Leaching tests described

Leaching of chemicals from complex materials or matrices is a complicated phenomenon in which many factors may influence the release of the specific organic compounds and inorganic ions. Important factors include major element chemistry, pH, redox, complexation, liquid to solid ratio, contact time, and biological activity. To describe fully the leaching of SWMs/COMs under field conditions, a battery of leaching tests was specifically designed to simulate various physical and chemical release mechanisms. 

This report describes the preparation and leach testing of fully radioactive zinc borosilicate glass, prepared from power reactor waste. Leach tests were conducted on this fully radioactive waste glass to ... 

Release rate data from actual radioactive waste forms is needed to evaluate the safety of emplacing nuclear wastes in geologic media. However, in addition to waste form development studies, such as the leach test just described, a comprehensive program was started to obtain release data from candidate waste forms for geologic disposal. 

One of the more important factors affecting the isolation of radioactive waste is the rate of release of the radioactivity from the solid waste form to the environment. The most probable mechanism for release and transport of radioactivity from a solid waste form is by leaching of radioactive isotopes with groundwater. The objective of leach-testing various waste forms is to evaluate the rate at which specific hazardous radionuclides migrate from waste if and when the waste form comes in contact with groundwater. In this paper, measurement of leach rates of radioactive waste by a method which incorporates neutron activation is described. 

The classical leach test methods currently in use, (the Soxhlet, Paige, Kelley, procedures described above in Description of Leach Rate Measurement Procedures as well as those described in... 

During development, evaluation of the consolidated materials was based primarily on two criteria, leachability and the concentration factor, i.e., the concentration of waste oxides on a volume basis. The concentration factor is directly affected by the residual porosity in a consolidated waste as well as by the dilution caused by the addition of consolidation aids. This factor can be as high as 1.2 g/cm3 for a fully dense ( 5 g/cm ) titanate waste prepared from the projected Barnwell plant solution composition. The factor is slightly lower for a titanate waste containing silicon and zeolite additions, which has a typical density of U.2 g/cm3. The leachability was determined by an "instantaneous leach test developed for fast, comparative evaluations of materials, the details of which are described elsewhere (l6). 

Column test (described in Dutch standard NEN 7343) is intended to simulate the percolation of (acidic) rainwater through granular materials in a road construction or landfill. The material is placed in a column with a diameter of 5 cm and height of 20 cm, and acidified demineralized water is then passed upwards through it. The eluate is collected in seven fractions at a liquid/solid ratio of between 0.1 and 101 kg-1. The leaching is calculated and expressed in mg kg 1 as a function of time, based on the analysis results. 

Cascade test (described in Dutch standard NEN 7349) provides information on long-term leaching from a granular material. In this test the material is brought into contact with acidified demineralized water five times in succession for 23 h. The cumulative L/S (liquid/solid) ratio is 100 1 kg1. This test also yields an emission, expressed in mg kg-1. 

For the purposes of describing leaching tests, the description of the leaching mechanisms hence the description of the types of tests are simplified into those which are relevant to granular materials and those which are suitable for monolithic materials. 

A compliance leaching test for granular waste material has been published (prEN 12457) which describes three different procedures shake test at liquid/solid (L/S) ratio = 2, L/S = 10 and a two-step shake test at L/S = 2 and 10. The leachant used is demineralized water. It is likely that the standard will be validated. The driving force behind this standard was the draft European Directive on the landfill of waste. 

Desai and Clarke (149) reported successful results using zinc-containing compounds. Sell et al. (ISO, 151) described surface treatment with chromium-copper-boron salts. Field weathering tests, leaching tests, and electron-probe microanalysis showed that this treatment was resistant to leaching and weathering. Water-soluble extractives in redwood and redcedar were fixed by treating the wood surface with dilute solutions of copper and chromium salts. This treatment permits direct application of latex paints to these woods (146). 

The JIS K0058-1 regulates the two leaching tests. One leaching test is for a sample with a practical form and size. Another leaching test is for a sample with a size below 2 mm. This leaching test is mainly applicable to the former sample. The leaching test for the latter sample will be described later. 

The flocculation reactions described above attach Fe or A1 oxides to the pollutants. At near neutral pH, these oxides have very low solubility product constants [4,5]. This binding to insoluble oxides effectively makes most captured pollutants non-leachable and suitable for landfill. It has been noted that many pollutants captured in this manner also formed acid resistant compounds that passed TCLP toxicity leach tests [6]. 

Tests giving a realistic approach to the study of leaching behaviour of the residues are described. Results of analysis (carbon, sulphur, major- and trace-elements) are discussed. Morphology, particle size distribution and enrichment effects on single particles are dealt with. A method for the comparison of the results of different leaching tests is presented. 

The reaction proces.ses can be described by a combination of results from leach tests and SIMS. The nominal composition and leach rates (g in - d" ) of a glass formulation, PNL 76-68 (Pacific North-West Laboratories), used as the. standard high-level nuclear waste glass matrix [4], are shown in Table 4. The definition of leach rate u.sed normalizes the loss (in g) to the proportion of that element in the nominal bulk composition. It will be seen that the leach rates for Cs, Na, Mo, Si and B exceeded the overall rate of mass loss from the gla.ss surface, whereas the elements Fe, Zn and Ti did not show significant loss to solution under these conditions. There were also several elements, e.g.. Ca. Ba, Cd and Sr, that were neither rapidly leached nor apparently retained in the surface layers. Studies described in the above-mentioned reviews, using XPS, FTIR, SIMS, SEM and dissolution rates, have established clearly that the primary reaction occurring in solution is the bond-breaking attack by OH at Si (or Al and... 

The combination of several of the above described approaches can be also used. Thus, precious metal catalysts can be supported on nanomaterials and combined with ILs. The supported gold NPs on graphene oxide (GO) with an ionic liquid framework (Au GO-IL) has been shown to be a highly active, and leaching tests, such as hot filtration test and AAS analysis, indicate that the catalytic reaction is mainly heterogeneous in nature. The reusability of this catalyst was tested for 5 x without a significant decrease in its catalytic... 

Most probably, the first - but non-fiberoptic - sensors for continuous use where those for pH and for oxygen. It has been known for decades that cellulosic paper can be soaked with pH indicator dyes to give pH indicator strips which, however, leached and thus were of the "single-use" type. The respective research and development is not easily traced back since it is not well documented in the public literature. However, in the 1970s, indicator strips became available where they pH indicator dye was covalently linked to the cellulose matrix, usually via vinylsulfonyl groups. These "nonbleeding" test strips allowed a distinctly improved and continuous pH measurement, initially by visual inspection. In the late 1980 s instruments were made available that enabled the color (more precisely the reflectance) of such sensor strips to be quantified and related to pH. Respective instruments are based on the use of LEDs and are small enough to be useful for field tests in that they can be even hand-held. This simple and low cost detection system is still superior to many of the complicated, if not expensive optical pH sensors that have been described in the past 20 years. 

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