Modified lignosulfonate dispersant for gypsum

The present invention relates to a non-set retarding lignosulfonate dispersing agent useful for making an aqueous calcined gypsum slurry, said dispersing agent produced by contacting an aqueous solution of a lignosulfonate with a salt of a multivalent metal selected from the group consisting of iron (II), iron (III), manganese (II) and cobalt (II) to form an aqueous solution of a multivalent metal salt and lignosulfonate having an acidic pH, and thereafter neutralizing said aqueous solution of said multivalent metal salt and lignosulfonate at an elevated temperature with an alkaline material.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to a modified lignosulfonate composition; 
its method of preparation and its use as a dispersant, particularly in the 
manufacture of gypsum wallboard. 
2. Description of Related Art 
The use of lignosulfonate as a dispersing agent in the preparation of 
gypsum wallboard is disclosed, for example, in U.S. Pat. No. 2,856,304. In 
the manufacture of gypsum products such as wallboard, lath, plaster board, 
sheathing or other products, calcined gypsum is formed into a slurry with 
a suitable amount of water and, where customary, with other additives such 
as paper fiber, wood fiber, starch, rosin, etc. 
In the preparation of wallboard or similar products, in particular, the 
slurry then is deposited between paper liners, pressed to the desired 
thickness by forming rolls, allowed to set and harden, cut to desired 
lengths, and passed through a dryer to remove excess moisture. A portion 
of the water used in making the slurry combines with the calcined gypsum, 
as water of crystallization, in forming the final set mass of interlaced 
crystals, but a large portion of the water must be removed in the dryer. 
Obviously, the drying process is more costly as the proportion of water to 
be removed from the formed board is higher. 
It is known that using lignosulfonate as a dispersing agent reduces the 
amount of water required to provide a flowable gypsum slurry during the 
deposition and forming steps. Consequently, by using lignosulfonate, the 
amount of water to be removed during the final drying step can be reduced, 
resulting in a significant economy of operation, particularly as regards 
lower energy costs. An ancillary benefit also often observed is higher 
board strength. It also is known that lignosulfonate exhibiting improved 
dispersing ability is prepared by base exchange of the lignosulfonate with 
various metals, including iron, aluminum, chromium and copper, by alkaline 
treatment, by oxidation and the like. See, for example U.S. Pat. Nos. 
2,935,504; 3,007,910; and 3,108,008. 
Unfortunately, lignosulfonates also tend to retard the hardening or cure 
rate of the gypsum board, referred in the art as set retardation. While 
this does not present a problem with slower forming operations 
characteristic of the prior art, with the advent of faster processes, set 
retardation has matured into a significant concern. In fact, while 
hydrolysis and oxidation reactions tend to enhance the dispersing behavior 
of the lignosulfonate, such treatments tend to exacerbate set retarding 
characteristics. 
In the prior art, the problem of set retardation has been dealt with 
primarily by adding various accelerating agents to the aqueous 
lignosulfonate-gypsum slurry. The prior art indicates that materials such 
as sodium chloride, aluminum sulfate, potassium sulfate, calcium sulfate 
dihydrate, and uncalcined or raw gypsum help to ameliorate set 
retardation. 
Finally, in U.S. Pat. No. 2,856,304 it is taught that calcining raw gypsum 
containing a small amount of lignosulfonate helps reduce the setting time 
of the calcined gypsum product. 
In accordance with the present invention, lignosulfonate is treated in a 
way which enhances its capability to disperse gypsum, while at the same 
time, avoids imparting to the lignosulfonate an undesirable increase in 
its set retardation characteristics. By using the modified lignosulfonate 
composition of the present invention, the amount of water needed to form a 
calcined gypsum slurry having the necessary plasticity is considerably 
reduced, and the production of gypsum shapes is simultaneously 
accelerated. 
DESCRIPTION OF THE INVENTION 
The present invention is broadly directed to a lignosulfonate composition 
which when used in preparing a calcined gypsum slurry exhibits an improved 
dispersing property and a lowered set-retarding characteristic. The 
composition is prepared by base exchange of a low pH lignosulfonate with a 
metal salt followed by alkaline neutralization at an elevated temperature, 
typically above 50.degree. C. The process preferably is conducted in a way 
that avoids excessive oxidation of the lignosulfonate. 
In one specific aspect, the present invention pertains to a non-set 
retarding lignosulfonate dispersing agent composition useful for making an 
aqueous calcined gypsum slurry which composition is produced by reacting 
an aqueous solution of a lignosulfonate with a salt of a multivalent metal 
selected from the group consisting of iron (II), iron (III), manganese 
(II) and cobalt (II) to form an aqueous solution of said multivalent metal 
salt and lignosulfonate having an acidic pH, and thereafter neutralizing 
said aqueous solution of said multivalent metal salt and lignosulfonate at 
an elevated temperature with an alkaline material. 
In another aspect, the present invention relates to a method for producing 
a non-set retarding lignosulfonate dispersing agent composition useful for 
making an aqueous calcined gypsum slurry comprising reacting an aqueous 
solution of a lignosulfonate with a salt of multivalent metal selected 
from the group consisting of iron (II), iron (III), manganese (II) and 
cobalt (II) to form an aqueous solution of said multivalent metal salt and 
lignosulfonate having an acidic pH, and thereafter neutralizing said 
aqueous solution of said multivalent metal salt and lignosulfonate salt at 
an elevated temperature with an alkaline material. 
In still another aspect, the present invention relates to the method for 
preparing a plastic slurry of calcined gypsum and water wherein a water 
soluble lignosulfonate is added to said slurry to reduce the water 
requirement for forming said plastic slurry, the improvement comprising 
using as at least a portion of said lignosulfonate, a non-set retarding 
lignosulfonate dispersing agent composition produced by reacting an 
aqueous solution of a lignosulfonate with a salt of a multivalent metal 
selected from the group consisting of iron (II), iron (III) manganese (II) 
and cobalt (II), to form an aqueous solution of said multivalent metal 
salt and lignosulfonate having an acidic pH, and thereafter neutralizing 
said aqueous solution of said multivalent metal salt and lignosulfonate at 
an elevated temperature with an alkaline material. 
The lignosulfonate used in the present invention can be sulfite lignin 
material recovered directly from the pulping of cellulosic materials using 
the sulfite process or the sulfonated lignin material produced by 
sulfonating the Kraft lignin recovered as a by-product when pulping 
cellulosic materials using the Kraft process. As used herein, the term 
Kraft lignin has its normal connotation, and refers to the lignin 
containing material typically recovered from alkaline pulping black 
liquors, such as are produced in the Kraft, soda and other well known 
alkaline pulping operations. Sulfonated lignin is obtained by the 
introduction of sulfonic acid groups into the Kraft lignin molecule, as 
may be accomplished by reaction of Kraft lignin with sulfite or bisulfite 
compounds, so that the Kraft lignin is rendered water soluble. Sulfite 
lignin is the water soluble reaction product of lignin inherently obtained 
during the sulfite pulping of wood, and is the principle constituent of 
spent sulfite liquor (SSL). 
In the present application, the term "lignosulfonate" therefore encompasses 
not only the sulfite lignin, but also sulfonated lignin. The lignin source 
for obtaining the lignosulfonate may be any common cellulosic material 
including hardwoods and softwoods and may be either crude or pure. Lignin 
recovered from the preparation of paper grade quality pulp in suitable. 
Typically, the lignosulfonate appears as one of its alkali metal or 
alkaline earth metal salts such as sodium, potassium, calcium, magnesium 
or ammonium lignosulfonate. 
In accordance with the present invention, an aqueous solution of a 
particular lignosulfonate salt first is prepared from a suitable source of 
lignosulfonate. One particularly convenient and preferred lignosulfonate 
source because of its cheapness and large supply is the spent sulfite 
liquor (SSL), directly recovered from the sulfite pulping of cellulosic 
materials, such as wood. In such material, in addition to the sulfonated 
lignin material, the lignosulfonate solution also will contain other 
materials, such as complex carbohydrates (wood sugars) and the like, 
common to such sulfite pulping by-products. Preferably, the SSL is 
treated, such as by fermentation using known procedures, to reduce or 
remove such additional ingredients. It also is often desirable to increase 
the solids content of the SSL by concentration pretreatment before using 
it in the process of the present invention. An aqueous lignosulfonate 
solution also can be prepared from by-product lignosulfonate solids by 
dissolving in water an appropriate amount of such solids. Lignosulfonate 
materials are available commercially and are obtained in various fashions 
from the various sources of lignin described above. Suitable commercial 
lignosulfonate products include LIGNOSITE.RTM. 100 and LIGNOSITE.RTM. CX, 
available from Georgia-Pacific Corporation. 
While the solids content of the lignosulfonate solution used to prepare the 
modified lignosulfonate of the present invention is not critical, it is 
preferred, based principally on processing considerations, that the solids 
content of the solution be between about 30 and 60 weight percent and more 
preferably between about 40 and 50 weight percent. 
In accordance with the present invention, it is important to avoid 
oxidizing, either by air or other chemical oxidants, the lignosulfonate 
material used to prepare the modified lignosulfonate composition of the 
present invention. In other words, the lignosulfonate used in the present 
invention should be a substantially non-oxidized form of lignosulfonate. 
While oxidation does improve the dispersing ability of the lignosulfonate, 
it generates an excessive amount of set-retarding species. 
As a general rule, solutions of lignosulfonates suitable for use in the 
present invention inherently exhibit a pH below about 7.0 and usually 
between about 4 and 6 in aqueous solution. However, if for some reason the 
pH of the lignosulfonate is at or above a pH of about 7.0, as will be the 
case if an alkaline treated lignosulfonate material is used, it may be 
necessary and generally will be preferred that sufficient acid be added to 
the solution to reduce the pH to below 7.0 and preferably to at least 
about 4. The acid can be added either before or after the subsequent 
addition of the metal salt. Any acid can be used for this purpose, 
although for convenience a readily available and inexpensive mineral acid 
should be used, preferably sulfuric acid. 
The lignosulfonate solution then is treated or contacted (reacted) with a 
preferably water soluble salt of a multivalent metal selected from the 
group consisting of iron (II), iron (III), cobalt (II) and manganese (II). 
Preferred multivalent metal salts include ferric sulfate, ferrous sulfate, 
manganese sulfate and cobalt sulfate, although other non-oxidizing salts 
of these metals also could be used. The iron salts are preferred. 
Generally, the metal salt is added to the lignosulfonate solution in an 
amount between about 1.0 and 10.0 weight percent metal cation based on the 
mass of lignosulfonate solids in the solution, and preferably between 
about 3.0 and 5.0 weight percent. 
It is an important feature of the present invention that the pH of the 
metal salt-treated lignosulfonate solution have an acid pH. A pH below 
about 6.5 has proven to be suitable. Preferably, the pH is below about 
5.0, and most preferably about 4.0 or below. Normally, the lower the 
solids concentration of the lignosulfonate solution that is being treated, 
the lower is the desired pH during the base exchange treatment with the 
multivalent metal salt. 
The lignosulfonate solution and metal salt thereafter are contacted 
(reacted) for a time sufficient to form the multivalent metal salt of the 
lignosulfonate and reduce the set retarding character of the 
lignosulfonate solution. Although not wishing to be bound to any 
theoretical explanation, it is believed that the metal salts react or 
interact with set retarding compounds in the lignosulfonate solution, 
possibly sugar acids, to form chelated species that exhibit lower set 
retarding tendencies than their precursors. 
Generally a reasonable contacting time or reaction time between the 
lignosulfonate solution and metal salt of about 5 to 30 minutes is 
sufficient to obtain the desired level of treatment. Shorter times tends 
to be less successful in producing the desired result of lower set 
retardation, while longer times do not seem to provide any added 
improvement and thus are unnecessary. The temperature of the 
lignosulfonate solution during this treatment is not critical, although 
higher temperatures permit the desired level of treatment to be achieved 
in shorter times. Moreover, since the subsequent treatment of the 
lignosulfonate solution in accordance with the present invention is 
conducted at an elevated temperature, it is convenient to perform this 
initial step at the same temperature. However, use of an elevated pressure 
and temperatures, for example, at or above 100.degree. C., both during 
this step and in the subsequent step tend to be unnecessary and 
uneconomical due to higher energy demands. 
Once the reaction between the lignosulfonate solution and the multivalent 
metal salt has proceeded to a desired extent, the temperature of the 
solution is raised, as may be needed, to above about 50.degree. C. 
Preferably the temperature of the lignosulfonate solution is adjusted to 
between about 80.degree. and 95.degree. C., and usually to about 
90.degree. C. 
At this point, the acidic lignosulfonate solution is neutralized with an at 
least partially water soluble alkaline material to a pH of about 7.0, 
preferably below about 8.0 and generally between about 6.8 and 7.2. A 
composition having acceptable set retarding and dispersion enhancing 
properties are not obtained unless the acidic metal salt-treated 
lignosulfonate solution is substantially neutralized. Increasing the pH 
beyond neutrality and into the alkaline regime, however, is not necessary 
and tends to be disadvantageous because it consumes more alkaline material 
than needed to obtain the benefits of the present invention. The 
neutralized solution then is kept at the elevated temperature for a time 
sufficient to stabilize the lowered set retarding and dispersing enhancing 
character of the lignosulfonate. A retention time of about 10 to 45 
minutes generally should be sufficient. The dispersing enhancing and lower 
set retarding modified lignosulfonate composition then is recovered, as an 
aqueous solution, and any solid impurities can be removed, for example, by 
centrifugation. 
Based on cost considerations a common inorganic base or alkaline reagent 
such as an alkali metal or alkaline earth metal hydroxide is used as the 
at least partially water soluble alkaline material, although any of a wide 
variety of other at least partially water soluble alkaline materials can 
be used. Suitable results have been obtained using sodium, potassium, 
ammonium, calcium or magnesium hydroxide. Because of the prevalence of 
calcium in the gypsum slurry, an alkaline calcium compound, such as 
calcium hydroxide, often is preferred. The amount of alkaline material to 
be added depends on the alkaline material actually used, the original pH 
level of the acidic lignosulfonate material and the desired final pH. 
Again, not wishing to be bound to any particular theory, it is thought that 
neutralization of the multivalent metal salt-treated lignosulfonate 
solution at the elevated temperature stabilizes the less set-retarding 
chelate species formed during the initial phase of treatment, without 
significantly affecting the dispersing enhancing ability of the 
lignosulfonate. 
The so-recovered, modified lignosulfonate composition of the present 
invention is suitable for preparing a slurry of calcined gypsum used to 
prepare gypsum wallboard. The lignosulfonate is suitably added in the form 
of an aqueous solution to the calcined gypsum. The modified lignosulfonate 
can be the aqueous solution produced directly from the process of the 
present invention or can be a subsequently isolated portion of the solids 
fraction of the solution. Preferably, the lignosulfonate is dissolved in 
water which then is used to prepare the gypsum slurry itself. 
Alternatively, lignosulfonate in dry form can be blended with the calcined 
gypsum, either wet or dry. 
Various aspects of the present invention now will be described and 
illustrated below in greater detail with reference to specific examples, 
in which the parts and percentages are by weight unless otherwise 
indicated.

EXAMPLES 
EXAMPLE 1 
An amount of 43.2 grams of solid ferrous sulfate heptahydrate was added to 
503.9 grams of an aqueous solution containing 49.2 wt % unneutralized 
fermented calcium lignosulfonate maintained at a temperature of 90.degree. 
C. The calcium lignosulfonate and ferrous sulfate heptahydrate reacted 
(were mixed) for 12 minutes. After adding the metal salt, the solution had 
a pH of 3.8. The aqueous material then was neutralized to a pH of 7.0 with 
a calcium hydroxide slurry and stirred for 19 minutes. Thereafter, the 
reaction mixture at 90.degree. C. was centrifuged for ten minutes at 5000 
rpm to remove insoluble impurities and recover an aqueous solution of a 
modified lignosulfonate composition. 
EXAMPLE 2 
An amount of 30.3 grams of solid cobalt sulfate heptahydrate was added to 
368.9 grams of an aqueous solution containing 49.2 wt % unneutralized 
fermented calcium lignosulfonate maintained at a temperature of 90.degree. 
C. The calcium lignosulfonate and cobalt sulfate heptahydrate reacted 
(were mixed) for 11 minutes. After adding the metal salt, the solution had 
a pH of 3.5. The aqueous material then was neutralized to a pH of 7.0 with 
a calcium hydroxide slurry and stirred for 23 minutes. Thereafter, the 
reaction mixture at 90.degree. C. was centrifuged for ten minutes at 5000 
rpm to remove insoluble impurities and recover an aqueous solution of a 
modified lignosulfonate composition. 
EXAMPLE 3 
An amount of 20.9 grams of solid cupric sulfate pentahydrate was added to 
308.2 grams an aqueous solution containing 49.2 wt. % unneutralized 
fermented calcium lignosulfonate maintained at a temperature of 90.degree. 
C. The calcium lignosulfonate and cupric sulfate pentahydrate reacted 
(were mixed) for 13 minutes. After adding the metal salt, the solution had 
a pH of 2.45. The aqueous material then was neutralized to a pH of seven 
with a calcium hydroxide slurry and stirred for 21 minutes. Thereafter, 
the reaction mixture at 90.degree. C. was centrifuged for ten minutes at 
5000 rpm to remove insoluble impurities and recover an aqueous solution of 
a modified lignosulfonate composition. 
EXAMPLE 4 
An amount of 22.8 grams of zinc sulfate heptahydrate was added to 294.1 
grams of an aqueous solution containing 49.2 wt. % unneutralized fermented 
calcium lignosulfonate maintained at a temperature of 90.degree. C. The 
calcium lignosulfonate and zinc sulfate heptahydrate reacted (were mixed) 
for ten minutes. After adding the metal salt, the solution had a pH of 
3.5. The material then was neutralized to a pH of seven with a calcium 
hydroxide slurry and mixed for 21 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 5 
An amount of 24.9 grams of ferric sulfate heptahydrate was added to 342.3 
grams of an aqueous solution containing 49.2 wt. % unneutralized fermented 
calcium lignosulfonate maintained at a temperature of 90.degree. C. The 
calcium lignosulfonate and ferric sulfate heptahydrate reacted (were 
mixed) for 15 minutes. After adding the metal salt, the solution had a pH 
of 1.7. The material then was neutralized to a pH of seven with a calcium 
hydroxide slurry and mixed for 20 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 6 
An amount of 17.6 grams of manganese sulfate monohydrate was added to 33.2 
grams an aqueous solution containing of 49.2 wt. % unneutralized fermented 
calcium lignosulfonate maintained at a temperature of 90.degree. C. The 
calcium lignosulfonate and manganese sulfate monohydrate reacted (were 
mixed) for ten minutes. After adding the metal salt, the solution had a pH 
of 3.45. The material then was neutralized to a pH of seven with a calcium 
hydroxide slurry and mixed for 17 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 7 
An amount of 54.7 grams of aluminum sulfate hydrate (natural alunogenite) 
was added to 257.0 grams of an aqueous solution containing 49.2 wt. % 
unneutralized fermented calcium lignosulfonate maintained at a temperature 
of 90.degree. C. The calcium lignosulfonate and aluminum sulfate reacted 
(were mixed) for ten minutes. After adding the metal salt, the pH of the 
solution was 0.55. The material then was neutralized to a pH of seven with 
a calcium hydroxide slurry and mixed for 24 minutes. The reaction mixture 
at 90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 8 
An amount of 25.2 grams of ferrous sulfate heptahydrate was added to 303.9 
grams of an aqueous solution containing 47.6 wt. % fermented ammonium 
lignosulfonate maintained at a temperature of 90.degree. C. The ammonium 
lignosulfonate and ferrous sulfate heptahydrate reacted (were mixed) for 
ten minutes. After adding the metal salt, the pH of the solution was 3.65. 
The material then was neutralized to a pH of seven with a calcium 
hydroxide slurry and mixed for 20 minutes. The reaction mixture at 
90.degree. was centrifuged for ten minutes at 5000 rpm to remove insoluble 
impurities and recover an aqueous solution of a modified lignosulfonate 
composition. 
EXAMPLE 9 
An amount of 24.0 grams of ferrous sulfate heptahydrate was added to 318.0 
grams of an aqueous solution containing 43.32 wt. % fermented magnesium 
lignosulfonate maintained at a temperature of 90.degree. C. The magnesium 
lignosulfonate and ferrous sulfate heptahydrate reacted (were mixed) for 
13 minutes. After adding the metal salt, the pH of the solution was 4.15. 
The material then was neutralized to a pH of seven with a calcium 
hydroxide slurry and mixed for 20 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 10 
An amount of 22.2 grams ferrous sulfate heptahydrate was added to 255.1 
grams of an aqueous solution containing 49.9 wt. % unneutralized fermented 
sodium lignosulfonate maintained at a temperature of 90.degree. C. The 
sodium lignosulfonate and ferrous sulfate heptahydrate reacted (were 
mixed) for 12 minutes. After adding the metal salt, the Ph of the solution 
was 3.65. The material then was neutralized to a pH of seven with a 
calcium hydroxide slurry and mixed for 16 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 11 
An amount of 21.0 grams of ferrous sulfate heptahydrate was added to 307.5 
grams of an aqueous solution containing 39.2 wt. % LIGNOSITE.RTM. AC, 
alkaline air oxidized calcium lignosulfonate, maintained at a temperature 
of 90.degree. C. The alkaline air oxidized calcium lignosulfonate and 
ferrous sulfate heptahydrate reacted (were mixed) for 10 minutes. After 
adding the metal salt, the solution had a pH of 5.2. The material was 
neutralized to a pH of seven with a calcium hydroxide slurry and mixed for 
20 minutes. The reaction mixture at 90.degree. C. was centrifuged for ten 
minutes at 5000 rpm to remove insoluble impurities and recover an aqueous 
solution of a modified lignosulfonate composition. 
EXAMPLE 12 
An amount of 23.8 grams of ferrous sulfate heptahydrate was added to 331.3 
grams of an aqueous solution containing 40.7 wt. % of a sulfonated Kraft 
lignin (POLYFON.RTM. T available from Westvaco, Inc.) at 90.degree. C. The 
sulfonated Kraft lignin and ferrous sulfate heptahydrate reacted (were 
mixed) for 11 minutes. After adding the metal salt, the solution had a pH 
of 5.15. The material then was neutralized to a pH of seven with a calcium 
hydroxide slurry and mixed for 20 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 13 
An amount of 20.5 grams of ferrous sulfate heptahydrate was added to 238.9 
grams of an aqueous solution containing 49.2 wt. % unneutralized fermented 
calcium lignosulfonate maintained at a temperature of 90.degree. C. The 
calcium lignosulfonate and ferrous sulfate heptahydrate reacted (were 
mixed) for 12 minutes. After adding the metal salt, the solution had a pH 
of 3.85. The material then was neutralized to a pH of seven with potassium 
hydroxide solution and mixed for 21 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 14 
An amount of 30.8 grams of ferrous sulfate heptahydrate was added to 381.8 
grams of an aqueous solution containing 46.3 wt. % unneutralized fermented 
potassium lignosulfonate maintained at a temperature of 90.degree. C. The 
potassium lignosulfonate and ferrous sulfate heptahydrate reacted (were 
mixed) for 13 minutes. After adding the metal salt, the solution had a pH 
of 3.75. The material then was neutralized to a pH of seven with a calcium 
hydroxide slurry and mixed for 21 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 15 
An amount of 23.4 grams of ferrous sulfate heptahydrate was added to 273.4 
grams of an aqueous solution containing 49.2 wt. % unneutralized fermented 
calcium lignosulfonate maintained at a temperature of 90.degree. C. The 
calcium lignosulfonate and ferrous sulfate heptahydrate reacted (were 
mixed) for ten minutes. After adding the metal salt, the solution had a pH 
of 3.65. The material then was neutralized to a pH of seven with a 
magnesium hydroxide solution and mixed for 39 minutes. The reaction 
mixture at 90.degree. C. was centrifuged for ten minutes at 5000 rpm to 
remove insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 16 
An amount of 21.8 grams ferrous sulfate heptahydrate was added to 254.2 
grams of an aqueous solution containing 49.2 wt. % unneutralized fermented 
calcium lignosulfonate maintained at a temperature of 90.degree. C. The 
calcium lignosulfonate and ferrous sulfate heptahydrate reacted (were 
mixed) for ten minutes. After adding the metal salt, the solution had a pH 
of 3.9. The material then was neutralized to a pH of seven with an 
ammonium hydroxide solution and mixed for 19 minutes. The reaction mixture 
at 90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 17 
An amount of 19.9 grams of ferrous sulfate heptahydrate was added to 232.1 
grams of an aqueous solution containing 49.2 wt. % unneutralized fermented 
calcium lignosulfonate maintained at a temperature of 90.degree. C. The 
calcium lignosulfonate and ferrous sulfate heptahydrate reacted (were 
mixed) for 11 minutes. After adding the metal salt, the solution had a pH 
of 3.1. The material then was neutralized to a pH of seven with a sodium 
hydroxide solution and mixed for 18 minutes. The reaction mixture at 
90.degree. C. was centrifuged for ten minutes at 5000 rpm to remove 
insoluble impurities and recover an aqueous solution of a modified 
lignosulfonate composition. 
EXAMPLE 18 
A 245.6 gram sample of a 40.0 wt. % neutralized iron lignosulfonate product 
generated according to the procedure of Example 1 was treated with 15 wt. 
% sodium hydroxide to a pH of 8.8. Thereafter, the alkaline solution was 
oxidized using 9 grams of 30-35 wt. % hydrogen peroxide for 24 hours with 
stirring at 25.degree. C., yield the lignosulfonate composition. 
PERFORMANCE TESTS 
Disperant Ability 
The dispersing abilities of the lignosulfonate compositions of Examples 
1-18 and an unneutralized fermented spent sulfite liquor control 
(LIGNOSITE.RTM. CX) were measured utilizing a water reduction test in 
which the amount of water required to produce a stucco slurry of a 
specific viscosity was determined. In all of the dispersion tests, 200 
grams of a commercially available stucco material was utilized. This 
stucco material consisted mainly of calcium sulfate hemihydrate, but also 
included small amounts of anhydrous calcium sulfate, calcium sulfate 
dihydrate, clays, carbonates, and various soluble salts. 
In each test, a stucco slurry was produced by adding to 200 grams of stucco 
a mixture (solution) of water, 0.02 grams sodium citrate, and 0.4 grams of 
the lignosulfonate dispersant solids. The sodium citrate functioned in 
these tests as a set retardant to prevent the slurry from hardening before 
the test patty could be made. The water mixture was added to the stucco, 
allowed to soak for 60 seconds, and then stirred for 60 seconds. 
The slurry then was poured into a brass cylinder having a 1.615 inch 
internal diameter and a height of 4.5 inches. The bottom of the cylinder 
was flat (closed) except for a centrally located 0.25 inch diameter 
orifice. For the tests, the cylinder was positioned two inches above a 
glass plate to form the stucco test patty. Slurry test samples were placed 
in the cylinder and the slurry was allowed to flow through the orifice 
onto a glass plate to form a stucco patty. The amount of water required to 
make a 6-inch test patty under this configuration with the lignosulfonate 
dispersant in the mixture was compared to the amount of water required to 
make a 6-inch test patty under the identical configuration without the 
lignosulfonate in the mixture (i.e., with water and sodium citrate alone). 
This difference in water is reported as percent water reduction. Higher 
water reduction percentages are indicative of improved dispersing ability. 
Set Retardation 
The test for assessing set retardation of a lignosulfonate composition 
involved a measurement of the time required for the stucco slurry 
containing the lignosulfonate to harden as determined by following the 
rise in temperature of the setting slurry as a result of the heat of 
hydration. 
According to the procedure, one hundred grams of the commercial stucco 
material identified above was utilized. This stucco material was added to 
a water mixture containing 0.2 gram of potassium sulfate, 0.2 gram of land 
plaster (finely ground calcium sulfate dihydrate), and 0.4 gram of the 
lignosulfonate dispersant. The land plaster and potassium sulfate are 
commonly added set accelerators for the commercial stucco. The amount of 
water used in each test was equal to 50% of the amount of water required, 
with each respective dispersant, to produce a 6-inch patty with 200 grams 
of stucco as determined above in the water reduction test used to measure 
dispersant ability. 
After addition of the water to the stucco, the slurry was allowed to soak 
for 30 seconds and then stirred in a paper cup (having a volume of about 
150 ml) for 30 seconds. Then a thermocouple was placed in the center of 
the mixture, and the temperature rise versus time was recorded until the 
temperature began to fall. The set time was recorded as the amount of time 
required for the measured temperature to achieve 95% of the total measured 
rise between the starting temperature and the maximum temperature. 
The results of the dispersant and set retardation performance tests are 
tabulated in Table 1 and show lignosulfonate materials with improved 
dispersing characteristics which are non-set retarding in the manufacture 
of gypsum wallboard. This was accomplished through the addition of certain 
metal salts to the aqueous lignosulfonate solutions followed by 
neutralization using calcium, sodium, potassium or ammonium hydroxide. 
When sulfonated Kraft lignin was utilized, the resulting product had 
improved dispersing and set retarding characteristics over 
lignosulfonates. This material, however, is less set retarding even before 
the addition of the metal salts. The samples prepared in which the 
lignosulfonates were alkaline oxidized before or after the addition of the 
metal salts had much improved dispersing ability but were more set 
retarding than material produced without oxidation. 
From the prior art it is known that a simple base exchange of a 
lignosulfonate with certain metals will produce a product with slightly 
improved dispersing ability. However, such modified lignosulfonates 
exhibit undesired set retarding characteristics. Adding one of these 
metals to a previously alkaline treated lignosulfonate produces a material 
exhibiting only slightly improved dispersing and set retarding 
characteristics relative to the base exchanged composition, but only if 
the solution is held at a pH of 7 or above and at an elevated temperature 
for an extended period of time. Nonetheless, even under those conditions 
the improvements observed in dispersing and set retarding characteristics 
tend to be only about one half as much as is obtained in the present 
invention. 
TABLE I 
______________________________________ 
Experimental Results 
Lignosulfonate 
Water 
of Example Reduction Set Time Metal 
Number (%) (Minutes) Cation 
______________________________________ 
1 8.2 9.56 Fe.sup.+2 
2 8.3 9.16 Co.sup.+2 
3 6.5 10.45 Cu.sup.+2 
4 7.8 10.53 Zn.sup.+2 
5 9.4 9.40 Fe.sup.+3 
6 7.4 9.94 Mn.sup.+2 
7 6.1 9.44 Al.sup.+3 
8 9.6 9.16 Fe.sup.+2 
9 7.2 9.64 Fe.sup.+2 
10 8.9 9.69 Fe.sup.+2 
11 10.4 10.46 Fe.sup.+2 
12 8.9 8.80 Fe.sup.+2 
13 8.6 9.23 Fe.sup.+2 
14 7.2 9.22 Fe.sup.+2 
15 7.5 9.84 Fe.sup.+2 
16 9.0 9.46 Fe.sup.+2 
17 8.4 9.21 Fe.sup.+2 
18 10.0 10.09 Fe.sup.+2 
Control 6.6 11.21 -- 
______________________________________ 
.sup.1 Lignosite CX. 
While certain specific embodiments of the invention have been described 
with particularity herein, it will be recognized that various 
modifications thereof will occur to those skilled in the art and it is to 
be understood that such modifications and variations are to be included 
within the purview of the application and within the spirit and scope of 
the appended claims.