4.4 Aluminosilicate by-products of production
4.4.1 Slags black and nonferrous metallurgy
The term "slag" is used as the name of waste generated during the smelting of various metals and the combustion of mineral fuels. Depending on the origin of the slags are divided into two large groups:
• metallurgical;
• the fuel.
They differ in chemical and mineralogical composition, crystalline structure, resulting in their chemical, physical and thus technical properties.
Metallurgy is traditionally one of the main "suppliers" of technogenic raw materials for the building materials industry, including the production of mineral binders. The tonnage of waste lies in the fact that technogenic raw materials have passed high-temperature treatment, the crystalline structure in the waste generated and they do not contain organic impurities.
In the metallurgical industry, the annual output of slag is about 45 million t – domain, almost 20 million tonnes of open-hearth, almost 10 million tonnes of ferrous metallurgy and 5 million tonnes of other metallurgical industries, not counting the huge number of toxins, accumulated in dumps of metallurgical enterprises. Only blast furnace slag each year merges in the dumps about 15 million tons melt the rest of the granulated. Even greater problems arise with slag, steelmaking and ferroalloys. Meanwhile, it is a valuable raw material used in the construction industry is not fully. From the specified amount of slag, only a small part of them is applied in various fields of industrial production as a secondary product and the rest goes to the dumps. Dumps take up thousands of acres of valuable lands, transportation of slag and content of the dumps require large funds. Therefore, the use of toxins, including the production of various construction materials is of great importance (savings, labour, natural resources).
The replacement of natural raw materials slag for production of construction materials allows to obtain significant economic benefits by reducing the transport distance of raw materials, cost reduction of the main production (metal), liquidation of dumps and the return of arable land, the recovery of the air basin and other activities on integrated use of natural resources.
Analysis of the slag processing abroad shows that in most developed countries, waste (80-100 %) are processed into raw material for the extraction of additional valuable products (rare metals, chemicals, etc.), and the rest is used in construction or used in agriculture as fertilizer.
Metallurgical slag formed in the smelting of iron from ores, process of obtaining iron from steel smelting of nonferrous metals and ferroalloys.
All metallurgical production with the use of electric furnaces are high temperature (1200-20000С), therefore all physical and chemical processes occurring during ore processing and synthesis of tumors, occur in a state of total melt mass.
The composition and properties of slags is influenced by the following factors:
1. Chemical and mineralogical composition of components of the charge for smelting.
2. The technology of obtaining metal (type of oven mode and temperature).
3. Technology and the rate of cooling of the melt (granulation, slow cooling in the dumps).
4. Chemical-mineralogical composition and structure of the synthesized neoplasms.
Metallurgical slag is divided into a slag of ferrous and nonferrous metallurgy.
Widespread ferrous metallurgy waste mainly generated in metallurgical furnaces for smelting iron, steel, ferroalloys.
Slags of ferrous metallurgy is the products of high – temperature interaction of fuel, ore, floodplains and gas environment.
Depending on the nature of the process and type of furnace slags of ferrous metallurgy classification:
– the domain;
– steelmaking;
– wastes production of ferroalloys.
The possibility of using blast furnace slag cement industry is so great that they may not be enough, so in this industry, being involved in the production of other metallurgical slag (Converter, Ferroalloy, open hearth, etc.).
Annually in non-ferrous metallurgy produces up to 10 million tons of slag, the use of which does not exceed 15 %. In large measure this is because in non-ferrous metallurgy slag contains valuable raw materials and processing them into building materials is less efficient than its potential extraction.
In the total output of slag ferrous metallurgy make up about half of the granulated slags of Nickel production, the third part – the dumping of copper smelting, and the remaining slags are presented granular copper and polymetallic and polymetallic otvarennymi.
The composition and properties they differ significantly from those of ferrous slags. For the production of many nonferrous metals primary raw materials are sulfide ores that contain significant amounts of iron. They relatively little oxides of calcium and magnesium, but often contains sulfur impurities, zinc, lead, Nickel, cobalt and some rare metals.
4.4.1.1 Blast furnace slag
Blast furnace slag is formed by the combination of gangue ore, ash of fuel and flux in the smelting process of cast iron. Iron ore, along with iron oxides, contain some amount of impurities (quartz sand, clay, carbonates of calcium and magnesium, phosphorus and sulfur, etc.), collectively known as waste rock. Some of them (phosphorus and sulfur) harmful effect on the quality of cast iron. Inorganic impurities are in the fuel loaded in the blast furnace for melting ore. Therefore, in the process of blast furnace it is necessary not only to restore the iron oxide, but also to free it from impurities introduced with ore and fuel.
As gangue in the ore is rarely fusible to remove the charge injected special additives – fluxes (fluxes), capable of forming with it the fusible connection.
As floodplains are usually used carbonate rocks – limestone, dolomite, etc. during the melting process, the carbonates enter into chemical interaction with the components of the gangue and the mineral part of fuel, forming fusible silicates and aluminosilicates of calcium and magnesium. At 1400-15000С these compounds melt in the form of molten slag that accumulates as a result of lower density over a layer of iron produced from a blast furnace.
When cooled, the fiery liquid slags depending on the speed of the process formed vitreous or close-grained structure, which is a complex mineral system.
The presence of silicate and aluminate phases in slags characterizes them as material, similar in composition to cement clinker and therefore are able to possess astringent properties.
On the activity and properties of the slag is affected by the way of cooling, which determines different levels of melt crystallization. At the cooling rate of the blast furnace slag are divided into medienakademie (pelletized with a crystalline structure) and bystrohodnye (in the form of pellets with a vitreous structure).
Basic slag by slow cooling represent a dense, well-crystallized structure. Numerous studies have shown the ability to dramatically enhance the hydraulic properties of slag through the introduction of various additives – activators and the intense heat and humidity treatment.
Therefore, the value of slag (or fly ash) is higher the more hydraulically active phases.
In this regard revealed several major areas of application of blast furnace slag in the production of binders:
1) as raw materials for the production of Portland cement;
2) as an additive to clinker in the production of slag Portland cement;
3) in the production of slag binders with the addition of activators;
4) in the manufacture of binders autoclaved;
5) upon receipt slag binders.
The main consumer of slag – cement industry, using annually 23-25 million tonnes of granulated blast furnace slag.
Since glassy slag, hydraulic activity is improved, blast furnace slag for the manufacture of binding agents, are granulated by rapid cooling with water, steam or air.
4.4.1.2 Electrotermometria wastes
Electrotermometria waste – a significant amount of industrial waste generated during the thermal method of producing phosphorus by heating in electric furnaces of the phosphate mineral raw materials (concentrates, rock phosphate and Apatite) in a mixture of quartz compounds. Output electrotermometria slag is on average up to 10-12 tons per 1 ton of phosphorus.
The processing of ore is carried out at a temperature of 1450-15500С, resulting extracted phosphorus:
Ca3(PO4)2 + 3SiO2 + 5C = 3CaSiO3 + P2 + 5CO (16)
The molten slag is subjected to rapid cooling (granulation). These slags are characterized by a predominance of clear, colorless glass. The resulting sintered silicate-calcium-magnesium minerals contain phosphate and fluoride in small quantities.
The ratio of CaO to SiO2 in the slag ranges from 1 to 1.3. Slags have low contents of oxides of Al and Fe.
In its properties to granulated phosphorus slag is identical to the domain so can be used as raw material for the production of binders.
Electrotermometria granulated slag according to the chemical composition shall meet the following requirements:
– content of SiO2, %, not less than 38;
– content of CaO + MgO, %, not less than 43;
– the contents of P2O5, %, not more than 2.5.
4.4.2 Nepheline (belit) slurries
The production of alumina from aluminum ore – bauxite produces waste in the form of belitovogo sludge emitted in the dumps millions of tons.
Raw material for production of alumina are bauxite and limestone, which after appropriate technological training in the form of wet pulp enters the rotary kiln for firing at a temperature of 1150-12500С. The obtained sintered subjected to treatment with alkali with the purpose of dissolving and desorption of oxides of Al and Na. Other components: C2S, CA, CF are removed in sludge form.
The slurry is an aqueous suspension of dispersed particles. Such wastes are ulunicoderange nepheline sludge of Achinsk alumina refinery. Depending on the raw materials distinguish white, nepheline and bauxite slurries. The output of sludge per ton of the product is 3-9 tons. Similarly, accumulated sludge dumps are located in huge quantities, and each year their stock is replenished.
The main components of sludge is the oxides of calcium, silicon, aluminum and iron. Chemical composition of nepheline sludge occupies an intermediate position between the Portland cement, blast furnace slag and calcium aluminate cement.
Calcium oxide and silica are associated in the β-modification of dicalcium silicate (Belite), the content of which reaches 55-85 % by weight. The iron oxides magnetite and hematite. There are aluminates of calcium. In addition, the composition of the sludge present in a small amount aluminates of Ca and Na, and CaCO3. The presence of significant amounts of water leads to partial hydration of minerals and the formation of hydrosilicates, hydroalumination and gidroperita.
According to the granulometric composition of the dried sludge is similar to fine-grained sand.
Numerous studies of domestic and foreign scientists found that all the slimes represent a weak base believe binder a substance that can exhibit hydraulic activity.
The main uses of nepheline sludge:
• production of high quality Portland cement by secondary firing charge consisting of sludge and appropriate corrective components.
• making self-nepheline binder (chemically bonded) by the introduction of additives – activator (lime, gypsum, Portland cement, etc.).
Nepheline binder is a product of joint grinding nepheline sludge (80-8 5%), lime or Portland cement (15-20 %) and gypsum (4-7 %). His mark of 100 to 250. Used binder for masonry and plaster solutions, as well as for concrete of normal and especially autoclaved. In the latter case, the brand strength there are up to 500 at the rate of 250 kg/m3. Features of concrete binder nepheline – low ectothermy, high adhesion to the steel reinforcement after autoclaving, increased stability in the mineralized waters.
Mixed binders on the basis of nepheline sludge are applied to the products of hardening under the conditions of autoclaving.
Similar in composition to nepheline wagamama are binders based on bauxite, sulfate, monocalcium and white sludge.
Bauxite, red sludge is formed as a waste processing bauxite – the main raw material for aluminium production. Waste is a lamellar, heterogeneous, non-sticky medium-hard partially cemented mixture with wide – from +5 mm (23 %) to -0.8 mm (28 %) – range particle size distribution.
Sludge humidity of 20-70 %, so they can be used after drying. The chemical composition of the waste is an aluminosilicate material. For example, the chemical composition of red mud of the Dnieper aluminum plant is ( % ): SiO2 – 6-8; Al2O3 – 15-18; Fe2O3 – 24-48; CaO 8-15; Na2O – 4-7. The low maintenance hair does not allow use of sludge as a raw material in the production of the binder. It is used only as a Supplement, lowering silicate module raw mix. It is also used for obtaining autoclaved concrete.
The sulfate sludge get when you replace soda with sodium sulfate in the production of alumina by sintering. They are characterized by the presence of sulfur-containing compounds of various degrees of oxidation.
Monocalcium sludge is formed upon receipt of alumina from alumino-silicate rocks by sintering of high charge. Can be used as the siliceous component of the raw material mixture in the production of Portland cement.
White sludge – waste chemical and metallurgical industries. They, along with a lot of hair contains 12-20% of hydroalumination.
All types considered sludge can be used as components of Portland cement raw mixtures and materials autoclaved. To enhance sludge in all types of binders based on them it is advisable to introduce additives of lime and gypsum.
Slurry binders are effective local astringent. In recent years, given that the complete processing of nepheline sludge to Portland cement for General construction purpose at the major alumina plants is impractical due to the high concentration of production in one company (over 10 million tons), created a number of new technological schemes for processing of nepheline sludge for various industries (figure 38).
In particular, the fundamentals of hydrochemical processing nepheline sludge by processing it soda, soda-lime potash solutions. In this case, reaction takes place:
Ca2SiO4 + 2Na2CO3 + H2O ↔ 2CaCO3 + Na2SiO3 + 2NaOH (17)
For the production of high-alumina cement, to restrain the shortage of raw materials, great importance is the use of aluminium-containing wastes of various industries.
Figure 38 – Perspective of the use of nepheline sludge
The use of sludge caustification and oxalate as raw materials of high-alumina cement enables to reduce the roasting temperature by 50–800S, to improve the utilization of Al2O3, from 4 to 0.5% (which results in improvement of mineral formation), to increase the strength of the cement aged 1 day more than 2 times, reduce pylones and the percentage of the dust fraction.
One of the large unused sludge is red slime, resembling a dispersion of clay raw materials and removed in the sludge collector in the form of pulp humidity of 70%.
4.4.3 Waste of mining industry and ore dressing
At many mining and smelting plants accumulate a huge amount of waste in the form of "tails" enrichment of various ores.
"Tails" are on the granulometric composition of fine sand with a particle size of less than 0.3-0.5 mm.
The mineralogical part of them consists mainly of quartz, feldspar, calcite, mica, kaolin.
Waste mining is advisable to use as placeholders and fine siliceous component in silicate heavy and aerated concrete.
4.4.4 Fuel ash, slag and ash-slag mixture
Among industrial waste is one of the first places in terms of education is ash and slags from combustion of solid fuels as primary source for electricity generation in our country are fuel-containing minerals (anthracite, brown and black coal, combustible shale, peat).
A considerable amount of slag and ashes formed during the combustion of solid fuels: brown coal, 10-15 %; coal 3-40 %; anthracite 2-30 %; peat 2-30 %; shale 50-80 %.
For many TES an annual output of ash and slag exceeds 1 million tons, and the stations that burn mnogosolnca fuel reaches 5 million tons.
A huge amount of ash and slag accumulated in landfills occupying valuable land. The contents of ash and slag dumps requires a significant investment. At the same time, ash and slag TPP are materials that have undergone high temperature processing and has received the specific properties that determine the possibility of their effective use in the production of various construction materials (including – in the production of binders), as evidenced by not only scientific research but also practical experience.
The waste of thermal power plants (TPP) is of great economic and ecological importance, because a lot of them, and the establishment and maintenance of stockpiles requires considerable resources. During the day, the thermal power plants with a capacity of 1 million kW burns 10,000 tons of coal and emit 1000 tons of slag and ash. Annually for such dumping of toxins (if the height of 8 m) required more than 1 hectares.
At the conclusion of a number of specialized organizations that are non-toxic ash waste. This opens up broader prospects for their cost-effective and environmentally safe use in the industrial, civil and road construction.
Today are known more than 100 technologies for the production of binders and concrete with ash waste. Perhaps the use of ash in the process of hydraulic works (manufacturing of precast concrete, manufacture of concrete in the construction of weirs, dams and other waterworks).
Volumes of use of fuel and mineral waste reach 62% in France and 76% in Germany, in Russia in 1998, was disposed of for less than 5% of the resulting ash and slag waste of thermal power plants (from 40 million tons disposed of only 1.8 million tons).
4.4.4.1 Processes occurring during the combustion of solid fuels
Ash and slag of thermal power plants represent the residue from the combustion of solid fuel. These are products of high temperature (up to 1200-17000С) mineral processing, burning part of the coal. Processing of solid fuel into thermal energy is performed either on the grate bars by firing lumps of raw materials (3-150 mm), or in furnaces of pulverized combustion pre-shredded material in suspension. Lump fuel is used only in small enterprises. The bulk of the ash and slag formed at thermal power stations from pulverized coal. Thus in chamber furnaces work waste of two types: fly ash and slag.
Slag is formed by sticking together the softened ash particles in the volume of the furnace or on the walls and accumulates in the slag hopper under the furnace. The grain size of the slag 1-50 mm.
Fly ash (hereinafter – ash from thermal power plants) is removed from the furnace with the flue gas and is captured at their cleaning in cyclones and electrostatic precipitators. The size of the ash particles less than 0.3 mm.
Over 80% of the mineral part of coal becomes ash, 20% slag. Therefore, the greatest practical interest for processing into building materials is ash from thermal power plants.
The mineral part of solid fuel usually includes clay minerals, micas, quartz, feldspars, sulfides, oxides and hydroxides of iron, carbonates of calcium, magnesium, etc.
During combustion of the components of the mineral changes, interact with each other and form various compounds which cause the formation of ash and slag with variable chemical and mineralogical composition depending on the temperature of fuel combustion and the composition of its mineral part.
Clay minerals and mica contained in the fuel, combustion consistently degidratirtee (lose water) and amerisource, i.e. moving from crystalline to amorphous. Amorphization occurs as a result of deformation and destruction of the crystal lattice of the mineral when heated.
Quartz grains in the fuel, combustion, almost no change. There is only them cracking and melting. Much stronger than fused grains of feldspars. Iron compounds in the combustion process pass into hematite or magnetite. Carbonates of calcium and magnesium dissociate with the formation of Cao, MgO, etc.
The organic part of the source fuel combustion process loses its volatile components and passes into the semi-coke (respektiere of the particle) and coke (sintered particles) with subsequent oxidation to co and CO2. Because of the uneven temperature in the combustion space, the completeness of these transformations varies considerably, and ash of thermal power plants may contain unburned organic residues with different properties.
Thus, in the combustion process to fully or partially burn the organic part and inorganic changes depending on the temperature and mode of firing, turning into a byproduct of the complex chemical and mineralogical composition.
4.4.4.2 Classification of waste ash
In order to more rational use of ash klassificeret them on various grounds. Due to the variability of composition and properties of these materials have not yet created a single classification that would cover all the signs.
On the physical condition of all ash materials may be submitted to:
a) slag – a product of sintering and melting of the most fusible of the ash with size of pieces up to 15-25 cm In most cases, slag has a cake mix low-porous vitreous structure. When burning brown and mixed coal slags are formed of a porous cellular structure;
b) ash – technogenic waste generated in thermal power plants by burning coal in a pulverized state, with a particle size less than 0,315 mm of the porous structure. This is a fine mass with a specific surface area of from 800 to 5000 cm2/g;
C) ash-and-slag mixtures (SSS) – technogenic wastes produced by the joint gidrogelevye ash and slag.
Depending on the place of deposition and the selection of ash are classified as follows (figure 39). Ash is a failure, drop out of the turbulent flows of gases in the bunker Podarochnoe space, has large particles with the highest true density. Fly ash emanating from the zone of combustion flue gases and collected in the cleaning devices, fine. The more stages of cleaning exhaust gases pass, falling out of the finer particles of ash. Small and tiny fraction of the ash contain the most spherical particles and little unburned organic residues.
Figure 39 – Classification of two evils depending on the place of deposition and the selection
According to the type of fuel combusted all ash waste classification:
• anthracite on the combustion of anthracite, polyatract and lean coal (A);
• coal combustion stone, except skinny, coal (KU);
• lignite combustion lignite (B).
There are a number of classifications of waste ash chemical composition. It is based on the content of various oxides: SiO2, Al2O3, Fe2O3, CaO, MgO. Depending on their ratio of ash divided into two classes:
I – ash solidifies in kamnevidnoe body after mixing with water;
II – ash that hardens just after mixing with water and lime, i.e. having pozzolanic properties.
Class of ash is determined by the value of the modulus of basicity:
Mo = (CaO+MgO / SiO2+Al2O3) (18)
Ash and slag with high content of CaO + MgO, it is advisable to use primarily as raw material for the production of binders and low-calcium as active fillers in cellular concrete, active mineral additives for cements and concretes, manufacture of bricks, artificial porous aggregates, etc.
Classification of ash and slag thermal power plant-phase structure allows for three possible phase components:
• glass that occurs when rapid cooling of the molten fuel components;
• partially crystallized phase formed during slow cooling of molten slag;
• amortyzowania substance inorganic part of the fuel.
The most active component of ash and slag glass. Amortyzowania clay substance is also an active component. Partially crystallized phase has a low activity. The ratio of these three phase components and their individual characteristics depends on hydraulic activity of ash and slag, and hence possible areas of their use.
Consider the most important areas of utilization of major ash waste containing up to 5% of carbon loss, depending on the number of them present in Cao:
1) Srednekaloriynye ash contain 20-30 % Soobs and 3 % Sasw. They have the properties of pozzolana and can be used for the production of mortar brands 10-20, autoclave products, mixed cementitious materials (additive to ash 5-20% of lime, gypsum, etc.), as hydraulically active additives to cement, and as a raw material for the cement industry.
2) High calcium ash containing 30-45 % Soobs and 9 % Sasw, represent the most valuable of the ash self-cementing material, ispolzuemye construction solutions of 50-100 stamps, various ash concrete for road, low-rise building and construction in rural areas (liquid mixing – water, 3 % HCl, or solutions СаCl2). High calcium ash added to cement in an amount of 30 %, not reduce the grade of the latter; increase the plasticity and frost resistance of products to mixed binder. Good properties of mixed binders on the basis of high-calcium ash and additives of 10-50 % of dump slimes of aluminous production.
3) Ultrasociality ash, composed of more than 45 % Soobs and more than 10% Sasw, can be used as a binder for autoclaved products when mixing with 3% HCl solution. It is most expedient to use them as lime-silicate component for the production of two-component cement from raw meal. Due to the presence of free lime being burned in the form of fused particles of the ash binder requires special technological processing (grinding or pre-damping) to be used in the binder to eliminate the arising volumetric deformation in the process of hardening ash.
4) the Main waste products in the ground state can be used as pozzolanic and hydraulically active additives.
Have high calcium ash and slag waste when the content of unburned coal more than 5% binding properties drastically deteriorate, and they are recommended for use in the cement industry as lime-silicate component of the raw batch.
4.4.4.3 Use of ash and slag waste in the building materials industry
Directions for use of fuel ash and slag (figure 40) in the building materials industry is diverse, however, the volume of their application in Russia, Ukraine, Kazakhstan and other States is small. For example, from 14 million tons ash and slag of power plants of Ukraine is 450 thousand tons. Ash Donetsk anthracite (and skinny) coals are formed at 1500-18000С, higher than the formation of brown - coal and angry, and contain 60-80% of vitrified particles.
Figure 40 – the areas of use of ash and slag of thermal power plants in the building materials industry
The dispersion of the evils of anthracite coal is also higher, they dominated fraction of less than 50 microns. However, the amount of unburned fuel in these ashes reaches 30 %, which is 2-6 times higher than the regulatory requirements for ashes to be used for production of silicate building materials.
It should be noted that thermal power plants of the Middle Urals sent to the dumps more than 11 million tons of ash and slag, and disposed of a total of 120 thousand tons.
From the fuel ash and slag can produce almost all construction materials, products and structures required in the construction of residential and industrial buildings, agricultural facilities, roads, waterworks, etc.
Quality manufactured of ash and slag waste construction materials determined the phase composition of the tumors that occur in the processing of gold - or secosteroid masses.
For example, a significant amount of silica (i.e. 51.2-55.7 per cent) and alumina (22,14-22,40 %), characteristic of ash and slag from combustion of brown coals of near Moscow, in combination with alkaline and sulphate additives provides increased activity of lime-ash binders, and rather high specific surface area of ash (3800 cm2/g) contributes to its use in the binder without further grinding.
The use of fuel ash and slag gives the possibility to produce concrete, ceramic, gold and shlakositallovye efficient building materials with improved technical properties, which in turn allows us to develop promising architectural and structural trends in industrial and housing construction.