Preparation Technology And Mechanism Of Autoclaved Bricks Made From Low Silicon Iron Tailings

The speed of iron tailings discharge obviously increases with the development of steel industry. However, the multipurpose utilization rate of iron tailings is low. The tailings are generally stockpiling in tailing pond, which not only cost lot, but also cause environmental contamination and safety problems. Low silicon iron tailing is an important constituent part of iron tailing. However, low silicon iron tailing is with characteristics of complex mineral constituent and fine particles, so its multipurpose utilization is difficult. The study selected two kind typical low silicon iron tailings (hematite tailings in Western Hubei and magnetite tailings in Jinshandian) as the main raw material based on the category of iron-bearing minerals to prepare autoclaved bricks. Meanwhile, the hydration reaction process in autoclave curing stage was studied and gradation design model of high tailing content autoclaved bricks was created. Finally, the technical economy possibility of autoclaved bricks from iron tailings was discussed. The specific research contents and results are as follows:(1) Preparation of autoclaved bricks from hematite tailings in Western HubeiThe characters of hematite tailings in Western Hubei were studied, which included chemical composition, mineral composition, grain composition and radioassay et al. The optimum technical parameters of preparing autoclaved bricks were determined. The optimum formulation was the mixtures of70%hematite tailings,15%lime and15%sand. Two-times stirring was used in stirring stage. The optimum forming pressure and moisture were20MPa and15%, respectively. The appropriate autoclave schedule was pressure rising time of2h, autoclave pressure of1.2MPa, constant pressure time of6h and natural depressurization. The compressive strength, flexural strength, compressive strength of hematite tailings autoclaved bricks after15freezing-thawing cycles and the mass loss of it with optimum process condition were21.20MPa,4.21MPa,18.36MPa and0.72%, respectively. They were well conformed to Autoclaved Lime-sand Brick Standard (GB11945-1999) for MU20autoclaved bricks.(2) Preparation of autoclaved bricks from magnetite tailings in JinshandianThe characters of dry and wet magnetite tailings in Jinshandian were studied, which included chemical composition, mineral composition, grain composition and radioassay et al. The optimum technical parameters of preparing autoclaved bricks were determined. The optimum gradation formulation was the mixtures of42%wet tailing,30%dry tailing of0.15-0.3mm fraction,5%dry tailing of0.3-0.45mm fraction,5%dry tailing of0.45-1.2mm fraction and6%dry tailing of0.45-1.2mm fraction. The lime content was12%. The optimum autoclave pressure and constant pressure time were1,2MPa and6h, respectively. The compressive strength, flexural strength, compressive strength of hematite tailings autoclaved bricks after15freezing-thawing cycles and the mass loss of it with optimum process condition were30.14MPa,5.98MPa,26.52MPa and0.74%, respectively. They were satisfied conformed to Autoclaved Lime-sand Brick Standard (GB11945-1999) for MU25autoclaved bricks. Compared the preparation of autoclaved bricks from the two kind different low silicon iron tailings, it was indicated that the preparation process and products rank should be decided based on the characters of tailings owing to the diversities of beneficiation process, associated minerals and particle size composition.(3) Hydration reaction process in autoclave curing stageThe samples with different autoclaved time were studied by XRD, DSC, FT1R and SEM in order to reveal the hydration reaction process in autoclave curing stage. It was found that hydrogarnet was firstly generated in hydration reaction process, then C-S-H (I) and tobermorite were created, and finally the tobermorite gradually transformed to xonolite.(4) Gradation design model of high tailing content autoclaved bricksThe Gradation design model of high tailing content autoclaved bricks was created, and the computational formula was as follow: Pdt=62.25(d,/dmax)0.22+37.75(d,/dmax)KAmong it:di-a certain grain size of aggregate, mm; Pdi-pass percentage of a certain grain size of aggregate di%; dmax-maximum grain size of aggregate, mm; K-Revise index number of gradation, K=0.39-1.25.(5) Technical economy analysis of preparing autoclaved bricks from iron tailingsThe Technical economy analysis of the project was discussed, which the annual output was150million standard autoclaved bricks. The total investment, annual cost of production, annual sale, annual profit were19,480million CNY,26.445million CNY,33.300million CNY and6.555million CNY, respectively. The investment would be took back after2.97years and the rate of return on investment was33.65%. Hence, the technical economy analysis of the project was feasible.