Determine whether sodium hexametaphosphate reacts with concentrated sulfuric acid
Thread Content
(Sodium hexametaphosphate) is a salt of sodium metaphosphate; it becomes acidic when dissolved in water. In my workshop, it is used as a softener for the circulating water in cooling tower tanks. Usually, the amount of sodium hexametaphosphate solution to be added is determined based on the phosphate content analyzed through chemical testing. However, recently it has been observed that once the pH of the circulating water is adjusted using concentrated sulfuric acid, adding sodium hexametaphosphate solution in the usual amount results in a phosphate content that exceeds the specified limits. And when no concentrated sulfuric acid is added, the amount of sodium hexametaphosphate aqueous solution used returns to normal. Note that the sodium hexametaphosphate aqueous solution here is the same solution that was prepared earlier, thereby ruling out any deviations caused by differences in preparation concentration.
Is it because the dosing points are too close to each other? Sodium hexametaphosphate tends to decompose, and concentrated sulfuric acid is a strong oxidizing agent; therefore, it’s possible that the sodium hexametaphosphate has decomposed.
Reply to 2# Ordinary life, but it’s not low-level; it’s actually high-level. Normally, the control range for inorganic phosphate in my workshop is 9–13. During regular analyses, the value was 9.7, and based on past experience with adding chemicals, about 3 cm of that chemical was needed to keep the value within the 9–13 range. However, the analysis conducted by Sinochem showed a value of 13.4. At that time, the operating conditions were stable and the water addition rate was normal; it was just the pH level that was slightly high. Concentrated sulfuric acid was used to address this issue.
In principle, the two do not react with each other; it is simply impossible for concentrated sulfuric acid to oxidize sodium metaphosphate； It is recommended that the poster check the following aspects: whether the methods used in the laboratory have been treated to resist interference. Or change the following testing methods.