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I need some acid-washed sand to smooth out boiling in diethyl ether synthesis. I aready have pre-washed sand for general filtration purposes, but it is not labeled as acid-washed.

Unfortunately, I have not found any reliable lab manual for acid washing of sand.

I found one reference instructing to wash 30 g of sand twice with 0.05 M sulfuric acid, then four times with distilled water.

However, other references instructing to use only hydrochloric acid and de-ionized water, but have not specified how much or the concentration.

Yet another reference says that sulfuric, hydrochloric or phosphoric acid can be used interchangeably.

I don't know how seriously should I take the acid washing step (for the ether synthesis from ethanol and sulfuric acid) and how to check whether it is properly washed (pH measurement?).

I know one can just purchase acid-washed sand, but I have excess of good quality sand and the professional acid-washed one is overly expensive.

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  • $\begingroup$ Ask yourself "why would I want do acid-wash the sand for this", and you will see. $\endgroup$ – Karl Jun 25 '18 at 18:46
  • $\begingroup$ I need to remove stuff that can interfere with chemical reactions. But I don't know what acids can remove what stuff and how strong it should be, how many washes should be done etc. ... $\endgroup$ – Libor Jun 27 '18 at 2:30
  • $\begingroup$ @Karl yesterday Frankly, I don't know why the sand must be washed with acid to be used in ether synthesis. No tutorial said WHY, only that the sand must be acid washed. I can only imagine the reasons but I am not a professional chemist and even looking up that information is hard for me as I don't know where to look. $\endgroup$ – Libor Jun 27 '18 at 2:38
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    $\begingroup$ Your syntesis runs at a low pH, the idea is to wash out previously any impurities that might dissolve in an acidic reaction pot and disturb your reaction. $\endgroup$ – Karl Jun 28 '18 at 21:30
  • $\begingroup$ Ahem. Why do you want to make diethyl ether? You're aware of the fire hazards of it's high density vapour, and that it will knock you clean off your feet if you take too large a noseful? And gives terrible headache if you inhale smaller amounts over a few hours. $\endgroup$ – Karl Jun 28 '18 at 21:37
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I have just started working with sand columns and was also surprised that I could not find any valid and trustworthy guidelines or process breakdown for acid-washing sand. However, I found this paper, which may answer some of your questions. In short, acid washing (or leaching) is supposed to remove impurities (mostly iron impurities) from the sand.

From the introduction of the paper:

Iron is one of the most troublesome impurities in silica sand because it impairs the transparency of high-quality glass, e.g. for tableware, and optical glass; it impairs transmission in optical fibers; it adversely affects the production of pure silicon products, e.g. silicon metal for photovoltaic application, silicon carbide.
One of the main tasks in the purification of silica sand is to further reduce iron compounds to a required level by a highly efficient method.

In table IV in the results section you can see a comparison between several acids with regard to their efficiency in removing iron and aluminum impurities. According to the data, sulfuric and phosphoric acids should be preferred. From what I understand, however, diluted HCl solution may be preferred by some, probably due to better price and availability, but that's just an assumption.

As for the procedure itself, I heard about adding a solution of 1% HCl to the sand, stirring and letting it stand for a few hours, and then washing with distilled water and decanting ~10 times, and then drying in an oven overnight. I don't have any valid reference for it, though.

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  • $\begingroup$ Thanks. I think one problem is that ion contents depends on the sand in question so maybe we can wash the sand once with distilled water, check pH and from that estimate the amount of acid needed, use excess and multiple washes. HCl is also great as it evaporates so the traces are easily removed - but washing is still needed as we don't want to corrode the oven. $\endgroup$ – Libor Aug 3 '18 at 2:21

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