Method of treating wastewater

Patent metadata

Field	Value
Publication number	US-11479490-B2
Application number	US-201816957464-A
Country	US
Kind code	B2
Filing date	Dec 27, 2018
Priority date	Dec 27, 2017
Publication date	Oct 25, 2022
Grant date	Oct 25, 2022

Abstract

A method of treating a waste liquid: an aluminum dissolution step of dissolving aluminum in an acidic waste liquid and performing separation into a first treated water and a reduced heavy metal precipitate; a gypsum recovery step of adding a calcium compound to the first treated water at a pH of 4 or less, and performing separation into a second treated water and gypsum; a heavy metal coprecipitation step of adding a ferric compound to the second treated water and performing separation into a third treated water and a heavy metal coprecipitate; an aluminum and fluorine removal step of adding an alkali to the third treated water and performing separation into a fourth treated water and a precipitate containing aluminum and fluorine; and a neutralization step of adding an alkali to the fourth treated water and performing separation into an alkali neutralization treated water and a neutralized heavy metal hydroxide.

First claim

What is claimed is:

1. A method of treating a waste liquid for recovering gypsum having a small amount of fluorine from an acidic waste liquid containing fluorine and a heavy metal and removing the heavy metal, the method comprising:
an aluminum dissolution step of dissolving aluminum in the acidic waste liquid to stably dissolve fluorine in the liquid as a fluoroaluminate ion and produce a reduced heavy metal precipitate and performing separation into a first treated water and the reduced heavy metal precipitate;
a gypsum recovery step of, after removing the reduced heavy metal precipitate, adding a calcium compound to the first treated water at a liquid property of a pH of 4 or less to produce gypsum, and performing separation into a second treated water and the gypsum;
a heavy metal coprecipitation step of, after removing the gypsum, adding a ferric compound to the second treated water to produce a ferric hydroxide precipitate, causing the heavy metal in the liquid to be coprecipitated with the precipitate, and performing separation into a third treated water and a heavy metal coprecipitate;
an aluminum and fluorine removal step of, after removing the heavy metal coprecipitate, adding an alkali to the third treated water to adjust a pH to 5.5 to 9.5 and produce a precipitate containing aluminum and fluorine while suppressing an amount of the precipitate, and performing separation into a fourth treated water and the precipitate containing aluminum and fluorine; and
a neutralization step of, after removing the precipitate containing aluminum and fluorine, further adding an alkali to the fourth treated water to adjust the pH to 9.5 to 11.8 and produce a neutralized precipitate of a heavy metal hydroxide, and performing separation into an alkali neutralization treated water and the neutralized precipitate of a heavy metal hydroxide, wherein
a reduction reaction occurs by dissolving the aluminum in the acidic waste liquid in the aluminum dissolution step, and an oxidation-reduction potential in the reduction reaction is +400 mV or less.

2. The method of treating a waste liquid according to claim 1 ,
wherein, in the aluminum and fluorine removal step, a liquid property of the third treated water is adjusted to a pH of 5.5 to 7.0 to suppress the amount of the precipitate and suppress precipitation of arsenic and zinc, thereby fluorine and aluminum are precipitated.

3. The method of treating a waste liquid according to claim 1 ,
wherein the acidic waste liquid containing fluorine and a heavy metal is wastewater from a non-ferrous metal smelter.

4. The method of treating a waste liquid according to claim 2 ,
wherein the acidic waste liquid containing fluorine and a heavy metal is wastewater from a non-ferrous metal smelter.

5. The method of treating a waste liquid according to claim 1 , wherein an amount of aluminum dissolved in the acidic waste liquid with respect to fluorine is 0.4 mol or more in the aluminum dissolution step.

6. The method of treating a waste liquid according to claim 2 , wherein an amount of aluminum dissolved in the acidic waste liquid with respect to fluorine is 0.4 mol or more in the aluminum dissolution step.

7. The method of treating a waste liquid according to claim 3 , wherein an amount of aluminum dissolved in the acidic waste liquid with respect to fluorine is 0.4 mol or more in the aluminum dissolution step.

8. The method of treating a waste liquid according to claim 4 , wherein an amount of aluminum dissolved in the acidic waste liquid with respect to fluorine is 0.4 mol or more in the aluminum dissolution step.

Assignees

• Mitsubishi Materials Corp

Inventors

• HARAGUCHI Daisuke
• Hayashi Hiroshi

Classifications

• C02F1/5227

  Processes for facilitating the dissolution of solid flocculants in water · CPC title

• C01F11/22

  Fluorides · CPC title

• C01G49/02

  Oxides; Hydroxides {(C01G49/0018 takes precedence)} · CPC title

• C01F7/50

  Fluorides · CPC title

• C01F11/46

  Sulfates (dehydration of gypsum {for the production of calcium sulfate cements} C04B11/02) · CPC title