Given some plant ash containing silica and sulfur, we need to find a way to extract the silica and sulfur using only resources available to a primitive person stuck on an island, with access to a forest, lake, and coal vein. (This is part 2 of my Primitive Technology series. Part 1)

I've imagined a way to extract the silica, but I am not sure if it would work. Can I get this reaction confirmed possible?

$$ \begin{align} \ce{SiO2(ash) + NaOH &->[Heat] Na2SiO3 + H2O}\tag{1}\\ \ce{Na2SiO3 + 2 HCl &->[Heat] 2 NaCl + SiO2 + H2O}\tag{2} \end{align} $$

I am unsure whether the sulfur content could be feasibly extracted in this scenario.


  1. Some plant parts, such as rice husk, have high silica content (over 90%).

  2. Coal and sea water typically have substantial sulfur content. Sulfur is a by-product of coke production.

  • 2
    $\begingroup$ For making sodium sulfate, heat gypsum hot enough to drive off all the waters of hydration and sulfur trioxide, leaving behind CaO. Of course, the sulfur trioxide plus water yield sulfuric acid, which can then neutralize NaOH to give sodium sulfate. This would be hard to do, for a number of reasons. Still, compared to the discovery of phosphorus, it does not look so bad. $\endgroup$ – Ed V Sep 6 at 17:59
  • $\begingroup$ Thanks for your reply about using gypsum. I guess maybe it's not feasible to extract the small amount of sulfur contained in plant ash. $\endgroup$ – R Dev Sep 8 at 18:55

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