METHOD OF PRODUCING CLAY ACTIVATED/CALCINED WITH CALCIUM ALUMINOFERRITE OR CALCIUM FERRITE AND CLAY COMPOSITION OBTAINED BY THE METHOD

Abstract

The present invention patent refers to a method of obtaining a clay composition activated/calcined with a fraction of calcium aluminoferrite or calcium ferrite and clay composition obtained by the aforementioned method, more precisely belonging to the field of industrial cement manufacturing, where said method discloses a process of forming calcium aluminoferrite or calcium ferrite in-situ to deliver an activated/calcined clay from red clay that is most appreciated for adding to a cement composition.

Claims

1.-4. (canceled)

5. A method of producing clay activated/calcined with calcium aluminoferrite or calcium ferrite and clay composition comprising: obtaining calcium aluminoferrite or calcium ferrite in-situ to change the color of the red clay during calcination in a clay oven activated/calcined at a temperature over 900? C. for approximately 45-90 minutes in counterflow to exhaust gases; said calcined red clay being acceptable to be added to cement.

6. The method according to claim 5, further comprising the following steps: providing a first raw material, namely, a mixture of clay and limestone typical for the manufacture of clinker for cement, or other sources of calcium oxide or calcium carbonate; and providing a second raw material, that is, the red clay produced in the activated/calcined clay oven; wherein the reaction between the first typical raw material CaO and Fe.sub.2O.sub.3, during calcination, should be measured in order to maintain the supply of CaO necessary for the stoichiometric ratio of the reactions
2CaO+Fe.sub.2O.sub.3.fwdarw.Ca.sub.2FeO.sub.5 and(1)
CaO+Fe.sub.2O.sub.3.fwdarw.Ca.sub.2FeO.sub.4(2)

7. A clay composition obtained by the method of claim 5, wherein the composition comprises activated/calcined clay from red clay including calcium aluminoferriteCa.sub.4Al.sub.2Fe.sub.2O.sub.10or calcium ferriteCa.sub.2FeO.sub.5 or Ca.sub.2FeO.sub.4.

8. The clay composition obtained by the method of claim 5, wherein the resulting composition is greenish or brownish gray color acceptable for use in cements.

Description

DESCRIPTION OF THE DRAWINGS

[0015] To complement this description in order to obtain a better understanding of the characteristics of this invention and according to a preferential practical embodiment hereof, the description is accompanied by a set of diagrams, where, in an exemplified way, although not limited, the following is represented:

[0016] FIGS. 1 and 2 represent diagrams where it can be seen that all products formed in the CaFeO method, in which the Ca.sub.2Fe.sub.2O.sub.5 product can be identified as C.sub.2F and the CaFe.sub.2O.sub.4 product can be identified as CF;

[0017] FIG. 3 shows a graph of the increase in the Ca/Fe ratio in the increase in reaction yield; and

[0018] FIG. 4 shows a graph of the X-ray diffraction patterns of calcium ferrites prepared from the mixture of CaO and Fe.sub.2O.sub.3 with Ca/Fe ratio between 0.33 and 3 in mass.

DESCRIPTION OF THE INVENTION

[0019] With reference to the drawings, the present invention patent refers to the METHOD OF PRODUCING CLAY ACTIVATED/CALCINED WITH CALCIUM ALUMINOFERRITE OR CALCIUM FERRITE AND CLAY COMPOSITION OBTAINED BY THE METHOD, more precisely it is a method of obtaining the clay composition activated/calcined with calcium aluminoferrite or calcium ferrite and clay composition obtained.

[0020] According to the present invention, the method of obtaining activated/calcined clay composition includes the in-situ generation of calcium aluminoferrite or calcium ferrite for correcting the color of activated clay. This method presents itself as an alternative to traditional methods of color control.

[0021] The modification of the color of red clay carried out in the activation/calcination step by the method of generation in-situ of calcium aluminoferrite or calcium ferrite is achieved by the combination of raw material for cement manufacturing in the basic phase of clinker manufacture for cement, notified limestone and/or clinker flour, similar sources of calcium oxide, and red clay calcined in an activated/calcined clay oven at a temperature over 900? C.

[0022] Said method of obtaining activated/calcined clay composition presents the following steps: [0023] (a) The mixture of clay and limestone and/or clinker flour is fed in the oven in counterflow to exhaust gases, produced by burning fuel, dragged inside the oven through an extractor hood. The activated/calcined clay is obtained at a temperature over 900? C., with a mixing residence time inside the oven of approximately 45-90 minutes; [0024] (b) Weighing the typical raw material mass for the manufacture of clinker for cement in the basic phase to be added in order to provide CaO necessary to maintain the stoichiometric ratio of the reaction (1), considering a typical raw material for the manufacture of clinker for cement of typical composition as an example for calculations, wherein:

TABLE-US-00001 SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 Na.sub.2O K.sub.2O (%) (%) (%) (%) (%) (%) (%) (%) 12.8 2.8 1.8 43.2 1.0 0.4 0.3 0.6
wherein 43.2% of the typical raw material mass for the manufacture of clinker for cement corresponds to the compound CaO (reagent of interest). Thus, the addition of 1 kilo of this typical raw material for the manufacture of clinket for cement to the system corresponds to the addition of 432 grams of CaO. According to the reaction (1) the stoichiometric ratio is 2:1, and two CaO mols are required to react with one mol of Fe.sub.2O.sub.3. The molar mass of CaO of approximately 56.1 g/mol and the molar mass of Fe.sub.2O.sub.3 of approximately 159.6 g/mol are considered. In a stoichiometric ratio with the estimated yield (75%) 112.2 grams of CaO and 159.6 grams of Fe.sub.2O.sub.3 are required to produce 203.8 grams of Ca.sub.2Fe.sub.2O.sub.5. Taking into account the data of typical raw material for the manufacture of clinker for cement considered it is necessary to add 260 g of typical raw material for the manufacture of clinker for cement in the method for reducing 159.6 g of Fe.sub.2O.sub.3. With regard to the temperature of the reaction, production data of Ca.sub.2Fe.sub.2O.sub.5 between 700? C. and 1300? C. were found, being the maximum yield of the reaction at a temperature of 1100? C. Due to the transformation characteristics of the activated/calcined clay, the use of temperatures between 900? C. and 1050? C. is indicated; [0025] (c) In possession of the thermodynamic data of the reagents and products involved in the reactions (1) and (2) it is possible to calculate Gibbs-free energy for the formation of both products. The first reaction has Gibbs-free energy of formation equal to ?59110.45 kJ/mol, while the second reaction presents Gibbs-free energy of formation equal to ?36 433,495. Due to the large negative Gibbs-free energy values of both reactions, it is concluded that these are spontaneous and the formation of Ca.sub.2Fe.sub.2O.sub.5 is more thermodynamically favorable (higher negative value); [0026] (d) The reaction between CaO and Fe.sub.2O.sub.3 leads to the formation, mainly, of two products: Ca.sub.2Fe.sub.2O.sub.5, known as Brownmillerite, and CaFe.sub.2O.sub.4 (see FIG. 1), both calcium ferrites. The formation reaction of the two compounds can be described by the reactions:

2CaO+Fe.sub.2O.sub.3->Ca.sub.2FeO.sub.5(1)

CaO+Fe.sub.2O.sub.3->CaFeO.sub.4(2)

[0027] The main parameter that leads to the formation of one product in detriment of the other is the Ca/Fe ratio. Studies indicate an increase in the formation of Ca.sub.2Fe.sub.2O.sub.5 for Ca/Fe>1, with 75% being the yield of a stoichiometric reaction (see FIG. 3). Though well-known according to Hirabayashi, et. al. (2006) that the increase of the Ca/Fe ratio to 3 culminates in the increase in the reaction yield, to ensure the economicity of the activated/calcined clay produced, we indicate only the addition of typical raw material for the manufacture of clinker for cement until the stoichiometric ratio of the reaction is maintained (1).

[0028] The composition of clay obtained is activated/calcined comprising calcium aluminoferrite or calcium ferrite, preferably a calcium aluminoferrite or calcium ferrite resulting from in-situ formation during calcination.

[0029] The activated/calcined clay of the present invention presents greenish gray or brown coloration, which allows the use thereof in cements, free of substantial deviations of color.

[0030] It is certain that when this invention is put into practice, changes may be made with regard to certain details, without this implying departing from the fundamental principles that are clearly substantiated in the set of claims, thus it is understood that the terminology used did not have the purpose of limiting.