The impact of high iron content in raw salt on the production of caustic soda using ion exchange membranes
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This post was last edited by sunjl1981 on 2013-1-6 20:47. Dear sea friends, let’s discuss the impact of high iron content in raw salt on the production of caustic soda using various ion exchange membranes -
These are the effects of various ion pairs on production; I hope this is useful to you. Calcium and magnesium levels should be ≤20 PPb; exceeding this level causes hydroxide precipitates to form on the membrane. Nickel ≤10PPb; excess levels cause hydroxide precipitation on the membrane. Strontium ≤0.1PPm; excess levels cause precipitation on the membrane. Sodium sulfate ≤7g/l; if the level exceeds this value, it diffuses through the membrane, resulting in precipitation on the membrane. Iodine forms iodate (IO3) at the anode and reacts completely with NaOH to produce Na3H2IO6; it is insoluble in strong alkaline conditions. At concentrations of 0.2–1 PPM, excessive amounts of it cause precipitation on the membrane under alkaline conditions. Aluminum/SiO2: <100 ppb; total aluminum content (soluble and precipitated forms): <5 ppm SiO2. Consequences of exceeding these limits: Under acidic conditions, aluminum will precipitate on the membrane. Barium ≤0.5PPm; excessive levels cause precipitation on the membrane. NaCO3 10—15g/l; excessive levels have the effect of damaging ion exchange resins. Fe ≤100ppb. (Variations may exist among different manufacturers)"
upstairs, only the indicators were mentioned without any explanation given. A high iron content has a significant impact on the lifespan of ion exchange membranes. Calcium and magnesium ions also play a role; iron ions can combine with OH ions on the membrane to form precipitates that accumulate there, resulting in an increase in resistance and voltage, which can eventually damage the membrane. Additionally, this affects the quality of NaOH – in ion exchange membrane caustic soda, the iron content is strictly regulated.
At the same time, iron ions affect the sulfonic acid layer and carboxylic acid layer of the ion membrane, primarily through exchange reactions that influence selective permeability.
It will form Fe(OH)3 precipitates with OH, which attach to the ion exchange membrane and cause the voltage to rise; as a result, the permeability of the ion exchange membrane decreases, reducing the current efficiency.