ritnms
Not a member yet
1551 research outputs found
Sort by
[Zn-3(PO4)(2)(H2O)(0.8)(NH3)(1.2)]
No full textThe structure of the title compound, ammineaquadi-mu(5)-phosphato-trizinc(II), [Zn-3(PO4)(2)(H2O)(0.8)(NH3)(1.2)], consists of two parts: (i) PO4 and ZnO4 vertex-sharing tetrahedra arranged in layers parallel to (100) and (ii) ZnO2(N/O)(2) tetrahedra located between the layers. Elemental analysis establishes the ammine-to-water ratio as 3:2. ZnO2(N/O)(2) tetrahedra are located at special position 4e (site symmetry 2) in C2/c. The two O atoms of ZnO2(N/O)(2) are bonded to neighbouring P atoms, forming two Zn-O-P linkages and connecting ZnO2(N/O)(2) tetrahedra with two adjacent bc plane layers. A noteworthy feature of the structure is the presence of NH3 and H2O at the same crystallographic position and, consequently, qualitative changes in the pattern of hydrogen bonding and weaker N/O-H center dot center dot center dot O electrostatic interactions, as compared to two closely related structures
The effect of the content of unburned carbon in bottom ash on its applicability for road construction
No full textThe content of unburned carbon is an important characteristic of bottom ash which could make it unsuitable for incorporation as aggregate for road construction. In this work, the effect of the content of unburned carbon in the bottom ash from the Serbian power plant "Nicola Tesla" on its applicability for road construction was examined. Four samples with different contents of unburned carbon, i.e., raw bottom ash, two size fractions obtained from it (2-5 and LT 2 mm) and bottom ash treated by the "float-sink" method, were investigated. When these materials were used as a component in the mixture: fly ash-Portland cement-bottom ash-water for road construction, it was found that only mixtures containing bottom ash with a lower carbon content (size fraction LT 2 mm and treated) were employable. The content of unburned carbon in the mentioned materials was determined by simultaneous DTA/TGA. This method was also used to investigate the composition of the hardened mixtures
Biodiversity and ecology of acidophiles used in microbiological processing of ores and mineral concentrates
No full textMikrobiološko luženje siromašnih ruda i jalovina nalazi danas veliku primenu, kako za dobijanje 'dopunskih' količina metala, tako i u konceptu zaštite životne sredine. Prirodni proces mikrobiološkog luženja, relativno jednostavnom tehnologijom, se stavlja pod kontrolu, usmerava, i na taj način koristi za sprečavanje nekontrolisanog odliva korisnih komponenti u vodotokove (koji u ovoj sredini predstavljaju polutante). Prema svetskim iskustvima, biološki tretman sulfidnih minerala, danas spada u kategoriju konvencionalnih tehnologija za dobijanje zlata i bakra. Takođe, pored ova dva metala, moguća je i ekstrakcija urana, kobalta, nikla i cinka iz polimetaličnih ruda. Ovaj rad predstavlja pregled dosadašnjih saznanja u vezi biodiverziteta acidofilnih mikroorganizama koji su uključeni u oksidaciju sulfidnih minerala, kao i prirode njihovih međusobnih odnosa. Razvojem i usavršavanjem novih tehnika za indentifikaciju mikroorganizama uvećala su se i saznanja o biodiverzitetu mikroorganizama sposobnih da rastu na haldama, odlagalištima i drugim sličnim mestima koja su za čoveka od komercijalne važnosti. Ovakva staništa karakteriše veoma heterogena sredina što utiče na vremensku i prostornu varijabilnost među populacijama mikroorganizama. Prilikom analize mikroflore uočen je iznenađujuće visok biodiverzitet, kao i pojava mikroorganizama iz razdela Firmicutes. Rezultati laboratorijskih eksperimenata u kojima su simulirani uslovi koji vladaju u sistemima kao što su bioreaktori, pokazuju da su mikrobiološki konzorcijumi otporniji i izdržljiviji u odnosu na čiste kulture acidofila. Takođe, i da su mnogo efikasniji u biološkoj oksidaciji ruda i koncentrata. .Microbiological leaching of low-grade ores and mine tailings is used nowadays as a method of supplying additional quantities of metal as well as protection of the environment. Natural processes of microbiological leaching, by use of relatively simple technology, are controlled and focused so that uncontrolled loss of useful components (pollutants in this environment) into streams and rivers is stopped. According to the international experience biomining of sulfide minerals is an established global biotechnology for recovering gold and copper. In addition to those two metals it is also possible to extract uranium, cobalt, nickel and zinc from polimetalic ores. This paper presents review of the current knowledge of the biodiversity of the acidofile microorganisms that participate in oxidation of sulfide minerals as well as the nature of their relationships. As the new techniques for identification of microorganisms are discovered and developed the knowledge of the biodiversity of microorganisms capable of growth on dump ores, mine tailings and etc., has increased. This knowledge is of great commercial importance. This type of habitat are characterised by heterogeneous growth environment which influences time and spatial differences in population compositions of the microorganisms. Due to recent research a high biodiversity of those microorganisms was described as well a presence of phylum Firmicutes. The results from the laboratory experiments which have simulated both stirred tank and heap boireactor systems have shown that microbial consortia are more robust than pure cultures of acidophiles, and also tend to be more effective at bioleaching and bio-oxidising ores and concentrates.
Cationic surfactants-modified natural zeolites: improvement of the excipients functionality
No full textContext: In this study an investigation of cationic surfactants-modified natural zeolites as drug formulation excipient was performed. Objective: The aim of this work was to carry out a study of the purified natural zeolitic tuff with high amount of clinoptilolite as a potential carrier for molecules of pharmaceutical interest. Materials and methods: Two cationic surfactants (benzalkonium chloride and hexadecyltrimethylammonium bromide) were used for modification of the zeolitic surface in two levels (equal to and twice as external cation-exchange capacity of the zeolitic tuff). Prepared samples were characterized by Fourier transform infrared spectroscopy, thermogravimetric, high-performance liquid chromatography analysis, and powder flow determination. Different surfactant/zeolite composites were used for additional investigation of three model drugs: diclofenac diethylamine, diclofenac sodium, and ibuprofen by means of adsorption isotherm measurements in aqueous solutions. Results: The modified zeolites with two levels of surfactant coverage within the short activation time were prepared. Determination of flow properties showed that modification of zeolitic surface reflected on powder flow characteristics. Investigation of the model drugs adsorption on the obtained composites revealed that a variation between adsorption levels was influenced by the surfactant type and the amount present at the surface of the composites. Discussion and conclusion: In vitro release profiles of the drugs from the zeolite-surfactant-drug composites revealed that sustained drug release could be attained over a period of 8 hours. The presented results for drug uptake by surfactant-zeolite composites and the afterward drug release demonstrated the potential use of investigated modified natural zeolite as excipients for advanced excipients in drug formulations
Biosorption as a new biotechnology with an aim of protection and balanced use of biodiversity
No full textUbrzan tehno-ekonomski razvoj, bez adekvatne zaštite životne sredine, je prouzrokovao pojavu velikog broja problema: zagađenje, otpad, gubitak biodiverziteta, uvođenje invazivnih vrsta, oslobađanje genetski modifikovanih organizama, itd. Zaštita i očuvanje prirodnih dobara i biodiverziteta zahteva integralni pristup u održivom upravljanju. Jedan od pristupa je i stimulisanje razvoja novih biotehnologija u funkciji očuvanja i uravnoteženog korišćenja biodiverziteta. Povećana industrijska proizvodnja je dovela do ozbiljnih problema u životnoj sredini uzrokujući starenje nekoliko ekosistema zbog akumulacije polutanata. Veliko interesovanje u svetu postoji za biološkim materijalom, bakterijama, algama, kvascima i gljivama, kao biosorbentima za uklanjanje teških metala, zbog njihove niske cene, dobrih performansi i dostupnosti u većim količinama. Biosorpcija se može definisati kao sposobnost određenih biomolekula (ili tipova biomase) da vežu ili koncentrišu određene jone ili druge molekule iz vodenih rastvora. Biosorbenti za razliku od monofunkcionalnih jonoizmenjivača, sadrže različite funkcionalne grupe. Ovi materijali, kao jeftini ali efikasni adsorbenti, predstavljaju dobro rešenje za uklanjanje metala, posebno teških metala iz vodenih rastvora. Različite vrste biosorbenata koje su smatrane za otpad dobijaju novu primenu i produžava im se životni ciklus. Pristup biosorpciji je multidisciplinaran sa tačke hemijskog, mikrobiološkog i procesnog inženjerstva i omogućava širi spektar remedijacionih tehnika u odnosu na jonsku izmenu. Ovaj rad predstavlja pregled savremenih trendova u biosorpciji i prikaz korišćenih biosorbenta za uklanjanje polutanata (teški metali i radionuklidi) iz kontaminiranih efluenata i voda. .Rapid techno-economic development, without adequate protection of the environment, caused a number of emergence problems: pollution, waste, loss of biodiversity, introduction of invasive species, release of o genetically modified organisms etc. Protection, conservation of natural resources and biodiversity requires an integrated approach to sustainable management. One approach is to stimulate the development of new biotechnology with an aim of saving and balanced usage of biodiversity. An increased industrial activity has intensified more environmental problems such as deterioration of several ecosystems due to the accumulation of pollutants. A vast array of biological materials, especially bacteria, algae, yeasts and fungi have received increasing attention for heavy metal removal due to their good performance, low cost and large available quantities. Biosorption has been defined as the property of certain biomolecules (or types of biomass) to bind and concentrate selected ions or other molecules from aqueous solutions. Biosorbents, unlike mono functional ion exchange resins, contains variety of functional sites. Advantages of these materials are their efficiency and low cost and application of biosorbents is good solution for removing metals, especially heavy metals from aqueous solutions. Different types of biosorbents that were considered for waste are getting a new application with extending product life cycle. Biosorption needs a multidisciplinary approach from the point of chemical, microbiological and process engineering, and allows a wider range of remediation techniques in relation to the ion exchange. This paper presents an overview of trends in biosorption and application of biosorbents for removing the pollutants (heavy metals and radionuclides) from contaminated effluents and water.
Passivation of chalcopyrite during the leaching with sulphuric acid solution in presence of sodium nitrate
No full textU radu su prikazani rezultati ispitivanja luženja halkopiritnog koncentrata rastvorom sumporne kiseline u prisustvu natrijum-nitrata. Izračunate standardne vrednosti Gibsove energije reakcija luženja i analiza E-pH dijagrama stabilnosti potvrdili su mogućnost luženja bakra i železa iz halkopiritnog koncentrata u ispitivanim uslovima. U oksidacionim uslovima pri niskoj vrednosti pH bakar prelazi u rastvor kao Cu2+, a železo kao Fe2+ i Fe3+. Rendgenska difrakciona i termijska analiza (TG/DTA) čvrstih ostataka dobijenih pri različitim uslovima luženja, pokazuju prisustvo halkopirita i elementarnog sumpora, čime je potvrđeno predviđanje da se sulfidni sumpor oksidiše do elementarnog oblika. Skenirajućom elektronskom mikroskopijom (SEM/EDX) utvrđeno je da se nastali sumpor taloži po površini halkopiritnih mineralnih zrna i usporava reakciju u kasnijoj fazi luženja. Taloženjem sumpora dolazi do promene mehanizma procesa iz kinetičkog u difuziono kontrolisani.In this work, the process of the chalcopyrite leaching in sulphuric acid solution was investigated. Sodium nitrate was used as oxidant in the leaching process. Chemical reactions of leaching and their thermodynamic possibilities are predicted based on the calculated Gibbs energies and analysis of E-pH diagrams. The negative values of the Gibbs energy show that all chemical reactions are thermodynamically feasible at atmospheric pressure and in a temperature range 25-90°C. At high electrode potential and low pH values, Cu2+, Fe2+ and Fe3+ exist in water solutions. The increase of temperature reduces the probability of Fe3+ existence in the system. The chalcopyrite concentrate, enriched in the 'Rudnik' flotation plant, with 27.08% Cu, 25.12% Fe, 4.15% Zn and 2.28% Pb was used in the work. XRD and DTA analysis of the concentrate reveals that the sample contains mainly the chalcopyrite with small amount of sphalerite. For the description of the reaction of leaching process the leach residuals, obtained at different conditions, were chosen for XRD, TG/DTA and SEM/EDX analyses. The elemental sulphur and chalcopyrite phases identified in leach residuals confirm our prediction that the elemental sulphur is formed during the leaching process. Accordingly, elemental sulphur is the main product of the reaction, while a minor amount of sulphide sulphur is oxidized to sulphate during the leaching. The sulphur formed during the reaction was precipitated at the particle surfaces, and slowed down the leaching rate in the final stage of leaching process. In the initial stage, the reaction rate was controlled by the surface reaction. The mechanism, latter has been changed into a diffusion controlled one
The influence of filler type on the corrosion stability of the sulfur concrete
No full textU radu je ispitana koroziona otpornost sumpornog betona u uslovima različitih hemijski agresivnih sredina. Polazne komponente za dobijanje sumpornog betona bile su agregat definisanog sastava, modifikovano sumporno vezivo i različiti punioci (talk, glinica, mikrosilika i elektrofilerski pepeo). Ispitivanje materijala na otpornost u agresivnim sredinama i to u 20% H2SO4, 10% HCl i 3% NaCl na sobnoj temperaturi praćeno je promenom mase i čvrstoće sumpornog betona u trajanju do 360 dana. Rezultati su pokazali da uzorci sumpornog betona sa elektrofilterskim pepelom i talkom imaju bolju korozionu otpornost u kiselim sredinama u odnosu na betone sa glinicom i mikrosilikom. Svi uzorci imaju izuzetnu korozionu otpornost u rastvorima NaCl, pri čemu su najbolji uzorci sa talkom kao puniocem. Radi poređenja, praćena je i otpornost klasičnog portland cementnog betona u istim sredinama.Sulfur concrete was prepared by using the initial components: sand as an aggregate, modified sulfur binder, and talc, alumina, microsilica, and fly ash as fillers. Portland cement concrete was made from the same aggregate and fillers and portland cement. The durability of the prepared concrete samples was tested in the following aggressive solutions: 10% HCl, 20% H2SO4, and 3% NaCl as a function of time. Changes in mass and strength of the sulfur concrete were monitored periodically during the immersion time of 360 days in above solutions. These changes were used as a measure of deterioration level. It should be highlighted that the samples with the ash and especially talc exhibit higher durability in the solutions of HCl and H2SO4 than the samples with alumina and microsilica. In the solutions of NaCl all samples have shown excellent durability while the samples with talc were the best. Portland cement concrete samples lost 20% of mass after two months and showed degradation of mechanical properties. By usage of sulfur for sulfur concrete production, a huge environmental problem regarding storage of waste sulfur from oil refining processes is solved. On the other hand, sulfur concrete with its low price has an excellent quality for the application in aggressive environments unlike the more expensive PCC
Metallic implants surface modification by deposition of hap coatings
No full textU radu ce biti prikazane mogućnosti primene plazma sprej postupka i elktroforetskog taloženja hidroksiapatitne prevlake na metalnu osnovu. U ortopedskoj hirurgiji implantati se najčešće izrađuju od legura titana ili nerđajućeg čelika na koje se nanosi hidroksiapatitna (HAp) prevlaka. Hemijski sastav sintetičkog hidroksiapatita je identičan onom koji čini mineralnu građu kostiju i zuba. Zato ga organizam prihvata kao biokompatibilan. Međutim, on nema zadovoljavajuću mehaničku čvrstoću da bi sam mogao da izdrži opterećenja u dužem vremenskom periodu. Njegovim nanosenjem na metalnu osnovu implantata dobijaju se dugotrajne i mehanički stabilne bescementne proteze.Hydroxyapatite coatings are being deposited on orthopedic implants metal surface to obtain biocompatibile cementless prostheses. There is chemical identity between synthetic hydroxyapatite and the one that makes teeth and bones mineral structure, so it can be easily accepted as biocompatibile by human organism. Disadvantage is the lack of long-term mechanical strength, what implies its application as a coating on an implant made of titanium alloy or stainless steel. There are several up to date technological methods for deposition these coatings on metallic implants, some of them are atmospheric plasma spray method. and electrophoretic deposition
Zn1.86Cd0.14(OH)VO4
No full textThe title compound, dizinc cadmium hydroxide tetraoxido-vanadate, Zn 1.86Cd0.14(OH)VO4, was prepared under low-temperature hydro-thermal conditions. It is isostructural with Zn 2(OH)VO4 and Cu2(OH)VO4. In the crystal structure, chains of edge-sharing [ZnO6] octahedra are inter-connected by VO4 tetra-hedra (site symmetries of both V atoms and their coordination polyhedra are.m.) to form a three-dimensional [Zn(OH)VO4]2- framework with channels occupied by Zn and Zn/Cd cations adopting trigonal-bipyramidal and distorted octa-hedral coordinations, respectively. Zn1.86Cd0.14(OH)VO 4 is topologically related to adamite-type phases, and descloizite- and tsumcorite-type structures
Phytotoxic Effect of the Uranium on the Growing Up and Development the Plant of Corn
No full textThe aim of this article is the determination of uranium accumulation in plants tissue in shoots and roots of corn-maize (Zea mays), grown on two types of soils, pseudogley and chernozem, together with its phytotoxic effect on the plant growth and development. The soils was contaminated with different rates (10 to 1,000 mg U(VI) kg(-1)) of uranyl nitrate (UO2(NO3)(2)center dot 6H(2)O). Vegetative tests performed with maize indicated uranium phytotoxic effect on plant height, yield, and germination of seeds. This effect was stronger on the plants grown on pseudogley in comparison with those grown on chernozem. Soil properties determined the tolerance and accumulation of U in plants. A linear dependence between the content of uranium in soil and in plants tissue, including maximal content of 1,000 mg U kg(-1), indicates that maize could be used for phytoremediation of uranium-contaminated soils