Immobilization Of Contaminants Research Articles

Three-year performance of in-situ solidified/stabilised soil using novel MgO-bearing binders.

A new group of MgO-bearing binders has been developed recently which showed improved sustainability and technical performance compared to Portland cement (PC). However, the application of these MgO-bearing binders in the Solidification/Stabilisation (S/S) techniques is very limited. This study investigates the three-year performance of a highly contaminated soil treated by in-situ S/S using MgO-bearing binders and PC. The core quality, strength, permeability and the leaching properties of the S/S materials were evaluated. The effects of binder composition, addition of inorgano-organo-clay (IOC) and the grout content on the properties of the 3-y S/S materials are discussed. It is found that although MgO alone provided negligible strength to the soil, it is superior in immobilising both inorganic and organic contaminants. Replacing MgO by ground granulated blast-furnace slag (GGBS) significantly enhanced the strength while also performed well in immobilising the contaminants. The improved pH buffering capacity was attributed to the low solubilities of brucite and hydrotalcite-like phases formed in the MgO-bearing binders, and was also the reason for the improved performance in stabilising contaminants. The addition of IOC slightly decreased the strength and the permeability of the S/S materials but inconsistent effect on the contaminant immobilisation was found depending on the binder composition. This study showed no degradation of the S/S materials after 3 y exposure to field conditions and has proved the applicability and the advantages of MgO-bearing binders over PC in S/S.

Biochar efficiency in pesticides sorption as a function of production variables--a review.

Biochar is a stabilized, carbon-rich by-product derived from pyrolysis of biomass. Recently, biochar has received extensive attentions because of its multi-functionality for agricultural and environmental applications. Biochar can contribute to sequestration of atmosphere carbon, improvement of soils quality, and mitigation of environmental contaminations. The capability of biochar for specific application is determined by its properties which are predominantly controlled by source material and pyrolysis route variables. The biochar sorption potential is a function of its surface area, pores volume, ash contents, and functional groups. The impacts of each production factors on these characteristics of biochar need to be well-understood to design efficient biochars for pesticides removal. The effects of biomass type on biochar sorptive properties are determined by relative amounts of its lingo-cellulosic compounds, minerals content, particles size, and structure. The highest treatment temperature is the most effective pyrolysis factor in the determination of biochar sorption behavior. The expansion of micro-porosity and surface area and also increase of biochar organic carbon content and hydrophobicity mostly happen by pyrolysis peak temperature rise. These changes make biochar suitable for immobilization of organic contaminants. Heating rate, gas pressure, and reaction retention time after the pyrolysis temperatures are sequentially important pyrolysis variables effective on biochar sorptive properties. This review compiles the available knowledge about the impacts of production variables on biochars sorptive properties and discusses the aging process as the main factor in post-pyrolysis alterations of biochars sorption capacity. The drawbacks of biochar application in the environment are summarized as well in the last section.

Biomass derived palygorskite–carbon nanocomposites: Synthesis, characterisation and affinity to dye compounds

Clay minerals can act as a uniform dispersion medium for nano-sized carbon particles. However, literature on the preparation and characteristics of palygorskite–carbon nanocomposites is scant. Using a hydrothermal carbonisation technique this study developed two nanocomposites on fibrous palygorskite from starch: the first without a post-synthesis treatment (Composite 1); and the second with an activation at 550°C for 3h (ramp at 10°Cmin−1) under CO2 environment (200mLmin−1) (Composite 2). A uniform dispersion of nano-scale carbon spheres was formed on partially destroyed palygorskite structures. Composite 2, which indicated the formation of graphitised carbon nanoparticles, generated a 17-fold greater specific surface area than Composite 1 and also created micro- and mesopores in its structure. The nanocomposites, especially in Composite 1, contained organic surface functional groups (CH, CC, CO) and indicated variable affinity to cationic and anionic dye compounds. While Composite 2 adsorbed a larger amount of anionic orange II dye (23mgg−1), Composite 1 adsorbed more cationic methylene blue (46.3mgg−1). Isothermal and kinetic modelling of the adsorption data indicated that in addition to electrostatic attraction for methylene blue adsorption on both nanocomposites, a pore diffusion mechanism was involved and the boundary resistance was greater for orange II than methylene blue adsorption. Being a material developed from green biomass (starch) and an abundant natural resource (palygorskite), these nanocomposites have immense potential for application in environmental remediation including in situ immobilisation of contaminants in soil.

Chemical stabilization of chromate in blast furnace slag mixed cementitious materials

Cement waste form (CWF) technology is among the leading approaches to disposing of metals and liquid low-level nuclear waste in the United States. One such material, saltstone, includes slag, fly ash and Portland cement to enhance the immobilization of contaminants (e.g., Cr, 99Tc) in alkaline liquid wastes. To evaluate the stability of such redox sensitive contaminants in saltstone, the effects of slag as a source of reductant on Cr immobilization was evaluated in aged (<300d) saltstone monoliths. Specifically, we investigated the effects of artificial cement pore waters on the Cr release and the spatially resolved Cr chemical state analysis using synchrotron based microfocused X-ray microprobe analysis. The microprobe analysis indicated the heterogeneous distribution of insoluble Cr(III)-species in saltstone. Although at most of 20% Crtotal was leached at the top few (2–3) millimeter depth, the release of Cr(VI) was small (<5%) at 5–30mm with slight changes, indirectly suggesting that Cr is likely present as insoluble Cr(III) species throughout the depths. The study suggests that this saltstone formulation can effectively retain/immobilize Cr under the oxic field condition after ⩽300d of aging time.

Interactions of nano-oxides with low-molecular-weight organic acids in a contaminated soil

Various low-molecular-weight organic acids (LMWOAs) play an important role in the mobilisation of contaminants and their subsequent uptake by plants. Nano-maghemite (NM) and an amorphous Mn oxide (AMO) were investigated for their stabilisation potential under simulated rhizosphere conditions in terms of their use during chemical stabilisation and aided phytostabilisation of metal(loid)s in contaminated soils. In order to understand the reactivity of these potential sorbents of contaminants in soils and subsequent mobility of metal(loid)s, a set of time-dependent batch leaching experiments was performed using a mix of acetic, lactic, citric, malic and formic acids simulating root exudates. Despite being relatively unstable under given conditions, the AMO proved to be an efficient amendment for rapid stabilisation of both metals and As compared to NM. Generally, low pH (∼4) and the presence of citrate complexes resulted in higher mobility of metals in the non- and NM-amended soil. In contrast, the presence of AMO in the soil accelerated the neutralisation reactions related to pH increase and (co-) precipitation of secondary Fe/Mn/Al oxyhydroxides. Mineralogical transformations of the AMO showed to be crucial for contaminant immobilisation.

Formation of secondary hematite and its role in attenuation of contaminants at mine tailings: review and comparison of sites in Zambia and Namibia

Mine tailings in African countries Zambia and Namibia have been investigated with an objective to determine the role of secondary hematite in immobilization of contaminants. Two sites, Chambishi and Mindolo, are located in the Copperbelt in Zambia with relatively humid climates and two sites, Berg Aukas and Kombat, are in Namibia, where the climate is semiarid. At the Chambishi site which is about 40 years old, a hardpan composed of hematite and gypsum has formed at a depth of about 60 cm and large amounts of Cu and Co have been deposited. At the much younger Mindolo site (30 years old, but most V remains in primary descloizite, embedded in a carbonate matrix while a relatively small amount of released V is incorporated into hematite. In contrast, released Zn and Pb are incorporated mainly into smithsonite and cerussite, which are less stable from an environmental viewpoint. Finally, at the Kombat mine tailings (< 5 years old), As released from pyrite is also incorporated into hematite, but Cu released by dissolution of chalcopyrite and bornite has precipitated as malachite, which is less stable than hematite. Water-leached concentrations of contaminants such as Cu, Zn, and Pb (also present in some carbonate phases) are an order of magnitude higher than water-leached concentrations of V and As which are bound to crystalline ferric minerals such as hematite and soluble only in the aqua regia fraction of sequential extraction. It seems that rapid formation of hematite under tropical climate conditions and incorporation of contaminants into this mineral phase is favourable for attenuation of released contaminants. These findings have implications at other mining sites with similar climates in Africa, South America and Asia.

The application of biosurfactants into removal of selected micropollutants from soils and sediments

The environment comprises soils and sediments in which micropollutants may accumulate and establish as a result of the secondary source of contamination. Micropollutants may migrate from soils into surface and grounds waters as well as cause an increase in bioavailability for organisms. Micropollutants contamination of sediments may result in the water pollution. As a result of chemical reactions taking place among the compounds present in the environment the derivatives, whose identification is fragmentary known at present, are formed. Remediation methods relying on the immobilization of contamination or its removal may be carried out in the place of its formation (in situ) or out of the place of its original location (ex situ). Bacteria being able to form biosurfactants are of an increasing interest as they have low toxicity as well as they can easily biodegradate. Therefore, in situ application of natural biosurfactants may be considered to be a good remediation alternative as they are not hazardous for water and soil organisms. On the one hand, high costs related to their production and application logy should be taken into account, however, their usage may be economically attractive. The aim of this study was to present the possibility of using biosurfactants as additives in removal processes of selected micropollutants from soil–water environment.

Immobilisation of Metals in Contaminated Landfill Material Using Orthophosphate and Silica Amendments: A Pilot Study

Immobilization and encapsulation of contaminants using silica and orthophosphate based chemical treatments are emerging technologies applicable to the management of metal contaminated soil. While the efficacy of orthophosphate treatment is well documented, there is a paucity of research on the application of silica or coupled orthophosphate and silica chemical treatments to metal contaminated soil. This paper presents a pilot scale bench study on the use of silica and coupled orthophosphate-silica treatments for the immobilization of metal contaminants in soil material obtained from the Thala Valley landfill, East Antarctica, which in places has petroleum hydrocarbons mixed with metalcontaminated sediment. The performance of the treatments trialed was assessed by the concentrations of copper, zinc, arsenic and lead released using the Toxicity Characteristic Leaching Procedure. The results of this pilot study demonstrate that the orthophosphate-silica treatment was the most effective and reduced leachable copper, zinc and lead by 95%, 96% and 99%, respectively, relative to the experimental controls. Further development of this technique will require additional research evaluating its long-term performance under a range of environmental conditions. Studies investigating potential adverse effects of silica and orthophosphate-silica treatments are also necessary, to demonstrate the environmental risk and efficacy of these remediation technologies.

Natural geochemical risk in the Pollino Massif: a case-study of chromium

Natural geochemical risk in the Pollino Massif: a case-study of chromium

Equilibrium and kinetic modeling of contaminant immobilization by activated carbon amended to sediments in the field

Addition of activated carbons (AC) to polluted sediments and soils is an attractive remediation technique aiming at reducing pore water concentrations of hydrophobic organic contaminants (HOCs). In this study, we present (pseudo-)equilibrium as well as kinetic parameters for sorption of a series of PAHs and PCBs to powdered and granular activated carbons (AC) after three different sediment treatments: sediment mixed with powdered AC (PAC), sediment mixed with granular AC (GAC), and addition of GAC followed by 2 d mixing and subsequent removal (‘sediment stripping’). Remediation efficiency was assessed by quantifying fluxes of PAHs towards SPME passive samplers inserted in the sediment top layer, which showed that the efficiency decreased in the order of PAC > GAC stripping > GAC addition. Sorption was very strong to PAC, with Log KAC (L/kg) values up to 10.5. Log KAC values for GAC ranged from 6.3–7.1 and 4.8–6.2 for PAHs and PCBs, respectively. Log KAC values for GAC in the stripped sediment were 7.4–8.6 and 5.8–7.7 for PAH and PCB. Apparent first order adsorption rate constants for GAC (kGAC) in the stripping scenario were calculated with a first-order kinetic model and ranged from 1.6 × 10−2 (PHE) to 1.7 × 10−5 d−1 (InP). Sorption affinity parameters did not change within 9 months post treatment, confirming the longer term effectiveness of AC in field applications for PAC and GAC.

Characterization of human manure-derived biochar and energy-balance analysis of slow pyrolysis process

Biochars have received increasing attention in recent years because of their soil improvement potential, contaminant immobilization properties, and ability to function as carbon sinks. This study adopted a pyrolytic process to prepare a series of biochars from dried human manure at varying temperatures. The thermal analysis of human manure and physicochemical properties of the resulting biochars illustrated that human manure can be a favorable feedstock for biochar production. In particular, the porous texture and nutrient-rich properties of biochars produced from human manure and may significantly enhance soil fertility when used as used soil additives. A temperature range of 500–600°C was optimal for human manure biochar production. Significantly, when the moisture content of the feedstock is lower than 57%, the system could not only harvest manure-derived biochar but also have a net energy output, which can be provide heat source for nearby users.

A review of the mechanical and leaching performance of stabilized/solidified contaminated soils

Stabilization/solidification (S/S) technology, which basically involves chemical fixation and immobilization of contaminants (primarily metals) in the matrix of cementitious binders, is widely used for treatment of contaminated soils. This paper presents a critical review of the performance of commonly used blended binder systems in S/S technology. The binders considered are Portland cement and blends of cement–fly ash, cement–slag, lime–slag, and lime–fly ash. This work compares and evaluates the performance of contaminated soils treated by the binders in terms of commonly used mechanical and leaching properties, including unconfined compressive strength (UCS), bulk density, hydraulic conductivity, and leachability. The long-term performance of S/S-treated soils is also reviewed. It was observed that the inclusion of slag in a binder blend gave superior performance compared to fly ash. Generally, the leachability of common contaminants in soil can be reduced to acceptable levels with approximately 20%–35% dosage of the different binders. The UCS was observed to be optimum around the optimum water content for compaction. The hydraulic conductivity was approximately 10−9m/s over time. Long-term performance of treated soils showed consistent effectiveness over a period of 5–14 years with fluctuations in mechanical and leaching behaviour caused by the complex nature and variability of S/S-treated soils.

Immobilization and Encapsulation of Contaminants Using Silica Treatments: A Review

The immobilization and encapsulation of contaminants using silica treatments is an emerging technology for the management of contaminated land. This article reviews the potential of silica treatments for the management of metals, hydrocarbons, and acid mine drainage at contaminated sites; and evaluates the effects of environmental conditions on silica treatment performance. The review demonstrates the potential of silica treatments for managing contaminated land; however, a paucity of research offers only a limited understanding of this technology. Further development of the technology will require additional research evaluating its long‐term performance under a range of environmental conditions. Field‐based experiments and studies investigating potential adverse effects of silica treatments are also necessary to demonstrate the safety, efficacy, and reliability of silica treatments. © 2013 Wiley Periodicals, Inc.

The functional roles of arbuscular mycorrhizal fungi in improving growth and tolerance of Vicia faba plants grown in wastewater contaminated soil

Wastewater contaminated soil poses serious environmental and health problems in Saudi Arabia and requires technological solutions for mitigating potential environmental risks. In spite the efforts of the Agriculture Ministry and agencies of water resources to overcome those problems, they still exist. In this concern, the effects of an arbuscular mycorrhizal (AM) fungus (Glomus deserticola Trappe and John) on growth, relative chlorophyll content and some mineral nutrients and heavy metal contents of broad bean (Vicia faba) plants grown in sterilized soil irrigated with different concentrations of wastewater were studied. Application of wastewater significantly reduced growth, chlorophyll content, nutrient contents, and levels of mycorrhizal colonization of bean plants comparing to control untreated plants, mainly at high concentrations. However, the rate of reduction was more pronounced in non-mycorrhizal treated plants. Mycorrhizal broad bean plants had significantly higher biomass, plant heights, leaf area, nutrients content (N, P, K), and relative chlorophyll content compared to those of non-mycorrhizal plants irrigated with or without sewage water. Under sewage water application, the AM colonization had greatly reduced the heavy metal contents (Zn, Co, Mn, Cu) in shoot and root tissues of the broad bean plants as compared to their equivalent non-mycorrhizal plants. This study indicates that growing broad bean plants with AM inoculum can minimize the heavy metals toxicity and increase growth and P uptake. In this regard, the AM fungi have a protective role to the host plants, and thus play important roles in soil contaminant immobilization processes. Therefore, the AM fungi are important in phytoremediation of heavy metals in wastewater contaminated soil. Key words: Arbuscular mycorrhizal, heavy metals, growth responses, Vicia faba, nutrients content, phytoremediation, wastewater water contaminated soil.

Lead immobilization in artificially contaminated kaolinite using magnesium oxide-based materials: Immobilization mechanisms and long-term evaluation

The immobilization of metals in soils is a cost-effective treatment that has recently received attention. However, poorly understood immobilization mechanisms and the longevity of the contaminant immobilization remain two of the main concerns related to the immobilization treatment. The objectives of this study were as follows: (i) to demonstrate that the use of commercial grade magnesium oxide (MgO) effectively immobilizes lead in artificially contaminated kaolinite; (ii) to elucidate the corresponding immobilization mechanisms; and (iii) to evaluate the long-term immobilization. A series of leaching tests performed at a solid-solution ratio of 1:10 (w/v) showed that the contaminated kaolinite without MgO treatment was vulnerable to acid attack, resulting in leached lead concentrations above the permissible level in Japan (0.01mg/L). MgO treatment effectively immobilized lead (<0.01mg/L), even when the pH of the leaching solution was 2.8, assuming 100years of soil exposure to acid rain. Comparison of the lead distribution in the kaolinite before and after MgO treatment, supported by the information obtained from TEM–EDS analysis, showed that MgO treatment reduced almost 100% of the exchangeable fraction, and the major portion of the desorbed lead was converted to carbonate.

Ants as bioaccumulators of metals from soils: Body content and tissue-specific distribution of metals in the ant Crematogaster scutellaris

Ants possess several features that make them good candidates as indicators of environmental contamination. Concentrations of six metals (Cu, Cd, Ni, Mn, Pb and Zn) were investigated in Crematogaster scutellaris, a myrmicine ant common throughout the Mediterranean basin. Concentrations of metals in ant bodies and soil samples from polluted and unpolluted sites were compared. Tissue-specific distribution of metals in a non-soluble form was examined using a novel technique that coupled histological imagery and micro-PIXE analysis. Zinc and cadmium accumulated in ants with respect to the soil. Copper body burdens were independent of soil concentration, while lower concentrations of nickel, manganese and lead were found in ants than in the soil, although ant body content was correlated with soil concentrations. Most of the metals were concentrated in the midgut, the Malpighian tubules and fat body, supporting the role of these organs as primary sites of metal storage and contaminant immobilization.

Adsorption kinetics of herbicide paraquat in aqueous solution onto a low-cost adsorbent, swine-manure-derived biochar

Biochars have received increasing attention in recent years because of their significant properties such as carbon sequestration, soil fertility, and contaminant immobilization. In this work, the adsorptive removal of paraquat (1,1 0 -dimethyl-4,4 0 -dipyridinium chloride, one of the most widely used herbicides) from aqueous solution onto the swine-manure-derived biochar has been studied at 25 C in a batch adsorption system. The adsorption rate has been investigated under the controlled process parameters including initial pH (i.e., 4.5, 6.0, 7.5, and 9.0), paraquat concentration (i.e., 0.5, 1.0, 2.0, 4.0, and 6.0 mg/L), and biochar dosage (i.e., 0.10, 0.15, 0.20, 0.25, and 0.30 g/L). Based on the adsorption affinity between cationic paraquat and carbon-like adsorbent, a pseudo-second order model has been developed using experimental data to predict the adsorption kinetic constant and equilibrium adsorption capacity. The results showed that the adsorption process could be satisfactorily described with the reaction model and were reasonably explained by assuming an adsorption mechanism in the ion exchange process. Overall, the results from this study demonstrated that the biomass- derived char can be used as a low-cost adsorbent for the removal of environmental cationic organic pollutants from the water environment.

Redox Oscillation Impact on Natural and Engineered Biogeochemical Systems: Chemical Resilience and Implications for Contaminant Mobility

Many geochemical systems fluctuate regularly from oxic to anoxic conditions (flooded soils and nuclear waste surface repositories, for instance). In these conditions many inorganic contaminants including Sb, Se, Cr, As, and U are highly sensitive to changes in redox conditions. These oscillations may result in changes to their speciation, toxicity, and mobility. We demonstrate through the combination of redox-stat batch-reactor experiments that periodic and cumulative changes to matrix mineralogy, contaminant speciation, and mineral surface properties occur following periodic cycles of reduction and oxidation. These changes result in both short-term (intra-cycle) and long- term (inter-cycle) changes to Kd values for a range of redox sensitive contaminants. These results demonstrate that naturally occurring redox oscillations may result in long-term immobilization of contaminants in the solid phase in addition to short-term variations in mobility.

Textural and chemical properties of swine-manure-derived biochar pertinent to its potential use as a soil amendment

Biochars have received increasing attention in recent years because of their properties pertaining to soil fertility and contaminant immobilization as well as serving as carbon sinks. In this work, a series of biochars were produced from dried swine manure waste by slow pyrolysis at different temperatures (i.e., 673–1073K). The characterization of the resulting biochars was examined for its relevance to its potential use as soil amendment. It was found that the pore properties, ash contents and pH values of all swine-manure-derived biochars basically increased as temperature increased, while the yield and nitrogen/oxygen contents decreased with increasing temperature as a result of pyrolytic volatilization during pyrolysis. From the organic and inorganic elements analyses, the manure-derived biochar was rich in soil nutrients such as N, P, Ca, Mg, and K. Furthermore, the pore, surface and chemical properties were also consistent with the observations of the SEM-EDS, XRD and FTIR. This result suggested that the mesoporous manure-derived biochar could be used as an excellent medium to soil environment.

Application of the Biosurfactant produced by Candida lipolytica in the Remediation of Heavy Metals

Soil that is accidentally contaminated with petroleum hydrocarbons can be remediated by physical, chemical, or biological methods. However, new trends in soil and water restoration avoid introducing synthetic chemicals. Among the remediation techniques available for contaminated sites, bioremediation is regarded as environmentally friendly because it preserves the soil structure, requires little energy input, and involves the complete destruction or immobilization of the contaminants, although the efficiency of biodegradation of oil pollutants is often limited by their poor water solubility. Despite their advantages, due to the high production costs biosurfactants are not extensively used. In this sense the lipopeptide biosurfactant produced by Candida lipolytica (UCP 0988), is an attractive alternative to the synthetic surfactants, showing properties in bioremediation of heavy metals. The biosurfactant reduced the surface tension of the production medium from 50 mN/m to 25 mN/m, with a yield of 8 g/L, after 72 h of fermentation. The biosurfactant showed a CMC of 0.03 %. The lipoprotein removed 96 % of Zn and Cu, and reduced the concentration of Pb, Cd and Fe. The optimization process of biosurfactant production, which permitted the reduction of costs, suggests its ample utilization according to commercial requirements.