GB2264943A

GB2264943A - Brickwork products

Info

Publication number: GB2264943A
Application number: GB9204799A
Authority: GB
Inventors: Klaus Baatjer
Original assignee: ETH UMWELTTECHNIK GmbH
Current assignee: ETH UMWELTTECHNIK GmbH
Priority date: 1991-01-25
Filing date: 1992-03-05
Publication date: 1993-09-15
Also published as: DE4102159A1; FR2688779B1; GB9204799D0; DE4102159C2; FR2688779A1

Description

1 Brickwork Products 2264943 The invention relates to brickwork products

with a content of harbour clay and a method for the manufacture thereof.

Quantitatively speaking, brickwork products are the most important group of ceramic materials used as building materials. Brick products are attained by burping loam, clay and clayey substances with additions of sand, brick powder, blast furnace slag or ash as lean material, wherein the clay loses its hydration water, which is accompanied by partial sintering and pore formation. Brick products are manufactured by crushing clay in edge mills or hammer mills and kneading with water and the lean materials on wet-grinding edge mills. Further includes shaping by extrusion presses, in and revolving presses or similar machines, chamber or tunnel driers and burning in chamber or tunnel kilns with direct or indirect heating by coal, oil or gas. The main types of brick products are clinker, facing tiles, facing bricks and roofing tiles as well as wall bricks. Roofing tiles can have variable shaping such as hollow tiles, interlocking -orocessina eccentric drying in annular 2 tiles or plain tiles. Today, wall bricks or burnt bricks are standardized and can be formed as solid bricks or perforated bricks, the latter being provided with perforations which extend vertically in relation to two parallel boundary faces. During the manufacture of brick products, waste is obtained in the form of brick rubble and.brick dust, which is generally ground and used as brick powder in ceramics, as a lean material for rich clays, or as a colouring addition in the artificial stone industry.

Natural clays are the main component of brick products. Natural clays refer to aluminium silicates with a so-called phyllosilicate structure and variable water content. The clay minerals are subdivided into different groups which differ distinctly in their chemical composition and in physical structure. Outwardly, clays are characterised in that they swell and become plastically deformable in the damp state, but retain their shape after drying and harden during burning, forming mullite. Natural clay deposits consist substantially of particles which have been formed by the weathering of aluminous minerals and which are not larger than 2 gm and because of their cohesive force also form sands and silts. If the proportion of the latter is high, the clay is referred to,ag"lean clay, whereas if the colloidal constituents are in the higher proportion, rich clays are present. Variable quantities 3 of iron compounds, manganese compounds, magnesium compounds, titanium compounds, phosphorus compounds and nitrogen compounds are present in the usual brown or yellowish clays. An important property of the clays is their ability to adsorb and bind a variety of metals and metalloids. Clays therefore also exhibit ion exchanger activities and it is today assumed that they can also have catalytic properties, particularly if a certain content of impurity ions is present.

However, this ability of the natural clay minerals also implies that, on the one hand, the composition can vary according to the deposit but that, on the othe,r, all clay minerals tend to bind radioactive isotopes - some quite selectively. It is known that the radioactivity of clay minerals has risen distinctly on account of the earlier above-ground atomic experiments and on account of the known reactor accidents, since the isotopes are washed out of the aerosols and are bound by clay minerals.

However, the essential properties of the natural clay minerals are also exhibited by the harbour clay or harbour mud, these being harbour, river and pond sediments which are carried into the corresponding water reservoirs by natural or artificial channels and are generally contaminated more heavily with metals, metalloids and organic compounds in comparison with A natural clay deposits on land. In the following, the term "harbour clay" is used to denote the type of sediments deposited under water, regardless of their respective origin. Since harbour clay generally needs to be periodically or continuously removed from harbour basins, the question arises as to what is to be done with these dredged sediments. Because they are partially contaminated with heavy metals and metalloids as well as organic compounds, they can not easily be used e.g. in agriculture, so that harbour clay is deposited on areas near harbours almost worldwide, which leads to considerable difficulties on account of the water- adsorptive capacity of the sediment. Harbour clay has not yet successfully been used instead of natural clay minerals from deposits on land in order to manufacture brick products, since processing difficulties occur when burning such products.

The fact that the manufactured brick products are contaminated with residual heavy metals such as mercury and arsenic have made any use thereof substantially impossible, since heavy metals can be washed out of the finished product through the effect of climate and in particular through the effect of water.

There is therefore furthermore a need for methods whereby harbour clay can be manufactured into brick products which are equally environmentally friendly to - or better than those which have been manufactured from natural clay deposits.

Surprisingly, it has now been established that it is possible to manufacture brick products with a content of harbour clay of up to approx. 50 % of the total mass which satisfy all requirements with regard to building physics and are harmless to the environment.

It has been shown that a large proportion of the terrestrial clay normally used can be replaced by harbour clay, in a proportion of up to 50% of its total mass, if the brick composition further contains up to 10 % fly ash as stabilisor and 10 % brick powder with a grain size distribution of between 0 and 3 mm as lean material. The proportion of fly ash is preferably around 5 %; the remainder of the composition consists of the usual natural terrestrial clay minerals. However, such compositions cannot be processed according to the method which is usual today, if pollution of the environment through the content of metals and metalloids and organic compounds is to be avoided. In accordance with the invention, the brickwork products are therefore manufactured in such a manner that the composition, which has been ground, elutriated and shaped in the usual manner, is subjected to low-temperature predrying. The shaped bricks are dried in drying chambers with the aid of warm air at an air temperature of only approx.

6 'C. This drying air is composed of the exhaust air from the burning kiln and a proportion of fresh air, the two air currents usually being preheated to approx. 110 C with the aid of a gas burner and thus enter into the system of drying chambers. The relatively low drying temperature is necessary in order to reliably prevent the-liberation of mercury and arsenic from the harbour cl ay.

The brick products are then subjected to high-temperature burning of approx. 1300 C, whereas normal burning temperatures are around 900 to 1000 'C. This high-temperature burning converts most of.the harmful substances, in particular metalloids, into gas form. The flue gases are repeatedly passed back through the high-temperature zone, so that organic compounds, in particular dioxins and furans, are substantially decomposed. The high burning temperature makes it possible to convert the majority of the harmful substances into the gaseous condition so that, with the aid of today's highly developed filter technology, it is easy to keep the pollution of the environment very low.

As comparative experiments have shown, in this method in accordance with the invention, the proportions of harmful substances in the flue gases are lower - some substantially lower - than the concentrations required 7 in the "TA-Luft". The flue dusts are caught in filters and are solidified and/or prepared in the usual manner, for example by pouring in a glass matrix. As experiments have shown, the residual substances obtained in the method of the invention are around 0.5 to a maximum of 1.5 % of the original quantity. Taking into account industrial safety requirements, these can be processed or deposited substantially more simply according to the method, since the spatial requirement is drastically reduced. Thus, up to 98.5 % of the harbour clay can be reutilized in an environmentally friendly manner.

The brick products manufactured in accordance with the invention satisfy all the usual requirements regarding building physics. Depending on whether they are burnt in an oxidising or a reducing manner, it is possible to achieve either a red or a blueblack colouration of the bricks. An analysis of the eluate shows that these bricks do not exhibit higher values for harmful substances than bricks made of natural terrestrial sediment, but that some are considerably lower in the eluate values. However, what is particularly surprising is the fact that the radioactive contamination is clearly reduced in these bricks manufactured from harbour clay and is only around 50 % of the values which are usual when using clays from terrestrial deposits.

Footnote: It is unclear whether "TA-Luft11 refers to some technical department for air or to a journal published by this department.

8 It is assumed that the relatively high radioactivity of clay minerals from terrestrial deposits can be explained by the ability of the clays to adsorb radioactive isotopes from the surrounding air, whereas the deposited sediments exhibit a lower contamination.

In the following, the invention is explained in more detail with reference to the examples.

Example 1

A raw brick mixture is produced in usual manner, consisting of 5 % by weight of brick powder with a grain size distribution of 0 to 3 mm, 5 % fly ash, 50 % harbour clay and 40 % natural clay from the clay deposits to be used in each case, and is shaped in usual manner.

The shaped brick bodies are then subjected for 4 days to lowtemperature predrying at an air temperature of approx. 60 C with a considerable addition of pre-heated fresh air.

The pre-dried shaped bodies are subsequently brought into a tunnel kiln with pre-heating zone., firing zone and cooling zone. The article to be burned and the air move in opposite directions in the tunnel kiln. The cold air entering the kiln is used to cool the burnt 9 articles, is heated in the firing zone, serves in the pre-heating zone to heat the brick products which have just been brought into the kiln and is then carried off into the atmosphere via the flue, having previously been passed repeatedly 4 to 6 times - through the hot-air zone by predetermined forced circulation. The burning kiln has a throughput capacity of around 60 Mg/d of burnt articles, the loss due to burning being around 15 % of the mass.

Example 2

In order to test the possible pollution of the,air through harmful substances resulting from the manufacturing process of the invention, analyses of the air in the drying chamber and in the exhaust gas from the drying chamber as well as in the exhaust gas from the burning kiln were carried out in the installation described in Example 1.

Organic substances could not be detected at a detection limit of between 5 mq to 10 mg/m 3 in the exhaust air from the drying chamber and in the drying chamber. The "TA-Luft11 allows a value of 20 rag/m 3 for organic substances of class 1. The contamination with inorganic gaseous chlorine and fluorine compounds and with cadmium, mercury, arsenic, cobalt, lead and chromium was also far lower than the values allowed by the "TA-Luft".

The exhaust gas from the burning kiln was discernibly contaminated with organic substances, though below the permitted values. The components hydrochloric acid, hydrofluoric acid and sulphur dioxide also appear in marked concentrations, but are considerably lower than the-critical boundary values. The mass flows of 0.16 kg/h and 1.45 kg/h, calculated for hydrochloric acid and sulphur dioxide, are still relatively low in comparison with the boundary values of 0.3 kg/h and 5 kg/h stated by the "TA-Luft". Even the values for cadmium, arsenic, cobalt, lead and chromium are non-critical. Only mercury was detected in a considerable concentration, which at around 0.37 mg/m 3 is clearly above the value of 0.2 mg/m 3 stated by the "TA-Luft". However, mercury contaminations can be eliminated almost completely by suitable filters.

Example 3

In order to compare the content of elutable materials and the total content of relevant metals and/or metalloids and the radioactivity, bricks produced in accordance with the invention were compared with commercial bricks from different brickworks. The eluate analysis was carried out by the quality assurance institute of Hamburg; the radioactivity measurement was carried out by the nuclear research institute of 11 KrUmmel. The results are reproduced in the following tables 1 and 2.

As can be seen, the eluate analysis shows that, in this respect, the brick products of the invention are fully comparable with the products which have been usual up til.1 now. When investigating the total content of metals and metalloids, it is even possible in some cases to detect a clearly reduced content in comparison with the standard commercial products and the measurement of the radioactivity shows the surprising result that the values in the bricks of the invention are reduced by around 50 %.

WANGDOC: 1587i TABLE 1

COMPARATIVE STUDIES OF DIFFERENT TYPES OF BRICK - ELUATE ANALYSIS PRODUCER: BRICKWORK BRICKWORK BRICKWORK BRICKWORK BRICKWORK BRICK WITH 1 2 3 4 5 SORS- CLAY (HARBOUR) QUANTITY mg/1 mg/1 mg/1 mg/1 M9/1 mg/1 pH value 9.7 8.15 7.71 8.88 9.2 9.2 Zinc < 0. 02 < 0.02 < 0. 02 < 0.02 <0.2 < 0.2 Cadium < 0.00005 < 0.00005 <0.00005 < 0.00005 <0.00005 < 0.00005 Lead <0.005 < 0.005 <0.005 < 0.005 <0.005 < 0.005 Chromium <0.002 < 0.002 <0.002 0.0062 <0.002 < 0.002 Nickel <0.005 < 0.005 <0.005 < 0.005 <0.005 < 0.005 Iron 0.023 1.2 0.0089 0.0059 0.0091 0.0091 1 ill 1 COMPARATIVE STUDIES OF DIFFERENT-LYPES OF.BRICK - TOTAL CONTENT PRODUCER: BRICKWORK 13RICKWORK BRICKWORK BRICKWORK BRICKWORK BRICK WITH 2 3 4 5 50'-. CLAY (HARBOUR) 1 QUANTITY mg/kg-TS mg/kg-TS mg/kg-TS 3.65 <is.

< 0.5 46.81 < 0.1 9.32 0.606 28.00 Arsenic Lead Cadium Chromium Copper Nickel Mercury Zinc 566.

13.53 0.5 < 0.5 28.93 4.09 3.99 0.459 0.90 <is. < 0.5 18.54 < 1.0 1.998 0.646 35.09 M9/kg-TS M9/kg-TS 99/kg-TS 2.67 < 0.5 < 0.05 61.60 < 0.1 7.32 0.239 30.33 2.32 < 0.5 < 0.05 88.79 6.52 20.64 0.486 41.625 TABLE 2

UNBURNED CLAY WITH 50 0-.

CONTAINED IN THE BRICK 2 3.95 0. 5 ' < 0.05 28.67 < 0.1 2.66 0.406 7.6 1 p- TABLE 2 (cont.) COMPARATIVE STUDIES OF DIFFERENT TYPES OF BRICK TOTAL CONTENT 1 2 3 PRODUCER: BRICKWORK BRICKWORK BRICKWORK BRICKWORK BRICKWORK BRICK WITHUNBURNED 50".- CLAY CLAY WITH (HARBOUR) 50 % CONTAINED IN THE BRICK 4 QUANTITY mg/kg-TS M9/kg-TS mg/kg-TS mg/kg-TS mg/kg-TS gg/kg-TS RADIOACTIVITY/ Ba/kcr Not Tested F K 40 - 610. 380. 340. 320. 260. 620.

Pb 210 - < 5.6 <3.3 < 4.6 <3.9 < 4.3 <0.3 Pb 214 - 96. 94. 38. 33. 60. 810.

Ra 226 - 56. 34. 29. 25. 38. 69.

Th 232 - - - - - - - Th 234 - < 9.4 18. < 7.4 <7.4 < 4.8 < 0.64

Claims

1. Brickwork products, characterised by a content of harbour clay.

2. Brickwork products according to Claim 1, characterised by a content of up to around 50 % harbour clay in the total mass.

3. Brickwork products according to Claim 1 or 2, characterised by a content of around 5 to 10 % by weight of brick powder.

4. Brickwork products according to Claims 1 to 3, characterised by a content of around 5 to 10 % by weight of fly ash.

5. A method for the manufacture of brickwork products according to Claims 1 to 4, characterised in that the shaped brick products are subjected to low-temperature pre-drying for a few days and subsequently to hightemperature burning with a maximum temperature of around 1300 C.

6. A method according to Claim 5, characterised in that the pre-drying is carried out at an air temperature of around 60 C.

tb,

7. A method according to Claim 5 or 6, characterised in that the air is passed back several times in the burning chamber.

8. A method according to Claims 5 to 7, characterised in that burning is performed in an oxidising or reducing manner.