Bitumen waste form

Low- and intermediate-level waste is currently converted to cement and bitumen waste forms, but the existing trend is toward an increase in the radiation safety levels and reliability of immobilization. From this point of view, LILW should also be incorporated in vitreous and crystalline matrices. Current Russian and US experience on vitrification of such waste demonstrates the potential of the melting/vitriflcation process. Major advantages of vitrification over bituminization and cementation are a greater waste volume reduction, higher productivity, and higher durability of the final product. 

Sobolev, I. A., Barinov, A. S., Oiovan, M. I., Oiovan, N. V., Startseva, I. V. Golubeva, Z. I. 2000. Long-term behavior of bitumen waste form. Materials Research Society Symposium Proceedings, 608, 571-576. 

The wide chemical variation of radioactive wastes which are extremely complex in composition require different methods of immobilisation and containment. The waste forms range from Low Level Waste (LLW), Medium Level Waste (MLW) through to High Level Waste (HLW). MLW can be embedded in cement or bitumen whereas HLW is either reprocessing waste immobilised in borosilicate type glasses or is the spent fuel when declared as waste. 

Cold-Water Process. The cold-water bitumen separation process has been developed to the point of small-scale continuous pilot plants. The process uses a combination of cold water and solvent. The first step usually involves disintegration of the tar sand charge, which is mixed with water, diluent, and reagents. The diluent may be a petroleum distillate fraction such as kerosene and is added in a ca 1 1 weight ratio to the bitumen in the feed. The pH is maintained at 9-9.5 by addition of wetting agents and ca 0.77 kg of soda ash per ton of tar sand. The effluent is mixed with more water, and in a raked classifier the sand is settled from the bulk of the remaining mixture. The water and oil overflow the classifier and are passed to thickeners, where the oil is concentrated. Clay in the tar sand feed forms emulsions that are hard to break and are wasted with the underflow from the thickeners. 

Foamed emulsions are disperse systems with two disperse phases (gas and liquid) in the disperse medium (surfactant solution). Water foamed emulsions are formed when foams or aqueous surfactant solutions are used to clean up oil deteriorated surfaces, in the process of oil flotation of waste waters, in firefighting when the foam contacts various organic liquids and in the processes of chemical defoaming (foam destruction by antifoams). Individual foamed emulsions can have practical importance e.g. a foamed emulsion of bitumen is used in road coating foamed emulsions from liquid fuels are used as explosives. 

The sand-reduction process is a cold-water process without solvent. In the first step, the tar-sand feed is mixed with water at approximately 20°C (68°F) in a screw conveyor in a ratio of 0.75 ton to 3 ton per ton of tar sand (the lower range is preferred). The mixed pulp from the screw conveyor is discharged into a rotary-drum screen, which is submerged in a water-filled settling vessel. The bitumen forms agglomerates that are retained by an 840-micron (20-mesh) screen and withdrawn as oil product. The sand readily passes through the 840-micron (20 mesh) screen and is withdrawn as waste stream. 

Several industrial systems involve emulsions, of which the following are worthy of mention. Food emulsions include mayonnaise, salad creams, deserts, and beverages, while personal care and cosmetics emulsions include hand creams, lotions, hair sprays, and sunscreens. Agrochemical emulsions include self-emulsifiable oils that produce emulsions on dilution with water, emulsion concentrates with water as the continuous phase, and crop oil sprays. Pharmaceutical emulsions include anaesthetics (O/W emulsions), hpid emulsions, and double and multiple emulsions, while paints may involve emulsions of alkyd resins and latex. Some dry-cleaning formulations may contain water droplets emulsified in the dry cleaning oil that is necessary to remove soils and clays, while bitumen emulsions are prepared stable in their containers but coalesce to form a uniform fihn of bitumen when apphed with road chippings. In the oil industry, many crude oils (e.g.. North sea oil) contain water droplets that must be removed by coalescence followed by separation. In oil slick dispersion, the oil spilled from tankers must be emulsified and then separated, while the emulsification of waste oils is an important process for pollution control. 

The waste concentrates are required to be appropriately solidified or conditioned to minimise the possibility of migration of radioactivity. The media in which the radionuclides are immobilised, are relatively stable, inert and impervious solid forms, commonly referred to as matrices . The commonly used matrices are cement cement composites, bitumen and pol)oners. Various conditioning aspects have been addressed in IAEA Technical Reports Series No. 222 [11]. 

Some wastes can be immobilized in thermoplastics, which are solids or semisolids that become liquefied at elevated temperatures and that cool to rigid but deformable forms. The thermoplastic material most used for this purpose is asphalt bitumen. 

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