Utilisation of lignite fly ash in oil sorption and energy saving during clinker production

Abstract The present study aims at developing an environmental application of lignite fly ash, which constitutes the main by-product of power production by lignite combustion and whose greater amount remains unutilised. In particular, its application in oil spill cleanup and the further utilisation of the resultant oilfly ash mixtures in energy saving during clinker production has been investigated. For the amelioration of the floating ability and the oil sorption capacity of lignite fly ash, the mixing with a cheap, light and porous agricultural by-product, such as sawdust, has been applied. The addition of 30-50% w/w sawdust results not only in amelioration of the behaviour of lignite fly ash when added to oil spill in marine environment, by contributing to better floating and total oil removal, but also in increase in its oil sorption capacity by up to 50-80%. The higher calorific value of the resultant oil-lignite fly ashsawdust mixtures rising up to that of oil and bituminous coal encourages their utilisation as alternative fuels in cement industry. The remaining after their combustion ash varies from 18 to 58% w/w and its chemical and mineralogical composition differentiates slightly from the initial one. Analyses showed that it is enriched in Al 2 O 3 , SiO 2 , reactive SiO 2 , Fe 2 O 3 , CaO, CaO f and SO 3 . An increase in phases, such as anhydrite, gehlenite, gismondine, portlandite, and a decrease in lime and calcite are observed. However, the change observed in its composition is not expected to change the composition of clinker produced

Transformation of Industrial By-Products into Composite Photocatalytic Materials

The transformation of both calcareous and siliceous Greek power station by-products (lignite ashes) into novel composite materials with photocatalytic properties for environmental application was investigated. Particularly, a comparison between the development of coated ceramic substrates and the modification of ash surfaces is attempted. Specifically, a) the sintering process (1000 °C, 2 h) of both fly and bottom ash (either calcareous or siliceous) for their conversion into compacted ceramic substrates coated with TiO2 slurry and then further thermally treated (500 °C, 1 h) to acquire TiO2 film consistency onto the ceramic substrate and b) the process of TiO2 precipitation on lignite ash surfaces in acidic solution after neutralization, and estimation of the TiO2 percentage, are compared. The microstructures obtained were examined by XRD and SEM-EDX analysis. Vickers microhardness was also determined for the ceramic microstructures, with satisfactory results (up to 356HV). The energy gap measurements of the coatings were found to be between 3.02eV and 3.17eV, which is located between the energy gap of anatase (3.23eV) and rutile (3.02eV). The coating mass was about 0.059 g/cm2. The photocatalytic activity under visible and UV irradiation was investigated in aqueous solutions of methylene blue and methyl orange organic dyes, with encouraging results. A main advantage of the processes proposed is the immobilization of TiO2 onto largely available secondary resources, which can lead to production of value-added ‘green’ photocatalysts for the treatment of industrial effluents in the framework of circular economy

Sintering lignite fly and bottom ashes via two-step versus conventional process

Lignite combustion class-C (highly-calcareous) fly ash and bottom ash were sintered employing two-step sintering (TSS) and compared to conventionally sintered ones. TSS sintering is a new promising approach mainly used to obtain effectively densified ceramics. This alternative process is generally characterized by the absence of the final stage of grain growth occurring upon conventional sintering and by the development of nanograin microstructure. The ceramic microstructures successfully obtained in the present research were characterized by means of X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray analysis as well as by density measurements. The effectiveness of the solidification process was thoroughly studied, and the specific microstructural features attained are compared between each other and evaluated in relation to the sintering method applied. The results show that the valorization of lignite calcareous ashes into ceramic materials is feasible through different sintering techniques

Effect of limestone and dolomite tailings’ particle size on potentially toxic elements adsorption

The aim of the study is the investigation of potentially toxic elements adsorption on limestone, dolomite and marble particles of different size. As parameters, rock particle size, solution concentration, contact time and presence of other elements in the solution have been investigated. Four fractions with different particle size (−4mm + 1mm, −1mm + 315μm, −315μm + 90μm, <90μm) have been studied. Batch experiments have been carried out at 20, 60, 120 min from monoelement and competitive Cd, Cu, Pb, Zn solutions at concentrations 5, 100, 500 mg/L, whereas fixed bed conditions have also been applied. In lower concentrations, adsorption reaches equilibrium after 60 min. 15% difference in Pb adsorption and 15-30% in Zn adsorption has been observed depending on particle size. However, according to Taguchi method particle size has not proven a determinative parameter, so as to make grinding and/or sieving necessary for their further utilisation. Cd and Zn adsorption from a competitive solution is lower, whereas Cu and Pb adsorption is similar. Adsorption capacity of materials rises up to 0.03 mg Cd/g, 0.60 mg Cu/g, 0.03 mg Pb/g, 0.60 mg Zn/g. In fixed bed conditions more than 93% element is adsorbed, of which only 4% is leached