Method of treating wastewater

Patent metadata

Field	Value
Publication number	US-11505480-B2
Application number	US-201816957485-A
Country	US
Kind code	B2
Filing date	Dec 27, 2018
Priority date	Dec 27, 2017
Publication date	Nov 22, 2022
Grant date	Nov 22, 2022

Abstract

A method of treating a waste liquid includes: 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 liquid property of a pH of 4 or less, and performing separation into a second treated water and gypsum; an aluminum and fluorine removal step of adding an alkali to the second treated water and performing separation into a third treated water and a precipitate containing aluminum and fluorine; and a neutralization step of adding an alkali to the third treated water and performing separation into an alkali neutralization treated water and a neutralized precipitate of a heavy metal hydroxide.

First claim

What is claimed is:

1. A method of treating a waste liquid for recovering gypsum having 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 metal 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;
an aluminum and fluorine removal step of, after removing the gypsum, adding an alkali to the second treated water to adjust a pH to 5.5 to 9.5 and produce a precipitate containing aluminum and fluorine, and performing separation into a third 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 third 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 metal 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 second treated water is adjusted to a pH of 5.5 to 7.0 to suppress precipitation of arsenic and zinc, thereby fluorine and aluminum are selectively precipitated.

3. 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.

4. 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.

Assignees

• Mitsubishi Materials Corp

Inventors

• HARAGUCHI Daisuke
• Hayashi Hiroshi

Classifications

• C01F11/46

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

• C01P2006/80

  Compositional purity · CPC title

• C02F1/70

  by reduction {(C02F1/4676 takes precedence)} · CPC title

• C02F2103/16

  from metallurgical processes, i.e. from the production, refining or treatment of metals, e.g. galvanic wastes · CPC title

• C02F2301/08

  Multistage treatments, e.g. repetition of the same process step under different conditions · CPC title