Adsorption Study for Removal of Boron Using Ion Exchange ... - ipcbee

2011 2nd International Conference on Environmental Science and Technology IPCBEE vol.6 (2011) © (2011) IACSIT Press, Singapore

Adsorption Study for Removal of Boron Using Ion Exchange Resin in Bach System Mahdi Parsaei1

Mohsen Salarpour Goodarzi2 2

1

Civil Engineering Department Institute of Hydrogen Economy, Energy Research Alliance, Universiti Teknologi Malaysia Kuala Lumpur, Malaysia [email protected]

Hydroulic and Hydrology Department Institute of Environment and Water Resources Management (IPASA), Universiti Teknologi Malaysia Johor, Malaysia [email protected]

³Mohamed Mahmoud Nasef Chemical Engineering Department³ Institute of Hydrogen Economy, Energy Research Alliance, Universiti Teknologi Malaysia Kuala Lumpur, Malaysia [email protected].

Abstract—Wastewaters containing boron pose a challenge to the conventional wastewater treatment techniques. Adsorption using ion exchange resins has been found to be effective for the removal of boron from effluent. In the present study, removal of boron from synthetic boric acid solutions containing high concentrations of boron by adsorption over an anion exchange resin (Amberlite IRA 743) was investigated on a batch basis. The effects of various process parameters on boron removal in terms of adsorption capacity were evaluated. The chosen parameters were initial concentration of solute in range of 402000 mg/L), initial pH of the sorption medium in range of 3-10, and mass of the adsorbent (10-110 g/L). Langmuir and Freundlich isotherm models were used to identify the model fitting the ion exchange equilibrium isotherm for boron adsorption under the present experimental conditions. The obtained results reveal that, the maximum boron adsorption capacity i.e. boron removal was found to be achieved at pH 9.5, initial concentration of 40 mg B/L and resin dosage of 110 g/L. Furthermore, the efficiency of boron removal was found to increase in with the increase of the resin dosage and the decrease in initial boron concentration. Langmuir isotherm was found to adequately describe the equilibrium relation between the resin and liquid phase of the ion exchange reaction in the present study. Keywords-boronremoval; ion exchange; resin; isotherm

I. INTRODUCTION Boron has recently come into sharp focus of researchers because of its unique characteristics and adverse effects it may cause afterwards. Many industries use boron compounds as their raw materials. The principal industrial uses of this element and its compounds are in the production of fiberglass insulation, borosilicate glass, and detergents. Other uses are in fertilizers, nuclear shielding and metallurgy [1]. The increasing use of boron in industries and

consequently its discharge to the environment as industrial wastes has become a serious threat to human, plants, animals, and ecological systems. Boron removal will be necessary in the near future since the fresh water in the world is decreasing. Removal of boron from seawater, which has become of interest as a drinking water supply, would be essential. There is no simple technique for removal of boron in aqueous solutions [2]. Studies have been conducted to remove boron from water and wastewater in order to decrease boron concentration to a certain range demanded by different standards. The investigations have indicated that the only method adapted for potable water is ion exchange using selective resins, in spite of their high costs. It also has been shown that chelating resins containing functional groups in the 1-2 or 1-3 position have higher selectivity for boron removal [3]. The trend is toward operating cost reduction which is an issue to deal with when using ion exchange resins. For boron removal process, not only the effectiveness of removal process, but also the availability and the cost efficiency should be considered as the most important characteristics for this process. The removal efficiency for reverse osmosis was about 40-80% and in alkaline solutions with higher pH (10-11) over 90%. But RO process is not effective because of the membrane cost, scaling, and stability. Another method for removal of boron was co-precipitation through which dilute boron solutions (1.6-0.16 mg/L) could be treated by 90% efficiency using aluminum sulfate and calcium hydroxide. However, the sludge was being produced at the end of this process made it an expensive process. Electrodialysis was another boron removal method. The boron removal efficiency in this process was about 40-75% that was not enough. Adsorption is a cost effective process too. Some adsorbents have been used by researchers were amorphous aluminum and iron oxides, kaolinite, allophone

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[4], acid soils [5], pyrohyllite [6], hydrous ferric oxide [7], chitosan resin [8], activated carbon [9], fly ash [10], and clays and soils [11]. Although ion exchangers seem not to be cost-effective considering their regeneration processes, they offer high removal efficiencies up to 99%. Not to mention that we can reduce the cost via producing new resins by local materials. The aim of this investigation is to conduct comprehensive studies on boron removal from aqueous solution using a commercial resin (Amberlite IR743) in batch system to obtain the interactions between dependent variable (Boron removal efficiency) and independent variables (Initial concentration, pH, and resin dosage). The present study utilizes the resin in different experimental conditions such as variable pH values, resin dosages, and initial concentrations. II. EXPERIMENTAL MATERIALS Experiments were conducted to study the effect of different operating parameters on sorption capacity and equilibrium time of the batch ion exchange system. From the experimental results obtained, equilibrium study was conducted. Finally, the interactions between removal efficiency of boron (%) and independent variables were achieved and analyzed. A. Amberlite IRA 743 The commercial anion exchange resin used in this study was Amberlite IRA 743 supplied from Merck DarmstadtGermany. Having Macro-porous polystyrene matrix on which N-methylglucamine functional group is attached makes this resin one of the most boron selective adsorbents. Methylglucamine functional groups are attached as seen in Figure 1. It is known that boron is retained through two steps. First off, borate ion is complexed by two sorbitol groups, and secondly a part of it is retained by a tertiary amine site which behaves like a weak basic [12]. The properties of this resin are presented in Table 1.

Moisture content

56

pH range

0-14

Uniformity coefficient

1.40

Maximum operation temperature (K)

373

Ionic form

OH⁻ 3

True density (wet; g/cm )

0.68

Prior to the experiments, the resin (Amberlite IRA 743 free base purchased from company of Sigma, Aldrich, Fluka and Supelco) was pre-treated. The studied commercial resin was first immersed in distilled water for 3-4 hours. Preequilibration was performed by rinsing the resin in a batch with HCl 0.1, 0.01, and 0.001 mol/L successively [13]. Finally, the resin was washed with deionized water in triplicate and then dried in the oven for 24 hours. B. Synthetic Solution The boric acid solutions used in this study were obtained synthetically in the lab using deionized water and boric acid (Assay>99.5%, DAE JUNG). Standard boron stock solution in concentration of 1000 mg B/L was prepared by dissolving 5.716 g of boric acid in 800 mL deionised water and diluting the sample to 1000 mL. Then, samples of 100 ml in 250 ml flask were prepared by diluting the stock solution to various concentrations of boric acid solutions in order to be used for the experiments. C. Mannitol Solution In order to perform titration for determination of the concentration of boron in the sorption media, a solution of mannitol was required to decrease the pH value of the boric acid solution and consequently makes it possible to conduct titration using conventional indicators. The mannitol solution was prepared through dissolving of 200 g mannitol in 800 mL deionised water. III. METHODS

Figure 1. Chemical structure of Amberlite IRA 743[12]

TABLE I.

CHARACTERISTICS OF AMBERLITE IRA 743 RESIN [12]

Properties

Value

Exchange capacity (mequiv./mL)

0.60

Particle size (mm)

0.40-0.60

Effective size (mm)

0.52

A. Adsorbent Concentration To determine the final concentration of boron in the sorption media, conventional titration was carried out. In phenolphthalein was practiced as an indicator. The titration was carried out using a mixture of 5 ml of each sample taken during agitation, 10 ml mannitol, and 35 ml distilled water. Every single titration was done three times to obtain an accurate result. B. Batch System for Removal of Boron In the batch system, the resin and solution are mixed in a batch tank (in this study was a 250 ml flask), the exchange is allowed to come to equilibrium, and then the resin is separated from solution. This study was conducted to define the equilibrium time and sorption capacity required for sorption of boron in boric acid solution using Amberlite IRA 743 ion exchange resin. Sample solutions with concentration

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of 100 mL were used as sample solutions, and flasks of 250 ml were used as batch systems. The initial concentrations of sample solutions were obtained through dilution of the 1000 mg B/L stock solution. Desired amount of resins weighted and used in each batch system. In case, pH adjustment was required, diluted solutions of hydrochloric acid and sodium hydroxide (0.1 N) were added to the solution in order to adjust the pH values. All the agitation processes were employed with the orbital agitator the speed of which was fitted to 140 rpm. C. Equilibrium Adsorption of Boron Equilibrium studies were conducted in this study. Bearing this on mind, adsorption isotherms were examined to demonstrate how resin (adsorbent) and boron (adsorbate) in the solution behave when contacting. In this regard, relevant experiments were carried out by contacting 100 mL boric acid solution with various dosages of resin. The following equation calculates the amount of adsorption at equilibrium:

IV. RESULT AND DISCUSSION A. Effect of Initial Concentration of Boron on Boron Removal Batch experiments were conducted for 120 minutes at 30⁰C to evaluate the effect of initial concentration of contaminant (B) on boron removal from aqueous solutions. The effect of initial concentration of boron on the removal of boron from boric acid solution was examined for concentrations of 40, 60, 100, 250, 500, and 1000 mg B/L at constant operating temperature of 30 ⁰C. The pH value was kept constant at the original value of the solutions. The results obtained are illustrated in Figure 2.

(1)

Where C₀ (mg/L) and Cf (mg/L) are defined as initial and final concentrations of boron respectively. V (L) is considered as the volume of the solution and M (g) is the mass of dry resin. In order to study the isotherm of the reactions, among several adsorption isotherm models, Freundlich and Langmuir were employed. The following experimental conditions have been applied to study the sorption equilibrium of the resin and consequently to achieve the optimum sorption capacity of the resin: • • • • •

Initial concentration (C₀) of 10 mg B/L Resin dosages of 10, 30, 50, 60, and 110 mg/L The solution original pH (4.8-5.3) Temperature of 30 ⁰C The agitation speed of 140 rpm

D. Effects of Adsorption Parameters To explore the effects of boron initial concentration on the removal of boron from aqueous solutions, the experiments were carried out using different initial concentrations of boron (40, 60, 100, 250, 500, 1000, and 2000 mg/L). To examine the effects of initial pH values on the removal of boron from aqueous solutions, 100 ml boric acid solutions with concentrations of 1000 mg/L and various pH values (3, 5, 7, 9, 9.5, and 10) were prepared and tested. And finally, in order to evaluate the effects of the amount of resin on the boron removal from aqueous solutions, 100 ml boric acid solutions with concentrations of 100 mg/L and original pH values (4.8-5.3) and addition of various resin dosages (10, 30, 50, 60, and 110 g/L) were prepared and tested.

Figure 2. Boron removal efficiency versus time at natural pH value of the sorption medium for various initial concentrations of boron

As shown in Figure 2, boron removal decreased with increasing boron initial concentration in the solution, where the removal efficiency for solution with initial concentration of 2000 mg B/L is 12.09% while the initial concentration of 40 mg B/L delivers the highest efficiency of 96%. For initial concentrations of 60, 100, 250, 500, and 1000 mg B/L the removal reached up to 91, 83.79, 82.70, 44.86, and 24.86 percentages respectively. According to Ho [14], the equilibrium would be reached faster at lower initial concentration, probably because the more sorption sites are available to catch the available ions, which means faster adsorption in lower concentrations. As a result, reaching the equilibrium condition increased when the initial concentration of the solution increased. B. Effect of Initial pH of Solution on Boron Removal Initial pH plays an important role for the adsorption of boron ions on the resin beads. The removal efficiency of boron removal in aqueous solution was evaluated in a batch system at constant temperature of 30⁰C and initial concentration of 1000 mg B/L, by varying the pH from 3 to

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10 and addition of 20 g resin in the batch system. The variation of the sorbed amounts of boron on resin is presented in Figure 3.

Figure 3. Boron removal efficiency versus time for different pH values of the sorption medium in 1000 mg B/L solutions

shown a high selectivity for the boron at high pH [16]. The resin acts as a chelating resin at a basic medium in its free amine form [17]. The boron complexation at basic pH is carried out by the hydroxyl groups, meaning the surface of resin is more negatively charged at basic media due to high OH ions present in the solution which attracts more positively charged boron ions. C. Effect of resin dosage on Boron Removal The effects of changing initial resin dosage in the sorption medium on removal of boron in terms of adsorption capacity was examined at different values including 10, 30, 50, 60, and 110 g resin/L, while other operational parameters such as temperature and initial boron concentration of solutions were kept constant (T=30⁰C, C₀=100 mg B/L, pH=natural). As depicted in Figure 4, the removal reached up to 99% by adding 11g resin to the 100 ml boric acid solution with concentration of 100 mg B/L. However, the removal efficiency for 10 g resin/L did not exceed 57% value. The removal efficiencies for remaining resin dosages including 30, 50, and 60 g/L reached up to 79, 95, and 98% respectively.

As shown in Figure 3, the maximum sorption was achieved at pH=9.5 with removal efficiency of 70%. The lowest efficiency, on the other hand, was achieved at pH=3. To put it simply, the favorable pH range can be claimed as pH values between 8 and 10, as displayed in Figure 4. For other pH values which are 5, 7, 8, 9, and 10, the removal efficiencies reached up to 24, 29, 54, 67, and 58 respectively.

Figure 5. Boron removal efficiency versus time for various amounts of resins

Figure 4. Variation of boron removal efficiency with pH of the sorption medium

Distribution of B(OH)3 and B(OH)-4 are controlled by pH of the solution which itself has a significant effect on removal of boron from aqueous solutions. These two species compete for the adsorption on the resin. According to Demircivi [15], the tetrahedral ions become dominant species at pH between 9 and 10 for boron concentrations below 3000 mg B/L. In addition, Amberlite IRA 743 has

The increase in removal efficiency by increasing the resin dosage can be explained by the fact that the number of available adsorption sites increases by an increase in dosage of resin and consequently this results in an increase in removal efficiency. Clearly, since increasing the adsorbent doses provides a greater surface area and adsorption sites, the equilibrium concentration decreases with increasing adsorbent doses for a given initial concentration. D. Equilibrium Isotherm The relation between sorption capacity and solution concentration can be defined by term adsorption isotherm. The Langmuir isotherm model has been used to describe the

experimental data well in the adsorption of boron by Amberlite IRA 743.

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V. CONCLUSION Ce/Qe = (1/QoKL) + (1/ Qo)Ce

(2)

Plotting of Ce/Qe vs Ce give a straight line with slope 1/Qo and intercept 1/QoKL. In this equation, Qe, the amount adsorbed per gram of adsorbent, corresponds to complete coverage. KL is the Langmuir constant (L/g), which is the energy constant, indicating the adsorptivity of the solute. The graph 1/Qe versus 1/Ce for boric acid solution was plotted. The resulted graph is shown in Figure 6. A straight line with positive slope and straight line correlation coefficient of R2=0.974 was obtained.

The results indicated that, in highly concentrated solutions of boric acid, an increase in initial concentration of boron, removal efficiency decreases drastically. It is been found out that the favorable pH range for removal of boron from a sorption medium is between 8 and 10, not to mention that the maximum boron removal was found to occur at pH value of 9.5. When the amount of resin was decreased in a solution of 100 mg B/L, because of providing larger contact surface area, a higher percent removal of boron was obtained in the same period of time. And last but not least, the empirical Langmuir isotherm was found to adequately describe the equilibrium relation between the resin and liquid phases of the ion exchange process. REFERENCES [1] [2]

[3]

[4] [5]

[6] Figure 6. Values of 1/Qe versus 1/Ce respresenting Lnagmuir isotherm model

[7]

The value of slope and intercept-Y obtained were 0.0365 and 0.3158 respectively. Constants “b”, representing Qe (mg/g), and “a”, representing the equilibrium constant, were calculated using the values of slope and intercept-Y obtained from the graph. The values obtained are b=3.166 mg/g and a=0.0115 L/mg (Table 2). TABLE II.

[8] [9]

[10] [11]

LANGMUIR ADSORPTION ISOTHERM CONSTANTS

Langmuir Isotherm

[12]

Qe (mg/g)

a (L/mg)

R2

3.166

0.0115

0.974

[13]

[14]

The good correlation coefficient values of Langmuir isotherms also explaining strictly localized monolayer sorption phenomenon. Langmuir sorption isotherm hints towards surface homogeneity of the sorbent. This leads to the conclusion that the surface of resin is made up of homogenous sorption patches and the fixed number of active sites are available for sorption with similar sorption capacity.

[15]

[16]

[17]

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