중금속 존재형태 및 광물학적 특성을 고려한 중금속오염 토양정화의 새로운 접근 = A new approach for enhanced remediation of metals-contaminated soil considering fractionation and mineralogy

다국어 초록 (Multilingual Abstract)

In this study, soil washing process based on the fractionation and mineralogy characteristics of heavy metals was developed in order to enhance the technical, economic, and environmental efficiencies. This study was composed as follows: (1) literature investigation in soil washing process provided with the information of site and metal characteristics as well as the process efficiency, (2) determination of metal extraction characteristics based on fractionation and mineralogy of metals, (3) applicability assessment of those extraction mechanisms using field soils, (4) proposal of screening matrix using parameters influencing on chemical extraction efficiency.
As a results of literature investigation related to chemical extraction in washing process for metal-contaminated soils with Cu, Pb, Zn, and As, it was found that soil texture, soil organic matter, contamination source, fractionation and mineralogy of metals, and washing conditions include type/concentration of washing agents highly influenced to the process efficiency in technical. However, it was difficult to confirm determining the parameters influenced on the chemical extraction efficiency because most of the literatures did not provide the same information of soil and contaminants. Among them, the type/concentration of washing agents as well as the fractionation/mineralogy of heavy metals as the contamination sources and site characteristics highly influenced to efficiency of the process. Therefore, the selection of the process conditions as well as the understand of site/metal characteristics are important to enhance the efficiency of the process.
Furthermore, two types of washing processes were carried out to determine metal extraction characteristics, which was representatively conducted for Pb. In the washing process to evaluate extraction characteristics of Pb presented in labile forms and Pb minerals from Pb-contaminated artificial and field soil samples, at first ferric iron based extractants include FeCl3 and Fe(NO3)3 did significantly enhance the Pb extraction from soils. These extractants could be used as an extracting agent for labile Pb in soils and PbO, PbCO3, Pb3(CO3)2(OH)2, and Pb5(PO4)3(OH) having a high solubility through ion exchange between Pb and hydrogen ions produced by dissociation of water molecule. In particular, ferric iron ions remained in solution during the washing process repeatedly produced the hydrogen ions which continuously extracted Pb into solution from soils. Futhermore, they could be used as an oxidizing agent for PbS through redox reaction between ferric iron and sulfide. FeCl3 was the most an applicable extractant to remediate contaminated marine sediment with Cu and Zn because of the unique characteristics include a high proportion of carbonates, organic matter and sulfides of marine sediment compared with inland soil. Cu was associated with organic matter and sulfides, which could be extracted by FeCl3 through redox reaction between ferric iron and sulfide and the complexation between organic matter and Fe instead of Cu. The labile Zn presented in the sediment was extracted by repeatedly ion exchange with hydrogen ions during the washing process. Actually, the excessive use of inorganic acids was effective to extract Cu and Zn. However, they induced a severe solution and sediment acidification, which contributed in a significant increase of agent costs in neutralizing wastewater and sediment.
Finally, we proposed a chemical extraction screening matrix on washing process to provide washing guideline as the characteristics of soil and contaminant through literature investigation for influencing parameters in chemical extraction. Based on the screening matrix, in addition chemical extraction process using twelve types of metal-contaminated soils with Cu, Pb, Zn, and As formed in various contamination sources was conducted and evaluated the applicability of screening matrix. There were a significant positive tendency between the extraction efficiency and metal/site characteristics which are matched with literatures. However, the characteristics of the soils and heavy metals investigated in the literature were inconsistent with most soil samples used in this study. Therefore, it will be necessary to continuously conduct literature investigations related to the characteristics of soils and heavy metals as well as the process efficiency, and to obtain as much data as possible.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1. Metal contamination of soil 1
• 1.2. Soil remediation techniques 2
• 1.2.1. General remediation techniques 2
• 1.2.2. Soil washing technique 2
• 1.3. Research scope and objectives 5
• Chapter 2. Literature review on soil washing 7
• 2.1. Metal characteristics 7
• 2.1.1. Fractionation 7
• 2.1.2. Mineralogy 9
• 2.2. Site characteristics 14
• 2.2.1. Soil texture 14
• 2.2.2. Soil organic matter (SOM) 14
• 2.2.3. Others 15
• 2.3. Influence of operation parameters on chemical extraction 16
• 2.4. Summary 20
• Chapter 3. Chemical extraction mechanism of Pb 21
• 3.1. Extraction of Pb adsorbed on soil 21
• 3.1.1. Materials and methods 21
• 3.1.1.1. Artificially Pb-contamination of kaolin 21
• 3.1.1.2. Soil washing 22
• 3.1.2. Results and discussion 23
• 3.2. Extraction characteristics of Pb minerals 29
• 3.2.1. Materials and Methods 29
• 3.2.1.1. Pb-contaminated kaolinite with Pb minerals 29
• 3.2.1.2. Batch soil washing process to test using extracting agents for Pb minerals 32
• 3.2.1.3. Kinetic washing 33
• 3.2.2. Results and discussion 33
• 3.3. Summary 44
• Chapter 4. Applicability of heavy metals extraction mechanisms to field soil 46
• 4.1. Labile Pb-contaminated field shooting range soil 46
• 4.1.1. Materials and methods 46
• 4.1.1.1. Characterization of soil 46
• 4.1.1.2. Soil washing 48
• 4.1.1.3. Evaluation of soil health 49
• 4.1.2. Results and discussion 50
• 4.2. Pb mineral-contaminated field shooting range soil 55
• 4.2.1. Materials and methods 55
• 4.2.1.1. Physicochemical properties of soil 55
• 4.2.1.2. Field washing tests 58
• 4.2.2. Results and discussion 58
• 4.3. Metal-contaminated dredged marine sediments 61
• 4.3.1. Materials and methods 61
• 4.3.1.1. Characterization of sediments 61
• 4.3.1.2. Sediment washing 66
• 4.3.2. Results and discussion 67
• 4.4. Summary 78
• Chapter 5. Screening matrix 80
• 5.1. Screening of operation parameters 80
• 5.2. Applicability of screening matrix for field soil 82
• 5.2.1. Materials and methods 82
• 5.2.2. Initial physicochemical properties of field soils 84
• 5.2.3. Washing characteristics 89
• 5.3. Summary 92
• Chapter 6. Conclusions 94
• References 98
• Appendix A. Supplementary data 115