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(‘Green’) chelant recommendations at pH ~3.5 ?
Are there any chelators (preferably readily biodegradable) that would still have good functionality for Fe3+/Ca2+/Mg2+ at low pH (~3.5)?
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7 Replies
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Not a chemist by as I understand any organic acid will react with metal ions? I mean coffee machine descales are usually citric or lactic acid. Also Citric acid is usually mentioned as weak chelator.
There is an option of Sodium phytate, not sure if it can be used at low pH, but lotioncrafter says it works under pH < 6: https://lotioncrafter.com/products/sodium-phytate
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thanks for your response. I have seen that is typical for many descaling products, but my understanding is that the lower the pH the more each of these acids exists in protonated form, making them less efficient as sequestrants. I think phytic acid sounds like a good option, just wanted to see if there were any others or additional things to consider.
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You could consider also MGDA or GLDA (although, at the pH you require, MGDA might be more appropiate).
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MGDA might be better than GLDA but at such low pH the only option seems to be phytic acid.
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@Abdullah Keep in mind that at low pH, cations (specially small ones) compete for binding sites with H+. That’s why you see that behavior shown in the graph. That shouldn’t be different if you had Phytic acid (I found a paper mentioning that no significant binding from Phytic acid to Ca2+ was found at pH lower than 5. The binding of group d metal ions (like Fe2+ and Cu2+) has the advantage of both relative cation size and back donation, which make complexes more stable.
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According to this chart i said phytic acid is stable at lower pH.
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I wouldn’t rely on supplier’s data. You might want to check this: https://pubmed.ncbi.nlm.nih.gov/3711890/
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