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Title: Flotation process for removal of precipitates from electrochemical chromate reduction unit

Abstract

This invention is an improved form of a conventional electrochemical process for removing hexavalent chromium or other metal-ion contaminants from cooling-tower blowdown water. In the conventional process, the contaminant is reduced and precipitated at an iron anode, thus forming a mixed precipitate of iron and chromium hydroxides, while hydrogen being evolved copiously at a cathode is vented from the electrochemical cell. In the conventional process, subsequent separation of the fine precipitate has proved to be difficult and inefficient. In accordance with this invention, the electrochemical operation is conducted in a novel manner permitting a much more efficient and less expensive precipitate-recovery operation. That is, the electrochemical operation is conducted under an evolved-hydrogen partial pressure exceeding atmospheric pressure. As a result, most of the evolved hydrogen is entrained as bubbles in the blowdown in the cell. The resulting hydrogen-rich blowdown is introduced to a vented chamber, where the entrained hydrogen combines with the precipitate to form a froth which can be separated by conventional techniques. In addition to the hydrogen, two materials present in most blowdown act as flotation promoters for the precipitate. These are (1) air, with which the blowdown water becomes saturated in the course of normal cooling-tower operation,more » and (2) surfactants which commonly are added to cooling-tower recirculating-water systems to inhibit the growth of certain organisms or prevent the deposition of insoluble particulates.« less

Inventors:
 [1];  [2];  [2]
  1. Knoxville, TN
  2. Oak Ridge, TN
Issue Date:
Research Org.:
UNION CARBIDE CORP
OSTI Identifier:
862691
Patent Number(s):
3989608
Assignee:
United States of America as represented by United States Energy (Washington, DC)
Patent Classifications (CPCs):
C - CHEMISTRY C02 - TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE C02F - TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
B - PERFORMING OPERATIONS B03 - SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS B03D - FLOTATION
DOE Contract Number:  
W-7405-ENG-26
Resource Type:
Patent
Country of Publication:
United States
Language:
English
Subject:
flotation; process; removal; precipitates; electrochemical; chromate; reduction; unit; improved; form; conventional; removing; hexavalent; chromium; metal-ion; contaminants; cooling-tower; blowdown; water; contaminant; reduced; precipitated; iron; anode; forming; mixed; precipitate; hydroxides; hydrogen; evolved; copiously; cathode; vented; cell; subsequent; separation; fine; proved; difficult; inefficient; accordance; operation; conducted; novel; manner; permitting; efficient; expensive; precipitate-recovery; evolved-hydrogen; partial; pressure; exceeding; atmospheric; result; entrained; bubbles; resulting; hydrogen-rich; introduced; chamber; combines; froth; separated; techniques; addition; materials; promoters; air; saturated; course; normal; surfactants; commonly; added; recirculating-water; systems; inhibit; growth; organisms; prevent; deposition; insoluble; particulates; subsequent separation; hydrogen partial; electrochemical cell; atmospheric pressure; partial pressure; conventional techniques; chemical process; manner permitting; hexavalent chromium; reduction unit; normal cooling; evolved hydrogen; conventional process; electrochemical process; resulting hydrogen; /205/210/376/

Citation Formats

DeMonbrun, James R, Schmitt, Charles R, and Williams, Everett H. Flotation process for removal of precipitates from electrochemical chromate reduction unit. United States: N. p., 1976. Web.
DeMonbrun, James R, Schmitt, Charles R, & Williams, Everett H. Flotation process for removal of precipitates from electrochemical chromate reduction unit. United States.
DeMonbrun, James R, Schmitt, Charles R, and Williams, Everett H. Thu . "Flotation process for removal of precipitates from electrochemical chromate reduction unit". United States. https://www.osti.gov/servlets/purl/862691.
@article{osti_862691,
title = {Flotation process for removal of precipitates from electrochemical chromate reduction unit},
author = {DeMonbrun, James R and Schmitt, Charles R and Williams, Everett H},
abstractNote = {This invention is an improved form of a conventional electrochemical process for removing hexavalent chromium or other metal-ion contaminants from cooling-tower blowdown water. In the conventional process, the contaminant is reduced and precipitated at an iron anode, thus forming a mixed precipitate of iron and chromium hydroxides, while hydrogen being evolved copiously at a cathode is vented from the electrochemical cell. In the conventional process, subsequent separation of the fine precipitate has proved to be difficult and inefficient. In accordance with this invention, the electrochemical operation is conducted in a novel manner permitting a much more efficient and less expensive precipitate-recovery operation. That is, the electrochemical operation is conducted under an evolved-hydrogen partial pressure exceeding atmospheric pressure. As a result, most of the evolved hydrogen is entrained as bubbles in the blowdown in the cell. The resulting hydrogen-rich blowdown is introduced to a vented chamber, where the entrained hydrogen combines with the precipitate to form a froth which can be separated by conventional techniques. In addition to the hydrogen, two materials present in most blowdown act as flotation promoters for the precipitate. These are (1) air, with which the blowdown water becomes saturated in the course of normal cooling-tower operation, and (2) surfactants which commonly are added to cooling-tower recirculating-water systems to inhibit the growth of certain organisms or prevent the deposition of insoluble particulates.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1976},
month = {1}
}

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