Preparation And Characterization Of Photocatalytic Electrolytic Manganese Residue Cement

The solid wastes produced from the electrolytic manganese dioxide or electrolytic metallic manganese industries have not been disposed properly. The electrolytic manganese residue (EMR) occupies large area of land and pollutes surrounding environment, which proved to be an important obstacle to the sustainable development of electrolytic manganese industry. Using industrial solid wastes to produce cementitious material is an effective way to achieve their reduction, recycling and harmless utilization. In this study, EMR is added into cement as an admixture to prepare EMR cement. Enriching the surface of EMR cement with TiO2may provide air-purifying and self-cleaning properties to the cement. And consequently improve the practical value of EMR in cement industry. The degradation efficiency of methyl orange and formaldehyde is used to evaluate the photocatalytic activity of EMR cement. The influence of the method of TiO2addition on the photocatalytic activity of the cement was investigated.In this study, the EMR after pretreatment is added into cement as an admixture to prepare cementitious material. The flexural and compressive strength, setting time and leaching toxicity were used to evaluate the mechanical properties of EMR cement. The influences of EMR content, water-cement ratio and TiO2content on the mechanical properties of cement were investigated. Experimental results indicate that the best EMR content in the cement was10%-15%, and the appropriate water-cement ratio was0.45-0.50. Moderate amount of TiO2can increase the hydration speed of cement. But the continuously increase of the TiO2content will decrease the strength of the cement, and increase the economic cost. So the massive incorporation of TiO2is not suitable.The method of TiO2addition was an important parameter influencing the photocatalytic degradation capability of cement. The mechanical mixing, sol-gel dip-coating and spraying coating were applied for the addition of TiO2and the degradation of methyl orange and formaldehyde were detected. The effect of TiO2content, calcination temperature, calcination time, coating times and the concentration of TiO2 suspension on the degradation rates were ascertained. Experimental results indicate that the best amount of TiO2in the mechanical mixed EMR cement was5%-8%, and the methyl orange and formaldehyde degradation efficiency were85.5%and8.1%, respectively. The photocatalytic degradation capability of cement with TiO2coatings was higher than that of mechanical mixed cement. As for the sol-gel dip-coated cement, the best methyl orange degradation efficiency94.2%was achieved after coated four times and calcined at500℃for2h. And the formaldehyde degradation rate was20.3%in this condition. The degradation efficiency of sprayed cement is much higher reaching up to98.2%for methyl orange and44.9%for formaldehyde with cement coated four times using15g/L-20g/L TiO2suspension. The photocatalytic activity of cement would decrease with the extention of service life, but the photocatalytic cement can be used sustainably.