Immobilization and Encapsulation of Contaminants Using Silica Treatments: A Review

Effect of liming on polycyclic aromatic hydrocarbons leaching from hydrocarbon-contaminated tectogenic industriosol

Soil stabilization/solidification is commonly employed remediation method for contaminated soils. Until now, limited attention has been given to the application of quicklime in polycyclic aromatic hydrocarbons (PAHs) contaminated soil. We treated a tectogenic industriosol spiked with 50 mg kg-1 of four PAHs (12.5 mg kg-1 each of fluorene (FLU), phenanthrene (PHE), fluoranthene (FLT) and pyrene (PYR)) using three different liming agents at 1% (w:w): quicklime (CaO), hydrated lime (Ca(OH)2) and carbonate calcium (CaCO3). All treated samples were leached in water at a solid-liquid ratio of 10, with subsequent analysis of leached soil and leachates for PAHs content. Results revealed that the addition of liming agents led to a reduction in FLU and PHE concentrations in treated soil by 6.81 ± 2.47% and 28.88 ± 4.18%, respectively, compared to a not-treated sol. However, no significant impact was observed on the 4-cycles PAHs (FLT and PYR). The addition of liming agents also significantly decreased the amount of PAHs in the leachate, by 100% for FLU and PHE, and by 74.9 ± 17.5% and 72.3 ± 34.8%, for FLT and PYR, respectively, compared to not limed soil. Among the liming agents, quicklime was the most effective in reducing the amount of 4 cycles PAHs in the leachate. Various mechanisms, such as encapsulation, volatilization and oxidation could contribute to this observed reduction. Quicklime treatment at a concentration of 1% w:w in PAHs-contaminated soil emerges as a promising technique to effectively reduce PAHs concentration in soils and mitigate PAHs mobility through leaching. This study also sheds light on the possibility to limit CO2 emissions and resources exploitation to assure the remediation process, thereby enhancing its overall environmental sustainability.

Critical Review of Field Studies of Chemical Surface Coatings to Mitigate Leaching from Mining Wastes

Source control of mine drainage and leachate from mining wastes is ideal, but there is limited use of control methods aside from removal of wastes to repositories or capping wastes in situ. In some locations, neither removal nor capping is possible; thus, there is renewed interest in understanding technologies for coating mining wastes. This paper presents the current state of knowledge from a critical review of the few field case studies where chemical coating technologies have been applied to mined surfaces (e.g. a highwall) or mining wastes. It also includes laboratory studies where the same technology was examined on the same type of waste material as the field studies. The chemicals used in field studies for coating mining wastes were magnesium oxide, potassium permanganate, silicate compounds, phosphate compounds, and a furfuryl alcohol resin sealant. Descriptions of the methods employed, and results obtained are provided. Limitations of the individual studies and of the technologies in general are discussed. Potential reasons why coating technologies have not been commonly used are presented, along with further research needs.

Microencapsulation of zinc plating waste using silicone polymers

This paper deals with the treatment of hazardous zinc-bearing waste using hydraulic binders and silicone polymers, with the aim to allow its safe disposal into landfill. The waste was solidified using hydraulic binders in the first step and then encapsulated using silicone polymers. Samples were characterised using x-ray fluorescence, x-ray diffraction, and scanning electron microscopy. The effectiveness of the process was evaluated by leaching tests in distilled water and in an acidic environment according to Toxicity Characteristic Leaching Procedure. The effect of porosity and pH on the release of pollutants was also studied. Zinc and chloride were identified as the most significant pollutants in the waste. Portland cement did not stabilize them efficiently. The two-step treatment with Portland cement and silicone binders decreased, in the best case, the concentration of zinc and chloride in acidic extracts from 12,400 mg/L and 38,300 mg/L to 21.9 mg/L and 74 mg/L, respectively, and the treated waste complied with regulatory requirements for hazardous waste disposal into landfills. The two-step treatment was also found as a more effective method than microencapsulation using a silicone binder alone. The factor that most affects leachability appears to be the porosity of the encapsulated waste.