DD212727A5 - PROCESS FOR IMPROVING THE PROPERTIES OF A POWDER - Google Patents

Abstract

An iron (II) sulfate hydrate product for use as a chromate reducing agent for dry cement is obtained from a commercial or commercial ferrous sulfate heptahydrate by e. or more treatments made, selected from mild drying, powder dipping, physical absorption and chemical absorption. The technical ferrous sulfate heptahydrate is blended in particular with fly axis or gypsum and subjected to mild drying at temperatures in the range of 20 to 60 degrees C.

Description

Berlin, 2.3.1984 63 221/17

Process for improving the properties of a powder

Field of application of the invention .

The invention relates to a method for improving a powder, in particular a method for producing a dry cement mixture.

O

Characteristic of the known technical solutions

In the European patent application Ur. 81110557.6 (publication IJR "0054314) is a method for preparing a dry Zementmischung.mit a reduced ode ^ r substantially eliminated content of water soluble chromate described which comprises milling a starting material \ containing a cement binder clinker and

having a content of water-soluble chromate, and adding a chromate reducing and / or neutralizing agent in a non-dissolved state and in an amount of from 0.01 to 10% by weight, based on the weight of the starting material, during or after milling to eliminate or substantially reduce the level of water-soluble chromate. The preferred reducing agent mentioned in the abovementioned patent application is iron (II) sulfate (FeSO ₄ .nH ₂ O), where η is normally the number 7, which is preferably provided with an oxidation-preventing coating A product of this type is a FeSO ₄ .7H ₂ O which is provided with an oxidation-preventing coating which also gives this particulate material suitable free-flowing properties.

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lends so that it can be conveniently stored and used in connection with the production of the cement product. For example, the product may be stored in silos, taken from and pneumatically transported, and the like. All of these handling properties depend on the ability of the product to be free-flowing and protected against excessive oxidation. Also, the coating tends to reduce the corrosivity otherwise associated with ferrous sulfate heptahydrate.

Although the above specific 9% FeSO. 7 H ₂ O product gives excellent results in the product described in the above European patent application and a cement product in which the added ferrous sulfate can completely reduce the released chromate ions, it would be advantageous to have a cheaper and lighter one be able to use available reducing agent in the process described in the aforementioned European patent application in view of the fact that the process is carried out on an industrial scale and large amounts of the reducing agent are consumed. It would also be desirable to further reduce the corrosivity of the iron (IIS sulfate reducing agent.

The normal commercial or technical iron (II) sulfate is a heptahydrate without the abovementioned coating. This heptahydrate contains a small amount of water and thus tends to become "snowy" (it resembles very melting snow) and it tends to cake or agglomerate when handled and confused in silos and hopper bins! * These properties make the commercial or technical ferrous sulfate heptahydrate for storage

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in ^ iioa and for pneumatic transport and the like, unsuitable; Therefore, the commercial or technical, ferrous sulfate in practice as a reducing agent in the. A further disadvantage is that technical or commercial ferrous sulphate heptahydrate has increased corrosivity compared to the coated iron (II) sulphate heptahydrate.

In the present application, the term "iron (II) sulfate heptahydrate ^{11 is} used to characterize the starting material.""Some of the treatments described below may result in the removal of a portion of the water of crystallization as is well known, but it is essential that the product properties of its water solubility B- substantially reserves, which are characteristic of the heptahydrate, and for convenience, the product is therefore characterized in the description and claims herein as heptahydrate or simply hydrate '.

Applicants have now tried to use iron (II) sulphate heptahydrate H! 'Subjecting drying processes to reduce its corrosiveness and to achieve free-flowing properties. However, Ea has been found to degrade the chromate-reducing ability of ferrous sulfate heptahydrate by the normal drying processes (some of the ferrous ions are oxidized to ferric ions during drying), and in the normal drying processes, too Tendency to cause agglomeration of the technical ferrous sulfate heptahydrate.

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Object of the invention

The aim of the invention is to avoid the oxidation of iron (II) sulphate heptahydrate,

Explanation of the essence of the invention;

The object of the invention is to achieve ^ that the Chromatreduktionsvermögen is substantially maintained and to achieve a favorable effect on the free-flowing properties of the product by mild drying.

In one aspect, therefore, the present invention relates to a process for producing a dry cementitious mix comprising milling a feedstock containing a cement binder clinker having a water soluble chromate content and adding a chromate reducing and / or neutralizing agent in a non-gelling dissolved state and in an amount of from 0.01 to 10% by weight, based on the weight of the starting material, before, during or after the grinding, in order to eliminate or substantially reduce the water-soluble chromate, wherein the reduction and / or neutralizing agent is an iron (II) sulphate hydrate product having a high ratio of ferrous ion to total iron and low corrosivity which has been prepared from a commercial or commercial ferrous sulphate heptahydrate product which has the inclination , in handling and storage in silos and feed hoppers zusa bake it, making sure that the loosely bound water of the product is not available due to mild drying for caking. The

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Drying is preferably carried out at a temperature of at most 120 ^° C., in particular of at most 80 ^° C., more preferably of at most 60 ^° C., and especially in the range of approximately. 20 to 60 ⁰ C performed,.

however, in most practical applications in connection with the above-mentioned process, it is preferred that the loosely bound water of the iron (II) sulfate heptawhydrate product be rendered unavailable by absorption in a physical or chemical manner as a cause of caking of the product.

In this context, by the term "physical or chemical absorption" is meant any absorption of water at a surface of a material or in the interstices in the matietal or interstices and on the surface of a material, and the chemical absorption refers any chemical reaction that removes the water, usually by combining it with the loosely bound water,

In its broadest aspect, the measures to make the loosely bound water unavailable as a cause of caking include one or more treatments selected from mild drying, powder dilution, physical absorption, and chemical absorption. "

The preparation of the dry cementitious mixture which comprises milling the starting material containing a cement binder clinker and adding the chromate reducing and / or neutralizing agent in a non-dissolved state,

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γ / during or after milling, as described in the above-mentioned European Patent Application Hr. 81110557.6 described.

In accordance with the present invention, a preferred method for absorbing the loosely bound water is to mix the technical or commercial iron (II) sulfatheptahydrate with a water absorbing material to obtain the resulting bis (II) sulfate hydrate by diluting the powder with an oxidation inhibiting powder The water-absorbent material may typically be a powder having a specific surface area greater than about 2000 cm / g, and is typically an inorganic material made from by-product materials. gypsum, filter dust and other products readily available in the cement industry (including cement). These are usually: the material to make a mixture of two or more of the above mentioned products,

The amount of water-absorbing material may vary within wide limits, for example, from 1 to 95% based on the resulting product.

A particularly useful and inexpensive water absorbing material is plug ash from coal power plants, it has been found that this fly ash has a specific surface area (measured by the method of Blaine) of about 2,000 to 3,000 cm / g, especially about 3,000 to 8,000

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, 4000 cm / g, is very suitable for absorbing the loosely bound water from the oleic (II) sulphate heptahydrate with complete retention of the reducing power of the ferrous sulphate heptahydrate. It has also been found that the fly ash has the pH of the Ferrous sulfate heptahydrate, which means that the fly ash treated ferrous sulfate heptahydrate has significantly less corrosivity compared to the starting VJ ferrous sulfate heptahydrate.

Another effect of adding a relatively large amount (about 20% by weight or more) of powder is that the iron (II) sulfate heptahydrate is diluted by the intervening particles of the powder, further counteracting agglomeration. The plug-in pouch is preferably calculated in an amount of 20 to 70 % _t, in particular in an amount of 40 to 70 %, preferably of about 50 % ₉ . to the total mixture, added.

Another interesting material with which the powder dilution of ferrous sulfate heptahydrate can be advantageously carried out is gypsum, either as such or in its less hydrated forms, which are hemihydrate and anhydrite, or in the form of a mixture from zv / ei or all these forms. It has been found that according to a specific embodiment of the invention, the gypsum, hemihydrate or anhydrite preferably has a pH of at most 7, in particular a pH in the range from 5 to 7, especially a pH of etv / a 6 when added to iron (II) sulphate heptahydrate.

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The powder dilution is usually carried out by mixing in a suitable mixing device, for example a paddle mixer or a kneader, or even in a high shear mixing or grinding device, but under conditions where excessive heating of the mixed material does not occur. , The material with which the i.sup.3 (II) sulfate heptahydrate is mixed may be initially in the form of a powder or in porin from the light of an agglomerated powder which is incorporated into powder-sized particles during mixing, or it may be incorporated into ^ orm of granules which are comminuted during mixing to powder size

Optimum results were obtained using a combination of mild drying and addition of an absorbent material. In this case, it is preferable to mix the iS-iron (II) sulfate heptahydrate and the absorbent material with each other and then to carry out the mild drying with the mixture thus obtained. It has been found that the addition of fly ash in an amount of 20 to 70% f, for example, from 40 to 70% _t particularly in a "amount of 'about 50%, based on the total mixture, followed J by a mild drying at no more as SO ⁰ C, in particular a drying at a temperature of about 20 to 60 ⁰ C, leads to a very suitable free-flowing powder with full retention of the reducing power and the reduced corrosivity. Gypsum, hemihydrate, anhydrite, or mixtures of two or all of these components may also advantageously be used in an amount of 20 to 70%, usually 40 to 70%, in particular in an amount of about 50% _t based on the total mixture, are added , followed by the same mild drying process.

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One important finding is that with materials that are waste products or readily available cheap products of the cement industry, the readily available and inexpensive sis (II) sulfate heptahydrate can be modified to a form that is easy to handle and meter in to cement and yet retains almost the full reducing power of ferrous sulfate heptahydrate. The total amount of the 2-acid (II) sulfate hydrate-containing composition of the invention added to the cement is of the order of 0.01 to 10 wt%, preferably of the order of 1 wt%, and this means the small amount of additive introduced into the cement together with the (II) sulfate hydrate does not result in any significant change in the properties of the finished cement product. If the powder to which the bis (II) sulfate heptahydrate is treated is plug ash or gypsum, it is noteworthy that plug ash and gypsum are considered desirable additives in cements.

embodiment

As is apparent from the following embodiments, calcium oxide can absorb the loosely bound water in a relatively small amount; this is due to the chemical reaction with the V / ater to form calcium hydroxide _e Although calcium is therefore able to absorb the loosely bound water of the iSisen (II) -sulfatheptahydrats, the resulting product, when calcium oxide used as the sole additive is usually not optimal for handling and dosing and it is often preferred not to use calcium oxide as a single additive, but rather with other materials.

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like ζ, B. plug pocket, which gives the product a higher degree of volume or mass ·

Bs is also possible to use a combination of plug ash with other materials, the loosely bound water absorb, 'z, as filter dust, bentonite, slag, etc. · It has been found that "cement as such is not the optimum absorbing powder and that its lime has a very high reactivity with the (II) sulphate when used alone, but this does not preclude the incorporation of cement and lime as components of a multicomponent material.

In accordance with the teachings of the present application that iron (II) sulfate heptahydrate can be effectively modified to a free flowing powder while retaining its reducing power by adding an absorbing or reactive substance and / or by drying, it is within the skill of those in the art Field of Combining the Measures to Achieve Optimum Combination of Free-flowing Properties, High Reducing Capacity, and Low Corrosivity. The presently preferred measures currently appear to be the combination of addition of about an equal amount of plug-in having a specific surface area of about 3000 to 4OOO cm / g or gypsum, hemihydrate and / or anhydrite, the compulsory mixing of the components, for example in a paddle mixer, and the mild drying of the resulting granular product

The granule product resulting from this process may be characterized as a substantially free-flowing powder of ferrous sulfate hydrate in admixture with plug ash or gypsum.

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wherein the iron (II) sulphate hydrate of the mixtures is readily soluble in water and a high ratio of salts (II) ions, for example greater than 80 %, preferably greater than 90 %, to the total iron content in the acid Normally, the iSisen (II) sulphate hydrate in the composition according to the invention has a substantially higher pH compared to the untreated iron (II) sulphate heptahydrate, the pH increasing in the Re'gel 1 pH unit or more, resulting in a decrease in the corrosivity of the product.

When used in the above process for reducing the water-soluble chromate content of cement, the inventive composition is used in the same manner as described for the iron (II) sulfate heptahydrate product used in the above-mentioned European patent application, but usually becomes larger Amounts used in accordance with the lower content of iron (II) ions due to the content of absorbing or reacting powders in the product.

Bine suitable plant for producing a bis (II) sulphate heptahydrate Zusan composition according to the invention is a paddle mixer with a JSntstaubungseinheit, in which the technical JSisen (II) sulfate heptahydrate with the material in the cone fly ash, can be mixed in conjunction with a drying drum into which the mixture is transferred after thorough mixing. If necessary, the dried product may be subjected to disintegration and thereafter the resulting free-flowing, stable oil (II) sulfate heptahydrate composition may be subjected to disintegration.

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with reduced corrosivity in the same way as the coated bis (II) sulphate heptahydrate product described in the above European patent application is stored and handled »

According to an embodiment of the invention in which the bis (II) sulphate heptahydrate is mixed with ^ ips, hemihydrate and anhydrite (or any mixture thereof) which is to be used as "starting material for the production of cement" in this case, it may be preferable in certain cases not to carry out any additional drying), the mixing ratio may, if desired, be adjusted so that the resulting mixture is directly suitable for addition to the cement as a total gypsum additive to the cement in question The type of cement to be produced may be the mixing ratio between iron (II) sulphate heptahydrate and gypsum, hemihydrate, anhydrite or a mixture of two or all of these components between 1: 2 and 1:50, preferably between 1: 5 and 1 ί 20, for example about 1: 10 amount *

) Although indicated in the present application in detail how an absorbent ¹ material, in particular plug ash can be used for solving the problems of agglomeration and acidity, the isenilljsülfatheptahydrat occur in an industrial or commercial ^ that as a reducing agent for addition to cement before, is used during or of the same after grinding ,, in order to eliminate the water-soluble chromate i _n d _em cement during the use of the cement according to the invention, other reducing agents that are used for the same purpose in a similar '''/ else and can where similar

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Handling problems related to caking or agglomeration and / or acidity are converted into a readily dispersible form having similar advantages as described herein by blending with an absorbent powder, especially an absorbent powder comprising fly ash , in the manner described herein, suitably combined with drying as described herein, and the improvement of these other reducing agents is within the scope of the present invention.

(Referred to in the examples äexi A ₉ 5 and 6) The reserve potential at Chromätreduktionsvermögen a cement, i.e., "h · the ability of the cement to reduce further amounts of chromate, can be determined by the following method:

30 g of the cement are stirred for 15 minutes with 30 ml of a solution containing 100 mg of Cr ⁶ VI. After filtering. the amount of Cr ⁺ in the filtrate is colorimetrically submerged

Application of the diphenylcarbazide method measured and expressed as ^ P mg Cr Vkg cement (M100).

The above procedure is repeated using a new portion of cement and a solution containing 50 mg Cr / 1, the amount of Cr is again expressed in mg Cr / kg cement (M5Ö).

The reserve potential for chromate-reducing capacity of the cement can then be calculated from the following formula:

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; . 50 χ Μ50 ν.

R »(50 '-) mg Cr ⁰⁺ Ag

- - MIOO - Μ50 ...

Example 1 .

In a laboratory paddle mixer, 1.5 kg of technical grade ferrous sulfate heptahydrate was mixed with an equal weight of ^J fly ash from a coal power plant, the plug ash having a specific surface area, as measured by the Blaine method, of 3300 cm / g. The mixing was continued for 5 "min.

After mixing, the resulting product was subjected to mild drying at 40 ^° C to a weight loss of 1.3%. Thereafter, the product was a dry, free-flowing powder with a rope size of about 0.5 mm.

Similarly, the Sisen (II) sulfate heptahydrate with \ 3 wt .-%, based on the -Sisen (II} sulfate, mixed pulveiförmigem calcium oxide, laughing mixing, the mixture was subjected to moderate drying at 40 ⁰ O. Again, there was obtained as a result, a free-flowing dry powder. The particle size was about 0.5 mm.

For these powders, the reducing power, measured as the content of Pe ⁺ in % of the total iron content, was determined by - »titration with potassium dichromate. Also, the pH of a 1% slurry was determined. The results are given in the following Table I.

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Table I Amount, based on the iron (II) sulphate heptahydrate , pH of a 1% slurry powder addition 100 % 3 % Reduction risks 5.1 3.5 - 4.0 Plug ash calcium oxide 99 % 97 %

f "\ is clear from the above data, that the addition of Plug ash to a dry powder under virtually complete retention of the initial reducing power of the iron (II) sulfatheptahydrats and having a pH value of 5.1» of a considerable increase compared to the original represents .pH value (3.3) of the technical ferrous sulfate heptahydrate, *

Calcium oxide (3 %) also results in a dry powder while retaining the reducing power, but not with the same pH increase.

Similar experiments were carried out with other materials including 10 % bentonite, which resulted in retaining the full reducing power, but the amount was obviously not sufficient to achieve free flowing properties of the resulting powder. Based on these results, it is reasonable to assume that a slightly higher amount of bentonite would give a satisfactory result.

Example 2

In a granulator-disk mixer, technical

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(II) sulphate hydrate with an equal weight of plug ash with a specific surface area (determined by the

· '2

Blaine method) of 4250 cm / g mixed and the mixture was passed through a drying drum. The results of these experiments, which were carried out on a pilot scale, are given in the following Table I:

Table II

Trial No.

test conditions

Intake air outlet air Hur ⁵ air production ^Ü C. ⁰ C per min kg / h

1 40,7 '29,3

2 39.9 28.5

3 no drying

34 34

11,4 13,7

The properties of the products obtained are given in the following Table III.

table III Reduction capacity pH of a 1% slurry Experiment No. T ^Jl 'powder properties 89 % 92 % . 88 % 4.4 4.0 4.5 1 2 3 Example dry, free flowing dry, free flowing slightly damp 3

In a mill plant for the production of cement with two cement mills connected in Heihe, iron

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, (II) sulfate heptahydrate mixed with fly ash and prepared as indicated in Example 2, Run No. 2, added to the second mill. The product was mixed by means of a hopper and a weigh-in feeder. From the weigh-in feeder, the product was transported by pneumatic transport over a distance of about 1 = 50 m to the inlet to the cement mill. The dosage was about 1 hour for 20 minutes {._) . carried out and the total consumption of the product was about 800 kg.

During the experiment, samples of the ferrous sulfate / KLugasche product were taken and every 10 minutes samples of cement were taken after the primary cement mill (without addition of the ferrous sulfate / plug ash product) and after the secondary mill (after addition of the EisendlJsulfat / KLugasche product) taken j.

The addition per hour of product was 583 kg to a cement / plug ash product of about 84 t / h cement and about 4 t / h of added fly ash. This corresponds to a dosage of about 0.7 % of the iron (II) sulfate / fly ash product .

Ea , it was found that the product in the hopper was as free flowing as the coated ferrous sulfate product normally used as the reducing agent and metered in by the same metering device. Overall, the iron (II) was sulfate / plutasche Product less dusty and comfortable to handle.

Table IV below shows the differences between

• · • a

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indicated suchs samples taken and it is the content of ^water-G hromat in the cement samples, as measured after one day, after 8 days, or ' indicated after 14 days respectively.

From the results given in the table it can be seen that the reference sample (after the primary mill) contains on average 6.2 mg Cr / kg cement and that the addition of about 0.7 % of the iSisendl sulfate / plug ash product, corresponding to about 0, 35 % PeSO. · 7H ₂ O, leads to a complete reduction of the content of water-soluble chromate compounds in the cement after the secondary cement mill.

Table IV

Sample content of water soluble ¹ - ~ chromate (mg Cr per kg) after -.

Day

meet

14

meet

Cement after the primary cement mill 2 • 11.20 a.m 2 6.0 11:30 2 5.8 11:40 2 6.0 11:50 2 6.2 12.00 p.m. - ' 6.2 12:10 2 - 12:20 2 6.4 12:30 6.5

6.0 6.0 5.8 5.8 6.0, 6.0 6.2 6.2 6.2 * 6.2 6.4 6.4 5.5 6.5

• a

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Table IV (Port setting)

Sample content of water-soluble kg chromate (mg Cr per kg) after

2 • 1 day 8 days 14 days Cement after the secondary cement mill 2 Time: 10 11.20 a.m. 10 0.4 0.4 0.4 11:30 10 <0.1 <0.1 <0.1 11:40 10 <0.1 C 0.1 ^ 0.1 11:44 3x2 4 ^ 0.1 £ 0.1 <0.1 11:55. 10 <o.i <0.1 <0.1 12.05 p.m. 10 <0.1 ^ 0.1 <0.1 12:10 10 <0.1 <O. 1 * 0.1 12:15 10 <0.1 ^ 0.1 <0.1 12:20 <0.1 ^ 0.1 ^ 0.1 12:25 <0.1 <O. 1 <0 · 1 15:00 ^ 0.1 <O. 1 0.1 at the. = in the morning " p.m. = noon Example 4

Continuing the experiments described in Examples 2 and 3, a production test was carried out on an industrial scale. In a paddle mixer / kneader unit, technical grade bis (II) sulphate heptahydrate with an equal weight of fly ash with a specific weight

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see surface area (determined by the Blaine method) of 3700 cm / g blended and the mixture was dried by passing it through a drying drum equipped with cams to promote contact between the drying air and the material stream. The drying air was measured by a gas heating unit, which was mounted on the iändhaube the drying drum, heated "During the test period ^{WUR {3e,} the outlet air temperature between 65 and 70 ⁰ G held and the Kate of the air flow was about 11 000 Nm / Hour (dry basis) held.

The mixture of 3S iron (II) sulfate heptahydrate and fly ash was introduced into the drying drum by means of a binwaage loader. By varying the feed rate up and down with continuous sampling and testing of the product removed from the drying drum installation, it was found that a production rate of about 7 t / hour gave optimum product quality with respect to the free flowing properties and the resulting Chromatreduktions ve fmögen, measured in % of Chromatreduktionsvermögens contained in the feed -3isen (II) sulfate heptahydrate. At this optimum production rate, a total amount of fly ash mixture was produced and bottled in road tankers for transport to the cement mill plant sulfate of about 95 t ^ü isen (II) /. The average sample of the 95 tonne test batch had a retained chromate reduction capability of 95 % and the pH of a 1 $ slurry was 4 »2.

The 95 t experimental batch of the dried mixture from the

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Ferrous sulfate heptahydrate and plug ash was used as a chromate reduction additive in the production of cement in two, equal, series-connected cement mills as used for the experiment described in Example 3. The additional feed rate was adjusted to maintain the same addition of Pe ⁺ to the second stage of the two series-connected cement mills as when using a known chroinate reduction additive in normal production.

It was found that the product from the test lot flowed freely in both the supply silo and the feed hopper and confirmed the normal production control sample and the test for determining the reserve potential for chromate reduction in the cement produced by the method described above, that the reserve potential of chromate reduction remained unchanged between about 30 and 40 mg Cr / kg cement when the type of chromate reduction additive of the coated-iron (II) sulfate heptane hydrate type used in normal production was changed to the product from the test batch, if the cement. mill discharge and the amount of contained in the feed of the chromate reduction additive Pe ^{+ were} kept constant.

These production control samples were also examined for their Cr ⁺ content after 8 and 14 days, and all these tests showed that the content of Cr ^{+ was} below 0.1 mg / kg cement. ·

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Example 5

In the same industrial mixing and drying plant used to carry out the experiment described in Example 4, a technical grade ferrous sulphate heptahydrate was mixed with an equal weight of gypsum and the mixture was converted into a powder having an optimum product quality with respect to the free flowing properties and the maintenance of the measured chromate reduction capacity.

The gypsum used for the experimental production was artificially produced industrial gypsum of the 'type normally used in the manufacturing process of the whole cement produced in Denmark. The technical data of the gypsum are given in Table V below.

Table V % (Dry basis) Chemical Analysis 97.50 CaSO ₄ . 2H ₂ O 0.40 ^P 2 ° 5 0.09 Al ₂ O ₃ 0.08 Pe ₂ O ₃ 0.25 Na ₂ O ₃ 0 _} 03 K ₂ O *. 0.30

98,63-

pH of 25% slurry = 6.0 moisture (dried at 40 ^° C.) = 5.6 %

/ Λ

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The drying air flowing through the drum was maintained at about 13 OOO UnrVh (dry basis) and the outlet air temperature was maintained between 65 ⁰ C and 70 ⁰ C during the experimental period. Under these working conditions in the drying drum, a value of about 8 t / h was found as the optimum production rate. At this optimum rate, a total of about 25 tons of bis (II) sulfate / gypsum mixture was prepared and placed in a road tanker for transport to the cement mill plant. Jäine average sample from the 25-t-test batch had a residual Chromatreduktionsvermögen of 98% and the pH value of I ^ weight slurry, which was prepared with the product, was _4} 5 ·

The 25-t test batch of the dried mixture of iron (II) sulfate heptahydrate and gypsum was used as a chromate reduction. additive in the production of cement in the same two interlinked cement mills as used to carry out the experiment described in Examples 3 and 4. The additional feed rate was adjusted to maintain the same addition of Pe as when using a known chromate reduction additive.

It was found that the product from the test lot flowed freely both in the storage silo and in the hopper and normal production control sampling and a test for determining the reserve potential of chromate reduction capacity in the cement according to the method described above confirmed the reserve potential Chromatreducing power unchanged between about 30 and 40 mg / kg remained when changing the

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Type of chromate reduction additive of the type coated iron (II) sulfate heptahydrate, as in normal Pro. Ductxo'n is used, to the product of the test batch, when the cement mill output and the amount of Pe contained in the feed of the chromate reduction additive were kept constant,

The production control samples were also examined for their Cr content after 8 and 14 days and all these tests showed that the content of Cr ^{+ was} below 0.1 mg / kg of cement.

Example 6

In the same industrial blade mixer / kneader unit used to carry out the experiments described in Examples 4 and 5, 1 part by weight of technical ferrous sulfate heptahydrate was mixed with 10 parts by weight of Gp ₃ ^ he mixed the same quality as it had been used in the process described in example 5 attempt ^ ine total of 22 t ^ isen (II) sulfate / gypsum - \ mixture was prepared and packaged for transport to the cement mill plant in open trucks , Analysis of an average sample of the test batch showed that 99 % of the chromate reduction capacity of the isene-C 1 sulfate used in the experiment was retained in the product. The pH of the product in a 1% slurry was 5x0.

The 22-tonne test batch was received at the cement mill plant and fitted with the equipment normally used to add gypsum to the cement mill.

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· This installation comprises a hopper with a picking stop and a system of rubber conveyors for transport and distribution onto the gypsum hopper silos for the cement mills. The test lot was placed in the gypsum hopper for the same two cement mills connected in series, such as they were used for the experiments described in Examples 3 and 4 and 5, and over a period of 5 hours, all 22 tons were introduced into the inlet of the first stage mill, in the form of a combined additive of gypsum and chromate reduction additive.

It was found that the iron (II) sulfate / gypsum mixture had the same handling properties as gypsum without the addition of iron (II) sulphate heptahydrate. "There were no difficulties in removal and transport during the experiment."

During the experiment, samples of the cement produced were taken at 30 minute intervals and examined to determine the reserve potential of chromate reduction compounds according to the method described above. The results of the experiments are given in the following Table VI.

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Table VI • Reserve potential for chroma reductant in mg Cr / kg cement Iron (II) sulphate and time 20 Gypsum (1,12 kg Pe ²⁺ Zt 10:30 16 formed cement) 11:00 18 11:30 15 12:00 20 12:30 16 13:00 17 13:30 19 14:00 17 14:30 20 known means 15:00 15 23 given to the mill 15:30 30 the second stage 16:30 36 (1.09 kg Fe ²⁺ Zt ge 17:00 40 formed cement) 17:30 35 13:00 39 19:00 '31 19:30 36 8:00 pm

Immediately after the consumption of the entire test batch, the normal gypsum charge for the first stage mill and the addition of a known ghromatreducing agent in the second stage mill were restored. Then it was found that the addition of Pe ⁺ Xn orm of a known agent in the mill of the second

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Stage with the same rate of addition as the joinder (II) sulfate / gypsum mixture into the first stage mill resulted in an increase in the reamer potential to chromate reduction capacity of about 20 mg Cr / kg cement. It is true that this higher demand for Pe upon feeding the chromate reducing agent to the first stage mill is due to the fact that the iron (II) sulfate in the first stage mill is exposed to the cement grinding process for a longer time.

Claims (22)

, -28- 2.3 · 1984 63 221/17 ffrfindungsansprach A process for improving the properties of a powder, in particular a dry cement mixture, characterized by milling a starting material containing a cement binder clinker and having a water-soluble chromate content, and adding a chromate reducing and / or neutralizing agent in a non-dissolved state and in an amount of from 0.01% to 10% by weight, based on the weight of the starting material, before, during or after milling to eliminate or substantially reduce the water-soluble chromate, wherein the reducing and / or neutralizing agent is one Is iron (II) sulfate hydrate product having a high ratio between ferrous ion and total iron and a low corrosivity produced from a commercial or commercial ferrous sulfate heptahydrate product which tends to cake when it is is handled and stored in silos and feed hoppers by holding the lock he made the bound water of the product unavailable as a cause for the caking by one or more treatments selected from mild drying, powder dilution, physical absorption and chemical absorption A method according to item 1, characterized in that the water isen loosely bound in the technical or handeisüblichen ^ (II) sulfate heptahydrate product as a cause of caking by drying at a temperature not exceeding 120 ⁰ C made not-available. " -29- 2,3,1984 63 221/17 Method according to item 2, characterized in that the temperature is at most 80 ^° C. 4. The method according to item 2, characterized in that the temperature is at most about 60 ⁰ G, 5 * Method according to item 2, characterized in that the temperature is in the range of about 20 to 60 ⁰ G. 6, method according to item 1, characterized in that the loosely bound water in the technical or commercial oil (II) sulphate heptahydrate product is not available by mixing the technical or commercial sis (II) sulphate heptahydrate with a water-absorbing powder has been made, The method according to item 6, characterized in that the water-absorbing powder is a powder having a specific surface area greater than about 2,000 cm / g, Method according to item 6 or 7, characterized in that the powder is a powder which can absorb water by reacting chemically with it, Method according to item 8, characterized in that the powder is selected from basic inorganic powders, 10, the method according to item 6, characterized in that the powder is selected from powders or powder mixtures which are obtained as by-products, as starting materials or waste products in the cement industry, such as, B, -30- "2.3.1984 63 221/17 Clay, fly ash, slag, lime, gypsum, pollen and products that are readily available in the cement industry, such as: Cement. 11. The method according to item 10, characterized in that the powder is plug ash from coal power plants. 12. The method according to item 11, characterized in that the fly ash is a plug ash with a specific surface area of about 2000 to 5000 cm / g, determined by the Blaine method is. 13. The method according to item 12, characterized in that the plug ash has a specific surface area of about 3000 to 4000 cm / g, determined by the Blaine method. 14. The method according to any one of the points β to 13, characterized in that the amount of added powder in the range of 1 to 95 %> based on the resulting product. 15. The method according to item 14, characterized in that the powder is Plugasche. 16. The method according to item 15, characterized in that the plug-ash is added to the diethylene sulfate heptahydrate in an amount of about 20 to 70 $, based on the resulting product. 17. The method according to item 16, characterized in that the plug ash to the iron (II) sulfate heptahydrate in an amount • · • · -31- 2.3.1984 63 221/17 from 40 to 70 %, based on the resulting product, is added. 18 · The method of item 17, characterized in that the plug ash the Bisen (II) sulfate heptahydrate in an amount of about 50% _t based on the resulting product is added. O 19 · ^ experience according to one of the items 6 to 18, characterized in that the addition of the powder is combined with the drying under conditions as indicated in one of the points 2 to 5 · Method according to item I9 _t, characterized in that the addition of 20 to 70 % fly ash, based on the total resulting product, with the drying at a _t . Temperature below 120 ⁰ C, preferably drying at a temperature in the range of about 20 to 60 ⁰ C, is combined. Process according to item 20, characterized in that the plug ash was added to the technical or commercial iron (II) sulphate heptahydrate in a mixer and the resulting mixture was dried in a dryer, for example a drying drum, and then disintegrated if necessary , Process according to item 10, characterized in that the powder is gypsum, 23. The method according to item 22, characterized in that the gypsum has a specific surface area greater than -32- 2.3.1984 63 221/17 2000 cm / g, determined by the Blaine method, has · 24 · The method of item 23 or 24, characterized in that the ^G ips the iSisen (II) sulfate heptahydrate in an amount from 1 to 95 $ »based on the resulting product is added" 25 · The method according to any one of items 22 to 24 in \ characterized in that the addition of ^G ips is combined with a mild drying of the resulting mixture. 26 · The method of item 25, characterized in that the addition of gypsum with the drying at a temperature below 120 ⁰ C, preferably drying at a temperature in .the range of from about 20 to 60 ⁰ C combined, · -27. Process according to item 25, characterized in that the gypsum is added to the technical or commercial JSisen "(II) sulphate heptahydrate in a mixer and the resulting mixture is dried in a dryer, for example a drying drum, and then optionally disintegrated. 28. Method according to one of the items 22 to 27, characterized in that hemihydrate or anhydrite or a mixture thereof is used instead of or together with gypsum. 29. The method according to any one of items 22 to 28, characterized in that the gypsum, the hemihydrate, the anhydrite or the mixture thereof has a pH of at most 7, in particular a pH "Vert in the range of 5 to 7, has ·. -33- 2.3.1984 63 221/17 30. The method according to item 29 »characterized in that the gypsum, the hemihydrate, the anhydrite or the mixture thereof has a pH of about 6 · 31 "The process of item 10, characterized in that the commercial or commercial oil (II) sulphate heptahydrate is mixed with gypsum which is used as a finishing material in the cement industry. Method according to item 31 », characterized in that the amount of gypsum is between 1 and 95% by weight, based on the resulting mixture. 33 · Procedure according to any one of items 29 to 32, characterized characterized in that the hemihydrate or anhydrite or a mixture thereof ι is used instead of or together with the gypsum. 34. The method according to item 32 or 33, characterized in that the mixing ratio between iron (II) sulfate heptahydrat and the gypsum, the hemihydrate, the anhydrite or the mixture thereof between 1: 2 and 1:50, in particular between 1: 5 and 1 : 20, for example at about 1:10. Method according to any one of items 31 to 34, characterized in that the gypsum has a pH of at most 7, in particular a pH in the range of 5 to 7. 36. The method according to item 35, characterized in that the gypsum has a pH of about 8. -34- 2.3.1984 _r 63 221/17 37. Dry cement mixture prepared by the method according to any one of items 1 to 36. 38. Process for the preparation of a water-soluble, im. essential free flowing oleic (II) sulphate hydrate product with a high ratio of ferrous iron to butanitrile and a low corrosivity from a commercial or commercial iSisen (II) sulphate heptahydrate product when handled and stored in silos and feed hoppers for caking, characterized in that the loosely bound water of the product is made unavailable as a cause for the caking by one or more treatments resulting from the mild drying combined with the powder dilution, the powder dilution, the physical absorption and the chemical absorption can be selected. Method according to item 38 _f, characterized in that the loosely bound water in the technical or commercially available fi fer (II) sulphate heptahydrate product is rendered unavailable by mixing the technical or commercial iron end sulphate heptahydrate with a water-absorbing powder. 40. Procedure according to item 3.9 », characterized in that the Water-absorbent powders a powder with a specific 2 see surface size of more than about 2000 cm / g. 41. Method according to Item 39 or 4'0, characterized in that the powder is a powder capable of absorbing water by reacting chemically with it « -35- 2.3.1984 63 221/17 42 · Procedure after. Item 41, characterized in that the powder is selected from basic inorganic powders 43. The method according to item 39, characterized in that the powder is selected from powders or powder mixtures obtained as by-products, as starting materials or waste products in the cement industry, such. B. on, plug ash, slag, lime, gypsum, filter dust, and products used in the cement industry. are easily accessible, such. B, cement, Process according to item 43, characterized in that the powder is coal fly ash fly ash, Method according to item 44, characterized in that the fly ash is a fly ash having a specific surface area of about 2000 to 5000 cm / g, determined by the Blaine method. Method according to item 45, characterized in that the fly ash has a specific surface area of about 3000 to
drive, has. about 3000 to 4000 cm / g, determined according to the Blaine method A method according to any one of items 39 to 46, characterized in that the amount of added powder is in the range of 1 to 95 % based on the resulting product. 48. Method according to item 47, characterized in that the powder is fly ash. -36- 2.3.1984 63 221/17 49 · The method of item 48, characterized in that the plug ash the iSisen (II) sulfate heptahydrate in an amount of about 20 to 70% _t based on the resulting product is added · 50 · Method according to item 49, characterized in that wirdo the fly ash to the Bisen (II) sulfate heptahydrate in an '* · amount of 40 to 70% _f based on the resulting product j was added 51. The method of item 50, characterized in that the fly ash to the I3isen (II) sulfate heptahydrate in an amount of about 50% _t based on the resulting product is added · 52 "Method according to any one of items 39 to 51", characterized in that the addition of the powder is combined with drying under conditions as specified in any one of items 2 to 5 ". Process according to item 52, characterized in that the addition of 20 to 70 % fly ash, based on the total resulting product, with drying at a temperature below 120 ⁰ C, preferably a drying at a temperature in the range of about 20 to 60 ⁰ C, is combined. . 54 · Method "according to item 53 characterized in that the fly ash to the technical or commercial JSisen (II) sulfate heptahydrate were added in a mixer \ '% va and the resulting mixture in a dryer such as a drying drum, is mixed and -37- 2.3.1984 63 221/17 then optionally disintegrated · 55, method according to item 44 », characterized in that the powder is gypsum. 56. Method according to item 55 »characterized in that the gypsum has a specific surface area greater than about 2000 cm / g, determined by the Blaine method. 57 · The method of item 55 or 56, characterized in that the gypsum which iäisen (II) sulfate heptahydrate in an amount of 1 to 95% _t based on the resulting product is added · 58, method according to any one of items 55 to 57 »characterized in that the addition of gypsum is combined with mild drying of the resulting mixture. 59 · The method of item 58, characterized in that the addition of gypsum _w ith a drying at a temperature below 120 ⁰ C, preferably a drying at a temperature in the range of about 20 to 60 ⁰ C, is combined · Process according to item 59, characterized in that the gypsum is added to the technical or commercial iron (II) sulphate heptahydrate in a mixer and the resulting mixture is dried in a dryer, for example a drying drum, and then disintegrated as required. -38- 2.3.1984 63 221/17 Process according to any one of items 55 to 60, characterized in that the hemihydrate or the anhydrite or a mixture thereof is used instead of or together with the gypsum. Method according to any one of items 55 to 61, characterized in that the gypsum, the hemihydrate, the anhydrite or the mixture, mixed with the normal (II) sulphate heptahydrate, have a pH of at most 7 », in particular a pH in the range of 5 to 7, has » Method according to item 62, characterized in that the gypsum, the hemihydrate, the anhydrite or the mixture thereof has a pH of about 6 · 64. A method according to any one of items 55 to 63, characterized in that the sulfuric (II) sulphate heptahydrate is mixed with gypsum, hemihydrate, anhydrite or a mixture thereof, the weight ratio between the sis (II) sulphate heptahydrate and the gypsum, the hemihydrate or the anhydrite in the range of from 1: 2 to 1:50, in particular between 1: 5 and 1:20, for example about 1:10. 65. A substantially free-flowing product containing water-soluble iron (II) sulfate hydrate prepared by the method of any one of items 38 to 63. 66. A substantially free-flowing powder composition containing ε-trisulphate hydrate in admixture with a water-absorbent powdery material, wherein -39- 2.3.1984 63 221/17 the iron (II) sulphate heptahydrate of the free-flowing powder is readily soluble in water and has a high ratio of iron (II) ions to the iron ore content in the iron (II) sulphate heptahydrate. Composition according to item 66, characterized in that the absorbent powdery material is selected from powders or mixtures of powders obtained as weaving products, starting materials or waste products in the cement industry, such as fly ash, slag, lime, Gypsum, filter dust, and products that are readily available in the cement industry, such as Bp Cement » 68 * Composition according to item 67 », characterized in that the pulverulent material is carbonaceous fly ash. 69 · Composition according to item 67 _9, characterized in that the powdery material is gypsum ·