Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Investigation of Trace Elements Content of Thermal Power Plant Ashes

The desire of mankind live within welfare has brought social and technologic developments. From social and technologic view, the development seemed to be proportional to the energy is consumed. As the growing world population, it should mean that the energy will increase as so. Especially in Turkey, where there is an increasing population with over average world population growing rate shows that the need for energy will increase. Nowadays coal is one of the most important sources of energy. Lignites that has low calorific value and high-ash are used in coal-burning thermal power plants with large capacity which were built to meet the needs of Turkey`s energy consume. In the result of burning of coal, it produces wastes like volatile ash, slag and chimney gases. In Turkey, about 45 million tons of coal is burned and average of 20 million tons of volatile ash is produced in one year. This large quantity of ashes constitutes problems for society and environment.

Within the context of this thesis studies a detailed literature review has been made on coal-fired power plants in the world and in Turkey and the properties of fly ash from the power plants. In the next phase two thermal power plants which are currently running in Turkey are chosen and ash samples had taken from those power plants. Over the taken ash samples a series of characterization, ore enrichment and leaching experiments were performed. On the ashes, particle size analysis, moisture content analysis, ore preperation, enrichment, hydrometallurgical and chemical testing, mineralogical analysis and trace element analysis’ were made. In the context of mineral processing studies laboratorty scale leaching experiments were carried out. In the light of the chemical and mineralogical studies, trace element contents of ashes were examined in detail. To evaluate the ashes, sulfuric (H₂SO₄), hydrochloric (HCl) and acetic (CH₃COOH) acids with leaching method was applied and opportunities of recovery of precious metals in the ash by optimum leaching parameters were investigated.

XRD analysis was performed to determine mineralogical structure of fly ashes. As a result of the XRD analysis; the sample of Yatagan Thermal Power Plant fly ash includes high percentage of quartz- SiO₂ and relatively low amounts of albite-Na (AlSi₃O₈) and calcite CaCO₃ minerals. But the sample of Soma Thermal Power Plant fly ash includes limestone, quartz-SiO₂, albite-Na (AlSi₃O₈), calcite CaCO₃, chlorite, serpentine, pyrite and montmorillonite minerals. It is determined that some part of the fly ash silica is crystalline quartz, while another part is converted into mullite (2SiO₂, 3Al₂O₃) because of the combination with aluminum and the rest has glassy structure. The structure of iron were found to be partially magnetite (Fe₂O₄) and hematite (Fe₂O₃) and the rest has glassy structure. Mineralogical studies have indicated that the uranium found as uranitite (UO₂) and thorium found as thorite (Th(SiO₄)) forms in Soma fly ashes. In Yatagan fly ashes the uranium found as uranitite (UO₂) and thorium found as monazite ((Ce, La, Nd)[PO₄]) and thorite (Th(SiO₄)) forms.

In order to determine the chemical content of a thermal power plant fly ash samples, complete chemical analysis’ were performed with ICP method. As a result of analysis, major oxides and trace element contents of both ashes have been revealed. Both samples’ V, Zr, Sr, U, Th and Ba were found to be high.

According to ASTM C618 standard, sample of Yatagan thermal power plant fly ash is in F fly ash class, because of sum of contents of SiO₂, Al₂O₃ and Fe₂O₃ is 72.38%. But the sample of Soma thermal power plant fly ash is classified at C fly ash class, because of being 64.54% of SiO₂, Al₂O₃ and Fe₂O₃ contents’ sum. These ashes are also located in high-lime ash class. Because they have above 10% CaO rate.

The result of leaching experiments using three different acid; the best result was obtained with usage of sulfuric acid (H₂SO₄) and under the condition of 30% solids, 120 g/t H₂SO₄ amount, 240 minutes leaching time and the 60°C leaching temperature. Also for the Yatagan thermal power plant fly ash sample; 97.12% of uranium dissolution yield, 91.21% of thorium dissolution yield, for the Soma thermal power plant fly ash sample; 94.71% of uranium dissolution yield, 93.21% of thorium dissolution yield was obtained.