A quick way to obtain ferrous sulfate from fertilizer

A quick way to obtain ferrous sulfate from fertilizer

The penultimate step on the path to obtaining a noble metal from radio components is the reduction of the latter from the corresponding chloride. Iron(II) sulfate is excellent for these purposes. Consider the equation for this reaction:
A quick way to obtain ferrous sulfate from fertilizer

HAuCl4 - hydrogen tetrachloroaurate (III) - a compound that is formed when gold is dissolved in aqua regia. We will not go deeper into this process for now, as it deserves a separate article.
So, sulfate (hereinafter iron(II) sulfate is meant) is one of the cheap and easily available reducing agents. In stores it can be found under the name “iron sulfate”, it is a fertilizer. But this is not a pure substance, the proportion of sulfate in it is about 50%, the rest is impurities. And before we can restore the gold, we need to purify our sulfate.

Will need


For this you will need:
  • Iron sulfate (sold in stores like “everything for the garden”; I bought a kilogram so that I would have enough for my head);
  • Sulfuric acid solution, also known as acid electrolyte for batteries (in car dealerships);
  • Alcohol, I used 95%;
  • Chemical or disposable tableware (cups, stirring spoons).

A quick way to obtain ferrous sulfate from fertilizer

We obtain iron sulfate from fertilizer


I use a glass jar to prepare the solution. Inside there is 500 ml of hot water, maybe a little less.
A quick way to obtain ferrous sulfate from fertilizer

Now measure out about half a glass of fertilizer:
A quick way to obtain ferrous sulfate from fertilizer

As you can see, the substance is yellow-brown in color; such dirty “sulfate” can only be used for its intended purpose - to spray vegetation. We have other goals.
Pour it into the jar:
A quick way to obtain ferrous sulfate from fertilizer

The solution turned an unpleasant brown color. The coloring occurred due to the reaction of the fertilizer with water:
A quick way to obtain ferrous sulfate from fertilizer

Iron in sulfate is oxidized to trivalent, and iron(III) hydroxide precipitates, which is actually the reason for its color.
In order to obtain the sulfate we are interested in from the resulting compounds, it is necessary to acidify the solution with sulfuric acid. Add in small portions until the solution brightens.
A quick way to obtain ferrous sulfate from fertilizer

In this case, the following reactions occur:
A quick way to obtain ferrous sulfate from fertilizer

The hydroxide reacts with the acid to form iron(III) sulfate (ion exchange reaction). It in turn reacts with atomic hydrogen, which is formed during the dissociation of sulfuric acid. The last reaction is redox.
Now the solution contains exactly the sulfate we need, but the solution itself is still cloudy. Let it sit and filter it, I used a chemical filter.
A quick way to obtain ferrous sulfate from fertilizer

A quick way to obtain ferrous sulfate from fertilizer

Insoluble impurities remained at the bottom of the jar:
A quick way to obtain ferrous sulfate from fertilizer

We rinse it and pour the filtered solution into it. It is much lighter and cleaner than the original.
A quick way to obtain ferrous sulfate from fertilizer

Ethyl alcohol displaces salts of dibasic acids from their solutions. We will use this property to obtain solid sulfate. We add alcohol to the solution, I poured 200 ml, which is equal in volume to a little more than half of the original volume of fertilizer.
Crystals of our sulfate appeared at the bottom.
A quick way to obtain ferrous sulfate from fertilizer

I left the solution for two days so that all the sulfate had time to precipitate.
A quick way to obtain ferrous sulfate from fertilizer

You can initially add more alcohol to make this process faster.
Drain the liquid, using tapping on the bottom and gentle heating, separate the sulfate from the jar and pour it onto a paper towel to dry.
A quick way to obtain ferrous sulfate from fertilizer

After a few hours, pour the sulfate into a glass jar, label the substance, and in this form it can be stored for a long time.
A quick way to obtain ferrous sulfate from fertilizer

Since crystalline hydrates precipitated, the formula of the substance is as in the picture. But this does not prevent us from using it for our own purposes, dissolving it in water anyway.

Conclusion


Safety precautions and compliance with the rules for handling acids are a given. Under no circumstances should we forget about them.
Clean substances to everyone!
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Comments (1)
  1. Guest Alexander
    #1 Guest Alexander Guests 10 June 2020 19:28
    3
    Where do redox reactions come from? Where does atomic hydrogen come from? How is iron (3) reduced to iron (2)?