Journal of the American Society of Mining and Reclamation, 2004
Selenium (Se) occurs in a wide variety of oxidation states and is a common element present in sed... more Selenium (Se) occurs in a wide variety of oxidation states and is a common element present in sedimentary geologic materials such as shale. Phosphate mining activities in southeastern Idaho have left shale materials near the surface, thus releasing the natural Se into a new weathering environment. In this study we are investigating the biogeochemistry of Se at remediated phosphate mining sites. Soil samples were collected from the rhizosphere of remediated sites and analyzed using microscopically focused X-ray absorption fine structure (XAFS) spectroscopy. A greenhouse study to measure the impacts of sulfate and manure amendments on plant bioavailability is also discussed in this paper. XAFS spectroscopy results provide knowledge of mineralogy and Se-oxidation state in the soils. XAFS spectroscopy revealed that Se exists in several different reduced forms in the parent shale materials, including elemental Se and ferroselite-type minerals. In weathered soils, Se was present as Se(IV)...
Efflorescent crusts consisting predominantly of the sodium carbonate minerals trona (Na 2 CO 3 • ... more Efflorescent crusts consisting predominantly of the sodium carbonate minerals trona (Na 2 CO 3 • NaHCO 3 • 2H 2 O) with minor thermonatrite (Na 2 CO 3 • H 2 O) are commonly developed on less vegetated portions of the Indo-Gangetic Plains of the state of Uttar Pradesh in India. Being highly soluble, the presence of trona alone explains the high alkalinity of the soil (pH 10.5). Occasional flooding followed by fast evaporation in this extensive flood plain is a possible cause of the formation of this mineral. Carbonate build-up will have a major impact on the Gangetic ecosystem in the future, causing declining bioproductivity.
The beneficiation of rare earth element (REE) minerals may include many different beneficiation u... more The beneficiation of rare earth element (REE) minerals may include many different beneficiation unit operations, but the final process choice typically depends on the inherent mineral characteristics. The Nechalacho REE deposit contains multiple low specific gravity, diamagnetic silicate gangue minerals (predominantly feldspars and quartz) and high specific gravity, iron oxide minerals (magnetite and hematite). The valuable REE minerals (REM) in the deposit consist of a variety of relatively high specific gravity, paramagnetic minerals. A process has been proposed to concentrate the value REM through a combination of gravity (rejecting silicate gangue) and magnetic (rejecting iron oxide gangue) separation steps prior to froth flotation. This work employed a laboratory-scale process including two different gravity separation steps (Knelson and Falcon centrifugal concentrators) followed by a series of varying intensity wet drum magnetic separation steps as well as dry induced roll magnetic separation and wet high intensity magnetic separation steps. The resultant fractions have been characterized by XRD, ICP-MS, and QEMSCAN to identify the optimum fraction for downstream flotation separation. The combination of a Knelson Concentrator with low intensity wet drum magnetic separation was found to efficiently concentrate REM while also rejecting high specific gravity iron oxide minerals. A novel finding from this study is the concentration of heavy REE-bearing zircon into coarse size fractions after grinding.
Large volumes of solid waste material will be produced during the commercial production of shale ... more Large volumes of solid waste material will be produced during the commercial production of shale oil. An alternative to the disposal of the solid waste product is utilization. One potential use of spent oil shale is for the stabilization of hazardous organic compounds. The objective of this study was to examine the adsorption of pyridine, commonly found in oil shale process water, by spent oil shale. The adsorption of pyridine by fresh and weathered samples of combusted New Albany Shale and Green River Formation oil shale was examined. In general, pyridine adsorption can be classified as L-type and the isotherms modeled with the Langmuir and Freundiich equations. For the combusted New Albany Shale, weathering reduced the predicted pyridine adsorption maximum and increased the amount of pyridine adsorbed at low solution concentrations. For the combusted Green River Formation oil shales, weathering increased the predicted pyridine adsorption maximum. The pyridine adsorption isotherms were similar to those produced for a cornbusted Australian oil shale. Although adsorption can be mathematically described by empirical models, the reduction in solution concentrations of pyridine was generally less than 10 mg/I at an initial concentration of 100 mg/I. Clearly, the observed reduction in solution pyridine concentrations does not sufficiently justify using spent oil shale as a stabilizing medium. However, data in the literature suggest that other organic compounds can be effectively removed from solution by spent oil shale and that adsorption is dependent on process conditions and organic compound type.
An increasing number of low-grade gold ore deposits are characterized by the presence of gold as ... more An increasing number of low-grade gold ore deposits are characterized by the presence of gold as solid solution into the mineral matrix of sulphide minerals which is not directly amenable to gold cyanidation. In order to liberate this submicroscopic gold the ore has to be oxidized before being subjected to gold cyanidation and exctraction. This is mainly done by autoclave pressure oxidation (AC POX) or roasting, two major technologies used by the mining industry. Very often, these ores contain an active carbonaceous compound which has the ability to adsorb, or preg-rob gold from the cyanide solution. Gold recovery can be adversely affected by preg-robbing on inherent carbonaceous material during autoclave pressure oxidation of sulphide ores. The time of flight (TOF) SIMS (TOF-SIMS) technique has been applied for direct determination of gold species on individual carbonaceous particulates from AC POX stream samples. The speciation of the gold preg-robbed on carbonaceous matter from CIL tail sample showed presence of both metallic gold and Au(CN) 2 compound. Direct quantification of the metallic and compound gold provided an estimate for the fraction of gold losses due to preg-robbing in carbonaceous matter.
Combinations of PFA (Pulverized fuel ash) mixed with composted municipal organic waste were compa... more Combinations of PFA (Pulverized fuel ash) mixed with composted municipal organic waste were compared to a local soil and a commercial potting soil "Promix" in an attempt to asses the potential performance of the manufactured growth medium. Results from growth trials were related to the physico-chemical characteristics of the mixtures and fruits were analyzed to determine potential metal uptake Dried fruit weights from tomatoes grown in mixtures of compost with 5, 10 and 20% PFA were significantly higher than the soil and soil with the recommended dose fertilizer. Fruit production for the 5% PFA mixture was 2.5x that from the soil and 25% higher than the soil + NPK. Fruit production in the 10 and 20% additions were >2x that in the soil. In all cases fruit production in the mixture was 30% higher than the trials with Promix. Analyses of variance indicates that the mixtures of PFA and compost are all significantly different from the control soil and rank the performance of treatments as follows PFA10:CP90> PFA5:CO95> PFA20:CP80. In all cases element concentrations reported in tomato fruit analyzed did not exceed the maximum reported concentration range normal for plants. Furthermore, with the exception of B and Fe, element concentration means for mixtures were not significantly different from the soil or PROMIX. Results from the trials indicate that a suitable potting medium can be created from PFA mixed with composted organic material. The physical and chemical composition of mixture promotes healthy and long-term growth without the need for fertilizers.
The objective of this study was to achieve Zn activation control in an industrial Cu flotation ci... more The objective of this study was to achieve Zn activation control in an industrial Cu flotation circuit treating a complex Cu-Pb-Zn-Au-Ag sulphide ore at the LaRonde Division of Agnico-Eagle Mines Limited (Quebec, Canada). In order to provide process relevant results, a laboratory testing methodology was developed to duplicate plant operational parameters. The action mechanisms of ZnSO 4 , TETA (triethylenetetramine) and NaHSO 3 used as depressants in order to limit ZnS activation were examined. Laboratory flotation tests with and without Cu 2+ ions (the ions responsible for ZnS activation) were performed. All depressants showed equal or better flotation performance relative to baseline tests. For example, in the presence of Cu 2+ , the Zn grade reduced from 32.2% to 17.5% in the copper rougher concentrate after adding 50 g/t ZnSO 4. TOF-SIMS analyses confirmed the relative decrease in surface Cu in the samples treated with ZnSO 4 and TETA. For the case with TETA, this indirectly indicates the formation of a copper TETA complex in solution, thereby reducing available Cu for transfer. The TOF-SIMS and XPS data indicate that the addition of ZnSO 4 and NaHSO 3 resulted in an increase in surface metal hydroxides and SO 3 on ZnS grains inhibiting both Cu and collector attachment. ZnSO 4 was subsequently tested with success in the LaRonde concentrator. The addition of 40 g/t ZnSO 4 at the conditioning (or cleaning) stage led to a 2% reduction in Zn content in the Cu and PM concentrate. Recently, improvements towards the control of copper sulfate addition in the downstream Zn flotation circuit resulted in the reduction of Cu 2+ in process water. As this "cleaner" water is recycled for Cu and PM flotation, the addition of ZnSO 4 is now used only as required.
ImportanceMetformin is often used as a first-line therapy for type 2 diabetes; however, frequent ... more ImportanceMetformin is often used as a first-line therapy for type 2 diabetes; however, frequent discontinuation with reduced kidney function and increased disease severity indicates that a comparison with any other group (eg, nonusers or insulin users) must address significant residual confounding concerns.ObjectivesTo examine the potential for residual confounding in a commonly used observational study design applied to metformin and to propose a more robust study design for future observational studies of metformin.Design, Setting, and ParticipantsThis retrospective cohort study with a prevalent user design was conducted using an administrative claims database for Medicare Advantage beneficiaries in the US. Participants were categorized into 2 distinct cohorts: 404 458 individuals with type 2 diabetes and 81 791 individuals with prediabetes. Clinical history was observed in 2018, and end points were observed in 2019. Statistical analyses were conducted between May and December 20...
Gold losses related to carbonaceous matter (CM) during processing are a significant problem in th... more Gold losses related to carbonaceous matter (CM) during processing are a significant problem in the gold processing industry. Inherent CM in gold ores can behave similarly to activated carbon in its ability to adsorb gold cyanide. This phenomenon is termed preg-robbing as the surface adsorbed gold cannot, for the most part, be recovered. Research has identified that gold adsorption by inherent CM is linked to the specific surface area, pore structure, degree of C disorder and surface functional groups. One of the strategies to inhibit CM preg-robbing prior to leaching is a chemical oxidation; a process linked to modification of the surface functionality. In this study, the variability in gold cyanide adsorption due to oxidation with different reagents has been investigated. Variability in gold cyanide adsorption by CM is examined in relation to structural and surface modifications using TOF-SIMS, XPS and Raman spectroscopy.
The Canadian Journal of Chemical Engineering, 2019
In the presence of Cu ions, a packed bed electrochemical reactor (PBER) was employed to deliberat... more In the presence of Cu ions, a packed bed electrochemical reactor (PBER) was employed to deliberately avoid or induce galvanic coupling between pyrite and Cu-activated sphalerite. The effect of galvanic interaction on Cu ions uptake and xanthate adsorption were investigated. Solution chemistry and surface chemistry studies (ethylenediaminetetraacetic acid extraction and time of flight secondary ion mass spectrometry) have observed that when sphalerite and pyrite were galvanically coupled, Cu ions migrated from the pyrite surface to the surface of the sphalerite. Along with the marked decrease in the adsorption of Cu ions on pyrite, xanthate adsorption on the minerals also dramatically dropped. The pseudo-adsorption rate constant for the minerals in the mixed mode is only 0.0583 s-1 , much less than that in the decoupled mode, which is 0.1368 s-1. This testing program shows that the galvanic coupling of minerals contributes to more copper transfer and Cu ions preferentially adsorbed by sphalerite rather than pyrite. This affects the pyrite surface and causes it to become xanthate unflavoured.
Changes in mineral surface properties during grinding play a key role in flotation performance. T... more Changes in mineral surface properties during grinding play a key role in flotation performance. ToF-SIMS surface chemical analytical studies have shown that flotation separation of sphalerite from chalcopyrite is significantly affected by the oxidation of metal species on the surface of sphalerite. The intensity of iron oxyhydroxyl species on the surface of sphalerite has a positive correlation with poor recovery of sphalerite. Given the link between the presence of oxide species on the surface of sphalerite and a lower recovery during Cu flotation, a laboratory study was initiated to evaluate the potential for sphalerite surface oxidation control and improve recovery through grinding. For the investigation, a ball mill which allowed for monitoring pulp chemistry during grinding was utilized to study the impact of grinding conditions on selective flotation of sphalerite. ToF-SIMS was used to identify and measure the variability in sphalerite surface species as a result of the different test parameters. Variable mill parameters include 2 types of grinding media, aeration conditions, addition of FeSO 4 , and altering the pyrite content in the feed ore. TOF-SIMS analyses of mill discharge samples identified higher intensities of iron oxyhydroxyl species on sphalerite surface subsequent to grinding with mild steel balls, in condition of aeration, use of FeSO 4 , and by increasing the pyrite content of the feed ore. The higher adsorption of iron oxyhydroxyl species on the surface of sphalerite should be consistent with the lower recovery. To verify this, bench scale flotation tests in the presence and absence of FeSO 4 were performed; results correlated iron oxyhydroxyl species with the poor sphalerite recovery.
The Thor lake deposit is a world class resource of rare earth (REE) metals and minerals in Canada... more The Thor lake deposit is a world class resource of rare earth (REE) metals and minerals in Canada. Development work to optimize a REE mineral recovery process flow sheet is underway, however, given the ore mineralogy; the developed reagent scheme is relatively complex. As part of a research project, micro flotation tests were conducted on a feed sample in order to examine factors affecting stream partitioning. SEM-EDX was performed to evaluate variability in grain composition between streams (concentrate and tails) and TOF-SIMS surface analysis was used to determine statistically significant differences in surface species particularly related to potential activation (or depression) of the examined mineral phases. SEM-EDX analysis reveal that the concentrate has a significantly higher proportion of REE bearing grains (carbonates and phosphates) relative to the tail (almost none were identified). Spectral fingerprinting by TOF-SIMS has allowed for the identification of all reagent spe...
The Nechalacho project is the most advanced large heavy rare earth elements (HREE) project outsid... more The Nechalacho project is the most advanced large heavy rare earth elements (HREE) project outside of China. Open circuit and locked cycle flotation tests along with pilot plant testing of rare earth elements (REE) concentration from the host rocks are accomplished with collectors of alkyl phosphates and the modifier of citric acid. In this study, the function of citric acid in the separation of rare metals against silicates is investigated by a combination of micro-flotation tests and time of flight secondary ion mass spectrometry (ToF-SIMS) surface chemical analysis. It was observed that there was little effect of citric acid on the REE recovery in the micro-flotation tests conditioned with de-ionized water (DIW). To evaluate the flotation response with excess secondary ions in the pulp, micro-flotation tests were performed to look at changes in recovery as a result of adding Al ions and the subsequent presence of citric acid. The results from three micro-flotation tests (DIW, DIW with the addition of 100 mg/L Al and DIW + 100 mg/L Al and 500 g/t citric acid) revealed that the addition of Al ions led to a decrease of REE grade, a lower REE minerals recovery and/or an unexpected promotion of silicates to the concentrate. Citric acid reduced the negative effect generated by the Al ions in the flotation, which was shown by an improvement in REE grade. ToF-SIMS surface analysis of undifferentiated grains from the tests with and without citric acid revealed that grains reporting to the concentrate are doing so in response to collector attachment in combination with having more secondary Al on their surface. Citric acid may partially form aqueous soluble metal-ligand complexes resulting in less Al ions on the grains surface, which were rejected to the tailings. Citric acid also may form chelation competing for adsorption on gangue minerals, resulting in a diminished effectiveness of the activation site.
Coal Combustion Byproducts and Environmental Issues
Even though both coal fly ash and sewage sludge are rich sources of bio-essential nutrients, one ... more Even though both coal fly ash and sewage sludge are rich sources of bio-essential nutrients, one of the major limiting factors in their use either individually or in mixture proportions as for amendment into agricultural soil is the presence of various metals likely to be potentially toxic at their elevated concentrations. This study evaluated the adsorption and distribution behaviours of selected metals in three different soils from India amended with mixtures of ash and sludge in various proportions at a maximum application rate of 52t ha-' and incubated up to 90 days at near field capacity moisture level. The properties of amended soils were affected significantly by sludge than the ash and the Freundlich distribution coefficients (KDs) of metals were marginally higher compared to their respective controls. The degree of impact of amendment on soil properties, distribution coefficients of metals and their adsorption affinity sequences, based on KDs, within and across soil types were determined. Sequential extraction indicated that, the concentrations of native metals in each soil type tends to be less in highly mobile and moderately mobile fractions than the resistant; and changed marginally following amendment while the distribution patterns remained more or less undisturbed. The sequential extraction of adsorbed metals at various equilibrating concentrations of their addition indicated shifts in the distribution patterns in each soil type. However, the changes in the partitioning of adsorbed metals were wide and clearly noticeable only at higher loadings and the metals showed propensity to accumulate preferentially in more mobile fractions, depending on the type of soil surface and substrate. The results indicated that at low rate of application, ash and sludge, though capable of changing the soil properties and its metal adsorption capacities to certain extent; they had no major influence on metal distribution patterns in the amended soils which mainly depended on the soil properties, type of metal and its concentration.
Time of flight secondary ion mass spectrometry (TOF-SIMS) was used to analyse the surface of two ... more Time of flight secondary ion mass spectrometry (TOF-SIMS) was used to analyse the surface of two different types of pyrochlore, high Fe pyrochlore and low Fe pyrochlore, from Niobec Saint-Honore mine deposit. Pyrochlore grains were analysed in order to identify a potential relationship between pyrochlore matrix composition, the corresponding surface expression and the related effect on cationic collector adsorption. TOF-SIMS analyses of pyrochlore surfaces from a conditioning test show that the species indicative of the cationic collector, favour the surface of Fe poor pyrochlore relative to the Fe rich variety. Lower collector signals on the surface of the Fe-pyrochlore are matched by higher relative intensities of Fe, OH, O and FeOH. The TOF-SIMS results illustrate a negative relationship between a cationic collector adsorption and the presence of Fe and Fe oxidation species on the surface of pyrochlore grains, and supports previous work which identified a negative correlation between matrix Fe content and pyrochlore floatability. The surface analysis illustrates the link between pyrochlore matrix chemistry, the expression of surface species and their effect on collector adsorption.
The influence of lead nitrate on rare earth flotation in the presence of hydroxamates as collecto... more The influence of lead nitrate on rare earth flotation in the presence of hydroxamates as collectors has been investigated by a combination of micro-flotation tests and time of flight secondary ion mass spectrometry (ToF-SIMS) surface chemical analysis. Micro-flotation tests identified a link between lead nitrate dose and an improved grade of REE minerals for concentrates. The testing also identified differences in the flotation behaviour of light rare earth (LREEs, La or Ce bearing minerals) and Y and Zr bearing minerals. TOF-SIMS analyses evaluated the variability in surface components on undifferentiated REE grains from the concentrates and tails samples in response to the varied lead nitrate dosing in micro-flotation tests. The surface analyses showed that both the REE grains and gangue phases reporting to the concentrate have higher relative surface proportions of both Pb and collectors as compared to those reporting to the tails. It is noted that the lead does not appear to be associated with an increase in collector adsorption, so the grade of REE can go up is not by selective adsorption of collectors. The significantly higher intensity of Pb species identified on the surface of the concentrate would suggest that lead addition can actually reverse the surface charge making it efficient for collectors to adsorb onto surfaces that they could not easily close to. It is also possible PbOH + potentially acting as a point activator.
Recently, upgrades towards a semiquantitative approach to mineral processing applications using t... more Recently, upgrades towards a semiquantitative approach to mineral processing applications using the time of flight (TOF) SIMS (TOF-SIMS) technique have been developed and implemented. Secondary ion yield at specific instrument parameters for matrix elements in the predominant ore minerals and their comparative normalization factors have been determined. Surface loading quantification for Cu on a variety of ore minerals has shown that signal intensity variability is related to the substrate matrix. Relative sensitivity factors for component loading have been determined and calibration curves for Cu loading on mineral surfaces have established with lower limits of detection in the range of 10 ppm. Given the new semiquantitative approach for surface characterization of minerals, a new test was developed to be used as a predictive tool in mineral flotation separation. The test protocol involved a two-chamber ball mill where Cu transfer between the pulp and specimen surface was measured by the semiquantitative TOF-SIMS approach. The test was applied to 13 ores. The reported experimental data on these ores demonstrated the ability of this technique to differentiate Cu transfer over a large dynamic range. The data also demonstrated that the surface loading of Cu on pyrite can be correlated, in some cases, with mineralogy. In others, however, the surface Cu loading observed is not congruent with the mineralogical assessment of the ore sample, but still linked with flotation behavior. This shows that the test could be used with mineralogy to better benchmark a sample before embarking on a flotation flowsheet development programme.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
This paper reviews the applications of time of flight secondary ion mass spectrometry (TOF-SIMS) ... more This paper reviews the applications of time of flight secondary ion mass spectrometry (TOF-SIMS) used for surface chemical analysis of mineral in the context of froth flotation. A wide range of applications are reviewed, including; interactions of reagents on the surface of mineral phases during flotation separation, determining the effects of various transferred ions from different minerals or the slurry, evaluation of hydrophobicity, identifying the relationship between mineral surface chemistry and contact angle, and evaluation of grinding effects. Conclusions indicated that TOF-SIMS, as a unique surface analysis technique, can potentially provide a direct determination of parameters which control the surface reactivity and consequently plays an important role in determining flotation behaviour of minerals.
The Thor lake deposit is a world class resource of rare earth (REE) metals and minerals in Canada... more The Thor lake deposit is a world class resource of rare earth (REE) metals and minerals in Canada. Development work to optimize a REE mineral recovery process flow sheet is underway, however, given the ore mineralogy; the developed reagent scheme is relatively complex. As part of a research project, micro-flotation tests were conducted on a feed sample in order to examine factors affecting stream partitioning. SEM-EDX was performed to evaluate variability in grain composition between streams (concentrate and tails) and TOF-SIMS surface analysis was used to determine statistically significant differences in surface species particularly related to potential activation (or depression) of the examined mineral phases. SEM-EDX analysis reveal that the concentrate has a significantly higher proportion of REE bearing grains (carbonates and phosphates) relative to the tail (almost none were identified). Spectral fingerprinting by TOF-SIMS has allowed for the identification of all reagent species investigated. Reagent signal intensity discrimination on test stream mineral surfaces was observed by the TOF-SIMS analysis using reagents at plant concentration levels. TOF-SIMS analysis confirmed that REE bearing grains reporting to the concentrate are doing so in response to collector attachment whereas grains reporting to the tail are doing so in response to a lack of collector and/or in combination with the presence of the depressant. The surface analysis of gangue phases reveal a similar reagent discrimination; the signal intensity of collector species was significantly higher on the concentrate samples relative to the tails while depressant species were significantly enriched on the surface of the gangue phases in the tail samples. A detailed evaluation of the surface species representing the various reagents used in flotation scheme revealed a distinct competitive relationship between two of the reagents. The surface analysis identified that when used in concurrently, there appears to be a negative feedback resulting in a significant reduction in loading for several of the collectors on grains reporting to the concentrate. An evaluation of the effect of reagents on REE mineral in pilot plant is currently under way.
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