Caustic solution having controlled dissolved aluminum content

Claim 1

A method of greatly extending the useful life of a caustic solution for etching aluminum by controlling the dissolved aluminum content of the caustic solution comprising the steps of: (a) providing a tank of etching solution containing sodium hydroxide, the balance comprising water; (b) etching aluminum in the etch solution thereby dissolving aluminum therein; (c) introducing a portion of the etch solution containing the dissolved aluminum to a reactor for purposes of lowering the aluminum content thereof; (d) treating the etch solution in the reactor with aluminum hydroxide to lower the dissolved aluminum content thereof by causing said dissolved aluminum to precipitate as aluminum hydroxide, aluminum hydroxide being maintained in the reactor in the range of 30 to 600 gms/liter of solution, the treatment capable of causing the dissolved aluminum to precipitate from the etch solution at a rate substantially commensurate with the rate of introducing aluminum during etching and capable of being effective when the solution has a mean residence time of less than 5 hours in the reactor; (e) removing a portion of the etch solution and aluminum hydroxide from the reactor on a substantially continuous basis, the aluminum hydroxide being separated from the etch solution to an extent which prevents precipitation of dissolved aluminum in the etching tank, the solution being removed from the reactor at a rate substantially commensurate with the rate at which it is introduced in step (c); and (f) recirculating the portion of solution to the etch tank thereby controlling the dissolved aluminum content of the etching solution.

Claim 2

A method of greatly extending the useful life of a caustic solution for etching aluminum by controlling the dissolved aluminum content of the caustic solution comprising the steps of: (a) providing a tank of etching solution containing sodium hydroxide, the balance comprising water; (b) etching aluminum in the etch solution thereby dissolving aluminum therein; (c) introducing a portion of the etch solution containing the dissolved aluminum to a reactor for purposes of lowering the aluminum content thereof; (d) treating the etch solution in the reactor with aluminum hydroxide to lower the dissolved aluminum content thereof by causing said dissolved aluminum to precipitate as aluminum hydroxide, aluminum hydroxide being maintained in the reactor in the range of 30 to 600 gms/liter of solution, the treatment capable of causing the dissolved aluminum to precipitate from the etch solution at a rate substantially commensurate with the rate of introducing aluminum during etching and capable of being effective when the solution has a mean residence time of less than 5 hours in the reactor; (e) removing a portion of the etch solution and aluminum hydroxide from the reactor on a substantially continuous basis, the aluminum hydroxide being separated from the etch solution to an extent which prevents precipitation of dissolved aluminum in the etching tank, the solution being removed from the reactor at a rate substantially commensurate with the rate at which it is introduced in step (c); and (f) recirculating the portion of solution to the etch tank thereby controlling the dissolved aluminum content of the etching solution.

Claim 13

A method of greatly extending the useful life of a caustic solution for etching aluminum by controlling the dissolved aluminum content of the caustic solution, the method comprising the steps of: (a) providing a tank of etching solution containing sodium hydroxide, the balance comprising water, the solution maintained at a temperature in the range of 110° to 145° F.; (b) etching aluminum in the solution at a rate not greater than 1.0 grams per liter of solution per hour and maintaining a dissolved aluminum content in the range of 0.32 to 0.40 times the total NaOH concentration in the caustic etch solution; (c) introducing a portion of the etch solution containing the dissolved aluminum to a reactor for purposes of lowering the aluminum content thereof; (d) treating the etch solution in the reactor with aluminum hydroxide to lower the dissolved aluminum content thereof by causing said dissolved aluminum to precipitate as aluminum hydroxide, the solution being maintained at a temperature in the range of 125° to 160° F. and aluminum hydroxide being maintained in the reactor at a concentration in the range of 200 to 500 grams per liter of solution, the treatment capable of causing the dissolved aluminum to precipitate from the etch solution at a rate substantially commensurate with the rate of introducing aluminum during etching; (e) removing a portion of the etch solution and aluminum hydroxide from the reactor on a substantially continuous basis, aluminum hydroxide being separated from the etch solution by filtering to an extent which prevents precipitation of dissolved aluminum in the etching tank, the solution being removed from the reactor at a rate substantially commensurate with the rate at which it is introduced in step (c); and (f) recirculating the portion of solution to the etch tank thereby controlling the dissolved aluminum content of the etching solution.

Claim 14

A method of greatly extending the useful life of a caustic solution for etching aluminum by controlling the dissolved aluminum content of the caustic solution, the method comprising the steps of: (a) providing a tank of etching solution containing sodium hydroxide, the balance comprising water, the solution maintained at a temperature in the range of 110° to 145° F.; (b) etching aluminum in the solution at a rate not greater than 1.0 grams per liter of solution per hour and maintaining a dissolved aluminum content in the range of 0.32 to 0.40 times the total NaOH concentration in the caustic etch solution; (c) introducing a portion of the etch solution containing the dissolved aluminum to a reactor for purposes of lowering the aluminum content thereof; (d) treating the etch solution in the reactor with aluminum hydroxide to lower the dissolved aluminum content thereof by causing said dissolved aluminum to precipitate as aluminum hydroxide, the solution being maintained at a temperature in the range of 125° to 160° F. and aluminum hydroxide being maintained in the reactor at a concentration in the range of 200 to 500 grams per liter of solution, the treatment capable of causing the dissolved aluminum to precipitate from the etch solution at a rate substantially commensurate with the rate of introducing aluminum during etching; (e) removing a portion of the etch solution and aluminum hydroxide from the reactor on a substantially continuous basis, aluminum hydroxide being separated from the etch solution by filtering to an extent which prevents precipitation of dissolved aluminum in the etching tank, the solution being removed from the reactor at a rate substantially commensurate with the rate at which it is introduced in step (c); and (f) recirculating the portion of solution to the etch tank thereby controlling the dissolved aluminum content of the etching solution.