Physico-chemical technique, soil washing and soil flushing for remediation of lead contaminated soils | |
| Author | Nukoon Tawinteung |
| Call Number | AIT Diss. no.EV-04-07 |
| Subject(s) | Soil pollution Soils--Lead content Soil remediation |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, Asian Institute of Technology; Inter-University Program on Environmental Toxicology, Technology and Management, Chulabhom Research Institute and Mahidol University |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-04-07 |
| Abstract | Lead contaminated soils including ash and mud from the abandoned batteries recycling and secondary lead-smelting factory were identified and investigated the potential to decontaminate by extraction technique. Likewise, fractionation and adsorption were also conducted to elucidate the retention mechanism of Pb by the soil. Ash and mud were collected from the point near the factory's stack. Whereas two contaminated soils and one reference soil were selected from the surrounding area of the factory based on their differing in a level of Pb contamination. Soil samples were collected from each soil pit in two layers: surface soil and subsoil (0-15, 15-30 cm) for further site characterization. Pb content of ash and mud samples was extremely high as expected with the average values of 106,537 and 11,477 mg kg- 1 respectively. Pb pools were found predominant in the first three fractions namely exchangeable, carbonate bound and Fe-Mn oxide bound resulting in high mobility factor (MF) with the average values of 60-70%. This indicated that high potential of Pb in mobilization, bioavailability and easily to release back to the natural environment. Therefore these contaminated materials should be managed in a proper way such as excavated and kept in a control area (landfill) to protect further remobilization. Particle size analysis of three studied soils showed that on less polluted and reference soils are sandy loam and heavily contaminated soil is sandy clay loam with clay content varied between 11-21 %. Soil pH of the study area was strongly acid to moderately acid (pH 4.8- 5 .9). Over the past 10-year contamination, deposits of Pb on the surface soil were 1,620 and 153 mg kg-1 for heavily and less contaminated soil, and only 15 mg kg-1 was found as a background level for the reference soil. The results of Pb adsorption experiment fitted very well to Langmuir equation. Further sorbed Pb by soils was highly significant conelated with sum of exchangeable base, Ca, Mg, Mn contents and silt particles with the r2 = 0.994, 0.954, 0.926, 0.818 and 0.947 respectively. Partitioning Pb of the studied soil into different chemical fractions indicating that more than 90% of total Pb was predominated by three following leading fractions: exchangeable, carbonate and Fe-Mn oxide. Meanwhile, the mobility of Pb as assessed by mobility factor (MF) was reached up to 75% indicating of high potential of Pb remobilization in this soil. This suggested that the newly added Pb from factory's activities remained in relative weakly bound forms. Perhaps relatively high leachability and biological availability can be expected. Therefore, this Pb contaminant was amenable to remediate by soil extraction technique. To further prove that such bound Pb could be washed off, both soil washing (ex-situ) and soil flushing (in-situ) techniques were employed for Pb removal performance evaluation. Particle size separation of soil into coarse (2.0-0.25 mm), medium (0.25-0.15 mm) and fine size(< 0.15 mm) was conducted before introducing soil washing to compare Pb removal efficiency with the indigenous soil (composite size). Using EDTA (2:1 mole to Pb) as a washing solution, Pb removal reaches up to 85-95% under the optimum condition (retention time ~ 60 minutes, liquid to solid ratio (LIS) at 5: 1 for coarse fraction and 10: 1 for smaller fraction). Leachability of Pb in the coarse size fraction soil was much easier than those from the finer size fractions as indicated by differences of the LIS ratios used. Removal of Pb from contaminated soil by EDT A extraction was possible however, the efficiency for this method was higher in the coarse texture soils. Thus particle size separation is recommended before application of the soil washing. Whereas for the smaller particle size perhaps more series of extraction is proposed. For soil flushing technique with three solvents tested as flushing solution: after 20 pore volumes of each solutions 85, 84 and 74% of Pb was removed by EDTA (2:1 mole to Pb), 1.0 M HN03 and 0.2 M ammonium citrate, respectively. Capability of the three flushing solutions to remove Pb from the contaminated soil could be ranked in the order EDTA ~ 1.0 MHN03 > 0.2 N ammonium citrate. However, the treated soils by all solvents required further Pb leach out especially for the heavily contaminated soil. The combination to other clean up techniques would be an alternative to reach the reference level depended on soil clean up criteria and land use. After flushing process, 1 M HN03 caused an increase in soil acidity to extreme acid condition (pH 2.0) resulting in adverse effects to physicochemical properties of the treated soil. A large scale (PVC column) experiment was also conducted using EDTA (2: 1 mole to Pb) as a flushing solution found that efficiency of Pb removal Pb was approximately 20% lower as compared with a bench scale of soil flushing result especially on heavily contaminated soil. Over all results have led to conclude that three factors seem to influence Pb removal by extraction technique. They include (i) initial Pb concentrations, (ii) Pb partitioning within soil or linkage forms and (iii) particle size of soil matrix. In addition, knowledge of Pb remobilization as measured by mobility factor (MF) would be helpful to determine the feasibility study of soil extraction technique for remediate of contaminated soil. In order to make use of both laboratory and bench scale experiments to implement further to a full-scale condition, alternative plans to clean up Pb contaminated site were simulated either soil washing and soil flushing of EDTA, HN03 and ammonium citrate solutions as well as physically sieve the soil or not sieving the soil. Cost, time and soil properties after treatment were taken into consideration for each scenario of soil remedy. In most scenarios, one run of extraction by EDTA (2: 1 mole to Pb) soil washing should be recommended due to less cost operation estimation at approximately 1 million US dollar (1.3 ha, with total mass 6,923 tons of soil in 30 cm depth), less time required and minimal adverse effects to physico-chemical properties of the treated soil. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-04-07 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Preeda Parkpian; Chongrak Polprasert; Skorn Mongkolsuk; |
| Examination Committee(s) | Seung-Hwan, Lee;Banerji, Shankha K.; |
| Scholarship Donor(s) | CRI;Mahidol;AIT Fellowship Program on Post-Graduate Education, Training and Research Program in Environmental Science, Technology and Management; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2004 |