Method of removing calcium from water containing calcium hydrogen carbonate in high concentration

• US 6,905,606 B1
• Filed: 01/28/2000
• Issued: 06/14/2005
• Est. Priority Date: 02/01/1999
• Status: Expired due to Fees

• Current Assignee: Stella Chemifa Kabushiki Kaisha
• Original Assignee: Stella Chemifa Kabushiki Kaisha
• Inventors: Miyashita, Masayuki, Fukudome, Toshirou, Kikuyama, Hirohisa
• Primary Examiner(s): Hruskoci, Peter A.
• Application Number:
  US09/890,470
• Time in Patent Office: 1,964 Days
• Field of Search: 210/702, 210/712, 210/713, 210/714, 210/724, 210/726, 210/915
• US Class Current: 210/724
• CPC Class Codes: C02F 1/5245 using basic salts, e.g. of aluminium and iron
• CPC Class Codes: C02F 1/66 by neutralisation; pH adjustment for degassing C02F1/20; using ion-exchange C02F1/42; for flocculation or precipitation of suspended impurities C02F1/52; for removing dissolved compounds C02F1/58
• CPC Class Codes: C02F 2101/14 Fluorine or fluorine-containing compounds
• CPC Class Codes: C02F 2103/346 from semiconductor processing, e.g. waste water from polishing of wafers
• CPC Class Codes: Y10S 210/915 Fluorine containing

Abstract

A method for removing calcium from water containing a high concentration of calcium bicarbonate, permitting a reduction of the calcium bicarbonate equivalent to 200-500 ppm calcium to the level in accordance with the water quality standards for industrial use, not by a method using a large amount of heat and power as heating and deairing, but by a simple chemical treatment. Calcium hydroxide is added to waste water containing a high concentration of calcium in a form of calcium bicarbonate for making them react with each other, and removing calcium by fixing it to calcium bicarbonate.

Claims

1. A method for removing calcium from waste water containing a concentration of calcium bicarbonate, the concentration of calcium bicarbonate being at least about 200 ppm, wherein the waste water is waste water defluorinated by adding calcium carbonate to primary waste water containing HF, comprising the steps of:

adding calcium hydroxide to the waste water containing a concentration of at least about 200 ppm of calcium in a form of calcium bicarbonate to cause the pH of the waste water to range from 8.5 to 10.5, the quantity of calcium hydroxide to be added ranging in 75 to 125% of the equivalent weight to calcium; and

removing the calcium by precipitation thereof in the form of calcium carbonate.

2. A method for removing calcium from waste water containing a concentration of calcium bicarbonate claimed according to claim 1, in which the quantity of calcium hydroxide to be added ranges in 90 to 110% of the equivalent weight to calcium.

3. A method for removing calcium from waste water containing a concentration of calcium bicarbonate claimed according to claim 1, in which the waste water contains about 200 ppm to 500 ppm of said calcium bicarbonate.

4. A method for removing calcium from waste water containing a concentration of calcium bicarbonate, the concentration of calcium bicarbonate being at least about 200 ppm, wherein the waste water is waste water deflourinated by adding calcium carbonate to primary waste water containing HF, comprising the steps of:

adding calcium hydroxide to the waste water containing a concentration of at least about 200 ppm of calcium in a form of calcium bicarbonate in a quantity of at least about 75% of the equivalent weight to calcium;

said adding step including that the calcium hydroxide added causes the pH of the waste water to range from 8.5 to 10.5; and

removing the calcium by precipitation thereof in the form of calcium carbonate.

5. A method for removing calcium from waste water containing a concentration of calcium bicarbonate claimed according to claim 4, in which the waste water contains said calcium bicarbonate of about 200 ppm to about 500 ppm.