Note: Descriptions are shown in the official language in which they were submitted.
~3~97
Suspension of Aqueous Magnesium Oxide
Technical Field
-
This invention relates to a novel slurry of hardburn
magnesium oxide in aqueous suspension. More particularly, the
invention relates to an aqueous suspension of magnesium oxide in
fine particle size which displays minimal hydration of MgO to
Mg(OH~2, controlled viscosity, and excellent suspension
stability at high magnesium oxide concentration. Such suspensions
are useful as bases for liquid animal feeds, fertilizers, etc.
Background Art
Magnesium oxide has numerous applications in both
agricultural and industrial fields. In the agricultural area,
particularly, magnesium oxide is useful as an animal feed additive
to raise magnesium blood serum levels, which prevents outbreaks of
hypomagnesemia in cattle, and in fertilizers as a vital source of
plant nutrient magnesium. In indus~ry, magnesium oxide is useful
as a boiler feed additive and is one of the primary reactant
materials in many chemical process reactions, such as acid
neutrali~ation, cation replacement, and hyrdation reactions.
For many oF these uses and applications, it is desirable to
provide an aqueous high concentration magnesium oxide suspension
slurry ~/ith minimal hydration of the MgO to MgtOH)2 to
facilitate handling and ease of incorporation into a resultant
product or reaction, or for use as a direct application material
as in the case, ~or example, of a boiler feed additive, as a
boiler and air heater neutralization agent, or a fertiiizer.
Slurries or suspensions of magnesium oxide which are not treated
as directed in this novel invention but which use MgO in tne
~e
37
surface area range so described by this invention and at
concentrations so described would exhibit excessive hydration of
MgO to ~lg~OH)2 and exhibit unacceptably high viscosity values
for normal pumping and transport.
Prior art animal feed sùpplements commonly contain sources of
nitrogen, phosphorous, and sugars, with MgO. The insoluble
magnesia, however, frequently settles and/or causes formation of
an immobile gel-like mixture. Various attempts have been made to
achieve suspension stabilization of MgO containing feed
supplements.
In U.S. Patent 4,219,57~, Jackman teaches the presence of
xanthan gum to stabilize feed supplements containing up to about
6% MgO. The xanthan gum is said to provide suspension
stabilization.
In Mickens et al., U.S. Patent 4,38~,966, an aninlal feed
suspension is taught wherein hydrated xanthan gum stabilizes the
suspension by increasing the viscosity of the liquid supplements
and forming a thixotropic gel. Lignin liquor may be added as a
source of carbohydrate or sugar nutrient, and MgO may be added as
an insoluble mineral nutrient.
Falcione et al., in U.S. 4,230,610, teach the use of
polyacrylates as a dispersant to reduce slurry viscosity and
permit utilization of 41.6% MgO in a pigment dispersion.
Sa~hill, U.S. 4,2~ 7, teaches an animal feed supplement
containing sufficient ammonium orthophosphate or sulfate to form a
gel, to which a dispersing agent such as gelatinized starch or
clay is added to stabilize the insoluble solid nutrient. Lignin
sulfonate may be utilized as a source of sugar or carbohydrate
nutrient.
The prior art, however, fails to disclose a concentrated,
stab1e, hydration resistant suspension of up to 50~ MgO wnerein
suspension stability is improved by the presence of a suspension
aid, and hydration is prevented by the presence of a surface
active agent.
'3~7
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Disclosure of Invention
The present invention is a highly concentrated sus-
pension slurry of hardburn magnesium oxide in water, u~ing
a suspension aid to maintain suspendibility and an anti-
hydration agent, preferably lignin sulfonate in a unique
application as a surface active agent to limit hydration of
MgO to Mg(OH)2. Such a slurry may have a concentration of
up to about 50~ MgO by weight.
Best Mode for Carryin~ the Invention
~igh purity hardburn magnesium oxide is typically
the product of reacting magnesium chloride solutions, for
example, seawater or magnesium chloride brine, with lime (CaO)
or dolomitic lime (MgO-CaO) to precipitate in~oluble magnesium
hydroxide which i~ then calcined, usually between 1150C and
1550C, resulting in aimagnesium oxide product Wit}l a surface
area of between 0O5 m2/g and 10 m2/g. Alternatively, magnesium
oxide with approximately the same surface area specification~
can be produced commercially by calcining natural magnesite
(MgC03).
For a suspension according to the pre~ent invention,
dry magnesium oxide powder in a screen size ranging from minus
50 Tyler mesh to minus 325 Tyler mesh is suitable. Most
preferably, a hardburn material which passes a 200 Tyler mesh
~creen is used. The fine particle ~ize is particularly
advantageouc in fertilizer formulations.
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The ratio of water to magnesium oxide can range from
approximately 1:1 to any le3ser oxide concentration, typically
between 8~ MgO and 50~ MgO~ more typically between 15 and 50~
MgO. It is preferred, for purposes of economy in storage and
shipment and, at the same time, to maintain long term stability,
to produce a magnesium oxide ~uspension 31urry of from 33%
MgO to 45~ MgO by weight.
A ~uspansion aid uRed in a concentration from 0.05
to 0.5% by weight is required for a slurry according to the
pre~ent invention. Preferred suspension agents include a
xanthan gum which i~ a heteropolysaccharide gum isolated from
the fermentation broth of many organisms of the xanthomonas
species and is commercially available in a form suitable for
practice in this inven-
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~Z~34~
tion. Alternate gums available for suspension use which arecommercially available include guar gum and xanthan gum
combinations. Guar gums are natural polysaccaride galactomannons
produced by milling and separation of the endosperm of the quar
seed kernel, a process very similar to milling flour from wheat~
Such natural gum combinations are produced by Hercules, Inc., and
are available under the trade name Genuzan.
Alternatively, colloidal suspending clays such as attapulgite
clay, sepiolite clay, or bentonite clay may be employed as the
suspending agent. Colloidal attapulgite and colloidal sepiolite
clay produce stable susp~nsions as a result of dispersion of its
bundles of needle-shapea crystal lattice to form a random lattice
that entraps liquid to increase suspension ability of the liquid
system.
Attapulgite colloidal clays are fully discussed in "Colloi~
Grades"; ~laden W. L., and Schwint I. A.; INEC; Vol 59; September,
l967; pp 58-69. Colloidal bentonite clay is a high colloidal
plastic clay ~hich has the unique characteristic of swelling
several times its original volume when placed in water and forms
thixotropic gels in water at relatively low concentrations.
Such clays including attapulgite, sepiolite and bentonite
must be present in concentrations from 0.5% to 5% by weight;
however, clays are not preferred for this invention as they often
adversely affect the storability of the magnesium oxide suspension
slurries at high MgO concentrations.
Hydrating of MgO to Mg(OH)2, which would normally be
expected to proceed at a rapid rate in this type of MgO
suspension, is greatly retarded by the unique addition of a
surface active dispersant, lending greatly improved chemical
stability to the product, greatly modifying viscosity and also
improving viscosity stability. Lignin sulfonates are preferred
for this purpose. Calcium lignin sulfonate and sodium lignin
sulfonate are the most readily available, but any commercially
available nletal lignin sulfonate would be appropriate so long as it
~C3~9~7
gives the desired viscosity rnodification.
The lignin sulfonates as used in this instant invention are
organics deriveà from sulfite pulping oF wood. Such lignin
products normally contain lignin sulfonates of a broad molecular
size range. A product known as Norlig A from ~he Reed Lignin
Company has been shown to be an effective dispersing agent in this
intent invention. Typical analysis on a moisture free basis for
this calcium lignin sulfonate is as follows:
Total Sulfur as S %3.0
Calcium as Ca % 4.0
Sodium as Na % 0.1
Reducing Sugars % 15.7
Methoxyl % 8.9
Lignin sulfonates are avai7able commercially in either a dry
powder form or an aqueous suspension composed of 50% to 60h
solids. Either of these lignin sulfonate forms is useful in the
present invention; howeYer, the liquid form is preferable because
of its lower cost and ease of handling. Lignin sulfonate
suspensions in the 50% to 60% solids range can be employed in
concentration levels of 1.0% to 5.~% of the total magnesium oxide
slurry suspension weight. However, the preferred range for this
material is from 2.5% to 4.0% by wei~qht. On a dry lignin basis,
the additions are at levels of from 0.5% to 3.0% by weight, and
the preferred range is from about 1.2 to about 2.4% by weight of
the suspension.
Other viscosity modifiers or dispersants may be used together
with, or instead of, the lignin sulfonates. Such modifiers
include, but are not limite~ to, the tripolyphosphates, methyl
naphthaline, and sodium sulfonates.
Suspensions according to the present invention can be
manufactured using any high speed mixing equipment, whether mixing
is accomplished by pump recirculation or turbine agitatiorl. The
resulting magnesium oxide suspension slurry may have a
concentration of up to about 5~~ ~tgO by weight.
-- 6 --
When properly formulated, a product in accordance with this
invention has a shelf life in excess of twelve weeks with minimal
settling without agitation. With minor agitation or recircu!a-
tion, the magnesium oxide suspension slurry can be stored for four
to six months with the masnesium oxide content remaining
substantially as magnesium oxide and with only limited hydration
of this component to Mg~OH)2. The suspension slurry should,
however, be protected from freezing. After shipping to its point
of use, such a suspension slurry may then be utilized by addition
to an animal feed supplement comprising, for example, urea,
molasses, and phosphoric acid and/or ammoniur.~ polyphosphate, as
set forth by Jackman, U.S. 4,219,572.
The following are examples of typical formulations and
results which can be expected in terms of long term viscosity
prGperties and limited hydration of the magnesium oxide content.
Hydration is in terms of loss on ignition of dried suspension
slurry sample.
Example l: Using a high speed mixer, a suspension of the
following ingredients was prepared:
53.70% Water
43.1 0,b Magnesium Oxide
0.20% Xanthan Gum
3,00% Lignin Sulfona~e (50-60% solids)
1 00. 00%
25Periodically, over a twelve week period, the viscosity of the
suspension was measured in centipoises as follows:
~2~3 ~9~
, . _ _ . . .
Viscos;ty Icps) 225 270 21B 218 219 210
Example II: As in Example I, d suspension of the following
ingreaients ~as prepared:
53.65% Water
43.10% ~lagnesium Oxide
0.~5% Xanthan Gum
3.00% Lignin Sulfonate (50-60% solids)
1 00. 00%
The twelve week viscosity measurements were as follows:
.. ... _~ ~--_ _ _ _
Week Initial¦ 2 4 6 8 lO l2
_ I ,~ ___ .._ _ .,. ._.
Yiscosity (cps) 407 1 374 35l 354 3~1 33~ 209
~ _ _ _ ~ ~ _
Over the same twelve week period, the MgO hydra-tion was measured
as a percent loss on ignition (LOI) of a dried sample minus
organics:
~ ~ . ___ - . _
keek Initi dl 2 4 6 8
LOI 2.0l 2 45 2.l5 2.59 2 00 ~
Example III: In the same fashion, a suspension of the following
ingredients was prepared:
50.90% Water
43.lO% ~agnesium Oxide
3.00% Attapulgite Clay
3.00% Lignin Sulfonate (50-bO% solids)
1 0~
Yiscosity measurelnents over a six week period were as follows:
~ 3 ~t7
~ ~ r--r
.. . _ . _
Vlscos;ty(cps) 380 170 349 550 945 l214 1514
Indus~rial A_pl_cability
A magnesium sxide suspension slurry of this invention is an
excellent source of magnesium for complete liquii suspension
fertilizer mixtures, or for direct magnesium application in liquid
suspension on soil or forage. The stability of such a slurry
helps to maintain stable viscosities with other fertilizer
- ingredients. To ensure top blending performance when using such a
slurry in combination with orthophosphates for suspension
for~ulations, however, the phosphate should be kept at or below
12% by ~eight P205 and the magnesiunl level should be kept at
or below 2.S% by height ~lg.
The following is a typical example of a fertilizer
formulation which may be obtained using an aqueous magnesium oxide
suspension slurry prepared in accordance with this invention.
Example IV. One ton oF a 12-9-12 liquid suspension ferti1izer
containing 2.5% ~lg is prepared according to the
following formulation:
18C lbs. Water
200 lbs. Magnesium Oxide Suspension as in Example II
600 lbs. 10-30-0
35 lbs. Clay
600 lbs. Nitrogen Solution ~30%~
385 lbs. Potash
2000 lbs.
The magnesium oxide suspension may be adued at any convenient
point in the batching sequence so long as the phosphate is not in
its most concentrated condition. Thus~ if phosphate base grade is
first in the batching sequence, the magnesium oxide suspension
should be added after the phosphate base has been diluted with
water or other fertilizer ingredients.
Fertilizer formulations, as above, may include additional
fertilizer materials such as calcium, zinc, manganese, ammonium
sulfate, and especially polyphosphates, but tridl bucket batches
may be required to determine acceptable viscosity levels.
It is understood that the above description of the present
invention is susceptible to considerable modification, change, and
adptation by those skilled in the art, and such modifications,
changes, and adaptations are intended to be considered to be
within the scope of the present invention, which is set forth by
the appended claims.
