Amorphous oxides of manganese as new sorbents of strontium ions

Samples with the best adsorption properties are selected as a result of investigations conducted on synthesis of manganese-dioxide-based materials and study of their physicochemical properties. Materials were selected on the basis of their low cost and the simplicity of their production technology. In the laboratory the synthesis and analyses of materials was carried out for selected samples. The sorption of a series of elements is studied for a more detailed investigation of materials obtained. The results obtained will promote the synthesis of materials with improved adsorption properties with the aim of their application for purification of water from strontium. It is shown that the most promising way for amendment of manganese oxide is modification of this material using acid-resistant oxides. These oxides are also less expensive than existing sorbents for strontium.     

Engineered magnetic oxides nanoparticles as efficient sorbents for wastewater remediation: a review

The rapid urbanization and industrialization is causing worldwide water pollution, calling for advanced cleaning methods. For instance, pollutant adsorption on magnetic oxides is efficient and very practical due to the easy separation from solutions by an magnetic field. Here we review the synthesis and performance of magnetic oxides such as iron oxides, spinel ferrites, and perovskite oxides for water remediation. We present structural, optical, and magnetic properties. Magnetic oxides are also promising photocatalysts for the degradation of organic pollutants. Antimicrobial activities and adsorption of heavy metals and radionucleides are also discussed.

     

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.     

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)...     

低分子量有机化合物对MnO_2和土壤氧化锰的还原溶解作用

为考察土壤锰氧化物的还原溶解行为,本文选取常见的根系分泌的8种有机酸(抗坏血酸、香草酸、柠檬酸、草酸、酒石酸、水杨酸、半胱氨酸和邻苯二甲酸)和1种酚类化合物(邻苯二酚),人工合成的Mn O2和5种富含氧化锰的土壤(广东徐闻的砖红壤、海南澄迈的砖红壤、云南昆明的砖红壤、浙江嵊县的红壤和江苏南京的黄棕壤),研究了有机化合物对氧化锰的还原溶解作用.结果表明,较低p H和较高温度有利于有机化合物对Mn O2的还原溶解.在p H 4.5—5.5和温度5—45℃范围内,不同有机化合物还原溶解Mn O2能力的大小顺序为:邻苯二酚半胱氨酸抗坏血酸香草酸柠檬酸草酸≈酒石酸水杨酸≈邻苯二甲酸.邻苯二酚、半胱氨酸和抗坏血酸对土壤中氧化锰也有较强的还原溶解能力.当5种土壤比较时,徐闻砖红壤中还原溶解出的锰量最高,其次为昆明砖红壤,嵊县红壤中还原溶解出的锰量最小.当有还原性有机化合物存在时徐闻砖红壤、昆明砖红壤和澄迈砖红壤中的氧化锰容易发生还原溶解反应,增加土壤中可溶态和交换态Mn2+的含量,并可能对植物产生锰毒害.     

Enhanced adsorption of arsenate on titanium dioxide using Ca and Mg ions

In this study, we report the effects of pH and divalent cations on the adsorption of arsenate (As(V)) by titanium dioxide (TiO₂) nanoparticles. The extent of As(V) adsorption on TiO₂ decreased with increasing pH due to the decrease of positively charged binding sites on the TiO₂ surface. The Langmuir maximum uptake capacity at pH 4 is about three times higher than that at pH 7. Here we show that the relatively low As(V) uptake at circumneutral pH could be substantially enhanced by the addition of common divalent cations such as magnesium and calcium. At a concentration of approximately 7 mM, magnesium and calcium increased the extent of As(V) adsorption from 2.1 to 6.5 and 7.7 mg As(V)/g TiO₂, respectively.     

Comparative adsorption of Pb(II) and Cd(II) ions on chestnut shell in aqueous system

In this study, high capacity Chestnut shell, a waste product from the chestnut sugar production industry, was successfully applied to remove Pb (II) and Cd (II) ions from aqueous solutions. Maximum adsorption capacities were found as 541.25?mg/g and 75.86?mg/g for Pb(II), and Cd(II) respectively. Several important parameters influencing the adsorption of Pb(II) and Cd(II) ions such as contact time, pH, temperature and effect of metal concentration were investigated systematically by batch experiments. Langmuir and Freundlich adsorption models were used to describe adsorption isotherms and constants. The thermodynamic parameters, such as standard free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°), of the adsorption process were calculated. The adsorbents were characterised by scanning electron microscopy. It has been observed from the experimental results that in case of both Cd (II) and Pb (II), pseudo 2nd order kinetic model. From the results, Chestnut Shell are considered as an effective, low cost and environmental friendly adsorbent for the removal of Pb (II) and Cd (II) from wastewater.     

The effects of <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> on the leaching of cobalt and strontium adsorbed onto soil particles

Bioleaching from soil artificially contaminated with analogues of radionuclides, Co and Sr, was carried out using a Fe-oxidizing bacterium, Acidithiobacillus ferrooxidans. Due to bacterial metabolism, the pH and dissolved Fe³⁺ concentration in a biotic slurry decreased and increased respectively, over time, but the concentrations of Co and Sr extracted from the soil showed no significant enhancement compared with those under abiotic control. In both cases, Co and Sr were leached from the soil during the initial period of the experiment, due to the initially low solution pH of 2.0, and the dissolved concentrations remained almost constant for the duration of the experiment (300 h). Since oxidation of Fe²⁺ by A. ferrooxidans led to the production of Fe precipitates and colloidal suspensions, the Co and Sr extracted into solution were most likely re-adsorbed onto the Fe solids. Also, A. ferrooxidans, without an external supply of Fe²⁺, extracted almost equal or greater amounts of Co and Sr from the soil than when Fe²⁺ was supplied. Under the same leaching conditions, the extent of Sr removal was much lower than that of Co. On the contrary to the high efficiency of microbial metal leaching in biohydrometallurgy for low-graded sulfide ores, which has been widely documented, conventional bioleaching techniques with A. ferrooxidans supplied with enough Fe²⁺ showed low efficiency for the removal of radionuclides loosely bound onto soil particle surfaces.     

Zero-valent manganese nanoparticles coupled with different strong oxidants for thallium removal from wastewater

• Nano zero-valent manganese (nZVMn, Mn⁰) is synthesized via borohydrides reduction. • Mn⁰ combined with persulfate/hypochlorite is effective for Tl removal at pH 6-12. • Mn⁰ can activate persulfate to form hydroxyl and sulfate radicals. • Oxidation-induced precipitation and surface complexation contribute to Tl removal. • Combined Mn⁰-oxidants process is promising in the environmental field. Nano zero-valent manganese (nZVMn, Mn⁰) was prepared through a borohydride reduction method and coupled with different oxidants (persulfate (S₂O₈²⁻), hypochlorite (ClO⁻), or hydrogen peroxide (H₂O₂)) to remove thallium (Tl) from wastewater. The surface of Mn⁰ was readily oxidized to form a core-shell composite (MnO_x@Mn⁰), which consists of Mn⁰ as the inner core and MnO_x (MnO, Mn₂O₃, and Mn₃O₄) as the outer layer. When Mn⁰ was added alone, effective Tl(I) removal was achieved at high pH levels (>12). The Mn⁰-H₂O₂ system was only effective in Tl(I) removal at high pH (>12), while the Mn⁰-S₂O₈²⁻ or Mn⁰-ClO⁻ system had excellent Tl(I) removal (>96%) over a broad pH range (4–12). The Mn⁰-S₂O₈²⁻ oxidation system provided the best resistance to interference from an external organic matrix. The isotherm of Tl(I) removal through the Mn⁰-S₂O₈²⁻ system followed the Freundlich model. The Mn⁰ nanomaterials can activate persulfate to produce sulfate radicals and hydroxyl radicals. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy suggested that oxidation-induced precipitation, surface adsorption, and electrostatic attraction are the main mechanisms for Tl(I) removal resulting from the combination of Mn⁰ and oxidants. Mn⁰ coupled with S₂O₈²⁻/ClO⁻ is a novel and effective technique for Tl(I) removal, and its application in other fields is worthy of further investigation.     

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.     

二氧化锰基纳米材料对重金属离子的去除及机理研究进展

重金属离子对人类健康和环境安全产生了严重威胁,因此重金属废水高效处理成为了环境领域最具挑战性的热点问题之一.二氧化锰(MnO_2)是一种环境友好型金属氧化物,具有来源广泛、成本低廉、形貌多样、晶型丰富、结构稳定、粒径可控等优异的性质,在重金属离子的去除应用上展现出巨大的潜力.近年来,人们利用MnO_2基纳米材料在重金属离子的有效治理方面开展了大量的研究.本文综述了MnO_2基纳米材料在重金属离子环境修复方面取得的研究进展,包括MnO_2的制备和改性方法,MnO_2基纳米材料在水溶液重金属离子去除中的应用及吸附作用机制,并对研究方向进行了总结和展望,旨在为进一步设计合成对重金属离子的吸附去除具有实际应用价值的MnO_2基纳米材料提供参考.     

三氯乙烯在模型吸附剂上的吸附特性

为了分别揭示矿物质、有机质在疏水性有机物吸附中的作用,文章研究了蒙脱石、高岭土、硅胶以及用腐殖酸修饰后的这3种模型吸附剂对三氯乙烯的吸附行为。采用批量吸附实验方法分别研究了三氯乙烯在不同吸附剂上的吸附。结果表明,硅胶、高岭土、蒙脱石对三氯乙烯均具有一定的吸附能力,吸附系数Kd值分别为10.3、3.13、1.15L·kg-1,硅胶的吸附能力明显高于高岭土和蒙脱石。3种无机模型吸附剂对腐殖酸表现出不同的吸附能力,蒙脱石最强,高岭土次之,硅胶最差,与对三氯乙烯的吸附能力正好相反。被腐殖酸修饰后3种模型吸附剂对三氯乙烯的吸附都明显增强,但增强程度不一样,当用8%腐殖酸(腐殖酸与模型吸附剂的质量比)修饰后,3种吸附剂对三氯乙烯的吸附Kd值均在23L·kg-1左右。虽然Kd随有机质的质量分数增高而上升,但是Kd值与有机质的质量分数不存在线性相关关系,特别是对于具有较高吸附能力的无机吸附剂,说明无机矿物本身结构对于吸附起到同等重要的作用。     

Determination trace amounts of copper, nickel, cobalt and manganese ions in water samples after simultaneous separation and preconcentration

In the present article, a simple, rapid, sensitive and economical method has been developed for the simultaneous separation and preconcentration of the trace amounts of copper, nickel, cobalt and manganese in water samples by using modified XAD-4 resins. The sorption was quantitative in the pH range 6.0–9.0, whereas quantitative desorption occurred instantaneously with 5.0 mL of 2 M HNO₃, and selected elements have been determined by using flame atomic absorption spectrometry. Dynamic ranges were 0.04–3.5, 0.1–6.0, 0.04–4.5 and 0.04–4.0 μg/mL for copper, nickel, cobalt and manganese, respectively. The detection limits were 9.2, 28.6, 12.3 and 5.7 ng/mL for Cu(II), Ni(II), Co(II) and Mn(II), respectively. The effects of the experimental parameters, including the sample pH, eluent type, interference ions and breakthrough volume, were studied for separation and preconcentration of Cu(II), Ni(II), Co(II) and Mn(II) ions. Determination of these ions in standard samples confirmed that the proposed method has good accuracy. The proposed method was used for the determination of these ions in water samples.     

Pomegranate husk as an adsorbent in the removal of toxic chromium from wastewater

The use of a new sorbent developed from the husk of pomegranate, a famous fruit in Egypt, for the removal of toxic chromium from aqueous solution has been investigated. The batch experiment was conducted to determine the adsorption capacity of the pomegranate husk. The effects of initial metal concentration (25 and 50 mg l^-1), pH, contact time, and sorbent concentration (2-6 g l^-1) have been studied at room temperature. A strong dependence of the adsorption capacity on pH was observed, the capacity increased as the pH decreased, and the optimum pH value was pH 1.0. Adsorption equilibrium and kinetics were studied with different sorbent and metal concentrations. The adsorption process was fast, and equilibrium was reached within 3 h. The maximum removal was 100% for 25 mg l^-1 of Cr⁶⁺ concentration on 5 g l^-1 pomegranate husk concentration, and the maximum adsorption capacity was 10.59 mg g^-1. The kinetic data were analysed using various kinetic models—pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion equations—and the equilibrium data were tested using several isotherm models, Langmuir, Freundlich, Tempkin, Dubinin-Radushkevich, and Generalized isotherm equations. The Elovich and pseudo-second-order equations provided the greatest accuracy for the kinetic data, while Langmuir and Generalized isotherm models were the closest fit for the equilibrium data. The activation energy of sorption has also been evaluated as 0.236 and 0.707 kJ mol^-1 for 25 and 50 mg l^-1 chromium concentration, respectively.     

Pomegranate husk as an adsorbent in the removal of toxic chromium from wastewater

The use of a new sorbent developed from the husk of pomegranate, a famous fruit in Egypt, for the removal of toxic chromium from aqueous solution has been investigated. The batch experiment was conducted to determine the adsorption capacity of the pomegranate husk. The effects of initial metal concentration (25 and 50 mg l^?1), pH, contact time, and sorbent concentration (2–6 g l^?1) have been studied at room temperature. A strong dependence of the adsorption capacity on pH was observed, the capacity increased as the pH decreased, and the optimum pH value was pH 1.0. Adsorption equilibrium and kinetics were studied with different sorbent and metal concentrations. The adsorption process was fast, and equilibrium was reached within 3 h. The maximum removal was 100% for 25 mg l^?1 of Cr⁶⁺ concentration on 5 g l^?1 pomegranate husk concentration, and the maximum adsorption capacity was 10.59 mg g^?1. The kinetic data were analysed using various kinetic models—pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion equations—and the equilibrium data were tested using several isotherm models, Langmuir, Freundlich, Tempkin, Dubinin–Radushkevich, and Generalized isotherm equations. The Elovich and pseudo-second-order equations provided the greatest accuracy for the kinetic data, while Langmuir and Generalized isotherm models were the closest fit for the equilibrium data. The activation energy of sorption has also been evaluated as 0.236 and 0.707 kJ mol^?1 for 25 and 50 mg l^?1 chromium concentration, respectively.     

纳米二氧化钛在老化环境条件下对铜诱导毒性的影响

纳米二氧化钛颗粒(nTiO₂)可以通过吸附表层水中共生重金属来改变它们对淡水无脊椎动物的毒性。然而,影响这种交互过程的几种环境因子的相对重要性仍不清楚。因此,本研究通过连续72 h的培养试验,评估了老化对Cu与nTiO₂对大型蚤Daphnia magna联合急性毒性的影响。在老化过程中,对老化时间以及离子强度、pH值和不同质量有机物质等因子都进行了考察。研究结果表明,尽管影响效应的大小不同,nTiO₂的存在往往减少了老化后Cu对大型蚤的诱发毒性,在没有nTiO₂的情况下,Cu对大型蚤急性毒性的EC₅₀值提高了3倍之多。此外,各种形态Cu的形成受到介质中的离子组成、pH值以及有机添加剂存在的影响,这一过程受到极大的调控,并随着老化时间对大型蚤生态毒性的响应有一定影响。尽管如此,该研究的结论对nTiO₂在淡水生态系统中不同环境条件下,改变重金属诱发毒性的潜在作用提供了有力的支持。然而,这种模式需要进一步验证,比如结合不同性质的重金属离子与不同的环境因素,如紫外线照射。
精选自Ricki R. Rosenfeldt, Frank Seitz, Ann-Cathrin Haigis, Johanna H?ger, Jochen P. Zubrod, Ralf Schulz, Mirco Bundschuh. Nanosized titanium dioxide influences copper induced toxicity during aging as a function of environmental conditions. Environmental Toxicology and Chemistry: Volume 35, Issue 7, pages 1766–1774, July 2016. DOI: 10.1002/etc.3325
详情请见http://onlinelibrary.wiley.com/doi/10.1002/etc.3325/full