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Adsorption of arsenic (V) by iron (III)-modified natural zeolitic tuff
No full textAdsorption of arsenic (V) by natural zeolitic tuff, modified with iron (III), was investigated. Also, the iron (III) adsorption characteristics by natural zeolitic tuff was evaluated. It was determined that iron (III) adsorption by starting zeolitic tuff was best represented by the Freundlich type of isotherm, having correlation coefficient (r (2)) of 0.990. Arsenic (V) adsorption by iron (III)-modified zeolitic tuff followed a nonlinear type of isotherm. The best fit of the experimental data was obtained using the Langmuir-Freundlich model (r (2) = 0.99), with the estimated maximum of arsenic (V) adsorption to iron (III)-modified zeolitic tuff of 1.55 mg/g
Kinetics of specific surface area change using the Boltzmann model
No full textSinterovanjem sistema 2MgO·2Al2O3·5SiO2, dobija se kordijerit, koji zbog svojih svojstava predstavlja izuzetno atraktivan keramički materijal. U cilju ispitivanja mogućnosti sniženja temperature formiranja kordijerita tokom procesa sinterovanja, izvršena su preliminarna ispitivanja mehanohemijske aktivacije stehiometrijske smeše polaznih komponenti. Efekti mehanohemijske aktivacije su praćeni termogravimetrijskom i diferencijalnom termijskom analizom. Specifična površina mehanički aktivirane smeše prahova je određivana BET i Coulter metodom. Kinetika povećanja specifične površine je analizirana tzv. Boltzmann-ovim modelom. Utvrđeno je da se sa povećanjem vremena aktivacije temperature na kojima se uočavaju fazne promene pomeraju ka nižim vrednostima. FFT IR analiza mehanohemijski aktiviranog praha nakon 24 meseci je pokazala da nije došlo do bitnih promena tokom 'starenja' materijala. Na osnovu dobijenih rezultata može se zaključiti da je mehanohemijska aktivacija imala uticaja na tretiranu praškastu smešu, pa se očekuje da se ovaj uticaj odrazi i na sniženje temperature formiranja kordijerita tokom procesa sinterovanja.During sintering of the 2MgO-2Al2O3-5SiO2 system, cordierite, an attractive ceramic material because of its properties, is obtained. Effects of mechanochemical activation of stoichiometric mixtures, performed to investigate possibilities of lowering cordierite formation temperature during sintering, were monitored by thermogravimetric and differential thermal analyses. Specific surface areas of the mechanically activated powder mixtures were determined by the BET method. Kinetics of the specific surface area increase was analyzed using the Boltzmann model. It was confirmed that with activation time increase, temperatures of phase transformations were shifted to lower values and, according to FTIR analysis no significant changes occurred during material aging. According to the obtained results, it may be concluded that since mechanochemical activation has an influence on the treated powder mixture, lowering of the cordierite formation temperature during the sintering process is expected
Surface properties of natural calcite filler treated with stearic acid
No full textIn order to obtain hydrophobic material, the water suspension of natural limestone with the high content of calcite (>95%), was treated with different amounts (0.5-4%) of stearic acid dissolved in chloroform. Thermal analysis showed that at lower initial concentrations of stearic acid (up to 2%), surfactant molecules are chemisorbed on calcite surface, while at higher initial concentrations acid molecules are additionally physisorbed on mineral surface. XRPD analysis of starting calcite as well as two modified products with 1.5 and 3% of stearic acid indicated that modification of calcite surface with both amounts of stearic acid, did not cause any changes in the structure of calcite mineral. It was confirmed that long chain stearic acid, in presence of water, alters the calcite surface to strongly hydrophobic, where reaction between stearic acid and Ca2+ ions occurs. Thus, the chemisorption of stearic acid on the calcite surface is responsible for retaining the lower surfactant layer on a charged surface while hydrophobic bonding causes formation of the upper surfactant layer The optimal amount of stearic acid needed to cover the calcite surface with a monolayer of organic molecules lies between 1.5% and 2%
Computational investigations of the binding mechanism of current influenza virus neuraminidase inhibitors: Correlation with experiment
No full textIn the context of the recent pandemic threat by the worldwide spread of H5N1 avian influenza, novel insights into the mechanisms of ligand binding and interaction between various inhibitors (zanamivir-ZMV, oseltamivir-OTV, DANA, peramivir-PMV) and neuraminidases (NAs) are of vital importance for the structure-based design of new antiviral drugs. Computational methods are herein shown to be a viable partner to experiment in the investigation of the binding modes of known NA inhibitors. Using the crystal structures of inhibitors bound to either group-2 or group-1 NAs, the AScore/ShapeDockscoring was shown to identify the binding modes in agreement with the experiment for all inhibitors docked in their own NA/inhibitor crystal structures. To investigate the effect of small changes in protein structure on predicted binding modes, in a set of 132 docking experiments (11 inhibitors docked in 12 group-2 NA structures) AScore/ShapeDock identified the correct binding modes of 116 complexes. In a total of 88 docking experiments (8 inhibitors docked in 11 group-1 NA structures) AScore/ShapeDock predicted 80 binding modes correctly. A small vHTS experiment, reflected by mixing the known activity molecules to a set of randomly selected molecules, confirmed the ability of the AScore/ShapeDock approach to extract biologically active molecules from inactive ones. By both outperforming other docking methods used previously in the literature and being quite reproducible, the AScore/ShapeDock protocol is suggested to be convenient for designing novel H5N1-NA inhibitors. To shed more light on the high resistance of H5N1 strains to various NA inhibitors, the three-dimensional models of H5N1-NA andN9-NA were generated by homology modeling. Traditional residues within the active site throughout the family of NA protein structures were found to be highly conserved in H5N1-NA, and a subtle variation between lipophilic and hydrophilic environments in H5N1-NA with respect to N9-NA was observed. Besides, molecular bases of the mechanism of H5N1-NA resistance to oseltamivir were elucidated in a systematic fashion. Using the crystal structure of the complex of H5N1-NA with OTV (PDB ID: 2hu0) as the starting point, the following question was addressed and correlated with the experimental data: How mutations at His274 by both smaller side chain (Gly, Ser, Asn, Gln) and larger side chain (Phe, Tyr) residues influence the sensitivity of N1 to oseltamivir? The smaller side chain residue mutations of His274 resulted in slightly enhanced or unchanged NA sensitivity to OTV, while His274Phe and His274Tyr reduced the susceptibility of OTV to N1. In contrast to the binding free energies, the net charges of Glu276 and Arg224, making charge-charge interactions with Glu276, were established to be more sensitive to detecting subtle conformational differences induced at the key residue Glu276 by the His274X mutations. Thus, deeper insights into the possibility of developing viable drug-resistant mutants were possible
Kinetics of chalcopyrite leaching by sodium nitrate in sulphuric acid
No full textHydrometallurgical processes offer a great potential for treating chalcopyrite ores and concentrates, and it results in increased metal recoveries and reduced air pollution hazards. In recent years interest for application of various reagents in a hydrometallurgical processing of sulphide concentrates has increased. The objective of this work was to examine the leaching of the chalcopyrite concentrate, from "Rudnik" flotation plant, by sodium nitrate in sulphuric acid media. The probabilities of various chemical reactions occurring was based upon literature data, thermodynamic analysis, and the products formed during the leaching process. The influence of various parameters was studied to optimize the conditions and to determine the kinetics of the reaction. An increase in temperature, sulphuric acid and sodium nitrate concentration, and decrease in stirring speed and particle size, enhanced the leaching rate of copper. The experimental data were best fitted by a mixed control kinetic model. An activation energy of 83 kJ/mol was found. Elemental sulphur was formed as the main leaching product and tended to inhibit the leaching rate. The leaching mechanism was confirmed by characterizing the concentrate and the leach residue using XRD and SEM/EDX analysis
Actual assortment of mineral fertilizers in Serbia and their quality and problems of applications
No full textU radu su analizirani podaci o domaćoj proizvodnji, uvozu, prometu i kontroli kvaliteta mineralnih đubriva u Srbiji pre i nakon 1990. godine, a sve u cilju tumačenja razloga i posledica njihove nedovoljne upotrebe u ishrani gajenih biljaka poslednjih godina. Prema tim podacima, sa prosečnom upotrebom đubriva na našim obradivim poljoprivrednim površinama (ispod 80 kg/ha, aktivne NPK materije), koja je za oko tri puta niža nego u razvijeno poljoprivrednim zemljama i oko 1/3 u odnosu na period pre 1990. godine u Srbiji ,može se zaključiti zašto su prinosi mnogih gajenih kultura, posebno žitarica, na donjoj granici rentabilnosti. Pored povećanja cena đubriva i nezavidnog ekonomskog položaja naših poljoprivrednih proizvođača, razlozi za ovakvo smanjenje upotrebe đubriva je i činjenica što je domaća proizvodnja istih drastično smanjena, a uvoz, promet pa i često kvalitet neusaglašen i neadekvatan našim stvarnim potrebama.In this paper were analyzed data from domestic production, import, turnover and quality control of mineral fertilizers in Serbia before and after 1990. The aim of analyze was to find reason and consequence of inadequate use of fertilizers for plant nutrition over the last years. According to this data average use of fertilize on our land (less than 80kg/ ha, active NPK matter), which is three times less then in other agricultural countries and third of use in Serbia before 1990, it can be conclude why production of many cultivated grass especially cereal grains is on low profitability range. In addition to increasing prices of fertilizers and unpromising position of agricultural producers, more reasons of reduction fertilizers use are: demagnification domestic production, import, turnover and very often unsuitable quality for our real requirement
The investigation of applicability of the Hollomon-Jaffe equation on tempering the HSLA steel
No full textHigh strength low-alloyed (HSLA) Cr-Mn-Si steels belong to a group of steels that can reach their full mechanical properties after quenching and tempering. Those properties depend both on the temperature and time of tempering. Knowing the tempering parameters, it is possible to reach the desired properties of the treated steel. Some results on investigating the Hollomon-Jaffe equation (in parametric form) application for tempering of HSLA steel, are shown in this paper. The experiments were performed in real production conditions, using a standard material. The quenching was performed at 870°C, the heating period was always 30 min, with subsequent cooling into the oil bath. The tempering was carried out in temperature range from 480 to 680°C, while tempering time varied from 15 min to 24 h. The degree of tempering is referred through the hardness values changing. The experimental results have shown a pretty well agreement to tempering parameters, included in Hollomon-Jaffe equation, for this kind of HSLA steel
Mechanical properties of the PVC mix containing modified calcite
No full textU radu su prikazani rezultati ispitivanja mehaničkih osobina PVC (polivinil hlorid) mešavine koja sadrži krečnjak sa kalcitom, kao osnovnim mineralom, modifikovanim stearinskom kiselinom 'suvim' i 'mokrim' postupkom. Ispitivano je: čvrstoća pri zatezanju, izduženje pri zatezanju, čvrstoća pri kidanju, izduženje pri kidanju i temperatura omekšavanja po Vikat-u. Rezultati su pokazali da PVC mešavina koja sadrži kalcit modifikovan 'mokrim' postupkom ima bolje mehaničke osobine od one koja sadrži kalcit modifikovan 'suvim' postupkom u uslovima kada je postignut najveći stepen obloženosti od 99.90%. Uzorak PVC mešavine koji sadrži kalcit modifikovan 'mokrim' postupkom sa 1.5% stearinske kiseline ima čvrstoću pri zatezanju 54.20 MPa i čvrstoću pri kidanju 38.20 MPa, dok uzorak koji sadrži kalcit modifikovan 'suvim' postupkom sa 3% stearinske kiseline ima čvrstoću pri zatezanju 53.20 MPa i čvrstoću pri kidanju 37.90 MPa. .This paper presents the results of mechanical properties testing of the PVC (Polyvinyl Chloride) mix containing limestone with calcite, as a basic mineral, modified by stearic acid using wet and dry procedures. The following testing was conducted: ultimate tensile strength, tensile elongation, breaking strength, elongation at break, and Vikat softening temperature. The results showed that the PVC mix containing calcite which was modified by wet procedure had better mechanical properties than the PVC mix containing calcite modified by dry procedure in conditions when the highest degree of coating of 99.90% was achieved. The PVC mix sample containing calcite modified by wet procedure with 1.5% of stearic acid had ultimate tensile strength of 54.20MPa and breaking strength of 38.20MPa, while the sample containing calcite modified by dry procedure with 3% of stearic acid had ultimate tensile strength of 53.20MPa and breaking strength of 37.90MPa.
Leaching mechanism of polymetallic pb-zn-cu concentrates using sulphuric acid in the presence of selected oxidant
No full textoai:ritnms.itnms.ac.rs:123456789/4Iscrpljivanje bogatih i pojava nestandardnih rudnih rezervi sulfidnih mineralnih sirovina nalaže potrebu za pronalaženje odgovarajućih mogućnosti prerade do danas nedovoljno iskorišćenih resursa i njihovu eksploataciju. Jedan deo ovih ruda predstavljaju polimetalične rude i kolektivni koncentrati iz kojih često nije moguće konvencionalnim postupcima prerade valorizovati obojene metale sa zadovoljavajućim stepenom iskoričćenja. Izučavanje postupaka za valorizovanje obojenih metala iz ovakvih sirovina vezano je za poznavanje oblika pojavljivanja obojenih metala u sulfidnim sirovinama, strukturno-morfoloških osobina minerala nosioca i fizičko-hemijskih mogućnosti za procesno tretiranje u cilju dobijanja metala uz zadovoljavajuće iskorišćenje. Nakon detaljnog uvida u procesne mogućnosti prerade ovakvih ruda i koncentrata, za analizu mogućnosti primene odabran je postupak luženja sulfidnih koncentrata rastvorom sumporne kiseline u prisustvu oksidansa pri normalnom pritisku. Za ispitivanja su korišćena dva polimetalična koncentrata: u prvom je bakar bio zastupljeniji u odnosu na cink i olovo (halkopiritni koncentrat), dok su u drugom sva tri minerala bila ravnomerno zastupljena (polimetalični koncentrat). Na osnovu literaturnih podataka izvršen je izbor oksidanasa i tokom eksperimentalnih istraživanja dokazano da je primena natrijum(I)-nitrata i vodonik-peroksida opravdana i adekvatna kod luženja polimetaličnih koncentrata sa različitim sadržajem halkopirita u rastvorima sumporne kiseline pri standardnom pritisku. Termodinamička analiza procesa luženja je obuhvatila proračun promene Gibsove energije hemijskih reakcija luženja i konstukciju E-pH dijagrama stabilnosti bakra, cinka, olova i železa u ispitivanim sistemima. Ispitivanjem uticaja kinetičkih parametara procesa (temperature, vreme, granulometrijski sastav, brzina mešanja, koncentracija H2SO4, koncentracija NaNO3 (H2O2)) halkopiritnog koncentrata na izluženje bakra određeni su optimalni parametri procesa luženja u sistemima H2SO4-NaNO3-H2O i H2SO4-H2O2-H2O. Dobijeni rezultati su iskoričćeni za određivanje kinetičkih zakonitosti, energija aktivacije i mehanizma odvijanja procesa. Ispitivanje uticaja temperature i vremena luženja polimetaličnog koncentrata na izluženje bakra, cinka i železa, poslužilo je za analizu uticaja sastava polimetaličnih sirovina na luženje bakra pri istim uslovima i ocenu stabilnosti sulfidnih minerala prisutnih u koncentratu. Proučavanjem mikrostrukture, strukturno-teksturnih i morfoloških karakteristika sulfidnih koncentrata i čvrstih ostataka nakon luženja doneti su pouzdani zaključci o uslovima i mogućnostima luženja bakra, cinka i železa, osnovnim hemijskim reakcijama i mehanizmu procesa luženja.Depletion of reach ore deposits of sulphide mineral raw materials as well as occurrence of nonstandard ore reserves indicated the necessity to investigate the treatment possibilities of resources that were inadequately exploited up-to –date. Polymetallic ores and bulk concentrates out of which is hard or impossible to valorize non-ferrous metals with satisfying recovery degree, using conventional treatment procedures, present a part of such ores. Non-ferrous metals valorization procedures investigation is associated with knowledge about the form of appearance of non-ferrous metals in sulphide raw materials, structural and morphological properties of the bearing mineral and physico-chemical possibilities of treatment process for the sake of metal obtaining with satisfying recovery degree. For analysis of application possibilities, after detailed insight into treatment process possibilities of such ores and ore concentrates, the leaching procedure of sulphide concentrates with sulphuric acid solution in the presence of oxidant, at standard pressure, was chosen. Two polymetallic concentrates are used for investigations: the first with higher copper content comparing to zinc and lead content chalcopyrite concentrate), and the second with even content of each of the three minerals (polymetallic concentrate). The oxidant was chosen based on literature data, and during experimental investigations it is proven that the application of sodium (I)-nitrate and hydrogen- peroxide was reasonable and adequate for polymetallic concentrates with different chalcopyrite content leaching in the slphuric acid solutions, at standard pressure. Thermodynamic analysis of leaching process encompassed the calculation of the Gibbs energy changes for chemical reactions of leaching, as well as E-pH diagrams construction for stability of copper, zinc, lead and iron at investigated systems. Optimal parameters of leaching process in the following systems: H2SO4-NaNO3-H2O i H2SO4-H2O2-H2O, are determined through examination the kinetic parameters (temperature, time, grain size distribution, agitation speed, sulphuric acid concentration, sodium (I)-nitrate and/or hydrogen-peroxide concentration) influence on the copper recovery degree during chalcopyrite concentrate leaching. Obtained results are used for determination the kinetic principles, activation energies and process mechanisms. Investigation the temperature and leaching time of polymetallic concentrate influence on copper, zinc and iron recovery degree, was used for analysis of polymetallic raw materials composition influence on the copper leaching at the same conditions, and for estimation the stability of the sulphide minerals assembled in concentrate. Microstructure, structure-textural and morphological characteristics examination of sulphide concentrates and leaching solid residues, contributed the reliable conclusions providing, concerning the conditions and possibilities of copper, zinc and iron leaching, fundamental chemical reactions and leaching process mechanism
Mineralogy of gold in polymetallic deposits of Serbia
No full textGold-bearing polymetallic sulfide deposits are common in Serbia, and mostly occur in the Karpato-Balkan and, to a lesser extent, the Serbo-Macedonian metallogenic province. These deposits - Coka Marin (Majdanpek), Grabova Reka (Blagojev Kamen), Lece (Medvedja) and Veliki Cip (Boranja) - are dominated by Cu and/or Pb-Zn mineralisation that contains a variety of Pb, Zn, Cu and Fe (± Sb, As, Bi) sulfides and sulfosalts, as well as native elements. Gangue minerals are composed of quartz, carbonates and rare silicates and barite. Based on their gold content these deposits can be divided in three groups: 1. polymetallic deposits with a high gold content (>1 g/t). 2. polymetallic deposits with an intermediate gold content (0.1 to 1 g/t), and 3. polymetallic deposits with a low gold content ( LT 0.1 g/t). Gold occurs as native gold or as an alloy with silver. Native gold ranges in size from 5 to 20 μm, with a few rare grains over 100 μm, as isolated grains or as microveins (in the first group of deposits). Its distribution within the deposit in uneven. Native gold in the second group is smaller in size (1-5 μm, rarely 20 μm), where it is uniformly distributed in a quartz-silicate matrix. The third group is of no economical importance. The subject of research has been the first group of polymetallic deposits