr(VI) onto organobentonite calculated from the Langmuir model equation was 10.04 ± 0.34 mg/g at 25°C. The results suggest that organobentonite is an effective adsorbent for Cr(VI) removal, with the advantage of being a low-cost material.

1. Introduction

The removal of toxic substances from water and wastewater has been a core interest of many scientists and researchers around the globe over the past decades [1]. The rapid growth of industrialization and urbanization has resulted in increased environmental pollution, which has been a serious cause of public concern [2]. Among these pollutants, contribution of heavy metals is a major concern because of their toxicity, bioaccumulation, persistence, and nonbiodegradable nature [3]. Heavy metals such as cadmium, zinc, lead, chromium, nickel, copper, vanadium, platinum, and silver are generated in electroplating, electrolysis depositions, conversion-coating, and anodizing-cleaning, milling, and etching industries [1, 4].

Chromium is used in industries such as metallurgy, electroplating, production of paints and pigments, tanning, wood preservation, and pulp and paper production. The chromium pollution associated with these industries has adverse effects on aquatic ecosystems [5]. Chromium is ranked as number 17 on the priority list of hazardous substances according to the agency for Toxic Substances and Disease Registry of the United States [6].

Heavy metal removal from the effluents can be achieved by physicochemical treatment processes such as ion exchange, coagulation-flocculation, chemical precipitation, evaporation, membrane filtration, electrochemical treatments, and adsorption [1, 4]. Adsorption process has attracted attention of many researchers because of its low cost, ease of operation, design flexibility, and high efficiency for removal of inorganic and organic pollutants from wastewater [1, 4, 7].

Clay minerals and their modified derivatives are a family of materials which can be used for the adsorption of most of the chemical contaminants from the aqueous solution [7]. Among this family of adsorbents, those based on montmorillonite have been used as adsorbents for cationic contaminants, including heavy metal cations [1] and cationic dyes [8]. Montmorillonite is a phyllosilicate that belongs to the group of smectites, and it is the main component of bentonite clay. The hydrophilic nature of bentonite makes this material an ineffective adsorbent of organic compounds [9] and chromate oxyanions [10]. In the interlayer space of the sodium bentonite, there are ions of compensation Na⁺, which cannot be exchanged by the Cr(VI) species because the chromium in the aqueous solution exists as and , depending on the pH of the solution [11].

Smectite clay minerals can change their naturally hydrophilic character into organophilic, acting as adsorbents for organic compounds and inorganic anions. The organophilization consists of cationic surfactant (quaternary ammonium salts) addition with a chain of twelve or more carbon atoms to aqueous dispersions at an inorganic cation (typically Na⁺) exchange by alkylammonium cations [7]. Intercalation of a larger size of the surfactant cations into layers of clay minerals not only changes the surface properties from hydrophilic to hydrophobic, but also greatly increases the interlamellar distance (basal spacing) of the layers, thus easing the attraction of organic molecules [9] and chromate anions [10, 12].

The adsorption of Cr(VI) on organoclays has been previously investigated [12–15]; however, the optimal conditions of the adsorption process of Cr(VI) in organobentonite have not been studied by the multivariate experimental design. In this study, the effect of the variables involved in the adsorption process of Cr(VI) on the organobentonite (pH, stirring speed, amount of adsorbent, contact time, and ionic strength) was evaluated. The response surface methodology (RSM) was used to analyze the effect of pH and adsorbent amount on the Cr(VI) adsorption efficiency by organobentonite and establish the optimal conditions of the adsorption process. Additionally, batch experiments are performed to obtain the Cr(VI) adsorption capacity at different temperatures.

2. Experimental

2.1. Reagents and Materials

The surfactant hexadecyltrimethylammonium bromide (HDTMA-Br, C₁₉H₄₂BrN, >98.0% purity) was purchased from Panreac®. The clay used was a Colombian bentonite sample from Armero-Guayabal (Tolima). The main clay mineral of the bentonite used in this study is the montmorillonite (48 wt%), and its mineralogical and chemical composition has been previously reported [16].

A stock solution containing 1000 mg of Cr(VI) per liter was prepared by dissolving 0.1 N K₂Cr₂O₇ (Titrisol, Merck KGaA, Darmstadt, Germany) in double-distilled water and was used to prepare the solutions by appropriate dilution. The pH of the aqueous solution of Cr(VI) as prepared was 4.6.

2.2. Synthesis of Surfactant-Modified Bentonite

The clay fraction (<2 μm) was obtained by gravitational sedimentation of the clay sample. Sodium bentonite (denoted as Na-Bent) was prepared from the clay fraction using a 5% suspension of clay in 1 M NaCl solution. The suspension was agitated for 24 h at room temperature, and the solution was separated from the clay by centrifugation at 10000 rpm. This procedure was repeated three times, and the homoionic Na-bentonite was repeatedly washed with distilled water until a negative test for chloride ions in the washing was obtained [17]. The Na-Bent was dried in an over for 72 h at 60°C, and then ground and sieved in a 100-mesh screen.

The organobentonite was prepared by cationic exchange between the bentonite homoionized with sodium (CEC of the Na-Bent of 63.02 meq/100 g) and a cationic organic surfactant, hexadecyltrimethylammonium bromide (HDTMA-Br). The proportion of the surfactant used in the synthesis of organobentonite was 1.5 times the proportion of cation exchange capacity of sodium bentonite, a value recommended in literature [18], with a procedure similar to that used in a previous study [19]. For this, 20 g of Na-Bent was added to 500 mL of distilled water, and the suspension was stirred for 12 h to generate the swelling of the bentonite, and then the suspension was added with 7.03 g of HDTMA-Br (dissolved in 100 mL of distilled water) and the mixture was stirred for 24 h. The organobentonite (denoted as HDTMA-Bent) was separated by centrifugation and washed repeatedly until a negative bromide test was obtained with 0.1 M of AgNO₃. Finally, the HDTMA-Bent was dried at 80°C for 24 h and at 100°C for 2 h and then ground and sieved in 100-mesh screen. Na-Bent and HDTMA-Bent were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption at 77 K. The diffraction patterns were taken to a LabX Shimadzu XRD-6000 diffractometer with Cu Kα radiation (steps of 0.02° 2θ and 2 s/step). Fourier transform infrared spectrometry (FT-IR) was recorded from samples pressed into pellets with KBr powder by using a Nicolet iS5 (Termo Scientific). Nitrogen adsorption-desorption isotherms were determined in a Micromeritics ASAP 2020 instrument at 77 K after outgassing the samples for 3 h at 90°C, followed by 2 h at 120°C in a vacuum.

2.3. Adsorption Experiments

Batch adsorption tests were carried out in 100 mL glass Erlenmeyer with 50 mL of the Cr(VI) solution of 50 mg/L and placed in a thermostated bath at 25°C with magnetic stirring. The initial methodological design to evaluate the adsorption of Cr(VI) was proposed with a unique approach, in which the effect of each factor (pH, stirring speed, amount of adsorbent, contact time, and ionic strength) was analyzed independently, maintaining the other constants according to the experimental conditions established in Table 1. The pH of the solution was adjusted with 0.1 M HCl and 0.1 M NaOH solutions, and the effect of ionic strength on the adsorption of Cr(VI) was carried out varying the concentrations of the NaCl solution.

The adsorbent was separated by centrifugation at 5000 rpm for 5 min, and the supernatant solution was filtered in a 0.22 μm membrane and then carefully transferred to glass flasks to determine the concentrations of chromium present in the aqueous medium. All the tests were performed in triplicate. The concentrations of the chromium were measured by flame atomic absorption spectrometry (iCE 3500, Thermo Scientific, Germany), with an air-acetylene flame. The removal efficiency onto the organobentonite was calculated using the following equation:where and (mg/L) are the liquid-phase concentrations of the Cr(VI) at initial and time t, respectively.

2.4. Experimental Design and Adsorption Isotherm

The influence of the adsorbent amount and pH on Cr(VI) adsorption was studied by the response surface methodology (RSM) approach based on the complete factorial design 3². The amount of Cr(VI) adsorbed at 25, 30, and 35°C was evaluated at different initial concentrations of Cr(VI) at the optimal conditions obtained from the experimental design. The equilibrium adsorption capacity () was determined by the following equation:where and are the initial and equilibrium concentrations of the Cr(VI) in the liquid phase (mg/L), is the aqueous phase volume (L), and is the mass (g) of the adsorbent.

3. Results and Discussion

3.1. Characterization of the Clay and Organobentonite

Figure 1 shows the diffraction patterns of sodium bentonite and organobentonite. The modification of the bentonite with the quaternary ammonium salt caused an increase in the basal spacing (d₀₀₁) of the layers from 1.6 nm to 2.1 nm brought about by HDTMA⁺ cation intercalation. Macías-Quiroga et al. [16] and Otavo-Loaiza et al. [19] have reported similar basal spacing values for this bentonite and the bentonite modified with HDTMA-Br. The increase in the interlayer spacing indicates that the HDTMA⁺ cations intercalated in the interlamellar space were arranged in the form of a pseudo-trimolecular layer [20].

To determine the specific surface area of bentonite and organobentonite, a model BET was used. External surface area and porous volume were assessed by t curves using the Harkins–Jura equation [21]. The specific surface area and pore volume of the bentonite were reduced from 59.9 to 2.5 m²/g and from 0.082 to 0.008 cm³/g, respectively, when the bentonite was modified with the surfactant (HDTMA-Bent). Similar results have been reported by Jacobo-Azuara et al. [22] when bentonite was modified with hexadecyltrimethylammonium bromide.

Figure 2 shows the FT-IR spectra of Na-Bent and HDTMA-Bent. The two spectra show the presence of –OH as stretching bands at 3622–3629 cm⁻¹. The large band at 1030 cm⁻¹ corresponds to the Si-O stretching vibration. The above signals can be considered characteristic of dioctahedral smectite [16, 23]. Broad bands centered near 3421–3427 cm⁻¹ and 1636–1639 cm⁻¹ are due to the–OH stretching mode of the interlayer water [24]. Adsorption bands of pure HDTMA at 2923 cm⁻¹ and 2849 cm⁻¹ correspond to the CH₂ asymmetric stretch modes and CH₃ symmetric stretch modes, respectively [25]. The band at 1468 cm⁻¹ is assigned mainly to N-C stretching of the cationic surfactant [9].

3.2. Adsorption Study

3.2.1. Effect of pH

The removal of Cr(VI) using organobentonite was highly dependent on the pH of the solution, as shown in Figure 3. The hexavalent chromium ions can exist as hydrogen chromate (), chromate (), or dichromate (), depending upon the pH of the solution [26]. At pH 3, the maximum removal by adsorption was found, and when the pH increased from 5 to 9, the removal of Cr(VI) decreased drastically. According to the Cr(VI) speciation diagram, the is the predominant specie in the pH interval 2–4, and ions are common at pH interval 2–6, and is the predominant specie in the pH range 9–12 [11]. The affinities of , , and ions to the modified bentonite are different, with the preference of the first two species in acid solutions [15].

Using SWAXS analysis (small-angle angle X-ray scattering) pattern recorded before and after adsorption of chromium, Majdan et al. [15] proposed the formation of alkylammonium chromates: (HDTMA) (HCrO₄), (HDTMA)₂Cr₂O_7, and to the lesser extent (HDTMA)₂CrO₄ in the interlayer space of the bentonite. The removal of the Cr(VI) occurs by electrostatic interaction between the species and with the surface of the positively charged organobentonite and with the alkylammonium cations located in the interlayer space [15]. In general, the highest adsorption of Cr(VI) occurred at pH between 3 and 4, with removals greater than 83.97 ± 0.97%, and this performance has been linked to the predominant adsorption of specie [27].

3.2.2. Effect of Stirring Speed

The stirring speed is an important parameter in the adsorption process since it influences the distribution of the solute in the bulk solution and the formation of the external boundary film [28]. The effect of the stirring speed on the removal of Cr(VI) onto organobentonite evaluated for a contact time of 1 h is shown in Figure 4. At 200, 250, and 300 rpm, the removal of Cr(VI) tended at a constant value, around 84.78 ± 0.95%. At low stirring speeds (100 and 150 rpm), slightly lower removals of Cr(VI) were obtained, which demonstrate that increasing the stirring speed (≥200 rpm) increases the turbulence in the mixing zone [29].

The removal of Cr (VI) was not positively correlated with the stirring speed between 200 and 300 rpm because the contact time of 1 h guaranteed equilibrium time conditions in the adsorption tests. It has been established that the stirring speed affects the equilibrium time, but the equilibrium adsorption capacity is not a function of the stirring speed [28]. The stirring speed increase causes an increase in the Reynolds number, in the energy dissipation, and in the turbulence in the mixing zone.

Several studies on adsorption of Cr(VI) in modified minerals do not include data of stirring speed [30] and others only specify the value used. For example, Thanos et al. [31] carried out all the experiments in batch reactors under continuous stirring at 600 rpm, and Hommaid and Hamdo [32] and Slimani et al. [33] report that the suspension was stirred at 150 rpm on a shaker and in a magnetic stirrer, respectively.

3.2.3. Effect of Amount of Adsorbent

Figure 5 shows the effect of amount of organobentonite on Cr(VI) adsorption. When the amount adsorbent step from 0.05 to 0.4 g of Cr(VI) removal increase from 25.65 ± 1.01 to 94.69 ± 1.32%, it was observed that the adsorption of the Cr(VI) increased rapidly with increasing amount of adsorbent from 0.05 to 0.20 g and slightly enhanced from 0.25 to 0.40 g. These results can be attributed to the increased adsorbent surface area and availability of more adsorption sites. However, it has been established that a higher availability of adsorption sites results in less effective utilization of the sites by the chromate ions due to saturation deficiency [31].

3.2.4. Effect of Contact Time

The contact time is one of the most important parameters for the industrial application of an adsorbent. A good adsorbent should not only provide high adsorption capacities, but also produce a fast process [28]. The influence of contact time on the Cr(VI) adsorption on organobentonite is shown in Figure 6. The Cr(VI) removal on organobentonite improved rapidly by the increase in contact time from 5 to 30 min. Between 30 and 60 min, the Cr(VI) removal increased slightly, and after 90 min, the adsorption capacity became constant and the adsorption achieved equilibrium.

Slimani et al. [33] evaluated the kinetic and thermodynamic parameters of chromium adsorption on a bentonite modified with HDTMA-Br and found that the adsorption of chromium was very fast at the beginning and then approached equilibrium after 15 min. Similar results were obtained by Thanos et al. [31] finding that chromate ion adsorption occurred at a very high stirring at the initial stages (t = 0–10 min) for four HDTMA-Br-modified minerals. Although it has been established that the removal of Cr(VI) using organoclay as an adsorbent occurs very rapidly, some researchers have employed high equilibrium times. Jacobo-Azuara et al. [22] manually shaked the solution for four to five times daily and found that 5 days are sufficient to reach equilibrium.

3.2.5. Effect of Strength Ionic

Wastewaters from different industries contain various types of salts, and their presence leads to high ionic strength, which may significantly affect the performance of the adsorption process [34]. The effect of the addition of NaCl on the Cr(VI) removal is shown in Figure 7. The Cr(VI) adsorption on organobentonite decreased slightly when increasing the concentrations of NaCl in the solution from 0.1 to 2.0 mM. The Cr(VI) solution of 50 mg/L was prepared by dissolving 0.1 N K₂Cr₂O₇ (Titrisol, Merck KGaA) in double-distilled water, and for the ionic strength tests, the pH of the solution was adjusted to 3.0, adding 0.1 M HCl. Therefore, the solution used in the adsorption tests contains H⁺, Cl⁻, K⁺, , and ions, which generate ionic strength. An increase in ionic strength generates the compression of the diffuse double layer on the adsorbent and affects the adsorption process [34].

Gładysz-Płaska et al. [35] studied the influence of ionic strength on Cr(VI) adsorption on HDTMA-clay, finding that an increase in the ionic strength of the solution resulted in a decrease in Cr(VI) adsorption. Under the test conditions (T = 293 K, pH = 5.8, 0.4 of HDTMA-clay, equilibrium time = 6 h, and 0.1 mmol/L NaCl), chloride ions reduced Cr(VI) adsorption from 59 to 25%.

In conclusion, the main variables that affected the adsorption of Cr(VI) on the organobentonite were the amount of adsorbent and the pH. Stirring speed above 200 rpm and contact time exceeding 90 min did not have a significant effect on Cr(VI) removal. As the solution used in the adsorption tests contains H⁺, Cl⁻, K⁺, , and ions, which generate ionic strength, in the subsequent tests, the addition of NaCl to the Cr(VI) aqueous solution was not considered.

3.3. Experimental Design

The effects of amount of adsorbent (A) and the pH (B) were analyzed using response surface methodology with a complete factorial design 3². The levels for A and B were 0.3, 0.4, and 0.5 g and 2.0, 3.0, and 4.0, respectively. The other variables, temperature, contact time, and stirring speed were kept constant at 25°C, 150 min, and 230 rpm, respectively. Design Expert version 9.0.6.2 (StatEase, Inc., Minneapolis, USA) was used for regression analysis of the obtained experimental data. In the optimization process, the response variable can be related to chosen variables by linear or quadratic models [36]. A quadratic model is given in the following equation:where is the predicted response, , , , and are the regression coefficients for the intercept and the linear, quadratic, and interaction coefficients, respectively, and are the independent variables, and = 2, i.e., the number of independent variables. The quality of the model fits was evaluated by the coefficients of determination (R² and adjusted ) and analysis of variance (ANOVA).

The levels of the tested variables and the observed response are shown in Table 2.

From the data for Cr(VI) adsorption in Table 2, a quadratic model was generated by RSM as it was statistically significant for the response variable. Analysis of variance (ANOVA) was applied for estimating the significance of the model at 5% significance level, and results are shown in Table 3. A model is considered significant if the value (significance probability value) is less than 0.05. From the values presented in Table 3, it can be stated that the linear terms A and B and quadratic terms A² and B² are significant model terms. The interaction term AB was not significant.

The model equation for uncoded (real) values of the quadratic model fitting experimental results is shown in the following equation:

The coefficient of determination (R²) and the adjusted () of the model were 0.951 and 0.939, respectively, which showed that this regression is statistically significant and only 4.90% of the total variations is not explained by the model.

Figure 8 shows the response surface plot that represents the interaction of the independent variables (amount of adsorbent and pH) on the removal of Cr(VI). In the pH range of 3.0 to 4.0, the removal of Cr(VI) is high and decreases at pH less than 2.5 or greater than 5.0. By means of mathematical optimization of the model, the values of the factors to which the maximum removal of Cr(VI) (93.16%) corresponding to pH of 3.4 and mass of adsorbent (Bent-HDTMA) of 0.44 g were determined.

Additional adsorption tests under the optimal operating conditions were carried out in order to evaluate the precision of the quadratic model. The experimental values and the predicted values with equation (4) are given in Table 4. Comparing the experimental and predicted results, it can be seen that the error between the experimental and predicted is less than 4.8%; therefore, it can be concluded that the generated model has sufficient accuracy to predict the Cr(VI) removal.

3.4. Adsorption Isotherms

The Cr(VI) adsorption isotherms at 25, 30, and 35°C were evaluated at different initial concentrations of Cr(VI) ranging from 10 to 120 mg/L at the optimal conditions obtained from the experimental design, 0.44 g of organobentonite, and pH of 3.4. The other conditions were the same as those used in the experimental design (V = 50 mL, contact time = 150 min, and stirring speed = 230 rpm). The adsorption isotherms of Cr(VI) onto organobentonite are represented in Figure 9.

Adsorption isotherms data were fitted to the nonlinear form of Langmuir and Freundlich models, which are the most frequently used models [37]. The Langmuir isotherm is represented by the following equation:where is the adsorbate equilibrium amount in the solid phase (mg/g), is the adsorbate equilibrium concentration in solution (mg/L), is the maximum adsorption capacity according to Langmuir monolayer adsorption (mg/g), and is a constant according to the Langmuir model (L/mg). The characteristic of the Langmuir isotherm can also be expressed using a dimensionless constant called equilibrium parameter (), which has the following form:where is the initial dye concentration in the solution (mg/L) and value indicates the isotherm type, whether it is unfavorable , linear , favorable , or irreversible [37].

The Freundlich isotherm model is an empirical relationship describing the adsorption of solutes from a liquid to a solid surface [37]. The form of the Freundlich equation is as follows:where ((mg/g)(L/g)ⁿ) and n are the Freundlich constants related to the adsorption capacity and adsorption intensity of the adsorbent, respectively. Calculated isotherm parameters and correlation coefficients at the three temperatures are listed in Table 5.

Cr(VI) adsorption data onto organobentonite fit well with the Langmuir model with R² greater than 0.993. The values, corresponding to the maximum adsorption capacity, were around 10.04 mg/g at 25°C, and the variation with the temperature was minimal. However, there is a slight decrease in the value of with the temperature increase (Figure 8). Exothermicity of the adsorption results from the electrostatic interaction on the negatively charged Cr(VI) ions with the positively charged alkylammonium ions. The separation factor () for the temperature range studied varied between 0.018 and 0.274, indicating the favorable nature of Cr(VI) adsorption on Bent-HDTMA, given that . The Freundlich model represented well the Cr(VI) adsorption data at low equilibrium concentrations, but deviated in the high concentration zone; hence, the coefficients of determination were less than 0.938. The values of 1/n in the range 0.1 < 1/n < 1 indicate that the adsorption is favorable.

Comparing with other low-cost adsorbents such as activated carbons prepared from coconut tree sawdust (3.46 mg/g at pH = 3.0) [38], mango kernel activated with H₃PO₄ (7.8 mg/g at pH = 2.0) [26], and groundnut husk (3.0 mg/g at pH = 3.0) [39], the adsorption capacity of the organobentonite synthetized in this study is higher (10.04 mg/g at pH = 3.4), indicating that this adsorbent has potential application for industrial wastewater treatment. The montmorillonite from Texas modified with octadecyltrimethylammonium bromide (9.61 mg/g at pH = 5.0) [40] and montmorillonite from Mongolia modified with hydroxyaluminium and cetyltrimethylammonium bromide simultaneously (7.64–9.09 mg/g at pH = 4.0) [25] presented values similar to those obtained in this study. However, the bentonite of San Luis Pososí (Mexico) modified with hexadecyltrimethylammonium bromide had a higher adsorption capacity (53.3 mg/g at pH = 3.0) [22], suggesting that the physicochemical and mineralogical characteristics of the starting clay and the organoclay preparation method affect the capacity of adsorption of Cr(VI).

4. Conclusions

In this study, the ability of organobentonite prepared from bentonite and a cationic surfactant (HDTMA-Br) to remove oxyanions of Cr(VI) in the aqueous solution was investigated. Response surface methodology (RSM) was used to optimize the conditions of Cr(VI) adsorption onto organobentonite, and the selected quadratic model can be used in predicting the Cr(VI) removal under the same conditions of the experiments. The optimal conditions for removal of Cr(VI) from an aqueous solution of 50 mg/L were pH of 3.4 and 0.44 g amount of the adsorbent. The percentage of Cr(VI) removal obtained was 93.16%. Stirring speeds above 200 rpm and contact times greater than 120 min did not have a significant effect on Cr(VI) removal. The error between predicted and experimental results for the removal of Cr(VI) is less than 4.8%, showing that the experimental results were in good agreement with those predicted from the quadratic model. Equilibrium data were well described by the Langmuir model with the monolayer adsorption capacity of 10.04 mg/g under optimal conditions at 25°C. The organobentonite can be a potential adsorbent to the remediation of water contaminated with chromium oxyanions, with the advantage of using as raw material for synthesis of the organoclay a natural, abundant, and low-cost mineral.

Data Availability

The data that support the characterization results of the organobentonite (XRD), the batch adsorption tests, and the complete factorial design data for optimization of Cr(VI) adsorption are found in the article in the form of tables and figures.

Conflicts of Interest

The authors declare that have no conflicts of interest.

Acknowledgments

The authors gratefully acknowledge Universidad Nacional de Colombia Sede Manizales for supplying the resources for this scientific research.

References

M. K. Uddin, “A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade,” Chemical Engineering Journal, vol. 308, pp. 438–462, 2017.
View at: Publisher Site | Google Scholar
S. Li and Y. Ma, “Urbanization, economic development and environmental change,” Sustainability, vol. 6, no. 8, pp. 5143–5161, 2014.
View at: Publisher Site | Google Scholar
R. Acharya, S. Martha, and K. M. Parida, “Remediation of Cr(VI) using clay minerals, biomasses and industrial wastes as adsorbents,” in Advanced Materials for Wastewater Treatment, U.-I. Shahid, Ed., pp. 129–170, Scrivener Publishing LLC, Hoboken, NJ, USA, 2017.
View at: Google Scholar
D. Lakherwal, “Adsorption of heavy metals: a review,” International Journal of Environmental Science and Development, vol. 4, no. 1, pp. 41–48, 2014.
View at: Google Scholar
M. Jaishankar, T. Tseten, N. Anbalagan, B. B. Mathew, and K. N. Beeregowda, “Toxicity, mechanism and health effects of some heavy metals,” Interdisciplinary Toxicology, vol. 7, no. 2, pp. 60–72, 2014.
View at: Publisher Site | Google Scholar
ATSDR, Substance Priority List, US Agency for Toxic Substances and Disease Registry, ATSDR U.S. Department of Health & Human Services, Atlanta, GA, USA, 2017, https://www.atsdr.cdc.gov/SPL.
R. Zhu, Q. Chen, Q. Zhou, Y. Xi, J. Zhu, and H. He, “Adsorbents based on montmorillonite for contaminant removal from water: a review,” Applied Clay Science, vol. 123, pp. 239–258, 2016.
View at: Publisher Site | Google Scholar
Z. Li, P.-H. Chang, W.-T. Jiang, J.-S. Jean, and H. Hong, “Mechanism of methylene blue removal from water by swelling clays,” Chemical Engineering Journal, vol. 168, no. 3, pp. 1193–1200, 2011.
View at: Publisher Site | Google Scholar
S. x. Zha, Y. Zhou, X. Jin, and Z. Chen, “The removal of amoxicillin from wastewater using organobentonite,” Journal of Environmental Management, vol. 129, pp. 569–576, 2013.
View at: Publisher Site | Google Scholar
V. Dimos, K. J. Haralambous, and S. Malamis, “A review on the recent studies for chromium species adsorption on raw and modified natural minerals,” Critical Reviews in Environmental Science and Technology, vol. 42, no. 19, pp. 1977–2016, 2012.
View at: Publisher Site | Google Scholar
R. L. Ramos, A. J. Martinez, and R. M. G. Coronado, “Adsorption of chromium (VI) from aqueous solutions on activated carbon,” Water Science and Technology, vol. 30, no. 9, pp. 191–197, 1994.
View at: Publisher Site | Google Scholar
B. Sarkar, Y. Xi, M. Megharaj, G. S. R. Krishnamurti, D. Rajarathnam, and R. Naidu, “Remediation of hexavalent chromium through adsorption by bentonite based Arquad 2HT-75 organoclays,” Journal of Hazardous Materials, vol. 183, no. 1-3, pp. 87–97, 2010.
View at: Publisher Site | Google Scholar
S. Pandey and S. B. Mishra, “Organic-inorganic hybrid of chitosan/organoclay bionanocomposites for hexavalent chromium uptake,” Journal of Colloid and Interface Science, vol. 361, no. 2, pp. 509–520, 2011.
View at: Publisher Site | Google Scholar
M. C. Brum, J. L. Capitaneo, and J. F. Oliveira, “Removal of hexavalent chromium from water by adsorption onto surfactant modified montmorillonite,” Minerals Engineering, vol. 23, no. 3, pp. 270–272, 2010.
View at: Publisher Site | Google Scholar
M. Majdan, O. Maryuk, S. Pikus, E. Olszewska, R. Kwiatkowski, and H. Skrzypek, “Equilibrium, FTIR, scanning electron microscopy and small wide angle X-ray scattering studies of chromates adsorption on modified bentonite,” Journal of Molecular Structure, vol. 740, no. 1-3, pp. 203–211, 2005.
View at: Publisher Site | Google Scholar
I. F. Macías-Quiroga, G. I. Giraldo-Gómez, and N. R. Sanabria-González, “Characterization of Colombian clay and its potential use as adsorbent,” The Scientific World Journal, vol. 2018, Article ID 5969178, 11 pages, 2018.
View at: Publisher Site | Google Scholar
L. Kiviranta and S. Kumpulainen, “Quality control and characterization of bentonite materials,” Tech. Rep., Posiva Oy, Eurajoki, Finland, 2011, Working Report 2011-84.
View at: Google Scholar
B. Erdem, A. S. Özcan, and A. Özcan, “Preparation of HDTMA-bentonite: characterization studies and its adsorption behavior toward dibenzofuran,” Surface and Interface Analysis, vol. 42, no. 6-7, pp. 1351–1356, 2010.
View at: Publisher Site | Google Scholar
R. A. Otavo-Loaiza, N. R. Sanabria-González, and G. I. Giraldo-Gómez, “Tartrazine removal from aqueous solution by HDTMA-Br-modified Colombian bentonite,” The Scientific World Journal, vol. 2019, Article ID 2042563, 11 pages, 2019.
View at: Publisher Site | Google Scholar
H. He, R. L. Frost, T. Bostrom et al., “Changes in the morphology of organoclays with HDTMA⁺ surfactant loading,” Applied Clay Science, vol. 31, no. 3-4, pp. 262–271, 2006.
View at: Publisher Site | Google Scholar
S. J. Gregg and K. S. W. Sing, Adsorption, Surface Area and Porosity, Academic Press, London, UK, 1982.
A. Jacobo-Azuara, R. Leyva-Ramos, E. Padilla-Ortega, A. Aragón-Piña, R. M. Guerrero-Coronado, and J. Mendoza-Barron, “Removal of toxic pollutants from aqueous solutions by adsorption onto an organobentonite,” Adsorption Science & Technology, vol. 24, no. 8, pp. 687–799, 2006.
View at: Publisher Site | Google Scholar
P. Djomgoue and D. Njopwouo, “FT-IR spectroscopy applied for surface clays characterization,” Journal of Surface Engineered Materials and Advanced Technology, vol. 3, no. 4, pp. 275–282, 2013.
View at: Publisher Site | Google Scholar
B. Fil, C. Özmetin, and M. Korkmaz, “Characterization and electrokinetic properties of montmorillonite,” Bulgarian Chemical Communications, vol. 46, no. 2, pp. 258–263, 2014.
View at: Google Scholar
B. Hu and H. Luo, “Adsorption of hexavalent chromium onto montmorillonite modified with hydroxyaluminum and cetyltrimethylammonium bromide,” Applied Surface Science, vol. 257, no. 3, pp. 769–775, 2010.
View at: Publisher Site | Google Scholar
M. K. Rai, G. Shahi, V. Meena et al., “Removal of hexavalent chromium Cr (VI) using activated carbon prepared from mango kernel activated with H₃PO₄,” Resource-Efficient Technologies, vol. 2, no. S1, pp. S63–S70, 2016.
View at: Publisher Site | Google Scholar
Z. Hu, G. He, Y. Liu, C. Dong, X. Wu, and W. Zhao, “Effects of surfactant concentration on alkyl chain arrangements in dry and swollen organic montmorillonite,” Applied Clay Science, vol. 75-76, pp. 134–140, 2013.
View at: Publisher Site | Google Scholar
G. L. Dotto, S. K. Sharma, and L. L. A. Pinto, “Chapter 8. Biosorption of organic dyes: research opportunities and challenges,” in Green Chemistry for Dyes Removal from Wastewater, S. K. Sharma, Ed., pp. 295–329, Scrivener Publishing LLC - Wyley, Hoboken, NJ, USA, 2015.
View at: Google Scholar
G. L. Dotto and L. A. A. Pinto, “Analysis of mass transfer kinetics in the biosorption of synthetic dyes onto Spirulina platensis nanoparticles,” Biochemical Engineering Journal, vol. 68, pp. 85–90, 2012.
View at: Publisher Site | Google Scholar
R. Leyva-Ramos, A. Jacobo-Azuara, P. E. Diaz-Flores, R. M. Guerrero-Coronado, J. Mendoza-Barron, and M. S. Berber-Mendoza, “Adsorption of chromium(VI) from an aqueous solution on a surfactant-modified zeolite,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 330, no. 1, pp. 35–41, 2008.
View at: Publisher Site | Google Scholar
A. G. Thanos, E. Katsou, S. Malamis, K. Psarras, E. A. Pavlatou, and K. J. Haralambous, “Evaluation of modified mineral performance for chromate sorption from aqueous solutions,” Chemical Engineering Journal, vol. 211-212, pp. 77–88, 2012.
View at: Publisher Site | Google Scholar
O. Hommaid and J. Y. Hamdo, “Adsorption of chromium(VI) from an aqueous solution on a Syrian surfactant-modified zeolite,” International Journal of ChemTech Research, vol. 6, no. 7, pp. 3753–3761, 2014.
View at: Google Scholar
S. M. Slimani, H. Ahlafi, H. Moussout, R. Chfaira, and O. Zegaoui, “Evaluation of kinetic and thermodynamic parameters of chromium adsorption on a organobentonite,” International Journal of Advanced Research in Chemical Science, vol. 1, no. 5, pp. 17–29, 2014.
View at: Google Scholar
T. Anirudhan and M. Ramachandran, “Surfactant-modified bentonite as adsorbent for the removal of humic acid from wastewaters,” Applied Clay Science, vol. 35, no. 3-4, pp. 276–281, 2007.
View at: Publisher Site | Google Scholar
A. Gładysz-Płaska, M. Majdan, S. Pikus, and D. Sternik, “Simultaneous adsorption of chromium(VI) and phenol on natural red clay modified by HDTMA,” Chemical Engineering Journal, vol. 179, pp. 140–150, 2012.
View at: Publisher Site | Google Scholar
S. Karimifard and M. R. Alavi Moghaddam, “Application of response surface methodology in physicochemical removal of dyes from wastewater: a critical review,” Science of The Total Environment, vol. 640-641, pp. 772–797, 2018.
View at: Publisher Site | Google Scholar
K. Y. Foo and B. H. Hameed, “Insights into the modeling of adsorption isotherm systems,” Chemical Engineering Journal, vol. 156, no. 1, pp. 2–10, 2010.
View at: Publisher Site | Google Scholar
K. Selvi, S. Pattabhi, and K. Kadirvelu, “Removal of Cr (VI) from aqueous solution by adsorption onto activated carbon,” Bioresource Technology, vol. 80, no. 1, pp. 87–89, 2001.
View at: Publisher Site | Google Scholar
S. Dubey and K. Gopal, “Adsorption of chromium(VI) on low cost adsorbents derived from agricultural waste material: a comparative study,” Journal of Hazardous Materials, vol. 145, no. 3, pp. 465–470, 2007.
View at: Publisher Site | Google Scholar
S. I. Rathnayake, W. N. Martens, Y. Xi, R. L. Frost, and G. A. Ayoko, “Remediation of Cr (VI) by inorganic-organic clay,” Journal of Colloid and Interface Science, vol. 490, pp. 163–173, 2017.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2020 Johnatan D. Castro-Castro et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

1787

Downloads

1118

Citations