The Toxicity Characteristic Leaching Procedure (TCLP) was developed by the U.S. Environmental Protection Agency to assess leaching potential of contaminants from waste, and to provide a test to classify hazardous waste. It is a batch leaching test where a waste (such as contaminated soil) and an extraction fluid are agitated for a predetermined time. Since TCLP employs an aggressive mixing technique, it is possible that hydrophobic contaminant-laden colloidal fractions may appear as “dissolved” constituents. In this study, TCLP was employed to determine the leachability of PAH contamination from a coal tar contaminated site. Generated colloids and the apparent aqueous concentrations of naphthalene and phenanthrene were measured at various mixing times in the extraction fluid.
A mathematical model was developed that predicted the apparent aqueous contaminant concentration in the filtrate. This model accounted for the presence of colloids in the filtrate, and quantified contaminant desorption from colloids. The fraction of colloid-bound contaminant was predicted to be negligible for naphthalene. However, phenanthrene was predicted to have a significant fraction of the total contaminant in the colloidal phase, while naphthalene was primarily dissolved. The desorption model and PAH desorption data are presented here to determine the extent of colloid-facilitated desorption during leaching tests. 相似文献
Sewage sludges from 19 Polish municipal treatment plants were investigated. Lysimeter leaching experiments on sludges and on sludge-quartz sand mixtures were made. A variety of plants was sowed in the lysimeters and the leachates were collected. Harvested plants as well as leachates were analysed for Pb, Cu, Cd, Ni, Zn and Cr concentration. Removal coefficients were established to characterize the mobility of these metals from the sludges. The high values of the correlation coefficient for cadmium and nickel suggested that water solubility of metal salts is mainly responsible for their mobility. 相似文献
Summary Increasing quantities of slurry (30, 60 and 90 m3/ha as well as 60 m3/ha + DIDIN) were applied to two sandy soils both in September and in December 1982. During the 1982/83 winter EUF-N was determined in soil horizons (0–30 cm, 30–60 and 60–90 cm).EUF-NO3 and EUF-Norg clearly reflected the different quantities of slurry applied. The retarding effect of DIDIN on nitrification could also be demonstrated by means of the EUF-N contents.Due to the mild and humid climate prevailing in the winter of 1982/83 slurry-NO3 of the September applications had obviously been leached out of the 0–60 cm soil layer in all treatments by February and even out of the 60–90 cm layer by March 24. Translocation of NO3 was also observed for slurry applied in December. But in this case on March 24 the EUF-NO3 contents in the 60–90 cm layer still reflected the quantities of slurry applied four months earlier.After slurry application the EUF-Norg fraction of a soil initially consists mainly of NH
4+
which is rapidly oxidized to NO3 and transferred in this form to deeper layers. As a consequence a rapid decline in EUF-Norg fraction is observed. It could therefore be expedient to consider the Norg and EUF-NH
4+
fractions separately when slurry applications are concerned. 相似文献
Different forms of metallic palladium (wire, foil and sponge) have been tested as potential catalysts in the Suzuki-Miyaura cross-coupling. All samples showed to be catalytically active for both electron-poor and electron-rich aryl bromides combined with a variety of arylboronic acids. Palladium wire has been recycled six times without decrease of activity. A series of poisoning experiments demonstrated that the true catalyst is a soluble form of palladium arising from a leaching process. Interestingly, metal leaching from palladium foil has been clearly evidenced by SEM. 相似文献
Strong seasonal increases in aquatic (stream, ground and hyporheic water) nitrate have been observed in a variety of ecosystems. In most cases, changes in hydrological and vegetative activity occur contemporaneously, making it difficult to determine whether soil leaching is being driven by increases in the availability of leachable N or is simply due to flushing of N that has accumulated over longer periods. Three studies were conducted to better determine controls on soil nitrate leaching in a near-pristine temperate floodplain ecosystem receiving large N inputs via N-fixation by red alder: 1) an artificial rainfall experiment was conducted to estimate N-leaching potential during the summer, when plant uptake is high and new inputs of organic matter are low; 2) soil solution, groundwater and surface water were sampled during a major autumn storm to document exchanges at the seasonal transition, when plant uptake is low and inputs of senescent organic matter are high; and 3) monthly samples of soil and aquatic nitrogen were collected in 1997 and 1998 to document seasonal patterns of N exchanges. Collectively, these studies demonstrate the importance of hydrologic factors in controlling N flux. Nitrate was rapidly leached from soils during actual and simulated rainstorms. Two pathways of nitrate leaching were identified. Localized flooding and direct leaching of streamside soils into surface waters contributed to high solute concentrations in peak flows. Nitrate that leached into interstitial waters was subject to various factors that could delay or reduce its delivery to surface waters. Greater residence time may increase the influence of this component of stormflow on ecosystem productivity. While soil nitrate pools were rapidly depleted during rainstorms, accumulation of soil nitrate occurred over summer dry periods. Large differences in soil and aquatic nitrate concentrations between two years with contrasting rainfall highlight the potential for inter-annual hydrologic variability to affect ecosystem nutrient cycling. 相似文献
Chemical acid leaching is an effective technique for extracting toxic metals from the finest fractions of polluted soils. Nevertheless, the use of large quantities of reagents and process water results in prohibitive operating costs. The purpose of this study was to evaluate the technical and economic advantages of recirculating water in a counter-current leaching process (CCLP). Five 1-h sulfuric acid extraction steps (at pH = 1.5) followed by three 5-min water-washing steps were applied to the fine particle fraction (<0.125 mm) of an industrial soil polluted by Cd (13.2 mg·kg?1), Cu (3 100 mg·kg?1), Mn (685 mg kg?1), Pb (550 mg·kg?1), and Zn (2 840 mg·kg?1). The leaching experiments were carried out at ambient temperature using a 10% soil suspension and in 1-L working volume stirred tank reactors. This paper presents results of conventional and counter-current leaching process (CCLP) tests and shows that the CCLP yields removal results for Cu (85%), Zn (86%), Mn (75%), and Cd (90%) that are similar to those obtained using the conventional leaching process. Moreover, the CCLP uses half of the quantity of acid and one-eighth of the amount of water that the conventional process uses. Metal precipitation with NaOH and Ca(OH)2 was applied to treat the acidic leachates, and good metal removal yields were achieved with both reagents. However, the large consumption of chemicals implies high operating costs. In addition, the precipitation causes considerable sludge production, particularly when using Ca(OH)2. Overall, the CCLP coupled to metal precipitation using NaOH and water recycling appears to be the most attractive option for the removal of toxic metals from this industrial soil. 相似文献