Eiki Kasai

De novo formation characteristics of dioxins in the dry zone of an iron ore sintering bed.

The objectives of this work are to understand the details of the mechanism of dioxin formation in the part of a sintering bed termed the dry zone, and to obtain ideas on how to prevent their formation. Sinter mixtures of various composition types were heated in a packed bed reactor, and dioxins in the outlet gas and in the sinter mixture residue were measured. The dioxin formation potential of a simple sinter mixture composed of iron ore, coke and limestone was markedly lower than that of fly ash from a municipal solid waste incinerator (MSWI). In consideration of this result, a series of experiments were conducted using a sinter mixture impregnated with CuCl2. Experimental results showed that dioxin formation was temperature-dependent in the range of 300-550 degrees C, with the maximum observed at around 300 degrees C, which was quite similar to that of fly ash from the MSWI. The homologue distribution of PCDD/Fs in gas and solid reflected the possible difference in carbonaceous materials in coke and activated coke. Gaseous hydrogen chloride acted as a chlorinating reagent for dioxin formation.

Thermodynamic properties of oxygen in RE-O (RE = Gd, Tb, Dy, Er) solid solutions

The oxygen potentials of four rare-earth metal – oxygen (RE–O: RE=Gd, Dy, Tb, Er) solid solutions have been measured by equilibration with yttrium – oxygen (Y–O) and titanium – oxygen (Ti–O) solid solutions. Rare-earth metal, yttrium and titanium samples were immersed in calcium-saturated CaCl2 melt at temperatures between 1093 and 1233 K. Homogeneous oxygen potential was established in the metallic samples through the fused salt, which contains some dissolved CaO. The metallic samples were analyzed for oxygen after quenching. The oxygen potentials of RE–O solid solutions were determined using either Y–O or Ti–O solid solution as the reference. This method enabled reliable measurement of extremely low oxygen potentials at high temperature (circa pO2=10−48 atm at 1173 K). It was found that the oxygen affinity of the metals decreases in the order: Y>Er>Dy>Tb>Gd>Ti. Values for the standard Gibbs energy of solution of oxygen in RE metals obtained in this study, permit assessment of the extent of deoxidation that can be achieved with various purification techniques. It may be possible to achieve an oxygen level of 10 mass ppm using an electrochemical deoxidation method.

Vapor pressures and enthalpies of sublimation of 17 polychlorinated dibenzo‐p‐dioxins and five polychlorinated dibenzofurans

An apparatus for vapor pressure measurement with a very small cell by the mass-loss Knudsen effusion technique was tested with solid benzoic acid and anthracene. The vapor pressure and enthalpy of sublimation results of the two reference compounds were in good agreement with accepted literature data. The vapor pressures at different temperatures of 17 polychlorinated dibenzo-p-dioxins (including dibenzo-p-dioxin) and five polychlorinated dibenzofurans (including dibenzofuran) were measured with the apparatus, and the enthalpies of sublimation of the 22 dioxins and furans were derived from the temperature dependence of vapor pressure. The results were systematically compared with the literature data.

Formation behavior of PCDD/Fs in PVC pyrolysis with copper oxide.

Formation and decomposition behaviors of PCDD/Fs during pyrolysis of polyvinyl chloride (PVC) with CuO have been investigated. These reactions proceed simultaneously, and the rate of decomposition exceeds that of formation with further retention. More 2,3,7,8-TCDD is formed when the dechlorination of PCDD/Fs proceeds significantly. Homologue profile patterns of PCDD/Fs show that the fractions of O8CDD and H6CDFs are relatively larger within PCDDs and PCDFs, respectively. Extremely large amounts of PCDD/Fs are obtained with the long retention time at 200 degrees C. The formation of PCDD/Fs decreases drastically with increase in the molar ratio of CuO/PVC. The acceptability of thermodynamic calculations on the formation of PCDD/Fs is also investigated. The thermodynamic calculated tendency of the effect of oxygen on the formation of PCDD/Fs agrees well with the experimental results, although absolute values of the amount of PCDD/Fs are much different.

Mechanochemical changes in gypsum when dry ground with hydrated minerals

Abstract Dry grinding of gypsum (CaSO4·2H2O) with hydrated minerals, such as talc, kaolinite or montmorillonite as an additive was conducted in a planetary ball mill in order to investigate the transformation of gypsum into its hemihydrate form ( CaSO 4 · 1 2 H 2 O ). This transformation of gypsum is accelarated by grinding and by the presence of hydrated minerals. The experimental results show that talc is the most effective additive, and the addition of 35 wt. % talc causes almost complete transformation after grinding for 2 h. The mechanism of the mechanochemical change of gypsum with the additives by mixed grinding is attributed to the transference of the water in the gypsum crystal structure into the additives.

Behavior of dioxin during thermal remediation in the zone combustion process

In the previous study, a new process concept for the thermal remediation of particulate/powder materials contaminated by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) has been verified. It leads to removal efficiencies of more than 99.9% in the soil contaminated by PCDD/Fs in terms of toxicity equivalent quantity (TEQ). However, details of the reactions and phenomena during the process, i.e., decomposition, vaporization, reformation and trap of PCDD/Fs and their relating compounds, have not sufficiently been clarified yet. The present study aims to examine experimentally the transport and fate of PCDD/Fs in the process. In the experiment, a laboratory-scale process simulator and a soil sample preliminary mixed with octachlorinated dibenzo-p-dioxin spiked by carbon-13 isotope (13C-OCDD) were used. The distribution of 13C-OCDD in the soil bed during the process was measured by applying a quench technique that rapidly cools-down the bed. Further, the total amount of 13C-OCDD discharged with outlet gas was measured. Using the obtained data, mass balance of 13C-OCDD in the process was estimated. The results show that about 99% of 13C-OCDD preliminary admixed with the soil was decomposed rather than released to the outlet gas. Only a trace amount of 13C-OCDD remained in the treated soil. In addition, a very small amount of other congeners having the 13C-cycles was detected in the treated soil and outlet gas although its TEQ values are not significant. These were probably formed by dechlorination reactions occurring in the process.

Numerical and Experimental Investigation on Heat Propagation Through Composite Sinter Bed With Non-Uniform Voidage: Part I Mathematical Model and Its Experimental Verification

The mechanisms of heat transfer through the sinter beds of the MEBIOS process are discussed and their comprehensive mathematical model is proposed. The MEBIOS process, the concept of which has been proposed earlier by the authors, allows using both coarse and fine particles of iron ores in the same sinter bed. The study includes two parts. The first part describes the model content and the results of its experimental verification. The model accounts for coal combustion, limestone decomposition, moisture evaporation/condensation, and melting/solidifying of solid phases. The model predictions are in good agreement with the experimental data. Typical numerical results of the sintering process and the key parameters influencing the process efficiency are discussed in the second part of the study.

Effect of dry grinding on ion-exchange characteristics of synthetic mordenite

The changes in ion-exchange characteristics of synthetic mordenite ground by a planetary ball mill under dry conditions were investigated using radioisotopes of 137Cs and 85Sr as tracers. The self-diffusion of Cs+ in the mordenite sample was facilitated in the initial stage of grinding, while it was leveled off for the further operation. The relative amount of Cs+ immediately exchanged in the mordenite sample was gradually styptic to a constant value with increase in grinding time after showing a rapid reduction in amount in the early stages of grinding. High selectivity of the mordenite sample for Cs+ against Sr2+ observed in acidic solution diminished obviously with an increase in grinding time.

Mechano-chemical changes in natural and synthetic zeolites by dry grinding using a planetary ball mill

Mechano-chemical effects of natural and synthetic zeolites induced by a dry grinding process using a planetary ball mill, which can be classified as a high-intensity grinder, was studied by various analytical methods, e.g. X-ray diffraction (XRD), radial distribution function (RDF) analysis, infrared absorption spectroscopy, thermogravimetric and differential thermal analyses, and the measurement of cation-exchange isotherms. Both zeolites became to be in an amorphous state in terms of X-ray powder diffraction patterns within certain grinding periods depending on their components. Mordenite tended to be in an amorphous state easier than clinoptilolite. Taking into account the results of infrared absorption analysis, the network structure of channels of the ground zeolite sample seems also to be considerably deformed and/or destroyed. The effect of dry grinding was also found on the amount of dehydration and it seems to be attributed to the decrease in the amount of crystalline water by making cations in the channels labile. However, the specific surface area and the saturated amount of adsorbed cations for the ground samples still showed certain large values comparing to, for example, clay minerals. The significant change was not confirmed by the RDF analysis for the XRD patterns. These suggest that the channels were not completely destroyed at the microscopic level even by dry grinding for a long time.

Formation and transport of PCDD/Fs in the packed bed of soil containing organic chloride during a thermal remediation process.

The authors previously proposed the concept of a new thermal remediation process for particulate/powder materials contaminated by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and experimentally verified its validity on the basis of process efficiency. However, contaminees such as soils and fly ashes from waste incinerators often contain a considerable amount of other chlorides, which may act as a main source of chlorine in the formation of PCDD/Fs via thermal processes. The present study aims to examine the formation and transport of PCDD/Fs in the packed bed of soil containing a chloride during the process. Polyvinyl chloride (PVC) polymer was mixed with soil sample as an organic chloride model. A laboratory-scale apparatus was employed as a process simulator. Further, a technique to quench the process was applied to observe the concentration distribution of PCDD/Fs in the solid bed in the vertical direction. The result shows that the PCDFs tend to form dominantly in the high temperature (calcination and/or combustion) zone and are successively trapped in the low temperature (wet) zone. Especially, TeCDF is the most dominant homologue contained in the wet zone and outlet gas. Although PCDD/Fs are once trapped at the wet zone, the concentration of the remediated materials gives fairly low value (1.9 pg/g-dry, 0.04 pg-TEQ/g-dry). It signifies that organic chlorides mingled in the solid contaminee not affect the removal efficiency of PCDD/Fs in the process. Nevertheless, attention should be paid to the potential emission of PCDD/Fs in the outlet gas due to the presence of organic chloride in the soil.