Microwave extraction of heavy metals from wet rhizosphere soils and its application to evaluation of bioavailability

Single microwave extraction of heavy metals Cr, Ni, Zn, Cu, Cd, and Pb by the extractants CaCl(2), EDTA, CH(3)COOH and HCl has been established. The experimental conditions were optimized. A microwave power of 60% and an extraction time of 25 min were adopted. Comparison of microwave extraction and conventional extraction methods revealed that results obtained by microwave techniques were generally in a good agreement with those obtained by use of extraction methods; use of the former resulted in substantial time saving and a better precision, however. Microwave extraction was used to evaluate the bioavailability of heavy metals in soils. Single correlation analysis was performed to establish the relationship between the concentrations of the extractable heavy metals in wet rhizosphere soils and their concentrations in wheat ( Troticum aestivum L.) grown on the soils under greenhouse conditions. The correlation coefficients between the extractable metals in soils and their concentrations in wheat roots were found to be 0.5398-0.7819, 0.6425-0.8073, 0.5568-0.8276, 0.5851-0.6087 for the extractants CaCl(2), EDTA, CH(3)COOH, and HCl, respectively.     

克拉玛依减渣热转化前后的溶解度参数研究

对克拉玛依减渣进行适度热转化,确定了其裂解深度最大且不结焦的条件。利用超临界萃取分馏技术,将克拉玛依减渣及其热转化残渣油分离成一系列窄馏分和萃余残渣,对窄馏分及萃余残渣的性质（相对分子质量、密度、残炭、C、H、N、S元素和金属元素等）进行了表征。用改进的方法测定了萃余残渣的溶解度参数,并根据性质计算了各个窄馏分的溶解度参数,克拉玛依减渣及其热转化残渣油萃余残渣的溶解度参数分别为18.27 MPa1/2和19.79 MPa1/2;从溶解度参数的角度解释了渣油加工过程中的分相、结焦等问题。     

The homogeneity of heavy metal deposition on glass fibre filters collected using a high-volume sampler in the vicinity of an opencast chrome mine complex at Kemi,Northern Finland

The homogeneity of heavy metal (Cr, Ni, Cu, Fe and Cd) distribution on glass fibre filters (Munktell MG 160, 203 x 254 mm, 75 g m(-2)) collected using a high-volume sampler (Wedding & Associates) at an opencast chrome mine complex at Kemi, Northern Finland was studied. The heavy metals in the total suspended particulate (TSP) material were analysed by inductively coupled plasma atomic emission spectrometry (ICP-AES) or graphite furnace atomic absorption spectrometry (GFAAS). The glass fibre filters were digested in a microwave oven using a mixture of aqua regia+HF acids. There was significant non-uniform distribution of heavy metals on glass fibre filters. The TSP material containing chromite was very difficult to dissolve by acid digestion. The results from X-ray fluorescence spectrometry (XRF), and from energy filtering transmission electron microscope (EFTEM) equipped with energy dispersive X-ray spectrometer (EDS), showed that insoluble residue left after microwave oven digestion with aqua regia+HF acids was probably partly due to chemical reactions occurring during microwave heating.     

Analytical applications of superacid dissolution of actinide and lanthanide substrates

The superacid system HF/SbF₅ is extraordinarily effective for total dissolution of actinide and lanthanide ceramic oxides, fluorides, and metals. Optical or gamma spectroscopy can be used directly on the solutions. Evaporation of the HF/SbF₅ solvent under vacuum leaves a residue which is easily dissolved by ordinary mineral acids. The resulting aqueous solutions are readily amenable to conventional analytical methods.     

Reduction and Hydrogenation with the System Hydrocarbon/Carbon [New Synthetic Methods (70)]

For the synthesis of organic compounds, reduction is an indispensible reaction type which is also widely used on an industrial scale. In industrial processes hydrogen is usually used as reducing agent, since strong reducing agents like alkali metals and hydrides can only be used to a limited extent for safety and economic reasons. Very economical reducing agents that are convenient to handle and have high potential application are hydrocarbons in presence of carbon. Hydrocarbon/carbon systems can be readily used instead of molecular hydrogen and expensive metal catalysts for the hydrogenation of compounds containing, for example, CC-, CO-, or NO-double bonds. Furthermore, these systems can be used for carrying out reductions which hitherto required strong reducing agents such as zinc, tin, alkali metals and hydrides. Especially suitable as economic sources of hydrogen are refinery products such as vacuum gas oil, fuel oil S or vacuum residue oil. Hydrocarbons are dehydrogenated to unsaturated systems and finally to carbon.     

Quantitative analysis of precious metals in automotive shredder residue/combustion residue via EDX fluorescence spectrometry

The recovery of precious metals from automotive shredder residue (ASR) dust/combustion residue is an option that is not usually considered due to the lack of available information. Therefore, before any disposal or recovery application can be considered, it is necessary to determine the significance of the levels and distribution of precious metal in ASR dust/ASR combustion residue. In the present study, quantitative analysis of precious metals (Pt, Pd, Au, Ag and Cu) in the ASR residue samples was performed using energy dispersive X-ray (EDX) fluorescence spectrometer. With the fundamental parameter (FP) method, the X-ray intensity is obtained and the quantitative analysis is performed using theoretical calculation. This method is very effective for quantitative analysis of unknown samples without standard samples. Further, in order to analyse the precious metal distribution within the ASR combustion residues, the microstructural characterisation and elemental mapping were also carried out with the aid of field emission scanning election microscopy combined with electron dispersive spectroscopy (FE-SEM EDS). Significant amount of Pt, Pd, Au, Ag and Cu element concentrations in the ASR residue were identified. Total precious (Pt, Pd, Au, Ag and Cu) metals obtainable values are representing about 12.23 wt% from its initial ASR dust/combustion residues. Considering their relevant concentrations, these metals should be properly recovered for recycling purposes before to dispose or landfill.     

Determination of heavy metals in soil, mushroom and plant samples by atomic absorption spectrometry

The concentrations of heavy metals in the soil, mushroom and plant samples collected from Tokat, Turkey have been determined by flame and graphite furnace atomic absorption spectrometry after dry ashing, wet ashing and microwave digestion. The study of sample preparation procedures showed that the microwave digestion method was the best. Good accuracy was assured by the analysis of standard reference materials. The relative standard deviations for all measured metal concentrations were lower than 10%. In all cases, quantitative analytical recoveries ranging from 95 to 103% were obtained. Metal accumulation factors were calculated for mushroom and plant samples. High ratio of plants to soil cadmium, zinc and copper concentrations indicate that these elements are accumulated by mushrooms. Results obtained are in agreement with data reported in the literature.     

Aging Process Effects on the Characteristics of Vacuum Residue Oxidation Products with the Addition of Crumb Rubber

This paper considers the effect of aging processes on viscoelastic characteristics of vacuum residue oxidation products modified with crumb rubber. Viscoelastic properties were compared to original bitumen raw material-vacuum residue and vacuum residue oxidation products during short-term and long-term aging. The complex shear modulus of the vacuum residue and its oxidation products decreased with an increase in temperature. Short-term aging resulted in increased shear modulus for all samples.The vacuum residue oxidation product modified with crumb rubber had the maximum values of the rutting parameter and fatigue parameter. There was an expansion of the temperature range of plasticity: for the vacuum residue oxidation product with crumb rubber, its value was 67.2 °C. The curves of the black diagram of the modified vacuum residue oxidation product are shifted towards smaller phase angles with the increase in the shear modulus, which indicates the increase in the stiffness and elasticity of the rubber bitumen binders. The vacuum residue oxidation product modified with crumb rubber corresponded to the rubber bitumen binder of the grade RBB 60/90, according to its physical and mechanical indicators.     

Soil bacteria sensitivity towards heavy metals – Experimental system optimisation using chemical speciation calculations

The ecotoxicological relevance of many laboratory studies on soil bacteria sensitivity towards heavy metals is limited because culture conditions are chosen which do not adequately represent field conditions. The influence of the composition of culture media on the speciation of copper in an oligotrophic model soil system has been investigated. The expected chemical speciation has been calculated to obtain information on the concentration of the bioavailable fraction and the totally dissolved copper. For control measurements of totally dissolved copper, vacuum filtration has been used. The results of the measurements are in a good agreement with the calculations. Therefore, the use of speciation calculations is postulated as a useful tool for the assessment of free metal concentrations at higher pH, where the concentrations of dissolved metals are too low to be measured by simple methods.     

Simultaneous determination of several trace metals by asv after preconcentration by adsorption as padap complexes on C(18)-bonded glass beads

Traces of zinc, lead, copper and cadmium are determined simultaneously by anodic-stripping voltammetry (ASV) combined with a preconcentration technique utilizing C(18)-bonded glass beads. The metals are collected as their 2-(2-pyridylazo)-5-diethylaminophenol (PADAP) complexes on a column of the beads and the complexes are eluted with a small volume of ethanol-hydrochloric acidchloroform mixture. The eluate is evaporated to dryness in the presence of hydrogen peroxide and the residue dissolved in a small volume of acetic acid-sodium acetate buffer. The concentrations of the metals are measured by ASV, Quantitative recoveries are obtained for 0.01-ng ml levels of the metals. Many ions which interfere in the direct ASV procedure do not interfere in the present method.     

Experimental Designs in the Optimization of a Microwave Acid Digestion Procedure for the Determination of Metals in Paper and Board Samples by Atomic Absorption Spectrometry

Abstract

A Plackett-Burman design was carried out in order to find the significant experimental parameters affecting Cd, Co, Cr, Cu, Mn, Pb, and Zn extraction by microwave energy in paper samples. Eight variables were studied and optimized by means of a factorial design. The design showed that HCl and HNO₃ concentrations were the significant parameters in the microwave extraction procedure. The trace elements were determined by FAAS and ETAAS under optimum conditions. The levels of metals present in commercial samples, representing different types of paper and board and manufacturers are lower than those provided by the legislation.     

Is microwave digestion using TFM vessels a suitable preparation method for Pt determination in biological samples by adsorptive cathodic stripping voltammetry?

The occurrence of Pt in environmental matrices is increasing since the introduction of automobile catalytic converters. Given that Pt is bioavailable and causes biological effects in plants and animals, respective biomonitoring programs are in high demand. But the analytical methods for conducting such programs have not yet been sufficiently established. Therefore, a study was carried out to develop a microwave digestion of biological samples, which allows a rapid determination of Pt by adsorptive cathodic stripping voltammetry.A high pressure microwave system was used and the digestion was performed in HNO₃ and HCl. After digestion the HNO₃ was evaporated with a microwave assisted vacuum concentration set. The study resulted in a procedural detection limit of 37.5 ng L⁻¹ and a relative standard deviation of 18%. A recovery study resulted in a Pt loss below 5%. The microwave assisted evaporation of HNO₃ performed satisfactorily and up to 500 mL of the sample solution could be used for the voltammetric measurements without any effect on the peak heights. A direct comparison of Pt concentrations conducted after microwave digestion and digestion by high pressure ashing showed similar values. However, these promising results were not persistent throughout the repeated analysis using the same Teflon vessels. The vessels did not endure the harsh conditions and due to aging processes the Pt loss consistently increased until Pt determination in environmental relevant concentrations became impossible. Quartz vessels could not be employed as an alternative to the Teflon vessels, due to a lack of compatibility with the vacuum concentration system. Consequently, the results of this paper show that there is a need for further development of more resistant Teflon materials.     

Contribution of perfluoropolyethers in vacuum industries

Perfluoropolyethers from hexafluoropropene photooxidation, are characterized by attractive physical and antiwear properties of chemical and thermooxidative stability, so as to allow their use as vacuum working fluids and as a base for high vacuum grease.The vacuum technologies, where residue pressures of aggressive chemical agents are involved, can benefit by the unique fluid's performances.     

油焦浆流变特性的研究

利用减压不同和石油焦制备成浆体燃料,然后考察了其流变性及温度、浓度和原料油对流变性的影响。结果表明,浆体为屈服假塑性流体并具有触变性,屈服应力值和粘度随着温度升高、浓度的降低而减小。原料油中的胶质和沥青质组分对浆体的流变特性和度有很大的影响,含有较多的胶质和沥青质原料油的浆体表现出更强的屈服假塑性和更高的粘度。     

Quantification of Inorganic Constituents in Brazilian Human Milk by ICP OES

A fast procedure to determine essential and toxic metals in Brazilian human milk by ICP OES is proposed. Mature and colostrum human milk samples were mineralized using closed-pressurized and high-performance microwave digestion oven. Aqueous calibration was performed for all analytes investigated. A reference material, Infant Formula, was analyzed to test the accuracy of the proposed methodology. Recovery rates ranged between 83 and 117%. The precision of the method was better than 3.3% (R.S.D.) for all analytes investigated. Higher concentrations, on average, of the metals studied in the colostrum human milk could be found in relation to the mature human milk.     

Simultaneous determination of traces of iron, cobalt, nickel, copper, mercury and lead in water by energy-dispersive x-ray fluorescence spectrometry after preconcentration as their piperazino-1,4-bis(dithiocarbamate) complexes

A bidentate chelating agent has been proposed to preconcentrate seven metal ions dissolved in an aqueous sample for their simultaneous determination using energy-dispersive x-ray fluorescence spectrometry. The metal ions are precipitated as their polymeric piperazino-1,4-bis(dithiocarbamate) chelates, which are then collected by vacuum filtration on a Millipore membrane filter for direct examination by x-ray fluorescence analysis. Iron, cobalt, nickel, copper and zinc are determined by means of their K x-rays and mercury and lead by means of their L x-rays. A detection limit in the μg1⁻¹ range can be achieved for all metals tested in 250-ml water samples with a counting time of 600 s. Effective precipitation of all metals occurs at pH 6–7. The recoveries of eight analyses of the metals in a multielement standard using the proposed method ranged from 97 to 105% and the precision ranged from 2.3 to 3.1%. High concentrations of calcium and magnesium do not interfere with the method. The method is simple, sensitive and accurate, and has been used for the simultaneous determination of the seven metals under study in environmental samples and synthetic mixtures.     

Systematic errors in vacuum and inert gas fusion analysis for oxygen in metals

Determinations of oxygen in metals by conventional vacuum or inert gas fusion are usually based on the assumption that oxygen is extracted from the melt wholly as carbon monoxyde. A qualitative thermodynamic approach is used to demonstrate that whilst this is true for most metals in the Periodic Table, a significant number of them can yield oxygen partially as gaseous species other than carbon monoxide, so that systematic errors are obtained. Practical suggestions are made to overcome this inconvenience. Vacuum fusion and neutron activation results on different metals are given.     

Determination of total metals in cultivated oysters (Crassostrea gigas) from the northwest coast of Mexico by microwave digestion and atomic absorption spectrometry.

Bivalves such as oysters often accumulate heavy metals, and therefore can be used to monitor changes of pollutant concentrations in the environment. Cultivated oysters from the northwest coast of Mexico are widely used for human consumption and thus have an important commercial value. Information was gathered on the concentration of these elements in oysters (Crassostrea gigas) cultivated on the coast of Sonora. Oysters were randomly collected from April to October 1997, from 6 different locations (65 individuals per site) in 4 different months. Metals were determined by microwave digestion followed by atomic absorption spectroscopy. The mean values (microg/g fresh weight) for each metal were: Cd, 0.76; Cu, 3.64; Zn, 17.71; Pb, 0.50; As, 0.05; Hg, 0.03; and Se, 0.21. The results show that, except for Cd, concentrations of regulated metals were under the maximum permitted values specified by regulatory agencies of Mexico and were comparable to those reported from other areas.     

Effect of waste tires addition on a low-temperature hydrovisbreaking process of vacuum residue

Most of the resources used for energy have a fossil origin and they are non-renewable materials. Using mixtures of waste materials with the currently used non-renewable materials can improve the renewability of the energy production. The goal of this work was to explore the effect of waste tire addition on a hydrovisbreaking process at low temperature. Four tests were carried out at 300 °C in H₂ with different feedstocks: (1) vacuum residue; (2) tires; (3) 37.5wt% tires + 62.5wt% vacuum residue; (4) 15wt% tires + 85wt% vacuum residue. Dynamic viscosity, simulated distillation, density, elemental analysis (C, H, N, S% content) by ICP and analysis of gaseous products by GC–MS were carried out for all products. Content of insoluble compounds in hexane was estimated for the products from test (1) and vacuum residue. TGA analyses of the tires were carried out. The addition of tires to the vacuum residue brought a positive effect to increasing the yield of lighter products in the final liquid product. Densities and composition determinated by elemental analyses were similar for feedstock and products. The dynamic viscosity (60 °C) decreased from 24,550 to 17,700 mPa s for test (1) and to 1640 mPa s for test (3).