SK177899A3 - Method of treatment of dry cement - Google Patents

Abstract

The method is based on the principle of adding dry undissolved ferrous sulfate to cement between the cement mill and the cement silo or the output packaging device. Ferrous sulfate in bulk form with a grain size of 0.1 to 0.8 mm in the form of monohydrate FeSO4. H2O is added in a ratio of 0.1 to 1% by weight to the finished cement directly at the outlet of the filter, located after the wind classifier, while it is gradually mixed and homogenized with the cement.

Description

Technical field

The invention relates to a method of treating dry cement.

BACKGROUND OF THE INVENTION

It is known that cement containing chromium compounds, when mixed with water, has adverse health effects in persons coming into contact with a mixture of such cement and water. They experience skin eczema caused by the presence of hexavalent Cr ⁶⁺ . There are several ways to reduce the Cr ⁶⁺ concentration in cement-water mixtures. The best known of these is the addition of ferrous sulphate _FeSO4-H2O for the cement, which ions of iron sulfate heptahydrate reduces the hexavalent chromium to the trivalent Cr ^{6 +} Cr ³ *, which is only slightly soluble in mixtures of water and cement. Cement with the addition of ferrous sulfate is generally known and has been described in a number of patents. For example, U.S. Pat. US 3,425,892 discloses a cement containing 0.1 to 5% ferrous sulphate (the purpose of adding ferrous sulphate was different here, related to retarding the cement solidification after processing). The literature describes the addition of ferrous sulphate to dissolved cement (Annex 3 to Circular Letter 15, published by the European CEMBURFAU Cement Association in Paris on 1.3.1979), which was sprayed together with gypsum in a cement mill. However, the results were not satisfactory, and the reduction of Cr ⁶⁺ was very limited. Somewhat better but still impractical results were achieved by spraying it on hot cement at the mill outlet. In European patent applications no. Nos. 54314 and 160746 (Int. Cl. ³ C 04 B 7/35) describe the addition of ferrous sulfate to cement in a dry, undissolved state. This method has proven to be widely used and in practice 0.4 to 0.6% by weight is considered to be the optimal amount of ferrous sulphate in dry cement.

The addition of dry, undissolved ferrous sulphate additive to dry cement always depends on the particular cement plant and is carried out in such a way as to minimize interference with existing technology while maintaining the quality and the lowest cost. Although it is generally

It is known that ferrous sulphate can be metered into dry cement in the part of the process between the mill outlet and the finished storage silo (in particular, the location is not exactly determined), in practice ferrous sulphate is usually added at the inlet of the cement mill. However, this is disadvantageous because its dosage is not accurate enough. If ferrous sulphate is overdosed, for example in an amount of 1% by weight or more, problems may arise in the processing of concrete made of such cement, and its setting time is considerably prolonged.

The purpose of the present invention is to achieve a dry cement treatment wherein the addition of dry, undissolved ferrous sulfate is dosed as accurately as possible, with an immediate response to the amount of cement produced. Another requirement is the economy of the solution, so as not to interfere with the existing technology of cement production.

SUMMARY OF THE INVENTION

Said objects of the invention are achieved by a dry cement treatment method based on the principle of adding dry, undissolved ferrous sulfate to the cement between the cement mill and the exit cement silo or packaging machine. And characterized in that the ferrous sulfate in particulate form with a grain size from 0.1 to 0.8 mm monohydrate FeSO4.H ₂ O is added in a ratio of 0.1 to 1%. into the finished cement directly at the outlet of the filter, located behind the wind screen, gradually mixing and homogenizing the cement. Among the advantages of the invention may be mentioned, in particular, the very precise dosage of ferrous sulfate, which is given by the essentially instantaneous dosage response, in the order of tenths of a second, to the amount of cement produced. In no case is there an overdose of ferrous sulphate, which could have undesirable effects when processing concrete from the cement thus produced.

The ferrous sulphate preferably has a grain size of up to 0.35 mm. When mixed with cement, the resulting mixture is more homogeneous.

Ferrous sulphate is added in an amount of 0.4 to 0.6% by weight, this amount being linked to the Cr ⁶⁺ content of the cement-containing components,

-3 especially clinker. The ferrous sulphate is mixed with dry cement by vibration and mechanical agitation, optionally in combination with centrifugal unwinding. The ferrous sulphate is mixed and horogenized with dry cement in an air stream. This gradual mixing along the entire transport path from the exit from the cement mill to the equipment or cement silo leads to a thorough homogenization of the cement and ferrous sulphate. At the same time, this solution is very economical, there is no need to interfere with the existing technology of cement production.

DETAILED DESCRIPTION OF THE INVENTION

FeSO4.H2O monohydrate is a fine crystalline gray substance with a small amount of accompanying elements (up to 1.0 wt.% Magnesium and about 0.4 wt.% Manganese). In water, it partially dissolves to solutions with an acid reaction, it is stable at normal temperature. Its specific gravity is 2650 kg / m ³ , bulk density 1270 to 1300 kg / m ³ , tapped weight 1400 to 1800 kg / m ³ (exact value depends on the fraction). Its granulometric composition is such that it contains 20 to 30% by weight. particles of less than 0.1 mm, 45 to 65% by weight. 0.10 to 0.25 mm, 10 to 20 wt. particles of 0.25-0.35 mm in size and not more than 1.0% by weight. particles larger than 0.35 mm.

In the manufacture of cement, ferrous sulfate monohydrate from the process container is dosed by means of a dosing scale that is electronically linked to the instantaneous weight produced amount of finished dry cement per finished product web, i. cement. From the metering scale, ferrous sulphate with a grain size of up to 0.35 mm is conveyed to a screw conveyor, which is conveyed over one or two belt conveyors of finished cement from the outlet of the filter located downstream of the wind screen. Here it is added to dry cement at a ratio of 0.4% by weight. (in alternative examples in a ratio of 0.5 or 0.6 wt.%). The mixing of the ferrous sulphate with the cement already takes place on said conveyor belt by its movement and vibrations. Further mixing takes place in a rotary cement weighing machine that follows the finished cement belt conveyor. The weighing machine rotates freely on the ferrous sulfate cement and is centrifuged from the rotating plate onto the weighing machine walls by gravity and falls into the weighing machine.

-4 elevator shafts. Further mixing of the mixture takes place in the elevator as it is collected into the elevator buckets. When the mixture is subsequently poured from the elevator buckets into the pneumatic conveying trough, the mixture is again mixed.

In a subsequent set of pneumatic conveying troughs, the mixture is conveyed to a cement silo. In this case, the mixture flows in the inclined troughs in the air stream over the aerated canvas carriers and is mixed very intensively and homogenized by this movement. Other belt conveyors, elevators and pneumatic conveying troughs can be included in the material transport. Further homogenization of the mixture occurs in the cement silo.

Industrial usability

The invention is useful in the manufacture of cement for construction.

Claims (6)

PATENT CLAIMS Process for the treatment of dry cement, based on the principle of adding dry, undissolved ferrous sulphate to the cement between a cement mill and a cement silo or an exit packing machine, characterized in that the ferrous sulphate in bulk form with a grain size of 0.1 to 0.8 mm in the form of FeSO ₄ .H ₂ O monohydrate is added in a ratio of 0.1 to 1% by weight to the finished cement directly at the outlet of the filter downstream of the wind screen, gradually mixing and homogenizing the cement. Treatment method according to claim 1, characterized in that the ferrous sulphate has a grain size of up to 0.35 mm. Treatment method according to claim 1 or 2, characterized in that the ferrous sulphate is added in an amount of 0.4 to 0.6% by weight. Treatment method according to one of the preceding claims 1 to 3, characterized in that the ferrous sulphate is mixed with dry cement by vibration and mechanical mixing. Treatment method according to one of the preceding claims 1 to 4, characterized in that the ferrous sulphate is mixed with dry cement by centrifugal spreading. Treatment method according to any one of the preceding claims 1 to 3, characterized in that the ferrous sulphate is mixed and homogenized with the dry cement in an air stream.