Sieved Size Fractions Research Articles

Characterization and acid leaching beneficiation studies of Anka (Zamfara State, Nigeria) copper ore deposit

The chemical and mineralogical characterization of the Anka copper was examined and its susceptibility to H2SO4 acid leaching was assessed. A crude sample of the ore, weighing 5 kg, was sourced from the mines, communiated, homogenized, and characterised the crude sample. A 100 g fraction of the crushed sample was subjected to fractional sieve analysis and each sieve retained was chemically analysed. The leaching process was carried out on 100 g of -125+90 µm sieve size fraction using H2SO4 acid and the resulting product was chemically analyzed. The characterization result reveals 42.271% CuO using the energy dispersive x-ray fluorescence spectrometer and the x-ray diffractometer shows that the ore is mainly composed of Cu-carbonate hydroxide in the form of malachite mineral. The scanning electron microscope micrograph suggests that the ore contains dispersed grains of sodium aluminium silicate and copper carbonate hydroxide in a silica-dominated matrix. The ore's liberation size was determined to be at the sieve size of -125+90 μm. Finally, the ore was discovered to be responsive to the H2SO4 acid leaching operation, leading to an enrichment of the feed from 42.27% Cu to a pregnant solution of 52.51% Cu and the residue from the leaching was analyzed to be 4.69% Cu.

Petrochronology of polygenetic white micas (Naxos, Greece)

AbstractNaxos in the Greek Cyclades preserves a type example of polymetamorphism. The southern and northern parts of the island record different Tertiary P–T histories between Eocene and Miocene times, including a blueschist facies event, one or more amphibolite/greenschist facies overprint(s) and contact metamorphism. Age attributions for these events are inconsistent in the literature. Here, we propose a new approach that combines electron probe microanalyzer (EPMA) characterization of the white mica (WM) with 39Ar‐40Ar–Rb‐Sr multichronometry. Textural–petrographic–compositional observations reveal that the polygenetic WM consists of five different generations: pre‐Eocene relicts, paragonite, high‐Si phengite, low‐Si phengite and muscovite. EPMA mapping of four WM samples, previously analysed by Rb‐Sr, reveals major element compositions heterogeneous down to the μm scale. Each WM consists of chemically distinct generations, documenting submicron‐scale retrogression of high‐pressure (HP) phengite grains to muscovite. Four WM samples from a N‐S traverse across the island were analysed by 39Ar‐40Ar stepheating, comparing coarse and fine sieve size fractions to obtain overdetermined K‐Ar systematics. Fine sieve fractions are richer in Cl than coarse ones. Linear arrays in Cl/K‐age isotope correlation diagrams show two predominant WM generations (one Cl‐poor at ca. 38 Ma and one Cl‐rich at <20 Ma). A lower‐grade sample from southern Naxos was less pervasively recrystallized, provides older ages and preserves at least three WM generations, including a relict WM with a pre‐Palaeocene K‐Ar age, consistent with the high Ar retentivity of WM in the absence of complete recrystallization. The age of the Cl‐poor end‐member WM approximates the age of the HP event, 38 Ma. Ar inheritance in Cretaceous mica relicts is heterogeneous at the single‐grain scale. Comparing the degassing rates of the WM fractions rules out ‘multidomain’ diffusion. As no sample is monomineralic, the degassing rate of each polygenetic mica is instead controlled by the mass balanced sum of the unrelated rate constants of its constituent minerals. Given the commonness of zoned and composite micas, the approach detailed here is potentially useful for reconstructing polyphase metamorphic histories worldwide.

Concentrations of tire wear microplastics and other traffic-derived non-exhaust particles in the road environment

Tire wear particles (TWP) are assumed to be one of the major sources of microplastic pollution to the environment. However, many of the previously published studies are based on theoretical estimations rather than field measurements. To increase the knowledge regarding actual environmental concentrations, samples were collected and analyzed from different matrices in a rural highway environment to characterize and quantify TWP and other traffic-derived non-exhaust particles. The sampled matrices included road dust (from kerb and in-between wheeltracks), runoff (water and sediment), and air. In addition, airborne deposition was determined in a transect with increasing distance from the road. Two sieved size fractions (2–20 µm and 20–125 µm) were analyzed by automated Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX) single particle analysis and classified with a machine learning algorithm into the following subclasses: TWP, bitumen wear particles (BiWP), road markings, reflecting glass beads, metals, minerals, and biogenic/organic particles. The relative particle number concentrations (%) showed that the runoff contained the highest proportion of TWP (up to 38 %). The share of TWP in kerb samples tended to be higher than BiWP. However, a seasonal increase of BiWP was observed in coarse (20–125 µm) kerb samples during winter, most likely reflecting studded tire use. The concentration of the particle subclasses within airborne PM80-1 decreases with increasing distance from the road, evidencing road traffic as the main emission source. The results confirm that road dust and the surrounding environment contain traffic-derived microplastics in both size fractions. The finer fraction (2–20 µm) dominated (by mass, volume, and number) in all sample matrices. These particles have a high potential to be transported in water and air far away from the source and can contribute to the inhalable particle fraction (PM10) in air. This highlights the importance of including also finer particle fractions in future investigations.

Laboratory IR spectroscopy of soils from Apollo 14, 15, and 16: Spectral parameters and maturity

Sieved size fractions (0–25 ​μm, 25–63 ​μm, 63–125 ​μm, and 125–250 ​μm) and bulk (unsieved) material from lunar soils from Apollo 14 (14163,135 and14259,672), Apollo 15 (15101,319 and 15401,147), and 16 (61220,41, 62231,55 and 67481,96) were analyzed in diffuse reflectance in the mid-infrared (3–18 ​μm). These soils reflect formation in a range of geological settings including basalt protoliths (Apollo 15), and feldspathic impact ejecta protoliths (Apollo 14 and Apollo 16). Mid-IR spectra analyses were made with the same samples using broad spot analyses using a diffuse reflectance set up, and by micro-FTIR under low vacuum and ambient laboratory conditions. Comparison of the data generated by the Broad Spot and micro-FTIR Techniques shows only minor differences in terms of both band positions and relative intensities.

Particle size distribution of hammer-milled maize and soybean meal, its nutrient composition and in vitro digestion characteristics

The mean particle size of ground grains influences both pig growth performance and gastric health although this effect is not consistent and the underlying reasons are not fully understood. The inhomogeneous nutrient content distribution in particles of different sizes and the characteristics of particles may be reasons for inconsistent findings. The objective of the present study was to determine the nutrient content and physical characteristics of individual size fractions of hammer-milled maize and soybean meal (SBM), and to relate it to in vitro digestibility. Maize and SBM were hammer-milled over a 6- and 2-mm size screen, respectively, and were sieved into seven fractions. Particle characteristics of the hammer-milled material were determined by dry sieving, wet sieving and image analysis methods; the nutrient composition including dry matter, ash, crude fibre (CF), crude fat (CFat), crude protein (CP), starch and in vitro digestibility of organic matter (OM), CP (SBM) and starch (maize) were measured and nitrogen-free-extract was calculated. The results show that the nutrient composition differed among fractions of ground maize and SBM (P < 0.001). A large difference in starch levels (754.2 vs 578.9 g/kg) of maize was observed between the various sieve size fractions whereas the CP content of SBM increased with larger sieve sizes. The in vitro digestibility of OM and CP was different (P < 0.001) among the various particle size fractions for both ingredients. However, the in vitro digestibility of starch did not differ between each size fraction in maize (P = 0.060). The regression models relating the nutrient composition and in vitro digestibility show that the digestibility of OM was positively related to the starch level (P < 0.001). As for SBM, CF (negatively) and CFat (positively) were correlated with OM digestibility (P < 0.001); ash and CF had a negative effect on the digestibility of CP, though CFat had a positive relation with the CP digestibility (P < 0.05). Using image analysis, the OM digestibility of different fractions of maize and SBM could be related to the projected perimeter (R2 = 0.933) and solidity (R2 = 0.704) of particles in a linear model. The presented data show that the nutrient composition and physical characteristics of materials among various size fractions of hammer-milled maize and SBM differ and may explain pig growth performance differences observed in commercial production.

Particle size, powder properties and the breakage behaviour of infant milk formula

Abstract Dairy powder breakage occurs in many processes and causes deterioration in powder properties but there is currently no research presented in the literature on dairy powder breakage behaviour. The breakage behaviour and the effect of powder properties of an infant milk formula and its sieved size fractions were investigated during three processing methods (powder venturi feeder, lab-scale dilute phase pneumatic conveyor, and laboratory high-speed mixer) based on the changes of particle size distributions (PSD) before and after breakage. Particle size influenced other properties and the breakage behaviour of powders. Four breakage mechanisms were found, dispersion, chipping, disintegration, and splitting, corresponding to the increasing degree of breakage. More intense processing conditions were needed to cause the same breakage mechanism for smaller-sized particles because of their higher powder strength. The breakage of samples with wide PSD often displayed a combination of breakage mechanisms due to the influence of particle size on breakage behaviour.

Changes in the geochemistry of fluvial sediments after dam construction (the Chrudimka River, the Czech Republic)

The Seč Dam Reservoir on the Chrudimka River (the Czech Republic) was studied as a possible barrier for the transport of solid particles related to fluvial pollution. To understand the damming-triggered changes in the sediment lithology and geochemistry and to establish the pollution chemostratigraphy of the reservoir deposits, we first characterized the grain-size control on the sediment composition, including concentrations of risk elements Cu, Ni, Pb, and Zn. To that end, we first examined the chemical composition of the sieved size fractions of sediments, and then we compared the grain-size parameters obtained by granulometry with the geochemical composition using either scatter plots or a compositional regression with functional covariates in framework of Bayes spaces. The onset of deposition in the dam reservoir outside of the inflow delta is marked by three major changes: (1) a decrease in the grain size and a corresponding increase in Al/Si and Ti and a decrease in K and Ca, (2) enhanced retention of the finest particulates, especially Fe and Mn, and (3) enhanced concentration of risk elements originating from local industry in the city of Hlinsko that started nearly coevally with the dam construction. In the inflow delta, these changes are not so straightforward: the lithology of the deltaic deposits resembles that of the pre-dam fluvial sediments, except for the fact they are polluted, although the pollution stratigraphy is poorly preserved. The peak of polycyclic aromatic hydrocarbons (PAHs) in the dam reservoir was found near the onset of the dam deposition. We found that Fe is the best-performing reference (normalizing) element for the geochemical background functions (GBFs), although Ti would provide better grain-size correction; clearly, post-depositional geochemical reactions also play a role. GBFs were used to calculate local enrichment factors (LEF) and show that the dam construction suppressed the downstream transport of Cu, Ni, and Zn pollution by more efficient retention and trapping of fine sediment components including Fe oxides, which are otherwise transported through the floodplain.

Effect of Milling Parameters on the Concentration of Copper Content of Hammer-Milled Waste PCBs: A Case Study

The current study reports optimization of hammer milling parameters to achieve crushed waste printed circuit boards (WPCBs) of − 16 BSS (British Standard Specification) sieve size. The WPCBs, having 22 wt% copper, have been crushed to − 16 BSS sieve size by means of a hammer mill. The result showed that initial milling takes place rapidly and then decreases gradually. Approximately 94% feed material is ground to − 16 BSS sieve size within 7 min, and further increase in the time does not affect the milling rate. It is also revealed that with the increasing feed rate, lower milling rate is experienced due to the distribution of impact energy among more pieces of WPCBs. Study of the size distribution of milled WPCBs (− 16 BSS sieve size) revealed that it follows the similar trend, and the crushed material is mostly concentrated in − 240 BSS and + 72 to − 52 BSS sieve size range. Further, 50–55% crushed fraction attains + 100 BSS sieve size, while the rest is smaller than this sieve size. Chemical analysis of the crushed material of various size fractions elucidated that a fraction above 100 BSS sieve size is copper rich (43 wt%), while − 100 BSS sieve size fraction has lesser copper because the nonmetals which account for majority concentration in WPCBs are milled to a finer size. Microscopic examinations of crushed fraction showed that copper has metallic luster and ruptured foil-type morphology. The fibrous structure of glass fiber and gray/black-colored polygon morphology of nonmetals were also visible.

Grain size dependent magnetic discrimination of Iceland and South Greenland terrestrial sediments in the northern North Atlantic sediment record

We use isothermal and temperature dependent in-field and magnetic remanence methods together with electron microscopy to characterize different sieved size fractions from terrestrial sediments collected in Iceland and southern Greenland. The magnetic fraction of Greenland silts (3–63 μm) and sands (>63 μm) is primarily composed of near-stoichiometric magnetite that may be oxidized in the finer clay (<3 μm) fractions. In contrast, all Icelandic fractions dominantly contain titanomagnetite of a range of compositions. Ferrimagnetic minerals preferentially reside in the silt-size fraction and exist as fine single-domain (SD) and pseudo-single-domain (PSD) size inclusions in Iceland samples, in contrast to coarser PSD and multi-domain (MD) discrete magnetites from southern Greenland. We demonstrate the potential of using magnetic properties of the silt fraction for source unmixing by creating known endmember mixtures and by using naturally mixed marine sediments from the Eirik Ridge south of Greenland. We develop a novel approach to ferrimagnetic source unmixing by using low temperature magnetic susceptibility curves that are sensitive to the different crystallinity and cation substitution characteristics of the different source regions. Covariation of these properties with hysteresis parameters suggests sediment source changes have driven the magnetic mineral variations observed in Eirik Ridge sediments since the last glacial maximum. These observations assist the development of a routine method and interpretative framework to quantitatively determine provenance in a geologically realistic and meaningful way and assess how different processes combine to drive magnetic variation in the North Atlantic sediment record.

Evaluation of morphological properties of railway ballast particles by image processing method

Abstract The properties of individual ballast particles affect the behavior of ballast layer under train loading. One of the most important individual properties is the morphological characteristics of ballast particles represented by surface texture and angularity. In the present study, the morphological properties of ballast particles are quantified by developing surface texture (ST) index and angularity index (AI) determined on two-dimensional aggregate images. For this purpose, four different types of fresh ballast aggregates (basalt, marl, dolomite and trachyte), rounded river aggregate and degraded ballast sample obtained from railway track are analyzed for each specific sieve size fraction by developed image processing method. Comparison of the developed method in the present study for determination of ST and AI with the previously developed morphological indices shows that there is a reasonable correlation between them. In addition, the results obtained from the air void contents of aggregates in loose condition validate that the developed indices for the evaluation of morphological properties of aggregates can characterize the angularity and surface texture of each individual ballast particle properly.

PGM Facies variations for Cu-PGE deposits in the Coldwell Alkaline Complex, Ontario, Canada

Accurate characterization of the platinum group mineral (PGM) assemblages for Cu-Ni-PGE deposits are typically constrained by sample size and the difficulty of finding statistically significant numbers of grains, which is expected given the low concentrations of platinum group elements (<2ppm), the great variety of PGM, and the likelihood that a few large grains (>75µm) can account for large fractions of total mass. Despite these limitations, an accurate survey of PGM from different deposit types would have significant value towards developing deposit models and respective exploration strategies. In this study, we present results for a comprehensive evaluation of PGM at four copper-PGE occurrences hosted within separate but co-genetic gabbro or troctolite intrusions in the Coldwell Alkaline Complex and confirm that accurate surveys are possible with sufficient sample material and efficient PGM concentration methods. The PGM concentration methods used include: (1) hydroseparation of sieved size fractions of pulverized material, and (2) panning of grain separates produced by electric pulse disaggregation of drill core specimens. A favourable comparison of the results has verified the reliability of each method and added confidence that the PGM assemblages identified at three of the four locations are fully characterized.Precious metal mineral (PMM) assemblages are determined for the Main zone and W Horizon at the Marathon deposit, and the main zones at each of the Geordie Lake deposit and Area 41 occurrence. A total of 10,824PMM grains (PGE and Au-Ag) and 68 mineral species, including 16 unknown minerals, were identified, of which 768 grains and 31 species occur at the Main zone, 523 grains and 41 species at Area 41,9485 grains and 43 species at W horizon, and 56 grains and 12 species at Geordie Lake. The PMM are grouped as follows: Pd-Ge, PGE-S-As, Pt-Fe alloy, Pd-Cu-Pb-Au, Pd-Ni-S, Pd-Pt-Sn, Pt-As, Pd-As, Pd-Pt-Sb-As, Pd-Pt-Bi-Te, and Au-Ag. All of the deposits were found to contain similar proportions of Pd-Pt-Sb-As, Pd-Pt-Bi-Te and Au-Ag minerals. But the W Horizon and Area 41 are distinguished from the Marathon Main zone and Geordie Lake deposits by the presence of minerals in the PGE-S-As, Pt-Fe alloy, Pd±Cu±Pb±Au and Pd-Ge groups.Taken together, the PMM assemblages for deposits in the Coldwell exhibit a strong correlation to PGE enrichment relative to the range for mantle Cu/Pd values (1000–10,000). And there is no relationship between the abundances of Pd-Pt-Bi-Te and Pd-Pt-Sb-As minerals that are commonly associated with hydrous phases, and the intensity of hydrothermal alteration. Thus minerals found only at the W Horizon and Area 41, where significant PGE upgrading has occurred, including Pt-Fe alloys, rustenburgite, marathonite, palladogermanide, unknown Rh-Ni-Fe-sulfide, Au-Pd-Cu alloy, braggite, coldwellite, laurite, zvyagintsevite, laflammeite, and unknown phases Pd5As2, Pd3As, Pd3(As,Pb,Bi) might be considered as index minerals for PGE enriched types of mineralization in the Coldwell.

Effect of particle size on the froth floatation of Sokoto phosphate ore

Effect of particle size on the froth floatation of Sokoto phosphate ore for its beneficiation has been investigated and established. The research has been conducted using various reagents, pH(s) at different sieve size fractions. Bench scale flotation tests were carried out on -250+180μm, -180+106μm, -106+75μm, -75+45μm and -45+38μm particle size fractions after screening in order to determine the optimum flotation feed size distribution using 1 liter Denver flotation cell. The results of the scoping flotation studies using a conditioning Pulp Density of 60%Solids, pH9, 800g/t reagent dosage for AERO704 Promoter (Fatty Acid) and flotation pulp density of 28.5% Solids show that +106μm particle size gave the highest assay content of 20.4% P2O5 with a recovery of 76.2% compared to +38μm (19.9%P2O5 and recovery of 43.2%) and +180μm (19.4%P2O5 and 24.1% recovery) in their floats (concentrates) but with no perfect separation as the tailings fraction also contained similar grades with slight differences.

Comparative Beneficiation Study of Gyel Columbite Ore Using Double Stage (Magnetic-to-Magnetic and Magnetic-to-Gravity) Separation Techniques

The comparative beneficiation study of Gyel columbite ore using double stage (magnetic-to-magnetic and magnetic-to-gravity), located in the vicinity of Gyel village in Jos South Local Government Area of Plateau State to metallurgical grade was carried out. The ore sample was sourced from 20 different pits each 1.5 × 1.5 × 2 meters deep, 50 meter apart covering a land of 50 hectares. The samples from the 20 pits were crushed, pulverized and homogenized. 200 kg of the homogenized ore sample was used for the experiment and laboratory works. Chemical characterization of the ore sample was carried out using energy dispersive X-ray fluorescence spectrometer (ED-XFR). Single and double stage concentration tests using magnetic and gravity methods were carried out respectively. The results of the chemical analysis of ore sample reveal that, Pit 1 contains 12.26% Nb2O5, 21.6% Fe2O3, 36.1% SiO2; Pit 20 contains 4.78% Nb2O5, 19.34% Fe2O3, 23.96% SiO2 and the homogenized sample contains 6.71% Nb2O5, 23.1% Fe2O3 and 27.0% SiO2 averagely. The liberation study reveals that the niobium of ore can be liberated over a range of sieve size fractions of -355 + 63 μm for the coarse and -63 + 45 μm for the fine particle size fractions. On the basis of this, sieve size fractions of -1400 + 355 μm (as coarse size), -355 + 90 μm (as medium size) and -90 + 45 μm (as fine size) were used for the concentration tests. The concentration test using the double stage processes revealed that the air-floatation followed by rapid magnetic method produced a concentrate with the highest percent assay of 54.48% Nb2O5 with a recovery of 96.53% followed by the rapid-to-rapid magnetic method which produced a concentrate assaying 52.12% Nb2O5 with a recovery of 86.96%. These results meet and surpass the 50% Nb2O5 stipulated as the acceptable metallurgical grade concentrate for niobium metal production in the literature.

Late Pleistocene glacial–interglacial shell-size–isotope variability in planktonic foraminifera as a function of local hydrography

Abstract. So-called "vital effects" are a collective term for a suite of physiologically and metabolically induced variability in oxygen (δ18O) and carbon (δ13C) isotope ratios of planktonic foraminifer shells that hamper precise quantitative reconstruction of past ocean parameters. Correction for potential isotopic offsets from equilibrium or the expected value is paramount, as too is the ability to define a comparable life stage for each species that allows for direct comparison. Past research has focused upon finding a specific size range for individual species in lieu of other identifiable features, thus allowing ocean parameters from a particular constant (i.e. a specific depth or season) to be reconstructed. Single-shell isotope analysis of fossil shells from a mid-latitude North Atlantic Ocean piston core covering Termination III (200 to 250 ka) highlight the advantage of using a dynamic size range, i.e. utilising measurements from multiple narrow sieve size fractions spanning a large range of total body sizes, in studies of palaeoclimate. Using this methodology, we show that isotopic offsets between specimens in successive size fractions of Globorotalia inflata and Globorotalia truncatulinoides are not constant over time, contrary to previous findings. For δ18O in smaller-sized globorotalids (212–250 μm) it is suggested that the offset from other size fractions may reflect a shallower habitat in an early ontogenetic stage. A reduction in the difference between small and large specimens of G. inflata between insolation minima and maxima is interpreted to relate to a prolonged period of reduced water column stratification. For the shallow-dwelling species Globigerina bulloides, no size–isotope difference between size fractions is observed, and the variability in the oxygen isotopic values is shown to correlate well with the seasonal insolation patterns. As such, patterns in oxygen isotope variability of fossil populations may be used to reconstruct past seasonality changes.

Investigating differential binding of polychlorinated dibenzo-p-dioxins/dibenzofurans in soil and soil components using selective supercritical fluid extraction

Supercritical fluid extraction (SFE) with pure carbon dioxide was performed at increasingly strong conditions to investigate differential binding of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) in two impacted soils, in their sieved size fractions, and in small (a few mg) samples of industry-related waste products separated from impacted soil. The binding strengths of PCDD/Fs were shown to be different in the two soils, and in their different soil particle size fractions. As might be expected based on surface area considerations, one soil showed the strongest binding in the smallest (<5μm) sieved fraction. However, the other soil showed the strongest binding in the larger sized fractions, possibly indicating that process-related particles could be controlling PCDD/F binding. Selective SFE of various types of particles including black carbon and charcoal (separated from soil), and from a suspected process anode residue did show different PCDD/F binding behavior ranging from quite weak binding (charcoal) to very strong binding (anode particles). Shifts to the stronger SFE fractions in the soils after activated carbon treatment agreed well with the decreases previously found in the uptake of PCDD/Fs by earthworms, as well as decreases in their freely-dissolved aqueous concentrations in soil/water slurries. These results show that, as previously demonstrated for PAHs and PCBs, selective SFE can be a useful tool to investigate differences in PCDD/F binding behaviors in impacted soils and sediments and their component parts, as well as a rapid tool for estimating the effectiveness of activated carbon treatments on decreasing the bioavailability of PCDD/Fs in soils and sediments.

Size-related stable isotope changes in Late Cretaceous planktic foraminifera: Implications for paleoecology and photosymbiosis

The paleoecology of Cretaceous planktic foraminifera during the Late Cenomanian to Coniacian period (∼ 95–86 Ma) remains controversial since much of the tropical marine record is preserved as chalk and limestone with uncertain geochemical overprints. Here we present δ 13C and δ 18O data from sieve size fractions of monospecific samples of exceptionally well preserved planktic foraminifera recovered during Ocean Drilling Program Leg 207 (Demerara Rise, western tropical Atlantic). Our results suggest that all species studied ( Hedbergella delrioensis, Heterohelix globulosa, Marginotruncana sinuosa, Whiteinella baltica) grew primarily in surface waters and did not change their depth habitat substantially during their life cycle. Comparison of size-related ontogenetic trends in δ 13C in Cretaceous and modern foraminifera further suggests that detection of dinoflagellate photosymbiosis using δ 13C is confounded by physiological effects during the early stages of foraminifer growth, raising doubts about previous interpretations of photosymbiosis in small foraminifera species. We propose that obligate photosymbiosis involving dinoflagellates may not have evolved until the Campanian or Maastrichtian since our survey of Cenomanian–Coniacian species does not find the δ 18O and δ 13C size-related trends observed in modern foraminifer–dinoflagellate symbioses.

Estimating the water content of hydrated minerals using reflectance spectroscopy: II. Effects of particle size

Visible-near infrared reflectance spectra for five particle size fractions of a Hawaiian palagonite (HWMK101) and a nontronite (ferruginous smectite, Clay Minerals Society source clay SWa-1) were measured under ambient, purged, and heated conditions to characterize the effects of surface and volume scattering on the relationship between absolute H 2O content and the strength of the 3 μm absorption feature. Both materials were ground and dry sieved to particle sizes of <25, 25–45, 45–75, 75–125, and 125–250 μm. Particles of the bulk palagonite have an approximate bimodal distribution consisting of small, amorphous particles < 5 μm in diameter mixed with crystalline and glass particles < 1 mm in diameter, whereas the nontronite particles are polycrystalline aggregates. We find that band parameters value relating the strength of the 3 μm hydration feature to water content increase with particle size for a given water content, regardless of whether reflectance or single scattering albedo spectra are used. Spectra generally increase in reflectance as particle size decreases, a result of the relative increase in volume to surface scattering. Spectra of large particles are commonly saturated in the 3 μm region due to an increase in optical path length, making an accurate estimate of water content indeterminate until the samples dehydrate to the volume-scattering regime. We find that the presence of fines in several of the size fractions of palagonite cause their spectra to be representative of the finest fraction rather than the mean particle size. The nontronite spectra appear to be representative of an effective particle size within the range of the sieved size fractions. Many planetary surfaces are expected to have a large number of small particles which can dominate their spectral signature. Our results for particles < 45 μm provide a reasonable model for estimating the H 2O content of hydrated asteroids and regions of Mars.

Simulation of wet ball milling of iron ore at Carajas, Brazil

Laboratory-scale batch grinding tests were performed on 2 sieve size fractions of the almost pure hematite mined at the Carajas mine of CVRD Brasil. Good first-order kinetics of grinding were obtained, both for dry grinding and for grinding with water, using the Bond test levels of ball load and powder load. However, the primary breakage distribution functions were not dimensionally normalized, as smaller particles produced proportionally more fines on primary breakage, possibly due to internal porosity of the ore. The test results were scaled to the conditions of a pilot-scale mill in normal closed circuit, and a ball mill simulator was used to predict the capacity, circulating load and size distributions, employing the size selectivity values calculated from the balance around the hydrocyclone. The simulation results were in reasonable agreement with the observed values. The technique was then extended to predict the behavior of a full-scale mill at a capacity of 308 metric tons/h and a circulating load of nearly 600%. Agreement between simulated results and plant test results was reasonable except that the simulator predicted a product (overflow) size distribution with a higher sharpness index than observed. The reason for this discrepancy is not known.

Mechanisms of Crystal Agglomeration of Paracetamol in Acetone−Water Mixtures

The mechanisms governing the influence of the solvent composition on the agglomeration in a crystallization process have been investigated. Narrowly sieved paracetamol crystals were suspended in supersaturated acetone−water solutions, and were allowed to grow at isothermal conditions, after which the agglomeration was recorded. In all experiments the same sieve size fraction was used as well as the same magma density. In each experiment the supersaturation was kept constant. Experiments were performed in different solvent compositions at different supersaturation, crystal growth rate, solution viscosity, and agitation rate. For a statistically sufficient number of particles from each experiment, the number of crystals in each product particle was determined by image analysis and multivariate data evaluation. From the resulting number distributions of crystals per product particle, parameters defining the “degree of agglomeration” were extracted. The experimental results clearly establish that there is an influence of the solvent composition on the degree of agglomeration, which cannot be explained by differences in crystal growth rate, or differences in solution viscosity. The degree of agglomeration is found to decrease with increasing solvent polarity. It is suggested that the mechanism by which the solvent influence relates to the crystal−solvent interaction and the physicochemical adhesion forces between crystals in the solution.

Influence of particle size and shape on the comminution of single particles in a rigidly mounted roll mill

In single-particle roll mill comminution, the degree of size reduction is controlled by the ratio of the nip size of the particle and the roll gap. However, the nip size or effective particle size of irregularly shaped particles is generally unknown. An experimental procedure is presented to assess nip size of irregularly shaped particles and to evaluate energy consumption and energy utilization in their comminution. A series of experiments in which the roll gap was successively reduced reveals that the height of a particle, that is, the particle's dimension normal to the plane in which it resides in its most stable position, is a satisfactory approximation of the nip size which can be conveniently measured with a slot classifier. The nip size or particle height is distributed in √2 and √4 sieve–size fraction according to a Gaussian normal distribution, the median size being roughly 80% of the geometric sieve size. The energy investment for comminuting single particles in a rigidly mounted roll mill varies with the nip size in the manner of a power function. Estimated Weibull coefficients of uniformity for dolomite, galena, and quartz are 7.5, 1.9, and 7.9. Product size distributions of comminuted nip-size fractions are self-preserving in a dimensionless size X/ X 50 and thus, the median size is a measure of product fineness. Grindabilities calculated from the linear reduction ratio energy relationships are 7.8, 14.0, and 4.5 t/kWh for dolomite, galena, and quartz, respectively. Single-particle grindabilities of these three minerals are power functions of the nip size. Dolomite and quartz data follow closely Rittinger's Law of Comminution.