# Is it possible to produce sulfuric acid at large scale by oxidizing and hydrating pyrite?

I was reading The Knowledge by Lewis Dartnell, which is a book about recreating our technology from scratch should we experience a civilization-ending apocalypse. The author thinks that acquiring vanadium catalyst for contact process is too difficult, so his recommendation to produce sulfuric acid is to: (1) bake pyrite, (2) react the sulfur dioxide produced with chlorine gas (electrolyzed from brine), using activated carbon as the catalyst, (3) then react the resulting sulfuryl chloride with water to produce sulfuric acid.

I don't know how hard acquiring vanadium is, but I think it will be easier to replicate the same process happening in acid mine drainage: $$\ce{2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4}$$

The iron(II) sulfate can then be baked to produce sulfur trioxide, which can also be processed into sulfuric acid.

I think this method would have been simpler. Am I correct? Is there another simple method of producing sulfuric acid?

• Well, you want to produce sulfuric acid which is reasonably highly concentrated. Because as a dilute acid, it´s not so very useful. – Karl Jun 2 '20 at 20:42
• Distillation shouldn't be too hard, no? Sulfuric acid also has a much higher boiling point than water, so boiling should be good enough in a pinch. – Ray Arifin Jun 2 '20 at 21:03
• Have you ever tried to distill even pure water? I guarantee you sulfuric acid is far, far worse. Plus I bet it´s an azeotrope. And definitely badly corrosive. ;-) – Karl Jun 2 '20 at 21:11
• A post-apocalyptic world should be littered with broken stainless-steel tools. A lot of the items in my toolbox are embossed with names that spell xxvanadyy. – Karl Jun 2 '20 at 21:16
• @Karl Thankfully, I have never needed to distill sulfuric acid, but I'm aware of the danger. Will the method I proposed make a very dilute acid, or at least more dilute than what the book recommended? Also, what's xxvanadyy? Google gave nothing on that. – Ray Arifin Jun 2 '20 at 21:17

Per a source, there is an iron bacteria path acting on FeS2 to create sulfuric acid:

Thiobacillus spp. are participants of active oxidative corrosion. They oxidize a range of sulfur compounds to sulfuric acid, and the acid released from the cells may attack alloys.

My experience, however, suggests that the easiest way to produce H2SO4 is by the action of a concentrated solution of Oxalic acid (used in commercial products) on magnesium sulfate (FeSO4 may also work, but likely leads to an iron impurity).

Per a source (old Wikipedia commentary) to quote:

Relationship to oxalic acid

The dissociation of protons from oxalic acid proceeds in a stepwise manner as for other polyprotic acids. Loss of a single proton results in the monovalent hydrogenoxalate anion HC2O4−. A salt with this anion is sometimes called an acid oxalate, monobasic oxalate, or hydrogen oxalate."

As such expected reactions:

$$\ce{MgSO4 + 2 H2C2O4 -> Mg(HC2O4)2 + H2SO4}$$

$$\ce{MgSO4 + Mg(HC2O4)2 -> 2 MgC2O4 (s) + H2SO4}$$

Be careful, the created Sulfuric acid could be very strong depending on the level of hydration.

Warning: Attempting (in the presence of H2C2O4) to produce fuming sulfuric by boiling down the solution can lead to a spontaneous ejection of the acid (reported in an old thread of mine).