Water softening process

• US 3,976,569 A
• Filed: 02/25/1975
• Issued: 08/24/1976
• Est. Priority Date: 02/25/1975
• Status: Expired due to Term

• Current Assignee: The United States of America as represented by the United States Energy Research and Development Administration
• Original Assignee: The United States of America as represented by the United States Energy Research and Development Administration
• Inventors: Thomas, David G., Sheppard, John D.
• Primary Examiner(s): Hart, Charles N.
• Assistant Examiner(s): Hruskoci, Peter A.
• Application Number:
  US05/553,048
• Time in Patent Office: 546 Days
• Field of Search: 210/20, 210/23 H, 210/23 F, 210/42, 210/46, 210/47, 210/51-53, 210/59, 210/60, 210/75, 210/193, 210/321 R
• US Class Current: 210/724
• CPC Class Codes: B01D 69/14 Dynamic membranes
• CPC Class Codes: C02F 5/02 Softening water by precipitation of the hardness

Abstract

This invention involves an improved process for softening hard water which comprises selectively precipitaing CaCO₃ to form a thin layer thereof, increasing the pH of said water to precipitate magnesium as magnesium hydroxide and then filtering the resultant slurry through said layer. The CaCO₃ layer serves as a thin permeable layer which has particularly useful application in cross-flow filtration applications.

Claims

1. An improved process for softening hard water feed which comprises selectively precipitating CaCO₃ from said feed at a pH sufficient to deposit a permeable filtration layer consisting essentially of CaCO₃ on a porous substrate, while flowing said feed tangentially past said substrate increasing the pH of said feed to precipitate magnesium as magnesium hydroxide and then flowing the thus treated water tangentially past the deposited CaCO₃ at a velocity and pressure sufficient to effect transpiration of the water through said CaCO₃ and substrate to produce a transpired clarified water product.

2. An improved process for softening hard water feed which comprises adjusting said feed to a pH in the range 8 to 10 and a temperature in the range of 15°

to 35°

C while flowing said water tangentially past a surface of a tubular porous substrate to cause deposition of a permeable filtration layer consisting essentially of CaCO₃ on said surface, adjusting said feed to a pH in the range of 10.8 to 11.5 which effects precipitation of magnesium as Mg(OH)₂ and then flowing the thus treated water tangentially past said CaCO₃ layer at a velocity and pressure sufficient to collect a transpired clarified water product from an opposite surface of said substrate.

3. The method according to claim 2 in which the substrate is a woven fabric.

4. The method according to claim 2 in which the velocity of the feed water flowing past said permeable layer of CaCO₃ is from 3 to 35 ft/sec and is at a pressure of from 15 to 70 psig.