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Substrate preheating and structural properties of power plasma sprayed hydroxyapatite coatings
No full textThe aim of the present study was to investigate the influence of substrate preheating on the structural properties of hydroxyapatite coatings (HACs) deposited by using the high power (52 kW) laminar plasma jet. The deposition experiments were performed within the 20-200 degrees C temperature range at different stand-off distances. The structural properties in the thickness direction and at the surface of the HACs were investigated by using the micro-Raman spectroscopy, scanning electron microscopy coupled with energy dispersive spectrometry, and X-ray powder diffractometry. The deposition without the preheating of the substrate produced HACs with crystallinity gradient in the thickness direction. At the stand-off distance of 80 mm, the preheating of the substrate at 200 degrees C practically eliminated the crystallinity gradient. At distances from the coating/substrate interface shorter than similar to 100 mu m, the increase of crystallinity with the preheating of the substrate was dominantly attributed to the recrystallization of hydroxyl-rich ACP into HA. At longer distances and higher initial substrate temperatures ( > 100 degrees C), the crystallinity changes were negligible, whereas the recrystallization of hydroxyl-deficient ACP into oxyapatite (OA) was also possible. The X-ray diffractometry indicated the deposition conditions under which a minimum residual stress was achieved. The results of the present study strongly suggested the relation between the ACP -> HA remystallization process and the bonding strength of the HACs
(Pb–Sb)-bearing sphalerite from the Čumavići polymetallic ore deposit, Podrinje Metallogenic District, East Bosnia and Herzegovina
No full textČumavići is a medium– to low–temperature hydrothermal Sb–Zn–Pb–Ag polymetallic vein–type ore deposit in the Srebrenica orefield, part of the Podrinje Metallogenic District, Eastern Bosnia and Herzegovina. The ore deposit occurs in the form of simple and complex veins along faults and fractures, as well as stockworks and disseminations hosted within Neogene volcanic rocks (pyroclastics and andesite lavas of calc–alkaline affinity). The deposit comprises sulfides (sphalerite, galena, stibnite, pyrite, marcasite, chalcopyrite, arsenopyrite, gudmundite, safflorite, löllingite, gersdorffite and acanthite), sulfosalts (berthierite, geocronite, boulangerite, semseyite, plagionite, jamesonite, bournonite, twinnite, andorite, fizéliyte, Ag–bearing tetrahedrite, stephanite, polybasite, pyrargyrite and argyrodite), native gold and silver, tungstates (hübnerite), oxides, and gangue quartz, chalcedony, Mn–siderite, anglesite, smithsonite, fluorite, gypsum and ludlamite. Three generations of sphalerite are recognized in the Čumavići deposit, evolving from Fe–rich to Fe–poor. The most common are yellowish to colorless Fe–poor varieties. Electron Probe Microanalyses of sphalerite free of micro–inclusions of galena and Pb–Sb-sulfosalts revealed wide compositional variations in minor- and trace–element contents (e.g., Fe, Cd, Mn, Cu, Sn, As, and In). Of particular interest are the lead and antimony content of sphalerite, which vary from 0.10 to 3.08, and 0.02 to 1.62 wt.%, respectively. Lead– and Pb–Sb-rich zones are the most common in sphalerite, while individual Sb–bearing zones are rare. These zones have fan–like forms with circular to wave-like, micron–scale bands, filled with galena or Pb–Sb sulfosalts. In the Pb–Sb zones, the Sb/Pb atomic ratio ranges between 0.3 and 1.5, similar to ratios between geocronite and jamesonite, thus suggesting the presence of micro– to nano–scale inclusion of sulfosalts within the sphalerite. The mean composition of all sphalerite samples is (Zn0.78–0.99,Fe< 0.01–0.21,Cu0.00–0.02,Pb< 0.01–0.01,Cd< 0.01–0.01,Sb< 0.01–0.01,Mn< 0.01–0.01)∑ 0.97–1.03S0.97–1.08 (Sn and As atomic proportions are < 0.01 apfu). In all sphalerite samples, excellent negative correlations have been determined between Fe and Zn, and ∑(Fe + Sb) and Zn. The studied mineralization shares many mineralogical and geological characteristics in common to polymetallic Sn–Ag–Sb deposits in Bolivia and elsewhere
Checking the formulation modeling process of industrial mill for different types of grinding bodies
No full textThis paper presents checking the formulation modeling process of industrial mill for different types of grinding bodies. It is known that changing the type of drilling bodies realizes various efficiency of grinding the mineral raw materials and/or different grinding fineness. This paper gives a hypothesis on bulk mass (density) of a mill batch as an influential factor to the size of specific grinding capacity of the specific mineral resources. The experiment was carried out in the industrial conditions of grinding when the Damkohler's criteria = was calculated [1]. Verification of this formulation was done in the industrial conditions, and testing results are present in this paper
Kinetic of thermal degradation of alginate-zeolite composites
No full textU ovom radu ispitivana je upotreba prirodnog i Fe(III)-modifikovanog zeolite kao aditiva alginatu u cilju poboljšanja njegovih termijskih i pirolitičkih osobina. Za tu namenu korišćeni su uzorci prirodnog (PZA) i Fe(III)-modifikovanog zeolita prekrivenih alginatom (FeA). Sagorevanje uzoraka praćeno je termijskim analitičkim tehnikama, diferencijalnom termijskom analizom (DTA) i termogravimetrijskom analizom (TGA). Uzorci su zagrevani u temperaturskom intervalu od 25 do 1000ºC pri različitim brzinama zagrevanja (od 5 do 20ºC). Na osnovu eksperimentalnih rezultata, merenjem gubitka mase, termijsko razlaganje natrijum alginata se jasno može podeliti u nekoliko koraka. Na osnovu kinetičkog modela pseudo-prvog reda određeni su kinetički parametri (aktivaciona energija i pred eksponencijalni faktor) koji se odnose na temperaturski interval od 180 do 500ºC. Dobijeni rezultati su pokazali da upotrebljeni zeoliti utiču na termijske osobine alginata kao i da smanjuju aktivacionu energiju potrebnu za njegovu pirolizu sa 87,30 kJ/mol za čist alginat na 72,75 kJ/mol za PZA i 63,35 kJ/mol za FeA. Ova ispitivanja mogu biti korisna za bolje razumevanje termijske stabilnosti alginatnih biokompozita i mogu dati informacije važne za termijske procese biorazgrađujućih materijala.In this work, natural and Fe(III)-modified zeolte were tested as additives for alginate in order to improve its thermal and pyrolytic properties. For that purpose the natural zeolite (NZA) and Fe(III)- modified zeolite coated with alginate (FeA) were used. Thermal degradation of the samples was investigated by using thermal analytic techniques, thermogravimetric (TG) and differential thermal analysis (DTA). The samples were heated from 25oC to 1000ºC at different heating rates (from 5 to 20ºC). From experimental results, thermal degradation of the sodium alginate could be clearly separated into several stages based on the weight loss and the weight loss rate. The kinetic parameters (activation energy and pre-exponential factor) for the main degradation phase (from 180 to 500ºC) thus were estimated by using the pseudo first-order assumption. The results showed that used zeolites affected the thermal properties of the alginate and reduce activation energy required for pyrolysis from 87.30 kJ/mol for pure alginate to 72.75 kJ/mol for NZA and 63.35 kJ/mol for FeA. These pyrolysis investigations can be useful for better understanding the thermal stability of these alginate biocomposites and provide necessary information for thermally processing wastes from these biodegradable materials
Kinetics of barite reduction from refractory barite-sulphide ore
No full textRefractory sulphide-barite ore was reduced with carbon in order to release lead, zinc, and copper sulphide from barite-pyrite base. Mineralogical investigations showed that due to the complex structural-textural relationships of lead, copper and zinc minerals with gangue minerals, it is not possible to enrich the ore using the conventional methods of mineral processing. The influence of temperature and time was studied to optimize the conditions, and to determine the kinetics of the barite reduction. The maximum removal of barite from ore was 96.7% at 900oC after 180 min. Chemically controlled kinetic model showed the best compliance with the experimental data. An activation energy of 142 kJ/mol was found
Removal of Pb2+ ions by raw corn silk (Zea mays L.) as a novel biosorbent
No full textThere is no data about the corn silk usage as adsorbent for lead removal. In the present study, the corn silk (CS), without any modification, was investigated for adsorption of Pb2+ ions from aqueous solutions. The CS before and after Pb2+ adsorption was characterized by SEM-EDX and ATR-FTIR. The effect of pH, contact time, CS dosage and initial metal concentration on process of adsorption was investigated using batch adsorption procedure. The experimental data were fitted to Langmuir and Freundlich isotherm models, and the best data fit was achieved with the Freundlich isotherm model. Also the Langmuir and Freundlich isotherm models constants R-L and n suggesting favorable adsorption of Pb2+ on the CS. Not only the ion -exchange mechanism was confirmed as an adsorption mechanism but the complexation process has also been verified according to results from ATR-FTIR spectra. Thermodynamic parameters were investigated too. Based on desorption study result, the adsorbent can be efficiently recovered. The present investigation qualified the corn silk (Zea mays L.) as a possible good adsorbent of lead from aqueous solutions
Synthesis and characterization of fluorapatite/polyethylene composite
No full textIn the present study, fluorapatite/polyethylene composite was prepared and
characterized by means of different techniques (XRD and TEM). The
effects of fluorapatite on the composite properties were investigated. It is
found that the fluorapatite–polyethylene composite has an immiscible intercalated structure
Pb(II) biosorption by selected waste biomass
No full textZaštita životne sredine na globalnom nivou zahteva evaluaciju otpadne biomase kao potencijalnog biosorbenta teških metala. Ovaj rad daje pregled korišćenja vodenog korova Miriophillum spicatum i njegovog komposta kao i odabranog poljoprivrednog otpada: kukuruzne svile, koštica breskve i kajsije kao biosorbenata jona olova. Ove biomase su okarakterisane Skenirajućom elektronskom mikroskopijom (SEM). Rezultati studija o efikasnosti ovog bio-otpada pokazuju da pored široke dostupnosti ova otpadna biomasa poseduje i značajne biosorpcione kapacite. Ovaj rad pruža kritički stav za buduće primene ovakve vrste biosorbenata otpadnog porekla, u tretmanu otpadnih voda zagađenih teškim metalima.Global concerns regarding environmental issues have required the evaluation of the waste biomass as potential biosorbents of heavy metals. This paper provides a review on using aquatic weed Myriophyllum spicatum and its compost and selected agricultural wastes: corn silk, peach and apricot stones as biosorbents of lead ions. These biomasses were characterized by Scanning electron microscopy (SEM). The results of the studies on adsorbent efficiency of these bio wastes show that they apart from their wide availabilities are enriched with appreciable biosorption capacities. The paper also provides a critical view concerning future applications of this kind waste biosorbents in treatment of heavy metal contaminated water
Identification of a Novel Series of Benzohopanes and Their Geochemical Significance
No full textseries of novel C-33-C-35 hexacyclic benzohopanes (C(33)b-C(35)b) were identified in 39 samples of coal extracts and 39 crude oils of different ages from all over the world. C(33)b and C(34)b homologues were isolated, and their structures were determined by nuclear magnetic resonance. The structure of C(35)b benzohopane was proposed based on the mass spectrum and its similarity with the mass spectra of structurally defined C(33)b and C(34)b homologues. The structures of the C(33)b-C(35)b hexacyclic benzohopanes are closely related to isohopanes; both groups are typical for terrestrial organic matter and can be useful in the correlation analysis. A possible pathway of formation of these novel benzohopanes and their hopanoid precursors with an additional branch in the aliphatic side chain is proposed. C(33)b-C(35)b hexacyclic benzohopanes are stable up to the maturity level corresponding to random vitrinite reflectance (Rr) of similar to 0.80%, which was demonstrated by analyzing the samples of different maturity and by the maturation simulation experiments: hydrous pyrolysis of two bituminous coals (Rr = 0.55 and 0.59%) and pyrolysis of an extracted bituminous coal (Rr = 0.56%) and its asphaltenes. This represents a confirmation that the formation of these novel benzohopanes is related to specific depositional conditions and microbial activity during diagenesis. Mature samples (Rr = 0.8%) and hydrous pyrolysate of the bituminous coals (Rr LT 0.60%) obtained at 330 degrees C show a distinct distribution of benzohopanes in comparison to immature and moderately mature samples, which is characterized by a low abundance of the b series benzohopanes and the presence of regular and numerous other benzohopane isomers. The latter most likely represent isomers of regular and novel benzohopanes with different substitution patterns on the aromatic ring. This isomerization of alkyl groups attached to the aromatic ring, leading to the formation of thermodynamically more stable isomers, is a well-known maturation scenario so far reported in the series of alkylated naphthalenes, phenanthrenes, and dibenzothiophenes. Therefore, in the same way, a distribution of benzohopanes can indicate thermal maturity. In addition to the novel benzohopanes, three series (2 alpha, 2 beta, and 3 beta) of their methylated derivatives were identified in numerous samples. Finally, a novel C-35 heptacyclic benzohopane with an additional cyclopentane ring was also observed in the studied samples, and its structure was tentatively identified based on the mass spectrum. Opposite to the hexacyclic C(33)b-C(35)b benzohopanes, the formation of the C-35 heptacyclic benzohopane does not require a specific hopanoid precursor with two branches in the side chain. Therefore, this compound seems to have less geochemical significance than the new hexacyclic benzohopanes
Designing of Synergistic Waste Mixtures for Multiphase Reactive Smelting
No full textElectric arc furnace (EAF) dust, together with a mill scale and coke were smelted in a laboratory electric arc furnace. These metallurgical wastes consist of a many different phases and elements, making the reaction process complex. Thermo-chemical analysis of the reactions in metal, slag, and gas phases was done, and used for modeling of the mixture composition and energy consumption required for smelting. Modelling was performed with the software named RikiAlC. The crude ZnO, slag, and metal phase were analyzed using the atomic absorption spectrometry (AAS), the optical emission spectrometry with inductively coupled plasma (ICP-OES), the X-ray diffraction (XRD), the scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS), and reflected and transmitted light microscopy. Also, in order to follow the behavior of this process the exhausted gases were monitored. The synergetic effects of the designed mixture may be recognized in minimizing energy consumption for the smelting process, improving the product yield efficiency, and reducing the negative environmental effects