CA2201822A1 - Reaction mixture for fabricating a binder from red mud and fluoroanhydrite - Google Patents

Abstract

A binder mixture for use in the fabrication of building materials comprises red mud, fluoroanhydrite, lime, silica sand or powder, and a sodium salt of a condensate of .beta. polynaphtalene sulfonate and formaldehyde. The mixture may further contain various fibres and fibrous material.

Description

~20 ~822 REACTION MIXTURE FOR FABRICATING A

BINDER FROM RED MUD AND FLUOROANHYDRITE

BACKGROUND OF THE INVENTION

10 1. Field of the invention:

The present invention relates to the development of a reaction mixture in view of fabricating a binder from red mud and fluoroanhydrite, which are two residues from the production of aluminum.

2. Brief description of the prior art:

Aluminum, Al, is produced from alumina, Al2O3, and alumina is extracted from bauxite, an ore containing alumina, iron oxide, 20 clay, etc.

Alumina is extracted by means of the so-called Bayer process consisting of attacking the bauxite with caustic soda. A first sub-product or residue of this extraction are the so-called red muds (these 25 muds are red due to the iron oxide they contain). Red muds are highly alkaline and, therefore, constitute, an environmental nuisance.

A second sub-product or residue of the production of aluminum is the fluoroanhydrite. This second residue is generated in the advanced countries upon production of aluminum from alumina. Up to now, no industrial application of fluoroanhydrite has been found, and transformation thereof into plaster is not cost-effective onto a market where natural gypsum is abundant and, accordingly, low cost.

On the industrial market of aluminum, alumina is usually imported directly from the producing countries, the red muds being left on the site. This solution reduces the costs connected to the transport but cause a major environmental problem to the alumina-producing countries.
10 Usually, alumina is extracted in the proximity of the bauxite deposits and cause environmental problems to many alumina-producing countries including: Guinea, Jamaica, Guyana, Brazil, India, and Australia. All these countries, except Australia, are Third World underdeveloped countries.
The Third World underdeveloped countries are faced with a tremendous, increasing need of housing. This need is accentuated around the big cities where rural migration converge. Fast population growth renders the situation even more problematic.
To solve this problem, most of the underdeveloped countries have adopted classical technologies for constructing residential buildings, using for example bricks fabricated from Portland cement. The cement used to make these bricks is generally imported or produced at 25 high cost. Importation of Portland cement is also difficult in countries having no port installations.

In the few Third World countries in which Portland cement is fabricated, the importation of the raw materials increases the - 220 t~2 ~
-production costs. This cost is even higher when bricks and concrete structures are fabricated. Also, the technologies employed by these few underdeveloped countries are heavy, cumbersome, bulky and far from being cost-effective.

Researches have therefore been conducted to develop simpler processes using low cost and/or local raw materials. Many solutions have been proposed in the last few years, in particular the fabrication of bricks made of burned clay and the manufacture of 10 pozzolanic bricks.

Production of bricks of burned clay presents the drawbacks of requiring the construction of ovens and consuming a non negligible portion of the local wood as source of energy. Although the 15 fabrication of pozzolanic bricks is of real interest, development thereof has been limited since the bricks harden slowly and their 7-day resistance is very weak and requires Portland cement to be developed.

Researches have also been conducted in view of using 20 the two residues of the production of aluminum, the red muds and the fluroroanhydrite, in an industrial process for producing building materials.
In particular, attempts have been made to solidify the red muds with different chemical products, for example cement, anhydrite and fluoroanhydrite. However, these researches have never conducted to a 25 practical industrial process since the performance of the obtained building materials was only ordinary in regions far from the important consumer areas or on a market of building materials where the competition was fierce.

~2~ ~2 2 The use of fluoroanhydrite in the Third World countries has never been envisaged because of the cost of transporting this sub-product or residue from the advanced countries to the underdeveloped countries. However, if big bags of fluoroanhydrite are charged as ballast 5 in ships leaving industrialized countries and returning off-load to take bauxite in the Third World countries (these ships need ballast), and then these big bags are transferred in trains or trucks returning off-load toward the bauxite processing plants, fluoroanhydrite can be transported at substantially no cost over thousands of kilometres toward the site of 10 production of red muds.

OBJECTS OF THE INVENTION

An object of the present invention is therefore to enable the use of the sub-products or residues of the production of aluminum, i.e. the red muds and fluoroanhydrite, in the production of building materials.
Another object of the present invention is to use the red muds and fluoroanhydrite in the production of binders hardening rapidly and having resistances fully compatible with the standards of the underdeveloped, Third World countries.
A further object of the present invention is to eliminate the environmental problems associated to the sub-products or residues of the production of aluminum, i.e. the red muds and fluoroanhydrite.

~2a ~2 2 _ SUMMARY OF THE INVENTION

More specifically, in accordance with the present 5 invention, there is provided a binder mixture for use in the fabrication of building materials, comprising the following components:
- red mud;
-fluoroanhydrite;
-lime;
- silica sand or powder; and - a sodium salt of a condensate of ~ polynaphtalene sulfonate and formaldehyde.

The binder mixture may further contain various fibres 15 and fibrous material.

The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive description of preferred embodiments thereof, 20 given by way of example only.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is concerned with the development of a reaction mixture susceptible to be used as a binder.
This mixture contains red mud, fluoroanhydrite, lime, silica sand or powder and a sodium salt of a condensate of ~ polynaphtalene sulfonate 1 8 ~ 2 and formaldehyde. Mixed in the presence of water, this mixture sets and hardens relatively fast; it can serve to the production of mortar and concrete. The setting can be accelerated by heating.

Setting and hardening of this mixture are caused by the crystallisation of the mineralogical phases having binding properties.
These phases are formed in accordance with multiple reaction processes depending upon the composition of the mixture and the process conditions. The functions of the main components are as follows:
1- Function of the components red mud + lime + fluoroanhydrite:

Mixed in the presence of water, these three components produce typical reactions which are briefly examined in the following description and which cause an increase of viscosity followed by a hardening of the paste.

a) Formation of hexagonal alumina-calcium hydrates:

At the beginning of setting and in particular when a very small proportion of fluoroanhydrite with low dissolution kinetic is used, fast supersaturation with calcium ions and aluminates can lead to formation of hexagonal calcium-aluminate hydrates 6 Ca++ + 4 [Al(OH)4]- + 8 OH- + 15 H2O ~
Ca2[Al(OH)5]2, 3 H2O + 2[Ca2Al(OH)6,OH,6H2O]

Generally, these hexagonal aluminates tend to transform into more stable tricalcium aluminate but they can also include the molecuies of the sodium salt of the condensate of ~ polynaphtalene sulfonate and formaldehyde. In that case, they produce sulfonate calcium-aluminate hydrates of the type:

[Ca4AI2(0H),2]2, (2-x) S03~eqI x OH-, y H20 (in the case of a lack of sulfonate) or [Ca4AI2(0H),2]2+, 2 S03~eqI x/2Ca++, x S03-, y H20 (in the case of an excess of sulfonate) b) Formation of tricalcium trisulfate-aluminate In the presence of a sufficient proportion of fluoroanhydrite, the hexagonal aluminates do not form or only non persistent hexagonal aluminates appear. The principal phase which crystallizes is then the tricalcic trisulfate-aluminate. This compound is formed from Al(OH)4 ~ ions coming from the red mud, and Ca++ and SO4--ions coming from the lime and the fluoroanhydrite. The main reaction is the following:

2AI(OH)4- + 6Ca++ + 4(0H)- + 3SO4-- + 26 H20 ~
Al203 3CaO 3CaS04 32 H20 This tricalcium trisulfate-aluminate forms a dense packing to ensure cohesion of the whole and determine the degree of resistance of the material.

220 ~82 ~

When the contents of fluoroanhydrite is insufficient, the calcium trisulfate-aluminate dissolves and releases its ions which react with the excess of aluminate to form calcium monosulfoaluminate in accordance with the following reaction:

2 [Al(OH)4]- + 4Ca++ +40H-+S04- + 15 H20 ~ Al203 3CaO CaS04 12H20 c) Formation of hydrated calcium silicate Hardening of the mixture is also due to the formation of a gel of calcium silicate by reaction between the silica from the red mud or the silica powder and the lime of the reaction environment. This reaction is expressed as follows:

2H2SiO4- + 3CA++ + 20H- ~ 3CaO 2SiO2 5H20 d) Reactions with the fluorine ions:

In the presence of lime, fluorine ions react with the calcium ions to produce calcium fluoride (CaF2). On the other hand, calcium silicate fluorinated hydrate may form by reaction between the silicic ions, the lime and the fluorine. Such reactions tend to reduce the mobility of the fluoride ions from the fluoroanhydrite and therefore to minimize eventual risks of pollution. These reactions can be expressed as follows:

F-+ Ca++ ~ CaF2 3H2SiO4-- + 4 Ca++ + 2F- ~ 3SiO2 3CaO CaF2 3H2O

e) Formation of hydrated calcium alumino-ferrite A reaction of the iron oxides from the red mud with the other components to produce phases close to the hydrated calcium alumino-ferrites is not excluded.

10 2- Function of the silica sand or powder:

The silica sand or powder incorporated into the mixtures has many functions:

15 - as a filler, it reduces the contents of water and therefore improves the compactness or density of the mortar or concrete;

- the particles of the filler serve as anchors to the acicular molecules of calcium trisulfoaluminate;
- silica fixes the alkalis provided by the red mud and produce calcium silicate sodium gels which strengthen the cohesion of the mortar. This function is better performed when the silica is active. To that effect, active silica powders such as silica fume, cristobalite, or otherwise 25 grinded sand. The reaction involved is the following:

-Si-OH + Na+ + OH- ~ Si-O-Na + H2O

-Si-O-Si- + 2NaOH ~ 2[-Si-O-Na] + H2O

~20 t~ ~
, 3- Function of the sodium salt (superplasticizer which is the key component of the invention):

The sodium salt of the condensate of ~ polynaphtalene sulfonate and formaldehyde has mainly a function of dispersing agent; it adsorbs on the particles of the mixture and prevents agglomeration of these particles. The dispersed particles can be brought close to each other without flocculation to give a dense suspension. The addition of this salt constitutes a major parameter since it reduces the contents of water, increases the mechanical resistances, and modify the morphology of the ettringite form (tricalciumsulfoaluminate) giving a very strong stability to the mixture.

In summary, with the present invention, crystallization of the essential phases of the hydrated Portland cement is obtained without requiring any firing to produce Portland cement clinker.

The mixture according to the invention therefore contains the following five principal components:

A- The red mud has been used as such without washing and prior heat treatment. However, it can be washed and calcined so as to increase the mechanical performance. The average chemical composition of red mud from Arvida, Québec, Canada is given in Table 1.

-~ ~20 ~82 ~

Table 1 SiO2 TiO2 Al2O3 Fe2O3 CaO Na2O L.O. I .
Percent 14.3 9.8 28.4 27.4 1.3 8.8 9.9 B- Fluoroanhydrite is an industrial residue generally presenting a gross multure; it should be grinded to a particle size smaller than 80,um. The more the particles are fine, the more their specific surface is large, the more the kinetic of the reaction is fast, and the more the initial resistances 10 are high. Industrial fluoroanhydrite generally contains more than 95% of CaSO4 but such a high purity is not required. Fluoroanhydrite can be simply replaced by anhydrite, gypsum or mixture of the three compounds.
The following table 2 presents, as an example, an average composition of fluoroanhydrite.
Table 2 CaSO4 CaF2 CaOou SiO2 Na Al Cl K Others CaC03 Percent 97.51.0 to 0.2to 0.2to 0.28 0.02 0.1 0.006<0.004 3.0 1.0 0.3 C- Lime, Ca(OH)2, is a product widely used in the chemical and building industry; it can be used in the mixture of the invention without any transformation .

25 D- We have used a sodium salt of a condensate of ,~ polynaphtalene and formaldehyde but a calcium salt could have been used. Other salts can fulfill equivalent functions. Examples are polymelamine sulfonate, ~ 2 0 ~ ~ 2 2 lignosulfonate, polyacrylate, etc. The quantities will be adapted to each salt to avoid the classical risks of late setting or of segregation.

E- Preferably, the filler will be a silica sand or powder or an active silica 5 powder. However, other pulverulent materials of various natures can be used.

Finally, a sixth component can be added:

10 F- Various fibres and fibrous minerals can be incorporated to the mixture, as well as sands and aggregates of different size in accordance with the aimed objective.

Examples:
The following mix designs B1 and C1 for 1 kg of dry red mud have been experimented:

Dry powders B1 C1 Red mud 1.000 1.000 Hydrated limeCa(OH)2 1.000 0.500 Fluoroanhydrite 0.350 0.175 Ground silica 0.390 0.390 Sand (concrete type) 5.100 5.100 Na PNS (% solid) 0.058 0.058 a 2 ~ 2 Mix design B1 has been mixed with different amounts of mixing water based on the weight of the dry materials according to the following Table:

Mixing waterf'C at 7 days After Er~.-r~:ncence Mix (%) (MPa) il"",er~ionBefore i"""er~ion After immersion heavily B1-1 18.4 17.0 fissured yes too many fissures heavily B1-2 15.5 20.5 fissured a few too many fissures heavily B1-3 14.5 26.0 fissured --- too many fissures B1-4 9.3 --- no fissures no no Mix design C1 has been mixed with different amounts of mixing water based on the weight of the dry materials according to the following Table:

Mixing waterf'C at 7 days After Ernort:ncence Mix (%) (MPa) immersionBefore i"""e,s;on After i",r"er:,ion C1-1 13.4 19.8 15.8 no no C1-2 11.9 26.9 19.0 no no C1-3 11.2 24.8 18.7 no no C1-4 9.8 29.6 19.0 no no Accordingly, (a) the amount of hydrated lime can vary 30 from 0.5 to 1.0 with respect to the amount of red mud, (b) the amount of fluoroanhydrite can vary from 0.175 to 0.350 with respect to the quantity 8 ~ 2 of red mud, (c) the weight of mixing water is preferably lower than 10% of the weight of the dry materials for mix design B1, and (d) the weight of mixing water is preferably lower than 15% of the weight of the dry materials for mix design C1.

The above experiment results show that the best, i.e. the safest mix design is C1 since it can be used with a wider range of water contents without presenting cracking problems when immersed in water after a 7-day setting in air.
The mixture according to the invention presents, amongst others, the following advantages:

- the mixture according to the invention incorporates presently unused 15 industrial residues.

- mortar is produced at low cost with a simple technology; the components are simply mixed to obtain a uniform mixture which is then poured into adequate molds or extruded as any natural clay;
- contrary to the more classical pozolonic binders, the binder mixture according to the invention sets relatively rapidly and can be de-molded after 24 hours; the kinetic of the reaction accelerates with temperature whereby the technology involved adapts to the tropical countries. When 25 extruded, the product according to the invention is self sustaining and can be piled very rapidly;

- the use of the sodium salt of a condensate of ,B polynaphtalene sulfonate and formaldehyde provides mortars having a low porosity and ~2~ ~8~ Z

therefore a low sensitivity to exterior conditions or agents; these mortars are water-resistant and reacts in the same manner as hydraulic binders and harden when immersed in water; and 5 - the technology involved in the fabrication of bricks is simple, it is similar to that involved in the fabrication of concrete and consumes a small quantity of energy; the mixture of the present invention can be molded in various shapes whereby it can be used to manufacture tiles, paving stones, pavestone, panels with the technique developed in Canada by the 10 company Unifix, etc. Extruded or molded bricks having a resistance in compression as high as 20 Mpa have been fabricated. These bricks do no present any phenomenon of efflorescence, and they keep a substantially constant volume when subjected to repeated cycles of wetting and drying.
Accordingly, numerous applications of the mixture according to the invention can be developed in the construction and also in the public works and civil engineering.

Although the present invention has been described hereinabove with reference to a preferred embodiment thereof, this embodiment can be modified at will, within the scope of the appended claims, without departing from the spirit and nature of the subject invention.

Claims (2)

1. A binder mixture for use in the fabrication of building materials, comprising the following components:
- red mud;
-fluoroanhydrite;
-lime;
- silica sand or powder; and - a sodium salt of a condensate of .beta. polynaphtalene sulfonate and formaldehyde.

2. A binder mixture as recited in claim 1, further containing various fibres and fibrous material.