Process for removing metals and recovering a chelating agent from a bleach plant waste liquor
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United States of America Patent
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-
Feb 15, 2000
Issued Date -
N/A
app pub date -
May 2, 1997
filing date -
Nov 4, 1994
priority date (Note) -
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Abstract
Provided is a process for removing metals from a bleaching plant spent liquor and recovering a chelating agent which includes the steps of: heating a spent liquor containing a chelate comprising metals bound in a chelating agent to a temperature of at least about 140.degree. C. to break bonds in the chelate and release metals from the chelate; increasing the content of at least one of carbonate or sulphide in an alkaline material comprising at least one of green liquor or white liquor to form a carbonate or sulphide enhanced alkaline material; contacting the heated spent liquor with the alkaline material to form a solution containing precipitated metals, wherein the alkaline material is added in an amount sufficient to precipitate a majority of the released metals out of the solution; filtering the solution to separate the precipitated metals from the solution and form a filtrate containing recovered chelating agent; and supplying at least a portion of the recovered chelating agent to a chelating washing stage in a bleaching plant to bond with metals released from pulp and form a chelate. Also provided is a method of reducing encrustations.
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