No abstract

Pyrite was heat treated on a thermo-gravimetric reactor (TGR) and a drop tube furnace (DTF) in CO2/N2 mixtures with different CO2 concentrations. The effects of CO2 on pyrite transformation were investigated. The reaction products were characterized by XRD and XRF. The results show that, the presence of CO2 can promote pyrite desulfurization and oxidation at 900°C and 1500°C. Pyrite oxidation seems to increase with CO2 concentration. TGR results show that hematite and magnetite are the final iron products at 900°C and higher CO2 concentration. DTF reaction samples generated at 1500°C with the presence of CO2 contain pyrrhotite and magnetite, indicating incompletion of pyrite desulfurization/oxidization due to a short residence time.

The use of coal fly ash for CO2sequestration has been proposed as a promising option for its utilization. However, research is quite necessary for advancing this technology. Indirect carbonation of high-calcium coal fly ash for CO2sequestration was investigated in this study. In these processes, calcium was first extracted from a high-calcium coal fly ash sample with NH4Cl solution. The obtained leachate was subsequently carbonated by bubbling CO2. It was shown that NH4Cl could extract about 35% of the total calcium into the solution under the conditions investigated. The dissolution of calcium is nearly accomplished in half an hour. Further increasing the extraction solution temperature (10-90°C) and the concentration of NH4Cl (0.5-3mol/L) only has subtle positive effects on the calcium extraction efficiency. The carbonation efficiency of the extraction leachate, namely the percentage of the calcium in the solution transformed into calcium carbonates is about 47%. The sharp drop in pH after bubbling CO2due to weak acid buffering capacity of the solution hinders the further precipitation of Ca2+. Calcium carbonate samples with a purity of up to 97% are obtained, meeting the purity requirements for industrial use.

A novel non-halogen flame retardant APESP, cyclotriphosphazene containing six aminopropyltriethoxysilicone functional groups N3P3[NH(CH2)3Si(OCH2CH3)3]6, was synthesized by menas of SN2 nucleophilic substitution reaction, using hexachlorocyclotriphosphazene(HCCP) and 3-aminopropyltriethoxy-silane (KH550) as material. Firstly the industrial grade HCCP was purified through recrystallization and sublimation. Then the reaction process was investigated to prompt the yield, and the optimum reaction conditions were as follows: triethylamine as acid-binding agent, tetrahydrofuran as solvent, HCCP/KH550/triethylamine molar ratio 1:7.2:7.2, dripping time: 1 hour, temperature: 67°C and reaction time: 20h. Maximum APESP yield reached 94.3%. The chemical structure and purity was characterized by element analysis, Fourier-transformed infrared spectroscopy (FTIR), mass spectrum, gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) analysis. The results showed that the structure of synthesized product is consistent with the theoretical structure, in which the chlorine atoms were completely substituted. The charge distribution calculation of HCCP and KH550 confirmed the reaction mechanism.

Adverse health effects of Fe and S in airborne particulate matter (PM) have been reported. However, little work has been done to characterize Fe and S in PM10 from coal combustion. In this study, a sub-bituminous coal (coal A) and a bituminous coal (coal B) were subjected to combustion in a drop tube furnace under air-and oxy-firing conditions. Size distribution and elemental composition of PM10 (PM with aerodynamic diameter 10 μm) were obtained by low pressure impactor and X-ray fluorescence techniques, respectively. The partitioning characteristics of Fe and S in PM10 were investigated. Data shows that particles of ~0.1μm contains the highest concentration of Fe for both coals under different combustion conditions. The concentration of Fe in the ultrafine particle mode decreases when switching from air combustion to oxy-fuel combustion with 21% O2. It increases when the oxygen concentration increases from 21% to 32% O2 during oxy-fuel combustion. Changing combustion conditions has little effects on Fe partitioning in particles >0.3μm. The concentration of S in PM10 increases with decreasing particle size, but changing combustion conditions have inconclusive influence. Fe and S are dominant elements in ultrafine particles, indicating a greater threat to human health.