Centrifugal Concentrators Research Articles

Platinum-Group Metals in Residual Soils and Potential Efficiency of Their Processing in Gravity Concentrators

The authors analyze geochemical data on residual soils of Svetloborsk and Nizhny Tagil massifs of the Ural Platinum Belt after tests aimed to determine content of platinum group elements, gold and silver in different zones of geological cross section. The scope of the analysis embraces theory of gravity concentration in the flows of suspended matter. The criterion of efficient dressability in gravity concentrators (hydraulic separation coefficient) is adapted as an alternative to the equal-settling factor inclusive of the influence of a particle shape. The presented calculated coefficients of hydraulic separation for different shape particles of olivine and platinum prove that flattened particles are separated more efficiently with centrifugal gravity concentrators. The theory is backed with the experimental data, and the conclusion on applicability of the proposed hydraulic separation coefficient is drawn.

TECHNIQUE AND TECHOLOGY OF RARE-METAL ORES DESINTEGRATION AND GRAVITY-BASED BENEFICATION

On the base of the analysis of centrifugal concentrators designs there has been justified the selection of apparatus for the rare-metal ores benefication. Process of pyrochlore ore grinding in mills of different types has been investigated and the expediency of use of impact-centrifugal action mills to ensure selectivity of minirals disclosure has been founded. Efficient technical and technological parameters of the centrifugal action mills have been justified on the base of active experimental method. The influence of disintegration metheds on technologival indication of rare-metal ore benefication of Mazurovske deposits in centrifugal Nelson concentrator has been analyzed.

Fluidized hydrocyclone for continuous centrifugal concentration

ABSTRACTThe continuous centrifugal concentration for heavy minerals of high mass weight has been a major challenge in the development of centrifugal concentrators. A pilot-scale fluidized hydrocyclone concentrator operating on hydrocyclone and fluidized bed separation was developed for continuous centrifugal concentration of a magnetite–feldspar mixture. It realized a continuous centrifugal concentration for the mixture and achieved an apparent concentration for heavy minerals; its separation performance is greatly related to the feed and water inlet pressures, the number of concentrating rings and the feed solid concentration, which is accordance with the theoretical description on the concentration process. It was concluded that this novel method may provide a potential in the continuous centrifugal concentration for heavy minerals.

Filter-Aided Sample Preparation: The Versatile and Efficient Method for Proteomic Analysis.

Filter-aided sample preparation (FASP) is a versatile and efficient way of processing protein extracts for bottom-up proteomic analysis. The method repurposes centrifugal ultrafiltration concentrators for removal of detergents, protein cleavage, and isolation of pure peptide fractions. FASP can be used for protein cleavage with different proteinases either with single enzymes or in a mode of successive multienzyme digestion (MED)-FASP. The FASP methods are useful for processing of samples ranging in their sizes from submicrogram to several milligram amounts of total protein. They also allow peptide fractionation, and isolation and quantitation of total RNA and DNA acid contents. This chapter describes principles, limitations, and applications of FASP. Additionally detailed FASP and MED-FASP protocols are provided.

Beneficiation of the Nechalacho rare earth deposit. Part 2: Characterisation of products from gravity and magnetic separation

The application of mineral beneficiation techniques to valuable rare earth element (REE) bearing minerals requires a significant amount of research. A previous paper (Jordens et al., 2016) described a series of physical separation processes employed to pre-concentrate rare earth minerals (REM) and reject iron oxide minerals from the Nechalacho Deposit. In addition to grade and recovery information it is important to understand the performance of these separations from a mineralogical perspective. Information on liberation, mineral associations, magnetic properties and size-by-size recoveries can be used to further improve process designs for this deposit.This work employs automated mineralogy (QEMSCAN), scanning electron microscopy and a vibrating sample magnetometer to characterise the products from laboratory gravity separation (Knelson and Falcon centrifugal concentrators) and magnetic separation (varying intensity wet drum magnetic separators). The information gathered is then used to identify the optimum fraction for downstream flotation separation. The selected flowsheet included a Knelson centrifugal concentrator and low intensity drum magnetic separation resulting in a total rare earth oxide (TREO) recovery of 11.75% and a TREO grade of 7.50%.

Beneficiation of the Nechalacho rare earth deposit. Part 1: Gravity and magnetic separation

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.

Concentrating membrane proteins using ultrafiltration without concentrating detergents

Membrane proteins (MPs) are of rapidly growing interest in the design of pharmaceutical products, novel sensors, and synthetic membranes. Ultrafiltration (UF) using commercially available centrifugal concentrators is typically employed for laboratory-scale concentration of low-yield MPs, but its use is accompanied by a concomitant increase in concentration of detergent micelles. We present a detailed analysis of the hydrodynamic processes that control detergent passage during ultrafiltration of MPs and propose methods to optimize detergent passage during protein concentration in larger-scale membrane processes. Experiments were conducted using nonionic detergents, octyl-β-D glucoside (OG), and decyl-β-D maltoside (DM) with the bacterial water channel protein, Aquaporin Z (AqpZ) and the light driven chloride pump, halorhodopsin (HR), respectively. The observed sieving coefficient (So ), a measure of detergent passage, was evaluated in both stirred cell and centrifugal systems. So for DM and OG increased with increasing filtrate flux and decreasing shear rates in the stirred cell, that is, with increasing concentration polarization (CP). Similar effects were observed during filtration of MP-detergent (MPD) micelles. However, lower transmission was observed in the centrifugal system for both detergent and MPD systems. This is attributed to free convection-induced shear and hence reduced CP along the membrane surface during centrifugal UF. Thus to concentrate MPs without retention of detergent, design of UF systems that promote CP is required. Biotechnol. Bioeng. 2016;113: 2122-2130. © 2016 Wiley Periodicals, Inc.

Size-by-size analysis of dry gravity separation using a 3-in. Knelson Concentrator

Centrifugal concentrators have been widely used to recover fine gold over the past few decades, the main drawback being the large volume of water required during the operation. As water is an increasingly important commodity, investigating dry processing to reduce water usage is of great importance. This work investigated using a laboratory scale Knelson Concentrator with a dry feed, and air being used to replace water as the fluidising medium and size-by-size testing of material. A synthetic ore comprised of tungsten and quartz was used to mimic a gold ore. Response surface methodology and central composite design were used for modelling and optimisation with the experimental variables being the motor power (MP) (%), air fluidizing pressure (AFP) (psi) and solid feed rate (SFR) (g/min). The observed results of the three size classes indicated that amongst the three variables; the motor power had the greatest impact when comparing to the other two variables. Different optimum conditions had been found for −425+150μm, −150+53μm and −53μm size fractions and these are 30% MP, 200g/min SFR and 10 psi AFP, 50% MP, 160g/min SFR and 11psi AFP, 65% MP, 200g/min SFR and 11psi AFP, respectively.

A design of experiments investigation into dry separation using a Knelson Concentrator

Enhanced gravity, or centrifugal, separators have revolutionised gold processing over the past decades, significantly increasing the recovery of fine (−100μm) free gold. One of the main drawbacks of centrifugal gravity concentrators is the large volume of water required (even if it is all recycled). With water becoming an ever increasingly important “commodity”, reducing this is of importance both from an environmental and a monetary point of view. This work investigated operating a laboratory scale Knelson Concentrator with a dry feed and using air as the fluidising medium. The feed used was a synthetic mixture of tungsten and quartz, used to mimic a gold ore. The response surface method and central composite design techniques were used to design the experiments and to model the results, with the experimental variables being the bowl speed (G-Level), air fluidising pressure and the feed rate. The models corresponded well to the experimental results, indicating that for this experimental setup, the optimal conditions were a bowl G-Level of 40G, a feed rate of 220g/min and an air fluidising pressure of 8psi.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based profiling as a step forward in the characterization of peritoneal dialysis effluent

Detection of glomerulonephritis and diabetic nephropathy using (i) peritoneal dialysate effluent, (ii) MALDI-TOF MS and (iii) bioinformatics tools.

Processing a rare earth mineral deposit using gravity and magnetic separation

Rare earth (RE) mineral deposits are typically processed using several different unit operations including flotation, gravity, magnetic and electrostatic separation techniques. Two of the most important beneficiation techniques for RE minerals are gravity and magnetic separation. Many RE minerals are found alongside low specific gravity gangue minerals thereby permitting the use of gravity separations to concentrate the heavy value RE minerals. Magnetic separation is used primarily to remove ferromagnetic gangue minerals as well as to separate individual paramagnetic rare earth minerals.This work investigated the use of a wet high intensity magnetic separation (WHIMS) in conjunction with gravity pre-concentration steps (Knelson and Falcon centrifugal concentrators) to beneficiate a rare earth ore. The results of these separation steps are related to the magnetic properties of RE minerals, based on literature and measurements conducted using a vibrating sample magnetometer (VSM).

Active Plasma Membrane P-type H+-ATPase Reconstituted into Nanodiscs Is a Monomer

Plasma membrane H(+)-ATPases form a subfamily of P-type ATPases responsible for pumping protons out of cells and are essential for establishing and maintaining the crucial transmembrane proton gradient in plants and fungi. Here, we report the reconstitution of the Arabidopsis thaliana plasma membrane H(+)-ATPase isoform 2 into soluble nanoscale lipid bilayers, also termed nanodiscs. Based on native gel analysis and cross-linking studies, the pump inserts into nanodiscs as a functional monomer. Insertion of the H(+)-ATPase into nanodiscs has the potential to enable structural and functional characterization using techniques normally applicable only for soluble proteins.

Extracellular Acidosis Is a Novel Danger Signal Alerting Innate Immunity via the NLRP3 Inflammasome

Local acidosis has been demonstrated in ischemic tissues and at inflammatory sites. Acidic extracellular pH triggers NLRP3 inflammasome activation and interleukin-1β secretion in human macrophages. Acidic pH represents a novel danger signal alerting the innate immunity. Local acidosis may promote inflammation at ischemic and inflammatory sites. Local extracellular acidification has been demonstrated at sites of ischemia and inflammation. IL-1β is one of the key proinflammatory cytokines, and thus, its synthesis and secretion are tightly regulated. The NLRP3 (nucleotide-binding domain leucine-rich repeat containing family, pyrin domain containing 3) inflammasome complex, assembled in response to microbial components or endogenous danger signals, triggers caspase-1-mediated maturation and secretion of IL-1β. In this study, we explored whether acidic environment is sensed by immune cells as an inflammasome-activating danger signal. Human macrophages were exposed to custom cell culture media at pH 7.5-6.0. Acidic medium triggered pH-dependent secretion of IL-1β and activation of caspase-1 via a mechanism involving potassium efflux from the cells. Acidic extracellular pH caused rapid intracellular acidification, and the IL-1β-inducing effect of acidic medium could be mimicked by acidifying the cytosol with bafilomycin A1, a proton pump inhibitor. Knocking down the mRNA expression of NLRP3 receptor abolished IL-1β secretion at acidic pH. Remarkably, alkaline extracellular pH strongly inhibited the IL-1β response to several known NLRP3 activators, demonstrating bipartite regulatory potential of pH on the activity of this inflammasome. The data suggest that acidic environment represents a novel endogenous danger signal alerting the innate immunity. Low pH may thus contribute to inflammation in acidosis-associated pathologies such as atherosclerosis and post-ischemic inflammatory responses.

Performance curve approach to optimising fluidising water for Knelson concentrators

Centrifugal concentrators such as Knelson concentrators (KCs) are commonly used in most gold processing plants to recover fine liberated gold particles. The decision to employ a gravity recovery circuit is primarily based on the amount of gravity recoverable gold (GRG) in the ore among other considerations. However, the conditions required to optimise the gold recovery in such devices used in plants cannot be determined by GRG test results as the separation of particles is based on the particle bed dynamics within the given unit which are different to those encountered in a three inch KC used for the GRG test. The significant operating variables that affect the performance of a KC are the size distributions of the gold and gangue, rotational speed of the bowl, fluidising water flowrate and the cycle time. Of these variables, the rotational speed is generally fixed, and the size distributions of the gold and gangue are determined by the comminution circuit employed. Thus, the fluidising water is the key variable that can be used to control the dilation of the particle bed to maximise the recovery of gold. This paper examines the validity of the GRG test for performance evaluation and discusses an alternative method based on performance curve of the device that can be used to evaluate the optimum fluidising water flowrate of an operating machine. The principles of determining the performance curve of the machine and its use are also discussed and illustrated with laboratory and plant data.

Characterization of Prefibrillar Tau Oligomers in Vitro and in Alzheimer Disease

Neurofibrillary tangles, composed of insoluble aggregates of the microtubule-associated protein Tau, are a pathological hallmark of Alzheimer disease (AD) and other tauopathies. However, recent evidence indicates that neuronal dysfunction precedes the formation of these insoluble fibrillar deposits, suggesting that earlier prefibrillar Tau aggregates may be neurotoxic. To determine the composition of these aggregates, we have employed a photochemical cross-linking technique to examine intermolecular interactions of full-length Tau in vitro. Using this method, we demonstrate that dimerization is an early event in the Tau aggregation process and that these dimers self-associate to form larger oligomeric aggregates. Moreover, using these stabilized Tau aggregates as immunogens, we generated a monoclonal antibody that selectively recognizes Tau dimers and higher order oligomeric aggregates but shows little reactivity to Tau filaments in vitro. Immunostaining indicates that these dimers/oligomers are markedly elevated in AD, appearing in early pathological inclusions such as neuropil threads and pretangle neurons as well as colocalizing with other early markers of Tau pathogenesis. Taken as a whole, the work presented herein demonstrates the existence of alternative Tau aggregates that precede formation of fibrillar Tau pathologies and raises the possibility that these hierarchical oligomeric forms of Tau may contribute to neurodegeneration.

Small free vibrations of an infinite cylindrical shell rotating on rollers

Small free vibrations of an infinitely long rotating cylindrical shell being in contact with rigid cylindrical rollers are considered. A system of linear differential equations for the vibrations of such a shell is derived. By using the Fourier transform of the solutions in the circumferential coordinate, a system of algebraic equations for approximately determining the vibration frequencies and mode shapes is obtained. It is shown that, for any number n of uniformly distributed rollers, the approximate values of the first n frequencies and mode shapes can be found explicitly. On the basis of the orthogonal sweep method, an algorithm for numerically solving the boundary value eigenvalue problem describing the vibrations of a rotating shell is developed. Analytical and numerical results are compared. The obtained approximate formulas for frequencies and the numerical algorithm can be used to design centrifugal concentrators for ore enrichment.

Molecular Identification of Carnosine Synthase as ATP-grasp Domain-containing Protein 1 (ATPGD1)

Carnosine (beta-alanyl-L-histidine) and homocarnosine (gamma-aminobutyryl-L-histidine) are abundant dipeptides in skeletal muscle and brain of most vertebrates and some invertebrates. The formation of both compounds is catalyzed by carnosine synthase, which is thought to convert ATP to AMP and inorganic pyrophosphate, and whose molecular identity is unknown. In the present work, we have purified carnosine synthase from chicken pectoral muscle about 1500-fold until only two major polypeptides of 100 and 90 kDa were present in the preparation. Mass spectrometry analysis of these polypeptides did not yield any meaningful candidate. Carnosine formation catalyzed by the purified enzyme was accompanied by a stoichiometric formation, not of AMP, but of ADP, suggesting that carnosine synthase belongs to the "ATP-grasp family" of ligases. A data base mining approach identified ATPGD1 as a likely candidate. As this protein was absent from chicken protein data bases, we reconstituted its sequence from a PCR-amplified cDNA and found it to fit with the 100-kDa polypeptide of the chicken carnosine synthase preparation. Mouse and human ATPGD1 were expressed in HEK293T cells, purified to homogeneity, and shown to catalyze the formation of carnosine, as confirmed by mass spectrometry, and of homocarnosine. Specificity studies carried out on all three enzymes were in agreement with published data. In particular, they acted with 15-25-fold higher catalytic efficiencies on beta-alanine than on gamma-aminobutyrate. The identification of the gene encoding carnosine synthase will help for a better understanding of the biological functions of carnosine and related dipeptides, which still remain largely unknown.

Riboflavin Is an Active Redox Cofactor in the Na+-pumping NADH:Quinone Oxidoreductase (Na+-NQR) from Vibrio cholerae

Here we present new evidence that riboflavin is present as one of four flavins in Na+-NQR. In particular, we present conclusive evidence that the source of the neutral radical is not one of the FMNs and that riboflavin is the center that gives rise to the neutral flavosemiquinone. The riboflavin is a bona fide redox cofactor and is likely to be the last redox carrier of the enzyme, from which electrons are donated to quinone. We have constructed a double mutant that lacks both covalently bound FMN cofactors (NqrB-T236Y/NqrC-T225Y) and have studied this mutant together with the two single mutants (NqrB-T236Y and NqrC-T225Y) and a mutant that lacks the noncovalently bound FAD in NqrF (NqrF-S246A). The double mutant contains riboflavin and FAD in a 0.6:1 ratio, as the only flavins in the enzyme; noncovalently bound flavins were detected. In the oxidized form, the double mutant exhibits an EPR signal consistent with a neutral flavosemiquinone radical, which is abolished on reduction of the enzyme. The same radical can be observed in the FAD deletion mutant. Furthermore, when the oxidized enzyme reacts with ubiquinol (the reduced form of the usual electron acceptor) in a process that reverses the physiological direction of the electron flow, a single kinetic phase is observed. The kinetic difference spectrum of this process is consistent with one-electron reduction of a neutral flavosemiquinone. The presence of riboflavin in the role of a redox cofactor is thus far unique to Na+-NQR.

Structural Analysis of Conserved Oligomeric Golgi Complex Subunit 2

The conserved oligomeric Golgi (COG) complex is strongly implicated in retrograde vesicular trafficking within the Golgi apparatus. Although its mechanism of action is poorly understood, it has been proposed to function by mediating the initial physical contact between transport vesicles and their membrane targets. An analogous role in tethering vesicles has been suggested for at least six additional large multisubunit complexes, including the exocyst, a complex essential for trafficking to the plasma membrane. Here we report the solution structure of a large portion of yeast Cog2p, one of eight subunits composing the COG complex. The structure reveals a six-helix bundle with few conserved surface features but a general resemblance to recently determined crystal structures of four different exocyst subunits. This finding provides the first structural evidence that COG, like the exocyst and potentially other tethering complexes, is constructed from helical bundles. These structures may represent platforms for interaction with other trafficking proteins including SNAREs (soluble N-ethylmaleimide factor attachment protein receptors) and Rabs.

Serine 64 Phosphorylation Enhances the Antiapoptotic Function of Mcl-1

Mcl-1 is an antiapoptotic Bcl-2 family member that is highly regulated and when dysregulated contributes to cancer. The Mcl-1 protein is phosphorylated at multiple sites in response to different signaling events. Phosphorylations at Thr163 (by ERK) and Ser159 (by glycogen-synthase kinase 3beta) have recently been shown to slow and enhance, respectively, Mcl-1 protein turnover. Phosphorylation is also known to be stimulated at other, as-yet uncharacterized sites in the G2/M phase of the cell cycle. Using an S peptide-tagged Mcl-1 T163A mutant, Ser64 was identified as a novel Mcl-1 phosphorylation site by mass spectrometry. Immunoblotting demonstrated that phosphorylation at this site was maximal in cells in G2/M phase, was enhanced by tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) treatment, was blocked by inhibitors of CDK (but not ERK or glycogen-synthase kinase 3beta), and was stimulated in vitro by CDK 1, CDK2, and JNK1. The half-life of a nonphosphorylatable S64A Mcl-1 mutant was indistinguishable from that of the wild type polypeptide. In contrast, this mutant failed to protect cells from TRAIL-mediated apoptosis, whereas reconstitution with the phosphomimetic S64E Mcl-1 mutant rendered cells TRAIL-resistant. This anti-apoptotic phenotype of the S64E Mcl-1 mutant was also associated with enhanced binding to the proapoptotic proteins Bim, Noxa, and Bak. A pharmacological CDK inhibitor that reduced Ser64 phosphorylation also sensitized cells to TRAIL cytotoxicity. Collectively, these observations not only identify G2/M-associated phosphorylation at Ser64 as a critical determinant of the antiapoptotic activity of Mcl-1 but also elucidate a novel mechanism by which CDK1/2 inhibitors can enhance the effectiveness of the cytotoxic cytokine TRAIL.