TPP Ashes As a Sorbent for Waste Water Purification from Ammonium Ions

A review of the use of waste from thermal power plants as secondary resources in industry and agriculture has been carried out. The results of a study of the structural-surface and physicochemical properties of ash and slag from a thermal power plant operating in an industrially developed region of the far north (the city of Apatity, Murmansk oblast) are presented. According to the data of chemical analysis, silicon and aluminum oxides predominate in their composition, the content of calcium oxide does not exceed 2.1%. It was established by the BET and BJH methods that the material has a predominantly mesoporous structure and a specific surface area of 17.8 m²/g that corresponds to the maximum observed in European medium-sized TPP plants. The phase composition of ash and slag was identified using the International Diffraction Database JCPDC-ICDD 2002; the dominance of quartz and calcium ferrite is noted in the mineral composition, but a significant part of the material is present in the X-ray amorphous state. It was found that, in terms of the main indicators, ash and slag correspond to the F-type of the international classification ASTM C 618, which makes it possible to recommend them for use as a sorbent in the treatment of domestic wastewater. The predominant extraction of the multicomponent composition of cationic forms from solutions was predicted from the pH value of the isoionic point equal to 7.63. Experimental data were obtained on model solutions in the range of concentrations of ammonium ions typical for municipal wastewaters of the city geographically adjacent to the TPP. Processing of the results obtained using the Langmuir sorption equations was carried out. The sorption capacity of ash and slag is 20.43 mg \({{{\text{NH}}_{4}^{ + }} \mathord{\left/ {\vphantom {{{\text{NH}}_{4}^{ + }} {\text{g}}}} \right. \kern-0em} {\text{g}}}{\text{.}}\) According to the results of experiments on the study of the kinetics of sorption on model solutions, the degree of extraction of ammonium ions when using ash and slag reaches 90% of the equilibrium concentration within 1 h, the sorption process is limited by external diffusion. An assumption is made about the expediency of using the spent sorbent, which is proposed as an ameliorant with a prolonged fertilizing effect, for the formation of bulk soils during the restoration of anthropogenically disturbed territories.