Calcined flint clay (45.6 wt.% Al2O3) and solid waste coal gangue were used to prepare low-density ceramic proppant by solid state sintering method. The density and breakage ratio of the ceramic proppant were systematically investigated as a function of sintering temperature. The morphology and phase composition of the ceramic proppant were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the ceramic proppant is composed of rod-like mullite and granular cristobalite. Bulk density and apparent density of the proppant first rise and then slightly decrease with increasing the sintering temperature, while breakage ratios under 35 MPa and 52 MPa pressure gradually decrease and then increase. As the sintering temperature increases up to 1400 °C, the ceramic proppant shows denser microstructure. The proppant sintered at 1400 °C have the best performance with 1.27 g/cm3 of bulk density, 2.79 g/cm3 of apparent density, 3.27 % of breakage ratio under 35 MPa closed pressure and 8.36 % of breakage ratio under 52 MPa closed pressure, which conform to the requirement of low-density ceramic proppant. The addition of solid waste can greatly reduce the preparation cost of the ceramic proppant.
Coal gangue is a kind of solid waste which is discharged from coal mining and coal washing. Dumped gangues do not only take a large land occupation but also pollute air and water. Treatment and utilizing of coal gangues has become the major issue for the coal industry to resolve. As major experimental material in this study, the coal gangue from Dawukou, Shizuishan, Ningxia province, China had been analyzed to have high-alumina content, and it could been used as alumina constituent for the preparation of sulphoaluminate cement. In this paper, alite-sulphoaluminate cements were prepared at 1330°C using coal gangue, limestone and gypsum as major main materials, fluorite and barite as minor materials. The result shows that major clinker minerals of the cement are sulphoaluminate, alite and belite, while major hydrate is ettringite, compressive strength of the cement is 48.9MPa after 7d. These experiments provide a new method of coal gangue comprehensive utilization.
Two-stage membrane bioreactor (MBR) system was applied to the treatment of landfill leachate from a solid waste disposal site in Thailand. The first stage anoxic reactor was equipped with an inclined tube module for sludge separation. It was followed by an aerobic stage with a hollow fiber membrane module for solid liquid separation. Mixed liquor sludge from the aerobic reactor was re-circulated back to anoxic reactor in order to maintain constant mixed liquor suspended solids (MLSS) concentration in the aerobic reactor. The removal of micro-pollutants from landfill leachate along the treatment period of 300 days was monitored. The results indicated that two-stage MBRs could remove biochemical oxygen demand (BOD), chemical oxygen demand (COD) and NH4+ by 97, 87 and 91% at steady operating condition. Meanwhile organic micro-pollutant removals were 50–76%. The removal efficiencies varied according to the hydrophobic characteristic of compounds but they were improved during long-term MBR operation without sludge discharge.