Summary of Geography doctoral thesis: Study on denaturation of Laterite ores by La2O3 and CeO2 to treat arsenic and phosphate in water

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Synthesization and structural characterization of nano La2O3, nano CeO2, nano La2O3- CeO2 on laterite by sol - gel combustion method using gelatin precursor; investigation the adsorption and desorption capacity of arsenic, phosphate on La2O3 nanomaterials, CeO2 nanomaterial, mixed oxides La2O3-CeO2 nanomaterial and La2O3-CeO2 nanomaterials on laterite.

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Nội dung Text: Summary of Geography doctoral thesis: Study on denaturation of Laterite ores by La2O3 and CeO2 to treat arsenic and phosphate in water

MINISTRY OF EDUCATION VIETNAM ACADEMY OF AND TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY DAO HONG DUC STUDY ON DENATURATION OF LATERITE ORES BY LA2O3 AND CEO2 TO TREAT ARSENIC AND PHOSPHATE IN WATER Major: Enviromental engineering Major code: 92 5. 03.20 SUMMARY OF GEOGRAPHY DOCTORAL THESIS Ha Noi - 2020
The thesis was completed in: Inorganic material room, Institute of materials science, Vietnam Academy of Science and Technology Science instructor 1: Assoc. Prof. PhD. Do Quang Trung Science instructor 2: Assoc. Prof. PhD. Dao Ngoc Nhiem Reviewer 1: Reviewer 2: Reviewer 3: The thesis will be defended at the university's doctoral thesis evaluation council, meeting in the Graduate University of Science and Technology, Vietnam Academy of Science and Technology at …… hour ……, date …… month …… year 2020. - Thesis can be found in: - The Library of Graduate University of Science and Technology - Vietnam’s National Library
Introduction 1. The urgency of the thesis Water potable resources contamination significantly affects on human health, especially underground water, one of the main water sources for Vietnamese people. To our knowledge, groundwater can be polluted by various contaminants like arsenic, ammonium, fluorine, nitrate, and phosphate... Regarding to arsenic pollution in groundwater in Vietnam, it has been studied by many national and international scientists. The results showed that there are many provinces and cities across the country with arsenic concentrations in excess of the regulation standards such as Hanoi, Vinh Phuc, Ha Nam... However, phosphate contamination and its accumulation in groundwater over time have not been much investigated in Vietnam. It is necessary to understand the presence of phosphate in water because it affects the quality of water sources and as much to human health. The sources for phosphate presence in groundwater can be explained by human activities such as using chemical fertilizers in agriculture, domestic wastewater, leachates, and livestock waste water... Up to date, to remove arsenic and phosphate in water, there are many methods such as: co-precipitation method, adsorption method, ion exchange method, and membrane method. In particular, the adsorption method is currently widely used because of its effectively high treatment efficiency, environmentally friendly methods, diverse precusor sources. The use of natural materials or the use of high-valence metals such as iron oxide, aluminum oxide, magnesium oxide resulted in good potentail phosphate removal. However, many researchers agreed that the oxides of rare earth elements have many more advantages. Some of them are widely applied in practice, especially for environmental treatment such as lanthanum, cerium in nano size. On one hand, the nano lanthanum oxides and nano cerium oxides have good ability to handle arsenic and phosphate. On the other hand, it is still quietly expensive in compare with other materials. Therefore, lanthanum oxide nanoparticles, cerium oxide are often deposited on laterite carriers for better economic efficiency. Laterite has many advantages compared to other materials in nature such as abundant reserves, simple mining and activation process, capable of handling high concentration of arsenic and phosphate. Therefore, the use of nano lanthanum oxide and cerium oxide nano as a material to treat arsenic and phosphate pollution in water was conducted in the thesis " Study on denaturation of Laterite ores by La2O3 and CeO2 to treat arsenic and phosphate in water”. The thesis was completed with the main following contents. 2. The main content of the thesis Synthesization and structural characterization of nano La2O3, nano CeO2, nano La2O3- CeO2 on laterite by sol - gel combustion method using gelatin precursor. Investigation the adsorption and desorption capacity of arsenic, phosphate on La2O3 nanomaterials, CeO2 nanomaterial, mixed oxides La2O3-CeO2 nanomaterial and La2O3-CeO2 nanomaterials on laterite. Testing the ability to handle arsenic and phosphate in groundwater samples at Phu Ly, Ha Nam with La2O3-CeO2 / laterite nanomaterials with the experimental model. New contributions of the thesis 1
Successfully synthesized 4 types of nano materials La2O3, nano CeO2, La2O3-CeO2 nano-mixed materials and modified La2O3-CeO2 nanomaterials on laterite by sol-gel combustion method using gelatin. Fully investigated the arsenic and phosphate adsorption capacity in water of the four types of nano materials La2O3, nano CeO2, La2O3-CeO2 nanomaterials and La2O3-CeO2 nanomaterials on laterite . 3. The layout of the thesis. The thesis consists of 95 pages with 25 tables, 49 figures and 98 references. The thesis is composed of a 2-page introduction, an overview of 28 pages, experimental and methodology of 12 pages, results and discussion of 54 pages and conclusions of 2 pages. CONTENTS OF THE THESIS Chapter 1. Literature review On the basis of document analysis, this chapter summarized arsenic and phosphate pollution in groundwater, the harmful effects of arsenic and phosphate pollution on human health. Especially, this chapeter provided the evident of the increasing phosphate concentration in underground water. The process of removing arsenic and phosphate has many methods such as co-precipitation method, ion exchange method, adsorption method. To treat arsenic in water thoroughly, it is possible to combine methods of precipitation, sedimentation and filtration. Currently, the adsorption method is widely applied because of its high treatment efficiency, environmentally friendly method, meeting the purpose of treatment requirements. The use of natural materials or the use of high-valence metals such as iron oxide, aluminum oxide, magnesium oxide resulted promissingly arsenic and phosphate removal. But recently, many researchers showed that the oxides of rare earth elements have many advantages, which are widely applied in practice, especially in environmental treatment such as lanthanum, cerium, especially in the form of nano. The nano lanthanum oxide and cerium oxide nano have good ability to handle arsenic and phosphate. However, to use lanthanum oxide nanoparticles, cerium oxide in water treatment applications and meeting economic efficiency conditions, nano-lanthanum materials and cerium are oftenly deposited on laterite carriers. Laterite has many advantages compared to other materials in nature such as abundant reserves, simple mining and activation process, capable of handling arsenic and phosphate... Therefore, the use of nano lanthanum oxide and cerium oxide nano as a material to treat arsenic and phosphate pollution in water was conducted in the thesis " Study on denaturation of Laterite ores by La2O3 and CeO2 to treat arsenic and phosphate in water” has significant scientific and practical implications. Chapter 2. Experimental and Methodology The content of chapter 2 refers to: Types of chemicals, materials and equipment used in the research. Modern analytical method to evaluate the material characterization such as: Thermal analysis method, X-ray diffraction method, X-ray energy scattering spectrum, electron microscope method, Infrared spectrum method (FT-IR), Raman scattering spectroscopy, method of determining the isoelectric point of a material. Synthesization process of nano materials La2O3, nano CeO2, nano mixed oxides La2O3-CeO2 and denatured nano materials La2O3-CeO2/laterite. 2
Figure 2.4. Synthesizing nanomaterials by Figure 2.5. Synthesizing nanomaterials sol - gel combustion method using gelatin on laterite Methods of analysis for arsenic, phosphate and rare earth metals. Atomic adsorption method for arsenic determination (AAS), colorimetric method for determination of phosphate concentration. Adsorption method. Static adsorption method, dynamic adsorption method. Chapter 3. Results and discussions 3.1. Synthesis of La2O3 nanomaterials and evaluation of phosphate and arsenic adsorption capacity 3.1.1. Synthesis of La2O3 nano materials Investigate of calcination temperature to the formation La2O3 phase. Intencity (a.u) o 560 C o 550 C o 450 C o 180 C 30 40 50 60 70 2 Theta (degree) Figure 3.1. DTA thermal analysis diagram Figure 3.2. XRD patterns of and TGA La(NO3)3/gelatin La(NO3)3/gelatin at different temperatures Results of DTA thermal analysis diagram from Figure 3.1 and results of XRD analysis calcined at different temperatures in Figure 3.2 showed that nanomaterial La2O3 is synthesized at temperature 550oC. So, the calcination temperature at 550oC was selected to synthesize La2O3 nanomaterials for further experiments. Effect of pH and gel forming temperature on the process of forming La2O3 phase. La2O3  La2O3   pH 5  100oC  pH 4 Intencity (a.u) 80oC Intencity (a.u) pH 3 60oC pH 2 40oC 35 40 45 50 55 60 65 70 2 Theta (degree) 35 40 45 50 55 60 65 70 2 Theta (degree) Figure 3.3. The XRD diagram of the La2O3 Figure 3.4. XRD diagram of nanomaterial nanomaterial sample was synthesized at La2O3 at different gel forming temperature 3
different pH levels The results of X-ray diffraction analysis in Figure 3.3 showed why pH 5 was selected to synthesize La2O3 nanomaterials in subsequent studies. The results on the XRD diagram in Figure 3.4 were La2O3 nanomaterials synthesis at different temperatures, gel formation temperature of La2O3 nanomaterials chose at 80°C. Morphology and structure of nano-material La2O3 The material morphology was characterized by TEM images (Figure 3.5). Results showed that La2O3 nanomaterials are spherical shape with average size smaller than 50 nm and relatively uniform. The surface area of the material determined by the BET Figure 3.5. TEM image of nanomaterial La2O3 method was 37.8 m2/g zero-charge point of nanomaterial La2O3 The results were shown in Figure 3.6, the La2O3 nanomaterial has a pHpzc value of 7.1. Figure 3.6. The zeta potential of La2O3 nanomaterials 3.1.2. Evaluation of phosphate and arsenic adsorption by La2O3 nanomaterials Phosphate adsorption results of La2O3 nanomaterials Effect of equilibrium time and pH on phosphate adsorption capacity The effect of equilibrium time and pH on phosphate adsorption capacity of La2O3 nanomaterial was shown in Figure 3.7. 3.8. Figure 3.7. Effect of phosphate adsorption Figure 3.8. Effect of pH on phosphate equilibrium time by nano-material La2O3 adsorption capacity of La2O3 nanomaterials The results of phosphate adsorption equilibrium were determined in 90 minutes. The effect of pH on the c phosphate adsorption apacity of La2O3 nanomaterial was obtained in Figure 3.8. The process of phosphate adsorption on nanomaterials La2O3 is highly dependent on pH, when the pH value is from 2 to 7.1 the phosphate adsorption capacity of the material increases and the adsorption capacity gradually decreases pH value. 7.1 to 9. Effect of initial phosphate concentration 4
Đường đẳng nhiệt hấp phụ Lăngmuir 250 r^2=0.979431 DF Adj r^2=0.97061571 Fi tStdErr=13.798889 Fstat=190.46738 Qmax = 210,05 mg/g b = 0,059 250 Using Table-curve calculation software to regress the experimental results of 200 200 phosphate adsorption of nanomaterial Dung lượng hấ p phụ phố t phát q (mg/g) Dung lượng hấ p phụ phố t phát q (mg/g) 150 150 La2O3 with Qmax = 210.05 mg/g with 100 100 regression coefficient r2 = 0.96. 50 50 0 0 0 50 100 150 Nồng độ ion phốt phát còn lại Cf (mg/l) Figure 3.9. Phosphate adsorption isotherms of La2O3 nano-oxide materials FT-IR spectrum of La2O3 nanomaterials before and after phosphate adsorption. FT-IR results in Figure 3.10 shown 1066.01 1107.01 La2O3 nanomaterials before and after 3608.06 1479.75 phosphate adsorption. The appearance of a the peak at 3608 cm-1 specific to the Intencity (a.u) 1426.66 1049.24 covalent oscillation of the group – OH 1481.61 on the surface of the material and the 3608.06 peaks at 1066 cm-1, 1107 cm-1 specific to b the group fluctuations of –OH bonded with material. When the presence of 4000 3500 3000 2500 2000 1500 1000 -1 Number of waves (cm ) PO43- occurred, new featured peak for 3- Hình 3.10. Phổ FT-IR của vật liệu nano La2O3. PO4 replacement -OH group is formed a) trước hấp phụ; b) sau hấp phụ photphat at 1049 cm -1. Arsenic adsorption results of La2O3 nanomaterials Effect of arsenic adsorption equilibrium time with nanomaterial La2O3 Figure 3.11. Arsenic concentration over time Figure 3.12. Effect of pH on arsenic adsorption Analysis results and Figure 3.11, arsenic adsorption equilibrium time of the material of nano-oxide La2O3 material is 120 minutes. The effect of pH on arsenic adsorption capacity of La2O3 nanomaterials in Figure 3.12, when the pH value changes from 2 to 7.1 the arsenic adsorption capacity of the material increases and the adsorption capacity decreases at pH 7.1 to 9. Effect of material concentration on arsenic adsorption capacity 5
From the experimental results and using the Table-curve calculation software regression calculations the arsenic adsorption experimental results of La2O3 nanomaterials showed that Qmax = 81.47mg/g with regression coefficient r2 = 0.98. The adsorption process follows the Langmuir isothermal adsorption equation. Figure 3.13. Arsenic isothermal adsorption lines of La2O3 nanomaterials 3.2. Synthesis of CeO2 nanomaterials and evaluation of phosphate and arsenic adsorption capacity 3.2.1. Synthesis of CeO2 nanomaterials Selection of the sample calcination temperature to form the CeO2 phase  CeO2    o 650 C Intencity (a.u) o 550 C o 450 C o 180 C 20 30 40 50 60 70 80 2 Theta (degree) Figure 3.14. DTA-TGA thermal analysis Figure 3.15. XRD patterns of Ce (NO3)4 gel at diagram of Ce(NO3)4/gelatin different temperatures. Results of DTA thermal analysis diagram from Figure 3.14 and results of XRD analysis calcined at different temperatures in Figure 3.15 of the gel sample Ce(NO3)4/gelatin showed that CeO2 nanomaterials synthesized at temperature 550oC. The effect of pH on gel creation process on the formation of CeO2 phase Results of X-ray diffraction analysis in Figure 3.16 show that pH 3 is the synthetic pH of CeO2 nanomaterials in subsequent studies. Results on XRD diagram of CeO2 nanomaterials synthesized at different gel forming temperatures. The results showed that at gel forming temperatures did not affect the formation of CeO2 phase. The resulting gel-making temperature at 80°C was selected to synthesize the CeO2 nanomaterial. 6
 CeO2    o  pH 4 120 C o 100 C pH 3 Intencity (a.u) Intencity (a.u) o 80 C pH 2 o 60 C pH 1 o 40 C 20 30 40 50 60 70 80 20 30 40 50 60 70 80 2 Theta (degree) 2 Theta (degree) Figure 3.16. XRD diagram of sample CeO2 Figure 3.17. XRD pattern of gel forming nanomaterial at different pH CeO2 nanomaterials at different temperatures Morphology and structure of CeO2 material Results of analysis of CeO2 nanomaterials with TEM images showed that the sample material is relatively uniform in size, has a spherical shape with an average size
Adsorption t (min) Co (mg/l) Cf (mg/l) q (mg/g) performance H(%) 30 10.01 5.52 8.96 10.4 60 10.10 3.72 12.5 62.5 90 9.99 3.45 13.04 65.5 120 10.0 3.45 13.10 65.5 The results of the study in Table 3.7 showed that the phosphate adsorption capacity increases with time and the phosphate adsorption equilibrium time of CeO 2 nano-oxide material at 90 minutes. Effect of pH on phosphate adsorption The results in Figure 3.20 showed that the adsorption of phosphate on CeO2 nanocomposites was highly dependent on the pH value of the solution. pH from 2 to 6.7 phosphate absorption capacity increased from 32.5 mg/g to 45.8 mg/g and pH from 6.7 to 9 phosphate absorption capacity decreased from 45.8 mg/g to 35.1 mg/g. Figure 3.20. Effect of pH on phosphate adsorption capacity on CeO2 nanomaterials Phosphate adsorption capacity by CeO2 nanomaterial Using Table - curve calculation software to regress regression results of phosphate adsorption on CeO2 nanomaterials showed that Qmax = 152.66 mg/g with regression coefficient r2 = 0.99. The adsorption process follows the Langmuir isothermal adsorption equation. Figure 3.21. Isothermal phosphate adsorption lines of CeO2 nanomaterials FT-IR spectrum analysis of CeO2 nanomaterials before and after phosphate adsorption 8
Through FT-IR spectrum results of 1114.47 1146.15 CeO2 nanomaterials, before and after adsorption of phosphate (Figure 3.22a, 3.22b), there were 3480 cm-1 wave numbers 1647.27 Intencity (a.u) a typical for the valence of –OH group on the material surface, 1647 cm-1 wave numbers 2927.82 1058.56 assigned to water molecules (H-O-H) and 1107.23 b wave numbers 1114 cm1-, 1146 cm1- typical for the group - OH associated with the material. In the presence of PO43- on FT - 4000 3500 3000 2500 2000 -1 1500 1000 IR spectrum after phosphate adsorption Number of waves (cm ) material has substituted - OH into a new peak of 1058 cm-1. It is shown that CeO2 Figure 3.22. FT-IR superposition of CeO2 nanomaterial can adsorb phosphate by nanomaterials. b) pre-adsorption of complex mechanism on the surface of the phosphate; a) after phosphate adsorption material. Arsenic adsorption results of CeO2 nanomaterials Investigation of arsenic adsorption equilibrium time of CeO2 nanomaterials The analysis results in Figure 3.23, the relationship between reaction time and arsenic concentration after reaction showed that the adsorption process occurred quickly in the first 90 minutes and reached equilibrium at 120 minutes. Therefore, 120 minutes is taken as the time to reach arsenic adsorption equilibrium for further Figure 3.23. The arsenic concentration remained after studies the reaction over time Effect of pH The results of analyzing the effect of pH on arsenic adsorption capacity on CeO2 nanomaterials are similar to arsenic adsorption on La2O3 nanomaterials. When the pH value changes from 2 to 6.7, the arsenic adsorption capacity of the material increases and the adsorption capacity decreases when the pH is from 6,7 to Figure 3.24. Effect of pH on arsenic 9 adsorption Determining the maximum arsenic adsorption capacity of CeO2 nanomaterials 9
Using Table - curve calculation software to regress regression results of arsenic adsorption on CeO2 nanomaterials showed that Qmax = 45.07 mg/g with regression coefficient r2 = 0.99. The adsorption process follows the Langmuir isothermal adsorption equation. Figure 3.25. Arsenic isothermal adsorption lines of CeO2 nanomaterials 3.3. Synthesis of La2O3-CeO2 mixed-oxides nanomaterials and evaluation of phosphate and arsenic adsorption capacity 3.3.1. Synthesis of nano materials La2O3-CeO2. Results of thermal analysis for selection of sample calcination temperature Figure 3.26. Thermal analysis diagram of Figure 3.27. X-ray diffraction diagram of gel gen sample La(NO3)3-Ce(NO3)4/gelatin sample La(NO3)3-Ce(NO3)4/Gelatin at different temperatures Results of DTA thermal analysis diagram from Figure 3.26 and results of XRD analysis at different temperatures in Figure 3.27 of the La(NO3)3-Ce NO3)4 gel sample, the La2O3-CeO2 nanomaterial was synthesized at 550oC. Effect of pH and gel forming temperature on the formation of La2O3-CeO2 phase Figure 3.28. The XRD diagram of the Figure 3.29. XRD diagram of nano sample (La2O3-CeO2) was made at different material La2O3-CeO2 sample was synthesized gel forming temperatures. at different pH. The results of X-ray diffraction analysis in Figure 3.29 showed that pH 4 is the synthetic pH of La2O3-CeO2 nanomaterials in subsequent studies.. 10
Results on the XRD patterns of nano materials La2O3-CeO2 made at different gel forming temperatures in Figure 3.28, gel forming temperature at 80°C were selected to synthesize La2O3-CeO2 nanomaterials. Investigate the metal ratio on gelatin to the process of forming La2O3-CeO2 phase The process of studying the effect of molar metal to gelatin ratio, The author conducted the molar ratio of La(NO3)3/Ce(NO3)4, which is 1/1, molar ratio (La(NO3)3 - Ce(NO3)4) / gelatin, respectively. 1/2; 1/3; 1/1; 2/1; 3/1. The author chose the ratio (La(NO3)3-Ce(NO3)4)/gelatin as 1/1 for further research. Figure 3.30. The XRD patttern of metal-to-metal (La2O3-CeO2)/gelatin at different ratios Morphology of nano materials La2O3-CeO2 Results of characteristic morphological analysis of surface of nanomaterials La2O3 - CeO2 by TEM image showed that the material has a spherical shape with relatively uniform size
a) b) Figure 3.33. X-ray scattering spectrum (EDS) of nano-material La2O3-CeO2 a) before and b) after phosphate adsorption Results of X-ray scattering (EDS) analysis of La2O3-CeO2 nanomaterials before and after adsorption are all presented with La, Ce and O components. Results of X-ray scattering (EDS) analysis of La2O3-CeO2 nanomaterials before phosphate adsorption did not show the presence of phosphate. Materials after adsorption of phosphate showed P and O appearances, as a result of phosphate adsorption on the surface of La2O3-CeO2 nanomaterials. Results of FT-IR spectrum analysis of La2O3-CeO2 materials before and after phosphate adsorption FT-IR analysis of La2O3-CeO2/gelatin nanomaterials before phosphate adsorption was found to have wave values of 3421 cm-1 assigned to the covalent oscillation characteristic of – OH. The peak at 1118 cm-1 is assigned to the –OH group valence oscillation associated with La2O3-CeO2 nanomaterials, when PO43- adsorbed, the Figure 3.34. FTIR of nano-materials material has a new characteristic peak for PO43- -1 La2O3-CeO2.a) before adsorption; b) after instead of - OH at 1060 cm . phosphate adsorption Raman spectrum of nano-material La2O3-CeO2 before and after phosphate adsorption 12
Figure 3.35 showed Raman analysis results of La2O3-CeO2 nanomaterials before and after phosphate adsorption. the figure showsed that Raman spectra before adsorption of phosphate, the materials have peaks of 1510 cm-1 and 1350 cm-1, which are typical for group oscillation of -OH on material surface. Materials after adsorption of phosphate indicated that peaks of 1045 cm-1 and 1058 cm-1 are new characteristic for phosphate elements, proving that the materials have Figure 3.35. Raman spectrum of nano materials the ability to adsorb phosphate on the La2O3-CeO2 a) before adsorption; b) after surface of the materials.. phosphate adsorption Characteristics of La2O3-CeO2 nano materials when arsenic adsorption X-ray scattering spectrum (EDS) of La2O3-CeO2 nanomaterials before and after arsenic adsorption a) b) Figure 3.36. EDX spectrum of nano materials La2O3-CeO2 a) before adsorption; b) after arsenic adsorption Results of X-ray scattering spectroscopy (EDS) in Figure 3.36 of La2O3-CeO2 nanomaterials before and after adsorption are all present with La, Ce and O components. Results of X-ray scattering (EDS) analysis of La2O3-CeO2 nanomaterials before arsenic adsorption were not found in the presence of arsenic. Materials after arsenic adsorption see arsenic appeared in Figure 3.36b. FT-IR analysis results of La2O3-CeO2 nanomaterials before and after arsenic adsorption 13
FTIR analysis results of materials before and after arsenic adsorption are shown in Figure 3.37. Material La2O3-CeO2 before and after adsorption appears with peaks at 3421 cm-1 and 3321 cm-1, which is typical for the valence of the group - OH of water on the surface of the material. The peaks at 1639 cm-1, 1464 cm-1, which are specific for the H - O - H group valence oscillation associated with the material. The peaks at 1118 cm-1, 1067 cm-1 typical for group oscillation - OH associated with nano-material La2O3-CeO2 (MOOH Bonding with metals La and Ce) Figure 3.37. FT-IR spectrum of nano materials (La3+ -Ce4+)/gelatin b) before arsenic adsorption, a) after arsenic adsorption Raman spectrum of La2O3-CeO2 nano-mixed oxides material before and after arsenic adsorption Figure 3.38 showed the Raman analysis results of La2O3-CeO2 nanomaterials before and after arsenic adsorption. In Figure 3.38b, the material has peaks of 1008, 1088, 1350, 1510 and 1448 cm-1 which is typical for H - O - H and - OH oscillations. Materials after adsorption of arsenic found that the material has a new peak peak of 831 cm-1 which is explained Hình 3.38. Phổ Raman của vật liệu nano La2 O3 -CeO2 b) trước hấp phụ; a) sau hấp by the replacement of group - OH by phụ asen group - O - As on the surface of the material. 3.3.3. Results of adsorption of phosphate and arsenic of nanomaterial La2O3-CeO2 Phosphate adsorption results of La2O3-CeO2 nanomaterials Phosphate adsorption equilibrium time Table 3.9. Effect of phosphate adsorption equilibrium time by nanomaterial La2O3-CeO2 t (min) Co (mg/L) Cf (mg/L) q (mg/g) 30 9.99 3.41 10.08 60 10.02 3.41 10.08 90 10.05 3.06 11.88 120 10.02 3.06 11.88 Table 3.9 showed that the phosphate adsorption capacity increases with the first 60 minutes, at 90 minutes and 120 minutes the phosphate adsorption capacity of La2O3-CeO2 14
nanomaterials changes insignificantly. Therefore, the adsorption equilibrium time is 90 minutes, which is used to study the later experiments Effect of pH on phosphate adsorption capacity The results shown in Figure 3.39 show that the adsorption of phosphate on La2O3-CeO2 nanomaterials is highly dependent on the pH value of the solution. In the pH range of 2 to 5.8, the phosphate adsorption capacity increases. When the pH is between 5.8 and 9, the phosphate adsorption Figure 3.39. Effect of pH on phosphate capacity decreases adsorption capacity on La2O3-CeO2 nanomaterials Effect of initial phosphate concentration on the adsorption capacity of La2O3-CeO2 nanomaterials Using Table - curve calculation software to regress regression results of phosphate adsorption on nanomaterials La2O3-CeO2 showed that Qmax = 123.74 mg/g with regression coefficient r2 = 0.98. The adsorption process follows the Langmuir isothermal adsorption equation Figure 3.40. Phosphorus adsorption isotherm of nanomaterials La2O3-CeO2 Results of evaluating the influence of competitive factors on phosphate adsorption of nano- materials La2O3-CeO2. Table 3.10. Effect of Fe(III), Mn(II), SO42-, Cl- on phosphate adsorption capacity on nano- materials La2O3-CeO2 Concentration (mg/L) 0 10 20 30 - 1 Fe(III) Adsorption capacity phosphate q 49.64 55.27 62.51 67.34 (mg/g) Concentration (mg/L) 0 0,5 1,0 5 - 2 Mn(II) Adsorption capacity phosphate q 49.64 64.12 65.73 68.14 - (mg/g) Concentration (mg/L) 0 50 100 200 250 2- 3 SO4 Adsorption capacity phosphate q 47.76 47.66 47.66 47.66 47.66 (mg/g) Concentration (mg/L) 0 100 150 200 250 - 4 Cl Adsorption capacity phosphate q 49.64 44.53 40.25 33.83 31.69 (mg/g) 15
The results in Table 3.10 showed that when Fe(III) concentration increases, the ability of phosphate adsorption of materials increased. Similarly, the effect of Fe(III), when Mn(II) concentration increases, the material ability to adsorb phosphate increased. For SO42- the results in table 3.10 showed that increasing SO4 2- concentration did not significantly affect the phosphate adsorption capacity of the material. Regard to Cl- ion, the results in the table 3.10 showed that, when the Cl- concentration increased, the phosphate adsorption capacity of the material decreased. Kinetic modeling of phosphate adsorption Figure 3.41. a) First order kinetic odsorption; b) The second order kinetic of phosphate adsorption on nanomaterial La2O3-CeO2 Table 3.11. Some parameters of the first order kinetic equation of phosphate adsorption on nanomaterial La2O3-CeO2 Concentration First order reaction photphat (mg/l) k1 (min-1) R2 χ2 qtn (mg/g) qlt (mg/g) 5 2.16 ×10-2 0.952 0.0169 9.4 4.58 -2 10 2.99 ×10 0.934 0.0153 17.04 3.98 Table 3.12. Some parameters of the second order kinetic equation of phosphate adsorption on nanomaterials La2O3-CeO2 Concentration Second order reaction photphat (mg/l) k2 (g/mg.phút) R2 χ2 qtn (mg/g) qlt (mg/g) 10 4.67×10-2 0.999 0.1 9.4 10.00 -2 10 1.51×10 0.999 0.05 17.04 17.54 Research results of phosphate adsorption kinetics in Table 3.11 (first-order kinetic model) and Table 3.12 (second-order kinetic models) find that the correlation value R2 = 0.999 of the second-order kinetic model larger than the first order kinetic model with R2 = 0.952 and R2 = 0.934 with this thesis conditions. Thus, phosphate adsorbed on nanomaterial La2O3-CeO2 follows the apparent second-order kinetic equation. Arsenic adsorption results of nano materials La2O3-CeO2 Effect of arsenic adsorption equilibrium time by nano-material La2O3-CeO2 16
Analysis results showed in Figure 3.42, the relationship of reaction time and arsenic concentration after reaction showed that the adsorption process occurred quickly in the first 90 minutes and reached equilibrium at 120 minutes. Figure 3.42. The concentration of arsenic and reaction time Effect of pH on arsenic adsorption The analysis of the effect of pH on arsenic adsorption capacity on nano materials La2O3-CeO2 found that when the pH increased from 2 to 5.8 arsenic adsorption capacity on the material increased from 18.4 mg/L to 19.52 mg/L and the adsorption capacity decreased from 19.52 mg /L to 12.4 mg/L at pH values from 5.8 to 9. Figure 3.43. Effect of pH on arsenic adsorption capacity Arsenic adsorption capacity by nanomaterial La2O3-CeO2 Using Table-curve calculation software to regress regression results of arsenic adsorption on La2O3-CeO2 nanomaterials. The result showed that Qmax = 90.06 mg/g with regression coefficient r2 = 0.99. The adsorption process follows the Langmuir isothermal adsorption equation Figure 3.44. Arsenic adsorption isotherm of nanomaterials La2O3-CeO2 Results of evaluating the interference ion on arsenic adsorption process of the material. Table 3.13. Effect of Fe(III), Mn(II), SO42-, Cl- on arsenic adsorption capacity nano materials La2O3-CeO2 Concentration (mg/L) 0 5 7 10 - 1 Fe(III) Adsorption capacity q (mg/g) 1.76 1.82 1.94 2.04 17
Concentration (mg/L) 0 5 7 10 - 2 Mn(II) Adsorption capacity q (mg/g) 1.76 1.82 1.90 2.02 - Concentration (mg/L) 0 50 100 200 150 3 SO42- Adsorption capacity q (mg/g) 1.76 1.76 1.76 1.74 1.74 Concentration (mg/L) 0 50 100 250 - 4 Cl- Adsorption capacity q (mg/g) 1.76 1.45 1.12 1.02 - The results of table 3.13 showed that when the concentration of Fe(III) changed from 0 to 10 mg/L, the arsenic adsorption capacity of nanomaterial La2O3-CeO2 increased from 1.76 mg/g to 2.04 mg/g. For Mn (II), when the concentration of Mn (II) was increased, the arsenic adsorption capacity of La2O3-CeO2 nanomaterial also increased. This phenomenon is because Mn (II) in the solution can oxidize As (III) to As (V) which is better adsorption on materials. With ion SO42- the result in table 3.13 showed that arsenic adsorption capacity decreases with increasing concentration SO42- but the concentration is negligible. Thus, ion SO42- does not significantly affect the arsenic adsorption capacity in the range of used concentration. The results of table 3.13 also showed that Cl- ion interfere arsenic adsoption capacity of material. The Cl- concentration increases from 0 to 250 mg/L reduced the arsenic adsorption capacity of La2O3-CeO2 nanomaterial from 1.76 mg/g to 1.02 mg/g. Arsenic adsorption kinetics Kinetic model of arsenic adsorption Figure 3.45. a) First order kinetics graph of Figure 3.45. b) The second order kinetic model of arsenic adsorption on nanomaterials La2O3- arsenic adsorption on nanomaterials La2O3-CeO2 CeO2 Table 3.14. Parameters of the first order kinetic equation of arsenic adsorption on La2O3-CeO2 nanomaterials Concentration First order reaction -1 2 asen (mg/l) k1 (min ) R χ2 qtn (mg/g) qlt (mg/g) -2 5 2.76×10 0.967 0.014 9.48 3.90 -2 10 4.15×10 0.978 0.017 1.99 7.36 Table 3.15. Parameters of the quadratic kinetic equation of arsenic adsorption on La2O3-CeO2 nanomaterials Concentration Second order reaction 18