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The only crater in Basaltic rock formed by meteorite impact in India ranking the third biggest in the world is the ‘Lonar Crater’. The Lonar crater [1,2,3] ( Latitude: 190 59I N and Longitude: 760 31I E ), in the Buldana District, Maharashtra, India is a oval shaped lake occupied by saline water located in Deccan trap. It has an average diameter of 1830 m and a depth of about 150 m. Maximum depth of brine [4] in lake is about 5.5 m. The lake silt is up to 30 m thick [4]. Crater floor [5] is covered by unconsolidated sediments and is almost flat, ranging in elevation above sea level from about 450 m near the base of the inner wall to about 468 m. The maximum elevation of the crater rim is more than 600m but is normally about 590 m. This shallow lake is only fed by rains and number of springs such as Dhar, Sitanahani , Ramgaya etc. Based on geological studies [6], it is postulated that the lake originated as a meteorite impact crater around 50-60 thousand years ago. The lake water [7] is alkaline, having pH about 10.5 and 10 times saltier than drinking water [8]. Alkalinity of the lake is mainly due to the higher percentage of Sodium Carbonate and hence was used previously as a source of washing soda [8, 9].

Ghosh and Bhaduri (2003), in their fairly detailed geochemical study of six target rock basalt and six impact melt rock samples, showed that the latter were somewhat enriched in the abundances of Al, Fe, K, CO, and Sr, depleted in those of Ti, Mg, Cr and Sc, compared to the basalt compositions [10]. Kearsley et al.(2004) reported the presence of some small (<10 um) iron-nickel particles in vesicles of Lonar  impact melts [11]. Shiloh Osae and co-workers (2005) have attempted [12] to provide detailed field Petrographic descriptions of varieties of impact melt rocks, breccia’s, and spherules found in and around Lonar  Crater and present largest data of major and trace element compositions of target basalts and impact breccia’s and spherules. Recently in June 2020 the color of lake water turned from green to pink and scientist reveal that pink color was due to Haloarchaea microbes present in the salty water [13]. In the view of importance of research the conservation of lake is mandatory. In past years culpability like unsuitable plantation inside the peripheral area of crater, maintenance and renovation of temple in the periphery of lake. Such human intervention is responsible for lake water pollution and strict monitory system needed to find out its cause and maintained the pollution free lake area [14,15]. Environmental Forensic study is yet required to know more about the contamination of Lonar Lake and its periphery by human activity so that further contamination can be prevented [16]. Proper action to be taken by consistent monitoring to avoid contamination [17,18].

We developed new type of glow discharge system for the purpose of doing the electrochemical analysis [19, 20, and 21]. The new system requires very less amount of electrolytic solution which acts as a one electrode and tungsten bar of length 40 mm and diameter 3 mm acts as a another electrode fused in glass capillary tube. The solid liquid junction is formed between upper surface of solution and tip of tungsten electrode when current is passed through the junction. A plasma film is generated along the interfaces between solid and liquid. The plasma pressure is very near to the atmospheric pressure [22]. We study the V-I characteristics of the plasma generated between tungsten electrode and the liquid which is to be investigated.

For the present study, a visit to the Lonar Lake was arranged and collected samples of lake water (brine), spring water in the lake, tube well water of nearby outside area of lake and sediment samples inside the lake (0 to 10 cm below the water at the bottom of the lake). Lake water, spring water and tube-well water samples having pH 10.27, 8.5 and 6.59 respectively.

The experimental arrangement for dc glow discharge used as shown in figure 1 and carried out voltage-current characteristics of samples collected from Lonar Lake such as lake water (brine),spring water, tube-well water and sediment. A 50 ml of these sample independently taken in this beaker. Using water as the anode and cathode the voltage-current characteristics and total intensity emitted during glow discharge were observed and recorded.

Dried sediment sample crushed into powder and observed the most interesting feature as the 40% magnetic material in the sediment. The powdered sample of sediment dissolved in water and concentrated HCl (1:1) and made 50 ml solution. Using this ready solution discharge parameter like V-I characteristics and total intensity measurement of dc-glow discharge was carried out. The quantitative chemical analysis of the sediment sample was also done. The magnetic elements Fe³⁺ and Ni were detected and confirmed by the chemical analysis. The Fe and Ni were separated by chemical analysis and made respective solutions. The dc glow discharge of these solutions were observed by using the experimental arrangement as shown in figure 1. Further Fe and Ni estimated gravimetrically, the solid material of Iron oxide and Nickel-dimethyleglyoxime complex respectively weighed in crucible as per routine gravimetric method. 

The electrolytic process leading to a luminescent glow at the interface of tungsten electrode as a cathode and sample of brine (Lake water) of Lonar Lake as anode which results  plasma of orange color but when Lake water used as cathode results the plasma of yellow color. This is best depicted by the current characteristic curve shown in the figure 2.

Thus orange and yellow color of plasma in the dc glow discharge indicates the spectral lines of metals and alkaline metals like Na and Ca contained in Lonar Lake water (brine). The intensity of orange glow is very low as compared to yellow glow.

For the comparative study of the chemical contents of the water inside and outside the lake, we have used the water samples of spring (Ramgaya) which is the source of water for the lake, and water from the tube-well in the vicinity of the lake. The voltage-current characteristics of spring water is obtained. The nature of the characteristic curve are displayed in figures 3(a) but in this case the negative resistance part is less than that exhibited by lake water. During glow discharge when spring water is used as anode the color of the plasma is found to be orange  for initial excitation and then the  color changes to yellow when current passed through the interface is increased. These colors of the glow indicate the presence of Ca and Na. But when spring water is used as cathode the color of the plasma is found as a combination of faint blue and violet with low intensity. These colors of the glow indicates the presence of the elements like Fe and Ti. These colors of the glow were matched with individual standard glow of the elements using the glow discharge system.

The voltage-current characteristic curve of the tube-well water is shown in figure 3(b) Negative resistance part is small and intensity emitted by the discharge remains relatively low. During the glow discharge when tube-well water is used as anode the color of the plasma was the combination of orange and yellow. This observation indicates the presence of Ca and Na.

 

Electrochemical behavior of sediment sample of Lonar Lake:

Dried sample of sediment spread on the plane paper and using bar magnet it was found that 2 gm sample of sediment contains about 40% magnetic material. This may be the interesting characteristic of the sediment. Solution of the sediment in the lake (sediment + water + HCl) was made. The variation of discharge current and intensity as a function of applied voltage during dc glow discharge with the solution as the anode and cathode using the same electrolytic cell as described before was carried out and shown in the figure 4 (a) and 4 (b)  respectively. In figure 4(a) nature of the curve remains standard as similar to that of standard electrolytic solution with negative resistance part. During the electrolytic process the glow discharge phenomenon occurs. When the dc voltage is applied across the electrolytic cell the current remains proportional up to 20 V and between 20 to 30 V the voltmeter and ammeter pointer fluctuates widely. At 35 V the orange intermittent sparking obtained with decreasing current. But when voltage increase from 35 to 45 orange glow disappear and faint sky glow obtained with decrease in current. At 50 V color of the plasma changes from sky to lavender. Above 50 V the current changes its sign i.e. it goes on increasing and plasma color gradually changes to violet. For further applied voltage discharge current increases continuously and intensity of violet color increases monotonously. On the same way when electrolytic cell used with cathode as the solution of the sediment the variation is shown in the figure 4 (b). In this case at high voltage during discharge only violet colored plasma obtained.

DC glow discharge with the solution of sediment as the anode and cathode

Thus during excitations in the interface of solid and liquid (sediment solution) standard electrolytic glow shows the orange plasma corresponds to Ca, faint sky corresponds to Fe, lavender corresponds to Ni  and violet plasma corresponds to Ti. From these results of electrolytic process of glow discharge of sediment solution it could be concluded that excitation of different plasmas obtained at atmospheric pressure in air and indicates the presence of Ca, Fe, Ti and Ni in sediment of lake water.

Total intensities of the spectral lines of the elements contained in the sediment solution were investigated as a function of discharge current is presented in the figure 4. It was found that intensity of the spectral lines depends on discharge current. Figure 5 shows the intensity of the glow discharge of the sediment sample as a function of wavelength. The experimental observation clearly shows intensity of spectral lines of the elements accumulate in sediment of lake water which could be clearly observed. The intensity emitted by Ti remains maximum and other spectral lines could be observed as Ca, Fe and Ni lines.

The separation of the Fe and Ni from the solution of sediment were done by chemical analysis. Using these solutions of Ni and Fe we observed the dc glow discharge. The observed dc-glow discharge of Ni and Fe were found similar to that of standard electrolytic solution of them. This confirmed the presence of Fe and Ni in the Sediment sample    

Geo-chemical behavior of sediment sample         

On the support of electrochemical analysis the geo-chemical analysis of the sediment were also carried out. Under this study semi-micro analysis of the sample were done. By this analysis confirmed the presence of Fe, Ni and Ti. Using the solution of the sediment Iron and Nickel estimated gravimetrically. The solid material of iron-oxide and nickel-dimethyl-glyoxime complex respectively weighed in silica crucible as per routine gravimetric method. By this method we obtain 19.46% pure iron and 0.6842 % nickel.  

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