AbstractLead-contaminated wastewater causes toxicity to aquatic life and water quality for water consumption, so it is required to treat wastewater to be below the water quality standard before releasing it into the environment. Duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcinated duck eggshell powder (CDP), and calcinated duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were synthesized, characterized, and investigated lead removal efficiencies by batch experiments, adsorption isotherms, kinetics, and desorption experiments. CDPF demonstrated the highest specific surface area and pore volume with the smallest pore size than other materials, and they were classified as mesoporous materials. DP and DPF demonstrated semi-crystalline structures with specific calcium carbonate peaks, whereas CDP and CDPF illustrated semi-crystalline structures with specific calcium oxide peaks. In addition, the specific iron (III) oxide-hydroxie eaks were detected in only DPF and CDPF. Their surface structures were rough with irregular shapes. All materials found carbon, oxygen, and calcium, whereas iron, sodium, and chloride were only found in DPF and CDPF. All materials were detected O–H, C=O, and C–O, and DPF and CDPF were also found Fe–O from adding iron (III) oxide-hydroxide. The point of zero charges of DP, DPF, CDP, and CDPF were 4.58, 5.31, 5.96, and 6.75. They could adsorb lead by more than 98%, and CDPF illustrated the highest lead removal efficiency. DP and CDP corresponded to the Langmuir model while DPF and CDPF corresponded to the Freundlich model. All materials corresponded to a pseudo-second-order kinetic model. Moreover, they could be reusable for more than 5 cycles for lead adsorption of more than 73%. Therefore, CDPF was a potential material to apply for lead removal in industrial applications.
IntroductionThe release of lead-contaminated wastewater from battery,steel, dye and pigment, pastic, and electronic industries causes environmental problems through its toxicity to aquatic life and water quality to water consumption. In addition, the dysfunctional systems of nerves, reproductive, respiration, blood, and many diseases of anemia, lead poisoning, and Alzheimer have been caused by receiving lead into the human body1. Therefore, it recommends removing lead from wastewater under the water quality standard which does not exceed 0.2 mg/L following USEPA standards before releasing it into the environment.Many methods have been applied for eliminating heavy metals in wastewater such as chemical precipitation, oxidation–reduction, coagulation-flocculation, and ion exchange; however, they also leave many concerns of incomplete treatment, expensive operating costs, and creating toxic sludges2. As a result, an alternative method of adsorption method is a good choice because it is an efficient and simple method with suitable operating cost including any choices of adsorbents o deal with the specific target pollutants. Various food wastes to eliminate heavy metals in wastewater in 2020–2022 are illustrated in Table 1. In the case of lead removals, eggshells are popularly used because they consist of calcium carbonate (CaCO3) and a hydroxyl group (–OH) which could highly adsorb lead in wastewater. Especially, duck eggshells are more CaCO3 content and porous than chicken eggshells3,4, so they could possibly remove higher lead than chicken eggshells. Moreover, no study has yet used duck eggshells for lead removal in wastewater. As a result, duck eggshells are a good alternative adsorbent among those adsorbents mentioned in Table 1. However, duck eggshells also need to improve efficiency to deal with a high lead strength concentration in industrial wastewater.Table 1 Various food wastes for eliminating heavy metals in wastewater.Full size tableMany modification methods which are pyrolysis, calcination, acid or alkaline treatment, and etal oxides have been used o improve material efficiencies of food wastes for heavy metal removals reported in Table 2. Among those metals, both the calcination process and adding metal oxides have been popularly used for increasing the adsorption capacity of heavy metal adsorbents. Thus, it is an interesting point to improve duck eggshell efficiency by using a calcination process or adding iron (III) oxide-hydroxide to confirm whether these two methods increase lead removal efficiency. In addition, no one to modify duck eggshell material with a calcination process along with adding iron (III) oxide-hydroxide. Therefore, this study is the first effort to synthesize duck eggshell materials with or without a calcination process or adding iron (III) oxide-hydroxide, to compare their lead removal efficiencies through batch experiments, and verify whether using a calcination process or the addition of iron (III) oxide-hydroxide increases material adsorption capacity.Table 2 The modificatio methods for improving materal efficiencies of food wastes for heavy metal removals.Full size tableDuck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were synthesized and characterize their specific surface area, pore volumes, pore sizes, crystalline formations, surface morphologies, chemical elements, and chemical functional groups by Brunauer–Emmett–Teller (BET), X-ray diffractometer (XRD), Field emission scanning electron microscopy and focus ion beam (FESEM-FIB) with energy dispersive X-ray spectrometer (EDX), and Fourier transform infrared spectroscopy (FT-IR). The point of zero charges and lead removal efficiencies of DP, DPF, CDP, and CDPF by batch experiments with varying doses, contact time, pH, and concentration were investigated. In addition, linear and nonlinear adsorption isotherms of Langmuir, Freundlich, Temkin, and Dubinin-adushkevich models were used o determine their lead adsorption patterns. Moreover, linear and nonlinear pseudo-first-kinetic, pseudo-second-kinetic, elovich, and intraparticle diffusion models were used to identify their rates and mechanisms for lead adsorptions. Finally, the desorption experiments were used to confirm material reusability.Materials and methodsRaw materialDuck eggshells used in this study are wastes from the local restaurants in Khon Kaen province, Thailand.ChemicalsFerric chloride hexahydrate (FeCl3·6H2O) (LOBA, India), sodium hydroxide (NaOH) (RCI Labscan, Thailand), sodium chloride (NaCl) (RCI Labscan, Thailand), 37% hydrochloric acid (HCl) (RCI Labscan, Thailand), 65% nitric acid (HNO3) (Merck, Germany), and lead nitrate (Pb(NO3)2) (QRëC, New Zealand) were used, and they were analytical grades (AR) without purification before use. 1% NaOH and 1% HNO3 were used for pH adjustments.Synthesis of duck eggshell materialsThe synthesis methods of duck eggshell materials o duck eggshell powder (DP), duk eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) are illustrated in Fig. 1a,b which is based on Praipipat et al. (2022)34 and Praipipat et al. (2023)14, and the details were described below:Figure 1The synthesis methods of (a) duck eggshell powder (DP) and calcined duck eggshell powder (CDP) (b) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF) and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageThe synthesis of duck eggshell powder (DP) and calcined duck eggshell powder (CDP)For DP, duck eggshells were washed with tap water to eliminate contaminations, and then they were dried overnight in a hot air oven (Binder, FED 53, Germany) at 80 °C. Next, they were ground and sieved in size of 125 µm. Then, they were kept in a desiccator before use called duck eggshell powder (DP). For CDP, it was cacined by a furnace (Chavachote,L9/12P, Thailand) in an air atmosphere at 900 °C for 3 h, and then they were kept in a desiccator before use called calcined duck eggshell powder (CDP).The synthesis of duck eggshell powder mixed iron (III) oxide-hydroxide (DPF) and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF)Firstly, 5 g of DP or CDP were added to 500 mL of Erlenmeyer flask containing 160 mL of 5% FeCl3·6H2O, and they were mixed by an orbital shaker (GFL, 3020, Germany) of 200 rpm for 3 h. Next, they were filtrated and air-dried at room temperature for 12 h. Then, they were added to 500 mL of Erlenmeyer flask containing 160 mL of 5% NaOH, and they were mixed by an orbital shaker of 200 rpm for 1 h. After that, they were filtered and air-dried at room temperature for 12 h. Finally, they were kept in a desiccator before use called duck eggshell powder mixed iron (III) oxide-hydroxide (DPF) or calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Chracterizations of duck eggshell aterialsVarious characterized techniques were used for characterizing duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF). Firstly, Brunauer–Emmett–Teller (BET) (Bel, Bel Sorp mini X, Japan) by isothermal nitrogen gas (N2) adsorption–desorption at 77.3 K and degas temperature of 80 °C for 6 h was used to identify their specific surface area, pore volumes, and pore sizes. Second, an X-ray diffractometer (XRD) (PANalytical, EMPYREAN, UK) in a range of 2θ = 5–80° was used for investigating their crystalline structures. Third, Field emission scanning electron microscopy and focus ion beam (FESEM-FIB) with energy dispersive X-ray spectrometer (EDX) (FEI, Helios NanoLab G3 CX, USA) which the samples were placed on aluminum stubs with gold-coating for 4 min using a 108 auto Sputter Coater with thickness controller MM-20 model (Cressington, Ted Pell Inc, USA) by analyzing at 10 kV accelerating voltage was used for studying their surface morphologies and chemical compositions. Finally, Fourier transform infrared spectroscopy (FT-IR) (Bruker, TENSOR27, Hong Kong) in a range of 600–4000 cm−1 with a resolution of 4 cm−1 and 16 scans over the entire covered range was used for determining their chemical functional groups.The point of zero charges of duck eggshell materialsThe points of zero charge of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) for lead adsorptions were investigated by using 0.1 M NaCl solutions with pH values from 2 to 12 which 0.1 M HCl and 0.1 M NaOH were used for pH adjustments which the method is referred from the study of Praipipat et al.14. Firstly, 0.1 g of duck eggshell material was added to 250 mL Erlenmeyer flasks containin 50 mL of each 0.1 M NaCl solution Then, it was shaken by an orbital shaker (GFL, 3020, Germany) at room temperature at 150 rpm for 24 h. After that, the final pH value of the sample solution was measured by a pH meter (Mettler Toledo, SevenGo with InLab 413/IP67, Switzerland) and ∆pH (pHfinal – pHinitial) was calculated. A point that is the crosses line of ∆pH versus pHinitial equal to zero is the value of the point of zero charges (pHpzc).Batch adsorption experimentsLead removal efficiencies of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were investigated through a series of batch experiments with varying values of four affecting factors of adsorbent dosage (2.5–15 g/L), contact time (1–6 h), pH (1, 3, 5, 7, 9), and initial lead concentration (10–70 mg/L). The initial lead concentration of 50 mg/L, a sample volume of 200 mL, pH 5,a shaking speed of 200 rpm, and a tmperature of 25 °C were applied as the control condition. The lowest value with the highest lead removal efficiency of each affecting factor was selected as the optimum value, and it was used for the next affecting factor study. The triplicate experiments were conducted for confirming their results. An atomic adsorption spectrophotometer (PerkinElmer, PinAAcle 900 F, USA) was used for analyzing lead concentrations, and Eq. (1) was used to calculate lead removal efficiency in the percentage:$${ ext{Lead}};{ ext{removal}};{ ext{efficiency}};left( \%
ight) = (C_{0} – C_{e} )/C_{0} imes 100$$
(1)
where C0 is the initial lead concentration (mg/L), and Ce is the equilibrium of lead concentration in the solution (mg/L).Adsorption isothermsThe adsorption isotherms of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron(III) oxide-hydroxide (CDPF) were determinedby various adsorption isotherms of linear and nonlinear Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models to explain their adsorption patterns. In addition, their adsorption isotherms are calculated by Eqs. (2)–(9)35,36,37,38:Langmuir isotherm:$${ ext{Linear}}:;C_{{ ext{e}}} /q_{{ ext{e}}} = 1/q_{{ ext{m}}} K_{{ ext{L}}} + C_{{ ext{e}}} /q_{{ ext{m}}}$$
(2)
$${ ext{Nonlinear}}:;q_{{ ext{e}}} = q_{{ ext{m}}} K_{{ ext{L}}} C_{{ ext{e}}} /1 + K_{{ ext{L}}} C_{{ ext{e}}}$$
(3)
Freundlich isotherm:$${ ext{Linear}}: ;log q_{{ ext{e}}} = log K_{{ ext{F}}} + 1 log C_{{ ext{e}}}$$
(4)
$${ ext{Nonlinear}}:;q_{{ ext{e}}} = K_{{ ext{F}}} C_{{ ext{e}}}^{1 }$$
(5)
Temkin isotherm:$${ ext{Linear}}: ;q_{{ ext{e}}} = RT/b_{{ ext{T}}} ln A_{{ ext{T}}} + RT/b_{{ ext{T}}} ln Ce$$
(6)
$${ ext{Nonlinear}}: ;q_{{ ext{e}}} = RT/b_{{ ext{T}}} l A_{{ ext{T}}} C_{{ ext{e}}}$$
(7)
Dubinin–Radushkevich isotherm:$${ ext{Linar}}:; ln q_{{ ext{e}}} = ln q_{{ ext{m}}} – K_{{{ ext{DR}}}} varepsilon^{2}$$
(8)
$${ ext{Nonlinear}}:;q_{{ ext{e}}} = q_{{ ext{m}}} exp ( – K_{{{ ext{DR}}}} varepsilon^{2} )$$
(9)
where Ce is the equilibrium of lead concentration (mg/L), qe is the amount of adsorbed lead on duck eggshell materials (mg/g), qm is indicated the maximum amount of lead adsorption on duck eggshell materials (mg/g), KL is the adsorption constant (L/mg). KF is the constant of adsorption capacity (mg/g)(L/mg)1 , and 1 is the constant depicting the adsorption intensity. R is the universal gas constant (8.314 J/mol K), T is the absolute temperature (K), bT is the constant related to the heat of adsorption (J/mol), and AT is the equilibrium binding constant corresponding to the maximum binding energy (L/g). qm is the theoretical saturation adsorption capacity (mg/g), KDR is theactivity coefficient related to mean adsorption energy (mol2/J2), and ε is the Polanyi potential (J/mol)14. Grphs of linear Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms were plotted by Ce/qe versus Ce, log qe versus log Ce, qe versus ln Ce, and ln qe versus ε2, respectively whereas graphs of their nonlinear were plotted by qe versus Ce39.For adsorption isotherm experiments, 15 g/L of DP or 10 g/L of DPF or 7.5 g/L of CDP, or 5 g/L of CDPF were added to 500 mL Erlenmeyer flasks with initial lead concentrations from 10 to 70 mg/L. The control condition of DP or DPF or CDP or CDPF was a sample volume of 200 mL, a shaking speed of 200 rpm, pH 5, a temperature of 25 °C, and a contact time of 4 h for DP, 3 h for DPF, 3 h for CDP, and 2 h for CDPF.Adsorption kineticsThe adsorption kinetics of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-ydroxide (CDPF) were identified by various adsorption kinetics of linear and nonlinear pseudo-first-order kinetc, pseudo-second-order kinetic, elovich, and intraparticle diffusion models to describe their adsorption rates and mechanisms. Moreover, their adsorption kinetic equations are calculated by Eqs. (10)–(16)40,41,42,43:Pseudo-first-order kinetic model:$${ ext{Linear}}:;ln , left( {q_{{ ext{e}}} – q_{{ ext{t}}} }
ight) = ln q_{{ ext{e}}} – k_{1} t$$
(10)
$${ ext{Nonlinear}}:q_{{ ext{t}}} = q_{{ ext{e}}} (1 – e^{{ – k_{1} t}} )$$
(11)
Pseudo-second-order kinetic model:$${ ext{Linear}}: ;t/q_{{ ext{t}}} = 1/k_{2} q_{{ ext{e}}}^{2} + , left( {t/q_{{ ext{e}}} }
ight)$$
(12)
$${ ext{Nonlinear}}:;q_{{ ext{t}}} = k_{2} q_{{ ext{e}}}^{2} t/left( {1 + , q_{{ ext{e}}} k_{2} t}
ight)$$
(13)
Elovich model:$${ ext{Linear}}:;q_{{ ext{t}}} = 1/eta ln alpha eta + 1/eta ln t$$
(14)
$$ ext{Nonlinear}}:;q_{t} = eta ln t + eta ln alpha$$
(15)
Intraparticle diffusion model:$${ ext{Linear}};{ ext{and}};{ ext{nonlinear}:;q_{{ ext{t}}} = k_{{ ext{i}}} t^{0.5} + C_{{ ext{i}}}$$
(16)
where qe is the amount of adsorbed lead on adsorbent materials (mg/g), qt is the amount of adsorbed lead at the time (t) (mg/g), k1 is a pseudo-first-order rate constant (min−1), and k2 is a pseudo-second-order rate constant (g/mg∙min). α is the initial adsorption rate (mg/g/min) and β is the extent of surface coverage (g/mg). ki is the intraparticle diffusion rate constant (mg/g∙min0.5) and Ci is the constant that gives an idea about the thickness of the boundary layer (mg/g). Graphs of linear pseudo-first-order, pseudo-second-order, elovich, and intraparticle diffusion models were plotted by ln (qe − qt) versus time (t), t/qt versus time (t), qt versus ln t, and qt versus time (t0.5), respectively whereas their nonlinear graphs were plotted by th capacity of lead adsorbed by adsorbent materials at the time (qt) versus time (t)39.For adsorption kinetic experiments, 15 g/L of DP or 10 g/L of DPF or 7.5 g/L of CDP,or 5 g/L of CDPF were added to 1000 mL of breaker with the initial lead concentration of 50 mg/L. The control condition of DP or DPF or CDP or CDPF was a sample volume of 1000 mL, a shaking speed of 200 rpm, pH 5, a temperature of 25 °C, and a contact time of 6 h.Desorption experimentsThe desorption experiments of duck eggshell materials were studied to investigate the possible material reusability which is referred from the study of Praipipat et al.14. The adsorption–desorption experiments in 5 cycles were used for confirming the abilities of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) for lead adsorption. The saturated DP or DPF or CDP or CDPF after lead adsorptionwas added to 500 mL of Erlenmeyer flask containing 200 mL of 0.5 M HNO3 solution, then it was shaken by an incubator shaker (New Brunswick, Innova 42, USA) at 200 rpm for4 h. After that, it was washed with deionization water and dried at room temperature, and DP or DPF or CDP or CDPF is ready for the next adsorption cycle. Equation (17) was used for calculating the desorption efficiency in percentage.$${ ext{Desorption}};left( \%
ight) = left( {q_{{ ext{d}}} /q_{a} }
ight) imes 100$$
(17)
where qd is the amount of lead desorbed (mg/mL) and qa is the amount of lead adsorbed (mg/mL).Result and discussionThe physical characteristics of duck eggshell materialsThe physical characteristics of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) are demonstrated in Fig. 2a–d. DP was a white color powder demonstrated in Fig. 2a hile DPF was a dark brown color powder which might be from the color of iron (III) oxide-hydroxide color added illustrated in Fig. 2b. For CDP, it was a white color similar to DP,but it was a finer powder than DP shown in Fig. 2c. Finally, CDPF was a light brown color powder shown in Fig. 2d. Therefore, a calcination process might affect to the material colors and their characteristics.Figure 2The physical characteristics of (a) duck eggshell powder (DP), (b) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), (c) calcined duck eggshell powder (CDP), and (d) calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageCharacterizations of duck eggshell materialsBETThe specific surface area, pore sizes, and pore volumes of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) by BET analysis are demonstrated inTable 3. For DP and DPF, their specific surface area, pore volumes, and pore sizes were 0.955 m2/g, 0.0009 cm3/g, 3.703 nm and 12.313 m2/g, 0.0081 cm3/g, 2.617 nm which DPF had a hgher specific surface area and pore volume approximately than 13-fold and ninefold of DP, whereas its pore size was smaller than approximately 1.4-fold of DP. Thus, the addition of iron (III) oxide-hydroxide helped to increase the specific area and pore volume with decreasing pore size14,44,45,46. For CDP, its specific surface area, pore volume, and pore size were 10.781 m2/g, 0.0065 cm3/g, and 2.540 nm which had the higher specific surface area and pore volume of approximately 11-fold and 7-fold of DP, and it had smaller pore size approximately 1.45-fold than DP which might result from the calcination process similar to previous studies47,48. For CDPF, its specific surface area, pore volume, and pore size were 34.930 m2/g, 0.0943 cm3/g, and 2.092 nm which demonstrated the highest specific surface area and pre volume with the smallest pore size than other materials resulting in the high lead adsorption capacity. Therefore, the calcination process along with adding iron (III) oxide-hydrxide is recommended to increase the specific surface area and pore volume with a small pore size for higher lead adsorption by duck eggshells than only the calcination process or adding iron (III) oxide-hydroxide. Moreover, since their pore sizes were in a range of 2–5 nm, all materials were mesoporous materials by the classification by the International Union of Pure and Applied Chemistry (IUPAC)49.Table 3 The specific surface area, pore size, and pore volume of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size tableXRDThe crystalline structures of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck egshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) by XRD analysis are presented in Fig. 3a–d. For DP and DPF, they demonstrated semi-crysalline structures with the specific calcium carbonate peaks of 23.08°, 29.40°, 35.98°, 39.41°, 43.18°, 47.50°, 48.48°, 57.40°, 60.62°, and 64.58° corresponded to JCPDS No. 05-058614. For CDP and CDPF, they illustrated semi-crystalline structures by observing the specific calcium oxide peaks of 18.12°, 28.70°, 32.29°, 34.16°, 37.46°, 47.05°, 50.90°, 53.94°, 64.24°, and 67.46° matched to JCPDS No. 01-077-201050. Moreover, DPF and CDPF observed the specific iron (III) oxide-hydroxide peaks of 33.92°, 41.80°, and 53.76° following JCPDS No. 29-071314 confirming iron (III) oxide-hydroxide added into DPF and CDPF.Figure 3The crystalline formations of (a) duck eggshell powder (DP), (b) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), (c) calcined duck eggshell powder (CDP), and (d) calcined duck eggshel powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageFESEM-FIB and EDXThe surface morphologies of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydoxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) by FESEM-FIB analysis at 1500× magnification with 100 µm illustrated in Fig. 4a–d. For DP and DPF, they were irregular structures with heterogeneous particle sizes, so iron (III) oxide-hydroxide added to DPF did not affect its surface morphology similar reported by another study14. In addition, the distributions of EDX mapping of DP and DPF are demonstrated in Fig. 4e,f. Carbon (C), oxygen (O), and calcium (Ca) were found in DP and DPF, whereas iron (Fe), sodium (Na), and chloride (Cl) were found in only DPF which might be from chemicals used in a process of the addition of iron (III) oxide-hydroxide similar to other studies14,28,39,51. For CDP and CDPF, their surfaces were irregularshapes similar to DP and DPF; however, they were smaller in size than DP and DPF which might result from a calcination process. The smaller particle sizes of CDP and CDPF might supporthigher lead adsorptions than DP and DPF similarly reports by other studies that calcined eggshells had a higher or developer porous structure than non-calcined eggshells48. Moreover, adding iron (III) oxide-hydroxide also did not affect the surface structure of CDPF similar to DPF. The distributions of EDX mapping of CDP and CDPF are demonstrated in Fig. 4g,h which found the same chemical elements of C, O, and Ca similar to DP and DPF, whereas CDPF had the same chemical elements as DPF with observing iron distribution on the surface of DPF and CDPF.Figure 4The surface morphologies and the distributions of EDX mapping of (a,e) duck eggshell powder (DP), (b,f) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), (c,g) calcined duck eggshell powder (CDP), and (d,h) calcined duck eggshell powder mixe iron (III) oxide-hydroxide (CDPF).Full size imageThe chemical compositions of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggsell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) by EDX analysis are reported in Table 4, and their distributions of EDX mapping are demonstrated in Fig. 4e–h. Carbon (C), oxygen (O), and calcium (Ca) were the main chemical components of all materials, whereas iron (Fe), sodium (Na), and chloride (Cl) were only found in DPF and CDPF which could be confirmed the successful addition of iron (III) oxide-hydroxide in both materials. For DP and DPF comparison, the mass percentages by weight of O, Ca, and C of DPF were decreased, whereas the mass percentages by weight of Fe, Na, and Cl were increased which might be from chemicals ferric chloride hexahydrate (FeCl3·6H2O) and sodium hydroxide (NaOH) used for the DPF synthesis. For DP and CDP comparison, the mass percenages by weight of O and C of CDP were decreased, whereas the mass percentage by weight of Ca was increased resulting from the effect of the calcination process similar to another study52 For CDP and CDPF comparison, the mass percentages by weight of O, Ca, and C were decreased. While, the mass percentages by weight of Fe, Na, and Cl were increased similar reason to DPF from chemicals used in the CDPF synthesis.Table 4 The chemical compositions of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size tableFT-IRFT-IR spectra of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) are illustrated in Fig. 5a–d to determine their chemical functional groups. O–H, C=O, and C–O were the main chemial functional groups of all materials similar found in other studies of eggshells48,53, whereas Fe–O was only found in DPF and CDPF. For O–H, it was the stretching of the hydroxyl group o the water molecule53. For C=O, it was the stretching of the carbonate group (CO32−) and C–O was the stretching of calcium carbonate (CaCO3) or bending out and in plane modes of CO32−50. For DP, it observed the stretching of O–H at 3401.15 cm−1, stretching of C=O at 1795.32 cm−1 and 1648.44 cm−1, and stretching of C–O at 1397.78 cm−1, 871.72 cm−1, and 711.32 cm−1. For DPF, it detected the stretching of O–H at 3368.78 cm−1, stretching of C=O at 1794.89 cm−1 and 1654.33 cm−1, stretching of C–O at 1363.55 cm−1, 870.01 cm−1, and 710.00 cm−1, and the stretching of Fe–O at 616.94 cm−1. For CDP, it found the stretching of O–H at 3640.22 cm−1, stretching of C=O at 1793.19 cm−1 and 1676.60 cm−1, and stretching of C–O at 1437.67 cm−1, 874.69 cm−1, and 711.85 cm−1 which found the evidence of water adsorption by alcium oxide (CaO) resulting from the calcination process at a position of O–H similar to other studies48,53. For CDPF, it detected the stretching of O–H at 3640.59 cm−1, stretching of C=Oat 1790.68 cm−1 and 1645.93 cm−1, stretching of C–O at 1397.62 cm−1, 871.27 cm−1, and 710.54 cm−1, and the stretching of Fe–O at 615.27 cm−1 which it also found the evidence of water adsorption by CaO similar to CDP.Figure 5FT-IR spectra of (a) duck eggshell powder (DP), (b) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), (c) calcined duck eggshell powder (CDP), and (d) calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageThe point of zero chargeThe point of zero charge (pHpzc) refers to a pH value at the net charge equal to zero of the adsorbent for realizing which pH value is good for adsorption by that adsorbent. In this study, the pHpzc of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell power (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) was investigated to identify which a pH value was good for lead adsorption for each material, and their rsults are demonstrated in Fig. 6. The pHpzc values of DP, DPF, CDP, and CDPF were 4.58, 5.31, 5.96, and 6.75, respectively. As a result, the calcination process and the iron (III) oxide-hydroxide increased the pHpzc of materials. Since a negatively charged material surface is preferred for capturing lead (II) ions, the pH of the solution (pHsolution) should be higher than pHpzc (pHsolution > pHpzc) to support a high lead adsorption. Therefore, the high lead adsorptions of all materials should be observed at pH > 4.Figure 6The point of zero charges of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageBatch adsorption experimentsThe efect of adsorbent dosageThe dosages from 2.5 to 15 g/L of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were used for the effect of adsorbent dosage, and their results are illustrated in Fig. 7a. Their lead removal efficiencies increased with increasing of dosages which might be from increasing active sites for capturing the lead. Their highest lead removal efficiencies were 99.74% at 15 g/L for DP, 100% at 10 g/L for DPF, 100% at 7.5 g/L for CDP, and 100% at 5 g/L for CDPF, respectively. Therefore, they were used as optimum adsorbent dosages of DP, DPF, CDP, and CDPF for the effect of contact time.Figure 7Batch experiments on the effects of (a) adsorbent dosage, (b) contact time, (c) pH, and (d) initial lead concentration of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell owder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageThe effect of contact timeThe contact times from 1 to 6 h of duck eggshell powder (DP), dck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were applied for the effect of contact time, and the results are shown in Fig. 7b. Their lead removal efficiencies increased with increasing of contact time, and the highest lead removal efficiency is found at the constant contact time. Their highest lead removal efficiencies were 98.96% at 4 h for DP, 99.29% at 3 h for DPF, 99.54% at 3 h for CDP, and 99.87% at 2 h for CDPF, respectively. Therefore, they were used as the optimum contact time of DP, DPF, CDP, and CDPF for the effect of pH.The effect of pHThe pH values of 1, 3, 5, 7, 9, and 11 of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF),calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were used for the effect of pH, and the results were presented in Fig. 7c. Their ead removal efficiencies were increased with the increase of pH values from 1 to 5, then they were decreased. At pH < 5, the increase of proton (H+) at pH 1–3 affected low lead adsorptions of all materials because of the competition of H+ and Pb (II) ions (Pb2+) agreed with the previous studies14,16,54. At pH > 5, their lead removal efficiencies were decreased because the hydroxide formation of lead such as PbOH+ (aq), Pb2(OH)3+(aq), Pb(OH)2 (aq) similarly reported by a previous study55 including the occurrence of lead precipitation (Pb(OH)2 (s)) resulted to lead removals at high pH values. The highest lead removal efficiencies of all materials were found at pH 5 for 95.12%, 96.78%, 98.41%, and 99.76% for DP, DPF, CDP, and CDPF, respectively. These results corresponded to the results of pHpc in this study and other studies that pH > 4 illustrated the highest lead removal efficiency related to pHpzc of lead removals in wastewater6,14,28,39,56. Therefore, pH 5 was used as the opimum pH of DP, DPF, CDP, and CDPF for the effect of concentration.The effect of initial lead concentrationInitial lead concentrations from 10 to 70 mg/L of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were applied for the effect of initial lead concentration, and the results are shown in Fig. 7d. Their lead removal efficiencies of duck eggshell materials were decreased with the increasing of initial lead concentration from 10 to 70 mg/L resulting from lack active sites for adsorb lead ions similarly found by other studies6,14,28,39,45,51,56. Lead removal efficiencies at 50 mg/L of DP, DPF, CDP, and CDPF were 98.35%, 98.94%, 99.04%, and 99.24%, espectively, and CDPF demonstrated a higher lead removal efficiency than others.In conclusion, 15 g/L, 4 h, pH 5, 50 mg/L, 10 g/L, 3 h, pH 5, 50 mg/L, 7.5 g/L, 3 h, pH 5, 50 mg/L, and 5 g/L, 2 h pH 5, 50 mg/L, respectively were the optimum conditions in dose, contact time, pH, and concentration of DP, DPF, CDP, and CDPF, so CDPF demonstrated the highest lead removal efficiency at high lead removal of 99.24% than other materials because it spent less material dosage and contact time than others. In addition, they could be arranged in high material efficiency to low being CDPF > CDP > DPF > DP. Therefore, adding iron (III) oxide-hydroxide along with the calcination process improved material efficiency, and CDPF was a potential material to apply in the wastewater treatment system.Adsorption isothermsThe adsorption patterns of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell power mixed iron (III) oxide-hydroxide (CDPF) for lead adsorptions were identified by linear and nonlinear models of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. For linear models,Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms were plotted by Ce/qe versus Ce, log qe versus log Ce, qe versus ln Ce, and ln qe versus ε2, respectively. For nonlinear models, all isotherms were plotted by Ce versus qe. The plotting graph results are illustrated in Fig. 8a–h, and the equilibrium isotherm parameters are illustrated in Table 5.Figure 8Graphs of (a) linear Langmuir, (b) linear Freundlich, (c) linear Temkin, (d) linear Dubinin–Radushkevich, and (e) nonlinear adsorption isotherms of duck eggshell powder (DP), (f) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), (g) calcined duck eggshell powder (CDP), and (h) calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) for lead adsorptions.Full size imageTable 5 The comparison of linear and nolinear isotherm parameters for lead adsorptions on duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck egshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size tableFor linear models, the Langmuir maximum adsorption capacities (qm) of DP, DPF, CDP, and CDPF were 4.655, 7.358, 9.643, and 14.205 mg/g, and Langmuir adsorption constants (KL) of DP, DPF, CDP, and CDPF were 2.672, 3.259, 4.548, and 6.579 L/mg. For Freundlich isotherm, the 1 values of DP, DPF, CDP, and CDPF were 0.405, 0.410, 0.417, and 0.422. Freundlich adsorption constants (KF) of DP, DPF, CDP, and CDPF were 2.888, 5.138, 7.528, and 11.402 (mg/g)(L/mg)1 . For Temkin isotherm, bT values of DP, DPF, CDP, and CDPF were 2974.345, 1995.668, 1409.381, and 1313.351 J/mol, and AT values of DP, DPF, CDP, and CDPF were 43.338, 67.719, 69.423, and 362.405 L/g. For the Dubinin-Radushkevich model, the maximum adsorption capacities (qm) o DP, DPF, CDP, and CDPF were 3.472, 5.236, 7.788, and 10.126 mg/g, and the activity coefficient (KDR) values of DP, DPF, CDP, and CDPF were 0.028, 0.027, 0.023, and 0.019 mol2/J2, respectively. Theadsorption energy (E) values of DP, DPF, CDP, and CDPF were 4.218, 4.303, 4.693, and 5.077 kJ/mol.R2 values of DP, DPF, CDP, and CDPF on the linear Langmuir model were 0.996, 0.977, 0.998, and 0.988, respectively, and their R2 values on the linear Freundlich model were 0.939, 0.991, 0.938, and 0.995, respectively. R2 values of DP, DPF, CDP, and CDPF on the linear Temkin model were 0.977, 0.955, 0.988, and 0.934, respectively, and their R2 values on the linear Dubinin-Radushkevich model were 0.941, 0.918, 0.968, and 0.882, respectively.For nonlinear models, the Langmuir maximum adsorption capacities (qm) of DP, DPF, CDP, and CDPF were 4.659, 7.364, 9.651, and 14.333 mg/g, and Langmuir adsorption constants (KL) of DP, DPF, CDP, and CDPF were 2.688, 3.259, 4.562, and 6.723 L/mg. For Freundlich sotherm, the 1 values of DP, DPF, CDP, and CDPF were 0.408, 0.413, 0.423, and 0.441. Freundlich adsorption constants (KF) of DP, DPF, CDP, and CDPF were 2.901, 5.145, 7.534, and 11.436 (mg/g)(L/mg) . For Temkin isotherm, bT values of DP, DPF, CDP, and CDPF were 2987.884, 2097.859, 1409.381, and 1342.407 J/mol, and AT values of DP, DPF, CDP, and CDPF were 43.443, 67.751, 69.423, and 377.582 L/g. For the Dubinin–Radushkevich model, the maximum adsorption capacities (qm) of DP, DPF, CDP, and CDPF were 3.827, 5.364, 5.292, and 11.216 mg/g, and the activity coefficient (KDR) values of DP, DPF, CDP, and CDPF were 0.034, 0.028, 0.029, and 0.022 mol2/J2, respectively. The adsorption energy (E) values of DP, DPF, CDP, and CDPF were 3.816, 4.241, 4.123, and 4.795 kJ/mol.R2 values of DP, DPF, CDP, and CDPF on the nonlinear Langmuir model were 0.998, 0.978, 0.998, and 0.989, respectively, and their R2 values on the nonlinear Freundlich model were 0.942, 0.992, 0.943, and 0.996, respectively. R2 alues of DP, DPF, CDP, and CDPF on the nonlinear Temkin model were 0.979, 0.960, 0.987, and 0.940, respectively, and their R2 values on the nonlinear Dubinin-Radushkevich model were 0.955, 0.919, 0.90, and 0.885, respectively.R2adj values of DP, DPF, CDP, and CDPF on the nonlinear Langmuir model were 0.997, 0.974, 0.997, and 0.986, respectively, and their R2adj values on the nonlinear Freundlich model were 0.930, 0.990, 0.932, and 0.995, respectively. R2adj values of DP, DPF, CDP, and CDPF on the nonlinear Temkin model were 0.975, 0.952, 0.985, and 0.928, respectively, and their R2adj values on the nonlinear Dubinin-Radushkevich model were 0.946, 0.903, 0.904, and 0.862, respectively.For R2 value consideration, since R2 values of DP and CDP in both linear and nonlinear Langmuir models were higher than Freundlich, Temkin, and Dubinin-Radushkevich models, its adsorption patterns corresponded to Langmuir isotherm relating to physical adsorption. While R2 values of DPF and CDPF in both liear and nonlinear Freundlich models were higher than Langmuir, Temkin, and Dubinin-Radushkevich models, their adsorption patterns corresponded to Freundlich isotherm relating to physiochemical adsorpton. Since the results of linear and nonlinear of all isotherm models had close values, it recommended plotting graphs to confirm the results34,57,58,59,60,61,62,63.Moreover, the comparison of the maximum adsorption capacity (qm) value of eggshell adsorbents for lead adsorption is illustrated in Table 6. All duck eggshell materials in this study had a higher qm value than the studies of Alamillo-López et al.64, Bayu et al.65, Kasirajan et al.66, and Peigneux et al.30. In addition, CDPF also had a higher qm value than the study of Hajji and Mzoughi54.Table 6 The comparison of the maximum adsorption capacity (qm) value of eggshell adsorbents for lead adsorption.Full size tableAdsorption kineticsThe adsorption kinetics of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-ydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) for lead adsorptions were investigated to describe by linear and nonlinearkinetic models of pseudo-first-order kinetic, pseudo-second-order kinetic, elovich, and intraparticle diffusion. For linear models, they were plotted by ln (qe − qt) versus time (t), t/qt versus time (t), qt versus ln t, and qt versus time (t0.5) for pseudo-first-order kinetic, pseudo-second-order kinetic, elovich, and intraparticle diffusion models, respectively. For nonlinear models, they were plotted by qt versus time (t). The plotting graph results are illustrated in Fig. 9a–h, and the adsorption kinetic parameters are presented in Table 7.Figure 9Graphs of (a) linear pseudo-first-order, (b) linear pseudo-second-order, (c) linear elovich model (d) linear intraparticle diffusion, and (e) nonlinear kinetic models of duck eggshell powder (DP), (f) duck eggshell powder mixed iron (III) oide-hydroxide (DPF), (g) calcined duck eggshell powder (CDP), and (h) calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) for lead adsorptions.Full size imageTable 7 The comparison of inear and nonlinear kinetic parameters for lead adsorptions on duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size tableFor linear models, the adsorption capacities (qe) of DP, DPF, CDP, and CDPF on a pseudo-first-order kinetic model were 2.641, 3.186, 3.805, and 8.144 mg/g, and their reaction of rate constants (k1) were 0.016, 0.018, 0.019, and 0.020 min−1. For a pseudo-second-order kinetic model, the adsorption capacities (qe) of DP, DPF, CDP, and CDPF were 3.505, 5.015, 6.892, and 10.730 mg/g, and their reaction of rate constants (k2) were 0.014, 0.015, 0.018, and 0.025 g/mg min. For the elovich model, the initial adsorption rate (α) of DP, DPF, CDP, and CDPF were 0.671, 0.712, 0.830, and 0.857 mg/g/min, and their extents of surface coverage (β) were 1.619, 0.935, 0.842, and 0.557 g/mg. For the intraparticle diffusion model, thereaction of rate constants (ki) of DP, DPF, CDP, and CDPF were 0.153, 0.217, 0.281, and 0.432 mg/g min0.5, and their constant Ci values were 0.963, 1.737, 2.431, and 3.455 mg/g.R2 values of DP, DPF, CDP, and CDPF on the linear pseudo-first-order were 0.988, 0.984, 0.981, and 0.983, respectively, and their R2 values on the linear pseudo-second-order kinetic models were 0.996, 0.995, 0.998, and 0.993, respectively. In addition, R2 values of DP, DPF, CDP, and CDPF on the linear elovich model were 0.961, 0.963, 0.948, and 0.964, respectively, and their R2 values on the linear intraparticle diffusion model were 0.799, 0.725, 0.721, and 0.756, respectively.For nonlinear models, the adsorption capacities (qe) of DP, DPF, CDP, and CDPF on a pseudo-first-order kinetic model were 2.850, 3.310, 3954, and 8.217 mg/g, and their reaction of rate constant (k1) were 0.017, 0.020, 0.021, and 0.022 min−1. For a pseudo-second-order kinetic model, the adsorption capacities (qe) of DP, DPF, CDP, and CDPF wre 3.520, 5.024, 6.998, and 10.792 mg/g, and their reaction of rate constants (k2) were 0.017, 0.019, 0.023, and 0.030 g/mg min. For the elovich model, the initial adsorption rates (α) of DP, DPF, CDP, and CDPF were 0.684, 0.756, 0.872, and 0.873 mg/g/min, and their extents of surface coverage (β) were 1.644, 0.989, 0.854, and 0.634 g/mg. For the intraparticle diffusion model, the reactions of rate constant (ki) of DP, DPF, CDP, and CDPF were 0.165, 0.218, 0.293, and 0.440 mg/g min0.5, and their constant Ci values were 0.978, 1.747, 2.443, and 3.551 mg/g.R2 values of DP, DPF, CDP, and CDPF on the nonlinear pseudo-first-order kinetic model were 0.984, 0.985, 0.983, and 0.982, respectively, and their R2 values on the nonlinear pseudo-second-order kinetic model were 0.998, 0.996, 0.997, nd 0.992, respectively. In addition, R2 values of DP, DPF, CDP, and CDPF on the nonlinear elovich model were 0.963, 0.967, 0.950, and 0.961, respectively, and their R2 values on the nonlinear intraparticlediffusion model were 0.795, 0.729, 0.722, and 0.758, respectively.Moreover, R2adj values of DP, DPF, CDP, and CDPF in the nonlinear pseudo-first-order kinetic model were 0.983, 0.984, 0.982, and 0.981, respectively, and their R2adj values in the nonlinear pseudo-second-order kinetic model were 0.997, 0.995, 0.996, and 0.991, respectively. R2adj values of DP, DPF, CDP, and CDPF in the nonlinear elovich model were 0.961, 0.965, 0.948, and 0.959, respectively, and their R2adj values in the nonlinear intraparticle diffusion model were 0.783, 0.715, 0.707, and 0.745, respectively.For R2 value consideration, since R2 values of DP, DPF, CDP, and CDPF in both linear and nonlinear pseudo-second-order kinetic models were higher than the pseudo-first-order kinetic, elovich, and intraparticle difusion models, so their adsorption rate and mechanism of both materials corresponded to a pseudo-second-order kinetic model which was chemisorption process with heterogeneous adsorption. Finally, it also reommended plotting both linear and nonlinear kinetic models for protecting against data mistranslations34,57,58,59,60,61,62,63.Desorption experimentsBefore duck eggshell materials are used in industrial applications, it is necessary to estimate the cost and economics of them and whether they can be reused. As a result, the desorption experiments investigated the possible reuse of duck eggshell materials for lead adsorption. The adsorption–desorption experiments in 5 cycles were applied for this study to check the material reusability of duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF), and their results are demonstrated in Fig. 10a–d. I Fig. 10a, DP could be reused in 5 cycles with high adsorption and desorption in ranges of 73.37–98.41% and 67.04–96.09%, respectively which adsorption and desorption were decreased by approximately 25% and 9%, respectively. For DPF, it also confirmed to be reusability in 5 cycles with high adsorption and desorption in ranges of 79.94–98.97% and 72.38–96.43%, respectively which adsorption and desorption were decreased by approximately 19% and 24%, respectively shown in Fig. 10b. For CDP could be reused in 5 cycles with high adsorption and desorption in ranges of 85.10–99.12% and 78.66–96.73%, respectively which adsorption and desorption were decreased by approximately 14% and 18%, respectively shown in Fig. 10c. For CDPF, it also confirmed to be reusability in 5 cycles with high adsorption and desorption in ranges of 89.49–99.54% and 83.19–97.23%, respectively which adsorption and desorption were decreased by approximately 10% and 14%, respectively shown in Fig. 10d. Therefore, all duk eggshell materials could be reused more than 5 cycles by more than 73%.Figure 10The desorption experiments of (a) duck eggshell powder (DP), (b) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), c) calcined duck eggshell powder (CDP), and (d) calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageThe possible mechanisms of lead adsorption by duck eggshell materialsThe possible mechanisms of lead adsorptions on duck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were explained by referring idea from the study of Praipipat et al.14 shown in Fig. 11a–d. Three main mechanisms were used for explaining their lead adsorption reactions which were surface complexation, electrostatic interaction, and ion exchange. For surface complexation, lead (II) ions (Pb2+) could be adsorbed by DP, DPF, CDP, and CDPF thrugh the sharing electrons of hydroxyl ion (–OH) in calcium carbonate (CaCO3) or calcium oxide (CaO) on their surface and the complex compounds of DPF and CDPF from adding iron (III) oxide-hydroxide in the formof DP∙Fe(OH)3 or CDP∙Fe(OH)3. For electrostatic interaction, the surface charge of the adsorbent plays an important role in lead adsorption which depends on the pH of the solution. In addition, the point of zero charge (pHpzc) of the adsorbent is used to indicate which charge of the adsorbent surface is. If the pH solution is lower than pHpzc (pHsolution < pHpzc), the surface charge of the adsorbent is positively charged which affects low lead adsorption because of the competition of lead (II) ions (Pb2+) and proton (H+) at an acidic pH condition. As a result, the high lead adsorption should be found at the pH of solution higher than pHpzc (pHsolution > pHpzc) with a negatively charged of adsorbent surface. Since the pHpzc of DP, DPF, CDP, and CDPF were 4.58, 5.31, 5.96, an 6.75, their lead adsorptions should occur at pH of solution > pH 4 by the process of electrostatic interaction68 agreed with the results of pH effect that the highest lead removal efficiencies of all materils were found at pH 5. For ion exchange, the substitution of calcium ions (Ca2+) from (CaCO3 or CaO) in DP, DPF, CDP, and CDPF surfaces by Pb2+ might happen through the ion exchange process69.Figure 11Possible mechanisms of lead adsorption on (a) duck eggshell powder (DP), (b) calcined duck eggshell powder (CDP), (c) duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), and (d) calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF).Full size imageConclusionDuck eggshell powder (DP), duck eggshell powder mixed iron (III) oxide-hydroxide (DPF), calcined duck eggshell powder (CDP), and calcined duck eggshell powder mixed iron (III) oxide-hydroxide (CDPF) were successfully synthesized. CDPF demonstrated the highest specific surface area and pore volume with thesmallest pore size than other materials, so the calcination process along with adding iron (III) oxide-hydroxide helped to increase specific surface area and pore volume with decreasing pore size which supports high lead adsorption. In addition, all materials were classified as mesoporous materials with a range pore size of 2–50 nm. DP and DPF demonstrated the semi-crystalline structures with specific calcium carbonate peaks, whereas CDP and CDPF illustrated the semi-crystalline structures with specific calcium oxide peaks. In addition, the specific iron (III) oxide-hydroxide was detected in only DPF and CDPF because of the addition of iron (III) oxide-hydroxide. Their surface morphologies were rough with irregular shapes, and the additional iron (III) oxide-hydroxide did not affect changing their surface characteristic. All materials were found carbon (C), oxygen (O), and calcium (Ca). Iron (Fe), sodium (Na), and chloride (Cl) were only found in DPF and CDPF from using chemicals in process of addition of iron (III) oxide-hydroxide. In addition, they also found iron distribution on DPF and CDPF surfaces. They consisted of carbon (C), oxygen (O), and calcium (Ca), whereas iron (Fe), sodium (a), and chloride (Cl) were found only in DPF and CDPF which could be confirmed the successful addition of iron (III) oxide-hydroxide in both materials. Three main function groups of O–H, C=O, and C–O were found in all materials similar found in other studies of eggshells, whereas Fe–O was only found in DPF and CDPF because of the addition of iron (III) oxide-hydroxide. The point of zero charges (pHpzc) of DP, DPF, CDP, and CDPF were 4.58, 5.31, 5.96, and 6.75, respectively, so the calcination process and addition of iron (III) oxide-hydroxide increased pHpzc of materials. For batch experiments, the optimum conditions of DP, DPF, CDP, and CDPF were 15 g/L, 4 h, pH 5, 50 mg/L, 10 g/L, 3 h, pH 5, 50 mg/L, 7.5 g/L, 3 h, pH 5, 50 mg/L, and 5 g/L, 2 h, pH 5, 50 mg/L, respectively, ad their lead removal efficiencies were 98.35%, 98.94%, 99.04%, and 99.24%, respectively. Thus, CDPF illustrated a higher lead removal efficiency than other materials because it spent less adsorbent dosage and contct time than DP, DPF, and CDP. Thus, adding iron (III) oxide-hydroxide along with the calcination process improved material efficiencies for lead adsorption. For the isotherm study, the Langmuir model was the best-fit model for DP and CDP explained by a physical adsorption process. While the Freundlich model was a good fit model for DPF and CDPF described by a physicochemical adsorption process. For the kinetic study, a pseudo-second-order kinetic model was the best-fit model for all materials related to a chemisorption process with heterogeneous adsorption. Moreover, all duck eggshell materials could reuse for more than 5 cycles for lead adsorption of more than 73%. As a result, all duck eggshell materials were high-potential materials for lead adsorption in an aqueous soluton, and CDPF demonstrated the highest lead removal efficiency. Therefore, CDPF was suitable to apply for industrial wastewater treatment applications in the future.For future works, the continuous flow study and th competing ions such as sodium (Na+) and magnesium (Mg2+) contaminated in real wastewater are recommended to study for confirming the specific lead adsorption by duck eggshell materials before applying in industrial applications.
Data availability
The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.
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Download referencesFundingThe authors are grateful for the financial support received from The Office of the Higher Education Commission and The Thailand Reearch Fund grant (MRG6080114), Coordinating Center for Thai Government Science and Technology Scholarship Students (CSTS) and National Science and Technology Development Agency (NSTDA) Fund grant (SCHNR2016-122), and Research and Technology Transfer Affairs of Khon Kan University.Author informationAuthors and AffiliationsDepartment of Environmental Science, Faculty of Science, Khon Kaen University, Khon Kaen, 40002, ThailandPornsawai Praipipat, Pimploy Ngamsurach & Rattanaporn TannadeeEnvironmental Applications of Recycled and Natural Materials (EARN) Laboratory, Khon Kaen University, Khon Kaen, 40002, ThailandPornsawai Praipipat & Pimploy NgamsurachAuthorsPornsawai PraipipatView author publicationsYou can also search for this author in
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PubMed Google ScholarContriutionsP.P.: supervision, project administration, conceptualization, funding acquisition, investigation, methodology, validation, formal analysis, visualization, writing—original draft, writing-review and editing. P.N.: investigation, visualization, writin—original draft. R.T.: investigation.Corresponding authorCorrespondence to
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Reprints and PermissionsAbout this articleCite this articlePraipipat, P., Ngamsurach, P. & Tannadee, R. Influence of duck eggshell powder modifications by the calcination process or addition of iron (III) oxide-hydroxide on lead removal efficiency.
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