Available leaching tests

A plethora of leaching tests has been developed, many of which were developed or are used based on a poor understanding of the controlling factors and leaching processes. The tests have been developed for many different purposes and most have been developed in isolation from each other. In effect, the tests 

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The Dutch Total Availability Leaching test (NEN 7341) was used to operationally quantify the elemental mass fraction available for leaching in the samples. The procedure involves two sequential extractions the first were conducted at a pH of 7.0 and LS of 100. For examination of mass fractions available for leaching, 8 g of sample was added to 800 mL of distilled, deionized water and stirred in a capped Teflon vessel. 

A number of reviews of available leaching tests have been carried out (Environment Canada 1990 Wallis etal. 1992 Ure etal. 1993 Quevauviller etal. 1995 CEN/TC/292/NNI 1994 Science of the Total Environmental Special Issue 1996 van der Sloot etal. 1997). Examples of leaching tests performed throughout the world are shown in Table 9.1. As shown in the table, there are more tests available for granular materials than there are for monolithic materials. 

The building material decree regulates the quantities dissolved from a construction material to the neighboring soil and the surface water. The standard values are established about Hg, Cd, Pb, Cr, As, Se, Cu, Zn, Ni, Ba, Sn, Sb, Co, Mo, V, Cl, SO4, Br, F, CN(free), CN , SCN . Dissolution quantities per 100 years are calculated from the results given by the tank leaching test (NEN 7345) and availability leaching test (NEN 7341). 

Batch tests (i. e., tests on individual waste materials) are conducted with the provided solid suspensions (e.g., soils such as Woodburn, Sagehill, and Olyic, as well as two bottom sediment samples) prepared with previously air-dried solids (i. e., soils and bottom sediments), ground to a uniform powdery texture for mixing with the eluates from the 24-h batch leaching test of the different SWMs/COMs. The concentrations of eluates in solution were designed to evaluate the capability of different environmental solids to adsorb available contaminants. The solid particles were fully dispersed with the aqueous phase to achieve complete adsorption. Common practice is to use a solid solution ratio of 1 g 4 ml [ 1 ], together with proper tumbling of the samples at a constant temperature (e.g., at least 24 h in a constant temperature environment of 20°C). 

It is important to differentiate between the two different types of sorption/ desorption tests (i. e.,batch and column-leaching), and the sorption characteristics determined from one should not be confused with the other. Sorption isotherms obtained with batch equilibrium tests are applied mainly to solid suspensions. The physical model, assumed with this situation, is one of a completely dispersed solid particle system, where all solid particle surfaces are exposed and available for interactions with the contaminants of concern. In contrast, column-leaching tests are performed with intact solid samples, and the sorption characteristics obtained from them are the results of contaminant interactions with a structured system where not all-solid particle surfaces are exposed or available for interactions with the contaminants. 

Most leaching tests are performed in a laboratory. Whilst leaching tests are designed and intended to reflect reality, there is a limited amount of data available from field tests which can be used to correlate with those from laboratory tests hence validate their performance in relation to the situation in the field. One of the most common errors in the interpretation of results from leaching tests is to assume that, based on the commonly used shaking test at a liquid to solid ratio of 10 1, the resultant leachant is representative of the concentration of contaminants that will emerge from the base of a deposit of the material tested. Even if it is assumed that the factors such as leachant used, pH and redox are correctly applied in the test, the concentrations of contaminants in the leachate represent an average of the concentration which will be leached... 

Aqueous extracts. Various bioassay protocols are available for testing soil elutriates or leachates. Historically these have previously been available for aquatic tests. However, it may be inappropriate to project effects generated with aquatic species to soil organisms or ecosystems. With the development of whole soil bioassays, the use of elutriate or leachate tests focuses now on the prediction of threats to groundwater (leaching of toxicants) or surface water (contaminant run-off). Tests using aqueous extracts address pollutants soluble in water, and therefore are a measure of mobile toxicants. 

Additional reassurance would be available from a limited number of leaching tests on samples of the irradiated graphite, and by comparing the final graphite properties (particularly the oxidation rate in air) with the predictions after storage but ahead of the dismantling operation. 

Extensive emission data are available on slag from the Cool Water IGCC plant. Table 4-6 summarizes RCRA test results (6). Scientists have also performed long-term leaching tests on coal gasification slag (19). 

Physical and chemical tests of the final product may need to address two concerns (1) whether the solidified waste exhibits any RCRA defined toxicity characteristics or could be delisted and (2) the potential long term fate of treated materials in the disposal environment. Three tests are available which address the first concern. These are the Extraction Procedure (EP Tox) (40 CFR 261, Appendix II, 1980) and the Toxicity Characteristic Leaching Procedure (TCLP) (40 CFR 261, Appendix II, 1986), and the Multiple Extraction Procedure Test (40 CFR 261, Appendix II, January 1989). It is important to note that these tests are not indicators of expected leachate quality but of potentials. A solidified product which cannot pass the appropriate test (EP Tox or TCLP) would be subject to classification as a hazardous waste. 

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. 

Simulation and predictive modeling of contaminant transport in the environment are only as good as the data input used in these models. Field methods differ from laboratory methods in that an increase in the scale of measurement relative to most laboratory methods is involved. Determination of transport parameters (i. e., transmission coefficients) must also use actual contaminant chemical species and field solid phase samples if realistic values are to be specified for the transport models. The choice of type of test, e.g., leaching cells and diffusion tests, depends on personal preference and availability of material. No test is significantly better than another. Most of the tests for diffusion evaluation are flawed to a certain extent. 

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