The purpose of this study was to suggest feasible disposal methods for heavy-metal-contaminated soil or mine tailings through solidification/stabilization. To improve the compressive strength and enhance the heavy-metal stabilization after solidification/stabilization, we used the industrial wastes (oyster shell powder and waste gypsum) and indigenous bacteria as immobilization agents. Three indigenous bacteria were isolated from each heavy-metal-contaminated soil or mine tailing site, and the bacteria were identified by cellular fatty acid composition analysis. The results of cellular fatty acid composition analysis showed that the closest strains of these bacteria are Brevibacillus centrosporus, Lysinibacillus sphaericus, and Bacillus megaterium. To the best of our knowledge, this research was the first report of biomineralization by Brevibacillus centrosporus. As a result of mixing additives with the optimum mixing ratio suggested in this study, the compressive strengths of specimens were satisfied in accordance with the US Environmental Protection Agency (EPA) waste treatment standard after 28 days of aging. Additionally, the results of the Toxicity Characteristics Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) analysis showed the successful immobilization of heavy metals after 28 days of specimen formation for solidification/stabilization.

About 4,800 soil drums were generated in the process of maintenance on KRR site (Korea Research Reactor) in Seoul. Most of the drums are processed by regulatory clearance in 2007-2008 and the remaining 1800 drums are currently stored in KAERI (Korea Atomic Energy Research Institute). To decide a treatment method of radioactive soil for final disposal, the soil is classified according to a particle size. Based on the results of the radioactivity concentration for the classified soil, methods such as regulatory clearance, decommissioning, and solidification were decided. Many papers show that radioactive soil is disposed of using a decontamination agent or other method. But it is difficult to decontaminate radioactive particles from fine soil particles because the adsorptive power of fine soil particles is too strong. This study was focused on finding a particle size distribution of radioactive soil that can be used as an operating range for cement solidification produced by a suitable ratio of radioactive soil for final disposal. Workability, free-standing water, compressive strength, immersion, and leaching tests were carried out to evaluate characteristics of the cement solidification. Cement solidification is the only method for final disposal because radioactive soil particle sizes below 500 μm exceed the regulatory clearance criteria (< 0.1 Bq/g). According to the test results for cement solidification, 0.4 water/cement and 0.5 soil/cement ratios are the most appropriate operating ranges.

The objective of this study is to investigate the immobilization properties of arsenic in solidification process using geopolymer binder. Metakaolin and fly ash were used as prime materials for geopolymer that was also called as activated metakaolin cement (or Si + Al cement). The immobilization of As in geopolymer was found to be very limited regardless of the oxidation state of As and the mixing ratio of As to the binders. These results may be ascribed to the low Ca contents in prime materials used and the structural property of geopolymer formed. It was generally accepted that As was immobilized into C-S-H (calcium silicate hydrates) via precipitation and sorption, when it was solidified with ordinary portland cement and/or lime. When Ca(II) or Fe(III) was used as stimulating agents, the As leaching was reduced by15 ~ 25% than that of control experiment. These limited improvements of As immobilization might be resulted from the extremely high pH in geopolymer reaction.