WO2018109173A1

WO2018109173A1 - Method for providing a hydraulically hardening binder and use of the cement composition based thereon

Info

Publication number: WO2018109173A1
Application number: PCT/EP2017/083050
Authority: WO
Inventors: Wolfgang Perbix; Winfried MALOMY
Original assignee: Firma Ibu Bau + Tec Ug (Haftungsbeschränkt); Hochschule Wismar; Firma Bn Umwelt Gmbh
Priority date: 2016-12-16
Filing date: 2017-12-15
Publication date: 2018-06-21
Also published as: EP3555016A1; DE102016124707A1

Abstract

A method for providing a hydraulically hardening binder free of asbestos fibre is intended to enable treatment of an asbestos-containing building material bound with calcium silicate hydrate, especially with cement, employing a thermal treatment step and using up as little resources as possible, while observing the relevant limits for health-hazard substances. The invention does this by subjecting an asbestos-containing starting material to both a thermal treatment and a dry deagglomeration, the thermal treatment seeing the starting material first heated in a homogeneous temperature environment over a heating period with rising temperature to a target temperature of at least 600°C and at most 800°C, preferably of about 700°C, and then held at the target temperature over a treatment period of at least 60 min and at most 180 min, preferably about 90 min, before being cooled to environment temperature.

Description

description

A method of providing a hydraulically setting binder and use of the cement based thereon

The invention relates to a method for providing a hydraulically hardening binder of calcium silicate hydrate, in particular cement-bound asbestos fiber-containing building materials, in particular for use as a base material and / or component in a cement base material. It further relates to the use of the fiber-free hydraulically setting binder obtainable by the process.

On the other hand, asbestos-containing cement-based building material offers due to its constituents and its usual composition an attractive starting material from which in the way of recycling a suitable for use as a building material hydraulically hardening cementitious and / or cementitious binder can be recovered. This recycled material can be used both in pure form and as an additional component of hydraulic binders, for example of cements and / or additives; A suitable and also intended binder for these uses is also referred to below as "cement base material", since it can be used as an essential component for a cement. In the described recycling of the binder, it is imperative in view of the current health regulations that the recyclate is free of health-endangering asbestos fibers.

For example, it is known from DE 197 18 606 A1 in this connection that asbestos fiber destruction can be brought about by "thermal reacting" the binder by thermal treatment of asbestos-containing material in a temperature range between about 600 ° C. and 1000 ° C. However, this has It has also been shown that, even after a treatment time of several hours, fibrous particles can be detected which have to be destroyed in a further, subsequent treatment step in order to obtain a fiber-free product after such a thermal treatment of asbestos cement products has been carried out as a result of the dehydroxylation caused by the preceding thermal treatment, such fiber elastics are present in a syrupy form. For example, when asbestos fibers, which are known to have a pronounced longitudinal characteristic slack when subjected to mechanical stress, break the transition products resulting from the thermal treatment transversely to the fiber axis, so that aftertreatment can produce particles of less than 5 μm in length. Such particles do not correspond to the fiber definition of the WHO and are considered to be harmless to health.

An alternative concept for asbestos fiber destruction is known from EP 0 672 469 A1. In this alternative method is provided to crush the asbestos fibers alone by a purely mechanical treatment by means of an eccentric vibrating mill (ESM) in particles harmless to health. In a further alternative approach, as known for example from DE 4 332 031 C1, a process for the preparation of natural or synthetic fibrous materials - in particular asbestos-containing materials - by cold embrittlement, multi-stage pulping and treatment in a centrifugal field to fiber-free stock suspensions or powders proposed. However, by means of these purely mechanical induced fiber destruction with or without cold embrittlement, the goal of producing a hydraulically setting binder cementitious / cementitious quality asbestos cement products can not be achieved, since this is the recovery of hydraulically active phases necessary for reuse as a cementitious binder is not achievable ,

The invention is therefore based on the object to provide an improved method for providing a hydraulically hardening binder, with the recourse to a thermal treatment step and thereby minimized use of resources reliable provision of a cementitious / cementitious binder is possible. In particular, the production of asbestos-fiber-free recyclates from asbestos cement waste and their utilization should be made possible by the recovery of hydraulically active phases with simultaneous fiber destruction. Furthermore, a particularly suitable use of the thus obtained cementitious binder should be specified.

With regard to the method, this object is achieved according to the invention by an asbestos-containing, preferably calcium silicate-bound, particularly preferably cement-bound starting material is subjected to both a thermal treatment and a dry deagglomeration, wherein the starting material in the thermal treatment initially predried in a homogeneous temperature environment, then with rising temperature to a target temperature of at least 600 C and at most 800 C, preferably heated by about 700 C and then maintained over a treatment period of at least 60min and at most 180 min, preferably about 90 minutes, at the target temperature.

In this context, "deagglomeration" is to be understood as meaning, in particular, a comminution process with which the particle agglomerates produced as a result of thermally induced solid-state reactions with the formation of low-strength sintered bridges are treated in the manner of a decomposition with comparatively low energy input Zemensteingefüge decomposed with comparatively low energy expenditure in particles and fiber relics, so that subsequently, if necessary, a targeted separate treatment of the exposed fiber relics is possible.

In contrast to a grinding process, the presently provided deagglomeration specifically serves for comminution of the previously thermally treated cement stone structure by dissolving the matrix into individual particles by separating the now only weak bonds between the primary particles newly formed by solid state reactions. It is resorted to that in the present process during the thermal treatment, a softening of the cement paste is made. This is based in particular on the dehydration of calcium silicate (CSH) as a result of the thermal treatment at about 700 C. This metastable phases, primarily of the calcium silicate, also referred to as meta-calcium silicate, with microporous structure. The resulting microporosity of the structure is reflected for example in a macroscopically observed high water absorption capacity of the former cement paste.

Solid-state reactions of the meta-calcium silicate with calcium (from portlandite or calcium carbonate) give rise to conversion products (a'-C2S), which are characterized by their comparatively high reactivity with respect to the conventional C2-Cs known from classical cement chemistry and the recyclate / recycling binder the desired rapid strength development to lend. This thermally initiated process takes place in the present case (at a temperature of preferably about 700 C) in the solid state - ie below the temperature of the occurrence of a melt phase - instead. In the course of the thermal treatment occurring production of recyclates / recycled binder from the fibrous cement stone structure take place at a comparatively low temperature solid state reactions, which in turn agglomerates are formed from the particles with microporous structures. These agglomerates in turn have microporous structures characterized only by comparatively weak sinter bridges, so that they can be "deagglomerated" by selected dry comminution techniques with relatively low energy input, comparable to the preparation of colored pigments 83% of thermally treated versus thermally untreated fiber cement boards.

At the same time, as a result of the thermal stress, the asbestos cement fibers are embrittled so that, after the thermal treatment of the asbestos cement, a softened structure of conversion products of the former cementstone (hydraulic phases newly formed by solid-state reactions) and brittle fibers is produced which is comparatively "light". - in the sense of: under comparatively low energy input - by disagglomeration into its components "particles" and "fiber relicts" to disassemble is.

The deagglomeration can thus be controlled by taking into account the required energy requirements so that particles with a certain particle size (according to commercially available cements) are obtained 5 m are present, these are auszuschleusen by means of classifier.

The invention is based on the consideration that the process for recycling asbestos-containing, calcium silicate hydrate, in particular cement, bonded material should be based on a thermal treatment step, thus the reliable destruction and removal of asbestos fibers while reactivating the binder by recovering hydraulically active To enable phases. However, subsequent comminution required in connection with known thermal treatment steps, which usually has to take place in mills suitable for ultrafine grinding, such as jet mills, is extremely complicated and thus uneconomical. In order to reduce this expense, the invention instead starts from the surprising finding that the thermal treatment is carried out with suitable Not only leads to the required dehydroxylation of the asbestos ingredients of the asbestos cement feedstock, but also to the dewatering of the hydrate phases of the cement paste and the subsequent solid reactions based new formation of cementitious / cementitious, hydraulically active phases and in conjunction with a suitable crushing technique (deagglomeration) the production fiber-free Recyclates made possible. In contrast to the cement clinker produced in the known cement clinker burning process, the recycling product thus does not require the high energy expenditure required for comminuting the cement clinker particles by breaking chemical bonds, given its completely different origin. On the contrary, the particles produced as a result of the low-temperature method now being used are agglomerates of smaller particles formed solely by release of water of hydration by solid-state reactions and thus not in the presence of a melting phase.

It has been shown in recent studies that it is in contrast to the known methods just taking into account the material nature of the output of the thermal treatment - these are agglomerates of solid bridges ("Sinterbrücken") associated primary particles in the course of thermal induced solid state reactions are obtained as conversion products - special comminution techniques are needed to produce a fiber-free product at a reasonable cost.

Using the above-described relationships, the invention is then based on disagglomerating the obtained after the lumped, possibly undivided plate-shaped feed material thermal treatment under application of limited (shear) forces in a dry process and in this case the fiber relics (from the Asbestos transformation) also in micrometer-fine particles to divide or thereby possibly not yet sufficiently shredded fiber relieves exposed so that they can be discharged .. The deagglomeration of the particle heaps (agglomerates) formed in the course of thermal treatment also serves the enlargement of the surface to possibly desirably further increasing the reactivity and achieving smaller particle sizes for a higher fineness.

The execution of said deagglomeration is made possible, in particular, by the preceding comparatively "gentle" thermal treatment, in which at first a predrying, preferably at a drying temperature of about 100 ° C., takes place. 120 C, more preferably at about 105 C, is made. Then, a comparatively moderate target temperature is set, which can also precede a comparatively slow, over a certain time interval extending warm-up step. This can be done, for example, by placing the predried material in the treatment oven, which has already been preheated to the target temperature, and thus heating up to the target temperature. Precisely by predrying at a preferred drying temperature of at least 100 ° C., the water bound in the feed can be controlled to escape. By drying at a temperature of preferably about 105 C to 1 15 C is physically removed, for example, in the pore spaces bound water, so that an "explosion" of the material by increasing the vapor pressure in the cement stone structure in the course of further heating up to the target temperature (at least 600 ° C.), which is particularly suitable for comminution by deagglomeration.

After the thermal treatment at the target temperature, the treated material is cooled back to ambient temperature. The intended for this process step cooling period is advantageously selected material-specific and adapted to the starting material and its composition. In a particularly advantageous embodiment, a comparatively fast and short-term cooling, in the manner of a "quenching" or "quenching", to ambient temperature within a cooling period of at most 10 minutes, particularly preferably of at most 1 minute is provided.

By means of the process step of deagglomeration, the previously thermally treated limestone structure is to be decomposed with comparatively low expenditure of energy into particles and optionally still existing fiber relics, so that subsequently-if necessary-a targeted separate treatment of the exposed, possibly still existing fiber relicts becomes possible. Advantageously, the thermally treated starting material is subjected to a mechanical deagglomeration, preferably by means of an attritor specially designed for deagglomeration, for example of the ultra-rotor type.

Due to the intended combination of the thermal treatment in the mentioned process control with the subsequent deagglomeration, an intermediate product is obtained, which preferably contains fine particles of cement together with possibly still present, exposed embrittled fiber skeletons. The latter, if they should still be considered as fibers within the meaning of the WHO criteria, should then be removed from the product to obtain a fiber-free recyclate. To achieve this, you can two preferred variants in terms of aftertreatment are provided independently or in combination with each other. In this case, on the one hand a discharge of the fibers, preferably by means of sifter and / or filter and / or on the other hand, a destruction of the remaining embrittled fibers, in particular by breaking, possible. Both variants mentioned are taken individually or in combination with each other as an independent invention.

In particular, following the described thermal treatment, it is possible to destroy the exposed and embrittled fiber fractures in a mechanical treatment process in the sense of breaking, so that the stated criterion of freedom from fibers in the recycled material is achieved. As has surprisingly been found, it is not necessary to resort to the mentioned thermal pretreatment of the otherwise customary and required integral comminution of all particles of the process output to a fineness <5 pm in order to achieve the property of freedom from fibers. Rather, this is achieved in the present case by advantageously providing a comminution process for mechanical deagglomeration, preferably in an attritor, for example an ultra-rotor, in which the particles are finely ground to a particle-fine particle size, for example a particle size of at most 20 μm. Advantageously, the comminution process is carried out during or after the dry deagglomeration until the fibers have a fiber length of at most 5 pm and / or a fiber content of at most 0.1 mass%. It is particularly preferred that the comminution process be carried out until the end product is asbestos-free as defined in the "Technical Rules for Hazardous Substances" (TRGS) using the detection method described in TRGS, the detection limit of which is 0.008% by mass.

Alternatively, in principle, an autogenous grinding, in particular by special ball mills or the like, are performed, which, in contrast to conventional units of this type by their special design give the grinding media a higher kinetic energy of the grinding media. Such mills are, for example, an eccentric vibrating mill or stirred ball mills. For example, when using the eccentric vibrating mill a little demanding criterion of fiber freedom (length <5 pm or fiber content <0.1 mass%) can be achieved if after a few minutes claiming pre-shredding by means of rods then 3, for safety reasons 4 hours ground with steel balls becomes. The output, however, indicates this Largest grain of on average about 20 μηι, so that the said use of an attritor with the achievable complete freedom of fiber is preferred.

For the alternatively or additionally provided particularly preferred aftertreatment by sifting and filtering the exposed, versprodeten Faserrelikte be discharged by means of an air classifier from the recyclate and by means of suitable particulate matter filter, eg. B. of the G3-type, are deposited.

The binder obtainable by the method described above is particularly preferably used for applications, in particular in a cement, for earthworks and / or civil engineering. The fiber-free recyclate produced by the process described above hardens hydraulically. It can be used both in pure form and as an additional component of hydraulic binders, for example of cements and / or additives. Its strength development and its 28-day strength are similar to those of standard cements. If rapid solidification is required from an application point of view, it is preferably used without delaying additives or additives. If, on the other hand, a solidification process analogous to the standard cements is required, solidification may be achieved by addition of a sulphate support, e.g. in the form of gypsum or hemihydrate, or by adding a commercially available retarder (concrete admixture).

The water claim of the recyclate is in view of its microporosity significantly above the commercial cements. This proves beneficial in a number of applications, for example in its use for soil improvement. Applications requiring lower water requirements are made possible by the addition of concrete liquefiers or plasticizers known from concrete technology.

The use of classical energy-intensive mills, such as those used for grinding the cement produced by liquid phase sintering in cement production, is not required in the comminution of the conversion products generated during the thermal treatment. Rather, the lower energy requirement for comminuting the conversion products can be advantageously used by the particularly preferred use of attritors, so as to optimize the efficiency of the treatment by efficient use of energy. For example, suitable attritors include a special shredding technique in one Air vortex mill, as it is available, for example, under the name ULTRA ROTOR. In contrast to classical grinding technology, as used, for example, for the treatment of relatively hard clinker produced by liquid phase sintering in the course of cement production, it is typically possible with such an air vortex mill to comminute soft to medium-hard materials. For this purpose, the materials - in the present application, the agglomerates - offset by an air flow in extreme turbulence and comminuted both autogenous - ie by the collision of particles - as well as grinding tracks and tools. This comminution happens especially at natural breakages. In the present case of the comminution of thermally treated cement stone structure, the natural fracture sites correspond to the microcracks occurring in the course of dehydration and / or the weak sintered bridges which were formed by the described solid state reactions at a comparatively low temperature level (700 C) and connect the primary particles. The efficiency of the comminution can be increased by the combination with classifiers.

The deagglomeration by means of such a fluidized-fluid mill is distinguished from grinding by conventional grinding techniques, in particular by the significantly shorter duration of the required comminuting process, ie the duration of the energy input: compared to, for example, two-stage grinding in a conventional mill, which lasts about 4 hours the residence time of the material in an air vortex mill for the purpose of deagglomeration is preferably only a few seconds or even <1 second.

As an alternative to the described units, attritors of different types can be advantageously used for energy-efficient deagglomeration, as are used, for example, especially for the treatment of color pigments and / or soft to medium-hard materials. The particular economic advantages of these technologies for the present application lie in the low energy consumption and in the usually short residence times of the feed material in the aggregate, so that comparatively high throughput rates can be achieved in the comminution of the agglomerates.

In principle, deagglomeration can also be achieved by means of special classical mills suitable for superfine comminution, with a lower energy input being sufficient than in the treatment of thermally unloaded cement stone fragments or clinker obtained from liquid phase sintering. The use of classic mills for the present application, however, usually requires comparatively long Residence times of the feed material in the mill, so that only very limited throughputs are to be realized, which put the economic viability of the method in question. In addition, the deagglomeration can not even be achieved on a case-by-case basis, since the compaction effect of, for example, ball mills sets the excitable particle size too high and the desired desogglomeration is not attainable in a dry state.

The advantages achieved by the invention are in particular that by the inventive combination of upstream thermal treatment and subsequent disagglomeration step and optionally undertaken visual process of asbestos, calciumsilikathydrat-, in particular cement, bound starting material to achieve the fineness of commercial cements or especially those of Comminution required by ultra-fine cements not required for grinding mineral hard rock as well as cement clinker high grinding energy, but with the significantly lower energy input one of the usual deagglomeration process, such as by using an ultra-rotor, can be guaranteed.

By the thermal treatment at preferably about 700 ° C, asbestos-free material can first be produced in the manner of an intermediate product. Due to the additionally provided comminution of the conversion products to a particle size of max. 5 pm, the recycling binder is also fiber-free. The end product is thus free of asbestos fibers, also in the sense of the "Technical Rules for Hazardous Substances" (TRGS) .The definition of asbestos fibers is that fibers which, according to their "chemical composition", belong to the six asbestos minerals according to section 2.2 , By the present invention, the criterion "asbestos-free" is met, since with the thermal treatment of the starting material at 700 ° C, which is required to activate the new binder anyway, a conversion of Asbestos is initiated, so that the final product because of its chemical mineralogical change is not considered more than asbestos - especially not more than chrysotile - to qualify.

As a subsequent second measure, the destruction of the fibers is effected by the comminution treatment. According to WHO and subsequently in the TRGS, a fiber is defined by the criteria length> 5 pm, diameter <3 pm, length-to-diameter ratio> 3: 1. With the above treatment, the entire, thermally pretreated material to a grain size of max. 5 pm to be crushed. If this succeeds, the binder is fiber-free according to WHO definition. An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

1 shows a flow chart with the method steps of a method for providing a fiber-free, hydraulically setting binder of asbestos-containing, calcium silicate hydrate, in particular cement, bonded building materials, and

2 is a flow chart showing the process steps of an alternative process for providing a fiber-free hydraulically setting binder of asbestos-containing, calcium silicate hydrate, especially cement, bonded building materials.

Identical parts are provided with the same reference numerals in all figures.

The method shown in FIGS. 1, 2 in each case by way of example by means of its method steps for providing a fiber-free, hydraulically setting binder is in each case provided for the treatment and recycling of cement-bound asbestos waste, the reliable provision of a recourse to a thermal treatment step while minimizing the use of resources Asbestos-free binder should be guaranteed.

For this purpose, the delivery of lumpy, possibly roughly pre-shredded or else undivided feed material is provided in method step 1. Basically, the material can be supplied in any form in the sense of "as loose material" or "in conventional units" (eg in big bags, which are used in particular for the transport of asbestos cements and thus the delivery form) of the preparation. The feedstock is subjected to a thermal treatment in a treatment step 2. The thermal treatment itself comprises several sub-steps. In a predrying step 4, the material to be treated is initially predried in a suitable environment over a drying period of about 2 hours at a drying temperature of about 105 ° C. in the exemplary embodiment. This ensures that physically bound water is removed from the feed material, so that subsequently an "explosion" of the material is avoided by increasing the vapor pressure in the cement paste in the course of further heating to the actual target temperature (at least 600 ° C.) This drying phase becomes the feedstock heated to a target temperature of at least 600 C and at most 800 C, preferably from about 700 C with constantly rising temperature.

The heating to the target temperature can take place in the embodiment, by the pre-dried items is introduced into the corresponding preheated treatment furnace. This is configured suitably adjustable so that the proposed thermal conditioning of the material from drying to cooling is possible. Alternatively, however, a continuous production process is conceivable: the material can be transported, for example by means of a transport device first through a furnace (section) for pre-drying and then into the temperature zone of the furnace or furnace section with the target temperature, before it then to cool from the oven is dissipated. The different temperature ranges could be achieved by connected (single) ovens or by different temperature zones in an oven, e.g. in the rotary kiln, be realized. Last but not least, final process management is a question of cost-effectiveness as a function of material throughput and energy input.

In the treatment step 6 subsequent to the predrying, the material to be treated is maintained at the target temperature over a treatment period of at least 60 minutes and at most 180 minutes, preferably about 90 minutes, before being cooled again to ambient temperature in a cooling step 8.

The thermal treatment ensures that the material to be treated is dewatered and the cement-stone matrix softened, whereby the asbestos fibers contained therein become brittle and their crystal structure collapses. As a result of the solid state reactions that occur, the desired recovery of the hydraulically active phases takes place.

In a deagglomeration step 10 following the thermal treatment, the particulate reaction products are dry deagglomerated, for example in an ultra rotor, and thereby comminuted to cement fineness. At the same time, the exposure of possibly still contained, now already embrittled fiber relics takes place. The deagglomeration step is based on the finding that the conversion product as a result of the thermal treatment is present in the form of particle agglomerates which can be separated into individual particles by separation of the weak bonds. On this basis, comminution is made possible with a comparatively low energy input (in contrast to the comminution of hard materials commonly referred to as "grinding", such as natural rocks used as aggregate for concretes, cement clinker, concrete, etc.). Thus, "deagglomeration" characterizes, in particular, comminution with targeted use of the present material properties, and the process step of deagglomeration can be controlled taking into account the required energy requirement in such a way that particles having a certain particle size (in accordance with commercially available cements) are achieved. In particular, the adhesive forces between the particles present must be overcome for deagglomeration.

In the following treatment, the methods differ according to. Fig. 1, Fig. 2 from each other, wherein a combination of the subsequent treatment steps may be provided. In the embodiment gem. 1, after the thermal treatment and deagglomeration, a method step 12 is provided for discharging the brittle fiber elements. This is done by sifting and filtering. In the alternatively or additionally provided subsequent treatment acc. 2, however, a treatment step 14 is provided, in which by mechanical grinding destruction of the remaining brittle Asbestfaserrelikte is done by breaking.

Subsequently, in both variants, the further use 20 of the recyclate. This has as essential properties: it is asbestos-free with a fiber content of at most 0.1 M%, it is hydraulically hardening and cementitious.

LIST OF REFERENCE NUMBERS

step

treatment step

pre-drying

treatment step

cooling step

de-agglomeration

step

treatment step

re-use

Claims

claims

1 . A method of providing a cementitious base material containing a hydraulically hardening binder, in which an asbestos-containing, preferably calcium silicate-bound starting material is subjected to both a thermal treatment and a dry deagglomeration, wherein the starting material is initially predried in a homogeneous temperature environment during the thermal treatment, then with rising temperature to a target temperature of at least 600 C and at most 800 C, preferably of about 700 C, heated and then maintained over a treatment period of at least 60min and at most 180 minutes, preferably about 90 minutes, at the target temperature.

2. The method of claim 1, wherein the thermally treated starting material is subjected to a dry mechanical deagglomeration.

3. The method of claim 1 or 2, wherein the predrying at a treatment temperature of at least 100 C, preferably from about 105 C to 1 15 C, is performed.

4. The method of claim 2 or 3, wherein for mechanical deagglomeration a crushing process, preferably in an attritor, for example an ultra-rotor, is provided, in which a comminution of agglomerates formed in the thermal treatment of primary particles to a particle size of at most 20 pm takes place.

5. The method according to any one of claims 1 to 4, wherein the dry deagglomeration is carried out until the content of fibers of a length of at least 5 pm is at most 0.1% by mass.

6. The method according to any one of claims 1 to 5, wherein during or after the dry deagglomeration still remaining fibers are removed with a fiber length of at least 5 pm by means of a classifier and / or filter.

7. Use of the obtainable by a method according to any one of claims 1 to 6 cement base as cement or in a cement, preferably for earthworks and / or civil engineering.