How to make bricks from iron tailings

1、 Production of unburned bricks from iron tailings
Ma’anshan Mining Research Institute has successfully produced unburned bricks using tailings from Qidashan and Waitoushan iron mines. This unburned wall brick is mainly made of fine tailings (SiO2>70%), mixed with a small amount of aggregate, calcium cementitious material, and additives, and mixed with an appropriate amount of water. After being evenly mixed, it is molded and formed on a 60t press under a pressure of 19.6-114.7MPa. After demolding, it is subjected to standard curing (natural curing) for 28 days to become a finished product, The process flow is shown in Figure 1. Two types of tailings bricks, Qidashan and Waitoushan, have been tested and found to meet the requirements of the No. 100 standard brick specified in the “Technical Conditions for Non Sintered Clay Bricks” issued by the National Building Materials Bureau.
Dalian University of Technology collaborated with Angang Dagushan Iron Mine to develop steam cured tailings bricks using iron sheet metal cabinet with oil spray tailings and lime as the main raw materials, with an appropriate amount of modified materials and additives. The physical properties of the bricks are relatively good, and their grades can meet the requirements of standard bricks above 100.
The Meishan Iron Mine beneficiation plant uses Meishan tailings to add some medium sand (ore: sand=3:1), followed by 3% cement, 8%~10% water, and 2%~3% F-1 admixture, to produce 240mm × 115mm × 53mm standard brick samples were then subjected to multiple tests such as bending strength, compressive strength, and fire resistance. The main technical indicators meet the requirements of the “Technical Conditions for Non Sintered Clay Bricks”, with a grade of 75 or above.
2、 Making wall and floor decorative bricks with iron tailings
Ma’anshan Mining Research Institute utilizes fine-grained tailings from Qidashan and Waitoushan iron mines, adds a small amount of inorganic cementitious materials, ordinary Portland cement, white Portland cement, and an appropriate amount of water, and after uniform mixing and stirring, uses a two-layer (base layer, surface layer) method to process decorative tiles. The production process is shown in Figure 2. The product has been tested and proven to have an average compressive strength of 19.6MPa and a flexural strength of 5.0MPa, with strong alkali and corrosion resistance. The production of decorative tiles from iron tailings has a simple process, low raw material cost, good physical properties, smooth and beautiful surface, and the decorative effect is equivalent to other similar decorative tiles (such as cement floor tiles and ceramic glazed tiles).
Tongji University collaborates with Masteel Gushan Iron Mine to use tailings powder with a particle size of less than 0.15mm as the main raw material, mixed with 10% to 15% quicklime powder, and pressed into various specifications and shapes for building clean water walls. If Portland cement is used as the bonding material, the effect will be better and the process can be further simplified. The decorative tiles produced are more suitable for external wall tiling. They can also be treated with unsaturated polyester resin and mixed with different colors of pigments to create monochromatic or natural marble patterned smooth tiles. They can also be made into dark brown glossy tiles with resin or other coatings without any pigments, replacing ordinary tiles, artificial marble, etc. for indoor decoration. The tailings bricks treated with atmospheric steam curing have a compressive strength of 12.4MPa and a flexural strength of 3.0MPa. When an appropriate amount of fly ash and a small amount of gypsum are added to the mixture, the strength can be increased to above 20.0MPa. Moreover, after testing, this type of tailings brick is still a material that can withstand atmospheric action.
3、 Iron tailings production machine pressed lime sand bricks
Based on the characteristics of the mine, the wire cutting and cnc turning of iron castings Beneficiation Plant uses tailings production machines to press lime sand bricks. The bricks are mainly made of iron tailings, with an appropriate amount of cement added. After dry mixing, they are evenly mixed, and a small amount of bonding material is added for rolling to improve their surface activity. After being pressed and formed by a brick press, they are naturally cured. The process flow is simple, without burning or steaming, which not only saves energy (about 0.16t of standard coal is saved per 10000 bricks compared to clay bricks), but also has no pollution. The produced lime sand bricks have accurate dimensions, clear edges and corners, neat appearance, and straight bricks, which can save the amount of plaster used, improve efficiency, and reduce cost. The mine completed a production line in October 1989, and the produced lime sand bricks have been tested and all physical performance indicators meet the technical requirements of the No. 100 standard for machine pressed lime sand bricks.
4、 Production of carbonized tailings bricks from iron tailings
Yuquanling Iron Mine has achieved success in developing and utilizing tailings as carbonized tailings bricks since 1986. Carbonized tailings brick is a masonry material made from tailings sand and lime as raw materials, prepared from billets, pressed into shape, and carbonized using carbon dioxide (CO2) from lime kiln exhaust gas.
（1） Principle
The semi-finished product of carbonized lime sand brick is formed by the hydration and hard solidification of quicklime, which first generates calcium hydroxide crystals. Then, the lime kiln exhaust gas carbon dioxide (CO2) is used for carbonization, and finally, calcium carbonate crystals (CaCO3) are generated. Combined with water evaporation from the hydrate, the product obtains the final carbonization strength. The chemical reaction process is as follows:
CaO+H2O → Ca (OH) 2
Ca (OH) 2+nH2O+CO2 → CaCO3+(n+1) H2O
（2） Process
Mix 80% to 85% tailings sand with 15% to 20% quicklime powder in proportion, add about 9% water, stir and dissolve, and then use an eight hole brick press to form. Before entering the kiln, dry or naturally dry, with a moisture content of less than 4%. Then enter the tunnel kiln for carbonization, with a carbon dioxide content of 20% to 40% and a carbonization depth of over 60%. After exiting the kiln, the finished product can be obtained.
The production process of this type of brick is simple, and the masks machine parts and equipment can be used for soil samples. There are no technical problems that are difficult to master. Wherever there are tailings, sand, and limestone, they can be produced in large quantities.
5、 Serpentine glazed tiles and tiles
The tailings discharged from the iron and steel industry in Weihai City are mainly serpentine slag, with an annual discharge of 100000 to 150000 tons. In order to solve the comprehensive utilization of serpentine slag, a feasibility test for the production process of serpentine slag glazed tiles was conducted from May to July 1987. The main mineral components of serpentine ancient slag are silicate minerals such as serpentine, olivine, diopside, tremolite, and hornblende. Its grinding particle size is fine and uniform, generally -0.256mm, with a content of 85%. In terms of the mineral composition, chemical composition, particle size and other physical and chemical properties of its slag, it can be directly used as the main raw material for making ordinary civil building decorative materials such as bricks and tiles.
（1） The production principle of serpentine slag glazed tiles and tiles
The production principle of serpentine slag glazed tiles and tiles is mainly based on the melting crystallization characteristics of their minerals. During the high-temperature melting process of minerals from solid to solid-liquid phases, the repulsive forces between molecules in the material increase, while the bonding forces between molecules decrease; During the crystallization process from solid-liquid phase to solid phase, the attraction between molecules in the material increases, and the binding force of intermolecular bonds increases. The serpentine slag glazed tile preform, which is rich in SiO2, Al2O3, CaO, MgO, and Fe3O4 as chemical characteristics, undergoes a high-temperature melting crystallization process to complete the physical and chemical reaction process of solid phase, solid liquid phase, and solid phase. This enhances the binding force between material molecules, leading to changes in hardness, strength, corrosion resistance, and water immersion of the fired tile, improving various physical properties of the original material.
（2） Production process
The main production processes of serpentine slag glazed tiles and tiles include: raw material preparation, rough forming, glaze processing, hot air drying, and melting crystallization.
Raw material preparation: Mainly based on the chemical composition and physical characteristics of slag, prepare raw materials with higher fire resistance and fineness than ordinary bricks and tiles. The raw materials for making billets should generally meet the following requirements: the chemical composition is SiO260% -70%, Al2O3 10% -25%, CaO+MgO 0% -25%, Fe3O 43% -15%, 22% for particles with a particle size greater than 0.25mm, 40% for particles with a particle size of 0.25-0.05mm, 45% for particles with a particle size of 0.05-0.005mm, and 12% for particles with a particle size less than 0.005mm. The plasticity index is less than 7 (according to the liquid limit plastic limit), the drying linear shrinkage is less than 12%, and the firing linear shrinkage is less than 8%.
Blank forming: The prepared raw materials are mixed into a plastic shape by a mud mixer and cut into blanks. The blanks are then sent to the mold and pressed into blanks under pressure, which are then sent to the drying room for drying.
Glaze processing: After the surface finish treatment of the near dry rough, spray the glaze, that is, spray the base glaze, colored glaze, etc. as needed. After hot air drying in the drying room, the moisture content is lower than 1% before kiln drying.
Melting crystallization: The dried blank is usually fed into the kiln using refractory materials such as specially made porous kilns and tunnel kilns. From the 0th to the 14th hour, an average hourly temperature rise of 50 ℃ can be achieved. From the 14th to the 20th hour, an average hourly temperature rise of 30 ℃ can be achieved. The temperature inside the kiln can reach 1000-1050 ℃, and when the material is in a solid melting state, it can be stopped for 4-6 hours to cool and crystallize.
This type of glazed tile has a simple production process, a wide range of raw materials, low cost, and broad utilization prospects.
6、 Three free tailings bricks
Ansteel produces three types of tailings bricks with no pressure, no steam, and no burning using iron ore tailings powder as the main raw material. This brick has been tested and fully meets the requirements of JC153-75MU10 standard, and has passed provincial technical appraisal.
（1） Main raw materials and quality requirements
The main raw materials for this brick are iron tailings powder, lime as the curing agent, and cement as the binder.
Iron tailings powder: The chemical composition, physical properties, and particle size distribution of iron tailings produced by the Sanshao beneficiation plant in Anshan area are shown in Tables 1 and 2. The density is 2.85g/cm3, the stacking density is 1480kg/m3, the mud content is not more than 3%, and the water content is not more than 2%.
Lime: Quicklime powder is a curing agent, with an effective CaO content of not less than 65% and a loose bulk density of 1100kg/m3. Its particle size distribution is shown in Table 3. The appropriate dosage is 10% to 20%.
Admixture fly ash: Fly ash comes from a wide range of industrial waste residues, with a density of 2.2g/cm3, a loose bulk density of 1000kg/m3, and a fineness of 0.08mm. The sieve residue of the square hole sieve is not more than 8%, the loss on ignition is not more than 7%, and the sulfur trioxide content is not more than 3%. The chemical composition is shown in Table 4. The appropriate dosage is about 15%.
Activator and composite admixture: The activator is hemihydrate gypsum (CaSO4 · 1/2H2O), and the composite admixture is a self formulated K-agent. The appropriate dosage is 0.5%~1.0%.
Cement; 325 or 425 Portland cement, ordinary Portland cement or slag Portland cement can be used. The dosage is controlled by the cost, and generally the cement dosage is not more than 15%.
（2） Mechanism
To achieve pressure free, steam free, and fire free tailings powder bricks, it is necessary to form silicates, aluminates, and hydrated sulfoaluminate hydrates from their raw materials at room temperature. The light diffraction analysis shows that there are many C-S-H tobermorite gel or crystals in the brick blank, and a small amount of hydrated calcium sulphoaluminate needle crystals exist. Because the composite additive added in brick making is an efficient surfactant, the dispersion and adsorption effects increase the hydration point of cement, improve the interface condition of cement, lime, tailings powder, and fly ash particles, accelerate the hydration reaction, and harden at room temperature to produce considerable strength. The Ca (OH) 2 generated by cement hydration further reacts with active Al2O3 and SiO2 in tailings powder and fly ash to form low alkaline silicate and aluminate hydrates, promoting the compactness and strength improvement of the brick structure.
（3） Process
Mainly including ingredients, mixing, aging, shaping, and maintenance
Mix according to the ratio of tailings powder: cement: fly ash: lime=6:1.5:1.5:1 or 7:1:1:1:1, and then add an activator (gypsum) to dry mix evenly. Add water and K-agent and manually stir evenly. The water consumption is generally 20% to 30% of the weight of tailings powder. After stirring, let it stand for 20-30 minutes. After aging, put it into the mold, smooth the surface, remove the mold after 24 hours, and cure it in air or water for one month. Its strength in water is about 20% to 30% higher than in air.
The use of this process to make bricks can extensively apply industrial waste slag, which is beneficial for exploring material resources and saving energy. The cost is reduced by nearly 10% compared to existing ash slag bricks.
7、 Vitrified brick
Beijing University of Science and Technology conducted an experimental study on the production of vitrified bricks using the tailings of Damiao vanadium titanium magnetite type. Laboratory products with various performance indicators that meet the requirements for commercial vitrification and silicification were made using the entire tailings of Damiao iron ore.
（1） Raw materials
Damiao Iron Mine Tailings: The main minerals are gangue minerals such as plagioclase, pyroxene, chlorite, and epidote. After grinding the tailings, chemical analysis was conducted, and the results are shown in Table 5.
Clay: The main mineral composition is montmorillonite, with the following chemical components: SiO268.04%, Al2O316.46%, K2O0.22%, Na2O2.31%, CaO0.29%, MgO6.20%, Fe2O3, and a loss on ignition of 5.92. Its dosage is 10%.
（2） Process
Mix tailings with clay in a certain proportion, grind the mixture to -0.043mm and not less than 98%. Then, add 5% water to the dried material to form pellets. The pellets are made into cylindrical warm billets under a pressure of 38 MPa, and then calcined at 1145-1150 ℃. After polishing, the burnt samples can be used to obtain coffee colored vitrified bricks. After testing, all performance indicators meet the requirements of commercial vitrified bricks.
If calcined in a reducing atmosphere, the brick and charcoal powder are placed in the same saggar and sealed, while the brick and charcoal powder do not come into direct contact. Otherwise, the part of magnetite that comes into direct contact with the charcoal powder structural parts mould is reduced to ferrous oxide and metallic iron, resulting in melting flow phenomenon. The result is a black body with a bright black color after polishing.
The raw tailings of Damiao Iron Mine can be made into coffee colored vitrified bricks and black sloping bricks that meet the quality standards of commercial vitrified bricks. From the perspective of green billet strength and firing temperature range, expanded experiments and industrial experiments can be conducted.