Determination of magnesium in zinc sulfate solution
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This post was last edited by Yang Qing on 2020-12-11 09:55. Practical issue: In the production process of wet-process zinc oxide (zinc oxide is obtained by adding sodium carbonate to a zinc sulfate solution to form basic zinc carbonate, which is then calcined), there are requirements regarding the magnesium content in the zinc sulfate solution; too high a magnesium level results in insufficient purity of the zinc oxide. According to the process requirements, the magnesium ion concentration in the solution should not exceed 500 mg/L. Current status: The magnesium content before magnesium removal is between 1000–5000 mg/L. It contains 90–120 g/L of zinc; magnesium is removed by precipitation with sodium fluoride, so sodium ions are also present in the solution. Current equipment available: spectrophotometer, atomic absorption spectrometer (acetylene flame), and titration analysis equipment. The detection does not require very high precision; an error of 10% is acceptable. For a solution like this, what is the reliability of using flame atomic absorption directly? Is it necessary to use spiking to verify it? Titrimetric analysis? It seems the content is too low. I’d like to hear if any fellow sailors have any good suggestions
This is essentially close to constant-level analysis; it cannot be analyzed directly using atomic absorption spectroscopy. It is estimated that a dilution of nearly 1000 times is required, which will certainly affect the accuracy. It is recommended to use volumetric analysis; complexometric titration is a more reliable method. For the titration conditions of zinc and magnesium, it is possible to find acidity ranges that do not affect each other as well as appropriate indicators. If ion chromatography is available, it allows for better analysis of alkali metal impurities, as the dilution ratio is not as high as that in atomic absorption.
This post was last edited by Yang Qing on 2020-12-11 at 10:22. Magnesium has high sensitivity, which makes it seem unreliable. Let’s try titrimetric analysis; experiments show that it is possible to start at pH 5.6 using xylene orange until a bright yellow color is reached, after which chloride buffer can be added for complexometric titration with chromotropic acid T. It seems that the zinc content is high, which results in a smaller volume in subsequent titrations; however, when high detection precision isn’t required, it might be better than atomic absorption. Additionally, if calcium ions are present, they can be shielded using oxalic acid or oxalates; the people in the laboratory are conducting experiments on this… Thank you, Teacher Q, for your guidance! We should recommend purchasing ion chromatography
The interference caused by calcium can be considered as part of magnesium; it’s convenient to determine the total amount of calcium and magnesium using complexometric titration, by treating them as one type of impurity and calculating everything based on magnesium levels. That should work.
From the perspective of process control, it is entirely possible to handle it in this way. Thank you!