And other industrial branches

The wastes of chemical-technological industries can be classified according to: content of representative chemical component and technological assignment in the production of construction materials.

According to the content of characteristic chemical component there are distinguished: phosphorus- and fluorid-containing slags, gypsum and lime containing products, ferrous, siliceous and other materials.

The chemical products according to the technological assignment in the production of construction materials are divided in such groups:

1. The raw materials (for the production of cement, gypsum, lime, etc.).

2. Intensifiers of technological processes (fusing agents, reducer of hardness, granular forming agents, etc.).

3. Admixtures-modifiers of material properties (alloying substances, plasticizers, hardening accelerators, etc.).

Classification according to the technological assignment is very conditional, because the same chemical product, being the waste product of production, depending on a particular range of its application, can be attributed to the different groups. For example, phosphogypsum for the production of gypsum binder or sulphuric acid belongs to the first group of chemical waste products, and entered at burning of cement clinker - to the second one, at the cement grinding for adjusting of setting time - to the third one.

The slags of electrothermal production of phosphorus, gypsum-containing, lime and ferrous waste products, polymer products and others are the most valuable raw materials for the production of construction materials from the production wastes of chemical industry.

Phosphoric slags are the by-product of production of phosphorus by the thermal method in electric furnaces. At the temperature 1300-1500 °C calcium phosphate reacts with the coke carbon and silica, resulting in the phosphorus and slag fusion formation. Slag pours off from furnaces in the flaming state and granulates with wet-processing. There are 10- 12 tones of slag on 1 t of phosphorus.

The chemistry of phosphoric slags is close to composition of blast-furnace. Total content of calcium oxide and silica in them achieves at 95 % at their ratio 0.9- 1.1.

The peculiarities of phosphoric slags are the contents of Р₂О₅ and CaF₂ and reduced amount of Al₂O₃ in them. The differences between the content of P₂O₅ and CaF₂ and coefficients of basicity, determining physical and chemical properties of slag fusions and peculiarities of granulation, substantially influence on phase composition, structure and properties of slags.

Most of the phosphoric slags are used in the cement industry. Phosphoric slag meets the requirements, specified to active mineral admixtures of artificial origin. Comparatively low content of А1₂О₃ causes the lower hydraulicity of phosphoric slags in comparison with blast-furnace slags.

It is possible to obtain slag pumice, cotton wool and cast elements from the phosphoric-slag fusions. Phosphoric slag wool is characterized with the long thin fibres and average density 80-200 kg/m³. It has bulk density 600-800 kg/m³ and glassy fine-pored structure.

From the slags of electrothermal production of phosphorus the slag glass-ceramics with the strength up to 400 MPa are obtained, possessing the raised resistance in corrosive environments and at high temperatures.

Possibility of application of phosphoric slags as a basic component of ceramic masses is set, for example at a facing tile manufacturing. The slag, being a fluxing agent, promotes formation of the required amount of liquid phase and improves sintering of ceramics.

The gypsum wastes can be formed at the production of the followings products: mineral acids (phosphogypsum, boron gypsum, fluorogypsum), organic acids (citric gypsum, etc.), the chemical treatment of wood (hydrolytic gypsum), treatment of water solutions of some salts and acids (silica gypsum, titanium gypsum, etc.), cleaning of industrial gases, containing SO₂ (sulfogypsum); production of salts from a lacustrine leach (leach gypsum).

The phosphogypsumis the most gypsum-contained waste product of chemical industry. So, 3.6-6.2 tones of phosphogypsum appear per 1 t of extraction phosphoric acid in account of dry substance.

Phosphogypsum contains from 80 to 98% of the gypsum and can be attributed to gypsum raw material. High dispersion of phosphogypsum (S_sp.s.= 3500-3800 sm²/g) allows to exclude the crushing and coarse grinding from a technological process. At the same time, high humidity of phosphogypsum (up to 40%) complicates its transportation and preparation and results in the considerable fuel consumption for drying. Presence of water-soluble admixtures in phosphogypsum, in particular phosphorus- and fluorine-containing ones complicates processing of production wastes in comparison with processing of natural gypsum stone, causes the necessity of washing, neutralization and other technological operations and stipulates higher thermal consumptions accordingly. At ordinary technology gypsum binders based on phosphogypsum are low-strength that is explained with the high water consumption of phosphogypsum, stipulated by the large porosity of the formed semihydrate. If the water consumption of ordinary gypsum plaster is 50-70 %, for obtaining the paste of normal consistency from phosphogypsum binder without additional treatment, the required amount of water is 100-120 %. It is possible to reduce a little the negative influence on building properties of phosphogypsum of the admixtures contained in it, by re-crushing of phosphogypsum and shaping of elements with the method of vibrocompaction.

The basic methods of phosphogypsum preparation in production of gypsum binders can be divided into 4 groups:

1. Washing of phosphogypsum by water;

2. Washing in combination with neutralization and sedimentation of admixtures in water suspension;

3. Method of thermal decomposition of admixtures;

4. Introduction of neutralizing, mineralizing and crystallization regulative admixtures before burning and after it.

The methods of the first and the second groups are related to formation of large amount of polluted water (2-5 m³ per 1 t of phosphogypsum), large expenses on their removal and cleaning. Most of methods of thermal disintegration of admixtures (the third group) are based on burning of the phosphogypsum until formation of soluble anhydrite with its further hydration and reburning to the semihydrate. They do not have the wide use yet, the same as the as well as the methods of the 4^th group. The rare admixtures are required to realize the last one and they do not provide permanent properties of binder.

Knauf enterprise offers three variants of manufacture of binder from phosphogypsum depending on the area of its further use. The principle scheme of these three variants is presented in the Fig.20.12.

The dry mixtures, where the filling materials, plasticizers, retarding admixtures and, if it is required, other components are contained in their composition, are effective range of application of binder from phosphogypsum. Application of dry gypsum mixtures instead of the cement and lime ones allows to increase the labour productivity: at the floors arrangement - in 2-3 times, at wall plastering - in 1.3-1.5, tamping of oil and gas wells - in 1.5-2.5 times.

The phosphogypsum can be applied as mineralizator at burning of Portland cement clinker and as admixture for adjusting of cement setting in place of natural gypsum in the cement industry. Admixture of 3-4 % phosphogypsum in the batch allows increasing the saturation coefficient of clinker from 0.89-0.9 to 0.94-0.96 without the decline of the productivity of kilns, to promote resistance of lining in the area of sintering because of uniform formation of steady daubing and promotes the obtaining of the easy grinding clinker. The mechanism of mineralizing action of phosphogypsum is stipulated by the catalytic influence of SO₃ at temperatures below 1400°C, causing the decline of fusion viscosity, increase of its amount and formation of intermediate compounds, bonding СаО. The certain positive influence is rendered by the admixtures of phosphoric anhydride and fluorine.

The convenience of phosphogypsum is determined for replacement of gypsum at the milling of cement clinker. High content of sulphuric anhydride and presence of admixtures of water-soluble compounds of phosphorus and fluorine causes higher effect of retardation of phosphogypsum on setting time, than a gypsum stone. It allows decreasing of retarding admixture dosage in comparison with ordinary for gypsum.

Admixture of phosphogypsum does not influence at the cement strength, there can be an insignificant decline of the strength only in the early terms of hardening. Wide application of the phosphogypsum as the admixture at the production of cement is possible only at its pre-drying and granulation. Humidity of granulated phosphogypsum should not exceed 10-12 %.

CaSO₄+2C=CaS+2CO₂↑;

3CaSO₄+CaS=4CaO + 4SO₂↑.

Sulphureous gas is caught and transferred in sulphuric acid. The calcium oxide reacts with SiO₂, Аl₂О₃ and Fe₂O₃, forming the clinker minerals.

Along with production of binders and products on their basis, other ways of phosphogypsum utilization are known. Experiments have shown that admixture up to 5 % of phosphogypsum in batch at the production of brick intensifies the process of drying and promotes the high quality of the elements.

Along with phosphogypsum, the other gypsum by-products (boron gypsum fluorogypsum, sulfogypsum (Fig.20.14), etc.) can be also successfully used for the construction material manufacturing, and foremost binder matters.

It is possible to use the lime, ferrous and other waste products of chemical industry along with the gypsum-containing wastes.

Carbide lime can be used for the obtaining of lime-silica binder and steam-cured materials on their basis.

The feldspar sands, burnt blast rocks, overburdens of iron-ore deposits, dumping blast-furnace slags and ore cleaning wastes can be used as silica components. On soda factories, pulp-and-paper mills and nitrogenous-fertilizer enterprises a large amount of raw materials, containing calcium carbonate is accumulated as waste products. One of industrial directions of these resources application is obtaining of belite-lime binder and lime-sand brick on its basis. Presence the wastes of chloride and calcium sulfate in their compositions considerably promotes the reactivity of raw meal, allowing operate the binder burning at 950-1000°C.

The pyrite drosses are used as correcting iron-containing admixture in cement production. Because of change technology of sulphuric acid obtaining, the output of pyrite drosses is presently diminished and they are replaced by other iron-containing waste products in the cement production.

It is possible to utilize the products, with large sulphur content, for making of sulphuric cement, as impregnating compounds, at making of products from rubber, ebonite, plastics as filler of asphalt mixes. The obtaining of sulphuric cement is possible by melting of sulfur- containing rock with addition of fine-dispersed acid resistant filling agent and plasticizer. Compositions with sulphuric cement are heated to 145-155⁰C before the use and quickly used. Concretes on the basis of sulphuric cements and heavy-weight aggregate have an average density 2300-2400 kg/m³ and compressive strength 30-35 MPa. It is especially effectively to apply them in construction of chemical enterprises, highway engineering and hydroengineering, where a high-early-strength concrete with a high inoxidizability is required.

The enterprises of construction materials, located near-by hydrolytic factories, can utilize lignine - one of the most capacious wastes of hydrolytic industry.

Now there are the followings basic directions of application of hydrolytic lignine: as fuel-burning admixture in the production of ceramic materials; cutting replacer in building elements; raw material for the obtaining of phenol- lignine polymers; plasticizer and intensifier of grinding.

A series of waste products of chemical industry as solutions and sludges can be used as admixtures at the production of concretes and mortars, road-construction and other materials.

The materials on the basis of large-tonnage waste products of metallurgical, fuel and energy and chemical industry, were considered above. Along with them, the production wastes of wood processing, metal mining industry, industry of construction materials itself, municipal economy, can be used with success for the production of various construction materials. So, the simultaneously extractive rocks, dry and wet cleaning wastes at mining and processing of iron-ores, fluxes and refractiries, nonferrous metals; siftings at the production of crushed stone from igneous, metamorphic and sediment rocks are suitable for the production of construction materials.

At the certain chemical-mineralogical composition the crushed waste rock can be used for the obtaining of different binders. The carbonate and marl wastes are the raw materials for the production of air-hardening and hydraulic lime, Roman cement, composite binders. The silica-alumina materials in composition with carbonates can be added in the complement of raw meal for the obtaining of Portland cement clinker. In some cases they have certain advantages before traditional raw materials.

The cleaning wastes of mining and other industries can be widely used in the production of autoclave construction materials. Researches, conducted in the last years, have shown that it is expedient to utilize not only quartz sands but also clay sands, loams, aeolian soil, some types of clays, feldspar and clayey sands, a series of other rocks for the production of autoclaved materials.

The various types of wastes form in the production of different artificial construction materials in the process of the technological processing of raw material, and also as spoilage and others. Majority of these wastes at impossibility of their returning in a basic production can be used for the obtaining of other construction materials.

The hard domestic waste, waste caused by destruction of old buildings, constructions and road coating, construction waste, threadbare tires, waste paper, rag, broken glass, belong to the wastes of municipal economy.

Growth of volume of solid domestic waste in different countries changes from 3 to 10% per year. Solid domestic waste contain in average to 40% of literary garbage, 3-5% of ferrous metals, 25-40% food waste, 1-2% plastics, 4-6% textile, up to 4% of glass. It is possible to make about 750 kg of paper from one tone of literary garbage. It is also widely used for the carton production. The use of one tone of literary garbage in the production of paper and carton allows to save up to 4 m³ of wood.

Utilized rubber elements such as conveyer bands, hoses and worn-out car tires are the large-tonnage wastes. It is possible to select for the repeated use about 700-750 kg of rubber, 130-150 kg of chemical fibers and 30-40 kg of steel from 1 tone of the waste at the complex application of rubber- caoutchouc materials and metal, contained in worn-out tires.

A rubber chips and micronized rubber powders can be applied as ingredients of rubber compounds. Thus get the rubbers, with the row of technical properties exceeded the materials, not containing the reclaims.

The technologies of roll and tiled materials based on the rubber-cord waste are developed. The worked-out rubber is applied also in the production of waterproof construction materials, materials for slabs, glues, mastics and sealants.

It is also effectively to use the plastic waste products to the reprocessing. The waste products are preliminary collated and purified from extrinsic particulates, and then exposed to grinding, agglomeration and granulation. Different building elements can be obtained from the chips. It is expedient to introduce the secondary raw materials into the polymer compositions in an amount of 40-50% of primary along with plasticizers, filling agents and stabilizers.

Packing and bottle polymer containers can be processed in finishing tiles and other elements.

It is possible to manufacture press-compositions with the required properties from the secondary polyethylene and polystyrene raw materials in mixture with the sand. The high strength indexes of such materials allow in combination with high waterproofness, for example, in Japan to utilize slabs from them for coating of sea-bed withthe purpose ofcreation of the stations on fish breeding.

High waterproofness of the most of polymer waste products allows to utilize widely them in different materials, applied for sealing of joints between the panels of buildings, and also for coverage of parts of buildings, working under the water or in the conditions of increased humidity.

The large amount of so-called concrete scrap appears as a result of dismantling of buildings and structures, and also the accumulating of subquality products on the enterprises of the precast reinforced concrete. Processing of concrete scrap is directed mainly on the obtaining of the secondary aggregates and reinforcing steel.

Date: 2015-12-18; view: 746