Why can we not use zinc for extracting copper from a solution containing $\ce{Cu^2+}$ ions even though it is a better reducing agent than $\ce{Fe}$? I am studying metallurgy and I cannot understand why zinc cannot be used.
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$\begingroup$ Just saying it, but many metallurgical process and reagents have an economic aspect to the choices made. $\endgroup$– user79161Commented May 24, 2019 at 8:52
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2 Answers
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We can.
But I see few reasons why it is not used:
- Iron is much cheaper than zinc.
- There can be remaining residue of iron/zinc, coated by copper, or just being excessive. While copper can be melted away and iron stays, zinc would melt together with copper, causing unwanted impurity (unless wanted for making brass alloys)
- If we remove copper for environmental concerns, then by using zinc, we would just replace one evil by another. While both metals are essential for life in small amounts, both are toxic in larger amounts. ( So does iron, but at much higher level)
- Removing dissolved iron from waste is easier than removing zinc.
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Do you know that the American Chemical Society has listed zinc as an "endangered" element? According to them, within hundred years the supply of zinc will be scarce. The best reducing agent in the world is the cathode of an electrolytic cell. Copper(II) is quite easy to reduce by electricity. Why waste an endangered element?
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$\begingroup$ In fact, the similar is done during electrolytic copper purification on the industrial level. $\endgroup$– PoutnikCommented May 25, 2019 at 7:41
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$\begingroup$ Time to properly process primary batteries and iron/steel with zinc anti-corrosive coating. $\endgroup$– PoutnikCommented May 25, 2019 at 14:09