Fabrication of Poly(γ-glutamic acid)-coated Fe3O4 Magnetic Nanoparticles and Their Application in Heavy Metal Removal

In this study, poly(γ-glutamic acid)-coated Fe3 O4 magnetic nanoparticles(γ-PGA/Fe3 O4 MNPs) were successfully fabricated using the co-precipitation method. Fe3 O4 MNPs were also prepared for comparison. The average size and specific surface area results reveal that γ-PGA/Fe3 O4 MNPs(52.4 nm, 88.41 m2·g 1) have smaller particle size and larger specific surface area than Fe3 O4 MNPs(62.0 nm, 76.83 m2·g 1). The γ-PGA/Fe3 O4 MNPs can remove over 99% of Cr3+, Cu2+and Pb2+, and over 77% of Ni2+in deionized water, much higher than γ-PGA and Fe3 O4 MNPs, attributed to the larger specific surface area of γ-PGA/Fe3 O4 MNPs. With the solution pH higher than 6.0, γ-PGA/Fe3 O4 MNPs demonstrate better removal activity. The adsorption isotherm of γ-PGA/Fe3 O4 MNPs for Cr3+fits the Freundlich model well, with the adsorption capacity of 24.60 mg·g 1. γ-PGA/Fe3 O4 MNPs are strongly attracted by permanent magnet, so it is easy to separate them completely from water. With their high efficiency for heavy metal removal and easier separation, γ-PGA/Fe3 O4 MNPs have great potential applications in water treatment.

Magnetic properties and heavy metal contents of automobile emission particulates

Measurements of the magnetic properties and total contents of Cu, Cd, Pb and Fe in 30 automobile emission par-ticulate samples indicated the presence of magnetic particles in them. The values of frequency dependent susceptibility (χfd) showed the absence of superparamagnetic (SP) grains in the samples. The IRM20 mT (isothermal remanent magnetization at 20 mT) being linearly proportional to SIRM (saturation isothermal remanent magnetization) (R2=0.901), suggested that ferrimagnetic minerals were responsible for the magnetic properties of automobile emission particulates. The average contents of Cu, Cd, Pb and Fe in automobile emission particulates were 95.83, 22.14, 30.58 and 34727.31 mg/kg, respectively. Significant positive correla-tions exist between the magnetic parameters and the contents of Pb, Cu and Fe. The magnetic parameters of automobile emission particulates reflecting concentration of magnetic particles increased linearly with increase of Pb and Cu content, showed that the magnetic measurement could be used as a preliminary index for detection of Pb and Cu pollution.

Heavy Metals in Urban Soils of Xuzhou, China: Spatial Distribution and Correlation to Specific Magnetic Susceptibility

The investigation of the anthropogenic contamination by heavy metals of soils is very important for environmental planning and monitoring in urban areas. In the present study, surface soils (0-20 cm) samples from 167 sampling sites in Xuzhou (China) were collected in 2010 and analyzed for heavy metals including Zn, Pb, Fe, Mn, Cu, Cd, Sr, Ba Cr, Ni and Mo via inductively coupled plasma/mass spectrometry (ICP-MS). Compared with their levels in natural soils of China, these metals investigated exhibited a slight build-up in Xuzhou topsoils. The multivariate statistical analyses including factor analysis (FA) and cluster analysis (CA) were performed. The obtained results enabled the identification of two main groups of metals, discriminating Ni, Mo and Cr from Zn, Pb, Fe, Mn, Cu, Cd, Sr and Ba. Signifcant associations between Pb, Zn, Fe and specific magnetic susceptibility (c) indicated that specific susceptibility can serve as proxies for these metals levels in Xuzhou urban soils.

The assessment of heavy metal pollution in river sands of Jalingo,Nigeria using magnetic proxy parameters,pollution,and ecotoxicological indices

The measurement of environmental magnetic properties and metal contents of sands from Nukkai(NKR),Mayo-Gwoi(RMYG)and Lamurde(LR)rivers located in Jalingo,Nigeria are reported.We seek to determine the extent of anthropogenic impact on the river sands using magnetic-proxy-parameters,pollution and ecotoxicological indices and multivariate statistics.Measurements of magnetic susceptibilityχ,frequency-dependentsusceptibilityχfd%,anhystericremanent magnetization,isothernal remanent magnetization and X-ray fluorescence were undertaken.The average values of theχ(in×10^(-8)m^(3)kg^(-1))were 24.53,12.76 and 39.27 for NKR,RMYG and LR sites respectively,implying that the magnetic minerals in the sands were mostly ferrimagnetic.The meanχfd%value of 2.64%,4.85%and 3.53%for NKR,RMYG and LR respectively suggest that the study area was dominated by multi-domain magnetic grain sizes.The value of the S-ratio is~1 in all river samples,suggesting that low coercivity magnetic minerals(e.g.,magnetite)dominated the samples.The mean concentrations of Ti,Zr,Sn,Ba and Pb were higher than the background values in the studied samples.All the estimated pollution indices puts the level of pollution of the river sands between low and moderate pollution with Sn,Ba and Pb as the elements of concern.Multiple sources of metal contents such as fertilizers,pesticides,waste dumps and vehicular sources etc.were found.Significant positive correlations between magnetic parameters(particularly,SIRM)and some heavy metals and pollution/ecotoxicological indices were obtained,showing that magnetic methods could be used as a geochemical proxy for pollution assessment.

Magnetic Properties as Indicators of Cu and Zn Contamination in Soils

Concentrations of copper (Cu) and zinc (Zn) and various magnetic parameters in contaminated urban roadside soils were investigated using chemical analysis and magnetic measurements. The results revealed highly elevated Cu and Zn concentrations as well as magnetic susceptibility in the roadside soils. The mean concentrations of Cu and Zn in these roadside soils were almost twice those in average Chinese soils, with the mean magnetic susceptibility of the roadside soils reaching about 179 × 10-8 m3 kg-1. This enhanced magnetic susceptibility was attributed to the presence of anthro-pogenic soft ferrimagnetic particles. A low frequency-dependent susceptibility (2.5% ± 1.0%) observed in the roadside soils indicated the coarse multidomain (MD) ferrimagnetic grains to be the dominant contributor to magnetic susceptibility. The Cu and Zn concentration of the soils had highly significant linear correlations with magnetic susceptibility (P ≤ 0.01), anhysteretic remanent magnetization (P ≤ 0.01), and saturation isothermal remanent magnetization (P ≤ 0.01). This suggested that heavy metals were associated with ferrimagnetic particles in soils, which were attributed to input of traffc emissions and industrial activities. Scanning electron microscopy and energy dispersive X-ray spectra of magnetic extracts of the roadside soils further suggested the link between the magnetic signal and concentrations of heavy metals. Thus, the magnetic parameters could provide a proxy measure for the level of heavy metal contamination and could be a potential tool for the detection and mapping of contaminated soils.

Integration of chemical fractionation, Mosbauer spectrometry, and magnetic methods for identification of Fe phases bonding heavy metals in street dust

Street dust is one of the most important carriers of heavy metals(HMs)originating from natural and anthropogenic sources.The main purpose of the work was to identify which of Fe-bearing phases bind HMs in street dust.Magnetic parameters of the Fe-bearing components,mainly magnetically strong iron oxides,are used to assess the level of HM pollution.Chemical sequential extraction combined with magnetic methods(magnetic susceptibility,magnetization,remanent magnetization)allowed determining the metal-bearing fractions and identifying the iron forms that aremostly associated with traffic-related HMs.The use of Mossbauer spectrometry(MS)supplemented bymagnetic methods(thermomagnetic curves and psarameters of hysteresis loops)enabled precise identification and characterization of iron-containing minerals.The classification of HMs into five chemical fractions differing in mobility and bioaccessibility revealed that iron is most abundant(over 95%)in the residual fraction followed by the reducible fraction.HMs were present in reducible fraction in the following order:Pb>Zn>Mn>Cr>Ni>Fe>Cu,while they bound to the residual fraction in the following order:Fe>Ni>Cr>Mn>Pb>Cu>Zn.The signature of the anthropogenic origin of street dust is the presence of strongly nonstoichiometric and defected grains of magnetite and their porous surface.Magnetite also occurs as an admixture with maghemite,and with a significant proportion of hematite.A distinctive feature of street dust is the presence of metallic iron and iron carbides.Magnetic methods are efficient in the screening test to determine the level ofHMpollution,while MS helps to identify the iron-bearing minerals through the detection of iron.

磁性生物炭合成及其对重金属吸附机制的研究进展

磁性生物炭(Magnetic biochar,MBC)因其磁分离能力和广阔应用前景而受到研究者广泛关注。MBC中碳基结构特征(如形貌、比表面积、官能团等)和铁氧化物形态及分布受多因素影响,如原料来源、热解温度、合成方法等。然而,MBC特性与合成条件的关联性以及MBC对重金属的吸附机制有待进一步研究。本文通过阐述合成条件对MBC特性的影响及其吸附重金属机制,提出关于未来MBC吸附重金属研究的一些科学问题,这将为认识MBC的环境效应提供重要的基础信息。

湿法磁选对粉煤灰中铁和重金属元素的分布影响研究

对煤粉锅炉粉煤灰(FA1灰)和循环流化床锅炉粉煤灰(FA2灰)采用湿法磁选的工艺达到降低其重金属含量的目的。利用扫描电子显微镜、激光粒度仪和X射线衍射仪表征两种粉煤灰在不同磁感应强度和不同磁选溶液浓度条件下磁选前后高磁性和弱磁性部分的形貌、粒度分布和物相分析,同时测定其铁元素和5种重金属元素(Hg、Pb、As、Cr、Cd)的含量变化,发现磁选后两种粉煤灰铁回收率随着磁感应强度增强而逐渐增加,高磁性组中重金属元素含量与弱磁性组有明显差异。结果表明:在磁感应强度为8000 Gs和磁选溶液浓度为20%(质量分数)时,FA1的铁回收率为71.2%,FA2的铁回收率为47.0%。此时FA1磁选后Pb含量差值为0.2 mg/kg、Cr含量差值为9.2 mg/kg、As含量差值为1.1 mg/kg;FA2磁选后Pb含量差值为18.1 mg/kg、Cr含量差值为25.0 mg/kg、As含量差值为9.1 mg/kg。

Fe_(3)O_(4)/Au单晶异质结的磁各向异性研究

基于铁磁/重金属异质结结构的纯自旋流电子器件具有低功耗、非易失性等优点,是当前自旋电子学研究的核心内容。该文利用超导量子干涉仪以及铁磁共振测量系统等手段,对分子束外延法生长的铁磁/重金属异质结Fe_(3)O_(4)/Au单晶薄膜的静态及动态磁性能进行了系统研究。研究表明,随薄膜厚度的增加,Fe_(3)O_(4)的单轴磁各向异性逐渐减小而磁晶各向异性逐渐增强。Au覆盖层的引入有助于单晶超薄膜的晶格弛豫,进而有效增强了Fe_(3)O_(4)的磁各向异性。该研究为铁磁/重金属异质结的构建提供了新的思路,有望推动其在纯自旋流电子器件中的实用化进程。

Heavy metal removal from aqueous solutions by chitosan-based magnetic composite flocculants

In this study,three magnetic flocculants with different chelating groups,namely,carboxymethyl chitosan-modified Fe_(3)O_(4)flocculant(MC),acrylamide-grafted magnetic carboxymethyl chitosan flocculant(MCM),and 2-acrylamide-2-methylpropanesulfonic acid copolyacrylamide-grafted magnetic carboxymethyl chitosan flocculant(MCAA)were prepared,synthesized,and characterized by photopolymerization technology.They were applied to the flocculation removal of Cr(Ⅲ),Co(Ⅱ),and Pb(Ⅱ).The effect of flocculation condition on the removal performance of Cr(Ⅲ),Co(Ⅱ),and Pb(Ⅱ)was studied.Characterization results show that the three magnetic carboxymethyl chitosan-based flocculants have been successfully prepared with good magnetic induction properties.Flocculation results show that the removal rates of MC,MCM,and MCAA on Cr(Ⅲ)are 51.79%,82.33%,and 91.42%,respectively,under the conditions of 80 mg/L flocculant,pH value of 6,reaction time of 1.5 hr,G value of 200 s^(-1),and precipitation magnetic field strength of 120 mT.The removal rates of Co(Ⅱ)by MC,MCM,and MCAA are 54.33%,84.99%,and 90.49%,respectively.The removal rates of Pb(Ⅱ)by MC,MCM,and MCAA are 61.54%,91.32%,and 95.74%,respectively.MCAA shows good flocculation performance in composite heavy metal-simulated wastewater.The magnetic carboxymethyl chitosan-based flocculant shows excellent flocculation performance in removing soluble heavy metals.This research provides guidance and ideas for the development of efficient and low-cost flocculation technology to remove heavy metals in wastewater.

Magnetic records of heavy metal pollution in urban topsoil in Lanzhou,China

This study is a systematic analysis of the magnetic characteristics and heavy metal elements in soil samples collected from Lanzhou City,China.The 117 surface soil samples were measured to study the feasibility and effectiveness of environmental magnetism for evaluating heavy metal pollution in urban soils.Results of the study indicate that low-coercivity magnetite dominates the magnetic properties in the samples.The high values of the soil magnetic mineral concentration parameters and low values of magnetic particle size parameters are distributed throughout the northern area of Xigu District,the industrial zones of the eastern section of Chengguan District and the districts of the narrow sections connecting Chengguan District and the other three districts;these parameters are fundamentally consistent with the distribution of the high values of the Pollution Load Index and Nemerow Pollution Index.Semi-quantitative studies which use the environmental magnetic method to monitor pollution of heavy metals(such as As,Cr,Cu,Ni,Pb,Zn,and Fe) have shown that when xlf≤35×10-8 m 3 kg-1,it is unpolluted;when 35≤xlf <150×10-8 m3 kg-1,it is moderately polluted to unpolluted;when 150≤xlf <365×10-8 m 3 kg-1,it is moderately polluted;when 365≤xlf <750×10-8 m3 kg-1,fd %<2.7 and ARM /SIRM<0.2×10-3m A-1,it is moderately to highly polluted;when xlf ≥750×10-8 m3 kg-1,xfd %<2.7 and xARM/SIRM<0.2×10-3m A-1,it is highly polluted.The region of moderately to highly polluted distribution is caused by industry and vehicles,showing that the change of pollution in Lanzhou City bears the trend of "vehicle emission + industrial".

Magnetic response to atmospheric heavy metal pollution recorded by dust-loaded leaves in Shougang industrial area, western Beijing

Fifty-five evergreen tree's leaves growing less than one year were collected from Shougang industrial area in western suburb of Beijing, including steel plants and its ambient residential areas, recreational parks and farmlands. Rock magnetic properties and heavy metal contents were studied. The results show that the magnetic properties of leaf samples are predominated by low-coercivity magnetite, and both the concentration and grain size of magnetite particles gradually decreased with the distance from the main pollution source increases. Moreover, there is a significant linear relationship between magnetic parameters (the low-field magnetic susceptibility, saturation isothermal remanent magnetization and anhysteretic remanent magnetization) and heavy metals contents (Fe, Pb, V, Cr and Zn) (0.73≤R≤ 0.88). Hence, the magnetic parameters of leaves can serve as a proxy for quick detecting of the recent atmospheric metallic pollution.

Iron reduction in tidal flat sediment indicated by magnetic measurements and its significance in the study of heavy metal pollution

Magnetic measurements and chemical analysis were conducted on the anoxic core sediment from the tidal flat along the southern bank of Yangtze Estuary. The synchronous increase in magnetite and heavy metal concentration at a depth of 54 cm is revealed, which reflects the anthropogenic input due to the near shore sewage discharge. However, the heavy metal concentration declines at the top of sediment column (4—20 cm) with the reduction of fine magnetite grains, as indicated by the magnetic measurements. It is inferred that selective dissolution of finer magnetite happens under the reduced environment. Such a phenomenon is significant for the heavy metal pollution study in the tidal flat sediments.

Magnetic normalization of particle size effects in a heavy metal pollution study of intertidal sediments from the Yangzte Estuary

Magnetic, granulometric and geochemical analyses were conducted on an intertidal sediment core from the Yangtze Estuary to evaluate the possibility of normalizing samples for particle size effects in a heavy metal pollution study by means of magnetic proxies. It has been found that the magnetic parameter XARM, indicating fine grained ferrimagnetic minerals, correlates well with the clay content and organic matter concentration of the sediments. XARM also shows significant relationship with heavy metals. Therefore XARM is proposed as a proxy for clay content in the sediments, and can be used to compensate for the particle size effect in sedimentary heavy metal records, where magnetic minerals are not subject to significant post-depositional alteration.

低阶煤热解磁化及其半焦产物中硫和重金属分布特性

用热解和磁选相结合的方法,研究了不同热解温度下甘肃褐煤和山西次烟煤热解磁化及其半焦产物中硫和重金属的分布特性。通过ICP-OES和ICP-MS分别对半焦中的硫和重金属元素含量进行分析测定,利用XRD和SEM-EDS对半焦的矿物组成和表观形貌进行了表征。结果表明,甘肃褐煤和山西次烟煤在最佳条件下的磁选脱硫率最高可以分别达到52.37%和17.54%;这与黄铁矿在热解过程中的相变行为有关。山西次烟煤半焦的磁选脱硫率低于甘肃褐煤半焦主要是由于其伴生矿物质的赋存包裹和有机质对黄铁矿在热解过程中的转化产生了影响。Ni和Cr与Fe-S矿物的亲和性较强,其随硫更多地富集到磁性半焦中;在800℃时,甘肃煤和山西煤磁性半焦中Cr含量分别比非磁性半焦中多8698.25和32327.47μg/g。低阶煤热解磁化及其半焦产物中硫和重金属的分布特性为脱除煤中硫和重金属元素提供了数据支撑和新思路。

磁性黄原酸化壳聚糖合成及表征

以壳聚糖、二硫化碳、四氧化三铁为原料,戊二醛为交联剂,采用超声波辅助合成了一种核-壳结构的磁性黄原酸化壳聚糖重金属捕集剂(FSiCS)。通过测定水溶液中Sb(Ⅲ)的去除率来评价FSiCS的性能。当CS2用量为3.0 mL、NaOH质量浓度为90 g/L、反应时间为60 min+60 min、超声功率为160 W、戊二醛用量为150μL、反应温度为50℃时,合成的FSiCS性能最佳。通过傅里叶红外光谱仪(FTIR)、扫描电镜(SEM)对其进行结构表征。FTIR分析表明,FSiCS中含有—SH、N—C=S、C=S、C—S等含硫基团或化学键,能够与Sb(Ⅲ)发生配位作用;SEM分析表明,FSiCS的粒径为100~250 nm,呈圆球形或棱角分明的多边形。

壳聚糖/磁性核桃壳生物炭的制备及其对高浓度Pb(Ⅱ)的吸附

以核桃壳粉作为生物质原料,依次采用H_(2)O_(2)和FeCl_(3)为改性剂,在限氧条件下制备磁性核桃壳生物炭,然后以壳聚糖为改性剂、聚乙二醇为交联剂,制备了壳聚糖/磁性核桃壳生物炭复合材料(CS/MWSB),采用SEM、FT-IR、N_(2)脱附、XRD、XPS、VSM技术对其形貌和理化性质进行表征,并通过静态试验考察了CS/MWSB对模拟废水中Pb(Ⅱ)的吸附性能。结果表明:CS/MWSB的表面有大量微孔结构,表面负载球状Fe_(3)O_(4)颗粒和壳聚糖,CS/MWSB的活性基团和芳香基团有所增加;壳聚糖负载量为30%的CS/MWSB对Pb(Ⅱ)的吸附能力最强;对于初始浓度为400 mg/L的Pb(Ⅱ)溶液,当吸附剂投加量为4 g/L时,在pH为5.0、温度为40℃吸附3 h时,CS/MWSB对Pb(Ⅱ)的吸附率达90.86%,吸附容量为89.86 mg/g;CS/MWSB对Pb(Ⅱ)的吸附符合准二级动力学方程,吸附过程以化学吸附为主。CS/MWSB可用于对于高浓度Pb(Ⅱ)废水的处理。