Study On Preparation And Performance Of Autoclaved Brick Using Polysilicon Residue

Polysilicon residue is solid waste produced in the production of polysilicon. At present, the main disposal methods of polysilicon residues include stockpiling and landfilling. However, these methods not only take up a lot of land resources, which will result in serious environmental pollution, but also increase the operating costs of enterprises. In this paper, the preparation technology of new type wall material, MU10 and MU25 polysilicon residue autoclaved brick, by alkali-activation was investigated, which presents great significance for solid waste utilization, environment protection and new type wall-material development.Effects of raw material dosage, molding process, ageing time and autoclaving process on the properties of polysilicon residues autoclaved bricks were studied. The mechanism of strength formation of polysilicon residues autoclaved brick was explored, and durability tests of products were performed. Research results obtained are as follows:1. The MU10 autoclaved brick was prepared with polysilicon residues, lime, sand and water by mixing materials, aging process, compression moulding and autoclaved curing. The results show that average compressive strength of autoclaved bricks is 11.5 MPa when the materials proportion of m(polysilicon residues):m(lime): m(sand)=40:10:50 with the water to materials ratio is 15%, autoclaved temperature at 180?for 6h. The mechanical properties of autoclaved bricks can satisfy the MU10 standard in Autoclaved lime-sand brick (GB11945-1999).2. Fly ash was used as an active reinforcing phase to improve the mechanical strength of MU25 autoclaved brick based on the research of MU10. The MU25 autoclaved brick was prepared with polysilicon residues, fly ash, lime and sand by mixing materials, rolling compaction, aging process, compression moulding and autoclaved curing. The results show that average compressive strength of autoclaved bricks could reach 27.8MPa when the proportion of m(polysilicon residues):m(lime): m(fly ash):m(sand)= 13:27:10:50 with water to materials ratio of 22.1%, autoclaved at 170? for 5h. The MU25 autoclaved brick could meet the Chinese standard, Autoclaved lime-sand brick (GB 11945-1999).3. The average density, water absorption rate and softening coefficient of MU10 autoclaved brick was 1450kg/m3,27.3% and 0.68, respectively. While the average density of MU25 autoclaved brick was 1700kg/m3 and the water absorption rate was 22.5% with a softening coefficient of 0.84. The freeze-and-thaw resistance of MU10 autoclaved brick prepared by polysilicon residues was relatively lower, while MU25 polysilicon residues autoclaved brick has shown excellent resistance to freeze-and-thaw cycles. For both kinds of autoclaved bricks, the mechanical strength was improved after carbonization and no lime blowing phenomenon or efflorescence phenomenon occurred during durability tests.4. The remaining Si in polysilicon residues reacted with Ca(OH)2 to produce new nano fibrous substances under autoclaved condition and its infrared absorption peak was at 981cm-1.5. The main compositions of hydration products of MU25 polysilicon residues autoclaved brick were found to be tobermorite, gismondine and xonotlite.