Abstract

In this study, schorl was used as an effective adsorbent for ciprofloxacin removal from wastewater. The adsorption performance, mechanism and effect of metal ion on sorption were investigated. Adsorption capacity reached a maximum (8.49 mg/g) when the pH value was 5.5. The pseudo-second-order kinetic model and Freundlich model could better describe the experimental data. The negative ΔH (–22.96 KJ/mol) value showed that the adsorption process was exothermic. The results also indicated physical adsorption existed on the adsorption process, which was in agreement with the analysis of X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy. The desorption rate could reach 94%, which suggested that schorl had a good desorption and regeneration performance. Coexisting ions, such as Cu2+ and Al3+, could obviously inhibit adsorption, and the inhibition from Al3+ was significantly higher than that from Cu2+. However, the additional Zn2+ could slightly promote the adsorption.

INTRODUCTION

Ciprofloxacin (CIP), a synthetic antibiotic, is a typical kind of fluoroquinolone (FQ) (Picó & Andreu 2007; Li et al. 2013). It is utilized for the inhibition of some diseases for humans and animals. However, because of the continuous increment of production amount and inappropriate discharge (Zhang & Huang 2007; Yang et al. 2010; Zhang et al. 2015), a series of problems occurred. As in previously published results, it is frequently detected in the environment (Kolpin et al. 2002; Martins et al. 2008). In pharmaceutical wastewater, the concentrations of CIP are as high as 28–31 mg L–1 (Larsson et al. 2007). Prolonged exposure to CIP could promote antibiotic-resistance of bacteria and their high potential risks to ecological and human health (Jiao et al. 2008; Kemper 2008). However, due to the low biodegradation rate and bacteria-inhibition effect, it was difficult to be removed by traditional biological wastewater treatment processes (Sarmah et al. 2006; Teske & Arnold 2008). Consequently, it is vital to determine an effective method for the disposal of CIP in wastewater.

In the past decades, several conventional processes such as biodegradation, chemical oxidation and adsorption were applied for the treatment of CIP in the solution (Li & Zhang 2010, Benitez et al. 2011, Hu & Wang 2016; Yu et al. 2016). Among these treatments, the adsorption process acquires a special importance because of the inexpensive nature and ease of operation. Natural minerals, such as aluminous oxide, magnetite, were often chosen as model sorbents for the removal of CIP from wastewater. The adsorption capacities of aluminous oxide and magnetite reached 13.6 and 12.7 mg/g, respectively (Gu & Karthikeyan 2005; Rakshit et al. 2013). These results demonstrated that minerals play an important role in the adsorption of CIP from aqueous solution. Hence, the natural adsorbents with low cost, simple process, good feasibility and high adsorption capacity are needed.

Tourmaline is a borosilicate mineral that consists of variable elements. The general chemical formula of tourmaline can be represented as XY3Z6[Si6O18][BO3]W4 (in which X is Na+, Ca2+ or vacancies; Y is Fe2+; Z is Al3+, Mg2+, Fe3+; W is OH, F, O). If size Y was occupied by a different element, the tourmaline could be divided into olenite (Al tourmaline), dravite (Mg tourmaline), alkali tourmaline and schorl (Fe tourmaline). The crystal structure of schorl belongs to the trigonal space group. Schorl also has a special property of spontaneous and permanent poles, which could produce an electric dipole. Hence, an electric field exists on the surface of the schorl granule (Nakamura & Kubo 1992; Xia et al. 2006; Wang et al. 2012). In addition, schorl can release negative ions. These unique features of schorl mean it can be widely used in various fields (Sergei & Alice 2002; Xu et al. 2009; Liu et al. 2013; Wang et al. 2013; Yu et al. 2014). Schorl was capable of adsorbing dyestuff and heavy metal ions (Guerra et al. 2012; Liu et al. 2016). However, there has been no research focusing on the disposal of antibiotics, especially CIP, by the adsorption onto schorl. If the schorl could remove CIP effectively by adsorption, it would expand its application. Moreover, because it is a low cost natural mineral and does not need to be modified further, it will not have problems such as secondary pollutions in some other chemical removal approaches.

The objective of this paper was to investigate the adsorption characteristics of CIP onto schorl. The affecting factors, such as pH, temperature and coexisting ions were investigated in the experiments. The adsorption isotherms and kinetics equations were used to explain adsorption performances. Efficient regeneration of the schorl adsorbent was also observed. This paper can provide a scientific basis and practical technology for the treatment of CIP in wastewater.

MATERIALS AND METHODS

Materials

Aluminum chloride hexahydrate, zinc chloride, copper chloride dihydrate, hydrochloric acid, and sodium hydroxide were of analytical reagents grade and were obtained from Nanjing Wanqing Chemical Co., Ltd (Nanjing, China). Ciprofloxacin hydrochloride (C17H18FN3OHCl, purity >98%) was purchased from Sigma-Aldrich, the molecular structure of ciprofloxacin is given in Figure 1. The schorl was obtained from Xinjiang Province of China.

Figure 1

The structure of CIP.

Figure 1

The structure of CIP.

Batch sorption experiments

All the adsorption experiments were carried out in 250 mL Erlenmeyer flasks with 0.1 g schorl, and 50 mL CIP solution was added. pH value was adjusted with 0.1 mol/L NaOH or 0.1 mol/L HCl. The mixtures were shaken at 240 rpm at different temperatures for 12 h. When it reached equilibrium, the solution was passed through a 0.22 μm filter before analysis. In the kinetic experiments, water samples were taken at predetermined time intervals. For the isotherm studies, the experiments were operated at different temperatures (288, 303 and 318 K). In order to determine the effect of heavy metal ions on the adsorption, the heavy metal ions were added into the CIP solutions (30 mg/L) according to certain mole ratios (CIP:M = 1:0, 1:1, 1:2, 1:5, 1:10). The desorption experiment was performed after the adsorption experiments, by adjusting the pH to 11 with 1 mol/L NaOH solution. The flasks were sealed and shaken at a speed of 240 rpm for 12 h. The CIP concentration was determined by a UV–Vis spectrophotometer (UV-1800) at a wavelength of 275 nm (Sun et al. 2016).

Characterization methods

The original and absorbed samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analyses. The structure of the samples was performed on an XRD-6100 diffractometer with Ni-filtered Cu Ka radiation, operating at 40 kV and 50 mA. The samples were scanned in the range of 10–80° (2θ) at a scanning rate of 7 min–1. SEM (Hitachi SU-1510) was operated with an acceleration voltage of 15 keV. The samples were measured on a VG ESCALAB MKII XPS system with Mg Kα source and a charge neutralizer. The FTIR spectra were obtained on NiCOLET iS5 spectrometer. The spectra were collected by accumulating 250 scans at a resolution of 4 cm–1 in the range of 400–4,000 cm–1.

Data analysis

The adsorption rate is one of the important parameters that affect the adsorption process (Srivastava et al. 2006; Hao et al. 2012). To characterize the adsorption process of CIP on the schorl, pseudo-first-order and pseudo-second-order kinetic models were applied to fit the experimental data. The equations can be represented as follows (Wan et al. 2013).

Pseudo-first-order kinetic model:  
formula
(1)
Pseudo-second-order kinetic model:  
formula
(2)
where qt (mg·g–1) and qe (mg·g–1) are the adsorption capacity of schorl at any time t (min) and the equilibrium adsorption capacity of schorl, respectively; k1 (min–1) and k2 (g·mg–1·min–1) are the adsorption rate constants of pseudo-first-order and pseudo-second-order equations, respectively.

Adsorption isotherms were used to evaluate the interaction between the adsorbent and the adsorbate. To further understand the adsorption mechanism, two typical models, Langmuir and Freundlich, were selected to analyze isotherm data and the expressions can be written as follows (Foo & Hameed 2010).

Langmuir isotherm model:  
formula
(3)
Freundlich isotherm model:  
formula
(4)
where qm is the maximum adsorption capacity (mg.g–1); is the equilibrium concentration of CIP (mg.L–1); kL is the Langmuir equilibrium constant; kF is Freundlich isotherm constants, which are indicative of the affinity of the binding sites; n is the nonlinearity constant reflecting the favorability of adsorption and the degree of surface heterogeneity and both were related to the adsorption capacity and intensity.
The thermodynamic parameters represent the change in free energy (), enthalpy (), and entropy () of the adsorption process was obtained from the temperature-dependent isotherms by using the Van't-Hoff equation:  
formula
(5)
 
formula
(6)
in which R is the gas constant (8.314 J/mol K), T is the absolute temperature (K); and K is the adsorption constant in the Langmuir equation, L/mol (Liu 2009); is the Gibbs free energy change, kJ/mol; is the standard enthalpy change, kJ/mol; is the entropy change, kJ/mol. The values of and were calculated from the slope and intercept of the plot of lnK versus 1/T.

RESULTS AND DISCUSSION

Kinetic studies

The effect of contact time on CIP adsorption is shown in Figure 2. The adsorption capacity was increased quickly, reaching about 75% of the finally adsorbed amounts during the initial 10 min. After this period, the adsorption rate was gradually slow and reached equilibrium in about 120 min. The adsorption capacity of CIP reached 7.2 mg/g. To further evaluate the adsorption kinetics of CIP on the schorl, pseudo-first-order and pseudo-second-order kinetic models were employed to fit the experimental data. The parameters are listed in Table 1. In comparison with the pseudo-first-order kinetic model, the pseudo-second-order kinetic model had a higher correlation coefficient value to describe experimental data. The results were similar to the adsorption of CIP onto activated carbons, ordered mesoporous carbon, bamboo-based carbon and layered chalcogenides (Li et al. 2015b; Peng et al. 2015; Sun et al. 2016). Furthermore, the theoretical values of qe in the pseudo-second-order kinetics were closer to the experimental qe than pseudo-first-order kinetics. In conclusion, the above results suggested that the adsorption process were well represented by the pseudo-second-order kinetic model.

Table 1

Kinetics constants and correlation coefficients for the adsorption of CIP by the schorl

T (K)   Pseudo-first-order model
 
  Pseudo-second-order model
 
k1 (min–1qe (mg/g) R2 k2 (g·mg–1·min–1qe (mg/g) R2 
288 0.289 5.49 0.943 0.0999 5.69 0.979 
303 0.238 6.68 0.914 0.0599 6.97 0.970 
318 0.191 6.60 0.924 0.0486 6.89 0.976 
T (K)   Pseudo-first-order model
 
  Pseudo-second-order model
 
k1 (min–1qe (mg/g) R2 k2 (g·mg–1·min–1qe (mg/g) R2 
288 0.289 5.49 0.943 0.0999 5.69 0.979 
303 0.238 6.68 0.914 0.0599 6.97 0.970 
318 0.191 6.60 0.924 0.0486 6.89 0.976 
Figure 2

Adsorption kinetics of CIP on the schorl.

Figure 2

Adsorption kinetics of CIP on the schorl.

Adsorption isotherms and thermodynamics

The adsorption isotherms of CIP absorbed on the schorl at different temperatures is shown in Figure 3. The equilibrium concentration of CIP increased with the increasing initial concentration. Isotherm parameters and the correlation coefficients are shown in Table 2. The adsorption process fits better with the Freundlich model in comparison to the Langmuir model, indicating multilayer physical adsorption. In the Langmuir model, the largest adsorption capacity qm was increased slightly from 8.54 to 9.68 mg/g with the increasing temperature, which suggested that temperature has little effect on the adsorption process. Schorl exhibited a lower adsorption capacity of CIP compared to CIP adsorbed on magnetite, aluminous oxide, ordered mesoporous carbon, bamboo-based carbon and layered chalcogenides, while it showed a higher adsorption amount in comparison with modified coal fly ash, zetolite and kaolinite (Table 3). As for the Freundlich model, all the constants n were greater than 1, giving an indication for the favorability of adsorption.

Table 2

The parameters of adsorption isotherms of CIP on the schorl at different temperature

T (K) Langmuir model
 
Freundlich model
 
qm (mg/g) KL R2 KF R2 
288 8.54 0.336 0.823 4.778 7.30 0.977 
303 9.16 0.262 0.805 4.24 5.46 0.966 
318 9.68 0.134 0.805 3.01 3.75 0.937 
T (K) Langmuir model
 
Freundlich model
 
qm (mg/g) KL R2 KF R2 
288 8.54 0.336 0.823 4.778 7.30 0.977 
303 9.16 0.262 0.805 4.24 5.46 0.966 
318 9.68 0.134 0.805 3.01 3.75 0.937 
Table 3

Comparison of maximum adsorption capacity (q max) of various adsorbents for CIP

Adsorbent qm (mg/g) Reference 
Modified coal fly ash 1.547 Zhang et al. (2011)  
Zeolite 5.79 Genç & Dogan (2015)  
Kaolinite 6.3 Li et al. (2011)  
Schorl 8.48 This study 
Magnetite 12.73 Rakshit et al. (2013)  
Aluminous oxide 13.6 Gu & Karthikeyan (2005)  
Layered chalcogenides 230.9 Li et al. (2015b)  
Ordered mesoporous carbon 233.37 Peng et al. (2015)  
Bamboo-based carbon 362.94 Peng et al. (2015)  
Adsorbent qm (mg/g) Reference 
Modified coal fly ash 1.547 Zhang et al. (2011)  
Zeolite 5.79 Genç & Dogan (2015)  
Kaolinite 6.3 Li et al. (2011)  
Schorl 8.48 This study 
Magnetite 12.73 Rakshit et al. (2013)  
Aluminous oxide 13.6 Gu & Karthikeyan (2005)  
Layered chalcogenides 230.9 Li et al. (2015b)  
Ordered mesoporous carbon 233.37 Peng et al. (2015)  
Bamboo-based carbon 362.94 Peng et al. (2015)  
Figure 3

Adsorption isotherms of CIP on the schorl.

Figure 3

Adsorption isotherms of CIP on the schorl.

The thermodynamic parameters were calculated from the Van't-Hoff equation. As shown in Table 4, the negative G values demonstrated that CIP absorbed on the schorl was a spontaneous process. As in previous studies, if the absolute value of ΔG was in the range of 2.1–20.9 KJ/mol, it was indicative of physical adsorption existing in the adsorption process, while it was between 80 and 200 KJ/mol, the adsorption should be associated with chemical adsorption (Liu & Liu 2008; Wu et al. 2016). The values of ΔG at different temperatures in this study were in the range between those of physical adsorption and chemical adsorption. Hence, CIP absorbed on schorl could be regarded as a physical adsorption enhanced by the electrostatic effect. The negative value of ΔH indicated that the adsorption process was exothermic. The ΔH evolved during adsorption were less than 40 KJ/mol, which was in agreement with the observed physical adsorption (Zhang et al. 2009; Sadasivam et al. 2010). The positive ΔS (0.0188 KJ/mol) value for CIP adsorption suggested an increase in the randomness at solid–solute interface during the adsorption process.

Table 4

The calculated values of thermodynamic parameters of CIP on the schorl

T (K) ΔG (kJ·mol–1ΔH (kJ·mol–1ΔS (kJ·mol–1
288 –28.19 –22.96 0.0188 
303 –29.03 
318 –28.71 
T (K) ΔG (kJ·mol–1ΔH (kJ·mol–1ΔS (kJ·mol–1
288 –28.19 –22.96 0.0188 
303 –29.03 
318 –28.71 

Effect of the pH

Previous studies reported that the pH has a major impact on adsorption (Gu & Karthikeyan 2005; Vasudevan et al. 2009). In the schorl system, the effect of pH on the CIP adsorption is shown in Figure 4. Adsorption capacity increased with the increasing pH and reached a maximum capacity (8.49 mg/g) at pH 5.5, then it decreased with the increment of pH value. It was dependent on the charge of schorl and the speciation of CIP molecule under different pH values.

Figure 4

Effect of initial pH on CIP adsorption by schorl ([CIP]initial = 50 mg/L, T = 303 K).

Figure 4

Effect of initial pH on CIP adsorption by schorl ([CIP]initial = 50 mg/L, T = 303 K).

The pH value of solution could affect both surface charge and density of the schorl, as well as the degree of protonation of the CIP. The schorl surface is, overall, negatively charged at pH > 2.5 (pHpzc) over the whole pH range, whereas CIP (pKa1 = 6.1, pKa2 = 8.7) exhibited pH-dependent speciation in its different forms as a cation (<6.1), zwitterion (6.1–8.7), and anion (>8.7) (Hongsawat et al. 2014). When the pH < pKa1, the cation was the dominant ciprofloxacin species in aqueous solution. CIP adsorbed onto schorl was primarily via electrostatic attraction between negative sites of schorl and piperazinyl groups of CIP. At the lower pH (pH = 3), the adsorption capacity was lower due to the weaker electrostatic attraction between the lower negatively charged of the schorl and CIP+. In addition, the existence of H+ would also affect CIP absorbed on schorl. When the pH was between pKa1 and pKa2, CIP existed as the zwitterion forms and adsorption capacities of the CIP decreased. At pH >pKa2, a sharp decrease was observed, which could be attributed to electrostatic repulsion. This result was in agreement with the ciprofloxacin adsorption on kaolinite (Li et al. 2011).

XRD, SEM, FTIR, XPS analysis

The XRD patterns of the schorls before and after adsorption are shown in Figure 5. The schorl matched with the standard card (No.43-1464), indicating that it was the typical pattern of schorl. It was observed that after adsorption the schorl shared the same characteristic diffraction peaks with the original schorl. No differences were found between the samples before and after adsorption. The SEM images are shown in Figure 6, the original schorl particles (Figure 6(a)) presented various shapes and the size was approximately 1–17 μm. As illustrated in Figure 6(b), the morphology of the absorbed schorl was almost the same as the original schorl. As can be seen from Figure 7, the peak at ∼424 cm–1, considered as the stretching O-Fe-O vibration at octahedral sites (Nadeem et al. 2010), the peak at ∼506, 705 and 1,028 cm–1 were the function groups of Si-O, O-Si-O, Si-O-Si (Mitra et al. 2007). The band at 1,267 cm–1 was a result of stretching vibration of B-O bonds. The peak at 3,559 cm–1 is attributed to O–H bond stretching (Li et al. 2015a). No new absorption peaks and peak shift phenomenon appeared on the FTIR of schorl after adsorption in the relevant wavelength region, indicating that the adsorption may be a physical adsorption.

Figure 5

XRD patterns of the schorl and the absorbed schorl.

Figure 5

XRD patterns of the schorl and the absorbed schorl.

Figure 6

The SEM images of the original schorl (a) and the absorbed schorl (b).

Figure 6

The SEM images of the original schorl (a) and the absorbed schorl (b).

Figure 7

FTIR spectra of schorl before and after CIP adsorption.

Figure 7

FTIR spectra of schorl before and after CIP adsorption.

XPS analysis was employed to ascertain the surface chemical composition of the samples. The bonding energies (BE) of 284.8, 532.1, 685.5, 74.8, and 102.8 eV corresponded to C1S, O1S, F1S, Al2p, and Si2p groups of schorl, respectively, and the Fe2p values were 711.3 and 724.8 eV. After adsorption, the new peaks formed, which were consistent with BE values of CIP (Polishchuk et al. 2009), demonstrating that CIP was successfully adsorbed onto the schorl. In comparison with the BE values of schorls before and after adsorption, except for the new peaks from the adsorbed CIP, they were almost not changed (±0.2 eV) (Table 5). Hence, it was demonstrated CIP absorbed on schorl, probably due to physical adsorption.

Table 5

Binding energies of elements in the schorl, CIP absorbed on schorl, CIP

  Schorl before adsorption Schorl after adsorption CIP 
284.8 284.8 284.8 
  286.4 286.3 
685.5 685.4  
  687.4 687.3 
400.7 399.9 399.8 
  401.4 401.2 
  531.3 531.3 
532.1 532.1  
  532.7 532.7 
Si 102.8 102.8  
Al 74.8 74.7  
Fe 711.3 711.1  
 724.8 724.7  
  Schorl before adsorption Schorl after adsorption CIP 
284.8 284.8 284.8 
  286.4 286.3 
685.5 685.4  
  687.4 687.3 
400.7 399.9 399.8 
  401.4 401.2 
  531.3 531.3 
532.1 532.1  
  532.7 532.7 
Si 102.8 102.8  
Al 74.8 74.7  
Fe 711.3 711.1  
 724.8 724.7  

Desorption experiment

The desorption rate is an important index to measure the recycling of adsorption materials. After the process of adsorption, the desorption experiment is performed by adjusting the pH to 11, and the result is shown in Figure 8. Obviously, a large portion of CIP was quickly desorbed from schorl in 20 minutes. The desorption rate reached 94%, which indicated that schorl had a good desorption ability simply by adjusting the pH values to 11. Electrostatic repulsion could be attributed to the CIP desorption at a high pH value.

Figure 8

Desorption of CIP by schorl on alkaline condition.

Figure 8

Desorption of CIP by schorl on alkaline condition.

Effect of coexisting ions

Several studies found that the concentrations of heavy metals in the solution could affect the adsorption capacity of CIP. In the presence of heavy metal ion, the CIP adsorption capacity changed, as illustrated in Figure 9.

Figure 9

Effect of coexisting ions on the adsorption of CIP on the schorl ([CIP]initial = 30 mg/L, pH = 5.5, T = 303 K).

Figure 9

Effect of coexisting ions on the adsorption of CIP on the schorl ([CIP]initial = 30 mg/L, pH = 5.5, T = 303 K).

Zn2+ had a weak impact on CIP adsorption. The existence of Zn2+ enhanced the CIP adsorption slightly. It is possible that CIP was adsorbed on schorl via Zn2+ bridging, a part of Zn2+ interacted with CIP to form complexes with a positive surface charge, which were more easily adsorbed on the surface of schorl, similar to the results of enrofloxacin sorbed onto a calcareous soil in the presence of Zn2+ (Graouer-Bacart et al. 2015).

On the contrary, the addition of Cu2+ or Al3+ obviously inhibited the adsorption. When the mole ratios were 1:1 (CIP: Cu or CIP: Al), the adsorption amounts of CIP were 5.99 and 4.71 mg/g, respectively. Furthermore, with higher concentrations of Cu2+ or Al3+, the adsorption capacity decreased further. The possible reason could be explained by two aspects: one is that heavy metal ions may compete with CIP for the active site on schorl surface (Jiang et al. 2006) and the other possible reason is that the formation of metal complexes has a lower affinity for the schorl surface than the CIP alone. This observation was similar to the result of Cu2+ which could decrease the CIP adsorption on sand media via competing adsorption under pH = 5.6 conditions (Chen et al. 2013). However, several studies pointed out that the presence of Cu2+ promoted sorption onto both kaolinite and montmorillonite (Pei et al. 2009). This may be related to the different characteristics of the minerals. In the same mole ratios, the inhibition from Al3+ was significantly higher than that from Cu2+. The reason may be concluded that the charge of the Al3+ leads to a higher affinity to the surface of schorl than Cu2+.

UV–visible spectroscopy

The spectrum of CIP after reaction and the solution of CIP adsorbed onto schorl in the presence of Zn2+, Cu2+ and Al3+ respectively, are shown in Figure 10. Pure ciprofloxacin exhibited three absorption bands at around 275, 315 and 323 nm. It was observed that the bathochromic shift observed from 275 to 278 nm in the presence of Cu2+ and Al3+ on CIP adsorption after the reaction. According to the adsorption study (Zhang et al. 2012; Muthumariappan 2013), a large portion of CIP could exist in the form of complexes with metallic cations (Cu2+, Al3+) in the solution. The result was similar to that of the adsorbed tetracycline onto zeolite beta (Kang et al. 2011). However, no absorbance peaks were shifted with the existence of Zn2+ in CIP solution, indicating no generation of ciprofloxacin zinc complex. This result verified the fact that CIP adsorbed on schorl via Zn2+ bridging on the above.

Figure 10

UV–Visible spectra of reaction solution under different conditions.

Figure 10

UV–Visible spectra of reaction solution under different conditions.

CONCLUSIONS

In the experiment, schorl was an effective adsorbent for ciprofloxacin removal from the solution. When the equilibrium pH value was 5.5, the maximum adsorption capacity was found to be 8.49 mg/g. The pseudo-second-order kinetic model and Freundlich model could well describe the experimental data. The negative ΔG and ΔH value indicated that the adsorption process was spontaneous and exothermic and it was physical adsorption. The analysis of XRD, SEM, FTIR and XPS were in good agreement with physical adsorption. The existence of Cu2+ and Al3+ has a negative effect on the ciprofloxacin adsorption, and the inhibition by the Al3+ was significantly higher than that by Cu2+. However, the addition of Zn2+ could slightly promote ciprofloxacin adsorption capacity. The desorption experiment indicated that schorl had a good desorption and regeneration performance.

ACKNOWLEDGEMENTS

This research was supported by the National Natural Science Foundation of China (51408612), the Natural Science Foundation of Jiangsu Province (BK20140660), the Qing Lan Project, the Fundamental Research Funds for the Central Universities (2015PT002) and the College Students Innovation Project for the R&D of Novel Drugs (J1310032).

REFERENCES

REFERENCES
Benitez
,
F. J.
,
Acero
,
J. L.
,
Real
,
F. J.
,
Roldan
,
G.
&
Casas
,
F.
2011
Comparison of different chemical oxidation treatments for the removal of selected pharmaceuticals in water matrices
.
Chem. Eng. J.
168
(
3
),
1149
1156
.
Chen
,
H.
,
Ma
,
L. Q.
,
Gao
,
B.
&
Gu
,
C.
2013
Effects of Cu and Ca cations and Fe/Al coating on ciprofloxacin sorption onto sand media
.
J. Hazard. Mater.
225–232
,
375
381
.
Foo
,
K. Y.
&
Hameed
,
B. H.
2010
Insights into the modeling of adsorption isotherm systems
.
Chem. Eng. J.
156
(
1
),
2
10
.
Graouer-Bacart
,
M.
,
Sayen
,
S.
&
Guillon
,
E.
2015
Adsorption of enrofloxacin in presence of Zn (II) on a calcareous soil
.
Ecotoxicol. Environ. Saf.
122
,
470
476
.
Gu
,
C.
&
Karthikeyan
,
K. G.
2005
Sorption of the antimicrobial ciprofloxacin to aluminum and iron hydrous oxides
.
Environ. Sci. Technol.
39
(
23
),
9166
9173
.
Guerra
,
D. L.
,
Oliveira
,
S. P.
,
Silva
,
R. A. R.
,
Leidens
,
V.
&
Batista
,
A. C.
2012
Characterization and application of tourmaline and beryl from Brazilian pegmatite in adsorption process with divalent metals
.
Int. J. Mining Sci. Technol.
22
(
5
),
711
718
.
Hongsawat
,
P.
,
Prarat
,
P.
,
Ngamcharussrivichai
,
C.
&
Punyapalakul
,
P.
2014
Adsorption of ciprofloxacin on surface functionalized superparamagnetic porous silicas
.
Desalin. Water Treat.
52
(
22–24
),
4430
4443
.
Jiang
,
K.
,
Sun
,
T.
,
Sun
,
L.
&
Li
,
H.
2006
Adsorption characteristics of copper, lead, zinc and cadmium ions by tourmaline
.
J. Environ. Sci.
18
(
6
),
1221
1225
.
Jiao
,
S. J.
,
Zheng
,
S. R.
,
Yin
,
D. Q.
,
Wang
,
L. H.
&
Chen
,
L. Y.
2008
Aqueous oxytetracycline degradation and the toxicity change of degradation compounds in photoirradiation process
.
J. Environ. Sci.
20
(
7
),
806
813
.
Kolpin
,
D. W.
,
Furlong
,
E. T.
,
Meyer
,
M. T.
,
Thurman
,
E. M.
,
Zaugg
,
S. D.
,
Barber
,
L. B.
&
Buxton
,
H. T.
2002
Pharmaceuticals, hormones, and other organic wastewater contaminants in US streams, 1999–2000: a national reconnaissance
.
Environ. Sci. Technol.
36
(
6
),
1202
1211
.
Larsson
,
D. J.
,
de Pedro
,
C.
&
Paxeus
,
N.
2007
Effluent from drug manufactures contains extremely high levels of pharmaceuticals
.
J. Hazard. Mater.
148
(
3
),
751
755
.
Li
,
Z.
,
Hong
,
H.
,
Liao
,
L.
,
Ackley
,
C. J.
,
Schulz
,
L. A.
,
MacDonald
,
R. A.
,
Ackley
,
C. J.
,
Schulz
,
L. A.
,
MacDonald
,
R. A.
,
Mihelich
,
A. L.
&
Emard
,
S. M.
2011
A mechanistic study of ciprofloxacin removal by kaolinite
.
Colloids Surf. B
88
(
1
),
339
344
.
Li
,
G.
,
Chen
,
D.
,
Zhao
,
W.
&
Zhang
,
X.
2015a
Efficient adsorption behavior of phosphate on La-modified tourmaline
.
J. Environ. Chem. Eng.
3
(
1
),
515
522
.
Li
,
J. R.
,
Wang
,
Y. X.
,
Wang
,
X.
,
Yuan
,
B.
&
Fu
,
M. L.
2015b
Intercalation and adsorption of ciprofloxacin by layered chalcogenides and kinetics study
.
J. Colloid Interface Sci.
453
,
69
78
.
Liu
,
Y.
&
Liu
,
Y. J.
2008
Biosorption isotherms, kinetics and thermodynamics
.
Separ. Purif. Technol.
61
(
3
),
229
242
.
Liu
,
N.
,
Wang
,
H.
,
Weng
,
C. H.
&
Hwang
,
C. C.
2016
Adsorption characteristics of Direct Red 23 azo dye onto powdered
tourmaline
.
Arab. J. Chem.
dx.doi.org/10.1016/j.arabjc.2016.04.010
.
Martins
,
A. F.
,
Vasconcelos
,
T. G.
,
Henriques
,
D. M.
,
Frank
,
C. D. S.
,
König
,
A.
&
Kümmerer
,
K.
2008
Concentration of ciprofloxacin in Brazilian hospital effluent and preliminary risk assessment: a case study
.
Clean Soil Air Water
36
(
3
),
264
269
.
Muthumariappan
,
S.
2013
Synthesis and characterization of ciprofloxacin–zinc (II) complex and assay studies in pharmaceutical drugs
.
J. Pharm. Res.
6
(
4
),
437
441
.
Nadeem
,
K.
,
Traussnig
,
T.
,
Letofsky-Papst
,
I.
,
Krenn
,
H.
,
Brossmann
,
U.
&
Würschum
,
R.
2010
Sol–gel synthesis and characterization of single-phase Ni ferrite nanoparticles dispersed in SiO2 matrix
.
J. Alloys Compd.
493
(
1
),
385
390
.
Nakamura
,
T.
&
Kubo
,
T.
1992
Tourmaline group crystals reaction with water
.
Ferroelectrics
137
(
1
),
13
31
.
Pei
,
Z.
,
Shan
,
X. Q.
,
Kong
,
J.
,
Wen
,
B.
&
Owens
,
G.
2009
Coadsorption of ciprofloxacin and Cu (II) on montmorillonite and kaolinite as affected by solution pH
.
Environ. Sci. Technol.
44
(
3
),
915
920
.
Picó
,
Y.
&
Andreu
,
V.
2007
Fluoroquinolones in soil – risks and challenges
.
Anal. Bioanal. Chem.
387
(
4
),
1287
1299
.
Polishchuk
,
A. V.
,
Karaseva
,
É. T.
,
Emelina
,
T. B.
,
Nikolenko
,
Y. M.
&
Karasev
,
V. E.
2009
Electronic structure and spectroscopic properties of norfloxacin, enrofloxacin, and nalidixic acid
.
J. Struct. Chem.
50
(
3
),
434
438
.
Rakshit
,
S.
,
Sarkar
,
D.
,
Elzinga
,
E. J.
,
Punamiya
,
P.
&
Datta
,
R.
2013
Mechanisms of ciprofloxacin removal by nano-sized magnetite
.
J. Hazard. Mater.
246
,
221
226
.
Sadasivam
,
S.
,
Krishna
,
S. K.
,
Ponnusamy
,
K.
,
Nagarajan
,
G. S.
,
Kang
,
T. W.
&
Venkatesalu
,
S. C.
2010
Equilibrium and thermodynamic studies on the adsorption of an organophosphorous pesticide onto ‘waste’ jute fiber carbon
.
J. Chem. Eng. Data
55
(
12
),
5658
5662
.
Sergei
,
V. S.
&
Alice
,
V.
2002
Electric induced transition in water cluster
.
J. Mol. Struct.
593
,
19
32
.
Srivastava
,
V. C.
,
Swamy
,
M. M.
,
Mall
,
I. D.
,
Prasad
,
B.
&
Mishra
,
I. M.
2006
Adsorptive removal of phenol by bagasse fly ash and activated carbon: equilibrium, kinetics and thermodynamics
.
Colloids Surf. A Physicochem. Eng. Asp.
272
(
1
),
89
104
.
Teske
,
S. S.
&
Arnold
,
R. G.
2008
Removal of natural and xeno-estrogens during conventional wastewater treatment
.
Rev. Environ. Sci. Biotechnol.
7
(
2
),
107
124
.
Vasudevan
,
D.
,
Bruland
,
G. L.
,
Torrance
,
B. S.
,
Upchurch
,
V. G.
&
MacKay
,
A. A.
2009
pH-dependent ciprofloxacin sorption to soils: interaction mechanisms and soil factors influencing sorption
.
Geoderma
51
(
3
),
68
76
.
Wan
,
M.
,
Li
,
Z.
,
Hong
,
H.
&
Wu
,
Q.
2013
Enrofloxacin uptake and retention on different types of clays
.
J. Asian Earth Sci.
77
,
287
294
.
Wang
,
C.
,
Zhang
,
Y.
,
Yu
,
L.
,
Zhang
,
Z.
&
Sun
,
H.
2013
Oxidative degradation of azo dyes using tourmaline
.
J. Hazard. Mater.
260
,
851
859
.
Wu
,
Y. F.
,
Zhang
,
L.
,
Mao
,
J. W.
,
Liu
,
S. W.
,
Huang
,
J.
,
You
,
Y. R.
&
Mei
,
L. H.
2016
Kinetic and thermodynamic studies of sulforaphane adsorption on macroporous resin
.
J. Chromatogr. B Analyt. Technol. Biomed. Life Sci.
1028
,
231
236
.
Xia
,
M. S.
,
Hu
,
C. H.
&
Zhang
,
H. M.
2006
Effects of tourmaline addition on the dehydrogenase activity of Rhodopseudomonas palustris
.
Process Biochem.
41
(
1
),
221
225
.
Yang
,
J. F.
,
Ying
,
G. G.
,
Zhao
,
J. L.
,
Tao
,
R.
,
Su
,
H. C.
&
Chen
,
F.
2010
Simultaneous determination of four classes of antibiotics in sediments of the Pearl Rivers using RRLC–MS/MS
.
Sci. Total Environ.
408
(
16
),
3424
3432
.
Zhang
,
H.
,
Li
,
G.
,
Jia
,
Y.
&
Liu
,
H.
2009
Adsorptive removal of nitrogen-containing compounds from fuel
.
J. Chem. Eng. Data
55
(
1
),
173
177
.