Abstract

This study determined the adsorption of Cd2+ and Pb2+ (100 mg·L−1 of each) in simulated wastewater by biomass xanthates made from starch, chitosan, wheat stalk and corn stalk. The results showed that the adsorption efficiency of Pb2+ and Cd2+ ions followed the order: corn stalk xanthate > wheat stalk xanthate ≥ chitosan xanthate > starch xanthate. The results of kinetic modeling showed that the adsorption process was characterized by physical-chemical adsorption, and that a second-order kinetics equation described the adsorption process well. The optimum conditions for the adsorption of Cd2+ and Pb2+ by corn stalk xanthate were: adsorption time 2 hours, temperature 20–25 °C, and pH 6–8. The results serve as a reference for treating wastewater containing Cd2+ and Pb2+.

INTRODUCTION

Because of rapid industrialization and urbanization, heavy metal pollution in soil is becoming more serious due to the large amount of industrial waste produced and the extensive use of pesticides and fertilizers. Soil heavy metal contaminants tend to accumulate in plants, animals and humans through the food chain, posing a serious threat to the ecological environment and human health (Cobbina et al. 2015; Jorge 2017). Generally two methods are used to treat soil contaminated with heavy metals: passivating stabilization and leaching. Soil leaching is a kind of remediation technology for heavy metal contaminated sites; this technique is not sensitive to the degree of heavy metal pollution, and metals can be removed permanently with high efficiency. Because soil leaching is broadly applicable for the remediation of sites having medium and high concentrations of heavy metals, it is widely used (Farooq et al. 2010). At present, the most important technical problem associated with this technology is the treatment of waste leachate. Due to the lack of effective heavy metal treatment techniques for the contaminated leachates that are generated, the wider application of leaching technology to treat soils contaminated by heavy metals is seriously restricted (Vijayaraghavan et al. 2009; Yao et al. 2016).

The commonly used means of treating waste liquid arising from leaching heavy metals from soil include precipitation, adsorption, ion exchange, electrochemical methods and biological methods, among others (Naushad et al. 2015a; Salman et al. 2015; Gaikar et al. 2016; Samadder et al. 2017). Among these, adsorption is most commonly used because it is highly efficient, requires less energy than other methods and offers a high level of environmental protection (Garg et al. 2007; Farooq et al. 2010; Rocha et al. 2015; Naushad et al. 2016a).

At present, many kinds of adsorption materials are commonly used, including active carbon, polymer/metal oxides, clays, polymers, and biopolymeric materials (Al-Othman et al. 2012; Pan et al. 2016; Alqadami et al. 2017b). Nevertheless, low cost, reliable, and efficient materials are still needed. Xanthate adsorptive materials (Tan et al. 2008; Magnacca et al. 2014) have been used successfully to adsorb heavy metals; they are obtained from raw materials such as starch, cellulose and chitosan. To prepare xanthate materials that are highly efficient, low cost and environmentally friendly from a wide range of raw materials, much attention has been paid to the research and production of these materials (Babel & Kurniawan 2003; Zhou et al. 2011).

During the preparation of biomass xanthate, some hydroxyl groups on the macromolecules (e.g., cellulose, starch and chitosan) are replaced by xanthan groups. The xanthan groups increase the number of active groups in the raw materials, thereby increasing the number of sites where heavy metals can be captured; the strength with which metal ions are adsorbed also is increased. Biosorption of heavy metals by biomass xanthate occurs through a complex mechanism. In general, the concentration of heavy metals in water is small because they are insoluble. However, when biomass xanthate is added in the presence of heavy metal ions such as Cd2+, Pb2+ and Cu2+, a chelation reaction produces a stable chelate precipitate that has a small solubility product; thus, the heavy metal ions are immobilized on the xanthate and removed from the liquid (Zhou et al. 2009; Salam et al. 2011).

At present, research on the adsorption of heavy metal ions in wastewater by biomass xanthate is in the developmental stage at laboratory scale. Coconut sawdust xanthate prepared at room temperature was shown to have an adsorption efficiency of 99.4% for Pb2+ at room temperature (Yadav et al. 2013). The saturated adsorption capacity of xanthate for Cu2+ was 103.97 mg·g−1 (Ai et al. 2015). Zhang et al. (2016) prepared hydroxypropyl cellulose xanthate to treat wastewater containing Cu2+ and demonstrated the material had a saturated adsorption capacity of 126.58 mg·g−1. Wang et al. (2017) used bagasse cellulose xanthate to treat wastewater containing Pb2+, Cu2+ and Zn2+ ions, and demonstrated saturated adsorption capacities for the three heavy metals of 558.9 mg·g−1, 446.2 mg·g−1, and 363.3 mg·g−1, respectively. Feng & Wen (2017) prepared cross-linked starch xanthate to treat wastewater containing Pb2+ and Cd2+, and demonstrated saturated adsorption capacities of 47.11 mg·g−1 and 36.55 mg·g−1, respectively.

The present study was undertaken because few studies have reported using xanthate materials to treat complex soil leachate containing Cd2+ and Pb2+. The objectives of this study were to determine the relative adsorption effectiveness of four kinds of biomass xanthate in removing Cd2+ and Pb2+ contained in soil leachate and to quantify the effects of pH and temperature on the adsorption efficiency. The intention was to provide a reference and basis for the application of biomass xanthate to treat waste leachate from heavy-metal contaminated soil.

MATERIALS AND METHODS

Preparation of biomass xanthate

To obtain alkali wheat stalk and corn stalk, samples (10 g) of wheat stalk (cultivar ‘Huaimai 28’, Lianyungang, Jiangsu, China) or corn stalk (from Beijing Fangshan District) were added to 200 mL of 20% NaOH solution, stirred for 24 hours, filtered and washed three times with distilled water, then dried for 15 hours at 60 °C. At room temperature and atmospheric pressure the alkaline stalk was added to 200 mL of 10% NaOH solution and 10 mL CS2 and allowed to stand for 3 hours at room temperature, after which 100 mL of 5% MgSO4 solution was added. The mixture was then stirred for 30 min, after which excess CS2 was removed by placing the mixture in a 70 °C constant temperature water bath for 30 min. Then, 1% diluted MgSO4 and water were added sequentially to leach the sample at room temperature. The resulting corn stalk xanthate and wheat stalk xanthate were designated ‘YCX’ and ‘XCX’, respectively.

The chitosan xanthate (QCX) and starch xanthate (DCX) were prepared by the method reported in previous studies (Beyki et al. 2014; Ai et al. 2015).

Adsorption of lead and cadmium in wastewater by xanthate

Adsorption experiments were performed by separately placing each of the four different xanthate materials (0.20 g) in 1 L of a solution of simulated wastewater containing CdCl2 and PbNO3 (Pb2+ and Cd2+ concentrations of 100 mg·L−1 each). Each mixture was then placed in a 25 °C constant temperature water bath and stirred continuously using a magnetic stirrer. Samples (approximately 5 mL each) were withdrawn from each mixture at the beginning of the experiment (0 hour), and thereafter at 5, 10 20, and 40 min and 1, 2, 3, 4, 6, 8, 12, 24 and 36 hours. Samples were filtered through a 0.45 μm membrane and the resulting filtrates were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES, Optima 5300 DV, Perkin Elmer, Inc., Waltham, MA, USA) to determine the Cd2+ and Pb2+concentrations (Wang et al. 2016b).

To determine the effects of external factors (pH and temperature) on the adsorption of Pb2+ and Cd2+ by biomass xanthate, the simulated wastewater was placed in a 100 mL plastic centrifuge tube with 0.20 g xanthate, and single-variable controlled experiments were conducted. The samples were subjected to six different temperatures (25, 30, 35, 40, 45, and 50 °C), six different pH values (3, 5, 6, 7, 8, and 10) and seven different reaction times (5 min, 10 min, 20 min, 30 min, 1 hour, 2 hours, and 4 hours). Samples were oscillated during each reaction and then filtered. The clear filtrates were analyzed for Cd2+ and Pb2+ ion concentrations by ICP-OES.

zTo reveal the adsorption mechanism of Cd2+ and Pb2+ on YCX, Fourier transform infrared spectroscopy (FTIR) was used to examine the YCX before and after the adsorption of Cd2+ and Pb2+. Dried samples were mixed with pure KBr in the proportion of 1:100 and ground into a fine powder. Then, the powder was pressed using a tablet-forming machine into a transparent sheet. The FTIR spectrum was produced by scanning in the range 400–4,000 cm−1.

Statistical analysis

The adsorption amount and kinetic adsorption of Cd2+ and Pb2+ on the biomass xanthates were analyzed using Microsoft Excel 2013 (Microsoft Corp., Redmond, WA, USA).

Equation (1) (Bogue 1915) was used to calculate the adsorption capacity of biomass xanthate for Cd2+ and Pb2+: 
formula
(1)
in which Q is the ion adsorption amount, mg·g−1; ρ0 is the concentration of ions in solution before adsorption, mg·L−1; ρe is the concentration of ions in solution after adsorption, mg·L−1; V is the volume, L; and m is the quantity of xanthate, g.
The kinetic parameters of adsorption were used to characterize the chemical reaction rate and reaction mechanism (Langergren & Svenska 1898; Khaled & Amin 2009; Boparai et al. 2011; Ferreira et al. 2015; Arabi et al. 2017). Equation (2) represents a quasi-second order kinetic reaction: 
formula
(2)
in which q is a unit adsorption amount of heavy metals (i.e., Cd2+ and Pb2+) by the adsorbent material (xanthate) at t time, and qe is the unit adsorption amount of heavy metals when adsorption equilibrium is reached. k2 is a second-order kinetic adsorption rate constant, and t is the adsorption time (McKay et al. 1998).

The experimental data were analyzed using SPSS statistical software (IBM Corp., Armonk, NY, USA). Origin 8.6 data analysis and graphing software (OriginLab Corp., Northampton, MA, USA) was used to produce figures.

RESULTS AND DISCUSSION

Cadmium and lead adsorption properties of biomass xanthates

During the adsorption process, the adsorption amount usually increases as the contact time increases until the adsorbate reaches adsorption equilibrium. The unit adsorption capacity of the four xanthate materials for Cd2+ and Pb2+ under different adsorption times is shown in Figure 1. Each material exhibited periods of rapid and slow adsorption for both Cd2+ and Pb2+. Between 0 and 1 hour, the Cd2+ and Pb2+ adsorption amount on each xanthate material increased rapidly. The adsorption rate gradually slowed between 1 and 2 hours, and adsorption equilibrium was gradually reached after 2 hours.

Figure 1

Adsorption of (a) Cd2+ and (b) Pb2+ from simulated wastewater by chitosan xanthate (QCX), starch xanthate (DCX), corn stalk xanthate (YCX), and wheat stalk xanthate (XCX).

Figure 1

Adsorption of (a) Cd2+ and (b) Pb2+ from simulated wastewater by chitosan xanthate (QCX), starch xanthate (DCX), corn stalk xanthate (YCX), and wheat stalk xanthate (XCX).

Nevertheless, the specific adsorption behaviors of the four xanthate materials differed. The adsorption of Cd2+ by QCX and DCX occurred rapidly in the period from 5 to 40 min, and after 40 min the adsorption quantity changed little (i.e., equilibrium was reached in approximately 40 min). In contrast, the adsorption of Cd2+ by XCX and YCX was slower within the period 5 min to 1 hour (adsorption quantities of 0.018 mmol·g−1 to 0.085 mmol·g−1, respectively) and the attainment of adsorption equilibrium took a longer time (8 hours). The rate of Pb2+ adsorption by all xanthate materials was rapid within 5 to 40 min, and adsorption equilibrium was reached after approximately 1 hour. The largest Pb2+ adsorption quantity was achieved by YCX; between 40 min and 1 hour, 0.121 mmol·g−1 was adsorbed, which increased to 0.133 mmol·g−1 at equilibrium (after 1 hour).

The experimental results showed that the adsorption capacity of the four xanthate materials was different for Cd2+ and Pb2+, and followed the order YCX > QCX > XCX > DCX. As the best adsorbent, YCX exhibited an adsorption capacity for Cd2+ and Pb2+ of 0.170 mmol·g−1 and 0.133 mmol·g−1, respectively. The degree of substitution of xanthate groups, which plays a major role in the preparation process of the xanthate materials, determines the capacity of the materials to absorb heavy metals. The difference in adsorption capacity of the xanthate groups is also caused by differences in their characteristics. The relatively weak adsorption capacity of starch xanthate may be due to its low stability and a structure that deteriorates easily (Cauletti 1973). The preparation of chitosan xanthate produces a salt that has a large particle size, and the coordination reaction occurs on the surface, so that the overall adsorption capacity is not high. The difference in adsorption capacity between corn stalk and wheat stalk is due to a greater degree of lignification of wheat stalk. Although wheat stalk has a high cellulose content, it also has a high degree of crystallinity and the free area for adsorption is relatively small. Thus, the type of cellulose xanthate in wheat stalk has fewer adsorption sites. In contrast, the preparation process and corn stalk fiber groups are more likely to introduce xanthate molecules than wheat stalk; therefore, maize stalk has better heavy metal adsorption performance than wheat stalk (Wang et al. 2016b).

Among the four kinds of biomass xanthate, YCX was the most effective adsorbent of both Cd2+ and Pb2+, in agreement with findings by Deng et al. (2012) and Wang et al. (2016b). Furthermore, for any given xanthate material, the adsorption of Pb2+ was more rapid than adsorption of Cd2+. This result also was obtained in research by Deng et al. (2012), who also showed that the adsorption and binding of Pb2+ to biomass xanthate was stronger than that of Cd2+. Although the ion radius of Cd2+ is smaller than that of Pb2+, the hydrated ion radius of Cd2+ is greater than the hydrated ion radius of Pb2+, leading to a stronger adsorptive force between Pb2+ and an adsorbent (Jauhar & Rita 2016). At the same time, the solubility product of a xanthic acid group and Pb2+ to form salt is less than that of Cd2+ to form salt, and the affinity of Pb2+ to a xanthic acid group is greater than that of Cd2+. Consequently, a coordination reaction occurs more easily with Pb2+ than with Cd2+, and the adsorption rate is also faster (Deng et al. 2012).

Adsorption kinetics of cadmium and lead in simulated wastewater

The quasi-second order kinetic equation describes all the adsorption processes (including outer membrane diffusion, surface adsorption and particle diffusion) that can accurately reflect the adsorption mechanism of Cd2+ and Pb2+ on the biomass xanthates examined in this study. Thus, the quasi-second order equation was adopted to describe the kinetic data of Cd2+ and Pb2+ adsorption on the four xanthate materials. In portraying these data graphically (Figure 2), the abscissa is time (t in hours) and the ordinate is the quantity t/Qt (mg·h−1·mg−1). The best fit equations for each heavy metal and each xanthate material are also shown in Figure 2. The range of the correlation coefficient R2 of equations describing Cd2+ adsorption was 0.989–0.9999, and the range of the correlation coefficient R2 of equations describing Pb2+ adsorption was 0.9979–0.9999. The high R2 values indicated that a quasi-second order kinetic equation described the Cd2+ and Pb2+ adsorption process involving the four biomass xanthate materials well. Furthermore, the form of the equation demonstrated that adsorption occurred via a physical-chemical composite process.

Figure 2

Quasi-second order kinetic equations describing adsorption of (a) Cd2+ and (b) Pb2+ from simulated wastewater by chitosan xanthate (QCX), starch xanthate (DCX), corn stalk xanthate (YCX) and wheat stalk xanthate (XCX).

Figure 2

Quasi-second order kinetic equations describing adsorption of (a) Cd2+ and (b) Pb2+ from simulated wastewater by chitosan xanthate (QCX), starch xanthate (DCX), corn stalk xanthate (YCX) and wheat stalk xanthate (XCX).

Effect of adsorption time on the adsorption of cadmium and lead by corn stalk xanthate

Figure 3(a) shows that as adsorption time increased, the amount of Cd2+ and Pb2+ adsorbed by YCX first increased rapidly, then slowed slightly, and finally achieved equilibrium. At the adsorption times of 1 hour and 2 hours, respectively, the unit adsorption amount of Cd2+ (0.091 mmol·g−1) and Pb2+ (0.067 mmol·g−1) by YCX reached the maximum. This occurred because there were abundant adsorption sites on the surface of YCX. The initial stage of adsorption mainly occurs at the surface interface (Simonin 2016), but as adsorption time increases, the adsorption gradually reaches a saturation state. This pattern is consistent with that described by the quasi-second order kinetic equations (described in the section ‘Adsorption kinetics of cadmium and lead in simulated wastewater’). The adsorption of Cd2+ and Pb2+ on YCX occurs either by chemical adsorption or via shared electrons. After comprehensive comparison, the recommended adsorption time when using YCX in the treatment of Cd2+ and Pb2+ in wastewater was determined to be ≥2 hours.

Figure 3

Effects of (a) adsorption time, (b) temperature and (c) pH on the capacity of corn stalk xanthate to adsorb Cd2+ and Pb2+ from simulated wastewater.

Figure 3

Effects of (a) adsorption time, (b) temperature and (c) pH on the capacity of corn stalk xanthate to adsorb Cd2+ and Pb2+ from simulated wastewater.

Effect of adsorption temperature on the adsorption of cadmium and lead by corn stalk xanthate

Figure 3(b) shows that as the temperature increased from 25 °C to 50 °C, adsorption of Pb2+ by YCX first increased, then decreased, and increased slightly again to reach equilibrium at approximately 40 °C. The overall change in the adsorption of Pb2+ was modest (0.054–0.068 mmol·g−1). However, in the same temperature range, the adsorption of Cd2+ gradually decreased (from 0.092 to 0.081 mmol·g−1) as the temperature increased (Alqadami et al. 2017b). These results indicated that the overall optimum temperature for adsorption of Cd2+ and Pb2+ by YCX was 20–25 °C. Wang et al. (2017) studied the effect of temperature on the adsorption of Pb2+ and Cu2+ by bagasse xanthate. They concluded that the mixing mechanism was dominant in the adsorption process and was mainly controlled by ion exchange and the complexation of cellulose xanthate with heavy metal ions. Because these results demonstrate that temperature has little influence on the adsorption of Cd2+ and Pb2+ by YCX, YCX will be relatively unaffected by seasonal temperature changes in the treatment of wastewater containing heavy metals. This stability is conducive to using YCX in practical applications.

Effect of pH on the adsorption of cadmium and lead by corn stalk xanthate

Solution acidity is an important factor affecting the migration and transformation of heavy metals in a liquid medium. Figure 3(c) shows that as the pH increased from low to high, the adsorption amount of Pb2+ first increased and then decreased, such that the maximum adsorption amount was at pH 7. Although some Pb2+ ions exist in the form of Pb(OH)2 at pH 6, the ionic product of lead xanthate from corn stalk is much smaller than that of Pb(OH)2. Therefore, the main reason for the decrease in Pb2+ concentration was its adsorption onto corn stalk xanthate. The adsorption of Cd2+ increased slightly (from 0.096 to 0.103 mmol·g−1) as the pH increased from 3 to 10. These results occurred because when the pH is low, a large amount of H+ occupies the active sites on the xanthate adsorbent, reducing the opportunity for Cd2+ and Pb2+ to bind (Naushad et al. 2017). Furthermore, the electrostatic effect of H+ at the interface also inhibits the approach of Cd2+ and Pb2+ ions. Therefore, the adsorption amount of the two metals is not high under highly acidic conditions. As the pH increases, a larger number of active sites become available to facilitate adsorption of Cd2+ and Pb2+.

In summary, the optimal pH for using YCX to treat wastewater containing Cd2+ and Pb2+ was in the range 6–8. Therefore, in practice, YCX can be combined with limewater treatment of wastewater containing high concentrations of Cd2+ and Pb2+.

Fourier transform infrared spectrometry characterization of corn stalk xanthate before and after adsorption of cadmium and lead

The changes of different functional groups in YCX as a result of Cd2+ and Pb2+ adsorption were qualitatively analyzed by FTIR. Wang et al. (2016a) studied the structural changes in different xanthates after Cu2+ adsorption. Figure 4 shows that compared with the pre-adsorption peaks in YCX at 3,000 cm−1 and 1,459 cm−1, the absorption peak strength increased following adsorption of Cd2+ and Pb2+; the band at 1,459 cm−1 was due to CH2 bending mode (Naushad et al. 2016b). The change of characteristic peaks at 1,050 cm−1 were attributed to the ether groups of the YCX, indicating that the reaction generated unsaturated bonds and C-OH. Similarly, the corresponding adsorption trough at 1,459 cm−1 was significantly weakened by the adsorption process, indicating that this was the deformation vibration of C-S in YCX. The original YCX coordinate reaction occurred, resulting in YCX-Cd. The spectral peak at 3,430 cm−1 in YCX-Pb obviously decreased in intensity, illustrating that -OH was also involved in the reaction (Ai et al. 2015; Zeng et al. 2015; Wang et al. 2016a; Alqadami et al. 2017a; Dil et al. 2017).

Figure 4

Fourier transform infrared spectra of corn stalk xanthate before (YCX) and after adsorbing Cd2+ (YCX-Cd) and Pb2+ (YCX-Pb).

Figure 4

Fourier transform infrared spectra of corn stalk xanthate before (YCX) and after adsorbing Cd2+ (YCX-Cd) and Pb2+ (YCX-Pb).

Adsorption experiment using corn stalk xanthate to treat wastewater containing cadmium and lead

The results of using corn stalk xanthate to treat simulated wastewater containing Cd2+ and Pb2+ are shown in Table 1. The Cd2+ and Pb2+ removal efficiencies were 99.21% and 83.3%, respectively.

Table 1

Effect of corn stalk xanthate on lead and cadmium concentrations in simulated wastewater

Element Pb Cd 
Initial concentration (mg·L−118.89 0.24 
Concentration after adsorption (mg·L−10.15 0.04 
Removal efficiency (%) 99.21 83.30 
Element Pb Cd 
Initial concentration (mg·L−118.89 0.24 
Concentration after adsorption (mg·L−10.15 0.04 
Removal efficiency (%) 99.21 83.30 

The adsorption capacities of YCX for the removal of Cd2+ and Pb2+ were compared with those of other adsorbents reported in the literature and the values are shown in Table 2. It is clear from Table 2 that the adsorption capacities of YCX were comparable with those of other materials. These results illustrate that corn stalk xanthate is a promising adsorbent for removing Cd2+ and Pb2+from wastewater.

Table 2

Comparison of adsorption capacities for Pb2+ removal

Adsorbents Adsorbent dosage (g/mL) pH T (K) Initial concentration of Pb2+ (mg L−1Removal of Pb2+ (%) Initial concentration of Cd2+ (mg L−1Removal of Cd2+ (%) References 
YCX 0.4/100 298 18.89 99.21 0.24 83.30 Present study 
Sodium dodecyl sulfate acrylamide Zr(IV) selenite 0.5/20 298 10 90.5 ∼ ∼ Naushad (2014)  
MWCNTs/ThO2 0.02/100 318 95.5 ∼ ∼ Mittal et al. (2016)  
Ti(IV) iodovanadate cation exchanger 0.1/50 298 20 94.8 ∼ ∼ Naushad et al. (2015b)  
EDTA-Zr(IV) 0.4/40 298 20 91   Naushad et al. (2015c)  
Polyaniline Sn(IV) tungstomolybdate nanocomposite 0.3/30 298 20 88   Bushra et al. (2015)  
Ash 0.01/100 298 25 98   Ghasemi et al. (2014a)  
Fe nanoparticles loaded ash 0.01/100 298 25 99   Ghasemi et al. (2014a)  
Sawdust activated carbon 0.05/30 298 100 96   Ghasemi et al. (2014b)  
Polyaniline Sn(IV) silicate 0.2/20 298   200 92 Naushad (2013)  
Curcumin formaldehyde resin 0.1/50 298   100 91.2 Naushad et al. (2015d)  
Adsorbents Adsorbent dosage (g/mL) pH T (K) Initial concentration of Pb2+ (mg L−1Removal of Pb2+ (%) Initial concentration of Cd2+ (mg L−1Removal of Cd2+ (%) References 
YCX 0.4/100 298 18.89 99.21 0.24 83.30 Present study 
Sodium dodecyl sulfate acrylamide Zr(IV) selenite 0.5/20 298 10 90.5 ∼ ∼ Naushad (2014)  
MWCNTs/ThO2 0.02/100 318 95.5 ∼ ∼ Mittal et al. (2016)  
Ti(IV) iodovanadate cation exchanger 0.1/50 298 20 94.8 ∼ ∼ Naushad et al. (2015b)  
EDTA-Zr(IV) 0.4/40 298 20 91   Naushad et al. (2015c)  
Polyaniline Sn(IV) tungstomolybdate nanocomposite 0.3/30 298 20 88   Bushra et al. (2015)  
Ash 0.01/100 298 25 98   Ghasemi et al. (2014a)  
Fe nanoparticles loaded ash 0.01/100 298 25 99   Ghasemi et al. (2014a)  
Sawdust activated carbon 0.05/30 298 100 96   Ghasemi et al. (2014b)  
Polyaniline Sn(IV) silicate 0.2/20 298   200 92 Naushad (2013)  
Curcumin formaldehyde resin 0.1/50 298   100 91.2 Naushad et al. (2015d)  

CONCLUSIONS

This laboratory study determined the effectiveness of biomass xanthates made from starch, chitosan, wheat stalk, and corn stalk in adsorbing Cd2+ and Pb2+ (100 mg·L−1, each) from simulated wastewater. The results justify the following conclusions.

The Pb2+ and Cd2+ adsorption efficiency of corn stalk xanthate is superior to that of the other xanthates (corn stalk xanthate > wheat stalk xanthate ≥ chitosan xanthate > starch xanthate). The adsorption of Pb2+ and Cd2+ on biomass xanthates occurs by physical-chemical adsorption and is accurately described by quasi-second order kinetics. The optimum conditions for the adsorption of Pb2+ and Cd2+ by corn stalk xanthate are adsorption time, 2 hours; temperature, 20–25 °C; and pH, 6–8.

ACKNOWLEDGEMENTS

This work was supported by The National Key R&D Program of China (2017YFD0800900) and the Beijing Science and Technology Project (Z161100004916017).

DECLARATIONS OF INTEREST

None.

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