Mechanism Of Deposit Formation Research Articles

Investigation on formation and combustion process of carbon deposits from coke oven riser during waste heat recovery

In the context of carbon neutrality, the widespread application of waste heat recovery systems in steel production is crucial for energy conservation and emission reduction. This study investigates the formation and combustion removal mechanisms of carbon deposits in coke oven risers during waste heat recovery by analyzing the physicochemical structure, combustion behavior, and kinetics of different layers. The results revealed that lower temperatures near the tube wall produced higher volatile content in the lower layer. Over time, the carbon deposits gradually graphitized from bottom to top. Under long-term heating and iron catalysis, the lower carbon deposits showed a higher order degree and poorer combustion performance. The middle layer, characterized by more pores formed during polycondensation, exhibited a larger specific surface area than other samples and burned slightly faster than the upper layer. Increasing heating and airflow rates could linearly enhance the combustion efficiency of carbon deposits. The random pore model accurately described the combustion process of the upper and middle layers, whereas the multi-stage weight loss in lower deposits aligned better with a multi-stage reaction random pore model. This research could further strengthen the understanding of carbon deposits in the riser and improve the removal effect, thereby promoting waste heat recovery from coke oven gas.

Formation mechanisms of Fe-dominated versus Fe polymetallic deposits in the West Tianshan, NW China: A magnetite perspective

The West Tianshan in the Central Asian Orogenic Belt is one of important Fe belts in China, where many submarine volcanogenic iron-oxide deposits constitute the Awulale metallogenic belt. The Dunde deposit is a Fe-Zn-Au deposit, whereas Chagangnuoer, Zhibo, and Beizhan are Fe-dominated deposits. To examine the factors controlling the formation of Fe polymetallic deposits, the texture and chemical composition of magnetite from the Dunde deposit were studied in detail and compared with those of other deposits in the same belt. The Dunde deposit magnetite can be divided into Mag-1, Mag-2, and Mag-3, which correspond to stages of retrograde, sulfide, and carbonate stages, respectively. They have experienced oxy-exsolution and coupled dissolution and reprecipitation (CDR), forming multiple generations of magnetite. The exsolution of gahnite in Mag-1 and 10 times higher Zr, Hf, Sc, Ta, Nb, Mn, and Zn contents in the all stages of magnetite than those of Fe-dominated deposits, indicating the Dunde magnetite was crystallized from high-temperature, high-salinity, Fe-Zn-rich fluids. The similar chalcophile element contents in host volcanic rocks between Dunde and other deposits indicate host volcanic rocks are not the reason for Zn enrichment in Dunde. The higher Mg + Mn and Si + Al contents in Dunde magnetite than magnetite of other deposits indicate stronger fluid-rock interaction. Extensive CDR texture in Mag-1 and Mag-2 and lower Zn in secondary magnetite indicate that Zn leached from Zn-rich magnetite may have also contributed to the formation of sphalerite in sulfide stage. Our study has demonstrated that high-temperature, high-salinity, Fe- and Zn-rich primary fluids, a higher degree of fluid-rock interaction, and repeated fluid infiltration are key factors controlling the formation of Fe-Zn polymetallic deposits, such as the Dunde deposit in West Tianshan.

Study on mechanism of particle aggregation and pore formation during loess air-fall deposition based on discrete element method

The pore structure of aeolian deposits is essential for predicting their mechanical properties and the climatic conditions during their deposition. The discrete element method (DEM) is a practical approach for analysing the formation and evolution mechanisms of aeolian deposits’ pore structure. However, the effect of particle shape and non-contact van der Waals force on deposits’ pore structure with different particle sizes needs further exploration to enhance the efficiency and accuracy of DEM simulations. We developed a VdwForce model for DEM that accounts for the van der Waals force’s long-tail effect, and we conducted loess air-fall numerical tests that matched laboratory simulation tests. DEM simulations and laboratory tests show that the deposits’ porosity increased as the median particle size decreased, whether using spherical or actual shape particles in simulations. When deposits formed by particles with actual shapes have dense packing structures, simulations utilising spherical particles of the same size produce larger porosities. The primary reason of the alteration in the pore structure of the loess air-fall deposits is the shift in the quantity and pattern of particle agglomerates caused by van der Waals attractive force. So, the aggregation process during air-fall was essential for forming overhead pore structures.

Sphalerite Records Cd Isotopic Signatures of the Parent Rocks in Hydrothermal Systems: A Case Study From the Nayongzhi Zn–Pb Deposit, Southwest China

AbstractMetal stable isotopes (e.g., Zn, Cd, and Cu) have been used to track metal sources in different types of hydrothermal systems. However, metal isotopic variations in sulphides could be triggered by various factors such as mineral precipitation and fluid mixing. Thus, tracking the metal sources of hydrothermal systems is still a big challenge for metal isotopes. In this study, we investigated the Cd isotopic systematics of sphalerite from the Nayongzhi Zn–Pb deposit, which is a Mississippi Valley‐type (MVT) deposit in the Sichuan–Yunnan–Guizhou mineralization province (SYGMP). We reinterpreted the published S isotope data for the SYGMP and found that the large S isotopic variations were controlled by Rayleigh fractionation between sulphide and reduced S. As such, a model that involves mixing of a metal‐rich fluid with a reduced S pool formed by thermochemical sulfate reduction (TSR) can explain the ore formation in the Nayongzhi deposit. Based on this model, no Cd isotopic fractionation was observed due to its low solubility in fluids during mixing, and thus the Cd isotopic variations of sphalerite were inherited from the source rocks. The large range of Zn/Cd ratios and uniform Cd isotopic compositions of the sulphides are similar to those of igneous rocks but different from those of sedimentary rocks, indicating that Zn and Cd were derived mainly from basement rocks (e.g., migmatite, gneiss, and granulite). Our results reaffirm that metal stable isotopes, particularly Cd isotope compositions of sphalerite, are powerful geochemical tracers for investigating the formation mechanisms of ore deposits.

Formation Mechanism of Deposits in Rotary Kiln during Steelmaking Dust Carbothermic Recycling

Rotary kiln has been widely used in hazardous waste treatment because of its strong adaptability to raw materials, high productivity, and simple processing technology. However, the formation of deposits reduces its performance period and profitability. This study characterized the deposit mineralogy and thermodynamically and experimentally investigated its formation mechanism. The results show that the main phases of the deposit are magnetite, monolithic iron, olivine, and yellow feldspar. They indicate that the deposit formation process was accompanied by the participation of alkaline and iron oxides. The intermediate product Ca2SiO4 can promote the generation of low melting point phases, such as CaFeSiO4 and Ca2Al2SiO7, which are the main phases of deposit materials. Additionally, the reduction intermediate product FeO facilitated the generation of a liquid ferrous mixture (Fe3O4-FeO and Fe3O4-FeO-Fe mixture), which in turn further promoted the growth of the initial deposit phase. The solid deposit formed and attached to the kiln inner wall, along with a decrease in temperature. These results are expected to provide an idea or approach for fundamentally solving the problem of deposits in the rotary kiln.

Mechanism of Fe-skarn formation in the Nanminghe iron deposit, China

Skarn iron deposits are important resources for iron-rich ores and their genesis has been a topic of debate. The Nanminghe iron deposit is a typical skarn iron deposit in Wu’an, Hebei Province, China which provides a good example to investigate the metallogenic mechanism. In this paper, we present a detailed study of the geology, petrography, and geochemical characteristics of magnetite in the Nanminghe iron deposit. Two types of magnetite can be identified in the massive ores: Mag1 is euhedral with radial cracks developed in the margin. It is a low-Si magnetite, with SiO2 content ranging from 0.07% to 0.92%, with an average value of 0.49%. The SiO2 content of Mag2 is from 0.90% to 3.29%, and an average value of 2.03%. The Mag2 is associated with quartz, goethite, and apatite. Geochemical characteristics of Mag1, together with the ore textures suggest its crystallization from an iron magma. There are significant differences in the geochemical characteristics between Mag1 and Mag2. Mag2 is rich in Nb, Ta, high field strength elements, large ion lithophile elements and has higher silica content. The Nb/Ta of Mag2 is higher than that of the original mantle. These characteristics as well as La/Ta vs Th/La, Th/U vs Sm/Nd and Nb/Ta vs Nb features show that Mag2 is formed in the environment of supercritical fluids. The δ56Fe of Mag1 is 0.157‰-0.172‰, with an average value of 0.166‰, and the δ56Fe of Mag2 is 0.119‰-0.160‰, with an average value of 0.139‰. The Fe isotope of Mag2 is lighter than Mag1. There is a negative correlation between δ56Fe and SiO2 of Mag1 and Mag2, suggesting that the lighter δ56Fe of Mag2 was caused by injection of Si-rich fluids. We propose a genetic model where we envisage that the iron-rich melt formed in the deep magma chamber by reaction of dioritic rocks and carbonates. Mag1 formed by cooling of the iron-rich magma, following which Si-rich supercritical fluid were injected into the deep chamber resulting in fluid overpressure. The iron-bearing melt-fluid migrated upward along the magmatic conduit, when Mag2 formed. Our study provides insights into the formation mechanism of skarn iron deposits.

Modeling and Parameter Identification of Spark Plug Deposit Formation Mechanism for Different Fuel/Lubricant Combination

Abstract The identification of model parameters is complex and requires many approximations and laboratory investigations. Here, a novel approach to identifying these parameters is proposed, which uses experimental data, and a parameter estimation method to minimize a cost function made up of errors between the predicted and experimental deposit thickness. Parameters are determined for various ethanol–gasoline mixtures and lubricants. Simultaneously, the thermal and electrical properties of deposits are studied, and this information, coupled with the identified parameters, is utilized to infer potential deposit formation sources, mechanisms, and other elements that will influence the characteristics of the spark plug. It is found that the deposit formation model along with the identified parameters has the potential to reliably estimate the deposit growth with time as good correlations have been observed between measured and predicted spark plug deposit mass for all fuels and lubricants. The thermal and electrical conductivity of the spark plug deposit increases with a high ethanol fraction and high viscous oil, which results in increased chances of side sparking.

Flue Dust Behaviour in FSF - Arsenic Condensation in Offgas Line Conditions

The suspension smelting oxidation step has favourable conditions to generate chemical flue dust from the low-boiling elements of the feed mixture due to the high particle temperatures in the reaction shaft where combusting sulphide mineral particles reach temperatures above the melting point of magnetite. Arsenic, antimony, lead, and zinc are common impurity elements of high volatility in copper concentrates. They tend to accumulate in the flue dust due to the high volatility and closed mode of the flue dust circulation practiced in most industrial smelting-converting processes. Then, the only outlets for the volatile impurities are the anodes and the discard slag. A separate flue dust treatment for impurity removal is an option but it creates an additional step for the smelting plant and cost in the processing. When the concentrate grades decrease, and their impurity levels rise this outlet for the trace elements may become necessary. The arsenic condensation mechanisms in dust-free conditions in the copper flash smelting process gas train have been recently studied in SO2-air-N2 gas mixtures. It seems that the formation mechanism of arsenic-containing dust deposits is kinetically constrained, and their chemistries are influenced by the condensation temperature and atmosphere.

Improved Comprehensive Mechanism for Initial Deposit Formation: The Role of Thermophoresis and Glue Effect in Solid Fuel Combustion

Improved Comprehensive Mechanism for Initial Deposit Formation: The Role of Thermophoresis and Glue Effect in Solid Fuel Combustion

Advances in metallogeny and tectonics of the Eastern Tethyan Realm: Introduction

The Tethys domain preserves one of the largest continent‐continent collisional orogenic belts on Earth. This belt can be divided into the Proterozoic to Palaeozoic Proto‐Tethyan orogenic belt, Late Palaeozoic to Triassic Palaeo‐Tethyan orogenic belt and Triassic to Cenozoic Meso‐ and Neo‐Tethyan orogenic belts. The Tethyan metallogenic domain, representing one of the three major metallogenic domains in the world, extends more than 10,000 km from east to west and has developed world‐class ore belts, such as the South‐east Asia tin ore belt, Sanjiang metallogenic belt in South‐west China, Gangdese–Pakistan–Iran porphyry copper belt and South‐east Europe epithermal gold belt. The geology of the Tethys domain has been studied for more than 100 years and many important advances have been made recently, although scientific issues remain controversial. This thematic section of Geological Journal contains 10 articles focusing on the formation of rocks and ore deposits, including petrology and geochemistry of magmatic, metamorphic and sedimentary rocks, and the formation mechanism of mineral deposits in the Eastern Tethyan Realm. These articles reflect new progress in related studies and provide important reference for future studies.

The nature of carbon deposits and their formation pathways during catalytic supercritical water gasification of glycerol

Supercritical water gasification (SCWG) is a promising technology to convert wet biomass to renewable natural gas. The present study sheds light on the chemical composition and the formation mechanism of coke deposits on a Ru/CNF catalyst during continuous SCWG of glycerol in a fixed-bed reactor. SCWG experiments were performed using pristine carbon nanofibers (CNF) and 5 wt% Ru/CNF catalysts, which suffered from partial deactivation. Transmission electron microscopy (TEM) indicated a 34–42 % dispersion loss independently of the conditions, only partially explaining the activity loss observed during the test at very high space velocity. When operated under thermodynamic conditions, no deposits could be observed. A nanometric layer of deposits on the catalysts was present under intermediate conditions, while in the kinetic regime (conversion of glycerol down to 4 %), significant carbon deposition was observed. The chemical compositions of aqueous phases and organic deposits extracted from the catalysts and support showed that the presence of Ru enhanced the formation of unsaturated compounds from glycerol. In particular, molecules containing aromatic rings were detected. The space velocity significantly affected the composition of the coke deposits. The number of carbons in the molecules increased from 5–25 to 10–45 when moving away from the thermodynamic regime (full conversion), and the O/C ratio significantly decreased from 0.3–0.6 to 0.05–0.3, maintaining a very broad H/C ratio. The extracted organic deposits contained various aromatic compounds but were mostly represented by unsaturated aliphatic compounds. All these results were used to elucidate a reaction pathway for the formation of organic deposits from glycerol.

Large-scale rare-metal pegmatite deposit formation driven by supercontinent assembly

Abstract Triassic rare-metal pegmatite deposits are widespread in East Asia; e.g., the western Kunlun and Songpan-Ganze belt in northern Tibet and the Altai belt in the heart of the Central Asian Orogenic Belt. However, rare-metal enrichment processes and deposit formation mechanisms are enigmatic. Most rare-metal pegmatites in East Asia formed at ca. 220–200 Ma in the Late Triassic and are genetically related to S-type granites. Whole-rock and zircon Li and Cs contents indicate that sedimentary rocks represent a fertile rare-metal source for the pegmatite deposits and that long-term chemical weathering plays a key role in the enrichment of rare metals. The formation of these widespread deposits in East Asia was associated with lithospheric extension induced by slab retreat along the periphery of the supercontinent during Pangea assembly.

Ash fouling behavior during the combustion of bituminous coal and high-Ca pyrolytic biochar under air and oxyfuel atmosphere

Co-combustion of coal and pyrolytic biochar under oxy-fuel atmosphere is a promising option for addressing CO2 problems in power plants, where the issue of ash fouling during combustion was considered in this study. A high-Ca pyrolytic biochar from pilot-scale trail and a high-Si Utah bituminous coal were selected for single- and co-combustion on a drop tube furnace (DTF) coupled with fouling sampling system under the atmosphere of air and oxy50 (CO2:O2 = 50:50 vol%) at 1300 ℃. The fouling deposits were collected and characterized by various techniques to investigate the formation mechanism of ash deposits. The results indicated that the combined effects of impaction and capture resulted in the different deposition propensity from coal and biochar combustion under both air and oxy50 conditions. Besides, co-firing can inhibit the formation of ash deposits during coal combustion under air atmosphere when the blended biochar was greater than 50%, while the deposition propensity of the blend with 80% biochar rapidly aggravated under oxy50 atmosphere. The fine particles act as “glue” to fix coarse particles from impaction were the main source of the inside deposits from coal combustion, whereas the inside deposits from biochar combustion were dominated by agglomerated and sintered fine particles. Co-firing can weaken the “glue effect” from coal combustion, and finally presented as mitigated deposition propensity of inside deposits. Switching to oxy50 condition, the enhanced sulfidation of deposits and scavenging of alkali metal suppressed the growth of inside deposits from coal combustion, while that had minor impact on biochar. The inhibitory effect of co-firing on inside deposits diminished with the increased biochar under oxy50, where the deposition propensity of the blend containing 80% biochar was higher than that in air-firing.

The origin of olivine basalts from Medvezhya Mount (Avachinsky group of volcanoes, Kamchatka): The evidence of assimilation of sulfide-bearing cumulates

The role and conditions of liquid immiscibility and crystallization of sulfide phase during evolution of subduction related magmas remains to be a debated topic, which bears relevance to mechanisms of porphyry copper deposit formation and evolution of the continental crust. We studied rare volcanic rocks with inclusions of magmatic sulfides in olivine – the basalts of Medvezhya Mount in the Avachinsky group of volcanoes. The rocks belong to primitive (Mg# = 66 mol. %) middle-K island arc olivine basalts. Olivine with normal zoning predominate (~98%) among phenocrysts. The olivine compositions are typical for Kamchatka basalts, except for an unusual trend of increase of MnO content from 0.20 to 0.55 wt. % and decrease of Fe/Mn from 60 to 35 with change of olivine composition from Fo87.8 to Fo78.2. Olivines of this group contain numerous inclusions of minerals of the spinel group varying in composition from chromium spinel to magnesian magnetite. Olivine phenocrysts with sulfide inclusions are characterized by the absence or weak reverse zoning and reduced contents of Ca, Ni, Mn, Cr, and Al. The estimated crystallization temperatures for olivines of the prevailing type are 1036–1241°C, for sulfide-bearing olivines – 1010–1062°C. The data suggest that crystallization of the main olivine population occurred under relatively shallow conditions and was accompanied by strong oxidation of the magmas. On the contrary, the zoning and composition features of sulfide-bearing olivine suggest its xenogenic origin and probable crystallization at conditions of deep crust from low temperature water-rich and/or low-Ca magmas. The results obtained confirm the possibility of saturation of oxidized island-arc magmas with sulfide phase at lower crustal conditions, but show that this process is rare and not typical for low-pressure crystallization stage.

Review of rare earth element (REE) adsorption on and desorption from clay minerals: Application to formation and mining of ion-adsorption REE deposits

Ion-adsorption rare earth elements (iREE) deposits are the globally predominant source of heavy rare earth elements (HREE), which are mainly discovered and mined in southern China. This paper reviews the genesis and mining mechanisms of iREE deposits. These deposits are mainly formed in the weathering crust of rare earth elements (REE)-rich granites, volcanic rocks and metamorphic rocks. During the weathering and eluviation, REE are released by the dissolution of REE-bearing minerals, depending on the weathering resistance of such minerals. Then, aqueous REE cations migrate downwards and are adsorbed by clay minerals. The adsorption and fractionation of REE are affected by variations in oxygen, pH and ionic species and strength. REE are mainly adsorbed on clay minerals through ion exchange and surface complexation. The former reaction cannot cause evident REE fractionation, whereas the latter induces an enrichment of HREE over LREE. The enrichment and fractionation characteristics of REE are also constrained by their occurrence states. REE with different occurrence states can be distinguished via sequential extraction, and the micro-occurrence states of REE can be probed using high-sensitivity, high-resolution characterisation. Furthermore, the leaching mechanism of iREE deposits is summarized, where REE are exchanged by foreign cations. Ammonium sulphate is the main leaching agent, but its excessive use can cause serious environmental pollution. Thus, leaching agents with little or no ammonium, such as MgSO4 and CaCl2, have been recommended. The controlling factors of REE leaching are the concentration of leaching agents, pH, temperature and solid/liquid ratio. The above summary deepens the understanding of the formation mechanism of iREE deposits and provides beneficial information for the efficient but green mining of iREE deposits.

Effect of CaO, Al2O3, and MgO Supports of Ni Catalysts on the Formation of Graphite-like Carbon Species during the Boudouard Reaction and Methane Cracking.

The investigation of the course of the Boudouard reaction and methane cracking was performed over nickel catalysts based on oxides of calcium, aluminum, and magnesium. The catalytic samples were synthesized by the impregnation method. The physicochemical characteristics of the catalysts were determined using atomic adsorption spectroscopy (AAS), Brunauer-Emmett-Teller method analysis (BET), temperature-programmed desorption of ammonia and carbon dioxide (NH3- and CO2-TPD), and temperature-programmed reduction (TPR). Qualitative and quantitative identification of formed carbon deposits after the processes were carried out using total organic carbon analysis (TOC), temperature-programmed oxidation (TPO), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The selected temperatures for the Boudouard reaction and methane cracking (450 and 700 °C, respectively) were found to be optimal for the successful formation of graphite-like carbon species over these catalysts. It was revealed that the activity of catalytic systems during each reaction is directly related to the number of weakly interacted nickel particles with catalyst support. Results of the given research provide insight into the mechanism of carbon deposit formation and the role of the catalyst support in this process, as well as the mechanism of the Boudouard reaction.

Special Characteristics and Stability Analysis of Bank Slope Deposits with Special Geotechnical Structures in High and Cold Valleys

Due to the special internal and external dynamic action of the Qinghai-Tibet Plateau, the high and cold valleys are typically characterized by high-steep terrain, dry and cold climate, lithologic diversity, complex geological structure, and frequent occurrence of earthquakes. In this study, the types of special geotechnical structures of bank slope deposits in high and cold valleys are summarized based on field investigation, field and laboratory tests, and numerical simulation. These special deposits include colluvial-deluvial deposits, terrace deposits, early debris flow deposits, and landslide deposits. The formation mechanism, physical and mechanical properties, and stability analysis of these deposits were studied. The results show that the formation mechanism of various deposits is different, which is closely related to the intense geological tectonic action, the weathering and unloading action intensified by freezing and thawing cycles, and the special rock and soil structure in the high and cold valleys. Different material compositions have obvious effects on the physical and mechanical properties of the deposits, thus affecting the stability and deformation characteristics of the deposits. Under natural and saturated conditions, the stability of different types of the deposits is different, which is mainly related to the special geotechnical structure of various deposits. Compared with that before the reservoir impoundment, the stability factor of various deposits after the reservoir impoundment is significantly reduced. The performances can be provided as a reference for evaluating the stability of bank slope deposits in high and cold valleys.

Investigation of pitch deposits throughout the fiber line of softwood pulp mill

The formation of detrimental pitch deposits can cause various problems at pulp and paper mills, as they can contribute to unscheduled shutdowns and even paralyze the operation of the entire mills. To understand, avoid and control of pitch deposits formation in pulp mills, we investigated the overall chemical composition of 16 pitch deposit samples collected from the fiber line of a softwood kraft pulp mill. Sodium salts were tentatively speculated as the dominant fractions of the pitch deposits in addition to the minor fractions of the extractives and carbohydrates. Low molar mass extractives from dichloromethane, acetone and water extracts were analysed by gas chromatography–mass spectrometry. The extractable fraction is chemically heterogeneous, representing the degradation products of carbohydrates, lignin, and woody extractives. Furthermore, new chlorinated stilbenes (monochloropinosylvin, dichloropinosylvin, trichloropinosylvin dimethyl ether, and dichlorinated pinosylvin monomethyl ether) and other chlorinated components (chloro-manoyl/epimanoyl oxide, 12- and 14-chlorodehydroabietic acids) were for the first time identified as part of pitch deposits in the fiber line. Moreover, significant amount of 3-hydroxy fatty acids was found from the drying stage, also representing novel pulp mill deposit compounds. Pinostilbene and pterostilbene are rarely identified from the industrial woody chips of Scotch pine. Overall, the investigation of extractive profile from pitch deposits may provide us with a new perspective to understand the formation mechanism of pitch deposits and study the binding behavior between the extractive and surfaces of the process equipment. The new findings may provide guidance for the pulp mills to design optimal strategies to avoid and control pitch deposits.

Elucidation of exhaust gas recirculation deposit formation mechanism based on chemical analysis of components

To comply with strict emission regulations, vehicles are equipped with exhaust gas recirculation (EGR) systems that control nitrogen oxide emissions by returning part of the exhaust gas to the intake air. However, since deposits form in the EGR piping and valves, leading to pipe clogging, valve sticking, and in the worst case, failure of these components, there is a need to clarify the mechanism of deposit formation to predict and reduce deposit accumulation. While most of the previous studies have focused on the powdery deposits that clog the EGR cooler, this study aims to elucidate the formation mechanism of both the lacquer-like hard deposits and wet soft deposits that cause EGR valve sticking by quantitative and molecular-level analyses. In these experiments, a portion of the exhaust gas from an actual diesel engine without soot removed by diesel particulate filter (DPF) was used. Deposits were continuously generated on a simulated EGR line with a downstream temperature gradient from the engine outlet, while measuring the inner wall temperature. The collected deposits were subjected to comprehensive chemical analysis. The analysis showed that 75 % of the solvent-soluble deposit components were polycyclic aromatic hydrocarbons (PAHs), which were the main component of the hard and soft deposits. Most of the PAHs in the hard deposits that formed at a high inner wall temperature were C17 or higher. The hard deposit with an inner wall temperature of 137 °C contained 0.016 mg/cm2 of 6-ring benzo[ghi]perylene and 0.26 × 10-3 mg/cm2 of 4-ring pyrene. On the other hand, the soft deposit is formed at an inner wall temperature of 80 °C, contained 0.022 mg/cm2 of pyrene, which is significantly more than in the hard deposit. This shows that PAHs in the exhaust gas condense when the gas temperature reaches their dew points, and that the deposits formed at higher inner wall temperatures contain more PAHs with higher boiling points. High-molecular weight aromatic compounds with oxygen and nitrogen functional groups were detected in the solvent-insoluble deposit components. These compounds were found to be derived from the polymerization of oxygenated and nitrogenated PAHs through dehydration condensation and cross-linking reactions.

From Hot Springs to Deep-seated Fluids: History of Hot Spring Studies from the Viewpoints of Energy and Material Circulations in the Solid Earth

The history of hot spring studies and research in Japan is reviewed mainly from the viewpoint of Earth science. Studies on the geochemistry of hot spring waters started with geochemical analyses of hot spring water in the 1830s. The relationships between the issuing mechanisms of hot springs and volcanism, active faults, and earthquakes have been studied since around 1910. These studies reveal sources and recycling paths of waters and dissolved materials in the Earth's crust and the upper mantle in relation to plate tectonics and subsequent volcanism. Microbiological studies on living organisms, such as algae, bacteria, and archaea, living in hot springs, began in the late 1880s, and have contributed to documenting the origins and evolution of life. Combined with mineralogical studies, minor and trace element analyses of hot spring water have contributed to an understanding of the formation mechanisms of ore deposits. Studies on hot spring waters triggered an understanding of the essential role of water in the Earth and its evolution.