Semi-dynamic Leaching Tests Research Articles

Long-term stability of KEtX/Cu(OH)2 matrix in landfill leachates

In this study, the long-term stability of KEtX/Cu(OH)2 matrix under early-period and late-period landfill leachates was evaluated using semi-dynamic leaching test (SDLT), X-ray diffractometer (XRD) and fourier transform infrared (FTIR) techniques. The results of SDLT after 60-day periods of extraction indicated that the cumulative leaching of Cu was only 0.72% and 3.34% of the total Cu in the KEtX/Cu(OH)2 matrix under early-period and late-period landfill leachates, respectively. The investigation of crystallinity and functional groups between the leached KEtX/Cu(OH)2 matrices after 1-day and 60-day periods of extraction using XRD and FTIR indicated that the KEtX/Cu(OH)2 matrices were perfectly unaffected by the extraction using early-period and late-period landfill leachates during the 60-day leach time. Consequently, the KEtX/Cu(OH)2 matrix had a stabilizing behavior extracted in landfill leachates.

Leaching and stabilizing characteristics of copper diethyl dithiocarbamate in an acetic acid solution

The leaching and stabilizing characteristics of synthetic copper diethyl dithiocarbamate (Cu‐DDTC) under 1 N acetic acid solution were characterized using semi‐dynamic leaching test (SDLT), ultraviolet‐visible spectrophotometer (UV‐visible), X‐ray diffractometer (XRD), fourier transform infrared spectrophotometer (FTIR), and scanning electron microscopy (SEM) techniques. The analyses of leached species of leaching solution by SDLT and UV‐visible indicated that the degree of degradation of various elements from the Cu‐DDTC complex could be classified as: N (25%) > S (20%) > Cu (0.7%) and no dithiocarbamate species in the liquid phase were detected. The copper species of insoluble Cu‐DDTC complexes were much more stable than those of copper solidification in cementitious matrix. The investigation of crystallinity showed that there were two unidentifiable peaks present in the XRD pattern of the leached Cu‐DDTC complex that might be attributed to new chemical interactions. The spectra obtained by FTIR analyses obviously showed that the major functional groups, such as C‐N, S‐C‐S, C=S, Cu‐S, and C‐H groups, were both present in the unleached and leached Cu‐DDTC complex. Microstrctural analyses by SEM revealed that the unleached and leached Cu‐DDTC complexes had the same morphologies, but the grain size of the leached Cu‐DDTC complex is much larger and compact than that of the unleached complex. Thus, it was suggested that the leaching and stabilizing characteristics of the insoluble Cu‐DDTC complexes consisted of the dissolution and decomposition of Cu‐DDTC and the chelating reaction between copper and NDDTC.

Long-term stability of KEtX/Cu(OH)2 matrix in landfill leachates

In this study, the long-term stability of KEtX/Cu(OH)2 matrix under early-period and late-period landfill leachates was evaluated using semi-dynamic leaching test (SDLT), X-ray diffractometer (XRD) and fourier transform infrared (FTIR) techniques. The results of SDLT after 60-day periods of extraction indicated that the cumulative leaching of Cu was only 0.72% and 3.34% of the total Cu in the KEtX/Cu(OH)2 matrix under early-period and late-period landfill leachates, respectively. The investigation of crystallinity and functional groups between the leached KEtX/Cu(OH)2 matrices after 1-day and 60-day periods of extraction using XRD and FTIR indicated that the KEtX/Cu(OH)2 matrices were perfectly unaffected by the extraction using early-period and late-period landfill leachates during the 60-day leach time. Consequently, the KEtX/Cu(OH)2 matrix had a stabilizing behavior extracted in landfill leachates.

Study of the remediation of a site contaminated with arsenic

Soil and rock-like material was collected from a former industrial site (arsenic factory) in order to study the degree to which the site is contaminated. Characterisation of the soil and rock-like samples indicated that the site is highly contaminated with arsenic: the soil material contains 2.5–3.5% (dry wt.%) of arsenic, the rock-like material up to 20%. According to Flemish norms ( VLAREBO, 1996) concerning the contamination of soils for industrial sites, remediation of the soil is required on a short-term basis when a value of 300 mg As/kg of dry solid is exceeded. In this paper, solidification/stabilisation with cement and/or lime for remediation of the site was studied. If later the solidified site material is landfilled, one of the criteria is that the arsenic concentration in the leachate, determined according to the DIN 38 414 S4 extraction test ( Deutsches Institut für Normung, 1984), must be lower than 1 mg/l ( VLAREM II, 1995). Solidification proved to be an efficient method to lower the amount of arsenic leached from the material to below the norm of 1 mg/l. The results of a semi-dynamic leach test indicated that arsenic was released very slowly from the solidified material: over the period of the leach test only 0.10% of the arsenic initially present was leached.

Influence of low temperature air oxidation on the dissolution behaviour of UO 2 and MOX spent fuel

The dissolution behaviour of pre-oxidised LWR UO 2 and MOX spent fuel was studied by means of semi-dynamic leaching tests. The fuels, irradiated to burn-ups of 53 and 39 GWd t −1 respectively, were thermally treated at 250°C in air for various times, up to different oxygen/metal (O/M) ratios. The leaching tests performed in deionised water at ambient temperature revealed, for both UO 2 and MOX, an instantaneous release strongly dependent on the oxidation degree. After this initial stage, a very low leaching rate, almost independent of the O/M-ratio, was measured. For both fuel types, the fission products considered showed a fractional release normalised to that of uranium higher than 1, due to either the larger inventory at grain boundaries as a consequence of migration upon irradiation or to the inherent higher solubility of some of these elements. In contrast to fission products, the fractional release of Pu from the UO 2 fuel was not affected by the oxidation level of the fuel and was one order of magnitude lower than the release of U. For MOX fuel, the intrinsic heterogeneity of the material due to Pu as fissile element being concentrated in agglomerates, led to a stronger release of this element relative to the U-matrix for the non-oxidised sample. After oxidation, which affects almost exclusively the matrix, the instantaneous release rate of Pu is again significantly lower in comparison to U.

Slaking mechanisms of mudstone liner immersed in water

The purpose of this research is to probe the slaking property of the mudstone meeting with water. The elemental, crystalline, and morphologic changes in the mudstone with three different water contents were characterized using X-ray fluorescence spectrometer (XRF), semi-dynamic leach test, X-ray diffractometer (XRD), and scanning electron microscopy (SEM)/energy-dispersive X-ray analysis (EDAX) techniques. The XRF and chemical composition analyses indicated that the mudstone contains high concentrations of silicon and aluminum and low concentrations of calcium, iron, potassium, and sodium. The XRD examination showed large amount of quartz and illite, minor calcium aluminate hydrate and calcium silicate hydrate, and small amount of unidentifiable peaks. The result of semi-dynamic leach test showed that the release of sodium is very rapid initially and the released calcium species increase largely in the final subsequent extractions. The microanalysis using SEM/EDAX indicated that the petal-like structures increase with the moisture content of the mudstone. Thus, it was inferred that the possible mechanisms of the mudstone meeting with water to lead to the slaking phenomenon are stated as follows. The sodium sulfate will rapidly dissolve from the mudstone, and the sulfate species and calcium aluminate hydrate form the platelet-like solid solution of 3CaO–Al 2O 3–CaSO 4·12H 2O making the mudstone lose its cementing reaction.

An evaluation of the solidification/stabilisation of industrial arsenic containing waste using extraction and semi-dynamic leach tests

Solidification/stabilisation of an industrial waste material containing large amounts of arsenic, as As 2O 3 (32 wt%), was studied. The waste was treated using solidification/stabilisation (S/S) with cement (Ecobind50), lime and blast-furnace slags (Betogrid) in order to reduce the leachability of arsenic. In order to optimize the procedure for S/S, 10 different S/S samples, differing in amount and combination of the binder materials were prepared. On these samples, extraction tests were performed, showing that the arsenic concentration in the leachate is correlated with the pH and the calcium concentration due to the formation of slightly soluble CaHAsO 3. A semi-dynamic leach test was performed in order to obtain quantitative information on the long term leachability of the contaminants (As, Sb, Pb) from monolithic S/S samples. A linear relationship between the cumulative fractions released and the square root of the leach time was observed, indicating that diffusion is the release mechanism. From the diffusion coefficient, the influence of the binder materials on the leachability of the contaminants could be deduced. All the elements considered have a low mobility in all samples. Ca has the highest mobility followed by As and Sb, whereas Pb has the lowest mobility. It appeared that increasing the amount of calcium in the S/S samples lowers the leachability of arsenic, addition of lime being more effective than addition of cement. This conclusion is in good qualitative agreement with the extraction tests.

95/05405 Solidification/stabilisation of arsenic-containing waste: Leach tests and behaviour of arsenic in the leachate

In this study, metallurgical-slag-based binder (MSB) with different dosages of calcium hydroxide (CH) was mixed with high-arsenic-containing mine tailings (HAMT) to form green mining fill samples (GMFs) for As solidification/stabilisation (S/S). The As leaching characteristics of the GMFs were evaluated using pH-dependent leaching tests, semi-dynamic leaching tests and toxicity leaching tests. The effective diffusion coefficient (De) decreased from 6.98 × 10−14 to 5.90 × 10−15 cm2/s and the leachability index (LI) increased from 13.53 to 14.73 after 3 wt.% CH was added to the GMFs. The GMFs containing 0 wt.% CH (GMF-0C) and those containing 3 wt.% CH (GMF-3C) reached pH = 2 with acid addition amounts of 9.0 meq/g-dry and 9.3 meq/g-dry at 90 d curing time, and the maximum As leaching concentrations of GMF-0C and GMF-3C reached 10.47 mg/L and 7.47 mg/L, respectively, indicating that GMF-3C exhibited better acid neutralisation and As retention capacities than GMF-0C. Further, a Tescan Integrated Mineral Analyser (TIMA) was used to analyse the dominant hydration products of GMF-3C, which revealed that calcium silicate hydrate, CASH, ettringite and zeolite phases represented approximately 22.5 wt.% of the products. These results provide an understanding regarding the safe large-scale utilisation of GMFs.

Solidification/stabilisation of arsenic-containing waste: Leach tests and behaviour of arsenic in the leachate

An industrial waste containing large amounts of arsenic (42 wt %) was studied. The waste was treated using solidification/stabilisation technology ( S S ) with cement and pozzolanic materials. Addition of lime appeared to be the major factor in reducing the concentration of arsenic in the leachate from the S S material through the formation of a slightly soluble calcium-arsenic compound in the leachate. To investigate the mechanism of leaching from the S S waste, semi-dynamic leach tests were performed (ANSI/ANS 16.1), but no direct conclusions concerning the release mechanism could be drawn from these tests, as equilibrium was reached during the intervals of static leaching of which the semi-dynamic leach test consists. Therefore, static leach tests were carried out that gave much information about the behaviour of arsenic in the leachate. Moreover, it is shown that arsenic in the leachate is mainly present as As(III) and evidence is presented for the formation of a CaHAsO 3-precipitate. It is concluded that semi-dynamic leach tests may give inaccurate information, if no preliminary study is made of the S S waste-leachate equilibrium.