Regarding the Fenton oxidation issue

Ferrous sulfate acts as a catalyst, accelerating the reaction, and this is generally determined through laboratory tests.

This post was last edited by zhaolijun on 2015-10-27 at 20:06. There really is no fixed ratio, as the printing and dyeing industry often uses large amounts of reducing agents, such as glucose or sodium thiosulfate, etc. And these reducing agents have a significant difference in the ratio of ferrous ions to hydrogen peroxide

The specific ratio needs to be determined through testing; different water qualities require different ratios, and the removal efficiency also varies accordingly.

Is there a difference between molar ratios and mass ratios? The proportions are determined through pilot experiments, and they can be converted into one another. You can use any parameter as a basis for determining the proportions

I’ve read in some materials that a molar ratio of 30% hydrogen peroxide to ferrous ion of 10:1 is used

Next, I would like to explain it from the perspective of the free radical mechanism. The oxidizing agent is a hydroxyl radical, derived from the decomposition of hydrogen peroxide, and the initiator is ferrous ion. That is, hydrogen peroxide is decomposed under the action of ferrous ions to produce hydroxyl radicals; these hydroxyl radicals attack organic substances, causing the organic molecule to lose electrons or undergo fission to form organic radical fragments. These fragments then react further with hydroxyl radicals, breaking down into smaller molecules, or they combine with other radicals to become stable, thereby terminating the chain reaction. Thus, there is a problem: to fully oxidize mineralized organic pollutants, a large amount of hydroxyl radicals are required, which means that an adequate supply of hydrogen peroxide is necessary. Simply having enough light-induced H2O2 is not sufficient; in order to convert it into hydroxyl radicals with higher oxidizing power, an adequate amount of the catalyst, ferrous ions, is also needed. This raises a problem: when hydrogen peroxide decomposes, not only hydroxyl radicals are produced, but also other radicals with weaker oxidizing properties. The more hydrogen peroxide there is, the more of these weaker radicals will be generated. On the other hand, an excess of ferrous ions leads to a large number of hydroxyl radicals. However, there is an issue related to the reaction rate – specifically, the need for a balance between the rate at which radicals are generated and the rate at which they react with pollutants. If too many radicals are produced too quickly, they don’t have time to react fully with organic substances before they collide and annihilate each other or with other radicals of weaker oxidizing power ； This requires researchers to make judgments based on the properties of the polluted substrate; for example, with substances that are prone to oxidation, the reaction proceeds slowly, and if there is an excess of ferrous ions, most of the hydroxyl radicals will be wasted ； For oxidizable substances, you will find that as the amount of hydrogen peroxide used increases, the COD removal rate also increases. Such substances can be treated using the Fenton process; it’s just a matter of determining the appropriate dosage. So what about those organics that are difficult to degrade—those that react slowly with free radicals? At this point, it is necessary to work on accelerating the reaction rate between free radicals and the substrate, in other words, to improve the efficiency of using hydrogen peroxide and shorten the reaction time. It should be noted that ferrous ions primarily act as catalysts in the generation of free radicals, while what we need to focus on is catalyzing the reaction rate between hydroxyl free radicals and the substrate. I cannot go into further detail regarding the specific methods; I hope that all this information can provide some inspiration for researchers working in this field.

There is no fixed ratio for this; it is generally determined through experimentation!

The ratio can only be determined based on the actual operating conditions on site

The information states that a molar ratio of hydrogen peroxide to ferrous ion of 30% at 10:1 is a bit high