Why should antimony electrodes for pH meters be used in oilfield wastewater?
Analyze the ions in oil field wastewater: it contains a large amount of calcium, potassium, sulfur, etc., as well as unknown suspended crude oil, well washing water and other substances, which can easily cause pollution to the electrode, making the measurement requirements for wastewater particularly strict.
Reasons why glass electrodes cannot be used:
① Glass electrodes are easily contaminated by oil and scale in alkaline solutions containing oil and large amounts of suspended solids, which affects measurement accuracy.
②In environments with higher temperatures (greater than 50°C), the service life is only about one month.
③Since the glass ball used for ion exchange at the lower end of the glass electrode is only 0.2mm thick, it is very fragile and easily broken.
④Due to the large internal impedance of the glass electrode, the signal connection requirements are very high. If there is slight pollution or condensation, the signal will be instantly distorted.
⑤ Glass electrodes will crack when exposed to temperatures below 0°C.
Why use metallic antimony electrodes? What are the advantages?
The antimony electrode is a redox electrode. When the surface of metal antimony comes into contact with the solution to be measured, the surface is oxidized to form Sb2O3. The potential difference between the metal antimony and the oxide depends on the concentration of Sb2O3, and the concentration of Sb2O3 is related to the concentration of Sb2O3 in the solution. It is related to the concentration of hydrogen ions. Therefore, the pH value of the solution can be measured by measuring the potential difference between antimony and antimony trioxide. In order to ensure continuous measurement of the pH value of the solution, the surface of the metal antimony electrode in contact with the solution to be measured should be inspected at any time. Clean the dirt and oxides to keep the fresh surface of the metal antimony electrode in contact with the solution being measured, thereby forming a new thin layer of Sb2O3. Repeating this operation several times can maintain the measurement accuracy of the pH value of the solution.
The advantages of antimony electrodes are: simple manufacturing, fast response, convenient for online measurement by industrial pH meters, and can be used in solutions containing cyanide, sulfide, reducing sugar, alkaloids, and water-containing alcohol; the disadvantage is the measurement accuracy of metal antimony electrodes Not high. When the pH is between 2 and 7, its linearity is within ±0.01pH. When pH=7~12, the deviation reaches 0.4~0.5pH. The pH-mV of metal antimony electrode has different slopes in alkaline solution, that is, the linearity of the conversion coefficient is poor. The pH-mV conversion temperature coefficient is not a constant and has a non-linear relationship. Table 1-1 shows the pH-mV conversion characteristics of metal antimony electrodes in three standard buffer solutions and the relationship between this characteristic and the solution temperature (the data range Mainly listed for oil field wastewater).
The measurement error of metal antimony electrodes in alkaline solutions is large, and as the temperature increases, the measurement error increases. Research shows that this is mainly due to the fact that the potential of Sb2O3 is greatly affected by temperature, and the degree of influence is different at different temperatures. Therefore, not only the temperature needs to be compensated, but also the temperature variation coefficient needs to be compensated. Since metal antimony has a strong temperature effect and does not have a fixed theoretical formula, when using computers for data processing, we strive to reflect the true value as accurately as possible through various compensation methods. After calculation using the Nernst formula, it is combined with temperature compensation. , the pH value of the solution can be obtained relatively easily.
