Removal of Excess Toxic Chloride and Fluoride Anions from Wastewater Employing Eggshells Waste Remains

Eggshells waste was investigated for its sorption abilityas an environmentally-friendly and cheap sorbent for removing excess anions from wastewater. The milled size of the waste was found to be ≤63 µm, with round and smooth morphology. Moreover, the Fourier transform infrared spectrometer spectrum showed functional groups such as carbonate and hydroxyl. The X-ray diffractogram of the eggshells showed the presence of calcite, which mostly compose of calcium and carbonate ions. Multivariate methodology was employed for optimization of factors that affect sorption studies; initial ions concentration which was found to be 24.45 and 23.24 mg/L, the sorbents dose which was found to be 85.20 and 81.56 mg/L, contact time, which were found to be 69.37 and 70.28 min and solution pH 7.19 and 7.97 for chloride and fluoride anion respectively. The eggshells also exhibited high percentage removal efficiencies for chloride (80.70% ± 2.01%) and fluoride ion (93.18% ± 1.67%) from real wastewater samples. The adsorption isotherm was satisfactorily fitted with Langmuir isotherm model. The thermodynamics kinetics studies showed that the adsorption of fluoride and chloride ions onto the eggshells was endothermic and spontaneous and the adsorption data followed second-order kinetics supporting that chemisorption process was involved.


INTRODUCTION
Processed wastewater is widely emp loyed to compensate for the shortage of benign and uncontaminated freshwater (Stevens & Batlo kwa, 2017). Wastewater treatment methodologies have been developed by several researchers for treating and reutilizing wastewater for use in irrigation, animal and hu man consumption, groundwater boost, nonpotable reuse and domestic activities. Nevertheless, the presence of excess and toxic anions such as chloride and fluoride ions in the wastewater pose a serious health hazard to aquatic animals and the environment (Chuang, Chang, Chang, & You, 2006). Agricu ltural act ivities such as the use of potash fertilizers for soil enrich ments, road salts, industrial activ ities and natural calamit ies have continuously increased the amount of chlorine and fluoride ions in the aquatic ecosystems (Butt & Riaz, 2017). Naturally, chloride and fluoride ions exist in fresh or ground waters in considerate concentrations and are essential to life. For examp le, ch loride ions are micronutrients essential for plant development and it constitute approximately 0.05% of the earth's crust (Hunt, Herron, & Green, 2012). It is required in lo w concentrations by most plants, and it plays an essential role in stomatal regulat ion. However, high levels of chloride ion may alter reproduction rates, increase species mortality and may also change the characteristic of the entire local ecosystem. Furthermore, as the concentration of chloride ion increases due to the abovementioned activit ies or reasons, and filters into underground waters and wastewaters, it may strain p lant respiration and change the quality of the wastewater effluent as well as drinking water (Asche & Lead, 2013). Fluoride on the other hand, is essential to human health specifically fo r the bones and dental health, however, this is plausible only at lo w levels (≤ 1.0 mg/ L)(Bhaumik et al., 2012). Consumption of high levels o f fluoride ions is detrimental to hu man health and aquatic life. For examp le, ingesting high levels of fluoride ions browning and mottling of the teeth, bones fluorosis (Fawell & Nieuwenhuijsen, 2003), depression (Crisp et al., 1998), urinary tract malfunction and red blood cell deformities (Thole, 2013). Henceforth, it is essential that the concentration of chloride and fluoride ions in recycled wastewater be considerably reduced to acceptable levels (200 mg/ L and 1.0 mg/ L for chloride and fluoride respectively) as set out by international monitoring agencies such as the World Health In this paper, pulverized eggshells were employed as an environmentally friendly and readily available adsorbent for the removal of excess toxic chloride and fluoride ions fro m wastewater sample. FTIR, SEM and XRD were emp loyed for characterization of the eggshells waste remains. The significance of various sorption parameters including pH, adsorbent dose, contact time, in itial concentration of the anions was investigated. Adsorption isotherm models were emp loyed to describe the adsorption equilibriu m data. Pseudo-first and second-order and intraparticle diffusion were emp loyed to investigate the kinetics of the adsorption process. The thermodynamic parameters, such as ΔG, ΔH and ΔS were also calculated fro m the adsorption measurements.

II. MATERIALS AND METHOD Materials and Instrumentation
The eggshells waste remains employed for this experiment was collected fro m the Moghul Refectory located on the main campus of the Botswana International Un iversity of Science and Technology (BIUST), Palapye, Botswana.
Ultra-pure water o f 18.0 MΩ/cm resistivity, Type I, was prepared by a Elix 5 M illipore water purification system fro m Merck, (Darmstadt, Germany) and was used to prepare all solutions. Reagents used were: SPA R white spirit Vinegar, which was emp loyed to treat the waste materials, was purchased from SPA R (Palapye, Botswana), elemental standard solution of Cl -, and Fwith a concentration of 1000 mg/ L and NaOH (97%) pellets were purchased from Rochelle Chemicals (Johannesburg, South Africa). For determination of size, morphology and nanoparticle composition, JSM 1700 SEM coupled with EDX, obtained fro m USA was used. The instrument resolution was about 50eV at amplification t ime o f 5 microseconds, it uses an Electron Dispersive X-ray (EDX) back scattering detector operated in spectra mode (elemental co mposition), point and shot mode and mapping mode (distribution of compounds). Analysis was done emp loying a Philips GSR v, 3.2 software. The SEM worked at beam voltage of 1.0 kV LED, low vacuum (typically 2 to 6 Torr), and utilizes a chamber gas (H2O) for imaging, charge suppression and sample hu mid ity.An E6700 Polaron range high vacuum evaporator sputter coater, obtained fro m the United Kingdom (UK), was used to coat the fish scales remains and untreated waste materials prio r to SEM-EDX analysis. Perkin Elmer System, Spectru m two Fourier transform infrared (FTIR)spectroscopy was used to determine the functional groups of materials. The FTIR spectra were recorded in the wavenu mber range 400-4000 cm -1 on a Perkin Elmer system 2000 FTIR. The adsorbents were kept at ambient temperature. 1mg of the adsorbents per 200 mg of KBR was weighed. The powder was pressed into pellets by using a 15 ton hydraulic press. The data were collected at 2.0 cm −1 resolution, and each spectrum was a result of 256 scans.A powder D8 Advanced Powder X-Ray Diffractometer (XRD) obtained fro m Bru ker (Karlsruhe, Germany) was emp loyed for characterizat ion of the eggshells waste remains. Meanwhile, the presence of chloride and fluoride anions effluents during the entire experiment were investigated by employing a Shimad zu S 150 ion chro matography system (SHIMADZU, Japan) obtained from SHIMADZU (Johannesburg, South Africa). The instrumental parameters were those recommended by the manufacturer. remove dirt and eggs remains. Then it was sun dried for 48hrs, after wh ich, it was pulverized emp loying a Fritsch pulverisette 5 pulverizer, operated at 400 rp m for 90 min in both milling and reverse mode. The pulverized materials were then sieved to 63 -200 micron mesh size, after which they were rewashed with deionized water several t imes to remove color and dirt. The p roduct was than treated with SPAR white spirit vinegar to remove inorganic pollutants. Finally, they were dried in an oven at 65 ± 2 ˚C for 6hrs 11.

X-ray Powder Diffraction (XRD)
A powder D8 Advanced Powder X-Ray Diffracto meter (XRD) analysis was emp loyed to investigate the physical properties as it relates to the crystallinity of the waste material. The XRD was operated with Cu Kα emission (ƛ = 1.54105Ǻ, 40 kV, 40 mA per sec) and with high efficiency linear detector of Lyn x Eye type. The scanning mode used was coupled with 2Ɵ/Ɵ on the scanning range 10˚ -120˚ values. The crystallite size of the sample was calculated by Deby-Scherrer method.

Fourier Transform Infrared Spectroscopy (FT-IR)
Fourier transform infrared (FTIR) spectrometer was emp loyed to identify the functional groups crazed on the surface of the eggshells waste remains. The FTIR spectra were recorded in the wavelength range 500-4000 cm-1 on a Nico let iS10 Thermo Scientific FTIR. The data were collected at 2.0 cm −1 resolution, and each spectrum was a result of 250 scans.

Scanning Electron Microscopy Coupled wi th Energ y Dispersive X-ray Spectroscopy (SEM-EDX)
Scanning Electron Microscope coupled with Energydispersive X-ray spectrometer (SEM -EDX) (JSM -7100F), was employed to determine the surface morphology of the eggshells waste and to determine its elemental composition. An E6700 Po laron range high vacuum pressure sputter coater (Quoru m Technologies, UK) was emp loyed to coat the eggshells wastes with carbon. These were then taken for SEM-EDX analysis, wh ich operated under high vacuum and beam accelerat ion voltage of 10.0 kV (the reco mmended operating voltage for organic material samples). The results fro m this analysis were then used to determine the surface morphology and elemental composition of the eggshells waste.

Batch Adsorption Studies for Cland F -Removal Employi ng Eggshells Waste
All experiments were carried out in batches and done in triplicates. A 100 mg/ L standard mixture of chloride and fluoride was prepared fro m 1000 mg/ L stock solution of each of the anions.

Opti mization of Adsorpti ve Parameters of the Eggshells Waste
Optimization studies were carried out by employing mu ltivariate optimization methodology. In this study, the eggshells were optimized by looking at four factors: contact time, pH, sorbent dosage, and initial concentration. These were first screened through the use of a two-level fract ional factorial design. This evaluates the significance of each factor towards the experimental output. The screening design was carried using the experimental conditions as described in Table 1. It was then filtered into a 100 mL volu metric flask and deionized water added to the mark. It was investigated for chloride and fluoride anions emp loying IC. The experiments were done in replicates to evaluate the adequacy of the method.

Application of the Opti mized Eggshells Waste Adsorption Method to Real Samples
The sorption nature of the eggshells waste remains was studied by applying the optimized parameters to wastewater samples collected fro m (1) WhereCi is the initial concentration of metal ions in wastewater sample. Cf is the final concentration of metal ion in wastewater after applying the eggshell waste remains.

Equilibrium studies
Adsorption equilibriu m studies were conducted to determine the nature of the adsorption isotherms and the adsorption capacity of the eggshells waste remains for the removal of chlo ride and fluoride. For the isotherm studies, the initial ions concentrations were varied fro m 10 to 100 mg / L using 1 g/ L (dry weight) eggshells waste powder. The adsorption flasks were ag itated in a rotary shaker at 400rp m and samples were collected at specified time intervals, followed by separation of the eggshells waste powder by filtration. The resulting solutions were analy zed employing IC for the residual anions concentrations.

Kinetic studies
Kinetic studies were carried out in a volu metric flask and samples were collected at different intervals of 15 min to 90 min. The samples were analysed for residual ions concentration. The kinetics of adsorption was studied by using three kinetic models, pseudo first order, second order and intra particle diffusion models.

Thermodynamic studies
The experiments were conducted at different temperatures in the range of 0 -50 ˚C in a rotary shaker for 90 min. The samples were filtered and analysed employing IC fo r the residual anions concentrations at the end of the experiments.

III. RESULTS AND DISCUSSIONS X-ray Powder Diffraction (XRD)
The XRD phase analysis of the eggshells waste powder was performed emp loying JCPDS (Joint Co mmittee on Po wder Diffraction Standards) card number 01-073-0293. It was evident that a compound, calcite with the chemical formu la CaCO3 was the majo r component of the eggshell waste powder with a with d-spacings 0·845, 0·784, 0·712, 0·684, 0·600, 0·563, 0·489, 0·389, 0·301, 0·289, and 0·200 corresponding to the calcite structure as shown in Figure 1. the eggshells powder surface resulting in high adsorption efficiency for chloride and fluoride ions by the eggshell waste powder (Tsai et al., 2006). Figure 2 shows SEM micrographs of the eggshells waste powder. The fish scale appears to have a round and smooth morphology with a particle size of ≤63 µm, wh ich are excellent characteristics associated with excellent adsorbents. The micrograph is characterized by having two regions, one being darker and the other being white. The white region is rich in inorganic material containing high proportion of calciu m and phosphorus, whereas the dark region is rich in protein because it has high proportion of carbon and oxygen as soon by Figure 3.

Fourier Transform Infrared Spectroscopy (FT-IR)
Eggshell is main ly co mposed of calciu m carbonate (94.03%) and it also contains calcite and calcareous soil. Eggshell has a cellu losic structure and contains amino acids; thus, it is expected to be a good adsorbent. Figure 4 below shows an FTIR of eggshells before removal (b lue) and after removal (pin k) of the chloride and fluoride ions from wastewater.

International Journal of Advanced Engineering Research and Science (IJAERS)
[  . It has been reported that the most prominent peak in FTIR spectra of eggshell particles matched with that of carbonate minerals. The peak at 2927.5 cm -1 is due to presence of C-H stretching mode (Tsai et al., 2006).

Opti mization of Adsorpti ve Parameters of the Eggshells Waste Remains
Experimental matrices were designed using Minitab for the optimization purposes. The yields were followed by the use of IC separation measurements of chloride and fluoride. Before performing the actual optimization, a ½ fraction factorial design was employed in order to assess the level of significance of each factor under investigation. The factorial design comes as a screening phase, which allows screening a relat ively large number of factors in a relat ively small number of experiments that cover the whole experimental domain, with the result identifying the most influential factors towards obtained yields. Analysis of data was in the forms of normal probability plots of standardized effects, and residuals plots; as shown by Figures 5 and 6, respectively.   /dx.doi.org/10.22161/ijaers.5.9.9  ISSN: 2349-6495(P) | 2456-1908(O) www.ijaers.com Page | 85  Figure 6 shows the residual plots for the yield obtained when using the eggshells waste powders. The plots probe into the distribution pattern of data points through the use of residuals. Residuals are the outcome of the difference between the observed and the fitted values (Ryan, 2006). Normal probability and histogram plots investigate whether the data obtained exh ibits a standard Gaussian distribution.
For normal probability plots, if the data points fall approximately along the straight line, then the residuals are said to be normally d istributed, meaning the data follows the Gaussian distribution (Ziegel, 2004), which was the case for this work. A plot of residuals against fitted responses (values) is used to detect unequal error variances and outliers, while the plot of residuals against order of the data checks for correlat ion of the residuals. The residuals against fitted values plot revealed a constant variance of the residuals about the center line. The plot of residuals against order of the data showed a randomized shifting pattern about the center line, signifying that the data was uncorrelated with each other. The plots for the eggshells show that the residuals were randomly d istributed, hence, signifying absence of systematic errors and hence adequacy of the model.

Fig.6: Residuals plots of standardized effects on the eggshells waste remains
Following the screening of significant factors using fractional factorial design, a response surface design was then created to determine the optimu m conditions of each factor. This was achieved through the use of a CCD. The optimal conditions obtained for the eggshells waste adsorption of chloride and fluoride an ionswere 24.45 and 23.24 mg/L for the in itial ions concentration respectively, the sorbents dose was found to be 85.20 mg/L (chloride) and 81.56 mg/ L (fluoride), contact time, were found to be 69.37 min (chlo ride) and 70.28 min (fluoride) and solution pH 7.19 (chloride) and 7.97 (fluoride). Furthermore, the regression coefficient, R 2 , was also used to assess the fit of the model to the experimental data which were 0.9901 (Cl -) and 0.9891(F -). The relat ive standard deviations (RSD) for the experimental data were obtained to be 1.4% (Cl -), and 2.21% (F -).

Adsorption Kinetics
The comparison of experimental sorption capacities (q exp) and the predicted values (qcal, k1, k2, kd, R 2 ) fro m pseudo first order, pseudo second order and intra particle diffusion constants are given in Table 3eggshells waste. The pseudo first order (p lot of log(qe-q) vs. t) was not satisfactory to explain the experimental data, whereas the calculated, q cal values derived fro m the pseudo second order model for sorption of the selected ions were very close to the experimental (qexp) values. The second order equation (plot of t/q vs. t) appeared to be the better fitting model than first order and intra part icle diffusion equations because it has higher R 2 value as shown in Figure 8

Thermodynamics Parameters
The results of these thermodynamic calculations are shown in Table 4. The negative values for the Gibbs free energy for all the selected ions, show that the adsorption process is spontaneous and that the degree of spontaneity of the reaction increases with increasing temperature. The overall adsorption process seems to be endothermic (∆H =39.37, and 53.26 kJmo l-1 for Cland Frespectively). Table 4 also shows that the ∆S values were positive (which imp lies that entropy increases as a result of adsorption). This occurs as a result of redistribution of energy between the adsorbate (chloride and fluoride anions) and adsorbent (eggshells waste powder). Before adsorption occurs, the anions near the surface of the adsorbent will be mo re ordered than in the subsequent adsorbed state and the ratio of free anions to anions interacting with the adsorbent will be higher than in the adsorbent state. As a result, the distribution of rotational and translational energy among a small number of ions increase with increasing adsorption by producing a positive value of ∆S and rando mness will increase at the solid solution interface during the process of adsorption. Adsorption will occur spontaneously at normal and high temperatures if ∆H>0 and ∆S>0.  IV. CONCLUSION In this paper, an attempt to employed eggshells waste remains as an ecofriendly adsorbent for removing fluoride and chlorideanions fro m wastewater was achieved. Adsorption studies were developed and evaluated. These studies demonstrated that pH, sorbent dose, contact time and concentration are significant factors in adsorption. The use of eggshell waste remain was found to be a green method therefore conserving the environment. Eggshells waste remains were proposed as cheap, easily availab le and efficient method for removal of ch loride and fluoride anions fro m the environ ment.The adsorption isotherm was more satisfactorily fitted with Lang mu ir isotherm model. The thermodynamics various kinetics models including the Pseudo-first-order, Pseudo-second-order and intra particle diffusion constants of the adsorption process, ΔH, ΔG and ΔS were evaluated. The results showed that the adsorption of nitrate and nitrite ions onto activated carbon was endothermic and spontaneous. The adsorption data followed second-order kinetics supporting that chemisorption process was involved.