CA1249497A - Suspension of aqueous magnesium oxide - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An aqueous magnesium oxide suspension is disclosed which comprises from about 8 to about 50% by weight MgO, based on the combined weight of water, MgO, suspension aid, and surface active dispersant. Suspension aids such as zanthan gum and guar gum are utilized in the presence of surface active lignin sulfonate dispersants to provide a highly stable concentrated suspension, useful as a base for fertilizers, animal feeds, etc.

Description

~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 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 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-M " rm/l l, ~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.

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:

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, . _ _ . . .
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.

Claims (21)

1. THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
   PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
   
   l. An aqueous magnesium oxide suspension, comprising:
   water; from about 15 to about 50 percent by weight magnesium oxide ranging in size from about minus 50 Tyler mesh to about minus 325 Tyler mesh; a suspension aid selected from the group consisting of from about 0.05 weight percent to about 0.5 weight percent xanthan gum, guar gum, mixtures thereof, and a colloidal clay; and an effective amount of an anti-hydration agent.
2. 2. A suspension as set forth in claim 1, wherein said suspension aid comprises xanthan gum, and said anti-hydration agent is selected from the group consisting of lignin sulfonates methyl naphthaline, sodium sulfonate, and mixtures thereof.
3. 3. A suspension as set forth in claim 2, wherein said magnesium oxide comprises from about 33 to about 45 percent by weight of the suspension.
4. 4. A suspension as set forth in claim 1, wherein said anti-hydration agent comprises from about 0.5 to about 3.0 percent by weight of the suspension of a lignin sulfonate, on a dry lignin basis.
5. 5. A suspension as set forth in claim 4, wherein said lignin sulfonate comprises from about 1.2 to about 2.4 percent by weight of the suspension, on a dry lignin basis.
6. 6. A suspension as set forth in claim 4, wherein said magnesium oxide comprises from about 33 to about 45 percent by weight of the suspension.
7. 7. A suspension as set forth in claim 4, wherein said suspension aid is xanthan gum.
8. 8. A suspension as set forth in claim 4, wherein said suspension aid is guar gum.
9. 9. A suspension as set forth in claim 4, wherein said suspension aid is a colloidal clay.
10. 10. A suspension as set forth in claim 9, wherein the clay is selected from the group consisting of attapulgite, sepiolite, and bentonite clays.
11. 11. A composition comprising a concentrated aqueous source of hardburn magnesium oxide, consisting of: water;
    from about 15 percent to about 50 percent by weight magnesium oxide smaller than about minus 50 Tyler mesh screen size; from about 0.05 weight percent to about 5.0 weight percent of a suspension aid selected from xanthan gum, guar gum, mixtures thereof, and a colloidal clay: and from about 0.5 to 3.0 weight percent of a surface active anti-hydration agent.
12. 12. A composition as set forth in claim 11, wherein said anti-hydration agent is selected from the group consisting of lignin sulfonates, methyl naphthaline, sodium sulfonate, and mixtures thereof.
13. 13. A composition as set forth in claim 12, wherein said suspension aid comprises xanthan gum.
14. 14. A composition as set forth in claim 12, wherein said magnesium oxide comprises from about 33 to about 45 weight percent, and said anti-hydration agent comprises from about 0.5 to about 3.0 percent by weight of a lignin sulfonate, on a dry lignin basis.
15. 15. A composition as set forth in claim 14, wherein said lignin sulfonate comprises from about 1.2 to about 2.4 percent by weight, on a dry lignin basis.
16. 16. An aqueous magnesium oxide suspension, comprising:
    water; from about 15 to about 50 weight percent magnesium oxide smaller than about minus 50 Tyler mesh screen size; from about 0.05 weight percent to about 5.0 weight percent of a suspension aid; and from about 0.5 to about 3.0 weight percent of an anti-hydration agent; said suspension having a viscosity of less than about 1000 centipoise.
17. 17. A suspension as set forth in claim 16, wherein said suspension aid comprises xanthan gum, and said anti-hydration agent is selected from the group consisting of lignin sulfonates, methyl naphthaline, sodium sulfonate, and mixtures thereof.
18. 18. A suspension as set forth in claim 17, wherein said magnesium oxide comprises from about 33 to about 45 percent by weight of the suspension.
19. 19. A suspension as set forth in claim 16, wherein said anti-hydration agent comprises from about 0.5 to about 3.0 percent by weight of a lignin sulfonate, on a dry lignin basis.
20. 20. A suspension as set forth in claim 19, wherein said lignin sulfonate comprises from about 1.2 to about 2.4 percent by weight of the suspension, on a dry lignin basis.
21. 21. A suspension as set forth in claim 19, wherein said magnesium oxide comprises from about 33 to about 45 percent by weight of the suspension.