Recovery of sodium hydroxide and aluminum hydroxide from etching waste
AssigneeThe Graver Company
InventorThomas A. Davis
Life of this patent
Estimating the term…
Abstract
A method for the recovery and recycling of sodium hydroxide from the waste solution of aluminum etching operations. The method utilizes a dialysis membrane column or stack to initially remove sodium hydroxide from the waste solution and return it to the etch tank base solution sufficiently concentrated to carry on the basic etching operation. The method permits the recovery of salable quantities of aluminum hydroxide.
Claims23
A method of recovering sodium hydroxide from an etch tank waste solution containing dissolved aluminum comprising:
- directing a stream of the waste solution into a diffusion dialyzer containing permeable membrane means that is permeable to sodium hydroxide and substantially less permeable to dissolved aluminum on one side of the membrane means;
- simultaneously directing a stream of water into the dialyzer on the opposite side of the membrane means whereby sodium hydroxide migrates through said membrane means from the waste solution stream into the water stream;
- and
- recycling the sodium hydroxide-containing stream back into the etch tank.
Apparatus for recovering sodium hydroxide and aluminum hydroxide from an etch tank waste solution comprising:
- diffusion dialysis means having channels on opposite sides of permeable membrane means that is permeable to sodium hydroxide and substantially less permeable to dissolved aluminum for receiving respectively a stream of the waste solution and a stream of water;
- pumping means for directing said two streams in opposite directions through the dialysis means on opposite sides of said membrane means;
- and
- settling vessel means for receiving the waste solution exiting from the diffusion dialysis means and collecting aluminum hydroxide precipitating therein.
A method of recovering sodium hydroxide and aluminum hydroxide from a sodium aluminate solution comprising:
- directing a stream of sodium aluminate solution into a diffusion dialyzer containing permeable membrane means that is permeable to sodium hydroxide and substantially less permeable to sodium aluminate on one side of the membrane means;
- simultaneously directing a stream of water into the dialyzer on the opposite side of the membrane means whereby sodium hydroxide migrates through said membrane means from the sodium aluminate solution stream into the water stream;
- directing the water stream exiting from the dialyzer into a sodium hydroxide storage vessel;
- and
- directing the sodium aluminate stream exiting the dialyzer into settling vessel means to precipitate aluminum hydroxide therefrom.
Dependencies are inferred from the claim text.