mechanical and chemical methods, the treatment is insufficient in case of immobilization of mercury species. The problem mainly concerns big sewage sl

Transcription

1 Pollution of soils and sediments with mercury. (mgr inż. Bartłomiej Cieślik, Gdańsk 2016 r.) 1. Introduction Trace elements sources in aquatic environments may be divided in two fundamental groups: anthropogenic and natural. Despite the popular opinion natural sources are the main source of trace elements in the environment on the global scale. However anthropogenic ones are generally major threat for the environment and human health. Widely understood human impact on the environment usually cause contamination of relatively small, local environments [1]. Natural sources generally cause impact on larger area resulting in lower concentration of pollutants on a considerable range. The contamination is commonly defined as amount of specific element which exceeds it s natural, background concentration [2]. It may differ depending on the characteristic of local topography, soils, fauna, flora, human population and many others. One of the main natural sources of mercury in the aquatic environment are volcanoes activity. Although the impact of such phenomena are considered relevant, those occur only in specific sparsely inhabited areas. [3]. Another natural sources which should be considered significant are weathering and erosion. Running off water cause soils and rock leaching which can contain certain amount of mercury. Since mercury is considered as volatile elements, it may also be transported to water body through precipitation [4]. Natural events like forest fires may also favor mercury mobility, through dust and ashes particles wind transport [5]. In contrast to narrow range of natural sources of mercury in aquatic environments, there is vast variety of anthropogenic ones. Probably the biggest anthropogenic source of trace elements are various combustion processes. Every combustion process in connected with ashes and dust fraction production. Such particles are generally containing large amounts of mercury [6]. The concentration of such individuals is relatively high since combustion process results in significant volume reduction and thus trace elements concentration increase [7]. Even if mentioned contaminants are retained on the filters systems, preventing long range transport with wind, generally such fraction are landfilled, which also may pose threat to environments. The kind of combusted media determines the composition of ashes, and concentration of transported pollutants. Coal and lignite combustion, biomass and waste incineration or even cement production are the main sources of such contamination [3, 8]. Second relevant anthropogenic source of trace element is broadly understood industry. Nonferrous metals smelters, arms industry or even pharmaceuticals production can contribute to contamination of environment with mercury [1]. The biggest problem is waste production which is inextricable linked with variety of goods production [9] Another anthropogenic source of trace elements are wastewater treatment plants. The wastewater treatment process is generally based on biological treatment. Even if supported by

2 mechanical and chemical methods, the treatment is insufficient in case of immobilization of mercury species. The problem mainly concerns big sewage sludge treatment plants, which are collecting huge amounts of waste waters from big, often heavy industrialized agglomerations [10]. However such considerable facilities are processing most of produced waste in general. One big sewage sludge treatment plant can process from 100 to 1000 times greater amounts of waste water which may be around 35 % of whole km 2 district production [11]. 2. Atomic absorption spectroscopy (AAS) It is an Analytical procedure for the quantitative determination of chemical elements using the absorption of electromagnetic radiation (light) by free atoms in the gaseous state. In analytical chemistry the technique is used for determining the concentration of a particular element in a liquid, solid or gaseous samples. AAS can be used to determine over 80 different elements in solution or directly in solid samples. However the measurements have to be conducted separately [12]. The technique requires standards with known analyte content to establish the relation between the measured absorbance and the analyte concentration and relies on the Beer-Lambert Law. During the analysis the electrons of the atoms in the atomizer can be promoted to higher orbitals (excited state) for a short period of time (nanoseconds) by absorbing a defined quantity of energy (radiation of a given wavelength from radiation source). The wavelength, is specific to a particular electron transition in a particular element. In general, each wavelength corresponds to only one element, and the width of an absorption line is only of the order of a few picometers (pm), which gives the technique high selectivity. The radiation flux without a sample and with a sample in the atomizer is measured using a detector, and the ratio between the two values (the absorbance) is converted to analyte concentration or mass using the Beer-Lambert Law. Beer-Lambert Law: In case of parallel, monochromatic, electromagnetic beam passing through absorptive medium the absorbance is proportional to concentration of the absorbing solution and optical depth (optical path length). A = log(io/i) = abc A Io I a b c absorbance intensity of a beam before passing through absorbing medium intensity of a beam after passing through absorbing medium proportionality constant width of absorbing solution concentration

3 3. Atomization of mercury There are several kinds of atomization techniques. The most frequently used are Flame atomization, Electrothermal atomization and Hydride generation technique. Except hydride generation, mentioned techniques can be used for atomization of almost any kind of element [13]. The cold-vapor technique is an atomization method limited to perform determination of mercury. The mercury is only metallic element to have a large enough vapor pressure at ambient temperature to use cold vapor technique. The method is based on converting mercury into Hg 2+ by oxidation and reduction in atomization tube. The mercury, is then introduced into a long-pass absorption tube by a stream of inert gas. The concentration is determined by measuring the absorbance of this gas at nm. Detection limits for this technique are in the parts-per-billion range making it an excellent mercury detection atomization method. 3.1 Radiation sources There are two main kinds of radiation sources: with specific radiation and with continuum radiation. The advantage of specific radiation sources is that only a medium-resolution monochromator is necessary for measuring AAS; however, it has the disadvantage that usually a separate lamp is required for each element that has to be determined. In case of mercury analysis using cold vapor technique this disadvantage is irrelevant. In contrast, a single lamp, emitting a continuum spectrum over the entire spectral range of interest is used for all elements. Obviously, a high-resolution monochromator is required for this technique, but such approach won t be discussed during the laboratory [13]. Hollow cathode lamps Hollow cathode lamps (HCL) are the most common specific radiation source. Inside the sealed lamp, filled with argon or neon gas at low pressure, is a cylindrical metal cathode made of or covered with the element of interest and an anode. A high voltage is applied across the anode and cathode, resulting in an ionization of the noble gas. The gas ions are accelerated towards the cathode and, upon impact on the cathode, break off cathode material that is excited in the glow discharge to emit the radiation of the material which is the element of interest [13]. Electrodeless discharge lamps Electrodeless discharge lamps (EDL) contain a small quantity of the analyte as a metal or a salt in a quartz bulb together with an inert gas, typically argon gas, at low pressure. The bulb is inserted into a coil that is generating an electromagnetic radio frequency field, resulting in a low-pressure inductively coupled discharge in the lamp. The emission from an EDL is higher

4 than that from an HCL, and the line width is generally narrower, but EDLs need a separate power supply and might need a longer time to stabilize [13]. 4. Instrumentation Sample devices and the block diagram with the most important components of AAS device with cold vapor atomization technique are presented below. Figure 1. Block diagram of atomic absorption spectroscopy with cold vapor atomization

5 Figure 2. Mercury analyser NIC, MA 2000 Figure 3. Mercury analyser NIC, MA Instruction During laboratories student will get familiar with cold vapor technique. The subject materials will be one of the following: - environmental samples: o water

6 o soil o sediment 5.1 Labwere and reagents - Mercury analyser, NIC, MA 2000 and MA laboratory scale - Pipette - Buffer solution, POCH; - Additive M and B, NIC - mercury standard solution, INORGANIC VENTURES - set of volumetric flasks 5.2 Laboratory procedure During full laboratory procedure the test sample have to be properly pretreated (grinded, homogenized, lyophilized, mineralized, filtered... depend on the case) and before final determination proper standard solutions have to be prepared and measured to adjust suitable calibration for measurement. After that the sample have to be analysed Calibration Firstly, base calibration solution have to be prepared. Use 100 ml glass volumetric flask. Take 1 ml of 1000 mg/l Hg calibration solution using pipette and dispense it to volumetric flask (Never take standard solution directly form standard solution flask! Always use separate vessel!). Fill the flask with diluent ( 0,01 M L-cysteine solution in case of MA 2000 instrument and 0,001 M L-cystein solution in case of MA 3000 instrument). Using base calibration solution prepare series of calibration samples by dispensing proper volume of solution to separate ceramic sample boats (maximum 500 ml in case of MA 2000 instrument and maximum 200 ml in case of MA 3000 instrument). If the test sample will be analyzed using Additive M or B make the addition and start the analysis in calibration mode Analysis Take pretreated test sample and weight appropriate amount to sample boats (maximum 500 mg in case of MA 2000 instrument and maximum 200 mg in case of MA 3000 instrument). If we assume that the test sample contains high organic load, add additive M or B as described in MA 2000 or MA 3000 manual. Every sample have to prepared in at least 3 repetitions. Start the analysis in sample mode.

7 Note: Additives and sample boats have to be thermal treated in 850 ºC for at least 1 h before the analysis and left to cool. 5.3 Report Student are obliged to prepare report within one week after laboratories and send it by to the lecturer in WORD file. Report have to contain: - Introduction were short description of laboratory experiment is presented - Calculation where calculation procedure with calibration curve and all data needed for performing the calculation is described. - Results where obtained results are presented in proper manner. - Summary where students have to compare obtained results with a data from the literature, avoiding poplar websites if possible, and present conscious conclusions. Using data from scientific data bases, like Elsevier's or similar, is preferred. 6. Reference [1] B. Gworek i J. Rateńska, MERCURY MIGRATION IN PATTERN AIR SOIL PLANT, Ochrona Środowiska i Zasobów Naturalnych, nr 41, pp , [2] W. Rafaj, I. Bertok, J. Cofala i W. Schöpp, Scenarios of global mercury emissions from anthropogenic sources, Atmospheric Environment, nr 79, pp , [3] Y. Hu i H. Cheng, Control of mercury emissions from stationary coal combustion sources in China: Current status and recommendations, Environmental Pollution, nr IN PRESS, pp. 1-13, [4] J. Domagalski, M. S. Majewski, C. N. Alpers, C. S. Eckley i C. A. Eagles-Smith, Comparison of mercury mass loading in streams to atmospheric deposition in watersheds ofwestern North America: Evidence for non-atmospheric mercury sources, Science of the Total Environment, nr 568, pp , [5] R. C. Cordeiro, B. Turcq, M. G. Ribeiro, L. D. Lacerda, J. Capitaneo, A. Oliveira da Silva, A. Sifeddine i P. M. Turcq, Forest fire indicators and mercury deposition in an intense land use change region in the Brazilian Amazon (Alta Floresta, MT), The Science of the Total Environment, nr 293, pp , [6] P. Burmistrz, K. Kogut, M. Marczak i J. Zwoździak, Lignites and subbituminous coals combustion in Polish power plants as a source of anthropogenic mercury emission, Fuel Processing Technology, nr 152, pp , [7] D. Saha, S. Chakravarty, D. Shome, M. R. Basariya, A. Kumari, A. K. Kundu, D. Chatterjee, J. Adhikari i D. Chatterjee, Distribution and affinity of trace elements in Samaleswari coal, Eastern India, Fuel, nr 181, pp , 2016.

8 [8] X. Qin, F. Wang, C. Deng, F. Wang i G. Yu, Seasonal variation of atmospheric particulate mercury over the East China Sea, an outflow region of anthropogenic pollutants to the open Pacific Ocean, Atmospheric Pollution Research, nr 7, pp , [9] Y. Pan, S. Tian, X. Li, Y. Sun, Y. Li, G. R. Wentworth i Y. Wang, Trace elements in particulate matter from metropolitan regions of Northern China: Sources, concentrations and size distributions, Science of the Total Environment, nr 537, pp. 9-22, [10] A. De Lucas, L. Rodriguez, J. Villasenor i F. J. Fernandez, Influence of industrial discharges on the performance and population of a biological nutrient removal process, Biochemical Engineering Journal, nr 34, pp , [11] R. Błażejewski i E. Den Boer, Co zrobić z osadami ściekowymi, Wodociągi- Kanalizacja, nr 143, [12] R. Bunsen i G. Kirchhoff, Chemical Heritage Foundation, [13] Agilent Technologies, Analytical Methods for Graphite Tube Atomizers.