Two frequency ultrasound in preparation of the samples of natural brines to determine mercury by “cold vapor” absorption

Abstract

Using of two-frequency ultrasound (US) in preparation of the samples of brines to determine Mercury by “cold vapor” absorption was studied. At this process US was used for: to destruct organic Mercury compounds, to carry out the process of Mercury extraction by ditizone in Carbon tetrachloride solution and to destruction and homohenization of Mercury extracts. It was found out by experiment that: to destruct organic Mercury compounds, also to destruct and homohenizate Mercury extracts using of simultaneous action of US of high and low frequencies is optimal. Comparison of the results, obtained with use of US of high (0.9-5.0 МHz)and low (18-100 kHz) frequencies show us that the best results were obtained with use of US of high (1.5-2.5 МHz) frequency. Change of frequency of low frequency US from 18 up to 100 kHz does not make the significant influence on the value of Mercury extraction at destruction of organic Mercury compounds. At this process intensity of low frequency US should be 1.5-2.5 W/cm2, of high frequency-2.5-3.0 W/cm2. The dependence between the degree of Mercury extraction and contain of fulvic acids (FA) in brines was determined. It was shown that for brines with contains of FA up to 10 mg/kg, the degree of Mercury extraction is 95-98%, for brines with contains of FA 10-20 mg/kg, the degree of Mercury extraction is 90-95%, and for brines with contains of FA above 20 mg/кg, the degree of Mercury extraction less than 90%. At using the standard methodic to determine Mercury in brines with contains of FA above 30 mg/kg, the degree of Mercury extraction less than 80%. At the destruction of Mercury extracts (Mercury (ІІ) dithizonates in Carbon tetrachloride) the maximal possible value of Mercury extraction was observed at simultaneous action of US of two frequencies- 18-100 kHz and intensity 1.5-2.5 W/cm2 , of frequency- 1.0-2.5 МHz and intensity 2.5-3.0 W/cm2 during 15-30 s. At Mercury extraction under US action the maximal possible value of Mercury extraction was observed at frequency- 500-800 kHz and intensity 0.3-0.5 W/cm2 during 1-3 min. The methodic to determine Mercury in natural brines with low end 0.0005 mkg/l was developed. The standard deviation of the obtained results is 0.06-0.09, according to standard methodic Sr ≥0.12. Simplification of reproducibility of the obtained results let us to control the tendency of fluctuations of Mercury content in natural brines as a result of anthropogenic pollution also as a result to using brines from various sources from various depth of the well.