FR2688779A1 - Brickwork products such as bricks, tiles or the like, containing harbour silt, and process for the manufacture of such products - Google Patents

Abstract

Brickwork products such as bricks, tiles, slabs or the like, containing harbour silt. The moulded products are first of all subjected to predrying at low temperature, for a few days, and then to firing at high temperature, the maximum temperature being of the order of 1300<o>C.

Description

BRICKWARE PRODUCTS, SUCH AS BRICKS, TILES OR

ANALOGUES, CONTAINING PORT SLIM, AND

MANUFACTURING PROCESS OF SUCH PRODUCTS

The invention relates to brickwork products, such as bricks, tiles, slabs or the like, containing port silt, and relates to a

process for making them.

Brick-making products constitute the quantitatively largest group of ceramic materials used as building materials. Brick-making products are obtained by firing clay, silt and clay masses with additions of sand, brick powder, high slag. furnace or ash as a degreaser The clay loses its water of hydration, which is accompanied by partial sintering and pore formation. with hammers, then kneading with water and degreasers in roller mixers The rest of the work involves shaping by extrusion in eccentric presses, rotary table presses or similar machines, then drying in dryers chamber or channel and firing in annular, chamber or tunnel furnaces, with direct or indirect heating by means of coal, fuel oil or gas Among the "products of brickworks ", one distinguishes, for the most part, vitrified bricks, plates for facade, facings, tiles as well as masonry bricks The tiles can be presented in various forms such as hollow tile, hollow tile with interlocking, flat tile, etc. masonry bricks or fired bricks are now standardized and can be in the form of solid bricks or perforated bricks, in which case they are provided with perforations extending perpendicular to two parallel boundary surfaces When manufacturing brick products , the offcuts come in the form of dust and fragments of bricks which are generally crushed and used in ceramics, in the form of brick flour, as a degreaser for fatty clays, or as

as a coloring additive in the artificial stone industry.

Natural clays are essential constituents of brick-making products By "natural clays" are meant aluminum silicates having what is called a phyllosilicate structure, and different water contents Clay minerals are classified into different groups which differ markedly by their chemical composition and physical structure Clays are externally characterized by the fact that they swell and become plastic when wet and, after drying, retain their shape and, when fired, harden with the formation of mullite For l 'essential, natural clays consist of particles caused by the disintegration of clay minerals These particles are not greater than 2 Rm and, due to their cohesive strength, also form sands and silts If the latter are present in high content , we then speak of lean clay.On the other hand, if the colloidal constituents have a greater presence, it is a question of fatty clays The usual brown or yellow clays contain varying amounts of compounds of iron, manganese, magnesium, titanium, phosphorus and nitrogen compounds An important property of clays is their ability to adsorb and fix the most different metals and metalloids. therefore have ion exchanger activities and it is now accepted that they can also have catalytic characteristics, in particular when there is a

3 O certain content of foreign ions.

However, this ability of natural clay minerals also implies that their composition may differ depending on the deposit and that they all tend to bind, and sometimes very selectively, radioactive isotopes. It is known that the radioactivity of clay minerals has clearly 3 5 increased due to old non-underground nuclear tests and due to known reactor accidents Indeed, isotopes are washed away

aerosols and fixed by silts and clay minerals.

Port clay or silt, however, has essential characteristics of natural clay minerals.These are port sediments, fluvial sediments and sediments of water bodies which are brought into the corresponding basins by natural or artificial water currents and which , as a general rule, have a higher load of metals, metalloids and organic compounds than that of natural clay In what follows, the terms "port silt" designate such sediments deposited under water, without taking into account their particular origin Port silt is generally removed from port basins, periodically or continuously, so that these dredged sediments pose a problem of use or discharge Their content of heavy metals and metalloids as well as organic compounds prevents use them as they are, for example in agriculture. As a result, almost everywhere in the world, port silt is deposited on areas close to ity of the ports, which creates notable difficulties due to the ability of the sediment to fix water The use of port silt instead of natural mineral clays, to make brickyard products, has so far failed due to difficulties of

treatment encountered when cooking such products.

The presence of residual heavy metals, such as mercury and arsenic, in products which would be made with such silts has heretofore made their use virtually impossible because heavy metals can be removed from the finished product by elution under the effect of actions

climatic, especially under the action of water.

There is therefore a need for a process making it possible to transform the port silt into brickyard products having an environmental compatibility at least as good as that of the products manufactured in

from naturally occurring clay.

This being the case, it has surprisingly been found that it is possible to produce brickyard products comprising port silt, and that with a content which can reach about 50% of the total mass, and that such products meet all the requirements. in terms of qualities

physical for construction and were ecologically flawless.

It turns out that much of the clay or terrestrial silt normally used can be replaced by port silt, and this up to about 50% of the total mass, if the brick mix additionally contains up to 10% fly ash as stabilizer and 10% brick powder with a particle size between 0 and 3 mm, as a degreaser. Preferably, the fly ash content is of the order of 5%. The remainder of the mixture is made up of the usual natural clay minerals. Such mixtures cannot however be worked according to the currently usual methods if one wishes to avoid pollution due to their content of metals and metalloids and organic compounds According to the invention , brickwork products are therefore manufactured by subjecting the mixture previously crushed, kneaded, mixed with water and molded, to pre-drying at low temperature.The molded products are dried in drying chambers using hot air, at a temperature of only around 600 C This drying air consists of the air leaving the baking oven and a certain proportion of fresh air These two air currents will in most cases be preheated to around 110 C , using a gas burner, then fed into the drying chamber system in this way The relatively low level of the drying temperature is necessary in order to avoid

with certainty the release of mercury and arsenic from the port silt.

The brickyard products are then subjected to high temperature firing, of the order of 13000 C, while normal firing temperatures are of the order of 900 to 1000 C. This high temperature firing has the effect that most harmful materials, in particular metalloids, pass in gaseous form The fumes are made to circulate several times through the high temperature zone, so that the organic compounds, in particular dioxyne and furan are very substantially decomposed The high cooking temperature allows to convert the major part of the harmful substances to the gaseous state, so that one can then, without problem, maintain the pollution of the environment at a very low level.

low by using filtering techniques that are now highly developed.

Comparative tests have shown that with the process according to the invention, the levels of harmful substances in the fumes were lower, and even in part much lower, than the limit concentrations imposed by the technical directives relating to air. 'air are captured in filters and compacted or treated in the usual way, for example by coating in a glass matrix. Tests have shown that with the process according to the invention the residual materials

remaining are of the order of 0.5 to 1.5% at most, of the initial quantity.

After having operated according to the invention, these residual materials are simpler to treat or to deposit while respecting occupational safety standards because their size is very greatly reduced.The port silt is therefore reusable, up to a maximum of approximately 98.5%, in

respect for ecological rules.

The brickworks produced according to the invention satisfy

all physical requirements for building materials.

Depending on whether the firing was oxidizing or reducing, it is possible to obtain a red or blue-black coloration of the products. The analysis of the eluted materials shows that, compared with the products originating from natural terrestrial deposits, the products according to the invention do not exhibit higher levels of noxious materials, sometimes even significantly lower levels of eluted matter One fact is particularly surprising: the radioactive charge with these brick kiln products made from harbor silt is significantly reduced and is only about 50% in value of what is otherwise usual when using clays from terrestrial deposits It is to be assumed that the relatively high radioactivity of clay or clay minerals from terrestrial deposits is explained by the adsorption capacity that clays exhibit to the soil. with regard to radioactive isotopes coming from the atmosphere while, on the other hand, sediments

deposited have a lower radioactive charge.

In the following, the invention is described in more detail in

considering examples.

Example 1

A raw mixture for bricks or tiles is produced in the usual way, comprising 5% by weight of brick powder with a particle size of 0 to 3 mm, 5% of fly ash, 50% of port silt and 40% of natural clay. coming from exploitable clay pits, and this mixture is molded in the usual way The raw bricks are then subjected for four days to a predrying at low temperature, with a large supply of preheated fresh air, for an air temperature of around 600 C.

The pre-dried raw parts are then introduced into an oven.

tunnel with preheating zone, cooking zone and cooling zone The material to be cooked and the air move in opposite directions in the tunnel oven The incoming cold air is used to cool the baked products, heats up in the zone and is used, in the preheating zone, to heat the fresh products introduced into the oven, then is sent to the atmosphere via the chimney after having passed 4 to 6 times, by forced circulation, through the air zone hot The baking oven has a capacity of around 60 Mg / d of baked products, the loss on ignition being equal to

about 15% of the mass.

Example 2

In order to control the possible load of the air with harmful materials, due to the manufacturing process according to the invention, in the case of the installation described in Example 1, analyzes of the air in the chamber were carried out. drying chamber and in the effluent gas from the drying chamber as well

than in the gaseous effluent leaving the baking oven.

In the air leaving the drying chamber, and in the drying chamber, it was not possible to detect organic matter, with a detection limit of between 5 mg and 10 mg / m 3 For organic matter of class 1, the technical directives concerning air authorize a value of 20 mg / m 3 Likewise, the loads in gaseous chlorinated and fluorinated inorganic compounds, as well as in cadmium, mercury, arsenic, cobalt, lead and chromium, were far below the values admitted by

technical guidelines for air.

The gases leaving the baking oven had a detectable load of organic matter, which was however lower than the admissible values. Similarly, the components of hydrochloric gas, hydrofluoric gas and sulfur dioxide were present in net concentrations, however notably lower than the critical limit values Mass flow rates 0.16 kg / h and 1.45 kg / h calculated for hydrochloric gas and sulfur dioxide are still relatively low when compared to the respective limit values

of 0.3 kg / h and 5 kg / h indicated by the technical directives concerning air.

The values for cadmium, arsenic, cobalt, lead and chromium are also not critical , is clearly above the value of 0.2 mg / m 3 authorized by the technical directives concerning air However, suitable filters allow

eliminate almost all mercury loads.

Example 3

To compare the content of elutable materials as well as the overall content of metals and / or metalloids consumed concerned and the radioactivity, bricks manufactured according to the invention were compared with commercial bricks from different brickworks. The analysis of the eluted materials was carried out. by the Qualitatssicherheitsinstitut Hamburg, and the radioactivity was measured by the Kernuntersuchungsinstitut Kr mmel Les

results are shown in Tables 1 and 2 presented below.

Analysis of the eluted materials shows that in this respect the products in accordance with the invention are entirely comparable to the usual prior products. Examination of the overall content of metals and metalloids even makes it possible to observe in part a clearly reduced content. compared to the usual marketed products, and the measurement of the radioactivity shows this surprising result: the values are reduced by approximately 50%

with the brickworks according to the invention.

Table I

Comparisons between various types of bricks analysis of eluted materials Manufacturer: brickyard brickyard brickyard brickyard brickyard Brick with 50% port silt. Quantity: mg / l mg / l mg / 1 mg / 1 mg / l mg / 1 Co p H Zinc Cadmium Lead Chromium Nickel Iron 9.7

<0.02

<0.00005

<0.005

<0.002

<0.005

0.023 8.15

<0.02

<0.00005

<0.005

<0.002

K 0.005

1.2 7.71

<0.02

<0.00005

<0.005

<0.002

<0.005

0.0089

8.88

<0.02

<0.00005

<0.005

0.0062

<0.005

0.0059

9.2 <0.2

<0.00005

<0.005

<0.002

<0.005

0.0091

9.2 <0.2

<0.00005

<0.005

<0.002

<0.005

0.0091

K, O = (O Comparisons between various types of bricks Total contents Manufacturer: brickyard brickyard brickyard brickyard A brickyard brick with 50% - raw clay content 50% Jim port in the brick Quantity: mg / kg-TS mg / kg-TS mg / kg-TS mg / kg-TS mg / kg-TS gg / kg-TS Arsenic Lead Cadmium Chromium Copper Nickel Mercury Zinc

Radioaktivi-

tee Bq / kg

K 40

Pb 210 Pb 214 Ra 226 Th 232 Th 234 13.53 <0.5 <0.5 28.93 4.09 3.99 0, 459 0.90 <15

<0.5

18.54 <, 1.0 1.998 0.646, 09 3.65 <15 <0.5 46.81 <0.1 9.32 0.606 28.00 2.67 <0.5

<0.05

61.60 <0.1 7.32 0.239, 33 2.32 <0.5

<0.05

88.79 6.52, 64 0.486

41.625

3.95 <0.5

<0.05

28.67

<'0.1

2.66 0.406 27.6 uncontrolled

<5.6

<9.4

<3; 3

94 '

<4.6

<7.4

<3.9

<7.4

260,620

<4.3 <0.3

810

38 69

<4.8 <0.64

o, o, (O

Table 2

Claims (5)

1 Brick-making products, such as bricks, tiles, slabs or analogues, characterized in that they contain port silt. 2 Brick-making products according to claim 1, characterized by a port silt content of up to about 50% of the total mass. 3 Brick-making products according to claim I or 2, characterized by a brick powder content of the order of 5 to 10% by weight. 4 brickwork products according to any one of claims 1 to 3, characterized by a fly ash content of the order of 5 to 10% in weight. A method of manufacturing brickyard products according to one any of claims I to 4, characterized in that the products of Molded brickworks are first subjected to a low temperature predrying, for a few days, then to a high temperature firing, the maximum temperature being of the order of 13000 C. 6 A method according to claim 5, characterized in that the predrying is performed with air at a temperature of approximately 60 C. 7 A method according to claim 5, characterized in that one makes circulate the air several times in the cooking chamber. 8 A method according to any one of claims 5 to 7, characterized in that the cooking is oxidizing or reducing.