Flocculation, filtration and selective flocculation studies on haematite ore fines using starch

The flocculation and filtration characteristics of typical Indian iron ore fines have been studied using starch as flocculant in the presence of an inorganic electrolyte, namely calcium chloride. The effect of various parameters such as pH, starch and calcium chloride concentrations and pulp density on the settling and filtration rates, turbidity of the supernatant and on residual starch and calcium ion concentrates has been investigated through a statistical design and analysis approach and subsequently optimised on a laboratory scale. The adsorption mechanisms of starch onto haematite have been elucidated through adsorption density measurements, infrared and X-ray photoelectron spectroscopic techniques. The rheological property of the polymer solutions of relevance to flocculations has also been investigated. Further, the role of metal ion-starch interactions in the bulk solution, has been studied. In order to understand the nature of polymer adsorption at the double-layer, electrokinetic studies have been carried out with the iron ore mineral samples using starch and calcium chloride. Based on the above findings, selective floculaation tests on artificial mixtures of iron ore minerals have been carried out to determine the separation efficiencies from the view point of alumina and silica removal from haematite as well as the control of alumina: silica ratio in Indian iron ores.

Influence of microstructure on the wear of grinding media

Owing to the complexity of the wear process, high stress grinding abrasion is quite different from two-body abrasive wear. Reported data on two-body abrasive wear reveal that the wear decreases with an increase in steel hardness. This relationship can be established without having to consider the microstructure of the steel grinding medium. However, it is known that hardness cannot be directly employed to predict the wear of steel balls under three-body grinding abrasion, as occurs during dry grinding of ores in ball mills. The present work suggests that the wear behaviour of grinding balls can be classified according to the microstructural family to which they belong. Thus, in this work on AISI 52100 steel, the separate groups of microstructures were spheroidite—pearlite, bainite, tempered martensite and martensite with retained austenite. It appears that wear behaviour of the first three groups follows the same trend as that observed for two-body wear. The data suggest that an optimum level of retained austenite could improve the wear resistance of microstructures containing martensite.

New chelating resins based on polybenzimidazole. Selective sorption of copper(II) from ammoniacal media on resin with anchored l-cysteine

Microporous polybenzimidazole (PBI) of 250–500 μm bead size has been epoxidized and subsequently reacted with l-cysteine in the presence of a phase-transfer catalyst at room temperature to obtain a sorbent having anchored l-cysteine, EPBI(Cyst). The sorption of Cu(II), Ni(II), Co(II), and Zn(II) in mildly acidic and ammoniacal solutions has been measured under comparable conditions on EPBI(Cyst) and Dowex 50W-X8(H+) resins. While the latter shows no appreciable difference in sorption of the four metals in acidic and ammoniacal media and has 40–60 % selectivity for copper(II) over the other three, EPBI(Cyst) shows a threefold increase in copper sorption and more than 90% copper selectivity over the other metals in ammoniacal media, compared to mildly acidic media. The copper binding constant and saturation capacity of EPBI(Cyst) in ammoniacal media decrease only slowly beyond pH 11.6 with the result that the resin shows significant sorption of Cu(II) even in strongly ammoniacal solutions. The sorbed copper is stripped with HCl relatively easily. The copper sorption kinetics on EPBI(Cyst) is unusually fast in ammoniacal media with more than 90 % of equilibrium sorption being attained in one minute.

Selective sorption of ferric ion onto a crosslinked resin bearing triphenylphosphinimine residues

A polymeric sorbent containing triphenylphosphinimine residues has been obtained from crosslinked chloromethylated polystyrene by azidation, using phase-transfer catalysis, followed by reaction with triphenylphosphine at room temperature. The sorbent exhibits 100 % sorption selectivity for Fe(III) in the presence of Cu(II), Fe(II), Ni(II), Co(II), Mn(II), and Zn(II) in aqueous media. In the absence of Fe(III), however, Fe(II) is selectively sorbed over the other metal ions, and in the absence of both Fe(II) and Fe(III), Cu(II) has the highest selectivity of sorption on the resin. The sorption of Fe(III) is sensitive to pH, being maximum at pH not, vert, similar 2 and falling sharply at both higher and lower pH values. The sorbed Fe(III) is easily stripped with dilute HCl and the resulting protonated resin is regenerated to its original sorption capacity by treatment with dilute NaOH at room temperature.

Src Homology 3-interacting Domain of Rv1917c of Mycobacterium tuberculosis Induces Selective Maturation of Human Dendritic Cells by Regulating PI3K-MAPK-NF-kappa B Signaling and Drives Th2 Immune Responses

Mycobacterium tuberculosis, an etiological agent of pulmonary tuberculosis, causes significant morbidity and mortality worldwide. Pathogenic mycobacteria survive in the host by subverting host innate immunity. Dendritic cells (DCs) are professional antigen-presenting cells that are vital for eliciting immune responses to infectious agents, including pathogenic mycobacteria. DCs orchestrate distinct Th responses based on the signals they receive. In this perspective, deciphering the interactions of the proline-glutamic acid/proline-proline-glutamic acid (PE/PPE) family of proteins of M. tuberculosis with DCs assumes significant pathophysiological attributes. In this study, we demonstrate that Rv1917c (PPE34), a representative member of the proline-proline-glutamic-major polymorphic tandem repeat family, interacts with TLR2 and triggers functional maturation of human DCs. Signaling perturbations implicated a critical role for integrated cross-talk among PI3K-MAPK and NF-kappa B signaling cascades in Rv1917c-induced maturation of DCs. However, this maturation of DCs was associated with a secretion of high amounts of anti-inflammatory cytokine IL-10, whereas Th1-polarizing cytokine IL-12 was not induced. Consistent with these results, Rv1917c-matured DCs favored secretion of IL-4, IL-5, and IL-10 from CD4(+) T cells and contributed to Th2-skewed cytokine balance ex vivo in healthy individuals and in patients with pulmonary tuberculosis. Interestingly, the Rv1917c-skewed Th2 immune response involved induced expression of cyclooxygenase-2 (COX-2) in DCs. Taken together, these results indicate that Rv1917c facilitates a shift in the ensuing immunity toward the Th2 phenotype and could aid in immune evasion by mycobacteria.

Ruthenium-Oxygen Coordination-Driven Self-Assembly of a Ru-8(II) Incomplete Prism: Synthesis, Structure, and Shape-Selective Molecular Recognition Study

Coordination-driven self-assembly of 1,3,5-benzenetricarboxylate (tma; 1) and oxalato-bridged p-cymeneruthenium(II) building block Ru-2(mu-eta(4)-C2O4)(MeOH)(2)(eta(6)-p-cymene)(2)](O3SCF3)(2) (2) affords an unusual octanuclear incomplete prism Ru-8(eta(6)-p-cymene)(8)(tma)(2)(mu-eta(4)-C2O4)(2)(OMe)(4)](O3SCF3)( 2) (3), which exhibits a remarkable shape-selective binding affinity for neutral phenolic compounds via hydrogen-bonding interactions (p-cymene = p-(PrC6H4Me)-Pr-i). Such a binding was confirmed by single-crystal X-ray diffraction analysis using 1,3,5-trihydroxybenzene as an analyte.

A Convenient Methodology for the Selective Reduction of Carboxylic Acids With Benzyltriethyl-Ammonium Borohydride—Chlorotrimethylsilane

A combination of benzyltriethylammonium borohydride and chlorotrimethylsilane (1:1) in dichloromethane (0-25°C) has been found to be a convenient reagent system for the selective reduction of carboxylic acids to alcohols.

Selective Flotation of Molybdenite and Chalcopyrite

Separation of molybdenite from chalcopyrite from the bulk concentrate of a low grade molybdenite ore from Chintamani, Kolar District, Karnataka, has been attempted in a modified Hallimond tube microflotation set-up. The flotation parameters studied are, sodium sulphide and potassium cyanide as depressants for chalcopyrite, pH, depressant concentration, steaming time and time of flotation. Selectivity index was used as a separation parameter. Steaming for 25 min followed by flotation for 7 min at 80 mg/l concentration of potassium cyanide and pH 9 gave the best results for separation of molybdenite. 19 ref.--AA

Laboratory studies on ball wear in the grinding of a hematite-magnetite ore

Marked-ball grinding tests were carried out under different grinding conditions and environments. Three types of balls were used, namely, cast hyper steel, high chrome cast iron and EN-31 (forged), which cover a wide range of chemical composition, microstructure and media hardness. The effect of pulp density on ball wear and grinding efficiency was also studied. Relative pulp viscosities at different percent solids for the ore slurry were also determined. As the Kudremukh ore contained about 0.2% pyrite, the effect of addition of pyrite on ball wear was studied separately. Results of marked-ball grinding tests indicated that ball wear increased with time and showed a sharp increase for wet grinding over dry grinding. Ball wear under wet grinding conditions was also influenced by the gaseous atmosphere in the mill. At 70% solids, the best results in terms of reduced ball wear coupled with satisfactory grinding efficiency were obtained. The influence of oxygen on the corrosive wear of grinding balls was increasingly felt only if sulphide minerals such as pyrite were also present in the ore. The various ball materials could be arranged in the following order with respect to their overall wear resistance: high chrome cast iron > EN-31 (forged) > cast hyper steel.Possible ball wear mechanisms involved in the grinding of Kudremukh ore are discussed.

Ball wear and its control in the grinding of a lead-zinc sulphide ore

Marked ball grinding tests were carried out in the laboratory with a lead-zinc sulphide ore under different experimental conditions using high carbon low alloy steel (cast and forged) and high chrome cast iron balls. Relative ball wear as a function of grinding period and milling conditions was evaluated for the different types of ball materials. The role of corrosion and abrasion-erosion in the wear of grinding media is brought out. Methods to minimise ball wear through control of mill atmosphere and addition of reagents are discussed.

Effect of microstructure and hardness on the grinding abrasive wear resistance of a ball bearing steel

Grinding media wear appears to be non-linear with the time of grinding in a laboratory-scale ball mill. The kinetics of wear can be expressed as a power law of the type w=atb, where the numerical constant a represents wear of a particular microstructure at time t = 1 min and b is the wear exponent which is independent of the particle size prevailing inside a ball mill at any instant of time of grinding. The wear exponent appears to be an indicator of the cutting wear mechanism in dry grinding: a plot of the inverse of the normalised wear exponent (Image ) versusHs (where Hs is the worn surface hardness of the media) yields a curve similar to that of a wear resistance plot obtained in the case of two-body sliding abrasive wear. This method of evaluating the cutting wear resistance of media is demonstrated by employing 15 different microstructures of AISI-SAE 52100 steel balls in dry grinding of quartz in a laboratory-scale ball mill.

Amino acid selective unlabeling for sequence specific resonance assignments in proteins

Sequence specific resonance assignment constitutes an important step towards high-resolution structure determination of proteins by NMR and is aided by selective identification and assignment of amino acid types. The traditional approach to selective labeling yields only the chemical shifts of the particular amino acid being selected and does not help in establishing a link between adjacent residues along the polypeptide chain, which is important for sequential assignments. An alternative approach is the method of amino acid selective `unlabeling' or reverse labeling, which involves selective unlabeling of specific amino acid types against a uniformly C-13/N-15 labeled background. Based on this method, we present a novel approach for sequential assignments in proteins. The method involves a new NMR experiment named, {(CO)-C-12 (i) -N-15 (i+1)}-filtered HSQC, which aids in linking the H-1(N)/N-15 resonances of the selectively unlabeled residue, i, and its C-terminal neighbor, i + 1, in HN-detected double and triple resonance spectra. This leads to the assignment of a tri-peptide segment from the knowledge of the amino acid types of residues: i - 1, i and i + 1, thereby speeding up the sequential assignment process. The method has the advantage of being relatively inexpensive, applicable to H-2 labeled protein and can be coupled with cell-free synthesis and/or automated assignment approaches. A detailed survey involving unlabeling of different amino acid types individually or in pairs reveals that the proposed approach is also robust to misincorporation of N-14 at undesired sites. Taken together, this study represents the first application of selective unlabeling for sequence specific resonance assignments and opens up new avenues to using this methodology in protein structural studies.

Grinding abrasive wear and associated particle size effect

The type of abrasion that the grinding medium experiences inside a ball mill is classified as high stress or grinding abrasion, because the stress levels at the surface of the medium exceed the yield stress of the metal when hard abrasives are crushed. During dry grinding of ores the medium undergoes not only abrasion but also erosion and impact. As all three mechanisms of wear occur simultaneously, it is difficult to follow the individual components of wear. However, it is possible to show that the overall kinetics of wear follows a simple power law of the type w = at(b), where w is the weight loss of the grinding medium for a specified grinding time t and a and b are constants. Experimental data, obtained from dry grinding of quartz for a wide range of times using AISI 52100 steel balls having various microstructures in a laboratory scale batch mill, are fitted to the proposed equation and the wear rate w is calculated from the first derivative of the equation. The mean particle sizes of the quartz charge DBAR corresponding to 50 and 80% retained size are determined by mechanical sieving of the ground product after a grinding time t and thus the relationship between wear rate and particle size of the abrasive is established. It is found that w increases rapidly with DBAR up to some critical size and then increases at a much lower rate.