Sorption behavior of cesium on various soils under different pH levels

In the present study we investigated the sorption behavior of Cs in four different soils (sandyloam, loam, clayloam and clay) by using batch experiment. Cs sorption characteristics of the studied soils were examined at 4 mgL(-1) Cs concentration, at various pH levels, at room temperature and with 0.01 M CaCl(2) as a background electrolyte. Among different soils the decrease of k(d) (distribution coefficient) of cesium, at all pH levels, followed the sequence sandyloam > loam > clayloam > clay, indicating that the particle size fractions and especially the clay content plays predominant role on sorption of Cs. The effect of pH on cesium sorption displays a similar pattern for all soils, depending on soil type. At acid pH levels less cesium was sorbed, due to a greater competition with other cations for available sorption sites. The maximum sorption of Cs was observed at pH 8, where the negative charge density on the surface of the absorbents was the highest. For all soils was observed significantly lower Cs sorption at pH 10.     

Impact of exotic and inherent dissolved organic matter on sorption of phenanthrene by soils

The impacts of exotic and inherent dissolved organic matter (DOM) on phenanthrene sorption by six zonal soils of China, chosen so as to have different soil organic carbon (SOC) contents, were investigated using a batch technique. The exotic DOM was extracted from straw waste. In all cases, the sorption of phenanthrene by soils could be well described by the linear equation. The presence of inherent DOM in soils was found to impede phenanthrene sorption, since the apparent distribution coefficients (K(d)(*)) for phenanthrene sorption by deionized water-eluted soils were 3.13-21.5% larger than the distribution coefficients (K(d)) by control soils. Moreover, the enhanced sorption of phenanthrene by eluted versus control soils was in positive correlation with SOC contents. On the other hand, it was observed that the influence of exotic DOM on phenanthrene sorption was related to DOM concentrations. The K(d)(*) values for sorption of phenanthrene in the presence of exotic DOM increased first and decreased thereafter with increasing the added DOM concentrations (0-106mgDOC/L). The K(d)(*) values at a low exotic DOM concentration (< or =28mgDOC/L) were 14.7-48.4% larger than their control K(d) values. In contrast, higher concentrations (> or =52mgDOC/L) of added exotic DOM clearly impeded the distribution of phenanthrene between soil and water. The effects of exotic and inherent DOM on phenanthrene sorption by soils may primarily be described as 'cumulative sorption', association of phenanthene with DOM in solution, and modified surface nature of soil solids due to DOM binding.     

A comparative study for the sorption of Cd(II) by soils with different clay contents and mineralogy and the recovery of Cd(II) using rhamnolipid biosurfactant

Recent research has demonstrated that biosurfactants, especially rhamnolipids, can enhance recovery of soil-bound metals. To propose the success of remediation process of soils by rhamnolipids, both sorption and desorption characteristics of soils having different clay mineralogy should be known exactly. To assess sorption of Cd(II), batch equilibrium experiments were performed using three soils characterized with different proportions of clay minerals from Eski?ehir region of Turkey. Soil pH, initial metal concentration and clay mineralogy affected the sorption process. For comparisons between soils, the sorption process was characterized using the Langmuir, Freundlich, Redlich-Peterson, Koble-Corrigan sorption models. The Freundlich model showed the best fit for the Cd(II) sorption data by the soils, while the Langmuir-type models generally failed to describe the sorption data. Soils with higher clay content characterized by having smectite as a dominant component had the greatest sorption capacity and intensity estimated by the KF and n parameters of the Freundlich model. The soil C has the highest sorption efficiency of 83.9%, followed by soils B and A with sorption efficiencies of 76.7% and 57.9%, respectively. After the soils were loaded by different doses of Cd(II), batch washing experiments were used to evaluate the feasibility of using rhamnolipid biosurfactant for the recovery of Cd(II) from the soils. The Cd(II) recovery of the soils were investigated as a function of pH, amount of Cd(II) loaded to the soils, and rhamnolipid concentration. Cd(II) recovery efficiencies from the soils using rhamnolipid biosurfactant decreased in the order of soil A>soil B>soil C. This order was the reverse of the Cd(II) sorption efficiency order on the soils. When 80 mM rhamnolipid was used, the recovery efficiencies of Cd(II) from the soils A, B, and C was found to be 52.9%, 47.7%, 45.5% of the sorbed Cd(II), respectively. Rhamnolipid sorption capacity of the soils in the presence of Cd(II) ions decreased in the order of soil A>soil B>soil C.     

Attenuating toluene mobility in loess soil modified with anion-cation surfactants

Soils, subsoils, and aquifer materials can be modified with hydrophobic cationic surfactants to increase their sorption capabilities for organic contaminants. The objective of this study was to examine in detail the sorptive characteristics of the natural loess soil and the resultant organo-modified soils for aqueous-phase neutral organic compounds (NOCs) in an attempt to define the operative sorptive mechanisms. Under the laboratory conditions, a series of modified loess soils in this study were prepared by replacing the cations of loess soil with both cationic surfactant hexadecyltrimethylammonium bromide (HDTMA-Br) and anionic surfactant sodium dodethylbenzene sulfonate (SDBS). Toluene was selected as an indicator to study the sorption behavior of the NOCs in loess soils. The sorption isotherms of toluene in soil samples obtained using the batch equilibration method. The results indicated that natural loess had a poor sorption capability for NOCs, and sorption isotherms of toluene appeared likely nonlinear and fit the Freundlich equation very well. When the soils were coated with large alkyl surfactants such as HDTMA-Br, sorption isotherms correspondingly became linear and the sorptive capability was prominently dependent on the quantity of hexadecyltrimethylammonium (HDTMA) and SDBS added into the soils. The study could provide an essential basis on attenuation of organic contaminants in the subsurface environment.     

Metal sorption on soils as affected by the dissolved organic matter in sewage sludge and the relative calculation of sewage sludge application

To evaluate the influences of sewage sludge-derived organic matters on metal sorption and on the resultant sludge loading estimates, a batch experiment was conducted to compare the sorption of Ni, Cu and Pb in sewage sludge filtrates (1:20 sewage sludge to water) on eight soils and the adsorption of metals in a reference solution which had the same matrix as the sewage sludge filtrate except dissolved organic material (henceforth referred to as reference solution). Metal sorption could be well fitted by linear isotherm and the dissolved organic matter in sludge significantly depressed the sorption (p<0.01). The main factor controlling sorption of Ni on different soils was dominated by soil cation exchange capacity (CEC) and sorption of Cu and Pb was by soil organic matter (SOM). The parameters obtained from the sorption isotherm equations were then used to estimate sludge loadings into the soils. When the sorption parameters derived from the reference solution were used for calculation, that is the effect of dissolved organic matter was not considered, the calculated safe application rates are approximately 47.8, 51.4, 34.2, 31.3, 21.7, 46.3, 187.1 and 27.6 t-sludge/ha for the Beijing, Jiangxi, Xiamen, Jilin, Guangdong, Wuhan, Gansu and Xinjiang soils, respectively. However, when the sorption parameters derived from the dissolved organo-metallic complexes are used for calculation, the corresponding application rates are reduced to approximately 6.0, 3.4, 1.9, 10.0, 6.3, 3.6, 7.3 and 3.5 t-sludge/ha, respectively. By this study we can get a conclusion that the effect of sewage sludge derived dissolved organic matter on heavy metal sorption and soil properties should be considered in the course of regulating the safe application rates of sewage sludge to soil.     

Simultaneous sorption and desorption of Cd, Cr, Cu, Ni, Pb, and Zn in acid soils II. Soil ranking and influence of soil characteristics

In Part I of this paper we reported, for each of 11 acid soils, the rankings of six metals according to their sorption from solutions containing all six, and according to their retention under desorption conditions. Here, we analyse the same data from a different perspective: for each metal, we rank the soils by their capacities to sorb and retain it as reflected by soil/solution distribution coefficients K(d100) measured using starting solutions containing 100mgL(-1) of each metal. We also ranked the soils for overall heavy metal sorption and retention capacities using Kaplan's compound measure K(dSigma), and we investigated the influence of soil characteristics on K(d100) and K(dSigma100) values. Overall capacity for sorption of heavy metals was positively related to HOM, kaolinite and Fe oxides contents, and negatively related to CEC and to vermiculite and haematite contents. Overall capacity for retention of heavy metals was positively related to HOM and kaolinite contents, and negatively related to CEC and vermiculite content. The good correlation between K(dSigma100)(sorption) and the first component extracted in a principal components analysis of K(d100)(sorption) values, and between K(dSigma100)(retention) and the first component extracted in a principal components analysis of K(d100)(retention) values, supports the adequacy of K(dSigma) as a measure of the overall capacity of a soil to sorb or retain heavy metals.     

Sorption behavior of tetrabromobisphenol A in two soils with different characteristics

Sorption of tetrabromobisphenol A (TBBPA) in soil influences its fate and transport in the environment. The sorption behaviors of TBBPA in two soils with different characteristics were investigated using batch equilibration experiments in the study, and the impacts of ionic strength and pH on the sorption were also evaluated. The results showed that the fast sorption rather than the slow sorption played a main role in the sorption process. The nonlinear sorption isotherms of TBBPA in the soils were observed and the Freundlich model could describe the sorption behavior of TBBPA well. The calculated K_F were 78.5 and 364.6  (mg/kg)(mg/L)⁻ⁿ for LN soil (loamy clay) and GX soil (silt loam), respectively. Soil organic matter (SOM) played a main role in the sorption of TBBPA, which contributed about 90% to the sorption in the soils. The desorption hysteresis of TBBPA was revealed in the single-cycle sorption and desorption experiments. The sorbed amount of TBBPA decreased with the increase in solution pH and increased with the increase in ionic strength. It was found that the effects of ionic strength on the sorption were mainly caused by the change of solution pH.     

Adsorption and desorption kinetics of carbofuran in acid soils

Carbofuran adsorption and desorption were investigated in batch and stirred flow chamber (SFC) tests. The carbofuran adsorption capacity of the soils was found to be low and strongly dependent on their clay and organic carbon contents. Carbofuran sorption was due mainly (>80%) to fast adsorption processes governed by intraparticle diffusion. The adsorption kinetic constant for the pesticide ranged from 0.047 to 0.195 min(-1) and was highly correlated with constant n in the Freundlich equation (r=0.965, P<0.05). Batch tests showed carbofuran desorption to be highly variable and negatively correlated with eCEC and the clay content. The SFC tests showed that soil organic carbon (C) plays a key role in the irreversibility of carbofuran adsorption. Carbofuran desorption increased rapidly at C contents below 4%. The desorption kinetic constant for the compound (0.086-0.195 min(-1)) was generally higher than its adsorption kinetic constant; therefore, carbofuran is more rapidly desorbed than it is adsorbed in soil.     

Removal of 2,4,6-trichlorophenol from a solution by humic acids repeatedly extracted from a peat soil

Humic acid (HA) is one of the major components of soil organic matter. It strongly affects the sorption behavior of organic and inorganic contaminants in soils. To obtain a better understanding of the interactions of contaminants with HA, a repeated extraction technique has been applied to a peat soil to obtain HA fractions with varying aliphaticity and aromaticity, which were subsequently correlated to the sorption properties of 2,4,6-trichlorophenol (TCP). HA fractions were extracted repeatedly using an alkaline solution and each HA fraction was separated into two portions with an air-drying or re-suspending (denoted as RSHAs) process. Solid-state (13)C NMR and elemental analysis demonstrated that the aromaticity and polarity of HAs decreased with extractions. Kinetic results indicated that air-dried HAs exhibited two-step first order sorption behavior with a rapid stage followed by a slower stage. The slower sorption is attributed to the diffusion of 2,4,6-TCP in the condensed aromatic domains of HAs. Conversely, sorption of 2,4,6-TCP on RSHAs was extremely rapid and could not be fitted with any kinetic model. For air-dried HAs the sorption capacity (K(oc)) was weakly correlated with the chemical compositions of HAs. However, a positive trend between K(oc) and aromaticity was observed for RSHAs. Compared with the results of air-dried HAs with their counterparts of RSHAs, it is therefore concluded that air-drying may alter the structure of HAs through artificially creating a more condensed domain in HAs. The structural alternation may result in an incorrect interpretation of the relationship between sorption capacity and chemical composition of HAs and a misjudgment of the transport behavior of 2,4,6-TCP in soils and sediments.     

Effects of rice straw ash amendment on Cu solubility and distribution in flooded rice paddy soils

Rice straw burning is a common post-harvest practice on rice paddy land, and it leads to the accumulation of rice straw ash (RSA) in paddy soil. To understand the role of RSA in determining the mobility and bioavailability of metal contaminants, this study investigated the effects of RSA amendment on the solubility and distribution of Cu in contaminated rice paddy soils with flooding incubation. The addition of RSA to the soils suppressed the release of Cu into the soil solutions, which was primarily attributed to the metal-binding capacity of the RSA. Additionally, after the soils were flooded, the increase in soil pH and decrease in redox potential resulted in the transformation of Cu into less soluble forms. The RSA amendment appeared to enhance the changes in pH and redox potential of the flooded soils and, consequently, the immobilization of Cu in the soils. The results suggest that the RSA can retard the bioavailability and movement of the metal in contaminated soils and, thus, lower the potential environmental risk of Cu toxicity.     

The structural and sorptive characteristics of high-surface-area carbonaceous material (HSACM) in soils

The structural and sorptive characteristics of the high-surface-area carbonaceous material (HSACM) isolated from soils were investigated. The HSACM contents in soils were first identified by the organic petrology method. A novel isolation method using acid demineralization, base extraction, and ZnBr(2) floatation sequential steps was developed to extract the HSACM from soil. The differences in structural and sorptive characteristics with the HSACM and the intact soil were investigated using nitrogen adsorption isotherms and trichloroethylene (TCE) sorption isotherms at low concentrations (0 to about 2 mg/L) both with and without tetrachloroethylene (PCE) as the cosolute. It was found that HSACM possesses a much higher specific surface area and pore volume as well as a smaller pore size than the original soil. Moreover, the sorption of TCE to HSACM is noticeably more nonlinear and competitive than to the original soil. A small amount of highly adsorptive HSACM is largely responsible for the nonlinear soil sorption of a single solute at very low concentrations.     

Effect of different extraction agents on metal and organic contaminant removal from a field soil

This paper presents an evaluation of different extracting solutions for the removal of phenanthrene, lead and zinc from a contaminated soil obtained from a former manufactured gas plant site. The field soil contained 50%-88% sand, 11%-35% fines, 2.7%-3.7% organic matter and high concentrations of phenanthrene (260 mg/kg), lead (50.6 mg/kg) and zinc (84.4 mg/kg). A series of batch extraction experiments were conducted using the field soil with different extracting solutions at various concentrations to investigate the removal efficiency and to optimize the concentration of each extractant. The results showed that removal efficiencies of different flushing systems were significantly influenced by their affinity and selectivity for the contaminants in the soil matrix. Non-ionic surfactants (Igepal CA720 and Tween 80) were found to be effective in removing phenanthrene, but they were ineffective in removing lead and zinc. Chelating agents (ethylenediamine tetra acetic acid, EDTA and diethylene triamine penta acetic acid, DTPA) and selected acids were effective in removing lead and zinc, but they were ineffective for the phenanthrene removal. Co-solvents and cyclodextrins were not effective for removal of any of the contaminants. A sequential use of the 0.2 M EDTA followed by 5% Tween 80 or 5% Tween 80 followed by 1 M citric acid was found to be effective for the removal of lead, zinc, and phenanthrene. Overall, it can be concluded that sequential use of different extracting solutions is required for the removal of both heavy metals and organics from field contaminated silty sand soils.     

Mobile system for extracting spilled hazardous materials from excavated soils

A technique was evaluated for the scrubbing or cleansing of excavated soils contaminated by spilled or released hazardous substances. Laboratory tests were conducted with three separate pollutants (phenol, arsenic trioxide, and polychlorinated biphenyls [PCB's]) and two soils of significantly different character (sand/gravel/silt/clay and organic loam).The tests show that scrubbing of excavated soil on site is an efficient approach for freeing soils of certain contaminants but that the effectiveness depends on the washing fluid (water + additives) and on the soil composition and particle-size distribution. Based on the test results, a full-scale, field-use, prototype system was designed, engineered, fabricated, assembled, and briefly tested under conditions where large (?2.5 cm) objects were removed by a bar screen. The unit is now ready for field demonstrations.The system includes two major soil scrubbing components: a water-knife stripping and soaking unit of novel design for disintegrating the soil fabric (matrix) and solubilizing the contaminant from the larger particles (?2 mm) and an existing, but re-engineered, four-stage countercurrent extractor for freeing the contaminants from smaller particles (<2 mm). The processing rate of the system is 2.3 to 3.8 m₃/hr (4 to 5 yd₃/hr), though the water-knife unit (used alone) can process 11.5 to 13.5 m₃/hr (15 to 18 yd₃/hr). The complete system requires auxiliary equipment, such as the EPA-ORD physical/chemical treatment trailer, to process the wastewater for recycling; under some circumstances, provision must be made to confine and treat released gases and mists. Treatment residues consist of skimmings from froth flotation, fine particles discharged with the used washing fluids, and spent carbon. The principal limiting constraint on the treatability of soils is clay content (high weight-percent), since breaking down and efficiently treating consolidated clays is impractical or not economically attractive. Most inorganic compounds. almost all water soluble or readily oxidizable organic chemicals, and some partially miscible-in-water organics can be treated with water or water plus an additive.During limited laboratory extraction tests, phenol was very efficiently removed from both organic and inorganic soils, whereas PCB and arsenic clung more tenaciously to the soils and were released less readily into the washing fluids. The extent to which the system has practical, cost-effective utility in a particular situation cannot be determined until preliminary, bench-scale lab work has been performed and acceptable limits of residual concentrations in the washed soil are adopted. Laboratory tests show that soil scrubbing has the capability of vastly speeding up the release of chemicals from soils, a process that occurs very slowly under natural leaching conditions.Note that this system requires excavation of the soil, which can subsequently be replaced or transported to a low-grade landfill. In situ washing of contaminated soil, a process in which the contaminated area is isolated for example, by grouting, and then water-flushed with removal of the wash water at a well-point is an alternative. The overall efficiency of the soil washing system is greater than that currently being achieved by in situ methods.Based on the laboratory program, a series of steps (water-knife size reduction; soaking; countercurrent extraction; hydrocyclone separation; and waste fluid treatment for reuse) was selected as the most suitable process sequence for the prototype system. The system was constructed for the U.S. (EPA) and is now being subjected to field evaluation. However, soils rich in humus, organic detritus, and vegetative matter can present special problems in the extraction of certain hazardous substances, which may not partition between the solid and fluid phases to a practical and necessary extent.     

Assessment of electrokinetic removal of heavy metals from soils by sequential extraction analysis

Electrokinetic remediation of metal-contaminated soils is strongly affected by soil-type and chemical species of contaminants. This paper investigates the speciation and extent of migration of heavy metals in soils during electrokinetic remediation. Laboratory electrokinetic experiments were conducted using two diverse soils, kaolin and glacial till, contaminated with chromium as either Cr(III) or Cr(VI). Initial total chromium concentrations were maintained at 1000mg/kg. In addition, Ni(II) and Cd(II) were used in concentrations of 500 and 250mg/kg, respectively. The contaminated soils were subjected to a voltage gradient of 1 VDC/cm for over 200h. The extent of migration of contaminants after the electric potential application was determined. Sequential extractions were performed on the contaminated soils before and after electrokinetic treatment to provide an understanding of the distribution of the contaminants in the soils. The initial speciation of contaminants was found to depend on the soil composition as well as the type and amounts of different contaminants present. When the initial form of chromium was Cr(III), exchangeable and soluble fractions of Cr, Ni, and Cd ranged from 10 to 65% in kaolin; however, these fractions ranged from 0 to 4% in glacial till. When the initial form of chromium was Cr(VI), the exchangeable and soluble fractions of Cr, Ni and Cd ranged from 66 to 80% in kaolin. In glacial till, however, the exchangeable and soluble fraction for Cr was 38% and Ni and Cd fractions were 2 and 10%, respectively. The remainder of the contaminants existed as the complex and precipitate fractions. During electrokinetic remediation, Cr(VI) migrated towards the anode, whereas Cr(III), Ni(II) and Cd(II) migrated towards the cathode. The speciation of contaminants after electrokinetic treatment showed that significant change in exchangeable and soluble fractions occurred. In kaolin, exchangeable and soluble Cr(III), Ni(II), and Cd(II) decreased near the anode and increased near the cathode, whereas exchangeable and soluble Cr(VI) decreased near the cathode and increased near the anode. In glacial till, exchangeable and soluble Cr(III), Ni(II), and Cd(II) were low even before electrokinetic treatment and no significant changes were observed after the electrokinetic treatment. However, significant exchangeable and soluble Cr(VI) that was present in glacial till prior to electrokinetic treatment decreased to non-detectable levels near the cathode and increased significantly near the anode. In both kaolin and glacial till, low migration rates occurred as a result of contaminants existing as immobile complexes and precipitates. The overall contaminant removal efficiency was very low (less than 20%) in all tests.     

Removal of contaminant metals from fine grained soils, using agglomeration, chloride solutions and pile leaching techniques

A leaching process based on the use of a HCl-CaCl2 solution, with total chloride concentration 4M, was investigated for the removal of contaminant metals from fine acidic soils. The possibility to apply this treatment on piles constructed on-site was also examined as a low cost treatment option. The soil sample used in the study was fine in texture, i.e. clay loam, acidic (pH 5.6), and contaminated mainly with Pb, up to 16000mg Pb/kg dry soil, due to past mining activities. The experimental work comprised all the treatment stages, including agglomeration of fine soil particles to increase the permeability of soil, leaching of the agglomerated soil in a laboratory column, removal of metals from the leachate, regeneration and recycling of the leaching solution and final washing of the treated soil. The initial agglomeration treatment resulted in the formation of coarse aggregates and the percolation of leaching solution through the soil column was maintained at high levels, i.e.75ml/cm(2) per day, during the whole treatment. A low amount of HCl acid was required for the removal contaminants from this particular soil, i.e. 0.44mol HCl/kg soil, due to the absence of acid consuming minerals. The extractions achieved were 94% for Pb, 78% for Zn and more than 70% for Cd. The co-dissolution of soil matrix was very limited, with a total weight loss about 3.5%. The final pH of the soil after washing was found to be 5.15, i.e. slightly lower compared to the initial pH of the soil. The results of this study indicate that chloride leaching, in combination with agglomeration and pile leaching techniques, can be a cost effective option for the removal of metal contaminants from fine acidic soils.     

Effect of low-molecular-weight organic acids on the adsorption of norfloxacin in typical variable charge soils of China

Batch equilibrium experiments were used to study the adsorption of norfloxacin (NOR) onto three kinds of variable charge soils in China, namely Rho-Udic Ferralisols collected from Yunnan, Ali-Perudic Ferrisols collected from Jiangxi and Typ-Hap-Udic Ferralisols collected from Guangdong. Results show that NOR is strongly adsorbed by the soils, with lg Kd-values (linear model) of 4.41+/-0.01, 4.50+/-0.02, 4.44+/-0.01 and lg Kf-values (Freundlich model) of 4.32, 4.45, 3.08 for the three tested soils, respectively. Both curves of the Freundlich equation and Langmuir equation for the three soils were in excellent linear correlation. Low-molecular-weight (LMW) organic acids, including citric acid, malic acid and salicylic acid were added in the presence of acetate buffer (pH 4.5) to test their effects on NOR adsorption. It was observed that the addition of LMW organic acids inhibited the NOR adsorption process. It was assumed that several effects, including soil pH, solid surface charge and competitive adsorption of co-existing cations, dominated the NOR sorption processes onto variable charge soils. Further studies should be performed to reveal the mechanism of the adsorption.     

Effect of illite and birnessite on thallium retention and bioavailability in contaminated soils

The influence of illite and birnessite (δ-MnO(2)) amendments on the retention and bioavailability of Tl in contaminated soils was investigated. The efficiency of both phases was evaluated using Tl uptake by white mustard (Sinapis alba L.), sequential extraction and sorption experiments. The obtained data demonstrate that the application of birnessite can effectively transform Tl from the labile (easily mobilizable) fraction to its reducible form, thus lowering Tl bioavailability in soil and subsequent accumulation by plants. The Mn oxide added to the soils reduced substantially Tl uptake; Tl levels in the plants decreased by up to 50%, compared to the non-amended soil. The effect of illite on the immobilization and uptake of Tl was less pronounced, and in the carbonate-rich Leptosol has not been proved at all, suggesting the importance of bulk soil mineralogy and nature of the soil sorption complex on the behavior of this amendment. Therefore, the general applicability of illite for Tl stabilization in soils seems to be limited and strongly dependent on soil composition. In contrast, the use of birnessite like soil additive might be an efficient and environment-friendly solution for soil systems contaminated with Tl.     

Stabilization of cadmium contaminated soils using synthesized zeolite

This research investigates the effect of synthesized zeolite on stabilizing Cd-contaminated soil, using 0.01 M CaCl₂ leaching solution in batch and column experiments. The zeolite was synthesized from fly ash obtained from a Coal-Fired Power Plant, by adding 2 N NaOH and subjecting to 90°C for 24 h. The experiment used two groups of soil samples: (1) addition of Cd to four series of background soils: Pinchen, Jente, Erlin and Chengchung; (2) actual contaminated soils from Chungsing and Tsasta sites. The result of the batch experiment indicates that the addition of zeolite reduces Cd leaching from all types of contaminated soils. The more zeolite added, the lower Cd concentrations were detected in the leaching solution. The stabilized Cd in soils in the presence of zeolite is also demonstrated in the column experiments; the leachate contains insignificant Cd, and Cd depth analysis of the soil columns shows little Cd migration. For example, for Pinchen and Jente soils, after 12 and 49 pore volumes of leaching solution, the remaining Cd levels in the soils were 12% and 35%, respectively, of the original Cd values with no zeolite added, as compared to 96% and 99% in the presence of 16% zeolite. The higher cation exchange capacity of the zeolite/soil mixtures and higher pH are responsible for stabilizing Cd in soils. The effect is most useful in application to the acidic sandy soils to prevent contaminated heavy metals from leaching.     

Mobility of copper in greenhouse soils

The mobility of copper (Cu) was studied in 13 soil samples from greenhouses in Falasarna, northwestern Crete, Greece. The spatial variability of Cu concentration in greenhouse soils and their physicochemical characteristics were examined. The results showed that the concentrations varied considerably, between 15 and 4900 ppb. Sorption and leaching experiments--kinetic and equilibrium--were conducted in uncontaminated and contaminated soils, respectively. Both leaching and sorption equilibrium experiments were performed as a function of pH. The leaching experiment results indicated that the total dissolved Cu concentration was between 10 and 15 ppb at a pH of 7.5, which is below the drinking water standards. The results suggest that the kinetics of Cu leaching were fast and the leachate concentration was relatively low, whereas Cu sorption kinetics were rapid and the sorbed concentrations were significant.     

Effects of aging on the extractability of naphthalene and phenanthrene from Mediterranean soils

The effects of aging on the extractability of naphthalene and phenanthrene were investigated using laboratory batch assays. Experiments have been conducted with three soil matrices: a silty clay and two soils with different organic contents. Aging was conducted under abiotic conditions in water saturated and nonsaturated conditions, under a constant temperature (20 degrees C). The mobility of sorbed contaminants was evaluated through successive extractions in water, methanol, butanol and dichloromethane. Experimental results showed a reduction of the extractability of both naphthalene and phenanthrene with increasing aging times. The observed effects of aging might be related to slow diffusion of naphthalene and phenanthrene in sorbent microporosity and/or organic phases and possible evolutions of pollutant-sorbent interactions.