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The Impact Evaluation of Zeolitization Parameters on the Properties of Sewage Sludge Ash

The incineration of municipal sewage sludge causes the formation of ash, which needs further utilization. The literature gives only few examples of the chemical sewage sludge ash conversion with the hydrothermal method. The effect of conversion depends on the properties of the raw material and the process parameters. According to the domestic and foreign test results of the conversion of fly ash from coal, the fusion method is more effective. The aim of the paper was to evaluate the impact of chemical sewage sludge ash conversion with the fusion method on the chosen properties of the obtained material. The applied conversion parameters were the ratio of sewage sludge ash:NaOH, the concentration of NaOH, the activation time and temperature as well as the crystallization temperature and time. In some of the samples, the introduction of the fusion caused the formation of the following, e.g. (hydroxy)sodalite, zeolite X and zeolite Y, zeolite P, (hydroxy)cancrinite. The temperature of the thermal treatment of sludge, the ratio of ash:NaOH and the crystallization time were the parameters having a statistically significant impact on the effect of zeolitization and the properties of the obtained material, but the changes of their values had little effect on the tested features of the modified ash. On the basis of the leaching of Cd, Cr and Ni from the samples after the conversion it was proven that a higher temperature of the thermal treatment of sewage sludge was favourable for the formation of permanent structures.