Column Leaching Tests Research Articles

The retention capabilities of soils at Batang Berjuntai and Ampar Tenang as natural clay liners for landfill systems using leaching column test and selective sequential extraction analysis

Clay liners have the ability to interact chemically with leachate. If suitable clay liner can be identified, it can help to attenuate the migration of leachate to groundwater and surface water. In this study, leaching column tests were used to determine the retention capability of heavy metals for two types of soils collected adjacent to a landfill in Selangor. The active landfill sites chosen are Kg. Hang Tuah in Batang Berjuntai (HM:S) and Ampar Tenang, Sepang (ARA) where the HMS samples are metasediment soil and ARA samples are river alluvium soil. Selective sequential extraction (SSE) was used to study the retention mechanisms of heavy metals in the soil columns obtained from leaching column test experiments. Acid digestion was later used to check the validity of the SSE results. Breakthrough curves for metasediment soil from Kg. Hang Tuah show good retention of heavy metal ions with relative concentration, C';Co (10. 1 - 10.5) compared to river alluvium soil from Ampar Tenang with relative concentration, Ce/Co (10. 1 - 10-4). This corresponds with the pH of the effluents and the pore fluid where the HMS samples are more alkali compared to ARA samples. Generally, HMS and ARA samples have same ranked order of buffering capacity; Cu:>Zn>Pb>Ni. The distribution of the heavy metals with soil constituents are ranked in the following phases: Exchangeable> Carbonates> Hydroxides> Residuals> Organics Abstrak: Pelapik lempung mempunyai keupayaan untuk bertindak secara kimia terhadap cecair larut lesap. Sekiranya pelapik lempung yang sesuai dapat dikenalpasti, ia dapat membantu bagi mengurangkan migrasi cecair larut lesap ke dalam air bawah tanah dan air permukaan.Dalam kajian ini, ujian kolum turasan telah digunakan untuk mengenalpasti keupayaan menahan logam-logam berat bagi duajenis tanah yang telah diambil berdekatan tapak pelupusan sisa di Selangor. Tapak pelupusan sisa pepajal yang aktifyang dipilih ialah di Kg. Hang Tuah di Batang Berjuntai (HMS) dan di Ampar Tenang, Sepang (ARA) di mana sampel HMS merupakan tanah metasedimen dan ARA pula merupakan tanah aluvium sungai. Rangkaian pengestrakan terpilih (SSE) telah digunakan untuk mengkaji mekanisma menahan logam-logam berat di dalam kolum tanah yang diperolehi daripada eksperimen ujian kolum turasan. Pencernaan asid telah digunakan untuk memastikan kesahihan keputusan SSE. Pecahan lengkung-lengkung bagi tanah metasedimen dari Kg. Hang Tuah menunjukkan penahanan ion logam berat yang baik dengan konsentrasi relatif, CICo (10·/ -1 0.5) berbanding tanah aluvium sungai dari Ampar Tenang dengan konsentrasi relatif, CICo (10./_104 ). Ini selari dengan nilai pH ejluen dan cecair liang yang menunjukkan sampel HMS lebih beralkali berbanding sampel ARA. Keseluruhannya, sampel HMS dan ARA mempunyai kedudukan susunan kapasiti menampan yang sama; Cu>Zn>Pb>Ni. Taburan logam­ logam berat dengan juzuk tanah telah disusun seperti fasa berikut: Tukarganti > Karbonat > Hidroksida > Residual > Organik

Evaluation of the stability of arsenic immobilized by microbial sulfate reduction using TCLP extractions and long-term leaching techniques

An investigation was conducted to evaluate the stability or leachability of arsenic immobilized by microbial sulfate reduction. Anoxic solid-phase samples taken from a bioreactor previously used to treat metal and As contaminated water using sulfate reducing bacteria (SRB) were subjected to the toxicity characteristic leaching procedure (TCLP) and long-term column leaching tests. The results from TCLP experiments showed that the concentration of As leached from solid-phase sulfide material (SSM) samples after an 18 h extraction time was <300 μg l −1, which is below the current maximum Australian TCLP leachate value for As, and thus would not be characterized as a hazardous waste. In terms of percent total As leached, this was equivalent to <8.5% for SSM samples initially containing 61.3 mg kg −1 As. The levels of As extracted by the TCLP was found to be significantly lowered or underestimated in the presence of dissolved oxygen, with As concentrations increasing with decreasing headspace-to-leachant volume ratios. The concentration of As was also consistently higher in nitrogen purged extractions compared to those performed in air. This was attributed to the dissolution of Fe–sulfide precipitates and subsequent oxidation of Fe(II) ions and precipitation of ferric(hydr)oxides, resulting in the adsorption of soluble As and corresponding decrease in As concentrations. According to the experimental data, it is recommended that TCLP tests for As leachability should be performed at least in zero-headspace vessels or preferably under nitrogen to minimize the oxidation of Fe(II) to ferric(hydr)oxides. In long-term leaching studies (∼68 days), it was found that the low solubility of the SSM ensured that rate of release of As was relatively slow, and the resulting leachate concentrations of As were below the current Australian guideline concentration for arsenic in drinking water.

Soil pH Variation Within a Soil. II. pH Variation in a Neutral and an Alkaline Soil

Soil pH variation exists in particles of every kind of soils, including alkaline soil. The objective of this study was to examine soil pH varia-tion in a neutral and an alkaline soil using the column-leaching method. Column-leaching tests were applied to two soils (Callaway and Mount Palomar) at the depths of 0–30 and 30–60 cm. Two replicates were applied to each column-leaching test. Acidification had started in both soils at the depths of 0–30 and 30–60 cm. The pH differentials between the highest pH value and the lowest pH value in leaching fraction in the neutral and the alkaline soils were within one pH unit, and were smaller than those in the acidified soils. This methodology can help understand the soil acidification process and its rate.

Soil pH Variation Within a Soil. III. pH Variation in Limed Soil

There are many methods for determining lime requirement, but no single method is suitable for all soils. A fast and efficient method to evaluate lime effect is needed. Soil buffering capacity tests and column-leaching tests were applied to the limed Van Rockel soil at the depth of 0–30 cm to evaluate pH distribution after liming. Two groups of the Van Rockel soil were taken for soil buffering capacity test and two replicates were applied to each column-leaching test. The objective of this study was to evaluate some relationships in pH variation in soil after liming. The buffering capacity of a soil depends on the rate of acidification of the soil. Equilibrium of pH value was reached at about collector #7 after which there was no change of pH value. It was concluded that pH differentials of the lowest and the highest fractions of 0.5 units indicated that liming had an influenced effect. Although adequate, more lime decreased soil pH differential not less than 0.3 units in all fractions.

Soil pH Variation Within a Soil. I. pH Variation in Soil Pores Observed in a Column-Leaching Method

The traditional method for determining soil pH is to measure the pH of mixed soil samples. The resulting measured soil pH as an average is used to represent the unsampled neighborhood. This average cannot really represent the actual soil pH value if spatially dependent heterogeneity of soil properties exists among the samples. The objective of this study was to develop a more complete understanding of soil pH in soil that had been acidified by use of nitrogen fertilizer. The soil samples obtained from the Van Rockel vineyard in Temecula, CA were taken to run a designed column-leaching test from four random test sites with two replicates per site at the depths of 0–30 cm, 30–60 cm, and 60–90 cm. The pH variation in soil pores was observed periodically through several column-leaching tests. When unsieved soil samples in an air-dried state were used to observe the changes in soil pH as shown by a column-leaching procedure, soil pH values during leaching increased gradually with elapsed time in a third or fourth order polynomial functional manner for the first 30 collectors (roughly 90 min) and approached nearly constant values for the last 10 collectors (roughly 30 min). There was a wide pH differential range (0.42–1.73 pH units) in acidified soil in different fractions. The early collection had pH values less than the traditional method and the late collection had pH values greater than the traditional method.

Release dynamic process identification for a cement based material in various leaching conditions. Part I. Influence of leaching conditions on the release amount

In this paper we investigate at laboratory scale the influence of the liquid/solid leaching conditions on the release of different chemical species from a reference porous material obtained by solidification of PbO and CdO with Portland cement. The pH influence on the dissolution of pollutants and the initial pore solution composition (target elements: Na +, K +, Ca 2+, Pb 2+, Cd 2+, SO 4 2 − ) were assessed by applying a methodology consisting of two equilibrium leaching tests, the Acid Neutralization Capacity (ANC) and the Pore Water (PW) tests and geochemical modelling. Samples of the same material were submitted in parallel to four different dynamic leaching tests in order to determine the influence of the sample shape (monolithic or granular) and eluate hydrodynamics (instantaneous L/S ratio, eluate renewal) on the leaching of the target elements. The comparison criteria were the eluate saturation state, the cumulative release and the released flux. Generally, the eluates obtained in the tests applied on granular material were more concentrated, even saturated for the eluate pH value with respect to Ca 2+, Pb 2+ and SO 4 2 − . The consequence of the eluate saturation is the slowing down effect on the dynamic release. The highest released flux was observed for the Monolith Leaching Test (MLT) involving the highest instantaneous L/S ratio and the lowest solid/liquid exchange surface and for which no saturation was observed, except Pb 2+ and SO 4 2 − in some eluates. The maximum cumulative released-mass was obtained for the Column Leaching Test (CLT) applied on granular material having the highest exchange surface, the lowest instantaneous L/S and a continuous input flow of the leachant. The experimental results demonstrate the significance of the liquid/solid contact type which is also a scenario specific parameter.

Definition of economic optimum for the leaching of high acid-consuming copper ores

The objective of any business is to maximize the value derived from the commodity produced. There is a point where additional expenditure does not return a value sufficient to justify the additional expense. The treatment of high acid-consuming copper ores is a perfect example of this principle. In this case, the relationship of acid consumed to the percentage of copper extracted is vital to the economic value of the final product. This paper describes a method of evaluating column leach test data to determine the economic optimum conditions for leaching high acid-consuming copper ores. The effect of acid consumption on the net economic value of the copper extracted is very significant in the case of high acid-consuming ores. The focus of this paper is the relationship of acid concentration in the raffinate and acid cure dosage to the economic value of a leach cycle.

Sorption and leaching behaviour of polar aromatic acids in agricultural soils by batch and column leaching tests

SummaryAromatic acids can reach the soil from direct anthropogenic activities or, indirectly, from the degradation of many aromatic compounds, such as pesticides or polycyclic aromatic hydrocarbons. Because of the anionic character of aromatic acids at the pH of most soil and sediment environments, they are expected to move rapidly through the soil profile and to pose a great risk of ground water contamination. We designed batch and column leaching tests to characterize the behaviour of three aromatic acids differing in their chemical structures, picloram (4‐amino‐3,5,6‐trichloropicolinic acid), phthalic acid (2,2‐benzenedicarboxylic acid), and salicylic acid (2‐hydroxybenzoic acid), in four European soils with different physicochemical characteristics. Batch experiments revealed that the persistence of the three acids in soil:water suspensions decreased in the order: picloram ≫ phthalic acid &gt; salicylic acid, and their dissipation curves were relatively independent of soil type. Sorption by the soils, their clay‐size fractions and model sorbents indicated much greater affinity of soil constituents for salicylic acid than for picloram or phthalic acid, most likely due to the ability of salicylic acid to form bidentate complexes with positively charged soil components. The extent of leaching of the aromatic acids in hand‐packed soil columns decreased in the order: picloram (90–96%) &gt; phthalic acid (25–90%) &gt; salicylic acid (0–37%), which was consistent with the sorption and persistence results of the batch tests. The organic C content, the amount of small‐size pores, and the initial concentration of aromatic acid in soil appeared to be important factors influencing the leaching patterns of phthalic acid and salicylic acid in the soils studied, but did not greatly influence the leaching pattern of picloram. Sorption and leaching of polar aromatic acids in soil can therefore vary considerably depending on the structural characteristics of the aromatic acid or soil type.

Geochemical effects of oxidation products and framboidal pyrite oxidation in acid mine drainage prediction techniques

Acid mine drainage predictive testwork associated with the Australian Mineral Industries Research Association (AMIRA) P387A Project: Prediction and Kinetic Control of Acid Mine Drainage (AMD) has critically examined static acid assessment and kinetic information from acid–base accounting techniques, including net acid production potential (NAPP), net acid generation (NAG) and column leach tests. This paper compares results on two waste rock samples that were obtained from the Kaltim Prima Coal mine (KPC) containing significant quantities of fine-grained framboidal pyrite. In agreement with other research, the authors' results indicated that framboidal pyrite is more reactive than euhedral forms due to the greater specific surface area of framboidal pyrite. This is evidenced by optical microscopy of reacted samples. Importantly, the results showed that NAPP testing is biased by the rapid acid generating oxidation of framboidal pyrite prior to, and during the acid neutralisation capacity (ANC) test. This can result in negative ANC values for samples containing significant framboidal pyrite (often “corrected” to zero kg H 2SO 4/t) when significant ANC is actually present in the sample. NAG testing using H 2O 2 indicated that samples containing a significant quantity of framboidal pyrite can result in the catalytic decomposition of the H 2O 2 prior to complete oxidation of the sulfide minerals present, requiring sequential addition of H 2O 2 for completion. A benefit of the NAG test, however, is that it assesses the net acid generation capacity of the sample without bias towards acid generation as is observed using NAPP methods. The kinetic NAG test also gives information on the reaction sequence of framboidal and euhedral pyrite. Periodic (kinetic) analysis of sub-samples from column leach tests indicated rapid oxidation of the framboidal pyrite compared to the euhedral pyrite, which was correlated with the greater framboidal pyrite surface area. Calculations to determine the sulfide/sulfate acidity derived from the oxidation of framboidal pyrite prior to; and during the ANC test have been developed to provide a better indication of the actual ANC (ANC Actual) of the sample. Paste pH values of <pH 4–5 may be one suitable trigger mechanism for the implementation of this new method. This has led to an improved NAPP estimation of total acid production. Together with NAG and column leach testing this improved methodology has resulted in accurate AMD characterisation of samples containing acidic oxidation products and framboidal pyrite.

Thermal treatment of stabilized air pollution control residues in a waste incinerator pilot plant. Part 2: Leaching characteristics of bottom ashes.

With the perspective of generating only one solid residue from waste incineration, co-feeding of municipal solid waste and air pollution control residues stabilized by the Ferrox process was investigated in the TAMARA pilot plant incinerator as described in Bergfeldt et al. (Waste Management Research, 22, 49-57, 2004). This paper reports on leaching from the combined bottom ashes. Batch leaching test, pH-static leaching tests, availability tests and column leaching tests were used to characterize the leaching properties. The leaching properties are key information in the context of reuse in construction or in landfilling of the combined residue. In general, the combined bottom ashes had leaching characteristics similar to the reference bottom ash, which contained no APC residue. However, As and Pb showed slightly elevated leaching from the combined bottom ashes, while Cr showed less leaching. The investigated combined bottom ashes had contents of metals comparable to what is expected at steady state after continuous co-feeding of APC residues. Only Cd and Pb were partly volatilized (30-40%) during the incineration process and thus the combined bottom ashes had lower contents of Cd and Pb than expected at steady state. Furthermore, a major loss of Hg was, not surprisingly, seen and co-feeding of Ferrox-products together with municipal solid waste will require dedicated removal of Hg in the flue gas to prevent a build up of Hg in the system. In spite of this, a combined single solid residue from waste incineration seems to be a significant environmental improvement to current technology.

Geochemistry of leachates from coal ash

Abstract The combustion of coal around the world for power generation produces huge volumes of fly ash. In Europe alone this amounted to about 40 Mt in 2000 of which less than 50% was utilized. The waste ends in lagoons, ash mounds, and landfill sites. Coal ashes have high concentrations of many trace elements, some of which are of environmental concern. Although the origin of elements in coals is not considered in this chapter, other aspects of the geochemistry are, and in particular the location of elements within the coal as this influences the behaviour of elements during combustion. During combustion many elements are volatile and are concentrated on the surfaces of the ash particles. Analyses of input coal and combustion residues from Eggborough power station (UK) demonstrate retention of the majority of elements in the solid combustion products, and analyses of size-fractionated fly ash have enabled the percentage surface association to be calculated, which for elements such as As and Mo is considerable. A consideration of the general leaching behaviour leads to the conclusion that it is the surface-associated elements that are most susceptible to leaching in the aqeous environment. The pH is an important control on trace element mobility in water, and in leachates from fly ash ranges from 3.3 to 12.3. High-sulphur coals generate acidic leachates, but not exclusively as the laboratory and field data demonstrate in case studies on UK coals. Batch and column leaching tests on fly ashes are reviewed and data presented for fresh fly ash and weathered fly ashes from two UK mounds dating back 17 and 40 years. The weathered ashes do have lower leachate concentrations than the fresh ash, but in spite of their ages they would not be considered to be inert. The batch leaching tests are of value in simulating high liquid-to-solid ratios encountered in ash lagoons, whereas the column leaching tests relate more closely to ash mounds. Finally, the results of field studies are reviewed and data presented for samples from boreholes in the two ash mounds. Analyses of the ash and extracted porewaters demonstrate depth-related changes due to reaction of the ash with the infiltrating water and whether or not equilibrium was established. Calculations demonstrate that the porewaters achieve saturation with respect to gypsum at depth in the boreholes. Infiltration over the years has led to detectable changes in the concentrations of some of the major elements in the bulk ash, such as Ca, and this enables realistic infiltration rates to be calculated. However, there are not comparable changes in the concentrations of the trace elements in the ash because the rate at which elements are being removed in solution is not sufficiently great.

A laboratory study of covers made of low-sulphide tailings to prevent acid mine drainage

Covers with capillary barrier effects (CCBE) are considered to be one of the most effective ways to control acid mine drainage (AMD) production from mine wastes. The use of low-sulphide tailings in CCBE has been proposed recently for cases where other types of material may be unavailable near the mining site. This paper presents leaching column test results showing that CCBEs with a moisture-retaining layer made of slightly reactive tailings, with three different sulphide contents, can effectively limit the production of AMD from the acid-generating tailings placed underneath. With these layered covers, the leachate pH was maintained near neutrality throughout the testing period. When compared to uncovered tailings, the efficiency of the cover systems for reducing the amount of contaminants in the percolated water was determined to be greater than 99% for zinc, copper and iron. This study shows that the use of low-sulphide tailings can improve the ability of a CCBE to limit gas diffusion by consuming a fraction of the migrating oxygen.

Evaluation of Leaching Tests for Cement Based Immobilization of Hazardous Compounds

A range or arsenic containing compounds, including arsenic trioxide, pentoxide and a lead arsenate insecticide have been stabilized using formulations of cement alone, cement + lime and cement + ferrous sulfate and subsequently exposed to a range of leaching regimes in order to compare their effectiveness for metal stabilization. Leaching tests used were two regulatory tests, the Toxicity Characteristic Leaching Procedure (TCLP) and the Australian Bottle Leaching Procedure (ABLP), as well as column leaching. Arsenic leachate concentrations from cement-stabilized lead arsenate insecticide were similar when subjected to either the TCLP or ABLP using the same leachant. Lead, known to be immobilized by means different to that of arsenic, yielded varying leachate concentrations when using either of the regulatory tests, even though the leachant was of the same type. The leaching of calcium influences the filtered arsenic leachate, whereas the leaching of lead is greatly affected by leachate pH. As expected, both regulatory tests generally proved to be very severe in terms of the masses of the hazardous constituents leached when compared to conceptually more realistic column leaching scenarios. Sodium arsenate-containing formulations behaved anomalously, with column leaching tests resulting in larger arsenic masses being leached than the regulatory tests. Sodium arsenate, known to inhibit cementation reactions, serves as a reminder of the perils that can be faced when generalizing the results obtained from leaching tests.

Speciation and characterization of arsenic in Ketza River mine tailings using X-ray absorption spectroscopy.

Ketza River mine tailings deposited underwater and those exposed near the tailings impoundment contain approximately 4 wt % As. Column-leaching tests indicated the potential for high As releases from the tailings. The tailings are composed dominantly of iron oxyhydroxides, quartz, calcite, dolomite, muscovite, ferric arsenates, and calcium-iron arsenates. Arsenopyrite and pyrite are trace constituents. Chemical compositions of iron oxyhydroxide and arsenate minerals are highly variable. The XANES spectra indicate that arsenic occurs as As(V) in tailings, but air-drying prior to analysis may have oxidized lower-valent As. The EXAFS spectra indicate As-Fe distances of 3.35-3.36 A for the exposed tailings and 3.33-3.35 A for the saturated tailings with coordination numbers of 0.96-1.11 and 0.46-0.64, respectively. The As-Ca interatomic distances ranging from 4.15 to 4.18 A and the coordination numbers of 4.12-4.58 confirm the presence of calcium-iron arsenates in the tailings. These results suggest that ferric arsenates and inner-sphere corner sharing or bidentate-binuclear attachment of arsenate tetrahedra onto iron hydroxide octahedra are the dominant form of As in the tailings. EXAFS spectra indicate that the exposed tailings are richer in arsenate minerals whereas the saturated tailings are dominated by the iron oxyhydroxides, which could help explain the greater release of As from the exposed tailings during leaching tests. It is postulated that the dissolution of ferric arsenates during flow-through experiments caused the high As releases from both types of tailings. Arsenic tied to iron oxyhydroxides as adsorbed species are considered stable; however, iron oxyhydroxides having low Fe/As molar ratios may not be as stable. Continued As releases from the tailings are likely due to dissolution of both ferric and calcium-iron arsenates and desorption of As from high-As bearing iron oxyhydroxides during aging.

Leaching of metals from soil contaminated by mining activities

Stabilization/solidification (s/s) is one of the most effective methods of dealing with heavy metal contaminated sites. The ability of lime and cement stabilization to immobilize Pb, Cu and Fe contained in a contaminated soil originating from an old mining and smelting area located along the Mediterranean Sea shore in northern Cyprus was investigated. The stabilization was evaluated by applying leaching tests. A series of tests were conducted to optimize the additive soil ratio for the best immobilization process. Additive/soil=1/15 (m/m) ratio was found to be the optimum for both lime and cement. Application of the US EPA toxicity characteristic leaching procedure (TCLP) on the soil samples treated with lime at additive/soil=1/15 (m/m) mixing ratios showed that Cu and Fe solubility was reduced at 94 and 90%, respectively. The results of cement treatment using the same ratio, reduced the solubility 48 and 71% for Cu and Fe, respectively. The Pb solubility was found to be below the regulatory limit of 5 mg/l so no additive treatment was needed. The optimum additive/soil amount (1/15) was selected for more detailed column studies, that were carried out in the acidic pH range. According to the results of column leaching tests, it was found that, the degree of heavy metal leaching is highly dependent on pH.

Sulfate leaching from recovered construction and demolition debris fines

Recovered soil fines are a product of the mechanical processing of construction and demolition (C&D) debris for recycling. C&D debris fines have been proposed as a substitute for soil in a number of applications. Questions have been raised regarding the potential environmental impact of sulfate leaching from particles of gypsum drywall in the soil fines. Sulfate has a secondary drinking water standard of 250 mg/l and may convert to hydrogen sulfide during some reuse scenarios. Soil fines were collected from 13 C&D debris recycling facilities in south Florida. A leaching study on the C&D debris fines was performed to examine sulfate leachate concentrations resulting from both batch and column leaching experiments. The sulfate concentrations resulting from the batch leaching tests ranged from 890 to 1600 mg/l. The results of the column leaching tests also resulted in high sulfate concentrations. The source of sulfate in the debris fines was the dissolution of gypsum wallboard. The results from a multiple batch test indicated that the mass of the gypsum content in C&D debris fines ranged from 1.5% to 9.1%. The amount of gypsum that would be applied via soil fines during a typical reuse scenario is greater than normal agricultural operations where gypsum is applied. When considering the beneficial reuse of C&D debris fines, site-specific hydrogeology and appropriate state and local regulations for allowable sulfate concentrations in groundwater should be considered.

PH influence on sorption characteristics of heavy metal in the vadose zone

Sorption is an important process in the modelling and prediction of the movement of heavy metals in unsaturated clay barriers. This experimental study investigates the effect of pH changes in the acidic range on the sorption characteristics of heavy metals such as: lead, copper and zinc in an unsaturated soil. A series of one-dimensional coupled solute and moisture leaching column tests, using different heavy metal solutions, were conducted on an unsaturated illitic soil at varying pH values. Variations of volumetric water content (VWC) with distance were measured for different time durations, and concentrations of heavy metals in the liquid and solid phases were analysed. Partitioning coefficient profiles of contaminants along the soil column were determined for each individual layer in the soil. Results from column leaching tests showed that the sorption characteristics of heavy metals are controlled by many factors which should be taken into consideration, i.e. the VWC, time of wetting, soil pH, and the influent heavy metal concentrations. Simplification of K d as a constant and of the VWC as a linear function cannot be considered a good assumption and may lead to an improper evaluation of the sorption phenomena and also to serious errors in predicting contaminant transport through unsaturated soils.

Change in soil's metal carrying capacity as a result of urban sludge addition

The present work investigates the behaviour of heavymetals accumulating in soils treated with urban sludge withrespect to untreated soils. Metal sorption during transportin the soils was evaluated by means of breakthrough curvesobtained via the soil column leaching test and the resultsof laboratory experiments were compared with those of fieldexperiments carried out on the same soil treated insitu with urban sludge. Soil column leaching tests showthat the amount of heavy metals retained in the soilincreases when the soil is treated with sludge both in situand in laboratory; the order of selectivity (Pb > Cu > Zn >Ni) remains similar for the two types of matrix.Experiments carried out both with soils treated with sludge in laboratory and in situ show a good agreementbetween the two sets of data as far as retention capacityis concerned; conversely, an increase in the soil resistance to pH change following acid input is observedwhen sludge treatments are carried out in situ.

Heavy Metals in Urban Soils of East St. Louis, IL Part II: Leaching Characteristics and Modeling

ABSTRACT The city of East St. Louis, IL, has a history of abundant industrial activities including smelters of ferrous and non-ferrous metals, a coal-fired power plant, companies that produced organic and inorganic chemicals, and petroleum refineries. Following a gross assessment of heavy metals in the community soils (see Part I of this two-part series), leaching tests were performed on specific soils to elucidate heavy metal-associated mineral fractions and general leachability. Leaching experiments, including the Toxicity Characteristic Leaching Procedure (TLCP) and column tests, and sequential extractions, illustrated the low leachability of metals in East St. Louis soils. The column leachate results were modeled using a formulation developed for fly ash leaching. The importance of instantaneous dissolution was evident from the model. By incorporating desorption/adsorption terms into the source term, the model was adapted very well to the time-dependent heavy metal leachate concentrations. The results demonstrate the utility of a simple model to describe heavy metal leaching from contaminated soils.

Contaminant Leaching Model for Dredged Material Disposal Facilities

This paper describes the hydrologic evaluation of leachate production and quality model, a screening-level tool to simulate contaminant leaching from a confined disposal facility (CDF) for dredged material. The model combines hydraulics, hydrology, and equilibrium partitioning, using site-specific design specifications, weather data, and equilibrium partitioning coefficients from the literature or from sequential batch or column leach tests of dredged material. The hydraulics and hydrology are modeled using Version 3 of the hydrologic evaluation of landfill performance model. The equilibrium partitioning model includes provisions for estuarine sediments that have variable distribution coefficients resulting from saltwater washout. Model output includes contaminant concentrations in the CDF profile, contaminant concentration and mass releases through the bottom of the CDF, and contaminant concentrations and masses captured by leachate collection systems. The purpose of the model is to provide sound information for evaluating the potential leachate impacts on ground water at dredged material CDFs and the effectiveness of leachate control measures.