Liquid Flotation Research Articles

Rare earth elements sequestration in phytoliths: Partitioning patterns and influencing mechanism

Rare earth elements (REEs) are integral to numerous high-tech industries, yet their biogeochemical cycling within ecosystems remains inadequately characterized. Recently, phytoliths have been identified as potentially significant sinks for REEs; however, their role in the cycling of these elements has been underestimated. In this work, we investigate the accumulation of REEs in phytoliths (PhytREEs) within the Greater Khingan Mountains region, employing an optimized wet oxidation method combined with heavy liquid flotation to quantify PhytREEs contents in surface soils. The results revealed an elevation-dependent pattern of PhytREEs concentration, with heightened levels at higher altitudes and diminishing concentrations towards the eastern plains. The enrichment coefficient of PhytREEs (ECPhytREEs) was found to be approximately 2.7 %, indicative of a moderately selective sequestration process. The multivariate analysis indicated that terrain complexity, climatic patterns, soil texture, and organic matter significantly influence the uptake and storage of REEs in plants, subsequently affecting their partitioning in phytoliths. Among these factors, the complexation of REEs with organic matter emerged as a pivotal mechanism facilitating their immobilization within phytoliths. Soil characteristics also play a non-negligible role in modulating REEs dynamics. Our findings highlight the predominant influence of climate on PhytREE storage, suggesting that climatic variables are the primary drivers modulating the bioavailability and ultimate sequestration of REEs within phytoliths. This study enhances our understanding of the biotic-abiotic interplay in the sequestration of REEs and underscores the need to incorporate phytoliths into models of terrestrial REE cycling.

Effectiveness of the improved method of lifelong diagnostics trichurosis of sheep

Today, the most accurate way to diagnose animal helminthiasis is laboratory research. Among them, lifelong coproovoscopy methods play a leading role in the study of the spread of gastrointestinal helminthiasis, particularly trichurosis, and in establishing the effectiveness of anthelmintics. Therefore, a promising research direction includes improving and testing modern methods of coproovoscopy for trichurosis in sheep. The work aimed to determine the diagnostic efficiency of the improved flotation method of coproovoscopy for trichurosis in sheep. In laboratory conditions, the effectiveness of well-known flotation methods and the proposed method of coproovoscopy in diagnosing sheep trichurosis were determined. The leading indicators of the effectiveness of laboratory methods were the indicator of the intensity of trichurous invasion, the coagulation ability of the flotation solution, and the crystallization time of a drop of flotation liquid on a glass slide. It was established that all methods of coproovoscopy used in the experiment have flotation properties relative to Trichuris eggs. However, the improved method of coproovoscopy showed a higher flotation ability concerning Trichuris ovis nematode eggs, where the proposed flotation liquid has pronounced coagulation properties concerning undigested feed residues, and also has a slow crystallization time of droplets on a slide, which is more than 50 min. The improved method uses a combined flotation liquid, whose main components were Ca(NO3)2, C12H22O11, and NaCl. The indicator of the intensity of trichuriasis invasion when using the improved method was 67.0 ± 17.5 eggs in 1 g of feces and exceeded the number of trichuriasis eggs detected by flotation methods using NaCl – by 2.3 times (P ˂ 0.001), C12H22O11 – by 2.1 times (P ˂ 0.001), NH4NO3 – 1.3 times (P ˂ 0.01), C12H22O11 + NaCl – 1.1 times. The obtained data on the effectiveness of the improved method of coproovoscopy allows us to recommend it for introduction into production for effective and accurate laboratory lifelong diagnosis of trichurosis in sheep.

Effect of the Water Hardness Level on Chalcopyrite Flotation Inhibition by the Disodium Carboxymethyl Trithiocarbonate

Disodium carboxymethyl trithiocarbonate (DCMT) is considered to have the potential to replace sulfide and cyanide as a new chalcopyrite inhibitor. However, the effect of its application in the industrial field is often not ideal, mainly because the flotation involves solid, liquid and gas three-phase flotation systems, leading to many influencing factors, especially the chemical changes in pulp caused by the liquid phase. In order to promote the industrial application DCMT, we studied the effect of water quality in the flotation liquid phase on the inhibition of DCMT on chalcopyrite. Water quality generally involves the physical, chemical and biological characteristics of water bodies. The water for beneficiation belongs to industrial water, and the main indicator of its water quality is the water hardness level. Flotation and contact angle studies showed that higher water hardness levels suppressed chalcopyrite inhibition by DCMT. Infrared and Raman spectra revealed that the free CO32− and Ca2+ in water coordinated with the residual organic chains on the surface of the pretreated chalcopyrite and was subsequently adsorbed onto the chalcopyrite surface. Moreover, the addition of DCMT dislodged the captured CO32− and Ca2+. X-ray photoelectron spectroscopy indicated that DCMT could adsorb on the chalcopyrite surface and compete with the Ca2+. When Ca2+ was trapped on the chalcopyrite surface, there were fewer adsorption sites available to the DCMT, resulting in a lower inhibition capacity. Simultaneously, the presence of DCMT promoted the release of Ca2+ from the chalcopyrite surface. Therefore, the influence of water quality must be considered when designing a flotation reagent system, and the water hardness level should be reduced to optimize the flotation process.

Dense liquid flotation: Can coarse particle flotation performance be enhanced by controlling fluid density?

• Bubble-load is optimized in bubble-particles aggregates of fine particles compared to coarser ones. • Coarser particles simulate the detachment behavior of finer particles at increased fluid SGs. • Increased critical detachment amplitudes at increased fluid SGs translate to better flotation performance for coarse particles in terms of recovery, rate, and maximum floatable size. • Increasing fluid SG beyond a limit increases the likelihood of detachment in the froth phase. • Particle weight in fluid is the major detachment force, and the effect of cell turbulence on coarse particle flotation performance is largely dependent on it. In this work, we investigate the influence of fluid density on bubble-particle detachment and coarse particle flotation performance. Detachment studies were carried out using an electro-acoustic apparatus in a dense liquid environment using a lithium heteropolytungstate (LST) mixture with subsequent flotation studies carried out in a micro flotation cell at varying fluid densities. Our results indicate that bubble load was inherently limited by particle surface area and weak particle–particle interactions at coarser sizes. Coarser particles tend to follow the detachment behavior of relatively finer particles at increased fluid density. We also found that flotation performance in terms of recovery, rate, and maximum floatable size can be enhanced by controlling fluid density within a stated limit beyond which detachment in the froth phase causes overall performance to drop.

Reconstructing vegetation and climate in the Nihewan Basin, North China, during the middle Pleistocene (~603–587 ka) to trace the evolution of human environments

Abstract Aims The Nihewan Basin of North China, considered the cradle of Eastern civilization, contains a set of late Cenozoic strata and artifacts used by Homo erectus in the early Pleistocene (~1.66 Ma to 780 ka) and the cranial bones and teeth of early H. sapiens from the late middle Pleistocene (~370 to 260 ka). Palynological studies provide an opportunity to explore the living environment of early humans. Methods Palynological samples from the Hutouliang Section (~603–587 ka) of the Xiaodukou Formation of the Nihewan Basin were treated by heavy liquid flotation. Based on the palynological assemblages from the section, vegetation and climate in the Nihewan Basin were reconstructed. Important Findings The dynamic vegetation changed from temperate needle- and broad-leaved mixed forest-steppe (mainly Picea, Abies, Betula, Juglans, Artemisia and Chenopodiaceae) to conifer forest (mainly Pinus, Picea and Abies), which saw the replacement of H. erectus by early H. sapiens. The comparison of the Nihewan Basin with other human sites around the world during the same period reveals that early humans preferred to live in caves, accompanied by relatively open steppe or forest-steppe environments, inhabited by numerous mammals. Therefore, it is inferred that the emergence of dense conifer forest and the disappearance of open steppe environments in the Nihewan Basin at approximately 603–587 ka provide new evidence that early humans followed most mammals to steppe or forest-steppe environments and thus left the Nihewan Basin. These new findings not only enrich our knowledge of early human behavior, such as their diet, migration and settlement, but also fill in gaps in paleovegetation and paleoenvironmental research in the Nihewan Basin during the middle Pleistocene (780–400 ka).

The Distribution of horse breeding parasitosis in seasonal and age aspects

Introduction. This article is reflected the research results of horse digestive sistem parasitosis distribution in an age aspect. 
 The goal of the work. The aim of researches was to learn distribution of horse parasitosis in the economies of different pattern of ownership depending on age of animals аnthelmintic efficiency of ivermectin on the indexes of coproovoscopy researches. 
 Materials and methods of research. The studies of distribution of helminthisms of animals conducted for a year, on results coproovoscopy researches by the improved method with the use of flotation mixture of solution of nitrate to the ammonium and bischofite, that added faeces to the test, carefully stirred a stick and filtered through the layer of gauze. The filtered mixture was defended, the count of eggs of helmints was conducted through 10, 15 and 30 minutes. For this purpose from the superficial layer of flotation liquid took off a metallic loop for 3 drops and carried on subject glass for microscopic researches. Gad-fly illnesses - by the exposure of larvae of gad-flies in faeces of animals after a dehelmintization.
 Results of research and discussion. All is investigational 78 heads of horse. It is set that the most widespread intestinal nematodosiss of horse are параскароз, strongyle and сyathostomin organs of digestion, stove invasions is on the autumn period of year. Coproovoscopy it is set researches, that extensiveness of strongyle invasion for horse presented 69,4%, paraskarosis 14,5%, and intensity of invasion, according to 4,36±0,64 and 3,54±1,36 copy /of eggs, in one drop of flotation liquid. In an age-old aspect staggered by helmints considerably higher for foals age 1-2. For them extensiveness of strongyle paraskarosis invasions presented, accordingly - 100% and 53,8%, and intensity - 6,48±1,44 and 2,28±1,03 eggs in one drop of flotation liquid.
 With age, animals the indexes of extensiveness and intensity of invasion went down. In particular, for animals 3-6 annual age extensiveness of strongyle invasion presented 88,2 paraskarosis - 11,76%, and intensity did not exceed, accordingly - 4,85±0,9 and 2,3±0,3 copy /of eggs in a 1 drop of flotation liquid. For adult horse 8-20 annual age extensiveness of strongyle invasion went down to 78,1%, and paraskarosis - 9,4%. However, intensity of invasion was at high level and presented, according to 3,3±0,67 and 6,38±3,82, copies of eggs in a 1 drop of flotation liquid. The simultaneous parasitizing is set for the horse of strongyle, cyathostomin, paraskarosis and claws - chorioptes.
 Conclusions and prospects for further research. The simultaneous parasitizing is set for the horse of strongyle, cyathostomin, paraskarosis and claws - chorioptes. The simultaneous parasitizing of strongyle registers oneself at the sapling/pl of horse, paraskarosis and larvae of gad-flies - gastrofilus, that is presented by the types of G. intestinalis and G. veterinus. The prospect of further researches is a study of specific composition of strongyle horse in the economies of the Sumy area

Influence of Moisture and Temperature Regimes on the Phytolith Assemblage Composition of Mountain Ecosystems of the Mid Latitudes: A Case Study From the Altay Mountains

Reconstruction of past ecosystems requires robust understanding of modern deposition patterns and taphonomy for the proxy in question. In phytolith analysis, much has been achieved in this respect in the last 20 years. However, many gaps remain and this study aims to test a few specific hypotheses that have been proposed by research in Northern Hemisphere. Our study area is Northern Altay, entirely within Russia, north of China. We collected 60 phytolith assemblages from modern soils at 300 to 2300 m a.s.l. elevations from 20 plots in triple replicates within 13 different plant communities in the summer of 2017. Communities range from forests to meadows to steppe to alpine tundra. We use a locally derived scheme of Sedelnikov to assign studied communities to ecological categories based on moisture and temperature availability. Standard oxidation and heavy liquid flotation methods of extraction have been used. Morphotypes were counted under x400-x1000 magnification on an optical microscope. We use a two-tier approach to phytolith morphotypes classification: a detailed one with >50 morphotypes and a shorter one with only sums of selected morphotypes. In the former approach, some interesting results can be obtained, for example, with various types of rondels (pyramidal vs. keeled) or large vs. small lanceolate. At the same time, using sums may be easier because the researchers can replicate these results better and less training is needed. However, there are fewer diagnostic options with the sums approach. Our results using discriminant analysis, canonical correspondence analysis and other multivariate statistical methods confirm earlier studies in the region and elsewhere that while a lot of redundancy in phytolith distributions occur, there are some selected morphotypes that can reliably distinguish communities at various positions along moisture and temperature gradients. We developed a regionally diagnostic key that allows researchers to quickly identify various plant communities based on their phytolith assemblages in soils and derive some transfer functions to directly infer moisture and temperature regimes of the past based on phytolith records in soils. Seven of 13 regionally important communities at medium elevations can be distinguished based on phytolith analysis using aggregated and more detailed morphotypes.

Ефективність способів дослідження проб ґрунту на наявність збудників кокцидіозів

One of the factors of transmission of parasitic diseases, including coccidioses of animals is objects of the environment contaminated by invasive elements. It is well known that the greatest intensity of coccidia oocysts contamination is characteristic of the soil - of the place where the exogenous stage of the pathogen development - invasive sporulated oocysts occurs. In this regard, an important issue for scientists and practitioners is the question of studying the actual soil contamination by invasive elements, since it allows predicting the epizootic well-being of herd animals and developing appropriate therapeutic and preventive measures. Thus, the aim of the work was to establish the effectiveness of soil examination methods for the presence of oocysts of eimeries. The paper presents data concerning comparative effectiveness of well-known methods - Romanenko (1968) and Hudzhabidze (1969), Dolbin et al. (2012), as well as an improved method for examining the soil for the presence of coccidia oocysts. The improvement of the new method was carried out by making changes in the indicators: the mass of the studied soil, the time of sedimentation with alkali, centrifugation modes. Also, the composition of the flotation liquid was modified, in which two-component solution (a flotation solution based on inorganic salt in combination with alkali) was used. Romanenko (1968) and Hudzhabidze (1969) used a prototype method. It has been established that the proposed method turned out to be the most effective in relation to the indicators of the number of positive samples, the total number of detected oocysts and their conversion to 1 kg of soil. So the improved method has a higher efficiency compared with the methods of Dolbin and Romanenko-Hudzhabidze according to the following indicators: the number of positive samples by 5 and 20 %; the number of detected oocysts in the studied samples was 26.21 and 53.45 %; the average number of detected oocysts per 1 kg of soil was 22.33 and 41.81 % (p <0.01), respectively. At the same time, the method turned out to be more effective than the techniques of Dolbin and Romanenko-Hudzhabidze in terms of the minimum indicators of the identified invasive elements by 60 and 86.67 %, and maximum - by 21.6 and 28.0 %, respectively.

Separation and Determination of Cadmium(II) in Wastewater by Bisolvent of Ester and Ionic Liquid Flotation System

Separation and Determination of Cadmium(II) in Wastewater by Bisolvent of Ester and Ionic Liquid Flotation System

Structure and pyrolysis behavior of the organic matter in two fractions of Yilan oil shale

Oil shale has been pyrolyzed for shale oil in industry to alleviate the shortage of petroleum in many countries. Some oil shales appear non-uniform in colour, suggesting different ash content and/or organic structure distribution throughout their deposition. This paper takes Yilan oil shale as the raw material to identify the structure and pyrolysis behaviour of the organic matter in fractions of different colour. The oil shale is separated into two parts by a heavy liquid flotation method and then subjected to acid treatments. The heavy part is gray and termed as YL-G-OM, while the light part is black and termed as YL-B-OM. These parts are characterized by proximate and ultimate analyses and 13C-nuclear magnetic resonance. Pyrolysis experiments are carried out in a TG-MS and a fixed-bed tubular reactor. The liquid product from the tubular reactor is analyzed by GC–MS and simulated distillation. Results indicate that the H/C ratios of YL-G-OM and YL-B-OM are 1.21 and 0.95, respectively. In comparison with YL-B-OM, YL-G-OM contains more aliphatic carbon and less aromatic carbon, and has a longer methylene chain and a lower condensation degree, which results in more liquid product and C2-C3 gas during pyrolysis. The yields of liquid product are 46.1 and 35.6% on daf basis for YL-G-OM and YL-B-OM, respectively. The liquid products of both samples contain about 80% heavy fractions including those trapped in the GC column, vacuum residue and vacuum gas oil, as well as some diesel (12.5–17.0%) and a little gasoline (3.3–4.3%). Co-pyrolysis of YL-G-OM and YL-B-OM shows a synergetic effect at temperatures between 425 and 460°C, which promotes formation of liquid product and reduces the phenolic content in shale oil. The synergetic effect may be attributed to reduced condensation of radical fragments generated by bond cleavage of organic matter.

Thermodynamics of ultra-sonic cavitation bubbles in flotation ore processes

Ultra-sonic enhanced flotation ore process is a more efficient technique for ore recovery than classical flotation method. A classical simplified analytical Navier-Stokes model is used to predict the effect of the ultrasonic waves on the cavitations bubble behaviour. Then, a thermodynamics approach estimates the temperature and pressure inside a bubble, and investigates the energy exchanges between flotation liquid and gas bubbles. Several gas models (including ideal gas, Soave-Redlich-Kwong, and Peng-Robinson) assuming polytropic transformations (from isothermal to adiabatic) are used to predict the evolution of the internal pressure and temperature inside the bubble during the ultrasonic treatment, together with the energy and heat exchanges between the gas and the surrounding fluid. Numerical simulation illustrates the suggest theory. If the theory is verified experimentally, it predicts an increase of the temperature and pressure inside the bubbles. Preliminary ultrasonic flotation results performed on a potash ore seem to confirm the theory.

OSL and pollen concentrate 14C dating of dammed lake sediments at Maoxian, east Tibet, and implications for two historical earthquakes in AD 638 and 952

Formation of dammed lakes provides exceptionally important information of continental geological processes, responding to tectonic and climatic influences. Establishing accurate geochronological frameworks within lake strata is challenging because the stratigraphy is often bereft of biostratigraphy and directly dateable material. Optically Stimulated Luminescence (OSL) and AMS 14C dating of pollen concentrates are well-established tools for dating lake sediments. Whether they are suitable for lake sediments in high-alpine settings remains uncertain. In this study, OSL and AMS 14C dating of pollen concentrate were conducted on the Diaolin section in a high-alpine setting in the eastern Tibetan Plateau. Good match of both dating results suggests that they are fit for dating lake sediments in high-alpine settings. More than 300 g of sediment is required for preparation of pollen concentrates. During the pretreatment, ∼3% NaOH solution should be added to the sample, and then heated until just boiling (≤5 min) because NaOH treatment easily destroys pollen grains. Applying the heavy liquid flotation with specific gravity of 1.74–1.76 is useful to isolate relatively pure pollen grains. Sieving with a 20-μm and 63-μm mesh can concentrate pollen grains substantially. The OSL and AMS 14C dating yielded the basal age of the Diaolin section (650 AD). This indicates that the dammed-lake formed around 650 AD, probably caused by the earthquake occurring in the study area in 638 AD. The seismites characterized by soft-sediment deformation and phyllite layer happened at 780–980 AD, probably corresponding to the earthquake occurring on November 20, 952 AD in the study area.

The first case of Demodex gatoi in Austria, detected with fecal flotation

Feline demodicosis is a rare parasitic condition caused by three different species of mites (Demodex cati, Demodex gatoi, and an unnamed species). D. gatoi inhabits the superficial skin layer (stratum corneum) and is easily transmitted between individual cats. A 2-year-old female spayed Cornish Rex was presented with alopecia and pruritus. The dermatological examination revealed bilateral alopecia and excoriations on trunk, limbs, and belly. The second cat in the household, a 3-year-old female spayed Thai, showed no clinical signs. Superficial and deep skin scrapings were performed and cellophane tapes applied, and living D. gatoi mites could be detected in both cats. Oral ivermectin (0.25 mg/kg every other day) was subscribed. Feces were collected from both cats and fecal flotation with sugar and zinc solutions performed. When compared to skin scrapings and cellophane tapes, D. gatoi was detected more frequently and in higher numbers in fecal samples. Our findings suggest that D. gatoi can be efficiently diagnosed with coproscopy, particularly in asymptomatic carrier animals. DNA was extracted from the flotation liquid, and a PCR protocol for the species verification was designed. A fragment targeting a 325-bp DNA fragment of the D. gatoi mitochondrial 16S rDNA gene was amplified with a 100% similarity to the D. gatoi entry in GenBank® (GI 421920216). We report the first finding of D. gatoi in Austria and propose fecal flotation as a valuable tool for mite detection. Fecal flotation liquid is suitable for DNA extraction and PCR-based species verification of D. gatoi.

Phytolith assemblages and opal concentrations from modern soils differentiate temperate grasslands of controlled composition on experimental plots at Cedar Creek, Minnesota

Researchers frequently assume that phytolith assemblages in modern soils reflect composition of recent vegetation because of the direct deposition of silica into the soil, once plants decay. This paper tests this assumption and determines whether temperate grasslands of different composition can be reliably detected based on their silica record in topsoil in a controlled experiment. The differences in total biogenic opal concentration (TBOC) and diversity of morphotypes were assessed in the Biodiversity II experiment (E120) at Cedar Creek Ecosystem Science Reserve, Minnesota, USA, where controlled mixtures of C3 grasses, C4 grasses, legumes, non-legume forbs, and woody shrubs (Quercus) were grown for a period of eight years. The plots have been manually maintained to contain the target species, and thus provide an opportunity to test numerous hypotheses regarding phytolith production patterns under diverse mixtures of plants. Soil samples were obtained from plots representing a variety of functional group mixtures. Pinch soil samples of 20 g from 10 random locations inside each plot were obtained. Phytoliths were extracted from each sample by chemically removing organics and carbonates and using heavy liquid flotation. A chemical dissolution method was used to obtain estimates of TBOC. Morphotypes were counted under a microscope. Morphotypes were analyzed on all plots against each other and against the morphotypes expected in the plants that grow on each plot using ANOVAs, linear regression, PCA and cluster analysis. Average above-ground biomass of expected phytolith producers was weakly but positively correlated with the TBOC values (R2 = 0.42). The morphotype analysis showed that species' composition was most accurately reflected in the phytolith assemblages on grass-dominated plots. For example, it was possible to distinguish C3, C4, or mixed grass-dominated plots from each other. Although the majority of phytoliths were from Poaceae, large shares were also from forbs and woody plants. Plots without any grasses still had some presence of grass phytoliths suggesting limited horizontal translocation and/or inheritance.

Modified flotation method with the use of Percoll for the detection of Isospora suis oocysts in suckling piglet faeces

The modification of flotation method for the examination of diarrhoeic piglet faeces for the detection of Isospora suis oocysts was elaborated. The method was based on removing fractions of fat from the sample of faeces by centrifugation with a 25% Percoll solution. The investigations were carried out in comparison to the McMaster method. From five variants of the Percoll flotation method, the best results were obtained when 2 ml of flotation liquid per 1 g of faeces were used. The limit of detection in the Percoll flotation method was 160 oocysts per 1 g, and was better than with the McMaster method. The efficacy of the modified method was confirmed by results obtained in the examination of the I. suis infected piglets. From all faecal samples, positive samples in the Percoll flotation method were double the results than that of the routine method. Oocysts were first detected by the Percoll flotation method on day 4 post-invasion, i.e. one-day earlier than with the McMaster method. During the experiment (except for 3 days), the extensity of I. suis invasion in the litter examined by the Percoll flotation method was higher than that with the McMaster method. The obtained results show that the modified flotation method with the use of Percoll could be applied in the diagnostics of suckling piglet isosporosis.

ALTERNATIVE SALINE SOLUTIONS TO FLOAT FORAMINIFERAL TESTS

Flotation has been widely used in studies of recent foraminifera in order to concentrate tests and save time during picking. In this paper, four flotation agents with different densities were compared: (1) trichloroethylene, TCE (C2HCl3), with a density of 1.46 g mL−1; (2) sodium nitrate/sodium thiosulfate solution, SNT (NaNO3 + Na2O3S2 · 5H2O), with a density of 1.46 g mL−1; (3) zinc chloride solution, ZC (ZnCl2), with a density of 1.70 g mL−1; and (4) sodium polytungstate solution, SPT (3Na2WO4 · 9WO3 · H2O), with a density of 2.50 g mL−1. Comparison was carried out by means of qualitative and quantitative data. Results showed that ZC and SPT were the best flotation agents, recovering 91% and 96% of the total tests, respectively, whereas TCE and SNT recovered 59.1% and 72.8% , respectively. Both quantitative and qualitative results significantly improved with a higher density of the flotation liquid. Therefore, substitution of TCE with ZC or SPT solutions is strongly encouraged, because they are, additionally, less harmful to health and the environment. ZC is the most cost-effective, since its results were not significantly different from those of the SPT treatment. Carbon tetrachloride (CCl4) was not considered in this comparative study, because it has been banned in many countries and it is highly harmful to health and the environment.

A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments

Tephrochronology, a key tool in the correlation of Quaternary sequences, relies on the extraction of tephra shards from sediments for visual identification and high-precision geochemical comparison. A prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes (e.g. chemical exchange in the sedimentary environment) and/or by laboratory analytical procedures. However, natural glasses, particularly when in the form of small shards with a high surface to volume ratio, are prone to chemical alteration in both acidic and basic environments. Current techniques for the extraction of distal tephra from sediments involve the ‘cleaning’ of samples in precisely such environments and at elevated temperatures. The acid phase of the ‘cleaning’ process risks alteration of the geochemical signature of the shards, while the basic phase leads to considerable sample loss through dissolution of the silica network. Here, we illustrate the degree of alteration and loss to which distal tephras may be prone, and introduce a less destructive procedure for their extraction. This method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity. In trials, this method out-performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations. The implications of this study are highly significant because (i) the current database of distal tephra records and their corresponding geochemical signatures may require refinement and (ii) the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures. It is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure.

High precision density comparison measurement of silicon crystals bythe pressure of flotation method

The development of a new density comparison measurement system forsilicon crystals using the pressure of flotation method (PFM) is described.The effective isothermal compressibility of a flotation liquid mixture of1,2,3-tribromopropane and 1,2-dibromoethane is obtained. Density comparisonmeasurements are presented for silicon spheres of mass 1 kg from the NationalResearch Laboratory of Metrology (NRLM) for the density standard and thedetermination of the Avogadro constant. The combined relative uncertainty ofPFM density comparison measurement for S4 and S5 NRLM silicon spheres is5×10-8. Adjusted densities are calculated from the comparison andabsolute measurements based on a least-squares analysis through a matrixformulation.

A Comparison of Three Methods for the Extraction of Phytoliths from Sediments

This paper compares three methods commonly used to extract fossil phytoliths from sediments. A basic procedure using heavy liquid flotation and oxidation is compared with two other procedures across a range of sediment types commonly encountered in archaeological studies. The three procedures are: (1) a heavy liquid flotation method (HLF); (2) a burning method (POW); and (3) another heavy liquid flotation method (HLFPol) similar to HLF, but adapted to allow the extraction of pollen and spores as well as phytoliths, within a single process. Comparisons of the resulting output using these three techniques for phytolith extraction show that different methods can produce different results, and therefore basic techniques should be modified according to the characteristics of the sediments for which they are used. While all the techniques showed similarities in assemblage results, there were problems associated with disaggregation and effective separation of light and heavy fractions, in particular with the POW procedure. The evidence suggests that morphotype selection occurred both within the physical sorting process and in the process of inverting slides to shed excess residue; in both cases it is difficult to suggest a solution to the problem. The results show clearly that the advantages gained by using the POW procedure are largely outweighed by the problems encountered with its use, and because of possible size/shape selection, it is not recommended for general extraction procedures. The heavy liquid flotation procedures, on the other hand, are shown to produce more concentrated residues with higher levels of clarity and less potential than the POW procedure for sample bias. The use of a non-toxic heavy liquid, sodium polytungstate, now allows the process to be used in relative safety. It is recommended that analysts use heavy liquid flotation procedures with chemical treatments specific to sediment requirements.

Quantitative determination of plant opal content in soils, using a combined method of heavy liquid separation and alkali dissolution

SummaryThe aim of this study was to improve the quantitative determination of the plant opal content (i.e. phytoliths) in soils.The proposed method is based on: (i) the separation of plant opal from the silt and sand fractions of the soil, using heavy liquid flotation (aqueous solution of ZnBr2, density = 1.92 g cm−3); (ii) the subsequent determination of alkali‐soluble silicon by atomic absorption spectrometry. Extraction and analytical procedures were tested on a broad sample of temperate and tropical soils with very different phytolith contents.Our investigations lead to the following conclusions: (i) a selective dissolution of opal in alkaline solutions (e.g. hot 0.5 m NaOH as proposed by Jones, 1969) is inaccurate so that a sink‐float method must be used before any dissolution procedure; (ii) to dissolve opal completely, a 0.5 M NaOH dissolution treatment at 150°C can be easily and successfully carried out in steel PTFE‐lined pressure vessels; (iii) the reproducibility of the determination is satisfactory for a step‐by‐step procedure (mean coefficient of variation = 13.4%).The comparison of this new method of quantitative assessment of soil opal with two other methods (gravimetric and phytolith‐counting methods), shows very highly significant correlations (P<0.001). Therefore, this procedure is a useful tool in studies connected with pedological and environmental history.