Leaching strength

The USY[26] obtained by high-temperature 923 K (650 °C) water vapor treatment is further treated with 0.1 3 mol/L HN03, 0.4mol/L AHFS, and 0.05 g/mL Na2H2EDTA at different leaching strengths, and the results are presented in Tables 6.7, 6.8, and 6.9. 

Table 6.7 Dealumination reaction results of hydrothermally treated (923 K 650° C ) USY with dilute HN03 of various leaching strengths...

Leaching strength represents the HNO3/AI molar ratio. 

Leaching strength represents the (NhUfeSiFe/Al molar ratio. 

From the three curves shown in Figure 6.13 it is seen that the EFAL-removal mechanisms for treatment of USY samples using dilute HNO3, AHFS, and EDTA are somewhat different. The residual EFAL states after dealumination with HNO3, AHFS, and EDTA at various leaching strengths characterized by Lynch using XRD and NMR techniques are presented in Table 6.10. 

Table 9.6 compares the residues from thermal waste treatment with respect to their long-term behavior. This assessment is usually made using leach tests in Table 9.6, the Swiss Technical Rule limits for residuals requiring a leach strength of pH 4 were used (Anonymous 1990 see Section 9.5.3). Tests have shown that the untreated and even the scrubbed electrostatic precipitator (ESP) filter residues do not meet these limits, and even the zinc content of ESP filter residue solidified with cement is only slightly below the limit at which landfilling would be permitted at a... 

Often, the immobilized product has a structural strength sufficient to prevent fracturing over time. Solidification accomplishes the objective by changing a non-solid waste material into a solid, monolithic structure that ideally will not permit liquids to percolate into or leach materials out of the mass. Stabilization, on the other hand, binds the hazardous constituents into an insoluble matrix or changes the hazardous constituent to an insoluble form. Other objectives of solidiflcation/stabilization processes are to improve handling of the waste and pri uce a stable solid (no free liquid) for subsequent use as a construction material or for landfilling. 

The PGS obtained by Wang and coworkers was a kind of thermoset elastomer with the Young s modulus of 0.282 0.025 MPa, a tensile strain of at least 267 zE 59.4%, and a tensUe strength was at least 0.5 MPa. The mechanical properties of PGS were well consisted with that of some common soft tissues. Although PGS is a thermoset polymer, its prepolymer can be processed into various shapes by solving it in common organic solvents such as 1,3-dioxolane, tetrahydrofuran, isopropanol, ethanol, and iV,M-dimethylformamide. Porous scaffolds can be fabricated by salt leaching. 

The separation of solids from liquids forms an important part of almost all front-end and back-end operations in hydrometallurgy. This is due to several reasons, including removal of the gangue or unleached fraction from the leached liquor the need for clarified liquors for ion exchange, solvent extraction, precipitation or other appropriate processing and the post-precipitation or post-crystallization recovery of valuable solids. Solid-liquid separation is influenced by many factors such as the concentration of the suspended solids the particle size distribution the composition the strength and clarity of the leach liquor and the methods of precipitation used. Some important points of the common methods of solid-liquid separation have been dealt with in Chapter 2. 

In 1997 and 1998, the authors306 307 also examined acid leached Raney copper catalysts, whereby the alloy was leached with either nitric or perchloric acid of 5, 14, or 27.5 wt% strength. The acid solution was added dropwise over 15 min to an equal volume of deionized water containing the alloy particles. After leaching at 50 °C, the particles were removed and washed to a pH of 7. Air drying at 120 °C was then carried out for one hour. The dissolution rates of catalyst components were observed to be functions of the extraction time (Table 56). 

Clearly, the acid leached catalysts (Table 57) displayed much lower BET surface areas and lower activities in comparison with the caustic extracted samples, the commercial catalyst, and the precipitated experimental catalyst (Table 55). The authors suggest that use of a weaker acid solution strength (perhaps <5%) for... 

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