Leaching test procedure

Two leach test procedures were used a modified IAEA dynamic leach test and a static leach test. In the former test the leachant was gently agitated on a mechanical shaker and was changed at selected intervals. A typical sampling schedule was three times daily for the first week, twice per day for week 2, once per day for weeks 3 through 5, and once per week through week 9. 

Development and Harmonization of Leaching Test Procedures From a practical point of view, leaching test procedures can be classified into static, dynamic and diffusion tests, and there are special concepts related to the long-term prognosis of metal release from waste materials ... 

Generally, there is no simple and easy theoretical procedure which can provide exact or nearly precise quantitative predictions of what and how much will be adsorbed/desorbed by any solid phase over a period of time [9, 136-139]. Understanding sorption/desorption characteristics of any solid phase materials requires two main laboratory experimental techniques (a) batch equilibrium testing, and (b) continuous solid phase column-leaching testing. These involve... 

Toxicity. The fourth characteristic that could make a waste a hazardous waste is toxicity (40 CFR 261.24). To determine if a waste is a toxic hazardous waste, a representative sample of the material must be subjected to a test conducted in a certified laboratory using a test procedure [toxicity characteristic leaching procedure, (TCLP)]. Under federal rules (40 CFR 261), all generators are required to use the toxicity characteristic leaching procedure test when evaluating wastes. 

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. 

Other workers, however, consider this proposed method of testing unduly tedious and offer constructive suggestions for accelerating leach tests ( ). Many of these proposed methods involve physical destruction of the waste form in order to increase the surface area exposed to the leachant. Such a procedure not only can alter the physical characteristics of the surface exposed to leaching but also can require the measurement of the surface areas of finely divided solids with the concomitant difficulties mentioned above. 

Leach rates for elements other than those listed in Table II can also be determined by this method. In fact, any element in the periodic table that is solid at room temperature and has an activation product with a half-life sufficiently long to allow leach testing can be studied with this technique. This method can also be applied to the study of the leach rates of alpha emitting actinides present in waste. In this case, standard carrier-free radiochemical procedures, coupled with low background alpha counting, would be invoked. 

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... 

Ray, I., and Thiele, H., Long Term Leaching of Silicate Systems Testing Procedure, Actinides Behavior and Mechanism, Karlsruhe Report KFK-2456 (1977). 

Field leaching tests, where wastes are stored in big tanks, are also performed. Field leachates are collected on a regular basis, chemically monitored and tested with (at least) the same bioassays as those used in the simulation leaching tests, so as to compare the results with the upper procedure. 

Briefly recalled, the WASTOXHAS approach consists in characterizing the ecotoxicological hazard potential of contaminant fluxes from waste leachate obtained under defined conditions with two different dynamic leaching procedures laboratory simulated leaching tests and field leaching tests. The approach developed below considered a specific scenario that simulates a waste deposit receiving rain or run-off water (Perrodin et al., 2002). 

Leaks in medical sources and seeds are detected by a vacuum immersion leach test. Because the internal volume of the medical sources is so small (3.6 x 10 mL, in the case of the ALC-P4C seed), the conventional helium leak test is not a valid leak test procedure. About 45 minutes is required to pump down the system before helium measurement is begun. If the internal volume of the test specimen is small, trapped helium would escape before helium assay begins. Therefore, leaks in encapsulated medical sources are detected by measuring the alpha activity of a nitric acid penetrant solution in which the source had been immersed. After immersion, pressure above the liquid is decreased to 2.5 psia for 3 min before venting to atmosphere. This procedure is repeated twice, then the sources remain in acid a minimum of 16 h at 20°C. 

TCLP Toxicity Characteristic Leaching Protocol (Procedure ), an EPA-required laboratory test to determine whether harmful amounts of material leach from wastes in simulated landfill disposal conditions. 

The last characteristic, the Extraction Procedure Toxicity Characteristic (EPRC), identifies hazardous waste by evaluating the potential of a waste to release toxic constituents to the ground water. The Toxicity Characteristic entails use of a leaching test to measure the tendency of a waste to leach, coupled with extract concentrations above which the waste is defined to be a regulated, or hazardous, waste. 

The program involved leaching selected industrial chemical process residuals with leachate derived from municipal refuse in a pilot-scale field facility measuring the concentration of the compounds which leached from the wastes and comparing these field concentrations to those in the EP and other candidate leaching tests. The Toxicity Characteristic Leaching Procedure or TCLP, is the outgrowth of these studies. 

The acceptability of a hazardous waste for land disposal in the United States is largely based on the results obtained from running the U.S. Environmental Protection Agency Extraction ftocedure(ET) test ts]. In this test, the waste is contacted with a mild acetic acid leachant for 24 hours, after which the leaShant is analyzed for specific metals which may have leached. This test procedure... 

Batch extraction of the particle fractions were performed using the U.S. EPA EP-toxicity test and a modified version developed in our laboratories. The 2 main differences in these tests are 1) the EP-toxicity test uses 0.5 N acetic acid to enhance leaching whereas the modified test uses 17.4 N glacial acetic acid and 2) the EP-toxicity test limits the amount of acid added to keep the pH at 5.0 + 0.5 to 40 ml so that the actual pH of the leaching medium may be well above pH 5.0 if additional acid is needed, whereas there was no limit as to how much 17.4 N acetic acid could be added to keep the pH at 5.0 + 0.5 in the modified test. The samples were placed on a shaker-table in a controlled temperature room (20 C) the pH was monitored and adjusted over a 24 hour period as specified in the EP-toxicity test procedure[ 9 ]. 

Some leaching tests were undertaken to ascertain the extent of trace metals contamination by sampling devices when collecting surface/deep sea water and snow/ice cores (52). Go-flow bottles, polyethylene tanks corers (especially knives and head) as well as all plastic items and Teflon components of the Differential Pulse (DP) ASV instrumentation used for the analytical determinations had to be preliminarily cleaned according to very stringent procedures. All this resulted in a significant abatement of the contamination by Cd and Pb. 

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