Separation and determination of dimethylarsenate in natural waters

A simple and efficient method for separation and determination of dimethylarsenate DMAs(V) was developed in this work. Two resins, a strong base anion exchange (SBAE) resin and iron-oxide coated hybrid (HY) resin were tested. By simple adjusting pH value of water at 7.00, DMAs(V) passed through the HY column without any changes, while all other arsenic species [inorganic arsenic and monomethylarsonate, MMAs(V)] were quantitatively bonded on HY resin. The resin capacity was calculated according to the breakthrough points in a fixed bed flow system. At pH 7.00 the HY resins bonded more than 4150 μg g-1 of As(III), 3500 μg g-1 of As(V) and 1500 μg g1 of MMAs(V). Arsenic adsorption behavior in the presence of impurities showed tolerance with the respect to potential interference of anions commonly found in natural water. DMAs(V) was determined in the effluent by ICP-MS. The detection limit was 0.03 μg L?1 and relative standard deviation (RSD) was between 1.1?7.5 %. Proposed method was established performing standard procedures: with external standard, certified reference material and the standard addition method

Uklanjanje arsena iz vode adsorpcijom na nekonvencionalnim materijalima

This paper deals with arsenic removal from water by adsorption with unconventional materials: natural materials (zeolite, bentonite, sepiolite, limonite, pyrolusite), waste materials (waste iron slag, waste sand filter) and modified materials (neutralized waste iron slag, iron(III)-hydroxide coated sand and activated carbon). Under the same conditions are investigated commercial sorbents to compare results. Arsenic removal by adsorption with unconventional materials is investigated in the batch reactor. The best results in batch reactor are obtained with waste materials. Waste iron slag and waste filter sand exhibited equilibrium sorption capacities of 50 μg/g and 30 μg/g, respectively, which is nearly equal to values obtained for the commercial sorbents. Due to the high content of CaO waste iron slag increases significantly water pH (pH=11). In order to minimize its deteriorating impact on the initial water quality, the waste iron slag was neutralized. The new, modified waste iron slag exhibited the highest sorption capacity, 55.U ovom radu su prikazani rezultati istraživanja efikasnosti uklanjanja arsena iz vode sorpcijom na nekonvencionalnim materijalima: prirodnim (zeolit, bentonit, sepiolit, limonit, piroluzit), otpadnim (otpadna šljaka, otpadni filtarski pesak) i modifikovanim (modifikovana otpadna šljaka, kvarcni pesak i aktivni ugalj impregnisani gvožđe(III)-hidroksidom). Pod istim uslovima paralelno su ispitivani komercijalni sorbenti radi poređenja rezultata. Uklanjanje arsena iz vode sorpcijom je ispitivana u šaržnom sistemu Najbolji rezultati u šaržnom sistemu dobijeni su sa otpadnim materijalima: za otpadnu šljaku i 30 μg/g za otpadni filtarski pesak (za Co=0,5 mg/L), što je u nivou vrednosti koje su dobijene za komercijalne sorbente za uklanjanje arsena. Zbog visokog sadržaja CaO, otpadna šljaka značajno povećava pH vrednost vode (pH= 11). Neutralizacijom otpadne šljake dobijen je nov materijal, modifikovana otpadna šljaka, većeg sorpcionog kapaciteta: 55

Analytical methods for arsenic speciation analysis

Arsenic exists in the form of various chemical species differing in their physicochemical behaviour, toxicity, bioavailability and biotransformation. The determination of arsenic species is an important issue for environmental, clinical and food chemistry. However, differentiation of these species is a quite complex analytical task. Numerous speciation procedures have been studied that include electrochemical, chromatographic, spectrometric and hyphenated techniques. This review presents the relevant research in the field of arsenic speciation analysis with novel applications and significant advances. Stability of arsenic species and each of the analytical steps (sample collection, storage, preservation, extraction) of the arsenic speciation methods is particularly evaluated. Analytical validation and performance of these Methods are also reviewed

Spatial variations in the distribution of trace ionic impurities in the water-steam cycle in a thermal power plant based on a multivariate statistical approach

In this study, a multivariate statistical approach was used to identify the key variables responsible for process water quality in a power plant. The ion species that could cause corrosion in one of the major thermal power plants (TPP) in Serbia were monitored. A suppressed ion chromatographic (IC) method for the determination of the target anions and cations at trace levels was applied. In addition, some metals important for corrosion, i.e., copper and iron, were also analysed by the graphite furnace atomic absorption spectrophotometric (GFAAS) method. The control parameters, i.e., pH, dissolved oxygen and silica, were measured on-line. The analysis of a series of representative samples from the TPP Nikola Tesla, collected in different plant operation modes, was performed. Every day laboratory and on-line analysis provides a large number of data in relation to the quality of water in the water-steam cycle (WSC) which should be evaluated and processed. The goal of this investigation was to apply multivariate statistical techniques and choose the most applicable technique for this case. Factor analysis (FA), especially principal component analysis (PCA) and cluster analysis (CA) were investigated. These methods were applied for the evaluation of the spatial/temporal variations of process water and for the estimation of 13 quality parameters which were monitored at 11 locations in the WSC in different working conditions during a twelve month period. It was concluded that PCA was the most useful method for identifying functional relations between the elements. After data reduction, four main factors controlling the variability were identified. Hierarchical cluster analysis (HCA) was applied for sample differentiation according to the sample location and working mode of the TPP. On the basis of this research, the new design of an optimal monitoring strategy for future analysis was proposed with a reduced number of measured parameters and with reduced frequency of their measurements

A New Approach in Regression Analysis for Modeling Adsorption Isotherms

Numerous regression approaches to isotherm parameters estimation appear in the literature. The real insight into the proper modeling pattern can be achieved only by testing methods on a very big number of cases. Experimentally, it cannot be done in a reasonable time, so the Monte Carlo simulation method was applied. The objective of this paper is to introduce and compare numerical approaches that involve different levels of knowledge about the noise structure of the analytical method used for initial and equilibrium concentration determination. Six levels of homoscedastic noise and five types of heteroscedastic noise precision models were considered. Performance of the methods was statistically evaluated based on median percentage error and mean absolute relative error in parameter estimates. The present study showed a clear distinction between two cases. When equilibrium experiments are performed only once, for the homoscedastic case, the winning error function is ordinary least squares, while for the case of heteroscedastic noise the use of orthogonal distance regression or Margart's percent standard deviation is suggested. It was found that in case when experiments are repeated three times the simple method of weighted least squares performed as well as more complicated orthogonal distance regression method

Arsenic removal from water using low-cost adsorbents: A comparative study

Inorganic arsenic removal from water using low-cost adsorbents is presented in this paper. Selective removal of As(III) and As(V) from water was performed with natural materials (zeolite, bentonite, sepiolite, pyrolusite and limonite) and industrial by-products (waste filter sand as a water treatment residual and blast furnace slag from steel production); all inexpensive and locally available. Kinetic and equilibrium studies were realized using batch system techniques under conditions that are likely to occur in real water treatment systems. The natural zeolite and the industrial by-products were found to be good and inexpensive sorbents for arsenic while bentonite and sepiolite clays showed little affinity towards arsenic. The highest maximum sorption capacities were obtained for natural zeolite, 4.07 mg As(V) g-1, and waste iron slag, 4.04 mg As(V) g-1

Inverse gas chromatography of chromia. Part II. Finite surface coverage

The interactions of n-hexane, benzene, chloroform, and tetrahydrofuran with dried (amorphous) chromia (I) and chromia heated at 1073 K (crystalline) (II), both obtained from a colloidal dispersion, and a commercially available chromia (III) were Studied by inverse gas chromatography (IGC) under Finite surface coverage conditions. The isotherms, in the temperature range 383-423 K, were used to estimate the surface area, the adsorption energy distribution, the isosteric heat of adsorption, and the spreading pressure on the surfaces of the solids. The uniformly reduced adsorption ability of the heated chromia was attributed to the dehydroxylation of the surface at the higher temperatures. Both solids showed an increased affinity toward chloroform molecules, as a result of strong acid-base interaction

Development of ion chromatography methods for the determination of trace anions in ultra pure water from power plants

A suppressed ion chromatography (IC) technique, using a carbonate/hydrogen carbonate or a hydroxide eluent, has been evaluated as a monitoring tool for the detection of major anions (F-, Cl-, NO3-, PO43- and SO42-) in ultra pure water and condensed steam from thermal power plants. An electrical conductivity detector with an anion-exchange column (IonPac AS14), an auto self-regenerating suppressor (ASRS), and an isocratic high-pressure pump system were used for the detection of low concentrations of inorganic anions. It was shown that the Suppressed IC technique provides a suitable means for preventing possible damage to generating equipment in power plants. The detection limits of the method for the anions of interest were LT 0.3 mu g/L

Investigation of different extraction procedures for the determination of major and trace elements in coal by ICP-AES and ion chromatography

This paper presents the extraction of major and trace elements from a coal sample, in deionized water, by using three different extraction techniques. Rotary mixing and ultrasonic extraction were examined for different extraction times, while the microwave-assisted extraction was performed at different temperatures. Metal concentrations (Na, K, Ca, Mg, Al, Fe, Mn, Be, Cd, Co, Cr, Hg, As, Ni, Se, Sb and Pb) in solution were determined employing inductively coupled plasma atomic emission spectrometry; whereas the results obtained for Na, K, Ca and Mg were compared employing ion chromatography. Comparing the rotary-and ultrasonic-assisted extractions, it was shown that the former technique was more efficient for the determination of Fe, Na and Pb, whereas the latter one proved more efficient for the determination of Co and Cr ions. Microwave-assisted extraction was shown to be the most efficient method for all the tested elements in coal. In addition, sequential extraction of the elements was realized using microwave digestion. The results of the sequential extraction experiments indicated associations of investigated elements with a mineral phase and organic matrix. Sequential extraction provided information on possible leaching of As, Cd, Co, Cr, Ni, Pb, Fe and Mn under environmental conditions

Boron removal by anion exchangers impregnated with citric and tartaric acids

The separation of boron compounds, boric acid and borax, with anion-exchange resins, before and after impregnation with citric and tartaric acids, has been studied. Three different commercially available anion exchangers were selected for this study. The results indicate that ion-exchanging on the examined resins is not quite effective for the removal of boron from boric acid and borax water solution. The presence of citric or tartaric acid is essential for the enhancement of the sorption capacity above that observed for the untreated resins. Sorption data show that citric acid is a more effective impregnant than tartaric acid