Method of decolorizing paper mill effluent liquid

Claim 2

combining said mixture under a pressure greater than atmospheric with said CO2 by-product of the burning of calcium carbonate mud, thereby converting calcium carbonate to soluble calcium bicarbonate,

Claim 3

pumping said mixture under pressure into a tank together with a fluid including an excess of carbon dioxide, CO2, and maintaining said mixture therein under a pressure greater than atmospheric for a time sufficient to effect substantial conversion of calcium carbonate, CaCO3, into soluble calcium bicarbonate, CaHCO3,

Claim 4

The method as claimed in claim 1 which includes the step of (4) separating the precipitate containing color-imparting substances from the remainder of the liquid.

Claim 5

pressurizing said liquid to greater than atmospheric in the presence of a fluid including an excess of carbon dioxide, CO2, whereby said calcium carbonate, CaCO3, is substantially converted to soluble calcium bicarbonate, CaHCO3, and

Claim 6

The method as claimed in claim 2 which includes the step of (5) directing the separated precipitate to a lime kiln for combustion conversion of CaCO3 to CaO.

Claim 7

discharging the pressurized liquid to atmospheric pressure whereby said calcium bicarbonate, CaHCO3, substantially converts to insoluble calcium carbonate, CaCO3, as a precipitate carrying therewith color-imparting substances present in said paper mill effluent liquid.

Claim 8

discharging the pressurized liquid comprising essentially calcium bicarbonate, CaHCO3, to atmospheric pressure whereby said calcium bicarbonate, CaHCO3, essentially converts to insoluble calcium carbonate, CaCO3, as a precipitate, carrying with said precipitate, in agglomerated fashion, color-imparting substances and entities carried in said paper mill effluent,

Claim 9

expose the resultant of steps (1) and (2) to a reduction in pressure to atmospheric pressure to convert soluble calcium bicarbonate to insoluble calcium carbonate which forms a precipitate of said calcium carbonate, said precipitate attracting and carrying color bodies therewith, and

Claim 10

discharging the liquid comprising calcium bicarbonate into a settling tank at atmospheric pressure whereby said calcium bicarbonate converts to insoluble calcium carbonate as a solid precipitate which attracts and carries color bodies in agglomeration or admixture therewith,

Claim 11

separating calcium carbonate precipitate and color bodies from said liquid whereby said liquid is essentially decolorized and

Claim 12

separate said precipitate and color bodies from said effluent.

Claim 13

separating effluent liquid from precipitate and

Claim 15

In a system of pulping wood by the kraft process wherein sodium hydroxide and sodium sulfide are the active pulping chemicals combined with wood chips to attack the binding components and resulting in the liberation of cellulose fibers and wherein black liquor recovered from the pulping reaction is concentrated and burned to recover sodium values in the form of green liquor including sodium carbonate and sodium sulfide, which green liquor is thence causticized with recovered lime to yield fresh pulping chemicals and a by-product comprising calcium carbonate mud, a portion of said calcium carbonate being desirably burned to yield reusable lime for said causticizing and resulting in by-product gases rich in CO2, said pulping process and recovery process resulting in a considerable amount of mill effluent liquid which is normally ecologically undesirable due to discoloration caused by the presence of color bodies; the improvement wherein said effluent mill liquid is treated in accordance with the following series of steps integrated into the pulping process just described, said steps being as follows:

Claim 16

exposing said effluent to a stimulus to effect residual precipitation, formation of color bodies and stabilization of effluent pH to from 7.8 to 8.4.

Claim 17

returning said precipitated calcium carbonate to said lime recovery.

Claim 19

The method as claimed in claim 6, wherein said pressure measures about 20 to 100 pounds per square inch gauge.