CA1077452A - Aqueous suspensions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Water-soluble salts of ethylenically unsaturated polymers function synergistically with inorganic salts to obtain superior reduction of water demand of dispersed inorganic solids. The disclosed invention is particularly adapted for use in the wet-grinding process for preparing portland cement.

Description

1~774SZ

The present invention relates to the use of particular ethylenically unsaturated polymers and in~
organic salt dispersant materials to achieve a reduction -in the water demand of finely-divided solids in water.
It relates particularly to this use as an improvement in wet process production of portland cement.
More particularly, the present invention relates to the use of particular polyelectrolytes of low mole-cular weight or styrene-maleic anhydride copolymers and -inorganic salt dispersant materials to achieve a reduc-tion in the water demand of finely-divided solids in water.
It is known that polyelectrolytes such as polyacrylic acid salts, copolymers of acrylic acid and acrylamide, hydrolyzed polyacrylonitrile and the like which are flocculants at higher molecular weights show different properties and act as dispersants at lower molecular weights show different properties and act as dispersants at lower molecular weights. Such polymers having molecular weights from a few thousand up to about 50,000, for example, have been recommended for use in various dispersant applications. See, for example, U.S. Patent Nos. 3,534,911 and 3,604,634, relating to the grinding of calcium carbonate.
Combinations of polyacrylates and certain in-organic compounds have also been used in forming foundry sand compositions and in clay benefication and drilling fluids and muds. For example, polyacrylic acids and alkali metal salts, e.g., sodium carbonate, sodium silicate and the like are disclosed in U.S. Patent No.

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17,899A-F -1-" :
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2,702,788 as resulting in increased drilling and Vi8-cosity and, hence, an increased yield of mud is obtained.
Typically, the polyacrylates are used in amounts of about 0.1 percent or more and the sodium carbonate in amounts of from about 3 percent, or more. See also U.S.
Patent Nos. 3,583,911, 2,552,775 and 3,220,946, which generally disclose similar applications. -It is also known that copolymers of maleic anhydride and divinyl ether, ethylene, propylene butylene and isobutylene or mixtures of olefins and hexadiene-1,5 function as water-loss preventives in drilling fluids.
See U.S. Patent No. 3,157,599.
The above copolymers have also been employed with alkali metal compounds in preparing beneficated clay compositions for use in drilling fluids. U.S.
Patent No. 3,216,934 teaches the use of such copolymers with from 1 to 7 percent by weight of an alkali metal salt such as, for example, alkali metal carbonates, hypo-phosphites, oxalates, phosphates, silicates, sulfites and tartrates, to increase yields of clay. Similarly, U.S. Patent No. 3,220,946 discloses the use of such maleic anhydride copolymers and certain alkali metal salts in clay benefication of sodium bentonites only.
Salts selected from the group consisting of sodium for-mate, calcium formate, calcium acetate, sodium thiocyanate, sodium sulfate, magnesium sulfate, calcium sulfate, lithium sulfate and potassium sulfate are employed to provide a postulated synergistic response with the copolymer in changing the rheological properties of clay. Salts such as sodium chloride, sodium bicarbonate, 17,899A-F -2-- ~07745Z

calcium carbonate and calcium chloride, however, are taught as being ineffective for ~uch uses.
It is also known that styrene-maleic anhydride copolymers are useful as water-demand reducing agents in the wet process for producing portland cement. Such copolymers are employed in amounts from 0.01 to 0.1 weight percent. See U.S. Patent No. 3,923,717.
A two-part study by the Portland Cement Association, Chicago Illinois, entitled "Slurry Thinners"
(Part I, Clausen et al., May 1953, Part II by Dersnah, March 1955) discloses the evaluation of various in-organic salt dispersants and mixtures thereof with other surface active agents in reducing the water content of -cement slurries in wet process applications.
Of the above prior art references only the '717 patent and the Portland Cement Association Study relate to a wet grinding process for making portland cement, wherein limestone and clay and, optionally, a small amount of iron oxide are ground in the presence of water to obtain a slurry of very fine particles.
Such slurry is then fed into a high temperature kiln where it is dried and calcined to form the clinker which is then ground to make portland cement. The water demand of the finely ground limestone-clay slurry is fairly high and usually requires a relatively large proportion of water, for example, from 30 to 50 percent by weight, usually from 25 to 35 percent, to obtain a -fluid, pumpable slurry. This limits the rate at which the slurry can be processed and fed to the kiln and it also requires a large fuel input to dry and calcine a given quantity of solids to the clinker stage.

17,899A-F -3-Many substanceæ with dispersant activity are available and have been tried in order to decrease the water demand of æuspended inorganic æolids in various high solids water suspensions or slurries for various applications. Most of theæe, particularly in the wet process for making portland cement, have proven rela-tively ineffectlve or undeæirable for one reason or another. Complex phoæphateæ are undesirable because they tend to hydrolyze at the warm temperatures developed during grinding and in storage of the slurry and because of the adverse effect of residual phosphate on the -~-properties of the final portland cement product. Ligno-sulfonates, alone and in combina~ion with inorganic salt dispersants have been tried for this use, but these require high addition levelæ for only marginal improve-ment. They alæo lose their activity rapidly during storage of the slurry. Many materials are alæo too expensive to be economically utilized in such operations.
It has now been discovered that the water demand of suspended inorganic solids necessary to make a pumpable slurry in the wet grinding process for making cement can be significantly reduced by use of a combination of water-demand reducing agents as described below.
Specifically, it has been discovered that mixtures of low molecular weight polyacrylic acid salts or mixtures of water-soluble salts of styrene-maleic anhydride copolymers and an inorganic compound such as alkali metal salts of carbonates, bicarbonates, silicates, oxalates, aluminates and borates and ammonium salts of carbonates, bicarbonates, oxalates and borates which 17,899A-F -4-` 107745,'~

form insoluble salts with calcium, are unexpectedly effective for reducing the water demand of solids sus-pended in water while maintaining desired pumpability levels of high solids-content aqueous suspensions, par-ticularly those encountered in the wet process for making portland cement. The action of the polyacrylic acid salt or the copolymers of styrene-maleic anhydride (hereinafter "SMA") in combination with the selected inorganic compound (hereinafter collectively referred to from time to time as "water-demand reducing system or agent(s)") represents true synergism, said combinations effectively reducing the water demand of suspended solids at concentrations where neither additive alone is as effective.
These water-demand reducing agents are extremely effective for reducing water demand while maintaining desired vi~cosity levels for pumping purposes in various kinds of high solids suspensions in water of finely divided minerals, particularly in raw cement slurries consisting largely of limestone and clay, usually with a small amount of iron oxide. In this latter application especially, the above-described water-demand reducing system has a unique combination of efficiency, stability and compatability in the wet grinding process slurried together with a lack of any adverse effects in the cal-cining process. A reduction in water content can be achieved so that, with the same volume feed to the cement kiln, increases in production can be obtained with lower fuel costs. Increasing the feed rate to the kiln while operating at normal fuel input results in even further 17,899A-F -5-iO7745Z

increases in clinker production. Retardation of set times are al~o obtained by use of the water-demand re-ducing system when recycle kiln dust (high in calcium oxide) is added to fresh cement kiln feed.
The invention resides in a wet process for the production of cement solids wherein limestone and clay are ground in the presence of water to form a pumpable kiln feed slurry, comprising the step of adding to said slurry an amount of a water-demand reducing system sufficient to synergistically reduce the water demand of said slurry, said system comprising (1) a water-soluble salt of an ethylenically unsaturated polymer having a molecular weight of from 1000 to 50,000 and (2) an in-organic compound selected from alkali metal salts of carbonates, bicarbonates, oxalates, silicates, aluminates or borates or ammonium salts of carbonates, bicarbonates, oxalates or borates, (1) and (2) being employed in a ratio of from 1:1 to 1:80.
The polyacrylic acid salt which can be employed in thi~ invention can be any such polymer salt having an average polymer ~olecular weight in the range of from 2000 to 50,000 and preferably in the range of from 2000 to 20,000. An especially preferred molecular weight is in the range of from 5000 to 10,000. The preferred polymer molecules are further characterized in that one-eighth one-half of them have terminal sulfonate groups. In another embodiment, polymers having a viscosity of from 75 to 150, preferably from 75 to 110, cps at 30 percent by weight solids and a molecular weight range from 5000 to 10,000 are preferred. The salt of the acid may be that of 17,899A-F -6-107745Z ., alkali metal or ammonium salts, such as sodium or potas- -sium. However, the sodium and ammonium salts are preferred over other alkali metal salts. -Polymers of acrylic acid which are useful in S this invention are readily prepared from the monomer by the action of heat, light, and/or catalysts. Catalysts -which are particularly effective for this polymerization are the organic peroxides. The properties and nature -~of the polymer can be varied over a considerable range by the proper choice of catalysts and/or reaction condi-tions. The polymer can be further modified by the addition of small amounts of copolymerization agents, such as acrylamides, acrylonitrile, methyl acrylate, ethyl acrylate, 2-methyl propenoic acid and the like. These copolymers of acrylic acid containing up to about 10 percent by weight of the copolymerization agent are useful and operable in the application of this invention.
Certain preferred polyacrylates of the present invention are most advantageously prepared by polymerizing acrylic acid in aqueous solution from 50 to 170C in the presence of a redox polymerization catalyst system.
The acrylic acid and a peroxy catalyst are separately and continuously dispersed into the aqueous medium at rates such that an effective and substantially constant concentration of the catalyst system is maintained in contact with the acrylic acid throughout the polymer-ization. A sulfite reducing agent, the preferred other component of the redox catalyst system, can be combined with the acrylic acid and the two added as a single aqueous solution, but preferably, the reducing agent 17,899A-F -7-.

.

is added separately and continuously as a third stream.
Suitable sulfite reducing agents include sodium metabi-sulfite, sodium sulfite or bisulfite, sodium formaldehyde-sulfoxylate, sodium formaldehyde hydrosulfite.
Other reducing agents can be used to obtain polymers of essentially the same molecular weight and molecular weight distribution, but which differ in not having terminal sulfonate groups and which may be slightly less advantageous in some solids suspensions.
A hypophosphite such as sodium or ammonium hypophosphite can be used as the reducing component of the redox catalyst system to obtain polymers having the same proportion of terminal phosphonate groups in place of the sulfonate groups derived from a sulfite. Other reducing agents provide the low molecular weight distribution effects although these do not supply tlle terminal sulfonate or phosphonate groups which are of added advantage, par-ticularly in reducing foaming tendencies. These reducing agents include urea, potassium thiosulfate, and oxidizable salts such as ferrous sulfate.
The peroxy catalyst component can be any peroxide useful as a polymerization catalyst. Suitable peroxides, which preferably are water soluble, include hydrogen peroxide, tert-butyl hydroperoxide, and salts of per acids such as sodium persulfate, potassium percarbonate, ammonium peracetate, sodium perbenzoate, sodium perborate, diiso-propyldipercarbonate and the like.
The concentration of peroxygen-containing catalyst can vary widely within limits from 0.1 to 10 percent based on the entire polymerization mixture and referring to active catalyst present in the system at any one time .
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during the process. Preferably, the amount of aqueous -medium and the rates of addition of catalyst and acrylic acid are adjusted so that a relatively high peroxy catalyst concentration is maintained. Total peroxy catalyst used based on the acrylic acid is preferably from 0.5 to 5 mole percent. The reducing agent is employed in at least a molar equivalent amount based on the peroxy component and preferably is used in a quantity from 20 to 100 percent excess. Both components of the redox catalyst system are preferably added as aqueous solutions of relatively high concentration. - -The aqueous polymerization medium is preferably ~-water but it may include up to about 30 percent by volume of a water-miscible organic solvent such as acetone, a lower alkanol, or dimethyl sulfoxide. Efficient stirring i of the polymerization mixture or agitation by other effective means is required so that the streams of peroxy ~-catalyst, reducing agent, and acrylic acid are quickly and thoroughly dispersed and intimately mixed in the polymerization medium. Superatmospheric pressure may be advantageous.
Other modes of polymerization may also be employed. These are well known in the art and the par-ticular process of preparing the polymers is not critical to this invention.
The polymer product is used in the form of a water-soluble salt, usually the sodium salt. Other such salts will serve as well, for example, the potassium and ammonium salts. Surprisingly, these low molecular weight polyacrylate salts in combination with an inorganic salt 17,899A-F -9-are substantially more effective in maintaining fluidity of aqueous suspensions, particularly high solids mineral suspensions, than analogous polymers of similar molecular weight. Thus, corresponding polymers such as polyacryl-amide, acrylamide-acrylic acld copolymers are inferior in this activity to the polyacrylates described herein even though these related polymers do havè dispersant properties.
Examples of other suitable water-soluble anionic polymers include trademarked products such as, for example, Dispex N-40, which is manufactured by Allied Colloids Manufacturing Company Ltd., Daxad (available from the W. R. Grace Co.) and Tamol 850 (Rohm and Haas). Other suitable materials available in acid form would include Goodrich K732 (Goodrich Tire and Rubber Co.) and Uniroyal ND2 (avaiable from Uniroyal Corp.).
The styrene-maleic anhydride copolymers which are useful in the present invention can be made by known processes such as are disclosed, for example, in U.S.
Patent No. 2,606,891; No. 2,640,891 or No. 3,085,994.
It is to be understood, however, that the process of making the styrene-maleic anhydride copolymer is not critical to this invention. Any styrene-maleic anhydride copolymer, within the molecular weight range and the mole ratio specified herein can be used, without regard to its method of preparation. The water content of the finished slurry can be as low as 25 percent and as high as 35 percent, by weight.
The styrene-maleic anhydride copolymer product is used in the form of a water-soluble salt, usually the sodium salt. Other such salts, for example, the potassium -;

17,899A-F -10--- , : -: . -- : . ;

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~077452 and ammonium salts will also serve, but not as well as the sodium salt. Surprisingly, these copolymeric salts are very effective in maintaining fluidity of the aqueous high solids mineral suspensions.
The water-soluble inorganic salts of copolymers of styrene and maleic anhydride which can be used in the present invention are those having a molecular weight of from 1000 to 5000. These copolymers are further charac-terized by a ratio of from 50 to 67 mole percent of styrene and from 50 to 33 mole percent of maleic anhydride.
The preferred copolymer molecules have a molecular weight of from 1200 to 3000 with a mole ratio of styrene to maleic anhydride of 1:1. These are particularly effec-tive as a component of the water-demand reducing system for limestone-clay suspensions used in wet grinding process for making cement.
The inorganic compound employed in the water--demand reducing system is a water-soluble salt of ammonium or an alkali metal radical which will form an insoluble salt with calcium and acts synergistically with the poly-acrylic acid salt or the SMA copolymer. The water-soluble inorganic salts which may be employed in the present invention are those which form insoluble salts with cal-cium and are selected from alkali metal salts, i.e., sodium or potassium salts, of aluminates, borates, oxalates, carbonates, bicarbonates and silicates or ammonium salts of borates, oxalates, carbonates and bicarbonates. Alkali metal silicate salts, especially orthosilicates, are -preferred as they exhibit the least tendency for the visco ity improvement to show some tendency to diminish 17,899A-F -11-1~77452 upon standing for periods of 18 hours or more although such viscosity reversion tendency is a significant factor to consider where slurries are temporarily stored prior to processing. Especially preferred are the alkali metal carbonate, bicarbonate and silicate and ammonium carbonate and bicarbonate salts. Where more alkaline slurries are employed, or where kiln dust having a high calcium oxide content is recycled to the slurry, the metal silicate and waterglass silicate salt forms are preferred whereas the orthosilicate form is desirably employed in less alkaline slurries. Similar consider-ations as to slurry alkalimity apply where less basic ammonium salts are utilized.
The water-demand reducing agents of the present invention can be added to the cement slurry sequentially or as a premixed solution. When added sequentially, it is desirable that the inorganic salt be added first, followed by the polyacrylic acid salt or by the SMA co-polymer. Preferably, the agents are added sequentially to the slurry, although the premix will be advantageous in certain situations.
In general any combinations of the polyacrylate or the SMA copolymer and of the inorganic salt which act synergistically to reduce the water demand of high solids-content aqueous suspensions are considered to be within the scope of the present invention. Generally, ratios of the polyacrylate salt to inorganic salt range from 1:1 to as high as 1:80, although ratios of from 1:1 to 1:10 are preferred. An especially preferred ratio range is from 1:1 to 1:~. A ratio of 1:4 consitutes a : .
., 17,899A-F -12-: . - : . , , :: . -preferred embodiment. Ratios of the SNA copolymer salt to inorganic salt range from about 1:1 to as high as about 1:10 although ratios of from 1:1 to about 1:6 are preferred. --An especially preferred ratio range is from 1:1 to about 1:4. A ratio of 1:3 constitutes a preferred embodiment.
The ratio employed will, as those skilled in the art will -~-recognize, vary depending upon the concentration of the ;
water-demand reducing system employed, the viscosity required for a particular operation, the grinding time, the type and composition of cement slurry being treated, and the like. Generally, in treating portland cement slurries, it has been found that concentrations of from 0.005 to 0.06 weight percent (based on slurry solids) of the polyacrylic acid salt used in comblnation with from 0.05 to 0.4 weight percent inorganic salt produce syner-gistic reduction of slurry water demand. In a preferred embodiment, concentrations of from 0.01 to 0.05 weight percent polyacrylic acid salt and from 0.05 to 0.2 weight ~- percent inorganic salt are employed. In another embodiment, polyarcylic acid concentrations of from 0.01 to 0.05 ~~ weight percent and inorganic salt concentrations of from 0.1 to 0.2 weight percent are preferred. Concentrations of from 0.0025 to 0.0125 weight percent (based on slurry solids) of the SMA copolymer salt used in combination with from 0.008 to 0.04 weight percent inorganic salt produce synergistic reduction of slurry water demand. In a preferred embodiment, concentrations of from 0.003 to 0.009 weight percent SMA copolymer salt and from 0.009 to ;
0.02 weight percent inorganic salt are employed. In another embodiment, SMA copolymer salt concentrations of - ~ .

17,899A-F -13-.

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from 0.003 to 0.006 weight percent and inorganic salt concentrations of from 0.009 to 0.02 weight percent are preferred.
Those skilled in the art will recognize that it is difficult to establish any one preferred concen-tration range for the polyacrylates or SMA copolymer and inorganic salts as this will depend upon the viscosity required for a particular operation as well as the parti-cular type of high solids suspension being treated. There are, for example, many different types of known and commercially available cement slurries of varying com-positions which can be treated according to the present invention. The desired synergistic concentrations can - readily~be determined by those skilled in the art according to known procedures and by those illustrated in the exam-ples set forth below.
In the wet process for making portland cement, the raw materials, including ingredients such as limestone, dolomite, oyster shells, blast furnace slag or other well ~20 known high calcium-containing products, are mixed with ~ -silicious materials, including slag, clay, shale or any other silica containing ingredient in amounts such that ~ -the calcium and silica materials constitute about 85 percent by weight of the clinker formed after heating in a kiln.
The remaining ingredients include aluminum-containing and iron-containing ingredients. The mixture of raw ingredients, using well-known process steps, is ground with addition of water to prepare an aqueous kiln feed slurry, which is then screened and pumped into storage tanks preparatory ~30 to further blending with other slurries or feeding into 17,899A-F -14-, , . ... , . . . ~ . ,., -,, . . ~ . .

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a clinker kiln. Usually, the portion which passes a 200 mesh screen is used for preparing the clinker. Such slurries usually contain from 30 to 50 percent by weight water.
On an emperical basis, the cements made by grinding the resulting clinker will contain SiO2 19-23%
A123 4-8%
Fe2O3 1.5-6%
CaO 62-67%
MgO .6-5%
Pumpable aqueous kiln feed slurry compositions containing from 0.005 to 0.06 weight percent (based on slurry solids) polyacrylate and from 0.05 to 0.4 weight percent inorganic salt constitute another preferred em-bodiment in the wet process for making portland cement.
Preferably, such slurry compositions contain from 0.01 to 0.05 weight percent polyacrylic acid salt and from 0.05 to 0.02 weight percent inorganic salt.
Compositions containing SMA copolymer to inor-ganic salt ratios of from 1:1 to 1:10, preferably from 1:1 to 1:4, constitute preferred embodiments in the wet process for making portland cement. Preferably, such slurry compositions contain from 0.0025 to 0.0125 weight percent SMA copolymer salt and from .008 to .04 weight -percent inorganic salt. Premix concentrate compositions containing SMA copolymer to inorganic salt ratios of from 1:1 to 1:10, preferably from 1:1 to 1:4, and most prefer-ably about 1:3, constitute additional embodiments of the present invention.

, 17,899A-F -15-' . .

The following examples are presented to illustrate the invention, but are not to be construed as limiting it in any manner whatsoever. The weight percent of water-demand reducing agents, unless other-wise specified is based on the solids present in the slurry being treated.
Example 1 The following illustrates the preparation of a polyacrylic acid which may be utilized in the present in-vention.
A reaction flask having multiple inlets and equipped with an efficient stirrer was charged with 1600 ml. of water and the water was heated to boiling. At this point, separate streams of 25 percent aqueous sodium persulfate and 25 percent aqueous sodium metabisulfite -were started into the boiling water. After 1-2 minutes, a third stream of acrylic acid was started into the boiling and agitated solution. All three streams were continued at essentially constant rates under the above conditions so that in about 90 minutes there had been added 1250 gm. of acrylic acid (17.3 gm. moles), 400 gm. of 25 percent aqueous metabisulfite solution (0.526 gm. mole), and 300 gm. of 25 percent aqueous persulfate solution (0.315 gm. mole). Rates were calculated so that addition of acrylic acid was completed 1 to 2 minutes before all of the persulfate and bisulfite had been added.
The reaction product was a clear, slightly viscous solution. To it was added about the theoretical quantity of 50 percent aqueous NaOH to convert the poly-acrylic acid product to its sodium salt, having final 17,899A-F -16-. , ~7745Z
. .
pH about 10. Vapor phase osmometric and membrane osmometric analysis of the product after dialysis to remove inorganic salts indicated respectively that the polymer (sodium form) was polyacrylic acid from 5000 to 10,000 molecular weight S and a viscosity of from 75 to 110 cps at 30 percent solids.
Elemental analysis indicated that about one-fourth of the - polymer molecules were terminated by a sulfonate group.
Example 2 - Various commercial samples of portland cement slurries were treated with polyacrylic acid salts and inorganic salt dispersants, both alone and in combination and the degree of reduction in water-demand of the dispersed solids was determined. In typical operations, a sample quantity of a ground, undried cement slurry is filtered to concentrate the same and raise the slurry solids content. About 100 ml. of such concentrated slurry is then stirred vigorously and the viscosity is deter-mined with a Brookfield Helipath ~iscometer. The slurry sample i8 diluted with a measured volume of filtrate, usually O.S ml. to S.0 ml., mixed and the viscosity re-determined. This process is repeated until a viscosity of less than about 4000 cps is obtained. Approximately 10 gms. of each slurry sample is weighed, evaporated to dryness at about 120C and reweighed. From the percent solids 80 obtained, a control logarithmic plot of vis-cosity versus percent solids is prepared and the percent solids at 4000 cps, (a viscosity value which is in the range preferred for pumpability in the wet process pro-duction of portland cement) is determined.

17,899A-F -17-., .

Inorganic salt test reagents are added to the cement slurry as received and the slurry concentrated as above and the viscosity versus solids plot determined.
The polyacrylate test materials or polyacrylates in combination with the inorganic salt are added to the cement slurry after the same has been concentrated as filtration of the cement slurries containing these addi-tives are well dispersed and are difficult or impossible to filter. Viscosity and solids determinations are -similarly plotted. ~
Comparisons of the solids density determinations -at 4000 cps for the untreated control slurries with slurries treated with each dispersant above and in com-bination can then be made to determine the degree of reduction in the water-demand of suspended solids.
In operations employing the above procedures, ~
samples of portland cement slurry (obtained from the ;
Oregan Portland Cement Co.) were treated with: -(1) 0.05 percent of the polyacrylate of Example -`
1 above;
(2) 0.2 percent of sodium carbonate (added before the slurry is concentrated);

(3) 0.2 percent sodium carbonate (added before the slurry is concentrated) and 0.05 percent ~
of the polyacrylate of Example 1 above; -

(4) a premixed combination of the same ingred-ients and amounts thereof used in (3).
The untreated cement slurry was found to have a solids density of about 63.25 percent at a viscosity of 4000 cps whereas the slurry treated with the polyacrylate 17,899A-F -18-alone (1) was determined to have slightly increased solids density of 65.8 pexcent at 4000 cps. The slurry (2) treated with sodium carbonate alone was determined to have a solids - desnity of about 66.6 percent. However, ~he slurry treated with sodium carbonate followed by the polyacrylate (mixture -3) unexpectedly exhibited a dramatic increase in solids density to 78.8 percent at 4000 cps. The same agents added as a premix (mixture 4) also caused a great increase in solids density to 76.5 percent at 4000 cps.
By comparison with the untreated control sample and the samples (mixtures 1 and 2) treated with only one . :.
of the water-demand reducing agents, the synergistic effect of the sodium carbonate - sodium polyacrylate combination in reducing water demand of the suspended solids and ~-:
increasing solids density at comparative viscosities is evident.
The slurry solids density for mixture (3) was increased (absolute values) by about 15 weight percent over the untreated control and from 12 to 13 weight percent over the slight improvements seen with mixtures (1) and (2). Relative gains of about 24.5 percent, 19.7 percent and 18.3 percent, respectively, over the control and mixtures 1 and 2 were thus obtained by mixture 3. The solids density for mixture (4) similarly increased about 13.2 weight percent (absolute) over the untreated slurry and about 10.7 and 9.9 weight percent over mixtures (1) and (2), respectively, thus amounting to relative gains of about 20 percent, 16.2 percent and 14.8 percent, respectively, over the untreated control and control samples 1 and 2.

17,899A-F -19-~07745Z

Example 3 In operations employing the procedures described in Example 2, samples of the same portland cement slurry were treated with sodium ortho silicate and sodium poly-acrylate water-demand reducing agents. The untreated control slurry had a solids density of 64.1 weight percent at 4000 cps while a slurry sample treated with 0.2 percent sodium ortho silicate had a solids density of about 64 - -weight percent at 4000 cps (thus having no affect on the slurry). A slurry sample treated with 0.05 weight percent sodium polyacrylate had a solids density of about 65.8 weight percent at 4000 cps. The slurry sample treated with 0.2 weight percent sodium ortho silicate was concentrated and 0.05 weight percent sodium polyacrylate added thereto, with the resulting slurry having a solids density of about 76.3 weight percent at 4000 cps, or a total gain over the untreated control and silicate treated control of about 19 percent and a gain of about 16 percent over the poly-acrylate-treated control. In an additional run, the silicate and polyacrylate were premixed and then added to the slurry. The resulting slurry had a solids density of about 75 weight percent.
Example 4 Samples of the portland cement slurry in Example 2 were treated as in Example 2, the untreated control sample having a solids density of 65.2 weight percent at 4000 cps and control~sample treated with 0.05 percent sodium polyacrylate having a solids density of 66.7 percent at 4000 cps. A control sample treated with 0.2 weight percent sodium oxalate was found to ; , ' `'.

17,899A-F -20-- : -. -,-- '' . ', -' ' ' . - ' . , ., - ~.............. - ~... , .. , ~ , ~07745Z

have solids density of 68.0 at 4000 cps. Concentration of the latter sample and addition of 0.05 weight percent sodium polyacrylate resulted in a slurry having a solids density of about 76 weight percent at 4000 cps. A
slight reversion in the slurry viscosity was noted after -a period of about 18 hours.
Example 5 A portland cement slurry (obtained from the Calaveras Cement Co.) having about 80 parts limestone, about 8 parts silica, about 10 parts clay and about 2 parts iron oxide was treated according to the procedure set forth in Example 2. The untreated control slurry was found to have a solids density of about 65.2 weight percent at 4000 cps. Addition of 0.05 weight percent sodium polyacrylate raised the solids density at 4000 cps to 68.6 weight percent while addition of 0.2 weight percent Na2CO3 to another sample raised the solids density to 70.4 weight percent at 4000 cps. Concentration of the latter sodium carbonate treated sample and addition . .
thereto of 0.05 weight percent sodium polyacrylate gave a slurry having a solids density of about 80.3 percent at 4000 cps, an increase in solids density over the other control samples varying from 10 to 15 weight percent, or total gains in density of from 14 to 23 percent.
: 25 Example 6 Additional evaluations utilizing portland cement slurries from the Calaveras Cement Co. were carried out as in Example 2 and the results are set forth in the following . Table I.

.

17,899A-F -21-1077~5Z

TABLE I
% SOLIDS DENSITY AT 4000 CPS -% % Sodium Polyacrylate ControlNa2CO3 0% .005~ .01 .02 .04 .08 ~ -. _ .
67.8 0 67.8 68.5 69.4 69.7 70.5 75.1 68.3 0.05 72.1 74.3 74.5 75.3 79.6 80.3 68.1 0.1 74.9 77.0 77.8 80.0 80.6 80.9 67.7 0.2 75.7 76.7 77.9 80.4 80.6 80.4 % . ~ -4 3 `~ ~
: . , 67.3 0 67.3 68.5 68.7 69.6 71.3 76.9 67.9 0.1 71.7 77.5 78.5 79.8 -- --66.0 0.2 70.1 -- -- 78.0 79.0 79.6 67.7 0.4 73.8 75.1 76.2 77.2 -- --- .. ~
The foregoing experiments demonstrate the syner- -gistic action of polyacrylates with inorganic salts as herein designated in discussing the water-demand of high solids density cement slurries. The reduction in water content provides cement slurries which have a higher solids loading per given volume of slurry and which can readily be pumped to the clinker kiln. Thus, equal volume feed rates of cement slurries treated according to the present invention provide for an increase in clinker production without increasing fuel costs for the calcination operation. The synergistic combinations of the present invention possess additional economic advantages in that relatively expensive polyacrylates can be used at rates which do not render their use prohibitively expensive.

17,899A-F -22-~07745Z

Example 8 A wet portland cement slurry obtained from a commercial source contained about 34 percent by weight water. The viscosity was determined by a Brookfield LTV :
viscometer employing a number S spindle at 20 RPM after : :
60 seconds of stirring. As received, this slurry was determined to have a viscosity of about 16,800 cps. A
30 weight percent aqueous solution comprising one part of the disodium salt of a 1:1 mole ratio of styrene-maleic anhydride copolymer having a molecular weight of about 1600 and three parts by weight Na2SiO2 was added in varying small amounts to samples of the slurry and the viscosity determined as above. The following results (weight percent being b~ ed on slurry solids) were recorded:
.' ' ':
~ ' 17,899A-F -23-~ . ~

TABLE II
Weight % Weight ~Viscosity :
Run No. SMA Copolymer 2 3 cps 1 * 0 0 16,800 2 .0028 .0085 9,200 3 .0057 ` .0170 3,000 4 .0068 .0205 2,000 .0079 .0239 1,000 6 .0091 .0273 500 7 .0102 .0306 ~340 8 .0113 .0341 ~200 .: .
9 .0114 0 9,800 --.0227 0 4,500 : -11 .0273 0 3,400 12 .0318 0 2,400 :
13 .0364 0 1,800 ::- :
14 .0409 0 1,200 .0455 0 800 :
-* = control Comparing runs 2 to 8 with runs 9 through 15, it is seen that the total concentration of the SMA-Na2SiO3 ~ : -system i8 the same as.the concentration of the SMA copolymer utilized alone. The synergistic effect of the SMA-Na2SiO3 system is evident from these data, the SMA-Na2SiO3 system requiring only about one-~ourth (or about a 75 percent decrease) the concentration of the expensive SMA copolymer to obtain slurries having (a) substantially the same or better viscosities than obtained with the SMA copolymer '' . ..

17,899A-F -24--` ~077452 alone in larger quantities, and (b) the same water con-tent as the high viscosity control sample but which instead have viscosities whiçh render the slurries readily pumpable.
The above experiments again demonstrate the syner-gistic action of the water-demand reducing system of the present invention in lowering the high viscosity (without addition of water) of the higher solids density slurries to manageable ranges, thus providing for the use of slurries -having higher solids densities and attendant benefits as -discussed herein.
In commercial operations, the water-demand reducing system is usually added once the slurry or slurries are formed in the grinding operations. Preferably, the system is added to the slurry formed after grinding.
Similar results can be obtained with SMA copoly-mers and inorganic salts specified herein. Having disclosed our invention, it is apparent to those skilled in the art that modifications may be made which do not depart from the spirit of the invention. The specific experiments presented in this disclosure are illustrative of the invention and are not intended to be limitations upon the true scope of the invention.

17,899A-F -25-

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A wet process for the production of cement solids wherein limestone and clay are ground in the presence of water to form a pumpable kiln feed slurry, comprising the step of adding to said slurry an amount of a water-demand reducing system sufficient to synergistically reduce the water demand of said slurry, said system comprising (1) a water-soluble salt of an ethylenically unsaturated polymer having a molecular weight of from 1000 to 50,000 and (2) an inorganic compound selected from alkali metal salts of carbonates, bicarbonates, oxalates, silicates, aluminates or borates or ammonium salts of carbonates, bicarbonates, oxalates or borates, (1) and (2) being employed in a ratio of from 1:1 to 1:80.

2. The process of Claim 1, wherein (1) is a polyacrylic acid having a molecular weight of from 2000 to 20,000.

3. The process of Claim 1, wherein (1) is a polyacrylic acid having a molecular weight of from 5000 to 10,000 and a viscosity of from 75 to 150 cps at 30 percent solids.

4. The process of Claim 1, wherein the inorganic compound is an alkali metal carbonate, bicarbonate or silicate, or ammonium carbonate or bicarbonate.

5. The process of Claim 2, wherein the poly-acrylic acid and the inorganic compound are employed in ratios of from 1:1 to 1:10.

6. The process of Claim 2, wherein the poly-acrylic acid salt is employed in concentrations of from 0.005 to 0.06 weight percent and (2) is employed in con-centrations of 0.05 to 0.4 weight percent.

7. The process of Claim 1, wherein (1) is a water-soluble salt of a styrene-maleic anhydride copolymer and wherein (1) and (2) are employed in a ratio of from 1:1 to 1:10.

8. The process of Claim 7, wherein the copolymer has a molecular weight of from 1000 to 5000.

9. The process of Claim 2, wherein the copolymer is characterized by a ratio of from 50 to 67 mole percent of styrene and from 50 to 33 mole percent of maleic anhydride.

10. The process of Claim 7, wherein the copolymer has a molecular weight of from 1200 to 3200 with a mole ratio of styrene to maleic anhydride of 1:1.

11. A pumpable kiln feed slurry prepared in accordance with the wet process of Claim 1 to produce portland cement.