Method for treating alkaline waste streams containing aluminum dissolved therein

Claim 2

IN A METHOD FOR TREATING AN ALKALINE WASTE STREAM CONTAINING ALUMINUM DISSOLVED THEREIN BY HYDROLYZING THE ALUMINUM, WHEREBY COLLOIDAL HYDROUS ALUMINUM WOULD BE OBTAINED, THE IMPROVEMENT COMPRISING CONDUCTING SAID HYDROLYSIS SUBSTANTIALLY COMPLETELY BY NEUTRALIZATION OF THE ALKALINE WASTE STREAM WITH AN ACID TO A PH OF SUBSTANTIALLY 7 IN THE PRESENCE OF A CRYSTALLINE ORTHO ALUMINUM HYDROXIDE HAVING AN AVERAGE PARTICLE DIAMETER OF ABOUT 0.5 TO ABOUT 500U IN AN AMOUNT OF ABOUT 1 TO ABOUT 5 KG PER DILOGRAM OF SAID ALUMINUM, WHEREBY NON-COLLOIDAL HYDROUS ALUMINUM IS PRECIPITATED ON SAID CRYSTALLINE ORTHO ALUMINUM HYDROXIDE, WHEREIN THE CONCENTRATION OF ALUMINUM IN SAID WASTE STREAM IS FROM 0.01 % TO THE SATURATED CONCENTRATION THEREOF.

Claim 3

The method of claim 1 wherein said crystalline ortho aluminum hydroxide added to said waste stream is one which is precipitated by cooling at a rate of about 0.05 to about 0.5*C/hr an aqueous solution of an inorganic hydroxide containing aluminum dissolved therein, under the addition of a non-crystalline hydrous aluminum oxide in such an amount that as a result of the dissolving of said hydrous aluminum oxide, the aluminum concentration of said aqueous solution becomes about 10 to about 100% excessive of the saturated concentration at the temperature at which said hydrous aluminum oxide is added.

Claim 4

The method of claim 1 wherein said crystalline ortho aluminum hydroxide added to said waste stream is one which is precipitated by cooling at a rate of about 0.05 to about 4*C/hr an aqueous solution of an inorganic hydroxide containing aluminum dissolved therein, under the addition of (a) a non-crystalline hydrous aluminum oxide in such an amount that as a result of the dissolving of said non-crystalline hydrous aluminum oxide, the aluminum concentration of said aqueous solution becomes about 10 to about 100% super-saturated concentration at the temperature at which said non-crystalline hydrous aluminum oxide is added, and (b) about 50 to 500% by weight, based on ortho aluminum hydroxide to be separated from said inorganic hydroxide aqueous solution by cooling, of crystalline aluminum oxide having an average particle diameter of about 0.5 to 500.

Claim 5

The method of claim 3 wherein as said non-crystalline hydrous aluminum oxide and said crystalline aluminum oxide to be added to said inorganic hydroxide aqueous solution, there is used a composite product formed of non-crystalline hydrous aluminum oxide and crystalline aluminum oxide, said composite being obtained as a precipitate when a solution containing aluminum dissolved therein is hydrolyzed in the presence of about 1 to about 5 Kg, per kilogram of the aluminum present in said solution, of a crystalline aluminum oxide having an average particle diameter of about 0.5 to about 500.

Claim 6

The method of claim 4 wherein said composite product is pelletized to an average particle size of about 1 to about 15 mm by revolution in the presence of a flocculating agent prior to adding it into said inorganic hydroxide aqueous solution.

Claim 7

The method of claim 5 wherein said waste stream is a waste aqueous solution of an inorganic hydroxide having aluminum dissolved therein, and said acid is an aqueous solution of at least one member selected from the group consisting of sulfuric acid, hydrochloric acid, nitric aciD, phosphoric acid and oxalic acid.

Claim 8

The method of claim 6 wherein said waste stream is a waste aqueous solution of sodium hydroxide containing aluminum dissolved therein.

Claim 9

The method of claim 7 wherein said crystalline ortho aluminum hydroxide has an average particle diameter of about 1 to about 100 Mu , and its amount present in the waste stream is about 2 to about 3 Kg per kilogram of the aluminum present in the waste stream.

Claim 10

The method of claim 1 wherein said waste stream containing aluminum dissolved therein is a waste aqueous solution of a water-soluble aluminum compound.

Claim 11

The method of claim 1 wherein said waste stream containing aluminum dissolved therein is one which is obtained by dissolving aluminum is an alkaline liquid.

Claim 12

The method of claim 10 wherein said alkaline liquid is an aqueous solution of an inorganic hydroxide.

Claim 13

The method of claim 11 wherein said inorganic hydroxide is sodium hydroxide.

Claim 14

The method of claim 1 wherein said waste stream containing aluminum dissolved therein is one which is obtained by dissolving an aluminum compound in an alkaline liquid.

Claim 15

The method of claim 13 wherein said alkaline liquid is an aqueous solution of an inorganic hydroxide.

Claim 16

The method of claim 14 wherein said inorganic hydroxide is sodium hydroxide.