Evaluation of acidity in late Permian outcrop coals and its association with endemic fluorosis in the border area of Yunnan, Guizhou, and Sichuan in China.

The junction area of Yunnan, Guizhou, and Sichuan provinces is the heaviest coal-burning endemic fluorosis zones in China. To better understand the pathogenicity of endemic fluorosis in this area, 87 coal samples from the late Permian outcrop or semi-outcrop coal seams were collected in eight counties of the junction area of Yunnan, Guizhou, and Sichuan provinces. The total fluorine and sulfate content, etc. in the coal was determined using combustion-hydrolysis/fluoride-ion-selective electrode method and ion chromatography, respectively. The results show that the total fluorine concentrations in the samples ranged from 44 to 382 µg g-1, with an average of 127 µg g-1. The average pH of the coals is 5.03 (1.86-8.62), and the sulfate content varied from 249 to 64,706 µg g-1 (average 7127 µg g-1). In addition, the coals were medium- and high-sulfur coals, with sulfur mass fraction ranging from 0.08 to 13.41%. By heating the outcrop coals, HF release from the coal was verified quantitatively without exception, while simulated combustion directly confirmed the release of sulfuric acid (H2SO4). The acid in coal may be in the form of acidic sulfate ([Formula: see text]/H2SO4) because of a positive relationship between pH and [Formula: see text] in the acidic coal. The possible reaction mechanism would be that a chemical reaction between the acid (H2SO4 or [Formula: see text]) and fluorine in the coal occurred, thereby producing hydrogen fluoride (HF), which would be the chemical form of fluorine released from coal under relatively mild conditions. The unique chemical and physical property of HF may bring new insight into the pathogenic mechanism of coal-burning endemic fluorosis. The phenomenon of coal-burning fluorosis is not limited to the study area, but is common in southwest China and elsewhere. Further investigation is needed to determine whether other endemic fluorosis areas are affected by this phenomenon.

Chemical Detection of Hydrogen Fluoride by the Phosphorus Congener of Cyclobutane-1,3-diyl.

Heteroaryl-substituted air-tolerant 2,4-bis(2,4,6-tri-t-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyls in the open-shell singlet state were synthesized by a sterically promoted regioselective S(N)Ar process. Here we demonstrate that these diyls are effective for capturing hydrogen fluoride (HF) generated by intermediary base-coordinated HF and amine-stabilized HF reagents. The hydrofluorination reaction predominantly occurred on the λ(3)σ(3)-phosphorus atoms to afford the energetically disfavored 1λ(5),3λ(5)-diphosphete. The positively charged t-butyl-substituted phosphorus atom trapped the fluoride anion, and the subsequent protonation was controlled by the steric effect. X-ray crystallographic analysis and an Atoms in Molecule study of the air-stable 1λ(5),3λ(5)-diphosphete bearing P-H and P-F bonds revealed that the delocalized ylidic linkages in the four-membered ring were almost identical, in contrast to the nonsymmetrically substituted 2,4-bis(2,4,6-tri-t-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl. Hydrofluorination efficiently induced a remarkable exchange of visible photoabsorption. The charge-transfer-type transition from highest occupied molecular orbital to lowest unoccupied molecular orbital was highly tuned, which is advantageous for the facile identification of HF. In contrast to hitherto known trapping reagents for HF based on cleavage of the H-F bond, several hydrofluorinated P-heterocycles were reconverted into the 1,3-diphosphacyclobutane-2,4-diyl by treatment with sodium hydride. However, in the hydrofluorination of the benzoyl-substituted 1,3-diphosphacyclobutane-2,4-diyl, fluorination and protonation occurred at the t-butyl-substituted phosphorus atom and the skeletal carbon atom, respectively, and the energetically preferable 1λ(5),3λ(3)-dihydrodiphosphete was isolated as a purple-blue crystalline compound. These findings are promising not only for the practical detection of HF but also for the development of fluorine technology based on the chemistry of phosphorus heterocycles.

Feasibility of hydrofluoric acid etched sand particles for enrichment and determination of polychlorinated biphenyls at trace levels in environmental water samples.

This study aims to investigate the feasibility of etched sand particles being used as solid-phase extraction adsorbents to enrich polychlorinated biphenyls (PCBs), which are typical persistent organic pollutants in the environment, at trace levels. Gas chromatography-tandem mass spectrometry was selected to detect the compounds. Etched sand particles exhibited excellent merits on the enrichment of PCBs. Related important factors affecting extraction efficiencies were investigated and optimized in detail. Under optimized conditions, low limits of detection (0.42 to 3.69 ng L(-1)), wide linear range (10 to 1,000 ng L(-1)), and high repeatability (1.9 to 8.2%) were achieved. The developed method was validated with several real water samples, and satisfactory results were obtained. All of these findings indicate that etched sand particles would be useful for the enrichment and determination of organic pollutants at trace levels in water samples.

Design and deployment of low-cost plastic optical fiber sensors for gas monitoring.

This paper describes an approach to develop and deploy low-cost plastic optical fiber sensors suitable for measuring low concentrations of pollutants in the atmosphere. The sensors are designed by depositing onto the exposed core of a plastic fiber thin films of sensitive compounds via either plasma sputtering or via plasma-enhanced chemical vapor deposition (PECVD). The interaction between the deposited layer and the gas alters the fiber's capability to transmit the light, so that the sensor can simply be realized with a few centimeters of fiber, an LED and a photodiode. Sensors arranged in this way exhibit several advantages in comparison to electrochemical and optical conventional sensors; in particular, they have an extremely low cost and can be easily designed to have an integral, i.e., cumulative, response. The paper describes the sensor design, the preparation procedure and two examples of sensor prototypes that exploit a cumulative response. One sensor is designed for monitoring indoor atmospheres for cultural heritage applications and the other for detecting the presence of particular gas species inside the RPC (resistive plate chamber) muon detector of the Compact Muon Solenoid (CMS) experiment at CERN in Geneva.

Detection of hydrofluoric acid by a SiO2 sol-gel coating fiber-optic probe based on reflection-based localized surface plasmon resonance.

A novel fiber-optic probe based on reflection-based localized surface plasmon resonance (LSPR) was developed to quantify the concentration of hydrofluoric acid (HF) in aqueous solutions. The LSPR sensor was constructed with a gold nanoparticle-modified PMMA fiber, integrated with a SiO(2) sol-gel coating. This fiber-sensor was utilized to assess the relationship between HF concentration and SiO(2) sol-gel layer etching reduction. The results demonstrated the LSPR sensor was capable of detecting HF-related erosion of hydrofluoric acid solutions of concentrations ranging from 1% to 5% using Relative RI Change Rates. The development of the LSPR sensor constitutes the basis of a detector with significant sensitivity for practical use in monitoring HF solution concentrations.

Evaluation of sampling methods for measuring exposure to volatile inorganic acids in workplace air. Part 2: Sampling capacity and breakthrough tests for sodium carbonate-impregnated filters.

In France, the MétroPol 009 method used to measure workplace exposure to inorganic acids, such as HF, HCl, and HNO3, consists of a closed-face cassette fitted with a prefilter to collect particles, and two sodium carbonate-impregnated filters to collect acid vapor. This method was compared with other European methods during the development of a three-part standard (ISO 21438) on the determination of inorganic acids in workplace air by ion chromatography. Results of this work, presented in a companion paper, led to a need to go deeper into the performance of the MétroPol 009 method regarding evaluation of the breakthrough of the acids, both alone and in mixtures, interference from particulate salts, the amount of sodium carbonate required to impregnate the sampling filter, the influence of sampler components, and so on. Results enabled improvements to be made to the sampling device with respect to the required amount of sodium carbonate to sample high HCl or HNO3 concentrations (500 µL of 5% Na2CO3 on each of two impregnated filters). In addition, a PVC-A filter used as a prefilter in a sampling device showed a propensity to retain HNO3 vapor so a PTFE filter was considered more suitable for use as a prefilter. Neither the material of the sampling cassette (polystyrene or polypropylene) nor the sampling flowrate (1 L/min or 2 L/min) influenced the performance of the sampling device, as a recovery of about 100% was achieved in all experiments for HNO3, HCl, and HF, as well as HNO3+HF and HNO3+HCl mixtures, over a wide range of concentrations. However, this work points to the possibility of interference between an acid and salts of other acids. For instance, interference can occur through interaction of HNO3 with chloride salts: the stronger the acid, the greater the interference. Methods based on impregnated filters are reliable for quantitative recovery of inorganic volatile acids in workplace atmosphere but are valuable only in the absence of interferents.

Emissions Control of Hydrochloric and Fluorhydric Acid in cement Factories from Romania.

From the available statistical data, cement factories co-process a range of over 100 types of waste (sorted both industrial and household) being authorized for their use as combustion components in clinker ovens. Therefore, the level of emissions is different depending on the type of fuels and waste used. The amount of industrial and municipal co-processed waste in the Romanian cement industry from 2004 to 2013 was about 1,500,000 tons, the equivalent of municipal waste generated in a year for 18 cities with over 250,000 inhabitants. The objective of this paper was to evaluate the emission level of hydrochloric acid (HCl) and hydrofluoric acid (HF) at the clinker kilns at two cement factories in Romania for different annual time intervals and to do a comparative analysis, to estimate their compliance with legislation in force. The measurements results showed average emission levels of about 0.578 mg/Nm3 for HCl and about 0.100 mg/Nm3 for HF, in the first hours of the evening, but decreased at the beginning of the third tour, at about 0.385 mg/Nm3 for HCl, respectively, to about 0.085 mg/Nm3 for HF. The evolution of HCl and HF emission levels during the last 4 years showed a variable distribution of these acids.

Epistaxis in a low level hydrogen fluoride exposed industrial staff.

OBJECTIVES: To assess the effect of exposure to hydrogen fluoride (HF) on the airway mucosa in an industrial setting. METHODS: A cross-sectional study encompassing 33 industrial workers in a flame soldering plant and 44 assembly workers unexposed to HF was performed by means of a questionnaire on symptoms and diagnosis regarding upper and lower airways as well as through conduct of a clinical examination of the exposed group. Air concentrations of HF that were monitored in winter amounted to 1.0 mg/m(3) and in summer time to 0.15 mg/m(3). RESULTS: A threefold risk for epistaxis (RR = 3.6, 95% confidence interval 1.1-11.0) was observed in the exposed group. Time from the start of exposure to HF until debut of a nose bleeding period varied from 1 month to 6 years. Mean induction (latency) time was 42 months. Mean duration of symptoms was 26 months, range 3-72 months, indicating that the exposure level in summer time was sufficient to maintain the propensity of almost daily nose bleeding. CONCLUSION: HF is an irritating vapor, even at relatively low air concentrations. We recommend an 8 hr TLV lower than 1.0 mg/m(3).

Formation of hydrogen fluoride by gamma and beta sterilisation in medical devices containing perfluoroheptane.

Infusion of hexadecafluoroheptane, a liquid perfluorocarbon released from repaired Althane dialysers was found to be the most probable reason for the deaths of 53 dialysis patients reported in the year 2001. This study focuses on toxic decomposition products generated due to gamma and beta sterilisation of hexadecafluoroheptane. The responsible dialysers were sterilised with a maximum dose of 45 kGy gamma irradiation. We investigated the influence of both 20-500 kGy gamma and beta irradiation on perfluoroheptane. Analysis of the irradiated samples verified the decomposition of perfluoroheptane in dependence on the dose of irradiation. Beta irradiation resulted in a higher degree of decomposition than the same dose of gamma irradiation. As decomposition products, hydrogen fluoride, CO2, and one saturated fluorinated hydrocarbon which could not be analysed exactly were identified. Even at 20 kGy gamma irradiation hydrogen fluoride was detectable. Our results provide evidence that hydrogen fluoride is generated as a highly toxic decomposition product when perfluoroheptane is sterilised with gamma irradiation as it was applied on the affected dialysers. There is no evidence of other toxic degradation products especially perfluoroisobutylene. Therefore, hydrogen fluoride or the dissociated fluoride ions might act as a toxic agent when medical devices containing liquid perfluorocarbons are sterilised by irradiation.

Organic and inorganic pollutants from cement kiln stack feeding alternative fuels.

In this work, an analysis of the emission of different pollutants when replacing partially the fuel type used in a cement kiln is done. The wastes used to feed the kiln were tyres and two types of sewage sludge. The increasing mass flow of sludge is between 700 kg h(-1) and 5,500 kg h(-1)1, for a total production of clinker of 150th(-1), whereas the fed tyres were in the flow range of 500-1,500 kg h(-1). Dioxins and furans, polycyclic aromatic hydrocarbons (PAHs) and other hydrocarbons, heavy metals, HCl and HF, CO, CO(2), NO(x) and other parameters of the stack were analyzed, according to the standard methods of sampling and determination, through more than 1 year in six series: one blank (no sewage sludge) and five more with increasing amount of sludge and/or tyres. The emission of PAHs and dioxins seems to increase with the amount of tyres fed to the kiln, probably due to the fed point used for this waste.

Continuous measurement of peak hydrogen fluoride exposures in aluminum smelter potrooms: instrument development and in-plant evaluation.

The aluminum smelting process continuously evolves both sulfur dioxide (SO2) and hydrogen fluoride (HF) gases. The vast majority of these evolved gases are captured by local exhaust ventilation systems and transported to fume treatment centers. Any gas escaping the ventilation systems could create the potential for workplace exposures. Currently, there are no commercially available sensors that are capable of selectively measuring peak concentrations (< 10 sec) of HF in the presence of SO2. This measurement capability is critical for facilitating a better understanding of the etiology of respiratory health effects. This article presents the development and in-plant testing of a portable, tunable diode-based HF sensor that shows equivalent or improved performance relative to NIOSH Method 7902 and is capable of measuring short-term personal peak HF exposure potentials in operating aluminum smelters.

Calcium fluoride recovery from fluoride wastewater in a fluidized bed reactor.

In order to contribute to better resource efficiency and industrial waste management leading to a sustainable production and consumption pattern new processes must be developed, which should be operated in such a way that waste production is reduced or avoided. Fluoride removal by precipitation generates huge amounts of a water rich sludge. Calcium fluoride is not recovered from the waste streams and it is not recycled due to the high water content and the low quality of the sludge. Crystallization process in a fluidized bed reactor (FBR) appears as an alternative technology to the conventional chemical precipitation process. In the crystallization process in a FBR silica sand is usually used as seed material, however silica is a deleterious impurity because it causes losses in the yield of HF and its content should be less than 1%. In this paper, granular calcite has been used as seed material in order to obtain synthetic calcium fluoride. According to the composition (CaF(2)>97%, SiO(2)<1%), the synthetic calcium fluoride from the crystallization process in a FBR is able to be recycled as raw material for the manufacture of hydrofluoric acid leading to a reduction of raw materials consumption. The crystallization process in a FBR to remove fluoride from industrial wastewaters contributes to an environmental friendly production, because it allows to reduce the waste production as well as to increase the recovery of materials.

Detection of HCl and HF by TTFMS and WMS.

In this work we discuss on a compact spectrometer based on DFB diode lasers for detection of chloridric and fluoridric acids. HCl and HF concentrations are determined through optical absorption of the P(4) line (lambda=1.7 microm) and the R(3) line (lambda=1.3 microm), respectively. Both lines belong to first overtone vibrational bands and their line strengths are 7.8 x 10(-21)cm/molecule for HCl and 2.8 x 10(-20)cm/molecule for HF. We chose these lines for their relative high intensities and because they are quite far from water vapour lines which represent the main interfering gas for trace-gases analysis. To detect these species we used two different high frequency modulation techniques: two-tone frequency modulation spectroscopy (f(1)=800 MHz and f(2)=804 MHz) was used for HCl while for HF we followed a simpler approach based on wavelength modulation spectroscopy (f=600 kHz). We demonstrate that the two techniques provide comparable detection limit of about 80 ppbV at atmospheric pressure. Positive testing of our spectrometer makes it suitable for in situ measurements of exhaust gases coming from waste incinerators.

Effect of acetic NaF solution on the corrosion behavior of stainless steel orthodontic brackets.

This study assessed the effect of acetic NaF solutions on stainless steel orthodontic brackets. Acetic acid was added to a 0.1% NaF solution to make two solutions, one with pH 3.5 and the other with pH 6. For the two different stainless steel brackets (Tomy, Dentaurum) used in this study, they had a similar elemental composition--except with Mo (molybdenum) in the Tomy bracket. The brackets were then immersed in the prepared test solutions for three days and their responses evaluated. In terms of hydrofluoric acid (HF) concentration, the 0.1%/pH 3.5 solution showed a high HF concentration at 227 ppm, while that of 0.1%/pH 6 solution was very low at 7 ppm. In terms of color change and element release, only the Dentaurum brackets in 0.1%/pH 3.5 solution showed an appreciable color change (deltaE* = 4.0) and released a great amount of elements (Fe, Cr, Ni, Mn) after three days. Otherwise, regardless of pH value and product, only minor color change (deltaE* < 1.0) and negligible element release occurred. In terms of surface modification, no visible changes in surface morphology were observed in any product after immersion in test solutions.

Trace anion determination in concentrated hydrofluoric acid solutions by two-dimensional ion chromatography I. Matrix elimination by ion-exclusion chromatography.

Since years, ion exclusion chromatography (ICE) has been the standard method to separate strong acid analyte anions from concentrated weak acid matrices such as hydrofluoric acid (HF). In this work, the commercially available IonPac ICE-AS 1 column was used to separate trace levels of chloride, nitrate, sulfate and phosphate from HF solutions at 20% (w/w). The efficiency of the separation was studied in more detail using techniques such as ion chromatography (IC), inductively coupled plasma optical emission spectrometry (ICP-OES) and ICP-mass spectrometry (ICP-MS). For 20% (w/w) HF solutions and at a water carrier flow-rate of 0.50 ml/min, the cut window was set from 8.5 to 14.5 min. Under these conditions, analyte recoveries of better than 90% were obtained for chloride, nitrate and sulfate, but only about 75% for phosphate. The HF rejection efficiency was better than 99.9%. It was found that the ICP techniques, measuring total element levels and not species, yielded significantly higher recoveries for phosphorus and sulfur compared to IC. Evidence will be given that part of the added phosphorus (approximately 15% for an addition of 10 mg PO4/kg) is present as mono-fluorophosphoric acid (H2FPO3). In the case of sulfate, the difference between IC and ICP-MS could be attributed to an important matrix effect from the residual HF concentration.

Trace anion determination in concentrated hydrofluoric acid solutions by two-dimensional ion chromatography II. Method performance study with a hydroxide eluent and a low noise suppressor.

The two-dimensional ion exclusion chromatography/ion chromatography (ICE-IC) approach is considered to be the method of choice for the determination of trace anions in concentrated hydrofluoric acid (48-50%, w/w). In order to achieve lower detection limits, this method was for the first time used with electrolytically generated and purified hydroxide eluents in combination with a low noise electrochemical suppressor. Compared to carbonate based eluents, the achieved gain in peak height sensitivity for chloride, sulfate, nitrate and phosphate is a factor of 6, 7, 16 and 13, respectively. The instrumental detection limits, based on the background noise, are 2, 0.2, 0.4 and 1.4 microg/kg HF 50% (w/w) for the same anions. Their method detection limits, calculated according to SEMI, are all within the 6-10microg/kg HF 50% (w/w) range and thus at least 10 times lower than the current Tier C grade requirements. The chromatographic run time could be shortened with some 10 min by the use of a relatively fast high-capacity hydroxide selective anion exchange column.

[Studies on spectral characteristics of solid propellant by remote sensing FTIR].

The infrared spectral characteristics of high-intensity IR solid propellant were measured in this paper using a Bruker EQUINOX55 remote sensing FTIR spectrometer. The emission spectra of the combustion flame were recorded in the range of 4700-1800 cm(-1) with a spectral resolution of 4 cm(-1). The combustion temperatures of solid propellant at the burning time of 0, 9, 18, 27 and 36 s calculated from the molecular rotation-vibration spectra were 1992.5, 1610.9, 2294.4, 2361.1 and 1916.9 K, respectively. Moreover, the spectral radiance distributions of the high IR flare material at different times were given, and the combustion product concentrations of HCl, HF, CO2 and CO were determined quantitatively. Results showed that remote sensing FTIR is a potential technology that can be applied to the measurement of IR spectral characteristics, especially to the identification of the IR objects, guidance and anti-guidance in the military, and the modification of the make-up of solid propellant.

Fluorine distribution in soil in the vicinity of an accidental spillage of hydrofluoric acid in Korea.

This study assessed the status of fluorine (F) in soil in the vicinity of a spillage of anhydrous hydrofluoric acid in Korea. Gaseous hydrogen fluoride dispersed was suspected to have contaminated the surrounding soil environment. Total and water soluble F concentrations in soil within a 1 km radius of the spillage were determined. Total F concentrations (mean=222±70.1 mg kg(-1)) were lower than the Korean limit value (i.e., 400 mg kg(-1)) and several reported measurements of background F concentrations in soils except for a single outlying case. Soluble F concentrations ranged from 0.111 to 6.40 mg kg(-1) (mean=2.20±1.80 mg kg(-1)). A negative correlation between the soluble F concentration of soil and distance from the spillage was observed. This indicates that the soluble F concentration has a crucial role in fractionating the F concentration arising from a 'non natural input' i.e., the spillage. The F content of rice samples seemed to be significantly influenced by the soluble F concentrations of soils. Rice samples collected from the control and affected areas contained 41 mg kg(-1) and 578 mg kg(-1) of total F, respectively.

Characterization of air contaminants formed by the interaction of lava and sea water.

We made environmental measurements to characterize contaminants generated when basaltic lava from Hawaii's Kilauea volcano enters sea water. This interaction of lava with sea water produces large clouds of mist (LAZE). Island winds occasionally directed the LAZE toward the adjacent village of Kalapana and the Hawaii Volcanos National Park, creating health concerns. Environmental samples were taken to measure airborne concentrations of respirable dust, crystalline silica and other mineral compounds, fibers, trace metals, inorganic acids, and organic and inorganic gases. The LAZE contained quantifiable concentrations of hydrochloric acid (HCl) and hydrofluoric acid (HF); HCl was predominant. HCl and HF concentrations were highest in dense plumes of LAZE near the sea. The HCl concentration at this sampling location averaged 7.1 ppm; this exceeds the current occupational exposure ceiling of 5 ppm. HF was detected in nearly half the samples, but all concentrations were <1 ppm Sulfur dioxide was detected in one of four short-term indicator tube samples at approximately 1.5 ppm. Airborne particulates were composed largely of chloride salts (predominantly sodium chloride). Crystalline silica concentrations were below detectable limits, less than approximately 0.03 mg/m3 of air. Settled dust samples showed a predominance of glass flakes and glass fibers. Airborne fibers were detected at quantifiable levels in 1 of 11 samples. These fibers were composed largely of hydrated calcium sulfate. These findings suggest that individuals should avoid concentrated plumes of LAZE near its origin to prevent over exposure to inorganic acids, specifically HCl.

Effect of fluoride concentration and pH on corrosion behavior of titanium for dental use.

Titanium is used as a metal for biocompatible materials such as dental implants or restorations because of its excellent chemical stability. However, the corrosion of Ti in the prophylactic fluoride-containing environment can become problematic. To clarify the effects of fluoride concentration and pH on the corrosion behavior of Ti, we conducted anodic polarization and immersion tests in NaF solution of various concentrations and pH values. The concentrations of dissolved Ti in the test solutions were analyzed by inductively coupled plasma mass spectroscopy. There were obvious limits of fluoride concentration and the pH value at which the corrosion behavior of Ti changed. The corrosion of Ti in the solution containing fluoride depended on the concentration of hydrofluoric acid (HF). When the HF concentration in the solution was higher than about 30 ppm, the passivation film of the Ti was destroyed. The results of this study revealed a relation between the fluoride concentrations and pH values at which Ti corrosion occurred and provided data on such corrosion in environments where the fluoride concentration and pH value are known.