Preparation And Performance Research Of Permeable Brick From Iron Tailings

In this paper,sintered permeable brick material was prepared by semi dry pressing method with iron tailings as main raw materials,expanded perlite and coal gasification ash as pore forming agent,Na₂CO₃ and albite as flux.The effects of different sintering temperature,molding pressure and flux content on bulk density,flexural strength,compressive strength,permeability coefficient,porosity and microstructure of permeable brick were studied;Using phosphogypsum,slag micro powder and fly ash as cementitious materials,calcium carbide slag as activator and aqueous solution of Na OH and the sodium water glass as binder,iron tailings unburned permeable brick was prepared.The effects of aggregate particle size,water cement ratio,curing temperature,cement and Na₂SO₄ content on flexural strength,compressive strength,permeability coefficient and porosity of permeable brick were studied.The main conclusions are as follows:（1）It is analyzed that the main components of iron tailings are Si O₂,Ca O,Fe₂O₃and Mg O.The main crystal phase components are Ca CO₃,Fe₂O₃,Si O₂,Al₂O₃.The internal iron oxide will undergo reduction reaction when heated to form high-temperature glass phase.It is analyzed that the main components of coal gasification ash are Si O₂,Ca O,Al₂O₃and Na₂O,which are mainly composed of amorphous vitreous minerals and unburned organic matter,which is conducive to improving the water permeability of sintered permeable brick..（2）The effects of sintering temperature,forming pressure and Na₂CO₃ content on the properties of sintered permeable brick from iron tailings are studied.The results show that the increase of sintering temperature is conducive to improve the mechanical properties and permeability coefficient of sintered permeable brick,but too high sintering temperature reduce the permeability coefficient and porosity.Increasing forming pressure is conducive to improve the strength of sintered permeable brick.Adding Na₂CO₃ flux is beneficial to improve the density of sintered permeable brick,when 4 wt%Na₂CO₃ was added,molded under 20 MPa pressure and sinterde under1130℃,iron Tailings sintered permeable brick could be made with the flexural strengthwas 4.01 MPa,the compressive strength was 29.39 MPa,the water permeability coefficient was 1.08×10^-2 cm/s and the porosity was 25.22%.（3）The orthogonal experiment of five factors and four levels was designed and carried out.The optimum process parameters for preparing sintered permeable brick were analyzed by range method:weigh the raw materials with the mass ratio of m（iron tailings）∶m（coal gasification ash）∶m（sodium feldspar）∶m（expanded perlite）=85∶7.5∶7.5∶20,and mix the expanded perlite with particle size range of 0.90～1.18 mm,and keep it at 1130℃for 3 hours.The variance analysis shows that the ash slag ratio and sintering temperature are the factors that have a significant impact on the mechanical properties of sintered permeable brick,and the ash slag ratio and the content of expanded perlite pore forming agent are the factors that have a significant impact on the water permeability and porosity of sintered permeable brick.（4）Iron tailings unburned permeable brick was prepared by steam curing at 60℃with aggregate particle size range of 0.9～2.36 mm and water cement ratio of 0.3.The results show that the increase of cement content is helpful to improve the flexural strength and compressive strength of unburned permeable brick,but the permeability coefficient and porosity will also be reduced;The increase of Na₂SO₄ content makes the flexural strength and compressive strength of unburned permeable brick increase first and then decrease,the permeability coefficient and porosity continue to decrease.When the Na₂SO₄ content is 4 wt%,the flexural strength and compressive strength of unburned permeable brick are the highest,which are 3.03 MPa and 28.1 MPa respectively.XRD shows that the addition of cement is conducive to the formation of amorphous calcium silicate hydrate in the vitreous body of slag and fly ash,and the addition of Na₂SO₄ is conducive to the formation of ettringite;Acicular ettringite is observed through the micro morphology,the addition of excessive Na₂SO₄ lead to the conversion of ettringite into single sulfur hydrated calcium sulphoaluminate and other substances,which reduced the mechanical properties of unburned permeable brick.