Effect of acetic acid on the leaching behavior of impurities in metallurgical grade silicon

To explore the potential of acid leaching in purification metallurgical grade silicon (MG-Si) for solar cells, the effect of acetic acid on the leaching behavior was investigated in the present work by focusing on the behavior of impurities affected by the addition of acetic acid to a conventional acid mixture composed of hydrochloric acid and hydrofluoric acid. The etching results reveal that the HCl–HF–CH₃COOH mixture is a better lixiviant for dissolving impurity inclusions in MG-Si. The extraction yield of impurities in HCl–HF–CH₃COOH leaching was found to increase by 7% compared to conventional HCl–HF leaching.     

Nitric acid purification from admixtures of volatile acids by fractionation during waste evaporation at a spent nuclear fuel reprocessing company

We present the results of the computer simulation of a method for better purification of nitric acid from HF and CH₃COOH admixtures by creating a stripping section in the fractionation column with HNO₃ scrubbing and by the feeding of a parasitic water flow to the bottom section. The production column in the evaporator section of the RT-1 plant at the PA ??Mayak?? was upgraded using the calculation results and test trials on real process high-level waste were performed, which made it possible to improve the purification of regenerated 12 mol/L HNO₃ from HF and simultaneously from HCl by a factor of 3?C5. The specification figures for three flowsheet of nitric acid regeneration that were used at different times since 1979 for commercial purification from halogens and radioactive contaminants were compared.     

Effect of demineralization and heating rate on the pyrolysis kinetics of Jordanian oil shales

The effect of mineral matter content on the activation energy of oil shale pyrolysis has been studied. Kerogen was isolated from raw oil shale by sequential HCl and HCl/HF digestion. Oil shale and kerogen samples were pyrolyzed in a Thermogravimetric Analyzer at different heating rates (1, 3, 5, 10, 30, and 50 °C/min) up to a temperature of 1000 °C. Total mass loss of all oil shale samples remained almost constant irrespective of the heating rate employed, whereas it decreased with the increase of heating rate for kerogen (74.5 to 71.4%). From the pyrolysis profile activation energy (Ea) was found to vary between 70 and 83 kJ/mol for oil shale, while 82-112 kJ/mol has been determined for isolated kerogen. An increase of both Ea and pre-exponential factor was observed with an increasing heating rate. It is concluded that the mineral matter in oil shale enhances catalytic cracking as is evident from the reduced Ea values of oil shale compared with those for kerogen.     

Characteristics of oil shale pyrolysis in a two-stage fluidized bed

Rapid pyrolysis of oil shale coupled with in-situ upgrading of pyrolysis volatiles over oil shale char was studied in a laboratory two-stage fluidized bed(TSFB) to clarify the shale oil yield and quality and their variations with operating conditions. Rapid pyrolysis of oil shale in fluidized bed(FB) obtained shale oil yield higher than the Fischer Assay oil yield at temperatures of 500-600 ℃. The highest yield was 12.7 wt% at 500 ℃ and was about1.3 times of the Fischer Assay oil yield. The heavy fraction(boiling point 350 ℃) in shale oil at all temperatures from rapid pyrolysis was above 50%. Adding an upper FB of secondary cracking over oil shale char caused the loss of shale oil but improved its quality. Heavy fraction yield decreased significantly and almost disappeared at temperatures above 550 ℃, while the corresponding light fraction(boiling point 350 ℃) yield dramatically increased. In terms of achieving high light fraction yield, the optimal pyrolysis and also secondary cracking temperatures in TSFB were 600 ℃, at which the shale oil yield decreased by 17.74% but its light fraction yield of 7.07 wt% increased by 86.11% in comparison with FB pyrolysis. The light fraction yield was higher than that of Fischer Assay at all cases in TSFB. Thus, a rapid pyrolysis of oil shale combined with volatile upgrading was important for producing high-quality shale oil with high yield as well.     

Pyrolysis kinetics for Green River oil shale from the saline zone

The nature of the organic and mineral reactions during the pyrolysis of Saline-zone Colorado oil shale containing large amounts of nahcolite and dawsonite has been determined. Results reported include a material-balanced Fischer assay and measurements of gas evolution rate of CH₄, C₂H_x, H₂, CO and CO₂, Stoichiometry and kinetics of the organic pyrolysis reactions are similar to oil shale from the Mahogany zone. X-ray diffraction and thermogravimetric analysis results are used to help determine the characteristics of the mineral reactions. Kinetic expressions are reported for dawsonite decomposition, and it is demonstrated that the temperature of dolomite decomposition is substantially lower than for Mahogany-zone shale because of the presence of the sodium minerals.     

Effect of demineralization on yield and composition of the volatile products evolved from temperature-programmed pyrolysis of Beypazari (Turkey) Oil Shale

In this study, the effect of the mineral matter of Beypazari Oil Shale on the conversion of organic carbon of oil shale into volatile hydrocarbon, polycyclic aromatic hydrocarbons (asphaltenes, preasphaltenes) and carbon in solid residue was investigated. Kerogen was isolated by successive HCl, HNO₃ and HF treatments. A series of temperature-programmed pyrolysis operation was performed with raw Beypazari Oil Shale, and each product of every demineralization process. A carbon balance of the pyrolysis process was established by determination of the recovery of total organic carbon as organic products, and carbon remaining in the reactor because of the coking reactions. The removal of the material soluble in HCl washing affected the conversion of organic materials in the pyrolysis reactions. Alkali and alkaline earth metal cations affect the reactivity of oil shales and the leaching of these mineral matters with HCl caused a slightly decreases in the conversion to volatile hydrocarbons. The removal of pyrites with HNO₃ did not affect the reactivity of the organic material in pyrolysis. But, removal of the material soluble in HF increased the conversion in pyrolysis reactions. It can be explained by the inhibitive effect of the silicate minerals. Complete removal of mineral matrix and isolation of kerogen increased the driving force for heat transfer since more heat was transferred from outside towards the inside of the oil shale particles, thus pyrolysis reaction might have occurred with ease and diffusion limitation might have decreased due to absence of mineral matrix.     

Changes to the organic functional groups of an inertinite rich medium rank bituminous coal during acid treatment processes

A South African inertinite rich medium rank bituminous coal was subjected to a series of acid treatment steps using concentrations of HF and HNO₃ ranging between 1.5 and 4 M, temperatures between 65 and 80 °C and reaction time between 1.5 and 3 h for each acid. A HF and HCl procedure was used to reduce mineral matter to less than 2.5%. Analyses indicate that oxygen and nitrogen containing species are incorporated in the coal structure during the HF/HNO₃ leaching processes, but not during the HCl/HF/HCl procedure. The HF/HNO₃ methods lead to increased amounts of = N-OH groups formed on the remaining coal structure, whereas the HCl/HF/HCl procedure did not. The -COOH content upon HCl/HF/HCl treatment increased slightly possibly due to protonation of COO⁻ groups by HCl. The results show that the CO₂ reactivity doubled after the HF/HNO₃ procedures and increased by a factor of 2.5 for the HCl/HF/HCl treatment. Surface areas of the treated coal samples increased with the highest increase for the HCl/HF/HCl method. The increased surface areas may cause the increased CO₂ reactivity. The results indicate that the described acid treatment procedures with mixtures containing nitric acid have slight, but measurable, effects on the coal structure.     

Quantitative study of the carboxylic acids in Green River oil shale bitumen

Bitumen fractions were extracted by a benzene/methanol reflux of Green River oil shale (GROS) before and after treatment with HCl, HF, and HCl/HF. Acid leaching released 80% more bitumen than could be extracted without acid treatment. This additional bitumen had greater concentrations of carboxylic acids and their salts than the untreated oil shale bitumen. The carboxylic acids were separated from all bitumen fractions (untreated, post HCI, post HF, and post HF/HCl) and individual acids were identified and quantified by gas chromatography—mass spectrometry and high resolution mass spectrometry. The same types of acids were present in all four bitumen fractions but showed significant differences in their relative abundances. These carboxylic acids and salts were present in the original GROS and were not formed during the treatment. The post-HCl bitumen fraction contained Mg and Fe salts of long-chain aliphatic carboxylic acids with carbon numbers in the range of 21–38. Significantly, even though calcium is the major cation in the carbonate minerals of GROS, no Ca was present in the ash of these carboxylic acid salts. These results indicate that there is a strong interaction between carboxylic acids present in GROS and its mineral matrix (especially carbonate minerals). These carboxylic acids are possible coupling agents that ‘glue’ mineral and organic material together. The treatment of the oil shale also resulted in the formation of highly purified kerogen, low in ash yield (2 wt %) which had undergone only very mild acid treatment.     

A study of trace element behavior in two modern coal-fired power plants I. Development and optimization of trace element analysis using reference materials

Analytical methods for solid samples taken from a coal-fired power plant were developed and optimized in order to facilitate a comprehensive series of measurement campaigns aimed at trace metal balance determinations in various coal-fired power plants. Commercial reference materials with certified trace element contents were used as model samples. A procedure which had been previously developed for the analysis of fly ash was found to give good recoveries in the case of both coal fly ash and coal in a two-laboratory intercomparison. This procedure was based on microwave digestion in a mixture of HNO₃ and HF in closed vessels. The digestion of samples of dolomitized limestone and gypsum rock was found to be successful under similar conditions but using a mixture of HNO₃, HCl and HF, although the precision of the determination was not as good as in the case of coal and coal fly ash. The digestion procedures developed and tested in this work can be recommended as simple and uniform methods in the analysis of power plant samples for a number of trace elements, exclusive Hg.     

Pyrolysis behaviour of Australian oil shales in a fluidized bed reactor and in a material balance modified Fischer assay retort

The pyrolysis behaviour of several Australian oil shales was determined using the material balance modified Fischer assay and a bench-scale fluidized bed pyrolysis reactor, with nitrogen or steam as the sweep gas. The assay oil yield, which ranged from 5.3 to 15.7 wt% of the dry shale, did not correlate well with the organic carbon contents of the shales. However, under both assay and fluidized bed pyrolysis conditions, a shale of high kerogen H/C had high organic carbon conversions to oil. Compared with the Fischer assay, nitrogen pyrolysis gave 7 ± 4 wt% more oil for the shales studied, and steam pyrolysis gave 15 ± 4 wt% more oil for all shales except one, which showed a 35 wt% increase in oil yield. However, the oils from both nitrogen and steam pyrolysis had lower H/Cs, higher sulphur and nitrogen contents, and more high boiling point fractions than those from the Fischer assay. Nitrogen pyrolysis oils were of higher quality than those produced by steam pyrolysis. With steam as the sweep gas, much more hydrogen and hydrogen sulphide were produced for all shales; in most cases, there was also more carbon monoxide and less hydrocarbon gases.     

Co-current combustion of oil shale - Part 1: Characterization of the solid and gaseous products

Co-current combustion front propagation in a bed of crushed oil shale (OS) leads to the production of liquid oil, of a flue gas and of a solid residue. The objective of this paper was to provide a detailed chemical characterization of Timahdit oil shale and of its smoldering combustion products. The amount of fixed carbon (FC) formed during devolatilization is measured at 4.7% of the initial mass of oil shale whatever the heating rate in the range 50-900 K min⁻¹. The combustion of oil shale was operated using a mix of 75/25 wt. of OS/sand with an air supply of 1460 l min⁻¹ m⁻². In these conditions, not all the FC is oxidized at the passage of the front, but 88% only, with a partitioning of 56.5% into CO and the rest into CO₂. A calorific gas with a lower calorific value of 54 kJ mol⁻¹ is produced. Approximately 52% of the organic matter from OS is recovered as liquid oil. The front decarbonates 83% of carbonates.     

Thermal degradation of shale oils: 1. Kinetics of vapour phase oil degradation

As vertical modified in-situ retorts (VMIS) have been scaled up and tested, the overall oil yield has declined and is generally lower than that observed in an above-ground process. This reduced oil yield could adversely affect the economics of VMIS retorting. Diminished yields are attributed to a combination of factors associated with scale-up such as in complete rubblization, wide particle size distributions (large blocks of shale), and poor flow distributions. Additionally, oil losses can occur by comparatively long exposure of the oil vapours to high temperatures, by exposure to successive condensation and revaporization of the oil as it travels down the retort, and finally by long time thermal exposure of the condensed oil retained in the bottom portion of large VMIS retorts. To study such vapour phase degradation of shale oil using oil produced from Occidental Petroleum's No. 6 VMIS retort, a tubular continuous flow reactor, with an on-line gas chromatograph for gas composition monitoring was used to study thermal degradation of shale oil under retorting conditions. Oil and a combination of gases including steam were metered into the preheater and then the vapours passed into a quartz tubular reactor where the temperature and residence time of the gaseous mixture were controlled. Complete mass balances were performed giving the weight fraction of oil converted to noncondensable hydrocarbon gases and coke. This experimental design is novel because high temperature thermal degradation of shale oil was studied for the first time under steady state flow conditions with carefully controlled residence time and temperature. A range of temperatures (425–625 °C) and residence times (2–10 s) were used in a series of factorial-designed experiments (3²) to accurately determine the effects of these variables. Results of the study showed that the addition of steam to the carrier gas did not reduce oil degradation losses but did react with the coke thereby changing the product gas composition and quantity. A first-order oil degradation rate expression was used to model the rate of oil loss. The calculated activation energy was 17.3 kcal mol^?1. Chemical analyses of the product liquids and gases confirmed previously reported findings that the oil loss indices (alkene/alkane, ethylene/ethane, naphthalene/(C₁₁ + C₁₂), and gas/coke) increase with increasing oil degradation.     

Textural study of a coal from villanueva de rio y minas (sevilla,spain) and of samples prepared from it by acid and heat treatments

A coal with high inorganic matter content from the mine of Villanueva de Rio y Minas (Sevilla, Spain) (VRMO) was classified by following the ASTM norms as a high volatile matter A bituminous coal. The starting coal was treated either with HCl (VRMH) or thermally at 1000°C for 2 h (VRMOC), the resultant yield values (referred to as VRMO, dry) being, respectively, 97 and 79%; also VRMH was either treated with HNO₃ (VRMN) or HF (VRMF), and the yield values (referred to as VRMH, dry) of the process were then 95 and 59%. The textural characterization of samples was effected by adsorption of CO₂ at 273 K and of N₂ at 77 K, as well as by mercury porosimetry. VRMN presents the highest value of the apparent surface area (S_D-R=219 m² g^?1) (CO₂, 273 K) and of the specific surface area of mesopores and macropores (S_me+ma=5.2 m² g^?1) (N₂, 77 K), while the greatest value of the cumulative specific surface area of macropores (S_ma=1.2 m² g^?1) (mercury porosimetry) corresponds to VRMOC; S values are expressed on a per gram of original sample basis. The micropore volume accessible to CO₂ at 273 K increases in both the HCl and the HNO₃ treatment and decreases in the HF and heat treatments. The HCl and HNO₃ treatments produce an increase of the mesoporosity; the HF treatment seems to affect in a special way the mesoporous texture. Furthermore, the heat treatment gives rise to a notable development of the macroporosity.     

Thermogravimetry and decomposition kinetics of British Kimmeridge Clay oil shale

The characteristics of volatile matter evolution and the kinetics of thermal decomposition of British Kimmeridge Clay oil shale have been examined by thermogravimetry. TG has provided an alternative to the Fischer assay for shale grade estimation. The following relation has been derived relating TG % volatiles yield to the shale gravimetric oil yield: oil yield (g kg^?1) = (TG volatiles, % × 5.82) ? 28.1 ± 14.5 g kg^?1. A relationship has also been established for volumetric oil yield estimation: oil yield (cm³ kg^?1) = (TG volatiles, % × 4.97) – 5.43. TG is considered to give a satisfactory estimation of shale oil yield except in certain circumstances. It is found to be less reliable for low yield shales producing <≈40 cm³ kg^?1 of oil (≈10 gal ton^?1) where oil content of the TG volatiles is low: volumetric yield estimation accuracy is affected by variations in shale oil specific gravity. First order rate constants, k = 4.82 × 10^?5s^?1 (346.3 cm³ kg^?1shale) and k = 6.78 × 10^?5s^?1 (44.6cm³ kg^?1shale) have been obtained for the devolatilization of two Kimmeridge oil shales at 280 °C using isothermal TG. Using published pre-exponential frequency factors, an activation energy of ≈57.9 kJ mol^?1 is calculated for the decomposition. Preliminary kinetic studies using temperature programmed TG suggest at least a two stage process in the thermal decomposition, with two maxima in the volatiles evolution rate at ≈450 and 325 °C being obtained for some samples. Use of published pre-exponential frequency factors gives activation energies of ≈212 and 43 kJ mol^?1 for these two stages in the decomposition.     

Gas evolution during pyrolysis of various Colorado oil shales

Rates of evolution of C0₂, CO, H₂, CH₄ and the C₂ and C₃ hydrocarbons during the pyrolysis of seven Colorado oil shales have been measured. These shales, which are from various depths at two different sites, yield 34–255 ¦ of oil per tonne raw shale (9–61 US gal of oil per short ton raw shale) and linear heating at a rate of 2°C min⁻¹ was used for the retorting of all samples. The objective of the study is to monitor variations in gas evolution from shales of different organic content and from various stratigraphic and areal locations. Comparisons between shales from each site are made together with correlations with data from Fischer assays. A kerogen concentrate (mineral fraction removed by HCl-HF treatment) and retorted shale from a Fischer assay are also included. The ability of a kinetic model due to Campbell et al. to predict gas evolution is tested and it is found necessary to modify slightly some of the stoichiometric coefficients to obtain good agreement. The resultant kinetic model should adequately describe the gas and oil evolution behaviour of shale from the upper portion of the Green River formation.     

Preparation of silica aerogel from oil shale ash by fluidized bed drying

The silica aerogel with high specific surface area and large pore volume was successfully synthesized using oil shale ash (OSA) via ambient pressure drying. The oil shale ash was burned and leached by sulfuric acid solution, and then was extracted using sodium hydroxide solution to produce a sodium silicate solution. The solution was neutralized with sulfuric acid solution to form a silica gel. After washing with water, the solvent exchange with n-hexane, and the surface modification with hexamethyldisilazane (HMDZ), the aged gel was dried by fluidization technique and also using a furnace to yield silica aerogels. The physical and textural properties of the resultant silica aerogels were investigated and discussed. The results have been compared with silica aerogel powders dried in a furnace. From the results, it is clear that the properties of silica powders obtained in fluidized bed are superior to that of powders dried in the furnace. Using fluidization technique, it could produce silica aerogel powders with low tapping density of 0.0775 g/cm³, high specific surface area (789 m²/g) and cumulative pore volume of 2.77 cm³/g.     

Determination of shale oil yields by petrographic analysis

Rundle-type oil shales from five Australian deposits (Rundle, Stuart, Condor, Byfield and Duaringa) contain abundant lamellar alginite that is easily recognized using fluorescence microscopy. Shale oil yield, as determined by modified Fischer assay, is directly related to the volume per cent of alginite in the parent shales for each of the above deposits. Data provided show that interdeposit estimates of shale oil yield, based on alginite content, are more reliable than estimates based on specific gravity of the parent shales. Application of petrographic techniques should provide rapid assessment of the shale oil yield for other deposits with Rundle-type oil shale. The method requires initial calibration of alginite content, in a limited number of samples, with Fischer assays.     

Sorption of Rare-Earth Elements and Ac on UTEVA Resin in Different Acid Solutions

The distribution of some rare-earth elements (REEs) on Uranium and TEtraValent Actinides (UTEVA) resin was determined from different concentrations of inorganic (HCl, HNO₃, HClO₄, HPF₆) and one organic acid – CCl₃COOH. Low sorption of all REEs in the range of 1 M–5 M HNO₃ was observed. In more concentrated HNO₃, a rapid increase of the distribution coefficients (K_d) was noticed with an increase in the atomic number of the lanthanides as well as in Y and Sc. The system UTEVA–CCl₃COOH showed a higher selectivity for Eu(III). Chromatographic elution profiles were checked in order to confirm the obtained K_d values.     

The conjugation and epoxidation of fish oil

Wilkinson's catalyst [RhCl(PPh₃)₃] has been used to conjugate fish oils in high yields under very mild reaction conditions. A catalyst load of 0.35 mol% of RhCl(PPh₃)₃, 0.43 mol% of (o-CH₃C₆H₄)₃P, and 0.87 mol% of SnCl₂·2H₂O in ethanol solvent at 60°C for 2 d produces 82% conjugated Norway fish oil affords 90% conjugated fish oil in 93% yield. The Sharpless epoxidation procedure has also been employed to epoxidize fish oils. Using 0.34 mol% of CH₃ReO₃, 8.15 mol% of pyridine, and 1.03 equivalents of aq. 30% hydrogen peroxide in methylene chloride solvent at 25°C for 6 h, the Norway fish oil ethyl ester can be 100% epoxidized in an 86% yield. The Capelin fish oil gives 100% epoxidized fish oil in a 72% yield. Decreasing the amounts of CH₃ReO₃ and pyridine used in the reaction results in partially epoxidized fish oils.     

Gas evolution during oil shale pyrolysis. 2. Kinetic and stoichiometric analysis

Nonisothermal rate measurements for the evolution of H₂, CH₄, C₂ hydrocarbons and C₃ hydrocarbons during the pyrolysis of Colorado oil shale have been analysed using the recent kinetic theory of Antony and Howard AIChE J. 1976, 22, 625. This analysis yields a simple set of rate expressions, which can be used for modelling kerogen pyrolysis under typical retort heating conditions. A stoichiometric representation of kerogen pyrolysis is also developed. These results are then used to derive a simple mechanistic picture of oil shale pyrolysis between 25 and 900 °C.