Surface chemistry considerations of gangue dissolved species in the bastnaesite flotation system

ABSTRACT: Inefficient flotation of bastnaesite remains a challenge in the production of rare earth elements. This study aimed to investigate the dissolution and adsorption behaviour of species that are commonly released into bastnaesite flotation pulp from Ca/Ba-bearing gangue minerals. The influence and corresponding mechanisms on the bastnaesite mineral surface and collectors, namely sodium oleate (NaOL), were evaluated experimentally based on micro-flotation, zeta potentials, in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-Ray photoelectron spectroscopy (XPS) analyses. The flotation recovery of bastnaesite significantly decreased from ∼95% to ∼25%, ∼15%, ∼80%, ∼25% when exposed to calcite, fluorite, barite, and mixed dissolved species, respectively. The zeta potential of bastnaesite was pH sensitive, indicating that H+ and OH− determine the surface potential of bastnaesite. Solution chemistry analyses revealed that the presence of the dissolved species differed at various pH values. In situ ATR-FTIR demonstrated the different effects of the dissolved species from calcite, fluorite, and barite on collector adsorption. The former two dissolved species mainly depressed the chemisorption of the NaOL monomers (RCOO‒), whereas calcite also affected the physical adsorption of the oleic acid molecular dimer (RCOOH·RCOO‒). Moreover, the barite dissolved species only affected the physical adsorption of the NaOL species. The results of XPS analysis revealed that dissolved species from these three gangues could pre-adsorbed onto bastnaesite and affected the interaction with the collector. Density functional theory calculations were employed to provide further theoretical insights into the interactions between the dissolved species from calcite, fluorite, and barite and NaOL

Effects of Spodumene Flotation Tailings on Mechanical Properties of Acid-Based Geopolymer Mortar

This study focuses on using spodumene flotation tailings (SFT) to prepare phosphoric acid-activated metakaolin geopolymer, in which the replacement of metakaolin (MK) by a high percentage (up to 75 wt.%) of tailings was achieved. The compressive strength of geopolymer mortar was significantly improved with SFT as aggregates. In addition, the mechanical properties could also be enhanced by an increased concentration of phosphoric acid (H3PO4) solution or a decreased aggregate particle size. The optimized geopolymer mortar composite was SFT:MK = 3:1, which was activated by H3PO4 solution with a concentration of 51 vol%, followed by curing at 55 °C for 24 h. On the other hand, properties of the geopolymer mortar could also be affected by the morphology of the aggregates. For example, SFT as aggregates could produce more interconnected pores compared to standard sand. The major chemical structural units of geopolymer mortar were -P-O-Al- and AlPO4, which could be spontaneously generated according to the thermodynamic calculation results. Finally, many aluminum ions and a small amount of silicon ions could be leached from the tailings under acidic conditions

Drug Combinations to Prevent Antimicrobial Resistance: Various Correlations and Laws, and Their Verifications, Thus Proposing Some Principles and a Preliminary Scheme

Antimicrobial resistance (AMR) has been a serious threat to human health, and combination therapy is proved to be an economic and effective strategy for fighting the resistance. However, the abuse of drug combinations conversely accelerates the spread of AMR. In our previous work, we concluded that the mutant selection indexes (SIs) of one agent against a specific bacterial strain are closely related to the proportions of two agents in a drug combination. To discover probable correlations, predictors and laws for further proposing feasible principles and schemes guiding the AMR-preventing practice, here, three aspects were further explored. First, the power function (y = axb, a > 0) correlation between the SI (y) of one agent and the ratio (x) of two agents in a drug combination was further established based on the mathematical and statistical analyses for those experimental data, and two rules a1 × MIC1 = a2 × MIC2 and b1 + b2 = −1 were discovered from both equations of y = a1xb1 and y = a2xb2 respectively for two agents in drug combinations. Simultaneously, it was found that one agent with larger MPC alone for drug combinations showed greater potency for narrowing itself MSW and preventing the resistance. Second, a new concept, mutation-preventing selection index (MPSI) was proposed and used for evaluating the mutation-preventing potency difference of two agents in drug combination; a positive correlation between the MPSI and the mutant prevention concentration (MPC) or minimal inhibitory concentration (MIC) was subsequently established. Inspired by this, the significantly positive correlation, contrary to previous reports, between the MIC and the corresponding MPC of antimicrobial agents against pathogenic bacteria was established using 181 data pairs reported. These results together for the above three aspects indicate that the MPCs in alone and combination are very important indexes for drug combinations to predict the mutation-preventing effects and the trajectories of collateral sensitivity, and while the MPC of an agent can be roughly calculated from its corresponding MIC. Subsequently, the former conclusion was further verified and improved via antibiotic exposure to 43 groups designed as different drug concentrations and various proportions. The results further proposed that the C/MPC for the agent with larger proportion in drug combinations can be considered as a predictor and is the key to judge whether the resistance and the collateral sensitivity occur to two agents. Based on these above correlations, laws, and their verification experiments, some principles were proposed, and a diagram of the mutation-preventing effects and the resistant trajectories for drug combinations with different concentrations and ratios of two agents was presented. Simultaneously, the reciprocal of MPC alone (1/MPC), proposed as the stress factors of two agents in drug combinations, together with their SI in combination, is the key to predict the mutation-preventing potency and control the trajectories of collateral sensitivity. Finally, a preliminary scheme for antimicrobial combinations preventing AMR was further proposed for subsequent improvement research and clinic popularization, based on the above analyses and discussion. Moreover, some similar conclusions were speculated for triple or multiple drug combinations

Azalomycin F5a Eradicates Staphylococcus aureus Biofilm by Rapidly Penetrating and Subsequently Inducing Cell Lysis

Antimicrobial resistance has emerged as a serious threat to public health. Bacterial biofilm, as a natural lifestyle, is a major contributor to resistance to antimicrobials. Azalomycin F5a, a natural guanidine-containing polyhydroxy macrolide, has remarkable activities against Gram-positive bacteria, including Staphylococcus aureus, a major causative agent of hospital-acquired infections. To further evaluate its potential to be developed as a new antimicrobial agent, its influence on S. aureus biofilm formation was evaluated using the crystal violet method, and then its eradication effect against mature biofilms was determined by confocal laser scanning microscopy, the drop plate method, and regrowth experiments. The results showed that azalomycin F5a could significantly inhibit S. aureus biofilm formation, and such effects were concentration dependent. In addition, it can also eradicate S. aureus mature biofilms with the minimum biofilm eradication concentration of 32.0 μg/mL. As extracellular deoxyribonucleic acid (eDNA) plays important roles in the structural integrity of bacterial biofilm, its influence on the eDNA release in S. aureus biofilm was further analyzed using gel electrophoresis. Combined with our previous works, these results indicate that azalomycin F5a could rapidly penetrate biofilm and causes damages to the cell membrane, leading to an increase in DNase release and eventually eradicating S. aureus biofilm

Receptor activator of NF-kappaB and podocytes: towards a function of a novel receptor-ligand pair in the survival response of podocyte injury.

BACKGROUND: Glomerulosclerosis correlates with reduction in podocyte number that occurs through mechanisms which include apoptosis. Podocyte injury or podocyte loss in the renal glomerulus has been proposed as the crucial mechanism in the development of glomerulosclerosis. However, the mechanism by which podocytes respond to injury is poorly understood. TNF and TNF receptor superfamilies are important in the pathogenesis of podocyte injury and apoptosis. The ligand of receptor activator of NF-kappaB (RANKL) and receptor activator of NF-kappaB (RANK) are members of the TNF and receptor superfamilies. We investigated whether RANK-RANKL is a receptor-ligand complex for podocytes responding to injury. METHODOLOGY/PRINCIPAL FINDINGS: In this study, RANKL and RANK were examined in human podocyte diseases and a rat model of puromycin aminonucleoside nephrosis (PAN). Compared with controls, RANK and RANKL were increased in both human podocyte diseases and the rat PAN model; double immunofluorescence staining revealed that RANK protein expression was mainly attributed to podocytes. Immunoelectron microscopy showed that RANK was localized predominantly at the top of the foot process membrane and the cytoplasm of rat podocyte. In addition, RANK was upregulated in mouse podocytes in vitro after injury induced by puromycin aminonucleoside (PA). Knockdown of RANK expression by small interference RNA (siRNA) exacerbated podocyte apoptosis induced by PA. However, RANKL inhibited significantly the apoptosis of podocytes induced by PA. CONCLUSIONS/SIGNIFICANCE: These findings suggest the increase in RANK-RANKL expression is a response to podocyte injury, and RANK-RANKL may be a novel receptor-ligand complex for the survival response during podocyte injury