Peatlands can ... The objective of this work was to investigate the interaction of arsenic species ... Keywords: Arsenic, biosorption, raw peat, experiments ... level of natural scattering of these elements, which is associated with surface ... Peat has a lake genesis, according to its botanical composition belongs to the fuscum-.
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THE BIOSORPTION OF ARSENIC FROM AQUEOUS SOLUTION USING RAW PEAT: PRELIMINARY RESULTS Dr. O.S. Naymushina1 Prof. Dr. O.L. Gaskova1, 2 1 2
Sobolev Institute of Geology and Mineralogy SB RAS, Russia Novosibirsk State University, Russia
ABSTRACT Removal of potentially harmful As compounds by adsorption onto biosorbents is a cost-effective alternative to the conventional treatment methods. Peatlands can accumulate arsenic originating from both natural and anthropogenic sources [1-3]. Wetland soils and sediments are subject to frequent changes in redox conditions, driven by fluctuations in the water table and shifts in biological activity. Under oxic conditions, natural organic matter (NOM) promotes arsenic release from metal-(hydr)oxides, thereby enhancing arsenic mobility [4]. Under strongly reducing conditions organic matter triggers the formation of arsenic-sequestering sulphides, leading to a reduction in arsenic mobility. Furthermore, the sorption of arsenic to NOM is increasingly thought to suppress arsenic mobility, but the binding mechanisms have remained elusive. The objective of this work was to investigate the interaction of arsenic species (As(III)) with raw peat, collected in Tomsk region, South Siberia. The effect of the initial As concentration, pH, contact time, was studied in experiments. Peat samples were analyzed before and after adsorption processes using atomic absorption spectrometry. The results showed that only 27% of As(III) precipitated on peat with selected experiment parameters, while, for example, for Cu(II), the result is much better and is 97%. All of this suggests that the experimental work should be continued with changing of the experimental conditions and improving the properties of peat by the modification method. Keywords: Arsenic, biosorption, raw peat, experiments INTRODUCTION Migration flows of heavy metals, due to human activities, already now far exceed the level of natural scattering of these elements, which is associated with surface geochemical processes. In the world over the last century, as a result of industrial activity, a huge amount of waste has accumulated. Located on the surface, it is constantly exposed to the oxidizing effects of atmospheric gases and drainage water. In this regard, it is extremely important to develop methods for improving the environmental situation and counteracting technogenic sources of danger. One of the methods of protecting the environment from heavy metal contamination is the use of geochemical barriers. The essence of the method is the transfer of polluting components into sedentary forms. It is possible to use both existing natural materials and purposeful creation of modified ones.
17th International Multidisciplinary Scientific GeoConference SGEM 2017
Among the requirements for geochemical barriers, the most important are the high sorption capacity with respect to a wide range of metals, the ability to quick and firmly binding of metal ions, the possibility of utilization, ecological purity, cheapness and accessibility. The use of peat as a material for binding and long-term retention of heavy metals allows, on the one hand, to guarantee the reliability and duration of conservation, on the other hand, to reduce production costs, since they are cheap to obtain. According to the latest abstract data, peat is an effective sorbent of arsenic and heavy metals [5-8], and large reserves of peat in Western Siberia, its unique composition and properties make it a promising source for obtaining efficient biosorbents. METHODS OF THE RESEARCH AND EXPERIMENTAL PART Sampling In 2016, expeditionary work was carried out in the Tomsk region (south of Western Siberia) with the sampling of peat and bog water. The solid samples were sampled, using a cylindrical sampler, and stored hermetically in polyethylene bags, which were placed in a dark cool place. The temperature, concentration of dissolved oxygen, pH, and Eh of the water samples were measured in situ using Multiparameter Edge HI2020-01, the content of rapidly changing components was measured using a field chemical laboratory. The surface water sample was filtered through a 0.45 nm membrane filter in order to determine element concentrations in solution and suspension. Laboratory research In laboratory conditions, a series of experiments were conducted to study the immobilizing capacity of raw peat. For this purpose, peat of a small weakly drained swamp Dark (Tomsk region, south of Western Siberia) was chosen. A complex of physicochemical methods was used to study the deposits. For studying the chemistry of peat the atomic absorption spectroscopy with flame and electrothermal atomization and the X-ray fluorescence analysis using synchrotron radiation were used. The concentration of the elements in bog water was determined at the Tomsk Polytechnic University by ionic chromatography for anions and by titrimetric analysis for cations. Trace elements concentrations in water were determined in acidified samples by ICP AS at the Analytical Centre of the Institute of Geology and Mineralogy of Siberian Branch of Russian Academy of Sciences. In the first series of experiments, water leaching of the elements from the peat was carried out in order to evaluate their yield to the solution from the sorbent material during the adsorption experiments. In the second series of experiments, a study was made of the sorption of arsenic on raw peat. The sample averaged by the quartering method was dried and finely powdered. For the experiment, solutions containing 10 mg/L of As were prepared. The experiments were carried out at a temperature of 20 ° C with agitation on an electric stirrer for 2 hours. Centrifugation was used to separate the solution from the solid phase. The solutions were then filtered and the concentration of the elements was determined by atomic absorption spectroscopy with flame and
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electrothermal atomization. The pH values were measured using Multiparameter pH Meter Edge HI2020-01. The experiment was performed in triplicate. RESULTS AND DISCUSSION Peat has a lake genesis, according to its botanical composition belongs to the fuscumpeat of the upper type. The peat deposits with the deepness of 3 to 6 m are composed of weakly decomposed (4%), low ash (1.9%), acidic (pH 3.5 - 4.0) peat. Down the section, ash content is increased to 8.2%; acidity is reduced to 4.7-5.3. The content of organic matter is 39.5%. According to the fractional composition of the organic matter of peat, humic and fulvic acids predominate, the content of which reaches 75.5 and 7.1%, respectively. Elemental composition of peat and chemical composition of bog water are presented in Table. 1. The content of potentially toxic elements in peat is low, except for iron (which improves sorption capacity). At the same time the bog water is ultra-fresh, the TDS value does not exceed 10 mg/L, acidic (pH 3.7), and rich in natural organic matter (NOM), the content of which is 94.8 mg /L. Fulvic acids form organomineral complexes, and therefore bog water is characterized by elevated concentrations of iron. The total Fe content in bog water is 1.4 mg/L. Due to the similar chemical properties, Mn, like Fe, is very common in bog water. Thus, the concentration of Mn in bog water reaches 31 μg/L. At extremely low TDS values (only 10 mg/L), some trace components have been found in the water of the bog in relatively high concentrations, in particular: aluminum (0.55 mg/L) and metals: Zn, Cu, and Ni, which actively form complex compounds with organic acids, which determines their greater ability to concentrate in such water types [9]. Table 1 shows the selective values of the elements in the water of the bog (ICP MS) and in the peat (AAS). Table 1. Chemical composition of bog water and peat pH
Fe
Al
Ca2+
Mg2+
K+
Na+
% Peat
Zn
Co
Ni
Cu
As
14.0
0.5
5.8
2.7
10.0
186,4
0,4
10,9
20,3
1,8
mg/kg
4.3 0.78
Bog water
Mn
0.14
0.40
0.05
0.03
0.03
11.0 μg/L
mg/L 3.7 1.4
0.5
3.0
0.6
0.6
0.4
31.1
The results show the rather low sorption properties of the sorbent under study with respect to arsenic, for a selected duration of the experiment and a water/solid ratio of 25, only 27% of As(III) is precipitated on peat (Table 2). At the same time, under identical experimental conditions, for Cu(II) the result is much better even at relatively low final pH 3.43 - this is 97%. It should be noted that after sorption of a large amount of Cu(II), much more of Fe, Al, Ca, Mg is transferred to the solution than in other experiments. Since the peat of upper type is a polyelectrolyte, the main reaction centers are hydroxyl and carboxyl groups, which determine the sorption capacity of the preparation [10]. Thus, all this may indicate an ion-exchange mechanism for the reactions of sorption of metals on peat.
17th International Multidisciplinary Scientific GeoConference SGEM 2017
Table 2. Results of the experiment on sorption of arsenic on peat, mg/L Experimental conditions
pHinit
pHeq As
2 g of peat + 50 ml H2O
4.25
Cu
Fe
Al
Са
Mn
Zn
3.86 < 1 0.25 1.2 1.2
0.12
0.10 3.6 1.5
2 g of peat + 50 ml As 4.25
3.59 8.1 0.055 4.0 4.0
0.65
0.18 11.2 7.6
2 g of peat + 50 ml As 4.25
3.76 7.9 0.047 2.2 2.2
0.38
0.087 7.1 3.9
2 g of peat + 50 ml As 4.25
3.7
0.41
0.14 7.2 5.0
2 g of peat + 50 ml Cu 2.99
3.43
