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Removal of Zinc Ions from Model Wastewater by Electrocoagulation

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Removal of Zinc Ions from Model Wastewater by Electrocoagulation Graduate Theses, Dissertations, and Problem Reports 2017 Removal of Zinc Ions from Model Wastewater by Electrocoagulation Xiujuan Chen Follow this and additional works at: https://researchrepository.wvu.edu/etd Recommended Citation Chen, Xiujuan, "Removal of Zinc Ions from Model Wastewater by Electrocoagulation" (2017). Graduate Theses, Dissertations, and Problem Reports. 5352. https://researchrepository.wvu.edu/etd/5352 This Thesis is protected by copyright and/or related rights. It has been brought to you by the The Research Repository @ WVU with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you must obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in WVU Graduate Theses, Dissertations, and Problem Reports collection by an authorized administrator of The Research Repository @ WVU. For more information, please contact [email protected]. Removal of Zinc Ions from Model Wastewater by Electrocoagulation Xiujuan Chen Thesis submitted to Benjamin M. Statler College of Engineering and Mineral Resources at West Virginia University in partial fulfillment of the requirements for the degree of Master of Science in Material Science and Engineering Xingbo Liu, Ph.D., Chairperson and Advisor Konstantinos A. Sierros, Ph.D. Jason P. Trembly, Ph.D. Material Science and Engineering Program Department of Mechanical and Aerospace Engineering Morgantown, West Virginia 2017 Keywords: Wastewater treatment, metals removal, electrocoagulation, Al electrodes Copyright 2017, Xiujuan Chen Abstract Removal of Zinc Ions from Model Wastewater by Electrocoagulation Xiujuan Chen This study has investigated the removal of zinc ions from the synthetic wastewater models by electrocoagulation (EC) with aluminum for both cathode and anode. The results showed that EC process had a great removal when it comes to zinc contaminated water. The effects of parameters on the EC performance have been systematically investigated, such as solution conductivity, electrode spacing, initial pH, current density and initial zinc concentration. Since the wastewater in real situations usually contains several types of metals, a series of mixed cases were also studied in this work. The results indicated that current density is critical to EC performance, in terms of the removal efficiency and energy consumption. The basic conductivity of the solution is required to decrease the EC voltage. It was demonstrated that the neutral pH is favorable for zinc removal by EC process, while the effect of electrode spacing on EC performance was not significant in this case. With a relatively low energy consumption of 0.35 kWh/m3, more than 99.5% of zinc ions were removed from the synthetic wastewater (zinc concentration 50 mg/L) within 20 min. Later with an energy consumption of 0.88 kWh/m3, highly similar removal efficiency has been achieved at zinc concentration of 250 mg/L at EC time of 50 minutes. The kinetic study for zinc removal was performed to describe the adsorption system during EC process. The results show that the removal of zinc ions by EC process follows the first-order model with current-dependent parameters. Additionally, the removal of zinc ions fitted well with the first order model at related low initial concentration, and fitted well with the pseudo-first order model at high initial concentrations. Different mechanisms of zinc removal were implied by comparing the results of the low initial concentration (≤ 250 mg/L) and the high one (≥ 500 mg/L). It was reasonable to conclude that, beside the co-precipitation effect of the aluminum hydroxides coagulants, the reduction of zinc ions at the cathode also contributed to the zinc removal, especially at a high initial concentration. The different removal pathways of metal ions usually exist at high initial concentrations of metal ions and alkaline pH medium. Acknowledgement First of all, I would like to thank my advisor Dr. Xingbo Liu for his continuous and careful guidance during my last two years here at West Virginia University. Without his effort, I could not have come so far. I would like to thank my committee members, Dr. Konstantinos A. Sierros and Dr. Jason P. Trembly, for their time to improve my research. Thank Dr. Weiqiang Ding, Dr. Qiang Wang and Dr. Redigolo from WVU Shared Facilities, Ms. Gabriela Perhinschi from NRCCE, for helping with the testing and analysis. Thank the cheerful members in Dr. Liu’s research group, Dr. Wenyuan Li, Dr. Greg Collins, Bo Guan, Meng Yao, Panpan Ren, Shanshan Hu, Zhipeng Zeng, Haiyang Li, He Qi and Nan Zhang, who always inspire and encourage me to go further. At the end, I would like to thank my husband Changle Jiang and my entire family. Without their support, I would not be able to finish my study here at Morgantown. iii Table of Contents List of Figures ............................................................................................................................... vi List of Tables ................................................................................................................................ ix 1. Introduction ........................................................................................................................... 1 1.1 Electrocoagulation .......................................................................................................... 1 1.2 Theoretical Background ................................................................................................ 2 1.2.1 General Theory of Electrocoagulation ...................................................................... 3 1.2.2 Aluminum Speciation ............................................................................................... 4 1.2.3 Iron Speciation .......................................................................................................... 7 1.2.4 Key Parameters for EC Process ................................................................................ 9 1.2.5 Current Density ......................................................................................................... 9 1.2.6 pH ............................................................................................................................ 10 1.3 Comparison of Electrocoagulation and Chemical Coagulation ............................... 10 1.4 Advantages and disadvantages of electrocoagulation ............................................... 11 1.5 Electrocoagulation for Heavy Metal Removal........................................................... 13 1.5.1 Heavy Metal Contaminations ................................................................................. 13 1.5.2 Current Technology for Heavy Metals Removal .................................................... 13 1.5.3 Research Goal ......................................................................................................... 14 2. Experimental Sections and Characterizations .................................................................. 15 2.1 Model Water Preparation ........................................................................................... 15 2.2 Device Setup .................................................................................................................. 15 2.3 Sampling ........................................................................................................................ 15 2.4 Characterizations ......................................................................................................... 16 3. Effect of Reactor and Water Matrix Parameters on Metal Ions Removal .................... 18 3.1 Reactor Parameters...................................................................................................... 18 3.1.1 Effect of Current Density on EC Performance ....................................................... 18 3.1.2 Effect of Electrode Spacing on EC Performance .................................................... 23 3.1.3 Effect of Electrodes Arrangement on EC Performance .......................................... 24 3.2 Water Matrix Parameters ........................................................................................... 25 3.2.1 Effect of Solution Conductivity on EC Performance ............................................. 25 3.2.2 Effect of Initial Solution pH on EC Performance ................................................... 27 3.2.3 Effect of Initial Concentration of Zinc on EC Performance ................................... 28 iv 3.3 Water Matrix Composition ......................................................................................... 29 3.3.1 Removal of Strontium by EC .................................................................................. 29 3.3.2 Mixed Contaminant Removal (Zn, Cu, Fe, Mn, Mg, Ca, Ba and Sr) ..................... 32 3.4 Energy consumption .................................................................................................... 34 4. Kinetic Study and Removal Mechanism ........................................................................... 35 4.1 Kinetic Modeling .......................................................................................................... 35 4.1.1 Kinetic Modelling at Different Current Densities .................................................
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