Ionometric determination of chlorine and fluorine in oil and gas-bearing wastewater

Abstract

Production and processing of oil and gas are associated with the formation of a huge bulk of wastewater of complex composition disposed in different ways after thorough treatment. Environmental control of the composition and degree of purification of oil and gas-bearing wastewater requires using effective methods for determining various pollutants, including chloride and fluoride. The object of the study was a sample of wastewater from the largest gas field «Mustakillikning 25 yilligi» in the Surkhandarya region of the Republic of Uzbekistan. It is shown that the sample is salty (dry residue is 34.1 – 31.7 g/dm3) and has a neutral reaction. The method of atomic emission analysis of water revealed high concentrations of potassium, sodium and sulfur, a significant amount of calcium and magnesium, and a significantly small number of other elements contained in water. Study of various methods of sample preparation for ionometric measurements of chloride ion showed that a significant proportion of chlorine is bound with organic components of water. It is shown that boiling (~100°C) or fusing at 800 – 850°C with NaOH eliminates the interfering effect of accompanying components (sulfur, iodine and organic matter) on the chloride determination. The results obtained provide quantitative determination of the total content of chlorine in water both in the form of a free chloride ion and in a bound state, probably in the composition of organochlorine compounds. The presence of fluorine in the organic part of the sample has not been revealed. The possibility of using a single sample preparation (boiling or fusing) for the determination of both chloride and fluoride ions has been shown. The interfering effect of the accompanying elements upon fluorine determination was masked by a buffer solution which regulated the total ionic strength. The developed procedures are easy to use, selective, and cost-effective. The correctness and accuracy of the developed techniques were evaluated and proved using a method of varying sample volume.