Method for preparing polyferric sulfate, flocculant, and wastewater treatment method

Abstract

This invention discloses a method for preparing polyferric sulfate, a flocculant, and a wastewater treatment method. The preparation method includes: mixing an acidic process waste liquid containing sulfuric acid and hydrogen peroxide with ferrous sulfate powder to form a reaction mixture; wherein the hydrogen peroxide in the acidic process waste liquid is used as an oxidant to react with ferrous sulfate; and heating the reaction mixture to a reaction temperature, and selectively adding additional hydrogen peroxide in an incremental manner to the reaction mixture to carry out a polymerization reaction, thereby forming a liquid composition containing polyferric sulfate having a target pH value.

Claims

1. A method for preparing polyferric sulfate, comprising: mixing an acidic process waste liquid containing sulfuric acid and hydrogen peroxide with ferrous sulfate powder to form a reaction mixture; wherein, The acidic process waste liquid is a piranha acid waste liquid from a semiconductor manufacturing process, and the hydrogen peroxide in the acidic process waste liquid is used as an oxidant to react with ferrous sulfate; and the reaction mixture is heated to the reaction temperature, and additional hydrogen peroxide is selectively added to the reaction mixture in an incremental manner to carry out a polymerization reaction to form a liquid composition containing polyferric sulfate; wherein the liquid composition has a target pH value.

2. The method for preparing polyferric sulfate as claimed in claim 1, wherein the target pH value is between -0.3 and 0.

25.

3. The method for preparing polyferric sulfate as described in claim 2, wherein the target pH value is between -0.2 and 0.

12.

4. The method for preparing polyferric sulfate as described in claim 3, wherein the target pH value is between -0.2 and 0.

08.

5. The method for preparing polyferric sulfate as claimed in any one of claims 1 to 4, wherein the liquid composition is used as a flocculant, and in the liquid composition, the total iron content of the polyferric sulfate is greater than 11% by weight, and the ferrous iron content is less than 0.1% by weight.

6. The method for preparing polyferric sulfate as claimed in claim 5, wherein the acidic process waste liquid comprises 1% to 10% by weight hydrogen peroxide and 10% to 80% by weight sulfuric acid, wherein the ferrous sulfate is ferrous sulfate heptahydrate, and the weight ratio of the acidic process waste liquid to the ferrous sulfate powder is between 10~60:80~160; wherein, The reaction temperature is between 50°C and 70°C.

7. The method for preparing polyferric sulfate as claimed in claim 6, wherein the hydrogen peroxide is an aqueous solution containing 20% ​​to 50% by weight of hydrogen peroxide, and the weight ratio between the hydrogen peroxide and the ferrous sulfate powder is between 30 and 70: 80 and 160.

8. A flocculant, characterized in that the flocculant is formed by the preparation method according to any one of claims 1 to 7 above, wherein, The polyferric sulfate has a total iron content greater than 11% by weight and a ferrous iron content less than 0.1% by weight.

9. A wastewater treatment method comprising: adding a flocculant as described in claim 8 to wastewater containing organic pollutants to cause the wastewater to flocculate and reduce its chemical oxygen demand.

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