Hydrofluoric Acid Dissolution Research Articles

Sustainable fluoride removal with scrap aluminum: Co-producing cryolite and hydrogen

This study presents a novel continuous process for fluoride removal and re- source recovery as cryolite, using a scrap aluminum-packed column. Efficient aluminum dissolution in hydrofluoric acid (HF) generates hydrogen gas and provides cost-saving alkalinity. The process achieves high efficiency (Al/F molar ratio of 2/6) within short Empty Bed Contact Times (15 min) and at low HF concentrations (500 mg/L). Solution pH plays a crucial role, with Al/F ratios above 1 achievable at pH below 4. The exothermic reaction requires temperature control, with a strong correlation (R²=0.99) between HF concentration and heat generation. Hydrogen production matches theoretical predictions. Cryolite synthesis was confirmed at optimized pH (5–5.5) with a 1:1 bypass ratio, achieving 98 % fluoride removal. XRD and SEM- EDS analyses verified cryolite formation. This approach offers a promising solution for industrial fluoride management, resource recovery, and clean hydrogen production.

Conodont biostratigraphy of a Carboniferous–Permian boundary section in siliceous successions of pelagic Panthalassa revealed by X-ray computed microtomography

Pelagic deep-sea siliceous successions in accretionary complexes preserve precious records of a vast deep seafloor that is now lost due to plate subduction. Microfossils are the key means of age assignment of these successions, but poor preservation due to tectonic deformation and metamorphism at the subduction zone hamper biostratigraphic records. X-ray computed microtomography, while not widely used in biostratigraphic studies until now, allows us to visualize fossils that are impossible or difficult to extract from host rocks due to poor preservation. In this study, we applied this method on conodonts from a pelagic chert–claystone succession in Okoshizawa, Iwaizumi Town, Northeast Japan, using a laboratory-based X-ray microscope. This work is a first close look at conodont biostratigraphy across the Carboniferous–Permian boundary in pelagic deep Panthalassa. We identified conodonts including ten species that are used as zonal markers in intensely studied areas such as around the East European Platform and Midcontinent United States. Based on the occurrence of conodonts, the studied section in Okoshizawa was correlated to the lower Moscovian to middle Artinskian. Confirmation of Moscovian to Artinskian age diagnostic conodonts from pelagic Panthalassa strengthens their role as global biostratigraphic indicators. By identifying more numerous specimens compared to the conventional hydrofluoric acid dissolution method, we were able to obtain information about conodont faunal characteristics around the Carboniferous–Permian boundary in pelagic deep areas of Panthalassa. The dominant taxa changed from Streptognathodus to Mesogondolella in the middle Asselian, probably reflecting an ecological takeover by the latter in the deep waters.

A straightforward separation scheme for the concomitant isolation of Lu, Hf, Sm, and Nd prior to isotope ratio and isotope dilution measurements following sample decomposition by Lithium metaborate fusion or Hydrofluoric acid dissolution

A straightforward separation scheme for the concomitant isolation of Lu, Hf, Sm, and Nd prior to isotope ratio and isotope dilution measurements following sample decomposition by Lithium metaborate fusion or Hydrofluoric acid dissolution

Reductive weathering of black shale and release of barium during hydraulic fracturing

Hydraulic fracturing is an important technological advance in the extraction of natural gas and petroleum from black shales, but water injected into shale formations in the fracturing process returns with extraordinarily high total-dissolved-solids (TDS) and high concentrations of barium, Ba. It is generally assumed that high TDS comes from the mixing of surface water (injected fluid) with Na–Ca–Cl formation brines containing elevated Ba, but the mechanisms by which such mixing might occur are disputed. Here we show that Ba in water co-produced with gas could originate from water-rock reactions, with Ba levels observed in produced waters reached on a time scale relevant to hydraulic fracturing operations. We examined samples from three drill cores from the Marcellus Shale in Pennsylvania and New York to determine the possible water-rock reactions that release barium during hydraulic fracturing. Two samples, one containing microcrystalline barite (BaSO4) and one without barite, contain elevated concentrations of Ba relative to the crustal average for shale rocks. A third sample is slightly depleted in Ba relative to the crustal average. Micro-XRF measurements and SEM/EDS analysis combined with chemical sequential extraction methods reveal that a majority of the Ba in all samples (55–77 wt.%) is present in clays and can only be leached from the rock by dissolution in hydrofluoric acid. Thus, a majority of barium in our samples is relatively inaccessible to leaching under hydraulic fracturing conditions. However, the balance of Ba in the rocks is contained in phases that are potentially leachable during hydraulic fracturing (e.g., soluble salts, exchangeable sites on clays, carbonates, barite, organics).We next studied how shale reacts with water at elevated temperatures (80 °C), low Eh (−100 to −200 mV), and a range of ionic strengths (IS = 0.85–6.4) that emulate conditions prevalent at depth during hydraulic fracturing. Our experimental results indicate that the amount of Ba released from the bulk rock has a positive correlation with the ionic strength of the reacting fluid. Between 5 and 25% of the total Ba in the rock can be leached from shale under ionic strength conditions and leachate compositions typical of produced waters over a contact time of just 7 days. We suggest that reductive weathering of black shale occurs during hydraulic fracturing due to: 1) Ba2+ in clays exchanging with Na+ and Ca2+ ions that are present in high concentrations in produced water, and 2) increased solubility and dissolution kinetics of barite under high ionic strength conditions. At the low Eh conditions prevalent during hydraulic fracturing the sulfate deficient water allows Ba to be dissolved into the produced water. Based on Ba yields determined from laboratory leaching experiments of Marcellus Shale and a reasonable estimate of the water/rock mass ratio during hydraulic fracturing, we suggest that all of the Ba in produced water can be reconciled with leaching directly from the fractured rock.

Re-evaluating digestion methods for highly siderophile element and 187Os isotope analysis: Evidence from geological reference materials

Here we evaluate measurement procedures currently used for the combined determination of highly siderophile element concentrations (HSEs: Re, Ir, Os, Ru, Pt and Pd) and Os isotope ratios in geological samples by isotope dilution mass spectrometry (ID-MS) applying high-temperature sample digestion using inverse aqua regia in closed glass vessels, such as Carius tubes or a high-pressure asher system (HPA). In particular, we address the question of whether an additional hydrofluoric acid dissolution step is required to release HSEs hosted in the silicate portions of rock samples. To do so, we conducted systematic experiments for basaltic (TDB-1 and BIR-1), ultramafic (UB-N and JP-1) and sedimentary (SCo-1, SDO-1 and JCh-1) reference materials with and without HF desilicification. Through the extensive tests on TDB-1—varying apparatus (microwave, Carius tube, high-pressure asher), conditions (temperature, duration, sample size) and protocol (HF desilicification before or after aqua regia attack)—we find the optimum digestion method is to use inverse aqua regia for digesting 1–2g of powder over long durations, such as Carius tubes heated to 240˚C for 72h, followed by an HF desilicification step after CCl4 solvent extraction of Os. For basaltic reference materials, the method provides significantly improved HSE recoveries—particularly Ru—largely due to the use of HF. Strong linear correlations between Os and Ir–Ru–Pt concentrations and isochronous behavior on a 187Re/188Os vs. 187Os/188Os diagram (1240±59Ma, MSWD=1.4) are observed for repeat dissolutions of TDB-1, reflecting sample heterogeneity due to minor minerals enriched in Os, Ir, Ru and Pt—most likely sulphides. In comparison, excellent reproducibilities were obtained for BIR-1: relative standard deviations (RSDs) for 1–2g aliquots were 6.9% Os, 5.1% Ir, 2.0% Ru, 5.1% Pt, 1.5% Pd and 0.7% Re (n=9). Thus, BIR-1 might be a useful candidate reference material for obtaining certified values with small measurement uncertainties. Unlike the basaltic reference materials, extraction of HSEs from ultramafic and sedimentary reference materials is largely independent of the use of HF. The data obtained by Carius tube for UB-N and JP-1 agree well with the literature data obtained using apparently more aggressive digestion techniques. The precision of our data for 0.5–2g aliquots of the sedimentary reference materials also compares favourably with limited data available in the literature.

Effects of hydrofluoric acid dissolution on organo–mineral associations in Cambisols and Andosols of Réunion

Interactions between organic matter (OM) and mineral phases represent a fundamental mechanism of carbon (C) sequestration in soils. They result in the formation of organo–mineral associations, which prevent rapid OM biodegradation. The density‐separation technique enables effective isolation of different types of organo–mineral associations in soil. However, analyses of OM in these organo–mineral associations are limited because the C contents are very small (<10 mg OM g−1 of soil) and mineral phases complicate direct studies of OM. Previous studies have shown that hydrofluoric acid (HF) dissolution is an effective treatment for OM analysis since the mineral phases are dissolved and C is concentrated in the extract. Nonetheless, few studies on the effects of HF dissolution have been directly carried out on organo–mineral associations. The main objectives of this study were to determine the effects of HF dissolution on organo–mineral associations and to establish the best HF treatment conditions for OM analysis. We chose two specific tropical soils, an hydric Andosol and an haplic Cambisol (Réunion), that varied in their mineralogy. After densimetric separation, we tested three HF concentrations and four contact times. Mineral removal was 94% for both soils at the most concentrated HF treatments. Aluminium and silicon compounds were largely dissolved after the first treatment, while iron‐rich residue accumulated after repeated HF treatments. XRD analyses confirmed the rapid dissolution of halloysite, gibbsite and quartz and the persistence of iron oxides. For the organo–mineral associations of the Cambisol, HF treatments did not enable us to obtain a usable signal with 13C NMR. For the organo–mineral associations of the Andosol, a four‐times extraction over 2 hours with 5% HF allowed us to acquire an effective signal with 13C NMR for OM qualitative analyses. However, a new compound made of aluminium and fluorine appeared with the 10% HF treatments for both soils. In order to compare and analyse the OM present in organo–mineral associations of these two soil types, we thus recommend using four 2‐hour treatments with 5% HF.

A Procedure for Rapid Determination of the Silicon Content in Plant Materials

An efficient, reliable and low-cost procedure to determine the silicon content in plant material is presented which allows to monitor the agricultural aspects like growth and yield. The presented procedure consists of a hydrochloric acid pre-treatment and a subsequent thermal oxidation. The method is compared to other processes like dissolution in hydrofluoric acid combined with ICP OES, energy-dispersive X-ray fluorescence spectroscopy (EDXRF) or aqua regia treatment.

Network structure–property relationship in UV-cured organic/inorganic hybrid nanocomposites

The UV-induced cross-linked network structures of methacryl-oligosiloxane nanoclusters (MONCs) were analyzed with a hydrofluoric acid dissolution derived gel permeation chromatography technique (HF-GPC) to study their network structure–property relationships. With this method the oligosiloxane cores were dissolved in HF and the remaining organic tethers underwent GPC analysis to observe the tether species and characterize the original cross-linked network structures. It was found that the MONC nanocomposites have a highly cross-linked structure, resulting in oligosiloxane cores which are completely isolated by short methacryl chain segments (two- or three-armed methacryl tethers). This structural analysis was found to be consistent with the macroscale properties of MONC nanocomposites when characterized with thermal (TGA) and thermo-mechanical (DMA and TMA) analyses.

Molecular monolayers on silicon as substrates for biosensors

(111) silicon surfaces can be controlled down to atomic level and offer a remarkable starting point for elaborating nanostructures. Hydrogenated surfaces are obtained by oxide dissolution in hydrofluoric acid or ammonium fluoride solution. Organic species are grafted onto the hydrogenated surface by a hydrosilylation reaction, providing a robust covalent Si–C bonding. Finally, probe molecules can be anchored to the organic end group, paving the way to the elaboration of sensors. Fluorescence detection is hampered by the high refractive index of silicon. However, improved sensitivity is obtained by replacing the bulk silicon substrate by a thin layer of amorphous silicon deposited on a reflector. The development of a novel hybrid SPR interface by the deposition of an amorphous silicon–carbon alloy is also presented. Such an interface allows the subsequent linking of stable organic monolayers through Si–C bonds for a plasmonic detection. On the other hand, the semiconducting properties of silicon can be used to implement field-effect label-free detection. However, the electrostatic interaction between adsorbed species may lead to a spreading of the adsorption isotherms, which should not be overlooked in practical operating conditions of the sensor. Atomically flat silicon surfaces may allow for measuring recognition interactions with local-probe microscopy.

Polyelectrolyte multilayer hollow capsules studied by small-angle neutron scattering (SANS)

Silica-templated polyelectrolyte (PE) hollow capsules with various template diameters and PE layer numbers were fabricated by using the layer-by-layer technique and subsequent core dissolution in hydrofluoric acid. The properties of the resulting freestanding polyelectrolyte multilayers (PEM) were characterized in an aqueous environment by means of SANS and compared with scanning force microscopy (SFM) data. The thickness of the capsule wall was found to be about 25% thicker and with correspondingly higher water content than the template-supported PE layers. The wall thickness increase as a result of core dissolution was anisotropic. The average single layer thickness of hollow capsules was independent of the surface curvature and decreased slightly with increasing PE layer number. SANS was used to determine whether the capsules were empty or contained the rest of the core. An annealing at 70 °C for 4 h induced capsule shrinking by about 20% at an ionic strength of 1 mol L−1. Furthermore, the capsule wall upon annealing increased in thickness by about 38%. These changes corresponded to a wall densification of about 13%.

Use of hydrofluoric acid dissolution for the concentration of dickite and nacrite from kaolin deposits: an FTIR study

AbstractA series of kaolin-rich mineral samples was treated with hydrofluoric acid (HF) and the residual material characterized using infrared (IR) spectroscopy, supplemented by scanning electron microscope (SEM) observations. By examining the hydroxyl-stretching region of the IR spectra before and after treatment with hydrofluoric acid, it was possible to identify the three kaolin polytypes – kaolinite, dickite and nacrite – with greater certainty. The SEM observations suggested that the rate of dissolution of the kaolin phase was largely dependent on particle size. In general, dickite and nacrite tend to occur in the coarser clay fractions, and for this reason the finer-grained kaolinite is preferentially dissolved by the HF treatment. However, in the Keokuk kaolinite, which occurs in exceptionally large particles, it was still possible to concentrate a dickitic fraction by HF treatment, suggesting that in some cases kaolinite may be more susceptible to HF dissolution for reasons other than particle size. The IR spectra of disordered kaolinite could be interpreted as arising from a mixture of kaolinite and dickite components. However, both components dissolve at the same rate in HF, supporting the idea that disordered kaolinite consists of an intimate association of randomly stacked dickite-like and kaolinite-like components.

Surface chemistry of ordered mesoporous carbons

Ordered mesoporous carbons (OMC) were produced by pyrolysis of hydrocarbons adsorbed in two different silica matrices (MCM-48 and SBA-15), followed by dissolution of the matrix in either hydrofluoric acid or sodium hydroxide. Some carbons were subsequently heat treated at temperatures of up to 1600 °C. The chemistry of the external surface was studied by X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectroscopy (SIMS). Information on the graphitic order of the surface of the mesopores was obtained from low-pressure nitrogen adsorption data. The external and internal surface of the OMC has a polyaromatic, graphite-like character. This character increases considerably with increasing pyrolysis and/or post-pyrolysis temperature, as expected. According to the XPS and the nitrogen adsorption data, this increase was especially pronounced for temperatures above 1100 °C. In spite of the different pore structures, only small differences in the polyaromatic character were found for OMC synthesised either in a MCM-48 or in a SBA-15 matrix. Differences exist for the non-carbon elements. When hydrofluoric acid is used for dissolution of the silica matrix, organic fluorine compounds are formed. Their concentration is higher when a MCM-48 matrix as opposed to a SBA-15 matrix was used. Dissolution of the silica matrix in sodium hydroxide yielded a less contaminated OMC as compared to dissolution in hydrofluoric acid.

Light Emitting Porous Silicon from Hydrogenated Amorphous Silicon

Light-emitting porous silicon layers have successfully been obtained from hydrogenated amorphous silicon (a-Si:H), by anodic dissolution in hydrofluoric acid. The maximum thickness of the porous layers is limited by an instability due to the high resistivity of a-Si:H. The high luminescence efficiency is well accounted for in a spatial confinement picture in which the microstructure of the porous material isolates the photogenerated electron–hole pairs from the non-radiative recombination centres. The temperature dependence of the photoluminescence efficiency and the dependence of the photoluminescence wavelength as a function of the microstructure typical size reveal that quantum confinement effects do not affect the luminescence, a feature consistent with the localized character of the electronic states. Finally, pushing light emission in the visible range has been achieved by making porous layers from hydrogenated amorphous silicon–carbon alloys.

Note on a new method of using hydrofluoric acid for the study of conodonts in cherts in the Torlesse terrane, New Zealand

Abstract. A number of papers have described procedures for the recovery of conodonts from cherts by dissolution in hydrofluoric acid (Ethington & Austin, 1993; Stone, 1987), but, in our experience, the techniques have generally led to fragmentation of the conodont specimens.A new method of etching by hydrofluoric acid allows observation of whole conodonts in chert samples. The method was developed on material of Permian age from New Zealand. Although this technique does not, at present, enable entire conodonts to be extracted from the rock, it makes it possible to photograph conodonts in even highly microbrecciated cherts, and the technique should be applicable to conodont-bearing cherts of any age.The new technique involves HF etching of the surface of small samples of chert, preferably split along bedding planes. Samples weighing about 5 kg were collected in situ from siliceous pelagites (cherts) from the Torlesse terrane, near Meyers Pass, South Canterbury (Ford, 1995). The blocks were split or chipped along bedding planes to produce a large number of thin, 5 cm square samples. These wafer-sized chips were placed in a 1 litre polypropylene (NOT glass) beaker, and covered with 35% HF.The chips slowly turned white over a period of 15–30 min as a reaction gel formed on the surface of each chip. When whitened, the HF was carefully decanted off and replaced with water. Taking care not to abrade the now soft skin of reaction gel, the samples were gently rinsed with water until the HF was neutralized sufficiently for . . .

Note on the use of hydrofluoric acid for the recovery of conodonts from Ordovician cherts in the Southern Uplands of Scotland and the significance of the conodonts

Abstract. Procedures have been described for the recovery of conodonts from cherts by dissolution in hydrofluoric acid (see Stone, 1987 for a review), but this technique rarely has been applied. Cherts are more widely distributed in southern Scotland than are limestones which have been the focus of most research on conodonts. The HF technique thus opens a new and possibly more widely applicable avenue for conodont research for southern Scotland than the traditional methods.Ordovician conodonts on the surfaces of red cherts were reported from several localities near Peebles by Lamont and Lindström (1957), and the same authors found conodonts in yellow silt-stones interbedded with cherts south of Abington. These localities were visited to obtain samples that we believed to have a high probability of containing conodonts in order to test the HF procedure on Scottish rocks. We found conodonts in red rocks like those reported by Lamont and Lindström at their Noblehouse and Ruddenleys localities. Unfortunately the rocks there are not cherts as they reported, but are red mudstones instead. Such rocks are not amenable to the HF techniques.Microscopic examination of grey cherts collected loose below Ravengill Burn (Grid Reference 26/921199, one of Lamont and Lindstrom’s localities) showed that they contained radiolaria, a common fossil in the cherts of Scotland. Small pieces of these cherts, aggregating about 50 g, were placed in dilute (10% by volume) HF. The acid was decanted episodically after periods ranging from 8 hours to 73 hours, and the undissolved material was wet-screened through a . . .

A hydrofluoric acid dissolution method for determining volcanic glass content of tephra derived soils (andisols)

The determination of volcanic glass content is essential for the classification of many Andisols in Soil Taxonomy. Previously, polarizing microscope and heavy liquid methods have been used to estimate glass content, but we suggest here an alternative method based on gravimetric analysis of glass-bearing samples before and after hydrofluoric acid (HF) dissolution treatment. A series of Bw and C horizons of weakly developed buried paleosols derived from post-c. 15 ka rhyolitic tephra deposits in North Island, New Zealand, was subjected to the HF treatment and glass contents calculated. Our results, corroborated by qualitative examination using a polarizing microscope, indicate that the HF dissolution method for these materials is simple, fast, and accurate, and, with further testing, could be applicable to all types of glass. Slight modifications to the method are probably needed where glass compositions or primary mineralogical assemblages vary significantly between samples. As well as being potentially useful for characterizing and defining Andisols, the method is likely to be applicable wherever estimates of the volcanic glass content of soils, paleosols, or tephra deposits are required.

Chemical reactivity of thermally activated clay minerals estimation by dissolution in hydrofluoric acid

The rapid estimation of the chemical reactivity of transitory phases (TACK synthetic pozzolanic binders) obtained by Thermal Activation of Clay Minerals between 500°C and 1000°C, can be obtained in less than one hour, using the σ = f(t) conductimetric curve associated to the congruent dissolution in dilute hydrofluoric acid at 25°C. Investigations on thermally activated kaolinite and montmorillonite has allowed to point out sensitive differences in the dissolution process according to the structure of the raw-material the recorded σ = f(t) curve is a two steps and a continous one for kaolinite and montmorillonite, respectively. Two different specific parameters can be measured either the conductivity variation associated to the first dissolution step, or the slope of the curve at time t=0 (initial dissolution rate). These parameters can be correlated to the short-time strength development of calcium hydroxyde-activated TACK binder, and have their maximal values for the thermal activation temperature which leads to the optimum disorganization state of the solid.

Effect of acid dissolution on the mineral matrix and organic matter of Zefa EFE oil shale

Kerogen of the Israeli Zefa oil shale was isolated and the changes which occur in the initial organic matter during the removal of the inorganic matrix were investigated. Benzene-methanol extraction dissolved the bitumens, hydrochloric acid and hydrofluoric acid dissolution removed the carbonate and silicate minerals and lithium aluminium hydride treatment destroyed pyrite mineral which was unaffected by the attack of acids. X-ray diffractograms and FTIR spectra of the original oil shale and its demineralized products were measured. Benzene-methanol extraction of the oil shale increased the resolution of peaks in the X-ray diffractograms X-ray diffractograms and FTIR spectra indicated the presence of calcite, α-quartz, kaolinite, illite and pyrite in the mineral matrix of the shale. Hydrochloric and hydrofluoric acid dissolution did not cause hydrolysis and oxidation of the organic matter. Lithium aluminium hydride treatment reduced the carbonyl functionalities to newly formed hydroxyl groups, therefore the kerogen isolated seemed to have a chemical composition different from that of the original oil shale.

Improved Background Correction in the Analysis Of Cadmium by Flame Atomic Absorption

Cadmium signals obtained by direct aspiration of highly concentrated solutions of rocks and other geochemical samples are swamped by strong matrix background signals. Mainly because of iron interference, the deuterium source or other continua are not satisfactory for background correction. In order to isolate atomic absorption by cadmium the total signal and the background signal have to be measured precisely. Sequential measurements in the double beam mode with electrodeless discharge lamps of cadmium and arsenic at 228.80 and 228.81 nm produced a set of uninterfered data for cadmium within marginally useful detection limits of (0.10 ppm in granite, 0.16 ppm Cd in limestone). Simple extraction of the sample powders with nitric acid dissolves only part of the sample matrix but most of the cadmium. In this way higher relative and absolute cadmium concentrations in solution and better detection limits are obtained (e.g. 0.02 ppm Cd in granite). This approach allows cadmium in geosamples at levels below 0.3 ppm to be determined more accurately than via hydrofluoric acid dissolution.

Anion exchange method for the sequential determination of uranium, thorium and lead-210 in coal and coal ash

A radiochemical procedure is presented for the sequential determination of uranium isotopes, thorium isotopes, and210Pb in coal and coal ash. This procedure consists of dry ashing the sample, a nitric—hydrofluoric acid dissolution, removal of iron with ether extractions, and separation of the elements of interest by anion exchange chromatography. Uranium and thorium isotopes are measured by alpha spectrometry, while210Pb is measured by beta counting its daugther activity,210Bi. For 10 g coal samples and 1 g ash samples, the chemical yields for the radioactivities measured were 70–80%, and the relative standard deviations for replicate analyses were generally less than 9%. The deviations of the means from the reference values were within the combined errors of each and were usually less than ±5%. Minimum detectable activities were about 0.02 pCi for uranium and thorium isotopes and 0.2 pCi for210Pb.