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Solution equilibrium calculations were performed in this study to understand the impact of contaminant metal ions on the precipitation efficiency of selected rare earth elements (Ce3+, Nd3+, and Y3+) using oxalic acid as a precipitant. Trivalent metal ions, Al3+ and Fe3+, were found to considerably affect the precipitation efficiency of REEs. When Al3+ and Fe3+ concentrations were increased by 1 × 10−4 mol/L, in order to achieve an acceptable cerium recovery of 93% from solutions containing 1 × 10−4 mol/L Ce3+, oxalate dosage needed to increase by 1.2 × 10−4 and 1.68 × 10−4 mol/L, respectively. Such great impacts on the required oxalate dosage were also observed for Nd3+ and Y3+, which indicates that oxalic acid consumption and cost will be largely increased when the trivalent metal ions exist in REE-concentrated solutions. Effects of the divalent metal ions on the oxalate dosage is minimal. Furthermore, solution equilibrium calculation results showed that the precipitation of Fe3+ and Ca2+ (e.g., hematite and Ca(C2O4)∙H2O(s)) likely occurs during the oxalate precipitation of REEs at relatively high pH (e.g., pH 2.5), which will reduce rare earth oxalate product purity. In addition to the metal ions, anionic species, especially SO42−, were also found to negatively affect the precipitation recovery of REEs. For example, when 0.1 mol/L SO42− occurs in a solution containing 1 × 10−4 mol/L Ce3+ and 4 × 10−4 mol/L oxalate, the pH needed to be elevated from 2.0 to 3.3 to achieve the acceptable recovery. Overall, findings from this study provide guidance for the obtainment of high-purity rare earth products from solutions containing a considerable amount of contaminant metal ions by means of oxalic acid precipitation. Accepted version

REE recovery from a kaolinite sample was conducted in the present study. The results of mineralogical analyses, salt leaching, and acid leaching tests confirmed that REEs predominantly existed as florencite (REEAl3(PO4)2(OH)6) in the material, and the proportion of ion-exchangeable and ion-substituted REEs was negligible. Mechanical grinding for 4 h completely destroyed the crystal structure of the material, but the recovery of total REEs was less than 20%, indicating that insufficient liberation of the REE-bearing particles is not the only factor leading to the low recovery. Thermal treatment of the raw material at 600 °C for 2 h largely enhanced the total REE recovery to as high as 92%. The improved recovery was ascribed to the thermal decomposition of crystallized florencite into an amorphous phase, which was proved through transmission electron microscopy - energy dispersive X-ray analysis. Findings from the study will contribute to REE recovery and comprehensive utilization of kaolinite.

Brassinosteroids (BRs) play essential roles in regulating plant growth and development, however, gaps still remain in our understanding of the BR signaling network. We previously cloned a grain length quantitative trait locus qGL3, encoding a rice (Oryza sativa L.) protein phosphatase with Kelch-like repeat domain (OsPPKL1), that negatively regulates grain length and BR signaling. To further explore the BR signaling network, we performed phosphoproteomic analysis to screen qGL3-regulated downstream components. We selected a 14-3-3 protein OsGF14b from the phosphoproteomic data for further analysis. qGL3 promoted the phosphorylation of OsGF14b and induced the interaction intensity between OsGF14b and OsBZR1. In addition, phosphorylation of OsGF14b played an important role in regulating nucleocytoplasmic shuttling of OsBZR1. The serine acids (Ser258Ser259) residues of OsGF14b play an essential role in BR-mediated responses and plant development. Genetic and molecular analyses indicated that OsGF14b functions as a negative regulator in BR signaling and represses the transcriptional activation activity of OsBZR1. Collectively, these results demonstrate that qGL3 induces the phosphorylation of OsGF14b, which modulates nucleocytoplasmic shuttling and transcriptional activation activity of OsBZR1, to eventually negatively regulate BR signaling and grain length in rice.

A kaolinite containing 245 ppm of REEs was used as a feedstock for REE recovery. Acid leaching test results showed that less than 20% of the REEs were leached using 1.2 mol/L HCl. However, after thermal treatment at 600 °C, a recovery of over 80% was obtained with a much lower acid concentration (0.01 mol/L). Meanwhile, only 3.91% Al, 2.34% Fe, 8.63% K, 9.32% Mg, 0.08% Ti, and 5.34% Ca were simultaneously extracted. Therefore, high-purity rare earth products are likely produced from the kaolinite. To achieve a more comprehensive utilization of the kaolinite, the residual solid after REE recovery was subjected to a selective leaching process to prepare porous silica. Comparisons among three different types of mineral acids showed that H2SO4 provided the best performance. The effects of different factors were investigated using the response surface methodology. A porous silica with as high as 336.95 m2/g specific surface area was ultimately produced.

Due to the increasing criticality of rare earth elements (REEs), it has become essential to recover REEs from alternative resources. In this study, systematic REEs leaching tests were performed on the calcination product of a coal coarse refuse using hydrochloric acid and different types of organic acid as lixiviants. Experimental results show that the recovery of REEs, especially heavy REEs (HREEs) and scandium (Sc), is improved by using selected organic acids. Citric acid and dl -malic acid afford the best leaching performances; whereas, malonic acid, oxalic acid, and dl -tartaric acid are inferior to hydrochloric acid. Results of zeta potential measurements and solution chemical equilibrium calculations show that malonic acid is more likely adsorbed on the surface of the calcined material compared with citric acid and dl -malic acid. The adsorption may reduce the effective concentration of malonic species in solution and/or increase the amount of REEs adsorbed on the surface, thereby impairing the leaching recovery. Compared with light REEs (LREEs), a stronger adsorption of the HREEs on the surface is observed from electro-kinetic test results. This finding explains why organic acids impose a more positive impact on the leaching recovery of HREEs. By complexing with the HREEs, organic acids can keep the metal ions in solution and improve the leaching recovery. The adsorption of Sc3+ on the surface is the lowest compared with other REEs. Therefore, rather than complexing, the organic anionic species likely play a function of solubilizing Sc from the solid, which is similar to that of hydrogen ions.

It is critical to separate carbon from fly ash due to its increasing amount being produced per year and component requirements for secondary utilizations. Flotation is an efficient technique to fulfill this task. Effects of diesel emulsification using sodium petroleum sulfonate on unburned carbon flotation from a fly ash sample were studied. Flotation tests showed that carbon recovery was increased from 41% to 86% using the emulsified collector at the same dosage level (0.5 kg/ton) as diesel. Zeta potential measurements indicated that both the carbon and emulsified collector droplets carried negative charges within the studied pH range. For fly ash particles with high carbon content, adsorption bands of carbonyl bond (C O) were detected in the FTIR spectra, which agreed with the XPS characterization findings. XPS analysis indicated that the emulsified diesel (ED) collector interacted more intensively with the surface carbon-oxygen groups relative to the normal diesel collector. Finally, the improved efficiency of ED is proved to be related to its polar groups and reduced oil droplet size. The polar groups of ED (mainly sulfonate) interacted with the surface oxygen containing groups (e.g., C O and COOH) through hydrogen bonding and Lewis acid base interaction.

Published version

The pretreatment of middlings and coarse refuse material collected from a Pocahontas No.3 coal source using calcination was investigated for the potential of improving the leaching recovery of rare earth elements. Calcination at 600 °C significantly and preferentially improved light REE (LREE) recovery to values in the range of 80–90% using 1.2 M HCl. The positive effect was due to the increased pore diameter and volume as well as thermal decomposition of the minerals associated with the LREEs. Heavy REE recovery was not increased after calcination at 600 °C due to the need for higher temperatures to achieve thermal decomposition of HREE minerals. Furthermore, some HREEs were also associated with sulfide minerals (e.g., pyrite) which were transformed into low-solubility oxides (e.g., hematite) after roasting at 600 °C. Based on the leaching characteristics of the major elements (Fe, Al, Ca and Mg) and REEs along with SEM-EDX data, it was concluded that REEs in the two samples mainly occurred as phosphate minerals. In the middlings, some of the minerals were completely encapsulated by kaolinite, which was less apparent in the coarse refuse. In addition, it was found that a portion of the REEs (10–25%) in the samples were associated with the organic matter and micro-dispersed minerals in the organic matrix, was released after calcination and easily recovered using 0.1 M (NH4)2SO4 solution at pH 5. Scandium primarily occurred in mineral forms with minimum amounts associated with ion-adsorbed clays and organic association.

In this study, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) was introduced as a depressant for the flotation separation of apatite from calcite. The micro-flotation test results showed that good floatability of both apatite and calcite were obtained at around pH 8.5 when using sodium oleate (NaOl) as collector. Mixed minerals flotation test results showed that an efficient separation of apatite from calcite was achieved using PBTCA as depressant, which presented a selective depression for the calcite. Zeta potential measurements indicated that the addition of PBTCA prior to NaOl did not interfere the interaction between NaOl and apatite while it decreased NaOl adsorption on calcite surface.

The effect of depressant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on the flotation separation of smithsonite from calcite was studied by micro-flotation and electro-kinetic tests. The micro-flotation results showed that good floatability of both smithsonite and calcite were achieved in the presence of sodium oleate. The depressant PBTCA selectively depressed calcite without interfering the floatability of smithsonite. The mixed minerals flotation results showed that efficiency separation of smithsonite from calcite was achieved using PBTCA as the depressant. Zeta potential measurements indicated that NaOl was able to adsorb on the PBTCA pre-treated smithsonite surface, but failed to adsorb on the PBTCA pre-treated calcite surface.

Despite that the negative effects of lizardite on pentlandite flotation have been realized, the lizardite effects under different slurry pH have not been sufficiently investigated. Micro-flotation test results showed that pentlandite recovery gradually decreased with the increase in slurry pH when lizardite slime existed. Both electro-kinetic tests and turbidity measurements indicated that hetero-coagulation between the pentlandite and lizardite particles occurred in the entire pH range, which failed to explain the lower recovery at high slurry pH. Zeta potential distribution measurements and sedimentation tests suggested that self-coagulation among lizardite particles occurred at higher pH, which increased the amount of lizardite slime coated on the pentlandite surfaces and thus reducing collector adsorption and flotation recovery. The particle interaction in the pentlandite/lizardite flotation system was investigated using DLVO theory and microscope observation. The findings of the study will contribute to the improvement in pentlandite flotation by regulating the particle interactions.

Effects of sodium chloride on the sulfidization flotation of cerussite (PbCO3) were investigated by micro-flotation tests, adsorption tests and zeta potential measurements. The micro-flotation test results indicated that sodium chloride effectively improved the sulfidization flotation performance of cerussite. The electrical double layers of cerussite particles were compressed in sodium chloride solution, thus providing more lead sites on the cerussite surface and promoting the adsorption of sulfide ions. In sodium chloride solution, more lead sulfide species were formed on the cerussite surfaces and improved its sulfidization flotation performance.

A novel method to improve carboxymethyl cellulose (CMC) performance in talc flotation is described in this paper. Micro-flotation results showed that using CMC as the depressant, strong depression on talc floatability was observed when the pulp pH was adjusted from low (4.0) to high (8.5), which improved the separation performance between chalcopyrite and talc. Zeta potential measurements illustrated that talc surface charge was less negative when the pH was regulated from acid to base than the situation that the pulp pH was altered from base to acid. ICP test and XPS results indicated that more magnesium ions were dissolved from the talc lattices at pH 4 and the hydrolyzed species of magnesium cations were adsorbed onto the talc surfaces when the pulp pH was adjusted to 8.5, and thus promoting the CMC adsorption on the talc surfaces, which further decreased its floatability.

Selective depression of calcite in a monazite-calcite flotation system was systematically studied using micro-flotation and electrokinetic tests as well as X-ray photoelectron spectroscopy (XPS) characterization and solution chemistry calculations. Monazite was found to be depressed by both sodium silicate and sodium hexametaphosphate when calcium ions appeared in solution. It was hypothesized that co-adsorption of calcium species (CaHCO3+ and CaCO3(aq)) and Si ( OH ) 4 as well as SiO ( OH ) 3 - via hydrogen bonding formed a compact layer over the monazite surface, thereby reducing octanohydroxamic acid adsorption by steric hindrance. The use of citric acid or EDTA formed soluble chelates (e.g. CaCit− and CaEdta2−) with the calcium ions which negated the flotation suppression effect. An XPS study indicated that both EDTA and citric acid chemically adsorbed on the monazite surface, while the adsorption on the calcite surface was achieved mainly through hydrogen bonding. EDTA was more effective than citric acid due to two reasons: (i) citric acid itself presented stronger depression effects and (ii) citric acid has weaker chelating properties for calcium. Using 2.5 × 10−4 M octanohydroxamic acid, 0.05 g/L sodium silicate and 6 × 10−5 M EDTA, monazite recovery of more than 90% was achieved while recovering only 20% of the calcite.

Rare earth elements and yttrium (REY) have attracted considerable attention over the last decade because of their vital roles in clean energy, consumer product, national defense and security applications, among other uses. Due to the retention of REY during coal burning, coal combustion ash is considered as potential alternative sources for REY. Understanding the content, speciation, retention and/or transformation behavior of REY during coal combustion not only expands our knowledge of the combustion behavior of the trace elements in coal, but also provides basis for modeling REY partitioning during coal combustion and for developing economically viable REY recovery technologies. This review makes a critical summary of recent progress in the study of REY in coal ash. The contents and the extraction potentials of REY in coal ash derived from 15 major coal-producing countries worldwide were summarized and evaluated. Various analytical methods for determining REY bulk contents and speciation, together with the solid sample pretreatment, analytical accuracy and precision, advantages and disadvantages were summarized and compared. Modern analytical approaches combined indirect methods (e.g., sequential extraction) shed light on the physical distribution, mineralogy, and the chemical state of REY in coal ash. Three types of REY occurrences in coal ash, including Si-Al glassy association, discrete minerals or compounds, and organic association (bound with unburned carbon) were defined in the review. The glassy association can be further divided into REY minerals closely bound to glass phases and dispersed throughout the glassy structure. REY partitioning in various emission streams, the size distribution, and their enrichment behavior in coal ash were discussed. Thermal behavior and transformation of various REY forms in coal during combustion process, including organic-associated REY, REY phosphates, REY carbonates, clay-bound REY and among others were summarized. Two possible retention mechanisms of REY by aluminosilicate glass at boiler temperature were proposed: the incorporation of the individual REY phases into the glass as inclusions and the diffusion of REY phases throughout Si-Al glass structures in the melting process. Feed coal mineral types, mineral-mineral associations, boiler conditions, and other factors control the retention process. After coal combustion, the speciation of REY in fly ash may be modified by the reactions of REY phases with flue gas components. Further, an overview of REY transformation mechanisms during coal combustion was deeply discussed. Finally, current extraction techniques for REY recovery from coal combustion ash were introduced. Future outlooks and research problems were also identified.

Leaching recovery of rare earth elements (REEs) from two natural kaolinite samples were investigated in this study. Using standard leach conditions without pretreatment, only 10% and 56% of the total REEs were leached from the raw samples, respectively. However, pretreatment by calcination at temperatures between 500 °C and 900 °C increased the leaching recovery of total REEs to values as high as 93% for both samples. Mineralogical characterization and acid leaching results suggested that the decomposition of the kaolinite structure occurs as a function of calcination temperature. Comparisons between the REEs and the major constituent elements of kaolinite showed that their leaching characteristics contrasted. Moreover, sequential chemical extraction results suggested that the fractions of REEs occurring in an ion-adsorption form were negligible. Therefore, the REEs were primarily associated with REE-bearing minerals of which, a portion was encapsulated in kaolinite aggregates while the remaining existed as liberated particles. These association characteristics were proven through SEM-EDX analysis. Based on the mineralogy characterization, acid leaching, and sequential chemical extraction results, it was concluded that the REEs have complicated modes of occurrence and association characteristics with kaolinite. The positive impacts of calcination on the leaching recovery of REEs are likely due to two mechanisms, i.e., (1) liberation of the encapsulated REE-bearing minerals through expansion of the kaolinite aggregates, and (2) conversion of the REE-bearing minerals into more soluble forms.

An innovative self-designed medium was packed in a bench-scale flotation column to study its influence on the flotation recovery of bauxite. Computational fluid dynamics (CFD) simulation was conducted to reveal the impact of the packing medium on the turbulent characteristics of collection zone in the column. Simulation results show that multilayer packing of the medium divides the collection zone into small units having different turbulent intensities, which is more suitable for flotation separation. The packing medium decreases the turbulence kinetic energy (from 1.08 &times, 10&minus, 2 m2/s2 to 2.1 &times, 3 m2/s2), turbulence eddy dissipation (from 3.71 &times, 2 m2/s3 to 9.8 &times, 3 m2/s3) and axial fluid velocity of fluid in the column. With three layers of packing, the recovery of Al2O3 increased by 2.11% and the aluminum to silicon content ratio of the concentrate improved from 5.16 to 9.72.

In this paper, the effect of sodium alginate (SA) on the flotation separation of molybdenite (MoS2) from chalcopyrite using kerosene as collector was systematically investigated. The results of single-mineral micro-flotation tests indicated that SA exhibited strong depression on chalcopyrite flotation while it imposed no impact on the floatability of molybdenite. However, in the chalcopyrite–molybdenite mixed-mineral flotation system, the presence of chalcopyrite significantly increased the depressing effect of SA on molybdenite flotation, leading to a considerable reduction in the flotation selectivity. The negative impact of chalcopyrite on the performance of SA in molybdenite flotation was eliminated by adding a certain dosage of kerosene prior to SA. A concentrate containing 53.43% of molybdenum (Mo) was obtained at 76.90% of recovery using 19 mg/L kerosene and 40 mg/L SA at pH 5.4. Zeta potential measurements indicated that the adsorption of SA on chalcopyrite surfaces was stronger than that on molybdenite surfaces, which agreed with the single-mineral flotation test results. The adsorption of SA on chalcopyrite was further confirmed to be chemisorption by Fourier-transform infrared spectroscopy (FTIR) spectra analyses. When Cu2+ appeared in solution, the flotation of molybdenite was strongly depressed by SA. Mechanism analyses indicated that more active sites were generated on molybdenite surfaces after the addition of Cu2+, thus promoting the adsorption of SA. Published version

Acute myocardial infarction (AMI) induced by ischemia hypoxia severely threatens human life. Cell apoptosis of neurocytes was identified to mediate the pathogenesis, while the potential mechanism was still unclear. Sprague Dawley (SD) rats were used to establish the AMI rat model. Real-time polymerase chain reaction (PCR) and Western blot were performed to detect gene expression in mRNA and protein levels, respectively. A TUNEL assay was carried out to determine cell apoptosis. The relationship between SRY-related HMG-box (SOX7) and miR-128 was verified using luciferase reporter assay. The expression of SOX7 was decreased, while miR-128 was increased in AMI rats and ischemia hypoxia (IH) induced H9c2 cells. Hypoxia induction significantly promoted the expression of interleukin (IL)-33 and soluble ST2 (sST2), and also promoted cell apoptosis. MiR-128 targets SOX7 to regulate its expression. Down-regulated miR-128 reversed the effects of IH on expression of SOX7, sST2 and cell apoptosis, while down-regulated sST2 abolished the effects of miR-128 inhibitor. In addition, overexpressed IL-33 abolished the effects of miR-128 inhibitor that induced by IH on the expression of SOX7 and cell apoptosis. In vivo experiments validated the expression of miR-128 on cell apoptosis. The present study indicated that miR-128 modulated cell apoptosis by targeting SOX7, which was mediated by IL-33/sST2 signaling pathway.

Recovery of rare earth elements (REEs), especially heavy and critical REEs, from alternative resources such as coal refuse has recently become increasingly important. A natural leachate containing 6.14 ppm of REEs with a pH value of 2.70 was collected from a coal coarse refuse pile and utilized as a feedstock for REE recovery tests. The pH value of the natural leachate was gradually increased in a step-wise manner using a sodium hydroxide solution which produced several precipitates. A precipitate containing about 1.1% total REEs was obtained in the pH range of 4.85–6.11 while recovering >80% of the REEs contained in the original leachate. The leaching and staged precipitation process enriched both the critical and heavy REE fractions. The ratios of heavy-to-light (H/L) and critical-to-uncritical (C/UC) REEs in the precipitate were much higher than the coarse refuse material (H/L: 1.54 vs 0.21, C/UC: 1.51 vs 0.34). Additionally, the precipitate contained 18.4% Al, 1.7% Zn, 1.4% Cu, 1.1% Mn, 0.5% Ni and 0.2% Co. A solution chemistry study indicated that the hydroxide and hydroxysulphate precipitates of Al, Si and Cu produced in the pH range of 4.85–6.11 contributed to the fractionation of the REEs and other metal ions such as Zn, Mn and Co to the precipitate. The iron hydroxide precipitates formed at lower pH values did not contain a significant amount of REEs. An explanation may be the competitive adsorption between Al, which was present at higher solution concentrations, and REEs on the iron hydroxide and/or hydroxysulphate precipitate surfaces as proven by results of precipitation tests conducted on model solutions. A product containing 94% of a rare earth oxide mix was obtained by re-dissolution of the REE enriched precipitates followed by selective precipitation using oxalic acid. The overall results including an economic assessment indicate that leachate solutions generated naturally from coarse coal refuse may be a valuable source of critical and heavy REEs that can be effectively recovered and concentrated using staged precipitation.

Objective: To determine the underlying mechanism of miR-34b/c in regulating doxorubicin (Dox)-induced myocardial cell injury. Methods: The viability of mouse myocardial cells HL-1 was detected by MTT assay. The apoptosis of HL-1 cells was detected by TUNEL assay. mRNA expressions of ITCH, TNF-α and IL-6 were measured by qRT-PCR. Protein levels of ITCH, NF-κB, TNF-α and IL-6 were measured by western blot. Dual luciferase assay was performed to detect the regulation of miR-34b/c on ITCH. Mouse model of cardiomyopathy was induced by intraperitoneal injection of Dox. Results: Dox reduced HL-1 cell viability and activated NF-κB pathway in HL-1 cells. miR-34b/c expressions were gradually up-regulated and ITCH expression was gradually down-regulated in Dox-treated HL-1 cells. miR-34b/c expression had negative correlation with the mRNA expression of ITCH. Besides, ITCH was a target of miR-34b/c. miR-34b/c mimic reduced cell viability, suppressed ITCH expression, increased TNF-α and IL-6 level, and promoted NF-κB expression in nucleus and cytoplasm of HL-1 cells. Whereas silencing miR-34 protected HL-1 cells through regulating ITCH. Finally, we demonstrated miR-34 antagomir-protected myocardial cells in mouse model of cardiomyopathy. Conclusion: miR-34b/c decreased HL-1 cell viability and promoted the secretion of proinflammatory cytokines in Dox-induced myocardial cells through ITCH/NF-κB pathway.

The majority of rare earth elements (REEs) existing in the feed to coal preparation plants report to the coarse refuse streams which are transported for permanent storage in contained piles. In this study, an integrated flowsheet was developed based on laboratory test data which combines physical separation, pyrite bio-oxidization, heap leaching, selective precipitation and solvent extraction processes. The test data was obtained from (1) characterization of a number of natural leachate and solid samples collected from different preparation plants which process coals from a number of coal seams and (2) laboratory acid leaching and selective precipitation tests results. The highly-valued critical REEs (i.e., Y, Nd, Eu, Tb and Dy) were selectively leached from the refuse samples in the natural environment due to the acid generated by pyrite oxidization. The leachate samples were evaporated to remove water and obtain residual solids (i.e., dissolved solids in the leachates). The total REE content in the dissolved solids from a given leachate sample was 380 ppm, which was higher than the REE content of the coarse refuse material that generated the leachate (322 ppm). Acid leaching tests recovered as much as 80% of the total REEs from the coarse refuse samples using a 1.2 M sulfuric acid solution. Afterwards, the pH of the leachate was increased in a step-wise fashion which resulted in the production of precipitates containing 0.3–1.1% total REEs. A significant amount of contaminants, such as Fe, Al, and Ca, were eliminated in the sequential precipitation process, which allowed further upgrading using oxalic acid precipitation and/or solvent extraction. In the proposed flowsheet, the coarse refuse is arranged in heap leach pads and the acid needed for REE leaching is primarily produced from pyrite bio-oxidization, which enhances the selectivity of REE recovery and significantly reduces the cost. The successful application of the flowsheet would result in significant benefits to both the coal and rare earth industries.

The flotation separation of scheelite from calcite using sodium humate (SH) as a potential depressant has been studied through micro-flotation experiments, zeta potential and Fourier transform infrared (FT-IR) spectra measurements. The flotation results indicate SH exhibited selective depression effect on calcite in the presence of sodium oleate, achieving the flotation separation of scheelite from calcite. Zeta potential results indicate that SH strongly absorbed on calcite surface but negligibly on scheelite surface, which prevents the adsorption of sodium oleate on calcite surface. The FT-IR results also show that SH can be adsorb on the surface of calcite. Results shown a higher Ca density on the calcite than on scheelite surface, and that calcite can accommodate the interaction of SH.

In order to clarify the effect of copper contents on the corrosion resistance of stainless steel in biological environment, 316L-0Cu (wt%), 316L-1.5Cu (wt%), 316L-4.5Cu (wt%) and 316L-7.5Cu (wt%) coatings were prepared by laser melting deposition (LMD), and the microstructure and corrosion behavior in simulated body fluids (SBF) were studied. The results show that the planar growth, cellular crystal and dendritic microstructure are formed in the four kinds of LMD-produced coatings. With the increase of copper contents, the microstructure is refined, the corrosion resistance is decreased first and then is increased. This is because the copper oxide precipitates at the high-density grain boundaries, which can promote the passivation behavior. Under the combined action of Cr2O3 and Cu2O, the corrosion resistance of 316L-7.5Cu coating is closest to that of 316L-0Cu coating.

Phosphatic clay is a waste material produced during the beneficiation of phosphate ore, which likely poses severe environmental problems. In this study, a phosphatic clay containing 258 ppm of total rare earth elements (REEs) was used as a feedstock for REE recovery. By reacting with 0.1 M HCl at 75 °C for 3 h, around 36 % of light REEs and 65 % of heavy REEs were extracted from the raw material. However, after calcination pretreatment at 600 °C for 2 h, the recovery was increased to 73 % and 81 %, respectively, which are close to the recoveries obtained from the raw material using a much higher acid concentration of 1.2 M. Based on the findings from sequential chemical extraction tests and scanning electron microscopy analysis, the positive impact was explained by the decomposition and conversion of REE-bearing minerals into more leachable species. Using a higher calcination temperature of 900 °C, recovery of both the light and heavy REEs was largely reduced relative to the raw material. Mineralogical analyses showed that the dominant minerals existing in the material, such as muscovite, were fused and sintered during the calcination at 900 °C. These reactions likely caused the decreases in the recovery. The results and findings from this study will contribute to the beneficial uses of phosphatic clay and the production of REEs.

The surface charge mechanisms of monazite were studied using electrokinetic tests, solution equilibrium calculations, crystal structure characterization, and electrostatic model predictions. The isoelectric point (IEP) of a natural monazite sample was found to occur at pH 6.0. To allow a theoretical study of the surface charge on monazite, fundamental values associated with cerium monazite (CePO 4 ) were utilized to quantify the isoelectric point (IEP) and point of zero charge (PZC) using solution equilibrium calculations and electrostatic models. The IEP and PZC of the cerium monazite were determined to be equal with a pH value of 7.2. Hydroxyl and hydrogen were found to be potential determining ions and preferential hydrolysis of the lattice ions played a minor role. The findings support the hypothesis that the charge of monazite surfaces in water is a result of protonation/deprotonation reactions. The difference in the IEP values obtained for the natural monazite and cerium monazite along with the wide range of values reported in literature may be partially explained by the amount of carbon dioxide dissolved in solution. When equilibrating with carbon dioxide at 10 –3.5 atm partial pressure, the IEP of the cerium monazite shifted to a solution pH value of 4.5.

The adsorption mechanism of octanohydroxamic acid (OHA) on monazite was studied using kinetic, isotherm, and thermodynamic adsorption tests as well as FTIR, titration, and micro-flotation experiments. The adsorption mechanism was described as a chemisorption/surface precipitation process. At low OHA concentrations, adsorption occurred by chemisorption as a result of the reaction between surface active sites and OHA molecules. With an increase in concentration and interaction time, surface precipitation occurred. For chemisorption, adsorption was an exothermic and entropy driven process and maximum adsorption was achieved at pH 9.0 due to more active sites. In an acidic environment, such as pH 3.0, adsorption was achieved via chemisorption and hydrophobic bonding. However, a strong basic and higher temperature environment contributes to surface precipitation of basic rare earth hydroxamate. FTIR tests showed the movement of CH 2 band position from 2924 cm − 1 to 2920 cm − 1 with increases in pH values from 3.0 to 6.0, 9.0, and 11.0, which corresponds to the status of chemisorbed and surface precipitated OHA, respectively.

The dissolution of minerals provides elevated concentrations of alkaline earth metal ions such as calcium (Ca 2+ ) in water which may have a significant influence on flotation performance. The effects of Ca 2+ ions dissolved from calcite surfaces on the flotation performance of a monazite-calcite system have been investigated using micro-flotation tests followed by fundamental collector adsorption studies. The results indicate that specially adsorbed CaOH + via hydrogen bonding competed with hydroxamic acid for the phosphate-oxygen active sites on the monazite surface and decreased its hydrophobicity due to hydration. Electrostatically adsorbed CaOH + on monazite increased the adsorption density of hydroxamic acid through a chelating interaction. At higher dosages of calcium and hydroxamic acid, bulk and surface precipitation of calcium-hydroxamate occurs in the monazite-calcium-hydroxamic acid system.

The separation of carbon from fly ash significantly improves the potential end-us of combustion byproducts. Froth flotation is the most effective separation technique for ultrafine material. Diesel dosages, conditioning time, and impeller rotating speeds' influences on carbon flotation performance were studied. From flotation products, + 25 and − 25 μm fractions were screened out to study their different flotation behaviors. At a given impeller speed, carbon recovery of +25 μm fraction increased significantly from 38.46% to 74.22% over a range of diesel dosage from 0.5 to 4.5 kg/t, while that of -25 μm fraction was relatively constant at 85% over the same diesel dosage range. Morphologies and microstructures of coarse and fine carbon were studied by using scanning electron microscope. Porous structures of coarse carbon were observed. It's difficult for diesel droplets of several microns to penetrate the pores of coarse carbon particles, which increases diesel consumption. Increasing impeller speeds from 1200 to 1600 rpm during conditioning improved the carbon recovery and separation efficiency of + 25 μm fraction by 79% and 110%, respectively, which significantly reduced diesel consumption. Flotation kinetic studies indicate that increasing impeller speeds during conditioning stage can improve the flotation rate constant and maximum carbon recovery for both + 25 and − 25 μm fractions.

Acid mine leachate (AML) may be a significant source of rare earth and other critical elements needed for the manufacturing of advanced electronics and renewable energy technologies. A systematic study was performed on a natural leachate collected from a coal preparation plant that treated bituminous coal containing elevated amounts of pyrite. The leachate contained 1.96 ppm total REEs, 2.52 ppm Zn, 2.15 ppm Ni, 1.22 ppm Cu, 0.77 ppm Co, and 25 ppm Mn. Sequential precipitation using simple pH control generated a pre-concentrate containing 0.82% total REEs, 1.08% Zn, 0.91% Ni, 0.50% Cu, 0.34% Co, 7.1% Mn. The pre-concentrate was further treated by re-dissolution using a 10 M HNO3 solution, which resulted in a solution pH of 1.5. The addition of oxalic acid to selectively precipitate the REEs followed by roasting of the precipitate generated a product containing >98% rare earth oxides. More than 95% of the Cu and Zn were recovered from the residual liquid using Na2S at pH 2 and 3, respectively. The CuS and ZnS contents in the corresponding concentrates were 60% and 58%, respectively. The majority of the Co and Ni remained in the residual liquid. Based on these findings, a process flowsheet was developed to recover the REEs and critical metals from AML.

Lithium recovery from the density fractions of Baker (namely West Kentucky No. 13) seam coal was investigated in this study. Proximate and elemental analyses showed that lithium contents in the 1.8–2.2 SG and 2.2 SG sink fractions were 185 ppm and 150 ppm, respectively, which are significantly higher than the average content of coal sources (12 ppm) and coal ashes (66 ppm) worldwide. Moreover, due to the high lithium contents and mass distribution, nearly 90% of the lithium present in the Baker coal sample was distributed in the two density fractions. Direct leaching using a HCl solution resulted in less than 10% lithium recovery, which was due to nearly 90% of the lithium being associated with insoluble solids as determined by the results from sequential extraction tests. Calcination of both density fractions under 600 °C for two hours followed by leaching resulted in recovery increases in the range of 70% to 80%. The pyro-metallurgical pretreatment step converted most of the associated lithium minerals to more easy-to-leach forms such as carbonate and metal oxide. Based on mineralogy characterization and leaching test results, it was concluded that the positive effects of calcination on lithium leachability resulted from the dehydration and disintegration of kaolinite as well as dehydroxylation and expansion of muscovite/illite. An analysis of the leaching kinetics revealed that the leaching rate of lithium was controlled by interface transfer and diffusion across the product layer and was negatively impacted when the calcination temperature exceeded 600 °C due to sintering of the kaolinite.

The impacts of calcination on the leaching recovery of rare earth elements (REEs) and other critical metals from a Baker seam coal refuse material were investigated in this study. Acid leaching test results showed that leaching recovery of the REEs, especially the light REEs, was increased significantly from around 24% to 80–90% after calcination under 600–750 °C for two hours. By considering the major element leaching kinetics and the mineralogical changes of the dominant minerals caused by calcination, two mechanisms were proposed for the improved leaching performance: (1) decomposition of difficult-to-dissolve REE-bearing minerals into soluble forms; and (2) liberation of REE-bearing minerals encapsulated in clays after calcination due to the dehydration and disintegration of the layered clay structure. Sequential chemical extraction tests showed that a significant fraction (around 75%) of the REEs in the raw material were present in an insoluble form. After calcination under proper temperatures (600–800 °C), the majority of the insoluble light REEs (LREEs) were converted into soluble forms. Changes in the modes of occurrence of the LREEs and phosphorous based on leaching rate and sequential leaching correlated well as a function of the calcination temperature. This finding in addition to SEM-EDX results tends to indicate the potential that the LREEs occur primarily as rare earth phosphates such as monazite in the untreated coal refuse material. The acid leaching and sequential chemical extraction results show that co-extraction of REEs and other critical metals such as Co, Mn, and Li is possible using a calcination-acid leaching procedure.

The modes of occurrence associated with rare earth elements (REEs) in bituminous coal sources were evaluated along with their potential recovery by calcination treatment at 600 ℃ followed by sequential extraction. The coal samples were collected from three different resources, i.e., Fire Clay, West Kentucky No. 13, and Illinois No. 6 seams. Sequential extraction tests indicated that the majority of REEs in the calcined samples occurred as metal oxides especially for the West Kentucky No. 13 calcined material (54% of total REEs), which is distinct from untreated coal and combustion byproducts from pulverized coal boilers reported in literature. In addition, heavy REEs were more likely associated with easily dissolvable forms (i.e., ion-exchangeable, carbonates, and metal oxides). The calcined samples were leached under weak acidic conditions with and without adding ammonium sulfate to recover REEs. About 13%, 24%, and 20% of the REEs were extracted from the Fire Clay, West Kentucky No. 13, and Illinois No. 6 materials, respectively, by leaching at pH 4.0. The addition of 1 M ammonium sulfate further increased the recovery values to 18%, 45%, and 32%, respectively. In addition, about 64% of HREEs were extracted from the West Kentucky No. 13 calcined material under this condition. As such, a significant portion of the REEs can be easily extracted from the samples obtained by calcining the coals at 600 ℃.

Rare earth elements (REEs) contained in coal and associated mineral matter exist in several forms including micro-dispersed minerals, ion adsorption onto clay surfaces, and chemically bound. Tests found that REEs can be effectively recovered from certain components of three coal sources by leaching under mild conditions followed by solvent extraction. A range of pH values were evaluated at solution temperatures of 25 and 75 ℃. When using 1.2 M of sulfuric acid, nearly 85% recovery of the REEs was extracted from the middlings material collected from an operating plant. Acid leaching of a second middling source from another plant resulted in 60% of the total REEs being recovered under the same leaching conditions. Solvent extraction treatment of the leachate produced from six different coal sources resulted in products containing up to 50% total REEs from feedstocks starting with around 300 ppm.

Flotation separation of scheelite from calcite is difficult due to the similarities in their surface properties. In this work, the flotation behavior of scheelite and calcite using oxidized paraffin soap(OPS), benzohydroxamic acid(BHA) and the mixed OPS/BHA collectors was investigated through micro-flotation experiments. The flotation results of single mineral experiments demonstrated a higher selectivity for the flotation of scheelite from calcite at pH 9 than individual OPS and BHA when using water glass as depressant. In order to probe the validity of the findings, mixed binary minerals experiments, contact angle and zeta potential experiments were also carried out successfully. Accepted version

Getting magnetite concentrate with extremely high Fe grade using reverse flotation method has become increasingly important due to the enhanced requirement of iron making industry. The coagulation in magnetite-concentrate flotation system may impose negative effect on flotation performance. This paper combined the DLVO calculation and microscope observation to study the coagulation behavior in the system. The result shows that the coagulation between fine magnetite and coarse silica particle is very likely to occur with energy barrier 1.5 × 10 −18 J at pH 10.0, which is much smaller than 1.6 × 10 −17 J and 3.3 × 10 −17 J for fine magnetite and fine magnetite-coarse magnetite particles. The coating of fine magnetite particle on silica surface was observed under microscope. Mechanical scrubbing increases the concentrate Fe grade and recovery by 1.5% and 8.5% respectively. Magnetite concentrate of 67.9% Fe grade and 71.5% Fe recovery was finally obtained.

The influence of conditioning on the flotation of pyrrhotite in the presence of chlorite was investigated through flotation tests, sedimentation tests, and X-ray photoelectron spectroscopy (XPS) analysis. The flotation results show that chlorite slimes dramatically impair the flotation of pyrrhotite. Sedimentation and flotation tests reveal that conditioning can effectively remove chlorite slimes from pyrrhotite surfaces, resulting in an enhanced flotation recovery of pyrrhotite. When mixed minerals were conditioned under the natural atmosphere, a faster conditioning speed and longer conditioning time decreased the flotation recovery of pyrrhotite. However, when mixed minerals were conditioned under a nitrogen atmosphere, a more intensive conditioning process provided better flotation results. XPS analyses illustrate that a faster conditioning speed and longer conditioning time under the natural atmosphere accelerates the oxidation of pyrrhotite, leading to a decrease in the flotation recovery of pyrrhotite. Published version

The activation mechanism of Pb(II) on the flotation of wolframite was systematically investigated. Micro-flotation test results showed that Pb(II) effectively improved the flotation of wolframite in the presence of benzyl hydroxamic acid (BHA). Maximum floatability of wolframite was achieved at approximately pH 8.5. Adsorption of the hydrolyzed species of Pb(II) occurred at this pH value, which provided more activated sites on the wolframite surface. As such, BHA-Pb complexes were formed on the wolframite surface, which increased the BHA adsorption. In addition, BHA-Pb complexes were also formed in solution, which replaced the Fe and interacted with the Mn on the wolframite surface. These findings were proved by the results of zeta-potential measurements, adsorption measurements, solution chemistry calculations, Fourier transform infrared spectroscopy (FTIR) analysis, and X-ray photoelectron spectroscopy (XPS) characterization. Accepted version

The effect of extraordinary degradation of phenol organics on the SnO 2 -Sb 2 O 3 /Ti electrode is investigated through experimental research and theoretical analysis. The phenol organics contained 4-chloro-phenol, 4-bromo-phenol, and 2-iodo-phenol. At a current density of 4 mA cm -2 and an electrolysis time of 12 h, the degradation efficiency of the phenols was over 98% with a relatively short degradation time, whereas the degradation time of the PbO 2 /Ti electrode surpassed 40 h while delivering 100% disposal efficiency. Therefore, the effectiveness of electrochemical (EC) oxidation by the SnO 2 -Sb 2 O 3 /Ti was superior to that of the PbO 2 /Ti electrode. At the same time, the SnO 2 -Sb 2 O 3 /Ti had higher oxygen generation potential and lower electron consumption than the other electrodes. This was mainly due to the effect of the middle Sb 2 O 3 layer, which due to its high porosity and good catalytic effect, contributed to a better catalysis than the SnO 2 part.