Nội dung

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 La2O3CeO2 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 sol - gel combustion method using gelatin Figure 2.5. Synthesizing nanomaterials on laterite Intencity (a.u) 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. o 560 C o 550 C o 450 C o 180 C 30 40 50 60 2 Theta (degree) 70 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  Intencity (a.u) Intencity (a.u) pH 4  pH 3 80oC 60oC 40oC pH 2 35 35 40 45 50 55 2 Theta (degree) 60 65 70 Figure 3.3. The XRD diagram of the La2O3 nanomaterial sample was synthesized at 40 45 50 55 2 Theta (degree) 60 65 70 Figure 3.4. XRD diagram of nanomaterial 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 equilibrium time by nano-material La2O3 Figure 3.8. Effect of pH on phosphate 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 Using Table-curve calculation software to regress the experimental results of phosphate adsorption of nanomaterial La2O3 with Qmax = 210.05 mg/g with regression coefficient r2 = 0.96. 200 200 150 150 100 100 Dung lượng hấ p phụ phố t phát q (mg/g) 250 50 50 0 0 50 100 Dung lượng hấ p phụ phố t phát q (mg/g) 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 0 150 Nồng độ ion phốt phát còn lại Cf (mg/l) Intencity (a.u) 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 La2O3 nanomaterials before and after 1107.01 1479.75 phosphate adsorption. The appearance of 3608.06 a the peak at 3608 cm-1 specific to the 1426.66 covalent oscillation of the group – OH 1049.24 1481.61 on the surface of the material and the peaks at 1066 cm-1, 1107 cm-1 specific to 3608.06 b the group fluctuations of –OH bonded with material. When the presence of 4000 3500 3000 2500 2000 1500 1000 -1 PO43- occurred, new featured peak for Number of waves (cm ) 3Hình 3.10. Phổ FT-IR của vật liệu nano La2O3. PO4 replacement -OH group is formed at 1049 cm -1. a) trước hấp phụ; b) sau hấp phụ photphat 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 Intencity (a.u) 650 C o 550 C o 450 C o 180 C 20 Figure 3.14. DTA-TGA thermal analysis diagram of Ce(NO3)4/gelatin 30 40 50 2 Theta (degree) 60 70 80 Figure 3.15. XRD patterns of Ce (NO3)4 gel at 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 120 C pH 4 o 100 C Intencity (a.u) Intencity (a.u) pH 3 pH 2 o 80 C o 60 C pH 1 o 40 C 20 30 40 50 60 2 Theta (degree) 70 80 20 Figure 3.16. XRD diagram of sample CeO2 nanomaterial at different pH 30 40 50 60 2 Theta (degree) 70 80 Figure 3.17. XRD pattern of gel forming CeO2 nanomaterials at different temperatures Morphology and structure of CeO2 material nh 8. Ảnh E của m u vật liệu nano CeO2 The zero-charge point of nanomaterial CeO2 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 <30 nm. The material has many hollow structure. The specific surface area of CeO2 nanomaterials was determined by the BET method which was obtained with value of 56.1 m2/g. The results obtained in Figure 3.19 were CeO2 nanomaterials with pHpzc value of 6.7. Figure 3.19. The zeta potential of CeO2 nanomaterials 3.2.2. Evaluate the phosphate and arsenic adsorption on CeO2 nanomaterials Results of adsorption of phosphate material to nano CeO2 Phosphate adsorption equilibrium time with CeO2 nanomaterials Table 3.7. Effect of phosphorus adsorption equilibrium time by CeO2 nanomaterials. 7 t (min) Co (mg/l) Cf (mg/l) q (mg/g) Adsorption 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