Cement-based waste forms

The densities of the final waste forms were 1.70 and 1.9 g/cm, and the compression strengths ranged from 1400 to 1900 psi (9.8-11.9 MPa) for both the chloride and nitrate waste forms. These values are significantly higher than the NRC land disposal requirement of 500 psi (3.5 MPa) for cement-based waste forms [17]. Thus, salt waste forms of the CBPC at high loadings are relatively dense hard materials that are suitable for salt waste... 

Lee JF, Bajt S, Clark SB, Lamble GM, Langton CA, Oji L (1995) Chrominm speciation in hazardous, cement-based waste forms. Physica B208 and 209 577-578... 

In the organic polymer process, a monomer and a catalyst are combined with the waste stream, and the polymer is allowed to form. The product is then containerized and disposed of. The polymer used in this technique is urea of formaldehyde (melamine). The advantages of this technique are that both solid and semiliquid waste can be processed and the weight of the processed solid is less than those produced from cement-based wastes, but they are biodegradable and must be containerized. 

Cement-based stabiUzation/solidification (S/S) is a technology for the in situ or ex situ treatment of hazardous wastes and hazardous waste sites. It is a process that uses cement and other additives or processes to physically and/or chemically immobilize the hazardous constituents of contaminated soils, sludges, sediments, or liquid wastes. The objective is to prevent the migration of contaminants in the environment by forming a solid mass. 

Jiang, W Wu, X. Roy, D. M. 1993. Alkali activated fly ash - slag cement based nuclear waste forms. Materials Research Society Symposium Proceedings, 294, 255-260. 

Abstract Solidification/stabilization treatment processes immobilize hazardous constituents in the waste by changing these constituents into immobile (insoluble) forms, binding them in an immobile matrix, and/or binding them in a matrix which minimizes the material surface exposed to weathering and leaching. Solidification/stabilization treatment processes can include aluminum silicate and cement-based fixation, pozzolanic-based fixation, or vitrification. 

Lime/fly ash pozzolanic processes combine the properties of lime and fly ash to produce low-strength cementation. Kiln dust processes involve the addition of kiln dust to eliminate free liquids and usually form a low-strength solid. Lime-based processes for solidification use reactions of lime with water and pozzolanic (siliceous) materials, such as fly ash or dust from cement kilns, to form concrete, called a pozzolanic concrete. Wastes of desulfurization of gases and other inorganic wastes can be immobilized by this method. 

Poon CS, Lio KW (1997) The limitation of the toxicity characteristic leaching procedure for evaluating, cement-based stabilized/solidified waste forms. Waste Manage 17 ... 

G. Dole, G. Rogers, M. Morgan, D. Stinton, J. Kessler, S. Robinson, and J. Moore, Cement-based radioactive waste hosts formed under elevated temperatures and pressures (FUETAP concrete) for Savannah River Plant high-level waste. Report No. ORNL/TM-8579 (Oak Ridge National Laboratory, 1983). 

The cement-based process consists of the mixing of the waste with cement and, possibility, other additives. The liquid waste or fluid sludge is used as the mix water for hydration of the cement. Cementation of the mixture occurs when the waste is added. First, a calcium-silicate-hydrate gel forms followed by the hardening of the material as thin, densely-packed, silicate fibrils grow and interface. Heavy metals in the waste are converted to insoluble hydroxides in the alkaline environment of the cement paste and trapped within the pores of the cement paste matrix. It is also possible that some of the metals may be physically... 

Figure 1 Examples of cement-based matrices used in the conditioning of radioactive wastes a) concrete container accommodating 4 primary waste forms b mortarforembedding metallic wastes.

Figure 6 Physico-chemical parameters and their couplings involved in the radiolysis of cement-based materials at the level of a waste form. Heterogeneous equilibria (solid solution and solution-gas) are located by a double red arrow.

Petrifix A process for solidifying aqueous wastes, converting them to a solid form suitable for landfill. Cementitious additives are used, based on the compositions used by the Romans for making Pozzolanic cements. Developed by Pec-Engineering, Paris, France. In 1979 it had been used in France and Germany. 

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