Heavy metals cement stabilization

SOLFIX is an ex situ stabilization technology that treats heavy metals by reacting contaminated soils and sediments with cement, pozzolanic materials, and other additives to chemically immobilize contaminants into an insoluble form. SOLFIX can be used either as a stand-alone technology or it can be incorporated with Hydro-SEP (a sediment washing technology) and ORG-X (a solvent extraction technology) into a three-step remediation process termed integrated sediment decontamination system (ISDS). 

METLCAP is a chemical cement that encapsulates, stabilizes, and solidifies hazardous heavy metals in solid form, in slurry form, or in solution. The cement is composed of magnesium oxychloride, which forms when magnesium chloride and magnesium oxide, with water, are mixed together with the metals. The hardened cement product is insoluble and itself becomes a usable resource as cement or as fill material. The METLCAP technology is applicable as an in sitn or ex situ treatment or for high-pressure injection grouting and construction of slnrry walls. Currently, the process is patented and commercially available from Stark Encapsulation, Inc. 

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. 

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. 

The incorporation of fly ash into Portland cement has been identified as one of the treatment parameters of cement composition to be evaluated. There is already an extensive experience database on the performance of fly-ash-modified Portland cement for heavy-metal immobilization and the solidification/stabilization (S/S) of radioactive waste. The United Kingdom (Wilding, 1992) and the United States (Huang et al., 1994) have used these materials, in the form of cement grouts, for the S/S of low- and intermediate-level radioactive wastes. In this section, we will review the known benefits of fly-ash-modified Portland cement over unmodified Portland cement, along with the anticipated improvements expected by the supercritical C02 treatment of modified Portland. 

Wilding, C. R. The Performance of Cement Based Systems. Cem. Res. 1992, 22, 299. Wilk, C. M. Stabilization of Heavy Metals with Portland Cement Research Synopsis Portland Cement Association Report IS007 PC A Skokie, IL, 1997. Young, J. F. Berger, R. L. Breese, J. Accelerated Curing of Compacted Calcium Silicate Mortars on Exposure to C02. J. Am. Chem. Soc. 1974, 57, 394—397. 

Successful stabilization/solidification of cadmium in the concentration 50,000 mg l1 of Cd2+, and lead in the concentration 10,000 mg T1 of Pb2+, in the cement matrix, was obtained. Low concentrations during leaching pointed out that the heavy metal containing waste could be successfully stabilized and immobilized on this way and landfilled, or safely utilized as the building material. 

Stabilization/solidification of hazardous liquids and sludges by combination of the waste with Portland cement to form a cement paste has been studied as a way to minimize environmental impact. The structure of the paste resists physical attack and the alkaUne nature of the material resists chemical attack, making the technique attractive as a disposal alternative for heavy metal sludges. 

T. M. Brown, Column Leach Testing of Heavy Metal Sludges Stabilized/Solidified with Portland Cement An Investigation of Release Meehanisms, M. S. Thesis, Univ. of New Hampshire, Durham, NH (1984). 

Bhatty, J.l. et al. (1996) Stabilization of heavy metals in Portland cement, silica fumel Portland cement and masonry cement matrices. PCA R P No 2067, Portland Cement Association, Skokie, IL, USA. 

Thermal desorption does not remove most heavy metals. Portland cement or another stabilizing agent can be added to treated soil when it is mixed with water in order to limit the mobility of metals in the treated soil. 

Heimann, R.B., Conrad, D., Florence, LZ., Neuwirth, M., Ivey, D.G., Mikula, R.J., and Lam, W.W. (1992) Leaching of simulated heavy metal waste stabilized/ soUdilied in different cement matrices. 

A second area of the applicahon of cements for environmental purposes is that of the stabilization/immobilization of Hquid toxic industrial waste, and in parhcu-lar that of hazardous heavy-metal waste streams containing chromium, vanadium, cadmium, and other metals. As noted in Sechon 5.2.4.2, both Cr and V can enter the inter-chain spaces of ettringite to replace groups (Buhlert and Kuzel,... 

Cements have been suggested as materials that could be used to immobilize heavy metals produced by various industries. Cadmium and its compounds are highly toxic and can effectively be retained in concrete provided the pH does not fall below 7. The main mechanism of Cd stabilization is related to its precipitation as cadmium hydroxide and physical entrapment. The possibility of Cd substituting Ca " by solid diffusion or dissolution mechanism, forming a precipitate of Ca Cd(OH)4 has been proposed by Goni, et al.,t l based on TG/DTG studies. 

Gluconic acid naturally occurs in plant, fruit, and foodstuffs, such as wine (up to 0.25%) and honey (up to 1%). Similar to other outstanding properties, gluconic acid has a good chelating capacity in alkaline pH its action is comparatively better than ethylenediaminetet-raacetic acid, nitrilotriacetic acid, and other chelators. Calcium, iron, copper, aluminum, and other heavy metals are firmly chelated in alkaline solution. It has been extensively used in the cleaning and construction industries as an additive to increase cement resistance and stability under extreme climatic conditions (Ramachandran et al., 2006). 

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