Sequestration of heavy metals from soil with Fe–Mn concretions and nodules

In recent years, heavy metal contamination has become a major environmental issue in many parts of the world. Fe and Mn oxides, oxyhydroxides and hydroxides have long been recognized as scavengers playing an important role in controlling the location, mobility and bioavailability of metal contaminants in soils. Fe–Mn concretions and nodules are discrete bodies made of soil or sediment materials cemented together under the influence of Fe and Mn oxides. Here metals sorption by Fe–Mn concretions and nodules are surveyed and critical reviewed. Valuable available literature data demonstrate that the formation of Fe–Mn concretions and nodules is the most efficient and durable process for metal contaminants sequestration in the soils. The papers discussed in this review show that the application of Fe–Mn concretions and nodules, as geochemical scavengers for remediating metal contaminated soils, is strongly recommended.     

Crystalline mesoporous transition metal oxides: hard-templating synthesis and application in environmental catalysis

Mesoporous silicas such as MCM-41 and SBA-15 possess high surface areas, ordered nanopores, and excellent thermal stability, and have been often used as catalyst supports. Although mesoporous metal oxides have lower surface areas compared to mesoporous silicas, they generally have more diversified functionalities. Mesoporous metal oxides can be synthesized via a soft-templating or hard-templating approach, and these materials have recently found some applications in environmental catalysis, such as CO oxidation, N₂O decomposition, and elimination of organic pollutants. In this review, we summarize the synthesis of mesoporous transition metal oxides using mesoporous silicas as hard templates, highlight the application of these materials in environmental catalysis, and furnish some prospects for future development.     

碱金属氧化物对V2O5-WO3/TiO2催化剂脱硝性能的影响

在V2O5-WO3/TiO2催化剂上负载碱金属氧化物（K2O,Na2O）,通过BET,XRD和SEM等方法对微观结构进行表征,研究不同含量碱金属氧化物对催化剂脱硝活性、N2O生成率和SO2氧化率的影响.结果发现,较大含量的碱金属对催化剂微观结构有一定影响.碱金属氧化物与催化剂表面V物种的结合生成部分碱金属盐（如KVO3）,改变了催化剂的表面结构,使催化剂中有效活性位的数量大大降低,从而导致催化剂活性降低.两种碱金属氧化物对催化剂的毒性顺序为K2O〉Na2O.     

几种金属氧化物TPS性能比较

通过程度升温硫化研究了ＣｕＯ,Ｆｅ２Ｏ３,ＳｎＯ２,ＭｎＯ２,ＣａＯ及ＺｎＯ等金属氧化物的脱硫性能,对各种金属氧化物的ＴＰＳ曲线进行比较发现,其硫化温度及速度都不相同,氧化锰的硫化温度最低,从３４５Ｋ开始有较强的硫化氢吸收峰出现;氧化铜的硫化在３７３Ｋ左右进行;对氧化铁和氧化锌,硫化从４７３Ｋ开始,而氧化锡的硫化在６５０Ｋ左右发生;氧化钙的硫化发生在７３５Ｋ。粒度对ＴＰＳ曲线有较明显的影响,粒度减     

红壤胶体铁氧化物界面有机氯的非生物转化研究进展

综述了红壤胶体铁氧化物的结构、形态及其转化;铁氧化物界面有机氯的非生物转化过程及其影响因素;异化铁还原作用下的有机氯转化过程。有机氯的非生物转化主要包括氧化转化与脱氯转化过程。氧化转化包括暗态下的化学氧化与光化学氧化过程;脱氯转化包括脱氢卤化、加氢脱氯、脱双卤、二聚脱氯与亲核置换脱氯等反应过程。有机氯的非生物转化主要受胶体界面pH、Eh、水溶性有机物、金属离子、铁氧化物形态与铁还原细菌等的显著影响。有机氯非生物转化的化学-微生物耦合机制、复合污染条件下重金属对界面有机氯非生物转化过程的影响机制、红壤胶体界面有机氯污染的综合调控技术方法等三个方面值得关注,有助于推动土壤胶体界面环境化学的发展。     

Chemistry and adsorption-desorption properties of manganese oxides deposited in Forehill Water Treatment Plant,Grampian, Scotland

Manganese oxide coatings on sand particles within filtration beds from a water treatment plant in Grampian, Scotland were examined to determine their control on metal mobility. This study first sought to characterise the oxides, notably their mineralogy and metal content, to provide a foundation for studies on the adsorption of dissolved metals from the treated water by the oxides. The oxides were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and analysed by flame atomic absorption spectrophotometry (AAS). These techniques showed the oxide coatings were amorphous but uniformly distributed over each sand grain. The oxides were selectively removed from the sand grains prior to analysis by AAS using a hydroxylamine hydrochloride selective leaching method. The compositional range of the extracts was 100–150 mg L⁻¹ Mn; 30–55 mg L⁻¹ Fe; 17–56 mg L⁻¹ Ca; 4.6–7.0 mg L⁻¹ Ni; 4.6–6.8 mg L⁻¹ Zn and 1.3–5.7 mg L⁻¹ Mg. When these results are expressed as mg of metal per mg of Mn, the metal content of the oxides is remarkably uniform: 0.25–0.37 mg Fe; 0.14–0.35 mg Ca; 0.035–0.042 mg Ni; 0.035–0.040 mg Zn; 0.01–0.04 mg Mg. The greatest metal concentrations were consistently found in the upper 3 cm of the filtration bed, and these decrease with increasing depth. After the beds are cleaned a more uniform distribution of metals occurs throughout the bed. The metals taken up by the manganese coating are retained over a wide pH range with the exception of Ca and Mg which desorb to a significant extent. The percentage of calcium and magnesium lost from the coating ranges from 30–94%, the amount being dependent on the final pH of the solution. The presence of manganese oxide in the filtration beds appears to be advantageous in terms of removal of transition metals from the treated water.     

Verglaste Filterstäube aus Müllverbrennungsanlagen

Solid waste residues from municipal solid waste incinerator flue gas cleaning systems basically consists of Al, Ca-silicates and metal oxides. At lower concentrations, environmentally harmful compounds such as alkali halide salts, heavy metals and traces of organic pollutants, e.g. PCDD, PCDF and PCB, are also present. For the reuse of the valuable materials (Al, Ca and metal oxides), an effective treatment technique for destroying the organic contaminants and separating the anorganic toxins from the non-toxic components has to be applied, which can only be achieved through thermal processing. Detailed investigations on vitrified electrostatic precipitator ash from municipal solid waste incinerator plants have shown promising results in regard to the mass balances, the chemical composition and the quality of the glass phase obtained.     

Nanomaterials for agriculture,food and environment: applications,toxicity and regulation

Nanotechnology is expected to have a beneficial influence on agriculture, food and environment, due to the unique properties of nanomaterials. However, little is known about their safety and potential toxicity. Here we review metal nanoparticles, nanometal oxides, carbon nanotubes, liposomes and dendrimers. We present the application of these nanomaterials in agriculture, food and environment for plant protection; disease treatment; packing materials; development of new tastes, textures and sensations; pathogen detection; and delivery systems. We discuss risk assessment of nanomaterials and toxicological impacts of nanomaterials on agriculture, food and environment. We then provide regulatory guidelines for the safer use of nanomaterials.     

Annual production and molecular weight as an influential factor for environmental distribution of chemicals — a case study in Japan

The changes promoted by treatment of a highly polluted soil with sulphuric acid or calcium hydroxide for changing its pH value are studied by controlling physical properties (particle size, TGA and DTA curves), evolution of metal species (exchangeable, as carbonates, related to Fe‐Mn oxides, linked to organic matter and residual) and metal uptake by plant cultures. Metal contents were determined, after wet digestion with HF—HNO₃—HC1O₄ when necessary, by AAS (Ca, Mg, Cu, Pb, Mn, Fe, Zn) or emission (Na, K). The treatment of soil with successive amounts of sulphuric leads to changes in particle size, hydration properties and exothermic peak for organic matter combustion. Very small changes were, however, detected in the alkaline treatment of soil. Soil treatments do not have practical influence on speciation of some metals (Na, K, Mg, Pb, Mn, Fe), but the intensity of the acid treatment leads to both an increase in the Cu extraction and a decrease in the Ca solubilization, probably through gypsum formation. In the case of zinc a maximum solubility in the middle of the range of acid treatment was observed. The comparison among extractants shows solubilities high for two pollutants (Pb, Cu), associated mainly to Fe—Mn oxides and organic matter, and low for two macrocomponents (Fe, K). The rest of metals, basically present in soil as carbonates or oxides, have intermediate extractions. Pot cultures weights depended mainly on both the treatment of soil (poor development in the more acid sample and drainage difficulties in the rest of acid treatments) and the situation (very low weights in laboratory runs as compared with outside), but the irrigation with water or a diluted sulphuric acid solution (at pH = 4.0) did not produce significant weight changes. Tendencies to increase plant pollution were observed for smaller soil pH, acid irrigation and probably for outside cultures, due to uptake by leaves.     

Speciation of Heavy Metals in Floodplain and Flood Sediments: a Reconnaissance Survey of the Aire Valley, West Yorkshire, Great Britain

A five-step sequential extraction technique was used to determine the chemical association of heavy metals (Pb, Zn, Cu and Cd), with major sedimentary phases (exchangeable, surface oxide and carbonate, Fe and Mn oxides, organic and residual metal ions), in samples from floodplain and recent flood sediments of the River Aire, West Yorkshire. Analysis indicates that metals Pb and Zn are primarily associated with the Fe and Mn oxides, Cu with the organic fraction and Cd with exchangeable and surface oxide and carbonate metal ions. Knowledge of the chemical speciation of heavy metals in river sediment, despite the procedure's inherent limitations, facilitates an understanding of their bioavailability, storage and remobilisation in floodplain and river channel environments.     

Metal speciation in sediments of polluted and non‐polluted lakes

A five‐step extraction procedure for metal speciation studies (copper, lead, nickel, manganese and zinc) was applied to the analysis of lake sediments characterised by different environmental features. A different partition of metals into the several metal forms was observed. Both the metal fraction sorbed or co‐precipitated on hydrous Mn‐oxides (especially lead and zinc) and that bound to organic matter (especially copper) are high in some samples. A prevalently anthropogenic origin of these metals may be hypothesised on the basis of existing knowledge of the equilibrium and change phenomena occurring among water, particulate and sediments. Conversely, the non‐solubilised forms of metals are abundant in the sediments of lakes that are certainly not polluted. The concentration of manganese is very high in the sediments of Antarctic lakes; sequential extractions show its lithogenic origin. In conclusion, a knowledge of the different types of metal associations in sediments and their percentage can facilitate understanding of both natural and anthropogenic metal enrichment of aquatic systems.     

催化臭氧氧化降解罗丹明B的初步研究

研究了过渡金属硝酸盐及Al2O3为载体担载催化剂在罗丹明B臭氧氧化过程中的催化作用,考察了温度、pH值以及催化剂浓度等因素对反应的影响.结果表明,过渡金属离子可显著地提高罗丹明B的脱色速率,而担载型过渡金属氧化物催化剂活性较低.较低的pH值和反应温度有利于罗丹明B的催化臭氧化.罗丹明B溶液经过催化臭氧氧化后COD去除率可提高24%.     

Nanoscale materials as sorbents for nitrate and phosphate removal from water

Excessive nitrogen (N) and phosphorous (P) release into run-off waters from human activities is a major cause of eutrophication. Several techniques are available to remove N and P-containing pollutants, such as chemical precipitation, biological treatment, membrane processes, electrolytic treatment, ion-exchange and adsorption. In order to remove low concentration levels of nitrate and phosphate, adsorption is a cost-effective solution. In this review, we present a list of nanoscale adsorbents such as zero-valent metal, metal oxides/metal hydroxides, and carbon-based materials. We discuss their adsorption capacities, isotherms, kinetics and mechanisms.     

土壤中锰氧化物的形态及其化学提取方法综述

土壤中锰元素主要来自于成土母质,风化后的锰主要以锰氧化物形式存在于土壤中.锰氧化物因具有比表面积大、表面电荷低、对金属的亲合力强、氧化还原电位高等特性,对土壤中痕量金属的环境行为存在重要影响.化学提取方法是研究土壤中不同固相组分的重要手段.本文首先从土壤中锰的来源及主要存在形态出发,介绍了不同价态锰(+2、+3、+4)...     

土壤重金属化学形态的生物可利用性评价

重金属化学形态是近年来土壤化学、植物营养和环境科学研究领域的一个热点和难点,利用重金属的化学形态分布和含量变化来评价重金属的生物可利用性,有利于全面研究重金属的危害性和治理重金属污染土壤。结果表明,水溶态和交换态的重金属易被生物吸收利用,而残留态重金属一般不被生物利用,其它形态如碳酸盐结合态、铁锰氧化物结合态和有机物结合态的生物可利用性主要取决于外界环境的变化。     

Graphene and its derivatives: synthesis,modifications, and applications in wastewater treatment

Graphene was discovered in 2004 and has attracted intensive interests because of its unique mechanical, electric, thermal, optical, and structural properties, which makes graphene a potential candidate for various applications. Graphene is being used as a composite or filler material with metals, metal oxides, and polymers for potential advanced applications in solar cells, lithium-ion batteries, photocatalysis and sensing. These applications depend upon the distinctive properties of graphene, which in turn depend on the adopted synthetic approach. This article reviews the recent developments in synthesis of graphene and related composite materials. The synthesis of graphene through exfoliation, epitaxial growth and direct growth via carbon source, and modification approaches by covalent and noncovalent methodologies are discussed. Graphene-based metal and metal oxide composites for the purification of wastewater using photolytic process are also presented.     

Redox reactions of iron and manganese oxides in complex systems

• Mechanisms of redox reactions of Fe- and Mn-oxides were discussed. • Oxidative reactions of Mn- and Fe-oxides in complex systems were reviewed. • Reductive reaction of Fe(II)/iron oxides in complex systems was examined. • Future research on examining the redox reactivity in complex systems was suggested. Conspectus Redox reactions of Fe- and Mn-oxides play important roles in the fate and transformation of many contaminants in natural environments. Due to experimental and analytical challenges associated with complex environments, there has been a limited understanding of the reaction kinetics and mechanisms in actual environmental systems, and most of the studies so far have only focused on simple model systems. To bridge the gap between simple model systems and complex environmental systems, it is necessary to increase the complexity of model systems and examine both the involved interaction mechanisms and how the interactions affected contaminant transformation. In this Account, we primarily focused on (1) the oxidative reactivity of Mn- and Fe-oxides and (2) the reductive reactivity of Fe(II)/iron oxides in complex model systems toward contaminant degradation. The effects of common metal ions such as Mn²⁺ , Ca²⁺, Ni²⁺, Cr³⁺ and Cu²⁺, ligands such as small anionic ligands and natural organic matter (NOM), and second metal oxides such as Al, Si and Ti oxides on the redox reactivity of the systems are briefly summarized.     

Cerium dioxide and composites for the removal of toxic metal ions

The presence of contaminants in potable water is a cause of worldwide concern. In particular, the presence of metals such as arsenic, lead, cadmium, mercury, chromium can affect human health. There is thus a need for advanced techniques of water decontamination. Adsorbents based on cerium dioxide (CeO₂), also named ‘ceria,’ have been used to remove contaminants such as arsenic, fluoride, lead and cadmium. Ceria and composites display high surface area, controlled porosity and morphology, and abundance of functional groups. They have already found usage in many applications including optical, semiconductor and catalysis. Exploiting their attractive features for water treatment would unravel their potential. We review the potential of ceria and its composites for the removal of toxic metal ions from aqueous medium. The article discusses toxic contaminants in water and their impact on human health; the synthesis and adsorptive behavior of ceria-based materials including the role of morphology and surface area on the adsorption capacity, best fit adsorption isotherms, kinetic models, possible mechanisms, regeneration of adsorbents; and future perspectives of using metal oxides such as ceria. The focus of the report is the generation of cost-effective oxides of rare-earth metal, cerium, in their standalone and composite forms for contaminant removal.     

固-液异相催化剂在环境科学领域中的应用

异相催化是催化反应的重要组成部分，其应用十分广泛。固一液异相催化作为环境科学领域中的一项比较新颖的技术，在研究污染物在多介质环境中的迁移转化行为、开发受污染环境修复及污废水处理新技术等诸多方面都具有很大的发展潜力。因此，对不同类型固一液异相催化剂在环境科学领域的应用研究逐渐成为国内外环境科学领域的研究热点之一。其中，金属和金属氧化物因对某些氧化一还原反应具有较好的催化作用，在饮用水脱氮、污废水脱卤及深度氧化处理等水处理领域的应用较为广泛；固态酸催化剂能催化聚合、裂化、水解反应，因此与某些有机污染物的降解密切相关；将同相催化剂固定化为异相催化剂，同样成为新技术开发的方向之一；天然催化剂对污染物在多介质环境中行为影响的研究近年来也屡有发表。此外，载体因对催化剂的活性及应用具有重要影响，也日益受到关注。文章对环境科学领域中固一液异相催化剂的应用研究进行了综述。     

Speciation evolutions of target metals （Cd,Pb） influenced by chlorine and sulfur during sewage sludge incineration

In sludge incineration, the thermal behavior of heavy metal is a growing concern. In this work, the combined analysis of metal partitioning behavior between vapor phase and condensed phase, speciation redistribu- tion in condensed phase and the difference of metal species in binding energy was carried out to investigate the possible volatilization-condensation mechanism of heavy metals in high-temperature sludge incineration. It was found that there were two steps in metal volatilization. The initial volatilization of heavy metal originated from their exchangeable （EXC）, carbonate bound （CAR） and iron- manganese bound （FM） fractions, which is primarily composed of simple substance, chlorides, oxides and sulfides. With the increase of chlorine and sulfur in sludge, the inner speciation redistribution of heavy metals occurred in condensed phase, which was an important factor affecting the potential volatility of heavy metals. A partial of metal species with complexed （COM） and residual （RES） fractions gradually decomposed into simple substance or ions, oxides and carbonates, which signifi- cantly strengthened the second volatility. In presence of chlorine, about 46% of Cd with the RES fraction disappeared when the volatility rate of Cd increased by 44.89%. Moreover, about 9% of Pb with COM fraction disappeared when there was an increase of nearly 10% in the volatilization rate. Thus, the second volatilization was mainly controlled by the decomposition of metal species with COM and RES fractions. By virtue of XRD analysis and the binding energy calculation, it was found that metal complex and silicates were inclined to decompose under high temperature due to poor thermo stability as compared with sulfates.