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“Optimization in the Treatment of Spent Pot Lining - a Hazardous Waste Made Safe”

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“Optimization in the Treatment of Spent Pot Lining - a Hazardous Waste Made Safe” A M.TECH THESIS ON “optimization in the treatment of Spent pot Lining - A Hazardous Waste Made Safe” MASTER OF TECHNOLOGY IN Chemical Engineering SUBMITTED BY Pankaj D. Indurkar Roll No. 212CH1074 Under the Supervision of Prof. Pradip Rath NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA 2013-2014 DEPARTMENT OF CHEMICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA CERTIFICATE This is to certify that the Project report entitled, “Optimization in the treatment of Spent Pot Lining - A Hazardous Waste Made Safe” submitted by Pankaj D. Indurkar, Roll No. 212CH1074 for the award of the Master of Technology Degree in Chemical Engineering at National Institute of Technology, Rourkela is prepared by him under my supervision and guidance. Date: Prof. Pradip Rath (Supervisor) ACKNOWLEDGEMENT I feel great pleasure in expressing my deepest sense of gratitude and sincere thanks to my guide Prof. Pradip Rath for his valuable guidance and grandeur during the project work, which it would have been very difficult task. I have no words to express my sincere thanks for valuable guidance, extreme assistance and cooperation extended to all the Teaching Staff Members of my Department. This acknowledgement would be incomplete without expressing my special thanks to Prof. R. K. Singh Head of Chemical Department for his support during the work. Last but not least I would like to thanks all the Non-Teaching staff members of the department and my colleague‘s friends those who helped me directly or indirectly for completing of this seminar successfully. Date: Mr. Pankaj D. Indurkar Roll No. 212CH1074 CONTENTS List of figure List of table Abbreviations Abstract Page No. CHAPTER 1: INTRODUCTION 1 1.1 Some facts about Aluminium 1 1.2 Spent Pot Lining (SPL) 2 1.3 Manufacture of Pure Alumina 2 1.4 Electrolysis of Alumina 3 1.5 Chemistry 5 1.6 Spent Pot Liner Waste Challenges 6 1.7 Objective of the project 7 1.7.1 Specific objective 7 CHAPTER 2: LITERATURE REVIEW 8 2.1 Thermal processes 9 2.2 Chemical processes 10 2.3 Rio Tinto Alcan—LCL&L Process 11 2.4 Alternate Processes to Primary Aluminium Smelting (Emerging Technologies) 12 2.5 Industrial use of SPL 13 2.5.1 Cement kiln 13 2.5.2 Pig iron and steel 14 2.5.3 Mineral Wool 14 2.5.4 Co-Processing SPL with Salt Slags 14 2.5.5 Ferro Alloys 15 2.5.6 Special products of 2nd cut 15 CHAPTER 3: MATERIALS AND METHODS 16 3.1 Materials 16 3.1.1 Instruments and its purpose 16 3.1.2 Chemicals used 17 3.2 Methods 17 3.2.1 Collection of sample 17 3.2.2 Experimental design 18 3.2.2.1 Definition of Experiment design 18 3.2.2.2 Objective of experimental designing 18 3.2.3 Conventional approach of optimization 18 3.2.4 Design of experiments by Taguchi method for optimization 18 3.2.4 Design of experiment by Response Surface Methodology 19 3.2.5 Leaching experiments 20 3.2.5.1 Cryolite precipitation 20 3.3 Characterization of spent pot liner 21 3.3.1 Thermo gravimetric Analysis (TGA) / DSC 21 3.3.2 XRD analysis 21 3.3.3 Ultimate and Proximate analysis 21 3.3.3.1 Moisture content 21 3.3.3.2 Volatile matter 22 3.3.3.3 Fixed carbon content 22 3.3.4 SEM-EDX analysis 22 3.3.5 Calorific value analysis 22 CHAPTER 4: RESULTS AND DISCUSSION 23 PART 1 4.1 Taguchi optimization of NaOH fallowed by HClO4 23 4.1.1 Treatment of sample 23 4.1.2 Alkali leaching 23 4.1.3 Acid leaching 23 4.1.4 Analysis of the S/N ratio 25 4.1.5 Analysis of variance 27 4.2 Classical approach of optimization for NaOH fallowed by HClO4 28 4.2.1 Effect of alkali concentration 28 4.2.2 Effect of acid concentration 29 4.2.3 Effect of L/S ratio 30 4.2.4 Effect of temperature 31 4.2.5 Cryolite precipitation 32 4.3 Characterization of raw and treated sample 33 4.3.1 Thermo gravimetric Analysis/DSC 33 4.3.2 XRD analysis 35 4.3.3 Ultimate and Proximate analysis 35 4.3.4 Particle size analysis by DLS 36 4.3.5 SEM- EDX analysis 37 4.3.6 Calorific value analysis 41 4.4 Response Surface Methodology of NaOH fallowed by HClO4 41 4.4.1 Analysis of variance 44 4.4.2 Contour Plot and Surface plot 46 4.4.3 Residual plot 58 PART 2 4.5 Taguchi optimization of NaOH fallowed by H2SO4 49 4.5.1 Analysis of the S/N ratio 50 4.5.2 Analysis of variance 51 4.6 Classical approach of optimization of NaOH fallowed by H2SO4 52 4.6.1 Effect of alkali concentration 52 4.6.2 Effect of acid concentration 53 4.6.3 Optimization of L/S 53 4.6.4 Optimization of temperature 54 4.6.5 XRD analysis 55 4.6.6 Cryolite precipitation 56 4.6.7 Proximate analysis 58 4.6.8 Calorific value analysis 58 CHAPTER 5: CONCLUSION 59 5.1 Future recommendations 60 CHAPTER 6: REFERENCES 61 LIST OF FIGURES Figure No. Figure caption Page no. Figure 1.1 Flow sheet of the Bayer process 2 Figure 1.2 Hall-Heroult Cell With process Flow Diagram 4 Figure 2.1 Spent pot linings 9 Figure 2.2 Rio Tinto Alcan—LCL&L simplified flow sheet. 11 Figure 4.1 Main effect plot for SN ratios 26 Figure 4.2 Contour plot of leaching percentage vs. alkali content, temperature 26 Figure 4.3 Contour plot of leaching percentage vs. L/S ratio, alkali concentration 27 Figure 4.4 Influence of alkali concentration on leaching percentage 29 Figure 4.5 Influence of acid concentration on leaching percentage 30 Figure 4.6 Influence of L/S on leaching percentage 31 Figure 4.7 Influence of temperature on leaching percentage 32 Figure 4.8 XRD analysis of fluoride precipitation at pH value of 9.5 32 Figure 4.9 XRD analysis of fluoride precipitation at pH value of 4.5 33 Figure 4.10 TGA under N2 flow 34 Figure 4.11 TGA under O2 flow 34 Figure 4.12 XRD analysis of Raw SPL, Treated SPL with NaOH and treated SPL 35 with NaOH fallowed by HClO4 Figure 4.13 Particle size analysis of raw SPL 36 Figure 4.14 SEM-EDX images of raw SPL 37 Figure 4.15 SEM-EDX images of water wash SPL 38 Figure 4.16 SEM images Raw SPL sample burned at 7500C for 1.5h and at 800 0C 39 Figure 4.17 SEM images of alkali treatment SPL at 1.5 M NaOH 40 Figure 4.18 SEM images of alkali followed by acid treatment SPL1.5 40 MNaOH+2.5M HCLO4 Figure 4.19 Contour plot of leaching percentage vs acid concentration L/S ratio & 46 Contour plot of leaching percentage vs alkali concentration, temperature Figure 4.20 Surface plot for leaching percentage vs acid concentration, alkali 47 concentration & Surface plot for leaching percentage vs acid concentration, L/S ratio Fgure 4.21 Surface plot for leaching percentage vs acid concentration, 47 temperature Figure 4.22 Residual plot for leaching percentage 48 Figure 4.23 Main effect plot for SN ratio 51 Figure 4.24 Effect of alkali concentration on leaching percentage 52 Figure 4.25 Influence of acid concentration on leaching percentage 53 Figure 4.26 Influence of L/S on leaching percentage 54 Figure 4.27 Influence of temperature on leaching percentage 55 Figure 4.28 XRD analysis of raw SPL, Alkali treated SPL, and treated SPL with 56 NaOH Fallowed by H2SO4 samples Figure 4.29 XRD analysis of fluoride precipitation at pH value of 9.5 57 Figure 4.30 XRD analysis of fluoride precipitation at pH value of 4.5 57 LIST OF TABLES Table no. Table caption Page no. Table 2.1 SPL typical components and concentration 8 Table 3.1 Instrument and its purpose 16 Table 3.2 Taguchi 4 factors 4 levels 19 Table 3.3 Ranges of experimental parameters 20 Table 4.1 Taguchi design of NaOH fallowed by HClO4 24 Table 4.2 Response Table for Signal to Noise Ratios 25 Table 4.3 Analysis of variance of SN ratio 28 Table 4.4 Proximate analysis of SPL samples 35 Table 4.5 Ultimate analysis of SPL samples 36 Table 4.6 Calorific values of Samples 41 Table 4.7 The central composite design with four independent variables 42 and experimental leaching percentage Table 4.8 Regression coefficient, p or probability for leaching percentage 43 Table 4.9 ANOVA for leaching percentage using Adjusted Sum of 45 Squares (SS) for tests Table 4.10 Taguchi design of NaOH fallowed by H2SO4 52 Table 4.11 Response Table for Signal to Noise Ratios 50 Table 4.12 Analysis of variance for SN ratio 52 Table 4.13 Proximate analysis of SPL samples 58 Table 4.14 Calorific value of raw SPL to treated SPL with H2SO4 58 ABBREVIATIONS SPL- Spent Pot Liner ANOVA-Analysis of Variance CHNS-Carbon, Hydrogen, Nitrogen, Sulfur L/S Ratio- Liquid to Solid Ratio RSM- Response Surface Methodology SEM- Scanning Electron Microscope EDX- Energy Dispersive X-ray TGA- Thermo-Gravimetric Analysis XRD- X-ray Diffraction GCV- Gross Calorific Value DSC- Differential scanning calorimetry LIST OF SYMBOLS x1 - Acid concentration x2 - Alkali concentration x3 - L/S ratio x4 - Temperature S- Response variable R2 - amount of variation in the observed response values ABSTRACT The increase in demand of aluminium leads to production of more Spent Pot Lining as well as more environmental problems.
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