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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.

The present study focuses on the evaluation of high calcium fly ash (HCFA), an inorganic waste material produced by electric power plants in large quantities. Properties of HCFA, such as mineralogical and chemical composition, fine particle size, porosity, floating ability and hydrophobicity makes its application in oil spill clean-up attractive. Its sorption capacity depends on its composition and the oil type. Its floating ability has a better result in thin oil spill layers, specifically its coarse fraction, which seems to outmatch due to its higher Si content. Hydrothermal treatment with NaOH solution, with or without a template (tetrapropylammonium bromide), despite the increase in porosity and the decrease in specific gravity, has rather reduced the hydrophobic character and therefore its affinity for oil. The change in Si/Al content by the addition of SiO 2 has proved to ameliorate its sorption capacity, but not its floating ability. The application of a HCFA-oil mixture as road construction material seems to be encouraging. It contributes to the elimination of dust production during the paving of a road with gravel, and ameliorates the soil strength, which encourages its application in soil stabilisation.

The present study investigated the utilization of an industrial by-product, lignite fly ash, in oil pollution treatment, with the further potential profit of energy production. The properties of lignite fly ash, such as fine particle size, porosity, hydrophobic character, combined with the properties, such as high porosity and low specific gravity, of an agricultural by-product, namely sawdust, resulted in an effective oil-sorbent material. The materials were mixed either in the dry state or in aqueous solution. The oil sorption behaviour of the fly ash-sawdust mixtures was investigated in both marine and dry environments. Mixtures containing fly ash and 15-25% w/w sawdust performed better than each material alone when added to oil spills in a marine environment, as they formed a cohesive semi-solid phase, adsorbing almost no water, floating on the water surface and allowing total oil removal. For the clean-up of an oil spill 0.5 mm thick with surface area 1000 m(2), 225-255 kg of lignite fly ash can be utilized with the addition of 15-25% w/w sawdust. Fly ash-sawdust mixtures have also proved efficient for oil spill clean-up on land, since their oil sorption capacity in dry conditions was at least 0.6-1.4 g oil g(-1) mixture. The higher calorific value of the resultant oil-fly ash-sawdust mixtures increased up to that of bituminous coal and oil and exceeded that of lignite, thereby encouraging their utilization as alternative fuels especially in the cement industry, suggesting that the remaining ash can contribute in clinker production.

The study aims at investigating the role of particle size of mineral tailings derived from limestone, limestone marble, dolomite and dolomitic marble in heavy metal adsorption, in both batch and fixed bed conditions, so as to estimate whether grinding and/or sieving is necessary for their utilization.Methods. Fractions of different particle size have been studied. Adsorption has been examined in batch conditions from solutions of 5 mg/l Cd, 5 mg/l Pb, 100 mg/l Cu, 100 mg/l Zn, and their mixed solution simulating electroplating wastewater, and also in fixed bed conditions.Findings. Total Cd and Cu adsorption is achieved on all the mineral fractions, whereas Pb and Zn show a difference up to 20% depending on particle size. Referring to the mixed solution, Cd and Zn adsorption is lower, whereas no significant differences in Cu and Pb adsorption are observed. Adsorption capacity rises up to 0.03 mg/g Cd, 0.60 mg/g Cu, 0.03 mg/g Pb, 0.60 mg/g Zn. In fixed bed conditions, metal adsorption greater than 93% is achieved. Furthermore, leaching not exceeding 4% indicates a good metal retention. Finally, Taguchi method has proven that the particle size effect is not so strong compared to other parameters, including solution concentration and time.Originality. The particle size of mineral tailings has not yet been investigated as a parameter affecting heavy metal adsorption. Furthermore, heavy metal adsorption has been examined from separate metal solutions and not from a mixed one. The present study aims at contributing to these two research fields.Practical implications. Τhe differences in adsorption between mineral tailings' fractions with different particle size are not as high as to make grinding of minerals necessary.