Study On The Detection Methods Of Sulfate Ions

Sulfuric acid and sulfate salts have been widely used in many fields including chemical engineering, metallurgy, electrolysis, printing and dyeing, papermaking, ore dressing, and pesticides. In recent years, it was found that in oilfield water, sulfate ions would not only lead to the indirect corrosion of oilfield pipelines, but also cause the blockage of ground pores and oilfield pipelines resulting from the precipitation between sulfate ions and calcium ions, magnesium ions, barium ions and strontium ions. Therefore, much attention has been paid to the determination of the content of sulfate ions in waste water from oilfields.Up to now, there are many methods for the determination of sulfate ions in water including weighting method, titration method, spectrophotometry, ion chromatography, turbidimetry, inductively coupled plasma emission spectrometry and so on. In this thesis, three different methods, namely weighting method, EDTA titration method and barium chromate spectrophotometry, were selected for detection of sulfate ions in water according to the real conditions in the testing center of Yanchang Oilfield Group.Through a series of comparative studies, we found that although weighting method was a classical method for detection of sulfate ions, which has the characteristics applicable over a wide concentration range and extremely high accuracy. But this method is time-consuming and not suitable for a laboratory with large amounts of detection task. EDTA titration method for detecting the content of sulfate ions in various samples, possesses the features of simple operation, easy to grasp, high accuracy, easy to observe the precipitation of barium sulfate using indicator, and easy observation of the end point. Barium chromate spectrophotometry, which obeys the Beer’s law in a certain scope, is an indirect method for determination of sulfate ions. Although a high accuracy could be obtained by this method, its operation procedure is complicated, especially for the production of standard curve, and also it has a high rigorous requirements for inspectors, which method is only applied to some scientific research units. As a whole, prior to selecting a method for detection of sulfate ions, it is necessary to take preliminary experiments for rough analysis of the sulfate content in samples, in order to choose a suitable detection method for sulfate ion content.