Single Mineral Systems Research Articles

Uncovering the hetero-hydrophobic attraction between the basal planes of molybdenite and talc under flotation conditions

The very close natural floatability of molybdenite and talc has been traditionally believed as the main reason for their separation problem. However, the interactions between the basal and edge planes of the two platy minerals remain unclear. Here the hydrophobic attraction between the basal planes was proposed as the dominating factor for that problem. Flotation tests in both single and mixed mineral systems were conducted using carboxymethyl cellulose (CMC) as talc depressant and sodium isobutyl xanthate (SIBX) as molybdenite collector. Zeta potential distribution, contact angle, in situ optical microscope observation, EDLVO calculation and surface energy analysis were applied to reveal the surfacial actions between the basal and edge planes of molybdenite and talc. Molybdenite and talc showed obvious floatability difference in single mineral system, however, their separation efficiency met with big decline in mixed mineral system. Zeta potential results demonstrated that, in the presence of CMC and SIBX, negatively charged particles of molybdenite and talc aggregated rather than electrostatically repulsed and dispersed. The contact angle and particle adhesion results showed a certain degree of selective attraction between the basal planes of molybdenite and talc. The EDLVO calculation suggested the attractive interactions were ranked as: Mb(basal)-Tlc(edge) > Mb(basal)-Tlc(basal) ≈ Mb(edge)-Tlc(edge) > Mb(edge)-Tlc(basal). The surface energy calculation pointed out that the fundamental reason for the separation problem was exactly the hetero-hydrophobic attraction between their basal planes.

Siderophore-Mediated Mobilization of Manganese Limits Iron Solubility in Mixed Mineral Systems.

Recent laboratory and field studies show the need to consider the formation of aqueous Mn(III)-siderophore complexes in manganese (Mn) and iron (Fe) geochemical cycling, a shift from the historical view that aqueous Mn(III) species are unstable and thus unimportant. In this study, we quantified Mn and Fe mobilization by desferrioxamine B (DFOB), a terrestrial bacterial siderophore, in single (Mn or Fe) and mixed (Mn and Fe) mineral systems. We selected manganite (γ-MnOOH), δ-MnO2, lepidocrocite (γ-FeOOH), and 2-line ferrihydrite (Fe2O3·0.5H2O) as relevant mineral phases. We found that DFOB mobilized Mn(III) as Mn(III)-DFOB complexes to varying extents from both Mn(III,IV) oxyhydroxides but reduction of Mn(IV) to Mn(III) was required for the mobilization of Mn(III) from δ-MnO2. The initial rates of Mn(III)-DFOB mobilization from manganite and δ-MnO2 were not affected by the presence of lepidocrocite but decreased by a factor of 5 and 10 for manganite and δ-MnO2, respectively, in the presence of 2-line ferrihydrite. Additionally, the decomposition of Mn(III)-DFOB complexes through Mn-for-Fe ligand exchange and/or ligand oxidation led to Mn(II) mobilization and Mn(III) precipitation in the mixed-mineral systems (∼10% (mol Mn/mol Fe)). As a result, the concentration of Fe(III) mobilized as Fe(III)-DFOB decreased by up to 50% and 80% in the presence of manganite and δ-MnO2, respectively, compared to the single mineral systems. Our results demonstrate that siderophores, through their complexation of Mn(III), reduction of Mn(III,IV), and mobilization of Mn(II), can redistribute Mn to other soil minerals and limit the bioavailability of Fe in natural systems.

The effect of crosslinking additives and molecular weight of starch depressants on pyrrhotite and pentlandite floatabilities

• Synthesized starches (paste starches and crosslinked starch) can depress hexagonal pyrrhotite and pentlandite at pH 9.2. • Paste starch with higher molecular weight and crosslinked starch showed a certain selectivity in a binary mineral system. • The presence of metal hydroxylate species on both minerals allowed their chemical interaction with starch groups according to surface analysis. • Crosslinking additives within starch structure promoted a mixed interaction with mineral surfaces via chemisorption and electrostatic attraction. Pentlandite is very important to the mining industry since it is the main source of metallic nickel. However, its separation from hexagonal pyrrhotite by froth flotation is challenging due to their similar floatabilities, and inefficiencies in this process generate environmental issues caused by emissions of sulfur oxide gases during the pyrometallurgy of nickel concentrates. Although successful, the current pyrrhotite depressant (diethylenetriamine - DETA) is also harmful to the environment which compels the research and development of non-toxic and biodegradable reagents such as polysaccharides. Therefore, three starch depressants for hexagonal pyrrhotite were used in this study. They include a paste starch with higher molecular weight (MW), a paste starch with lower molecular weight, and a crosslinked starch formed by mixing the lower MW paste starch and copper ions. We hypothesize that the presence of crosslinking additives such as copper provide a “driving” effect towards the gangue mineral. The performance of depressants was investigated in single and binary mineral systems. For single minerals, all depressants impacted hexagonal pyrrhotite and pentlandite flotation recovery. For the binary mineral systems, the higher MW paste starch and crosslinked starch showed an improved Ni separation efficiency of 90.5% and 85.6%, respectively, at an intermediate PIBX dosage (9.66x10 −6 M) compared to the lower MW paste starch (58.6%), demonstrating a certain selectivity. The choice of the most suitable starch depressant proved to be complex since both minerals were able to chemically interact with the starch depressants as verified via X-ray photoelectron spectroscopy (XPS). Hydroxyl groups present on the α-D-glucose units bound with surface metal (Fe and/or Ni) hydroxylate species while the crosslinked starch also interacts with the mineral surfaces by electrostatic attraction. These findings will contribute to the advancement of knowledge related to the use of polysaccharides as depressants for complex sulfide mineral systems.

Decoupling pyrite and arsenopyrite in flotation using thionocarbamate collector

Thionocarbamate collectors are noted for their high flotation selectivity against pyrite under alkaline condition. In this study, selectivity of O-isopropyl-N-ethyl thionocarbamate (IPETC) is investigated in decoupling flotation response of pyrite and arsenopyrite under single mineral and artificial composite systems. The influence of copper addition, collector adsorption behaviour and mineral surface speciation on flotation response were characterised using complementing electrokinetic and spectroscopic techniques. The results showed no pyrite and arsenopyrite flotation at pH 11 until CuSO4 (2.5 × 10−5 mol/l) addition where arsenopyrite displayed remarkably good, CuSO4 concentration dependent flotation response relative to pyrite. Collector concentration (> 4 × 10−6 mol/l IPETC) had little effect whilst the flotation response was highly pH dependent. The preferential IPETC adsorption on copper-treated arsenopyrite at pH ≥11, yielding 90% arsenopyrite and 11% pyrite concentrate recovery, was ascribed to chelate formation between sulphur and copper and a synergistic coordination of the σ bond of arsenic and deprotonated nitrogen of IPETC.

The clastic record of a Wilson Cycle: Evidence from detrital apatite petrochronology of the Grampian-Taconic fore-arc

Detrital apatite deposited before, during and after Grampian-Taconic arc accretion in western Ireland reveals dramatic changes in source provenance and provides a detailed detrital petrochronological record of a Wilson Cycle sited on the Laurentian margin. These determinations are made possible by recent improvements in source rock type diagnosis by apatite trace element analysis. In addition, by interrogating the proportion of apatite derived from peraluminous vs metaluminous melt and felsic vs mafic melt in detritus, temporal changes can be seen in the relative proportions of these magma compositions over time. We present combined trace element and U-Pb age data for detrital apatite in clastic formations from the South Mayo Trough, a uniquely well-preserved fore-arc basin accreted to the Laurentian margin during the Grampian-Taconic orogeny (∼ 475 – 460 Ma), which records the early phase of closing of the Iapetus Ocean. Apatite deposited before collision is derived from the Laurentian margin and mafic igneous rocks of the Central Iapetus Magmatic Province associated with the Neoproterozoic break-up of Rodinia / Pannotia leading to the birth of the Iapteus Ocean. Following the onset of ocean closure in the Cambrian, igneous apatite derived from the nascent Grampian-Taconic arc is detected. Apatite derived from felsic and peraluminous melts becomes progressively more dominant over apatite from more mafic and metaluminous sources as the arc evolves from an intra-oceanic to continental arc setting after collision. The subsequent Grampian-Taconic unroofing history recorded by detrital apatite records the transition from ancient Laurentian margin- and intra-oceanic arc-derived detritus, to the exhumation of the high-grade metamorphic core of the Grampian-Taconic orogen and the exposure of post-collisional continental-arc granitoids. Our results are in broad agreement with both the Grampian fore-arc provenance record (heavy mineral analysis, detrital zircon U-Pb and white mica Ar-Ar) and the Laurentian crustal reworking record derived from the geochemistry of volcaniclastic units in the South Mayo Trough. However, we also obtain novel provenance information undetected by detrital zircon in the South Mayo Trough, such as apatite derived from the Central Iapetus Magmatic Province. Critically this information is obtained from a single mineral system, which eliminates the need to consider differing mineral stabilities during weathering, transport and diagenesis. The high preservation potential for apatite in similar tectonic environments illustrates the potential to employ detrital apatite as a record of Earth's lithological composition in deep time.

Transport behaviour of low molecular weight organic compounds in multi-mineral clay systems. A comparison between measured and predicted values

Abstract Determining the retardation properties of argillaceous media for dissolved low molecular weight organic compounds (LMW—OC's) is still an open issue in the assessment of the migration behaviour of 14C in the near and far field of a deep geological repository of radioactive wastes. Here we report retardation factors of potential carriers of organic 14C (carboxylates and alcohols) in binary clay mixtures (kaolinite and illite) as well as in Opalinus Clay (OPA), the favoured host rock for the deep geological disposal of radioactive waste in Switzerland. The percolation technique with a pulse injection of the LMW-OC's was used for all measurements. The transferability of sorption values of the LMW-OC's gained on the single-mineral systems (kaolinite and illite, respectively) to the binary clay mixtures and to clay rock (OPA) was tested. For binary clay mixtures, percolation experiments were carried out using tritiated water and 36Cl− as the reference tracers. The retardation factors predicted by the component additivity approach (CA) were consistent with the measured ones. Deuterated water and bromide were used as reference tracers in experiments with OPA. Complex breakthrough curves of bromide and the test compounds were observed here. Heterogeneities of the pore space are proposed as the main reason to explain the complex structure of breakthrough curve. Additionally, (a)biotic degradation or transformation of the organic compounds over the long experimental duration possibly further added to the complexity of the results in some cases. The derivation of sorption distribution ratios (Rd), determined from the breakthrough curves was therefore inherently associated with large uncertainties. The transferability of retardation data gained on less complex systems to the conditions of OPA was tested using the CA and the global composite (GC) approach. Significant discrepancies were found between the measured values and those predicted by the CA approach. The discrepancies were found to be smaller using the GC approach. In that case, the results obtained for single- and binary clay systems were also used for calibration purposes. Retardation factors of the LMW-OC's in OPA were then predicted based on two empiric relationships. The observed discrepancies are most probably related to the different chemical composition of the aqueous solution (e.g. ionic strength, pH), the various mineralogical features (e.g. compaction), and the different hydraulic conditions within the clay systems (e.g. Darcy flux). The absence of anion-sorption in OPA may be particularly explained by differences in the pH of the OPA pore water and the pore water in compacted kaolinite samples.

A revised oxygen barometry in sulfide-saturated magmas and application to the Permian magmatic Ni–Cu deposits in the southern Central Asian Orogenic Belt

Oxygen fugacity is a key parameter in controlling the petrogenesis of mafic-ultramafic rocks and their associated sulfide mineralization, especially in convergent settings. This study uses new and previously published experimental data on olivine-sulfide pairs to reparameterize an expression for oxygen barometry using the distribution coefficient K D FeNi for Fe-Ni exchange between olivine and sulfide. We derive a new expression, ΔQFM = (9.775 + 0.416 ∙ C Ni − K D FeNi)/4.308, where ΔQFM denotes divergence from the fayalite–magnetite–quartz buffer. The revised oxygen barometry has been applied to the Permian magmatic Ni–Cu deposits in the Central Asian Orogenic Belt, NW China. The Ni–Cu deposits in the East Tianshan—North Tianshan, Central Tianshan, and Beishan—are considered as a single mineral system, whereas the spatially separated deposits in the East Junggar are considered as a separate system. The deposit of the East Tianshan group exhibits a large range of oxygen fugacity (QFM − 2 to ~QFM + 1) and Ni tenor (metal concentration in pure sulfide, ~ 5 to 16 wt%). The Poyi and Huangshannan deposits contain high-Ni tenor sulfides, varying from 12 to 16 wt%. The relatively high Fo values (> 85 mol%) and Ni contents (> 2000 ppm) in olivine of these deposits indicate that the high-Ni tenor sulfides were segregated from less differentiated high-Ni magmas that also had relatively high oxygen fugacity (~QFM + 1). The remaining Ni–Cu deposits in the East Tianshan—the Huangshandong, Huangshanxi, Hulu, Tulaergen, Tudun, and Xiangshanzhong deposits—have intermediate Ni tenors (5–8 wt%). These sulfides correspond to intermediate Fo values (80–84 mol%) and Ni contents (700–1400 ppm) in the coexisting olivine, illustrating that they were segregated from magmas with lower Ni contents thought to be the result of a large amount (15–20%) of olivine fractionation at depth. These magmas are more reduced (− 2 < ΔQFM < + 0.3) than the less evolved magmas (~QFM + 1). It is shown that the ΔQFM value calculated for the deposits in East Tianshan decreases with decreasing Fo value, indicating that the host magmas became gradually reduced during evolution, which can be explained by primarily oxidizing magma progressively assimilating crustal material containing reducing agents, such as carbon. The Kalatongke deposit in the East Junggar belt, with the lowest Ni tenors in sulfides (3–5 wt%) and low Fo values in olivine (< 78 mol%), was derived from relatively oxidizing magmas (~QFM + 1) that had experienced significant olivine plus clinopyroxene and plagioclase fractionation at depth. We propose that the variation in oxygen fugacity and Ni tenor in the Permian Ni–Cu deposits in the Central Asian Orogenic Belt is the result of gradual contamination and a variable degree of fractional crystallization.

Selective flotation of enargite from copper sulphides in Tampakan deposit

Recent research has demonstrated promising results showing the possibility of separating arsenic-copper sulphides from other copper minerals by controlling the potential of the flotation pulp. Most of these studies were conducted on single mineral systems, and the selective removal of arsenic-copper minerals in real ore systems is not well understood, particularly, the effects of mineralogical properties such as liberation and mineralogical association.In this study, two distinct ore samples, termed low arsenic sample (LAS) and high arsenic sample (HAS) were selected from the Tampakan copper-gold deposit in the Philippines, providing a range of arsenic levels. The selective separation of enargite from other copper sulphide minerals in a rougher flotation system under controlled pulp potential was investigated for both samples.

Characterization and Geochemical Modeling of Cu and Zn Sorption Using Mineral Systems Injected with Iron Sulfide: Case Study of Mine Waste Water, Wales, United Kingdom

Sorption of Cu and Zn was investigated using single and mixed mineral systems under sulfidic-anoxic condition to treat wastewater obtained from disused mine pits at Parys Mountain in, United Kingdom. Water courses are the recipients of these contaminants. In these water courses fishing activities exist. Attempt was made to reduce the Cu and Zn levels intake in the watercourses using mineral systems of clays and goethite. These were tested with the mine waste water for characterization of copper and zinc removal at variable pH, solid concentration and contact time. In addition, levels of saturation of hydroxyl complexes were modeled. Batch reactions conducted at ambient temperature (23±2°C) reveal all systems of assorted minerals sorbed more Cu than Zn. In addition, Cu sorbed on iron sulfide exhibited increase in sorption with increasing pH. There was cross cutting effect of Cu and Zn sorbed on iron sulfide at pH 6 and Cu sorbed on goethite at about pH 7, These indicate similar metal removal characteristics. Differences in removal of copper and zinc ions may be assigned to outer sphere complexation and specific adsorption of copper and zinc ions. Non-promotive Cp effect (i.e. decrease in metal removal with increase in concentration of particle) was observed in all minerals. This effect may be assigned to increase in aggregation of the mineral particle size. Ageing characterization progresses as residence time was increased. This may be assigned thiol (=S-H) and hydroxyl (=Me-OH) groups and sites of reactions. There is no link to stable hydroxylation of copper and zinc species that could significantly contribute to the removal of these metals.

Widespread evidence for high-temperature formation of pentlandite in chondrites

By investigating the compositional and textural evolution of sulfides within a wide range of relatively pristine, aqueously altered, and thermally metamorphosed chondrites we constrain the equilibration temperatures of sulfide minerals and compare them to the metamorphic history of their host meteorite. Sulfides in Mighei-like carbonaceous chondrites are complex as they equilibrated mostly between 100 and 135°C, but some may have equilibrated at temperatures up to 600°C. This is consistent with some CM chondrite sulfides forming at high temperature during chondrule cooling and others during low-temperature aqueous alteration and/or annealing. Karoonda-like carbonaceous chondrite sulfides equilibrated between 500 and 230°C, which is consistent with formation during cooling and annealing after thermal metamorphism. Sulfides in the LL chondrites equilibrated between 600 and 230°C, and are consistent with formation during chondrule cooling for Semarkona (LL3.00) and during cooling after thermal metamorphism for the equilibrated samples (types 4–6). Sulfides in the Rumuruti-like (R) chondrites equilibrated between 600 and 500°C, and are consistent with formation after thermal metamorphism. The sulfides within the brachinite equilibrated between 600 and 400°C, consistent with formation during cooling after thermal metamorphism.Contrary to the assertion that pentlandite is solely the product of low-temperature aqueous alteration in many chondrite groups, this study suggests that most sulfides in chondrites are formed at or upon cooling from high-temperature. The evaluation of a single mineral system within samples that retain petrographic context is vital to the interpretation of formation and alteration processes recorded by small extraterrestrial samples, such as those that have been returned by the spacecraft missions Stardust and Hayabusa and will be returned by OSIRIS-REx and Hayabusa2.

Where Lower Calcite Abundance Creates More Alteration: Enhanced Rock Matrix Diffusivity Induced by Preferential Dissolution

Fractured rocks are essential for flow, solute transport and energy production in geosystems. Existing studies on mineral reactions in fractured rocks mostly consider single mineral systems where reactions occur at the fracture wall without changing rock matrix properties. This work presents multicomponent reactive transport numerical experiments in a fractured rock from the Brady’s field, a geothermal reservoir at a depth of 1,396 m in the Hot Springs Mountains, Nevada. Initial porosity, permeability, mineral composition (quartz, clay, and calcite), and fracture geometry are based on microscopy characterization and X-ray tomography. The model was calibrated using a CO2-saturated water flooding experiment. Three numerical experiments were carried out with the same initial physical properties however different calcite content. Although total dissolved masses are similar among the three cases, abundant calcite (50% (v/v), calcite50) leads to a localized, thick zone of large porosity increase while low calci...

Arsenite Removal from Aqueous Solution using Mixed Mineral Systems Injected with Iron Sulfide under Sulfidic- Anoxic conditions 1: Reactivity and Removal Kinetics

The reactivity and removal kinetics of arsenite treated with single and mixed mineral systems of kaolinite, montmorillonite and goethite injected with iron sulfide under sulfidic- anoxic conditions has been investigated. Using empirical models derived from Freundlich isotherm model, injection of sulfidic-anoxic solution of iron sulfide onto the mixed mineral systems enhanced proton coefficient of all single minerals. Differences in sorption kinetics between the single and mixed mineral phases may be attributed to different types of reactive sites on the single and mixed mineral systems Except for iron sulfide, kinetic studies demonstrated three phase reactions attributed to outer sphere complexation, inner sphere complexation and intra-particle diffusion. Injection of sulfidic-anoxic solution of iron sulfide could not change the three phase reaction trend.

Arsenite Removal from Aqueous Solution using Mixed Mineral Systems Injected with Iron Sulfide under Sulfidic-Anoxic condition II. The role of solution composition and ageing

The role of solution composition and ageing of arsenite treated with single and mixed mineral systems of kaolinite, montmorillonite and goethite injected with iron sulfide under sulfidic- anoxic conditions have been investigate. Variability in arsenite sorption exists over the range of pH investigated. This variability in sorption may be attributed to the presence of thiol (≡S-H) functional group contained in solution under sulfidic-anoxic condition. Arsenite sorption exhibits a non-promotive Cp effect (i.e. sorption decreases as Cp increases for all mineral systems. the nature of ionic species formed in solution is affected by changes in the mineral/ solution ratio. All mineral systems but kaolinite-goethite exhibits a step up arsenite sorption up to 288 hours residence time and flattens g out over the remaining residence time of the reactions.

Inferring the distribution of iron oxidation species on mineral surfaces during grinding of base metal sulphides

Electrochemistry plays an important role in the flotation of base metal sulphide minerals. During grinding a galvanic interaction occurs between minerals and grinding media and controls the iron contamination on mineral surfaces, which depresses mineral flotation significantly. In this study, the galvanic interaction was quantified by measuring the iron oxidation species originated from grinding media by ethylene diamine-tetra acid (EDTA) extraction in single mineral and mixed mineral systems. It was found that the extent of galvanic interaction between minerals and grinding media was intimately associated with the electrochemical reactivity of minerals. The nobler the mineral, the stronger the galvanic interaction with grinding media, and the higher the amount of iron oxidation species from grinding media. For both galena and chalcopyrite a linear relationship was observed between the amount of iron oxidation species and flotation recovery in single mineral systems. This relationship was able to predict the iron oxidation species on galena and chalcopyrite surfaces when they were mixed with pyrite separately. The distribution of iron oxidation species onto the two minerals in the mixture changed with the ratio of the mineral surface areas and was correlated with mineral flotation recovery. The major cathodic mineral in the mixture was dictated by the combination of mineral surface area and reactivity and drew iron oxidation species from the grinding media.

Soil pH controls the environmental availability of phosphorus: Experimental and mechanistic modelling approaches

Abstract Inorganic P is the least mobile major nutrient in most soils and is frequently the prime limiting factor for plant growth in terrestrial ecosystems. In this study, the extraction of soil inorganic P with CaCl 2 (P–CaCl 2 ) and geochemical modelling were combined in order to unravel the processes controlling the environmentally available P (EAP) of a soil over a range of pH values (pH ∼ 4–10). Mechanistic descriptions of the adsorption of cations and anions by the soil constituents were used (1-pK Triple Plane, ion-exchange and NICA-Donnan models). These models are implemented into the geochemical code Visual MINTEQ. An additive approach was used for their application to the surface horizon of a Cambisol. The geochemical code accurately reproduced the concentration of extracted P at the different soil pH values ( R 2 = 0.9, RMSE = 0.03 mg kg −1 ). Model parameters were either directly found in the literature or estimated by fitting published experimental results in single mineral systems. The strong agreement between measurements and modelling results demonstrated that adsorption processes exerted a major control on the EAP of the soil over a large range of pH values. An influence of the precipitation of P-containing mineral is discounted based on thermodynamic calculations. Modelling results indicated that the variations in P–CaCl 2 with soil pH were controlled by the deprotonation/protonation of the surface hydroxyl groups, the distribution of P surface complexes, and the adsorption of Ca and Cl from the electrolyte background. Iron-oxides and gibbsite were found to be the major P-adsorbing soil constituents at acidic and alkaline pHs, whereas P was mainly adsorbed by clay minerals at intermediate pH values. This study demonstrates the efficacy of geochemical modelling to understand soil processes, and the applicability of mechanistic adsorption models to a ‘real’ soil, with its mineralogical complexity and the additional contribution of soil organic matter.

Experimental study and modelling of selenite sorption onto illite and smectite clays

This study provides a large set of experimental selenite sorption data for pure smectite and illite. Similar sorption behavior existed in both clays: linear within a large range of the Se concentrations investigated (from 1 × 10 −10 to 1 × 10 −3 M); and independent of ionic strength. Selenite sorption was also analysed in the illite/smectite system with the clays mixed in two different proportions, as follows: (a) 30% illite–70% smectite and (b) 43% illite–57% smectite. The objective of the study was to provide the simplest model possible to fit the experimental data, a model also capable of describing selenite sorption in binary illite/smectite clay systems. Selenite sorption data, separately obtained in the single mineral systems, were modeled using both a one- and a two-site non-electrostatic model that took into account the formation of two complexes at the edge sites of the clay. Although the use of a two-site model slightly improved the fit of data at a pH below 4, the simpler one-site model reproduced satisfactorily all the sorption data from pH 3 to 8. The complexation constants obtained by fitting sorption data of the individual minerals were incorporated into a model to predict the adsorption of selenium in the illite/smectite mixtures; the model’s predictions were consistent with the experimental adsorption data.

I–Xe dating: From adolescence to maturity

The I–Xe chronometer is based upon decay of now-extinct 129I where the ratio of accumulated daughter 129Xe to stable 127I reflects the iodine isotopic ratio at closure of the host mineral. Since none of the parent remains, I–Xe is by nature a relative chronometer but, when referenced by a standard mineral of known age, the I–Xe system becomes an absolute chronometer reflecting true closure times. Most iodine hosts are secondary minerals so the I–Xe system is unique in providing details of post-formational chronometry not readily available with other chronometers. The short half-life of 129I gives it exceptional precision. However, the secondary nature of iodine host minerals, combined with the inherent precision of I–Xe, were responsible for a large database of “whole-rock” I–Xe ages that were not easily interpreted. As this problem evolved historically, doubts were cast upon the viability of the I–Xe system as a chronometer which persisted until it was tested against other chronometers in single-mineral systems. Properly calibrated, absolute I–Xe ages reflect the true closure time of the host minerals, and sequences of closure times in different hosts provide cooling rates for the parent object.

Sorption of strontium onto illite/smectite mixed clays

Radioactive strontium is a by-product of the fission of uranium and plutonium and its mobility in the environment is largely dominated by sorption onto soil minerals, especially clays. In this study, the sorption behaviour of Sr in illite/smectite mixtures was analyzed from a mechanistic point of view. Sorption of Sr onto smectite and illite, previously homoionised in Na, was studied under different pHs, ionic strengths and radionuclide concentrations. Sorption experiments were also carried out with smectite and illite, mixed in two different proportions: 50–50% and 75–25%. Sr sorption data that were obtained from the single mineral systems were modelled considering both ionic exchange and surface complexation and using a non-electrostatic model. The selectivity coefficients and complexation constants obtained for the individual minerals were incorporated into a model to predict the adsorption of Sr in binary adsorbent systems and the model predictions were consistent with Sr experimental adsorption data.

Effect of Modified Dextrins on the Depression of Talc and Their Selectivity in Sulphide Mineral Flotation: Adsorption Isotherms, AFM Imaging and Flotation Studies

Three novel dextrin polymers of varying functional group chemistry but similar molecular weight have been used to depress talc in single and mixed mineral studies. The mixed mineral system was a model sulphide ore consisting of talc, pentlandite and chalcopyrite. Adsorption isotherms for the three polymers on both valuable and gangue mineral phases were determined to give initial clues as to the ability of the polymers to depress talc. Flotation testing revealed a distinct hierarchy of effectiveness of the polymers in the depression of talc in the single mineral system (MP Dextrin > CM Dextrin > Dextrin TYM) reflecting the observed adsorption affinity and adsorbed amount of the polymers on talc. Atomic force microscopy (AFM) imaging of the polymers on the basal plane of talc gave further insight to the observed single mineral flotation trends with differences observed amongst the polymers in terms of adsorbed layer thickness and coverage. A different order of effectiveness was observed for talc depression in the mixed mineral system (CM Dextrin ≥ MP Dextrin > Dextrin TYM). Competition between the valuable and gangue mineral phases for the uptake of MP Dextrin is responsible for its observed decrease in efficiency in mixed mineral flotation. All three polymers were found to be reasonably selective in their action although at high dosages the polymers began to affect the flotation of the valuable minerals.

Effect of Modified Dextrins on the Depression of Talc and Their Selectivity in Sulphide Mineral Flotation: Adsorption Isotherms, AFM Imaging and Flotation Studies

Three novel dextrin polymers of varying functional group chemistry but similar molecular weight have been used to depress talc in single and mixed mineral studies. The mixed mineral system was a model sulphide ore consisting of talc, pentlandite and chalcopyrite. Adsorption isotherms for the three polymers on both valuable and gangue mineral phases were determined to give initial clues as to the ability of the polymers to depress talc. Flotation testing revealed a distinct hierarchy of effectiveness of the polymers in the depression of talc in the single mineral system (MP Dextrin > CM Dextrin > Dextrin TYM) reflecting the observed adsorption affinity and adsorbed amount of the polymers on talc. Atomic force microscopy (AFM) imaging of the polymers on the basal plane of talc gave further insight to the observed single mineral flotation trends with differences observed amongst the polymers in terms of adsorbed layer thickness and coverage. A different order of effectiveness was observed for talc depression in the mixed mineral system (CM Dextrin ≥ MP Dextrin > Dextrin TYM). Competition between the valuable and gangue mineral phases for the uptake of MP Dextrin is responsible for its observed decrease in efficiency in mixed mineral flotation. All three polymers were found to be reasonably selective in their action although at high dosages the polymers began to affect the flotation of the valuable minerals.