What causes the product to turn red due to acidity?
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We use the organic amine method to desulfurize the flue gas from combustion; the resulting SO2 gas is used to produce acid. However, shortly after feeding SO2 gas into the acid production section of our system, the sulfuric acid turned red. Our own analysis suggests that the possible reasons are as follows: 1, the presence of iron ions causes it to turn red, but tests show that the iron ion content is very low. So, what level of iron ion content is required to make the product turn red due to acidity? 2. Some people say that it is the thiosulfate carried over from earlier processing steps that causes it to turn red. Why does thiosulfate make sulfuric acid turn red? What is the principle behind this? Could everyone please help analyze what other possible reasons there might be?
There are relevant discussions in this section: Red-colored sulfuric acid http://bbs.hcbbs.com/thread-640415-1-3.html; Light pink-colored concentrated sulfuric acid http://bbs.hcbbs.com/viewthread.php?tid=497766. Is the red color of the acid produced from smelting flue gas related to the volume of air used for baking? http://bbs.hcbbs.com/viewthread.php?tid=309806
Check the system for any parts made of phenolic fiberglass reinforced plastic (pipes, valves).
May I ask if pipes made of fiberglass-reinforced plastic can cause sulfuric acid to turn red? Why?