Cement-stabilization

In very dilute HCl solutions, specifically those with a pH above 5-48, the 4 1 5 phase was found to be insoluble. By contrast, addition of concentrated HCl to the 4 1 5 phase was shown to lead to formation of the 1 1 2 phase (Sorrell, 1977). Below 35wt% HCl, the 4 1 5 phase was found to dissolve congruently. Since the 1 1 2 phase was also found to dissolve congruently in hydrochloric acid solutions with concentrations above 23 wt %, it follows that there is a range of concentrations over which both phases are soluble in aqueous HCl. This behaviour explains why the zinc oxychlorides have proved to be unsatisfactory in attempts to use them as dental cements. The preparation of such cements from concentrated aqueous solutions of ZnClj results in the formation either of the 1 1 2 phase alone or of mixtures of the 4 1 5 and 1 1 2 phases, neither of which is stable in the presence of water. Preparing dental cements from less concentrated solutions also results in the formation of mixed phases, unless the bulk composition has excessive amounts of ZnO present. In these latter cases the cement stability is acceptable but it lacks both a workable consistency and a reasonable working time. 

The estimated operating costs were 6510/m of treated waste. This estimate inclnded binder costs of 85 cents per pound the labor costs eqnivalent to 4 fnll-time technicians at 70 per honr and the cost of the 55-gal barrels at 100 per barrel nsed to mix, cnre, store, and dispose of the waste. The operating costs of the baseline cement stabilization process are lower at 4300/m of treated waste (D20934H, p. 15). 

Table 1 displays the different operating parameters of the hypothetical Ceramicrete and cement stabilization systems. Table 2 provides additional cost information about this estimate and comparison. 

TABLE 1 Operating Parameters for the Ceramicrete and Cement Stabilization System Used for the Cost Estimate... 

Minimal volume increase (as compared to cement stabilization technologies)... 

For the cement stabilization option, a facility would be constmcted to dewater and treat the wastes. There would be a 7- to 21-day staging period of wastes for quality assurance operations. An online rate of 250 days a year was assumed. It is estimated that cement stabilization would result in a volume factor increase roughly 3.75 times the total volume of waste treated. This increase in volume is necessary to immobilize technetium present in the wastes and to achieve a final waste form that could withstand pressures of 500 pounds per square inch (psi). The cement would be placed in 4-ft by 4-ft by 8-ft steel containers that would serve as a mold and to facilitate the handling of the finished blocks (D114432, Appendix A). 

OTD estimated that cement stabilization would produce 2,080,600 yd of stabilized wastes that could not be delisted and would have to be stored as mixed waste. The Duratek vitrification system would generate 417,000 yd of waste that may meet criteria for delisting as hazardous wastes and could be stored as only radioactive wastes (D114432, Appendix A). 

Can support higher waste loadings and when solidified has greater compressive and tensile strength than conventional cement stabilization. 

Cement stabilization of heavy-metal-containing wastes... 

Baur, I. 2002. The Immobilisation of Heavy Metals and Metalloids in Cement-Stabilized Wastes A Study Focussing on the Selenium Oxyanions SeOs and Se024. PhD thesis, Swiss Federal Institute of Science and Technology (ETHZ), Zurich, Switzerland. 

Baur, I., Ludwig, C. Johnson, C. A. 2001. Leaching behaviour of cement-stabilized incinerator ashes A comparison of field and laboratory measurements. Environmental Science and Technology, 35, 2817-2822. 

The aim of this chapter is to present a conceptual model of the leaching process in landfills based on two exemplary field studies at a municipal solid waste incinerator (MSWI) bottom ash landfill, Landfill Lostorf, and a lysimeter investigation, Landfill Teuftal, containing cement-stabilized MSWI air pollution control (APC) residues. 

The lysimeter was located next to the landfill Teuftal in Muhlcberg (Canton Berne). It was constructed in the winter of 1990/1991 (AGW 1991 Ochs et aL 1999) and dismantled in December 1997. The lysimeter had two compartments, one containing cement-stabilized APC residues in the form of cubic blocks with an edge length of 0.5 m. This compartment was approximately 1.5 m deep with an area of 15-16 m2. The space around the edge and between the cement blocks (around 1 cm) was filled with sand. The compartment was covered with geotextile, gravel (0.8 m), and humus (0.3 m) layers. The cement-stabilized APC residue blocks were composed of APC residues (41%), Portland cement (22%), water (32%), and NaOH (3%). 

In the case of Lysimeter Teuftal, most dissolved heavy metal and metalloid concentrations are directly correlated to electrical conductivity. The plot in Fig. 7 shows the relative dilution of different components during a rain event in comparison to that of electrical conductivity. The trend is independent of the speciation of these components. It should be noted that there are three notable exceptions, namely Ni(H), Co(II), and Cu(II). The common property of these cationic species is that they are extremely insoluble under the highly basic conditions encountered in the leachates of cement-stabilized residues (pH 12.8). It is possible that precipitation is the cause of such behaviour. 

Leist, M., Casey, R.J. and Caridi, D. (2003) The fixation and leaching of cement stabilized arsenic. Waste Management, 23(4), 353-59. 

Rubin, J. B. Taylor, C. M. V. Paviet-Hartmann, P. Hartmann, T. Ash Cements Stabilized by Supercritical C02 Carbonation for Repository Overlayer. Proceedings of NATO Advanced Study Workshop—Turning a Problem into a... 

It is also known that small quantities of some compound could significantly reduce strengths and deteriorate the properties of cement solidified waste. That could be in the form of setting reduction, which could lead to the material disintegration and leaching. Examples of some waste components, which could give opposite effect to the cement stabilization, are given in Table 2. 

Before the demonstration testing, a surface and subsurface soil sampling program was conducted to characterize the storage area conditions. At the soil surface, a maximum indicated hot spot concentration of 2,3,7,8-TCDD was found to be 646 ppb. However, the maximum indicated 2,3,7,8-TCDD concentration was 998 ppb, found in the subsurface in the 15-cm-thick cement-stabilized soil. The... 

TCDD concentration in the soil beneath the cement-stabilized soil decreased to a value <1 ppb within a 1-m depth. 

The compressive strength of a cement-stabilized clay sample from a small two-arm kneadcr varies with mixing index according to the relation ... 

Calvanese G, Cioeei R and Santoro L (2002) Cement stabilization of tannery sludge using quaternary ammonium salt exchanged bentonite as pre-solidification adsorbent. Fnviron Technol, 23 1051-1062. 

Gutti, C.S. etal. (1996) The influence of admixtures on the strength and linear expansion of cement stabilized phosphogypsum. Cement and Concrete Research 26,1083-1094. 

Bell, F.G. 1995. Cement stabilization of clay soils with examples. Environmental and Engineering Geoscience, 1, 139-151. 

Geochemical speciation SEM/EDX and XRD mineralogical composition of the unleached material SOLTEQ-B (a modified version of MINTEQA2 that includes Berner s model of CSH dissolution) Prediction of leaching from cement-stabilized waste [3]... 

M. Buil, E. Revertegat and J. Oliver, in A Model to the Attack of Pure Water or Undersaturated Lime Solutions on Cement , Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes, Vol. 2, STP 1123 (TM. GiUiam and C.C. Wiles, eds.), ASTM, Philadelphia, (1992) 227. 

Over the last several decades, there has been a notable shift toward soft engineering, nonstructural solutions, including classical methods such as drainage and modification of slope geometry, but also some novel methods such as lime/cement stabilization, grouting, or soil nailing. The cost of nonstructural remedial measures is considerably lower than the cost of structural solutions. In addition. 

Figure 3.6 Effect of age of curing on compressive strength at different cement contents of soil-cement specimens. (Reproduced with permission from Bahar R. et al. Performance of compacted cement-stabilized soil published by Elsevier Limited, 2004.)...

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