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Kinetics of NiO and NiCl2 hydrogen reduction as precursors and properties of produced Ni/Al2O3 and Ni-Pd/Al2O3 catalysts
No full textThe objects of this investigation were the comparative kinetic analysis of the NiO and NiCl2 reduction by hydrogen during an induction period and elimination of the calcination during the synthesis of Ni/Al2O3 catalysts. The effect of temperature and time on NiO and NiCl2 reduction degrees was studied. Avrami I equation was selected as the most favorable kinetic model and used to determine activation energy of the NiO and NiCl2 reduction for the investigated temperature range (623-923 K) and time intervals (1-5 minutes). The investigation enabled reaching conclusions about the reaction ability and rate of the reduction processes. Afterward, Ni/Al2O3 catalysts were obtained by using oxide and chloride precursor for Ni. The catalysts were supported on alumina-based foam and prepared via aerosol route. Properties of the samples before and after low-temperature hydrogen reduction (633 K) were compared. Obtained results indicated that the synthesis of Ni/Al2O3 catalysts can be more efficient if chloride precursor for Ni is directly reduced by hydrogen during the synthesis process, without the calcination step. In addition, Ni-Pd/Al2O3 catalysts with different metal content were prepared by using chloride precursors. Lower reduction temperature was utilized and the chlorides were almost completely reduced at 533 K
Hydrophobization of limestone from the deposit 'Cancar' Aranđelovac using stearic acid
No full textU radu su prikazani rezultati ispitivanja mogućnosti hidrofobizacije kalcita Iz ležišta 'Cancar' firme 'Dobar kamen' - Aranđelovac, Srbija. Hidrofobizacija površine kalcita je vršena stearinskom kiselinom, a korišćeni uzorak je proizvod dobijen iz fabrike 'Dobar kamen' srednjeg prečnika zrna 29,14 μm. Koncentracije stearinske kiseline u eksprimentima su bile: 0,3; 0,5; 0,8; 0,9, 1; 2, 2,5, 3 i 4%. Rezultati hidrofobizacije su pokazali da je potpuna hidrofobnost (Io=99,9%) ovog uzorka kalcita postignuta pri koncentraciji stearinske kiseline od 3%.The paper presents the results of investigation of the possibility of hydrophobization of calcite from deposit 'Cancar' company 'Good stone' - Aranđelovac, Serbia. Hydrophobization of calcite surface is performed with stearic acid, and the sample which is used is a product made from the 'Good stone' mean grain diameter 29,14μm. The concentration of stearic acid in the experiment, were as follows: 0.3; 0.5; 0.8; 0.9, 1; 2, 2.5, 3 and 4%. Results showed that the hydrophobization degree of coating increases with increasing concentration of the stearic acid used for modifying. This indicates that was not changed orientation of the hydrocarbon chains in the adsorbed layer with increasing concentrations of stearic acid available for adsorption. Adsorption was always such that the molecules of stearic acid kept the orientation of its hydrophobic portion (the hydrocarbon chains) opposite to surface of the calcite. As the degree of coating can be taken as a measure of hydrophobicity of the obtained products, results suggest that complete hydrophobicity of the surface of calcite occurs at a concentration of 3%
Optimization of the arsenic removal process from enargite based complex copper concentrate
No full textU prikazanom radu ispitivana je selektivna ekstrakcija arsena iz kompleksnog koncentrata na bazi enargita iz rudnika bakra u Boru, korišćenjem Na-hipohlorita kao agensa za luženje. Osnovni cilj istraživanja sastojao se u utvrđivanju uticajnih parametara i njihovog međusobnog odnosa kako bi se ostvarilo maksimalno uklanjanje arsena iz ispitivanog koncentrata. Enargit (Cu3AsS4) spada u rasprostranjene kontaminante koncentrata bakra. Tokom procesa prženja i topljenja arsen obrazuje lako isparljiva jedinjenja koja vrlo negativno utiču na zagađenje ljudi, radne i životne sredine. Zakonska regulativa ne dozvoljava topionicama bakra da tope koncentrate sa više od 0,5% arsena. Za dobijanje optimalnih uslova procesa uklanjanja arsena iz kompleksnog koncentrata bakra na bazi enargita, korišćena je tehnika matematičkog modelovanja. Modelovanje je izvršeno primenom faktorskog dizajna na eksperimentalno dobijene podatke. Odabrano je pet karakterističnih parametara procesa - ulaznih varijabli, za koje se pretpostavlja da imaju uticaja na stepen ekstrakcije arsena: koncentracija rastvora hipohlorita, masa uzorka (koncentrata), brzina mešanja, temperatura luženja i vreme luženja. Faktorski (2n) dizajn zahtevao je izvođenje 16 eksperimenata sa šest replikanata. Nakon izvođenja 22 eksperimenta, rezultati ekstrakcije arsena uzeti su kao izlazna varijabla. Proračunom su dobijene jednačine modela prvog i drugog reda. Koeficijenti u modelu drugog reda ukazuju da temperatura luženja ima najveći uticaj na ekstrakciju arsena. Drugi faktor po značaju je vreme luženja. Pozitivni predznaci ispred ova dva najuticajnija parametra ukazuju da povećanje temperature luženja, odnosno vremena luženja, utiču na povećanje stepena uklanjanja arsena iz ispitivanog koncentrata. Najveća pozitivna interakcija zapažena je između koncentracije hipohlorita i brzine mešanja tokom procesa ekstrakcije. Proračun RMSE (root mean square error) pokazao je dobro slaganje između vrednosti dobijenih eksperimentalnim istraživanjem i vrednosti dobijene modelovanjem. Pouzdanost finalnog modela testirana je primenom ANOVA testa.Selective arsenic extraction from enargite based complex concentrate from Copper Mine in Bor (Serbia), using sodium hypochlorite as a leaching agent, was investigated in this paper. The aim was to assess the optimal conditions for the most efficient arsenic removal from the investigated concentrate, based on factorial design applied to experimentally obtained data. Five important factors with three factor levels were used as the input variables and experimentally obtained arsenic extraction yield was taken as the output variable. The first and the second final order model equations were obtained. It was found that the leaching temperature had the strongest effect on the arsenic extraction. The strongest positive interaction was between the sodium hypochlorite molar concentration and the stirring speed during extraction
Investigation of thermally induced processes in corundum refractory concretes with addition of fly ash
No full textThe effects that the fly ash addition has on the behavior of thermally resistant corundum concrete were discussed. Experimental program implied production of two refractory composites: "referent" concrete from 20 % of high-aluminate cement and 80 % of corundum aggregate, "recycled" concrete from 10 % of high-aluminate cement, 20 % of lignite coal ash, and 70 % of corundum aggregate. The fly ash was mechanically activated by a vibratory disk mill. In the concrete matrix, the ash had a role of cement partial replacement and microfiller. The mechanical and thermal properties of the concretes were studied at temperatures ranging from ambient to 1,400 A degrees C as adopted maximum. Mechanisms of thermally induced processes were observed by differential thermal analysis at 10, 20, and 30 A degrees C min(-1) heating rates. Referent and recycled concretes showed differences in calculated activation energies. The variations in refractory concretes performances were discussed with support of scanning electron microscope imagining and X-ray diffraction results. The recycled ash concrete exhibited properties that met the requirements for the castables, which proves it suitable for use in severe conditions at high temperature and highlights the reusing principle and possibility of cleaner and economically sustainable production
Pilot-plant flotation testing of copper, lead and zinc minerals from rich polymetallic ore
No full textThe investigation results presented in this paper were performed in order to examine the possibility of efficient processing of valuable minerals from the rich complex polymetallic ore with extremely high content of copper, lead and zinc (0.86% Cu, 4.46% Pb and 2.51% Zn). These tests were carried out in pilot-plant facility of the Laboratory for mineral processing in Institute for Technology of Nuclear and Other Mineral Raw Materials(ITNMS). The role of scientific research is to thoroughly investigate the flotation concentration of valuable components and to confirm the laboratory tests on which the technological scheme to produce a separate concentrates of copper, lead and zinc is defined, on pilot-plant scale. While performing those pilot-plant tests, it was found that it is possible to produce three commercial products from this ore, following a copper, lead and zinc rough concentrates single-stage cleaning
Biosorption of heavy metals by agro waste biomass
No full textHeavy metals pollution of wastewater has become an important issue with respect to the environmental and
human health. Biosorption, using the agro waste materials is observed as the low-cost and eco-friendly method for
removal of heavy metals from wastewater. This paper promotes the biosorption process as a potential alternative to
the conventional methods for t removal of heavy metals from wastewater. The biosorption capacity of different agro
waste materials has been also discussed with focus to the operating parameters, which affected the biosorption
process. Mechanisms involved in biosorption of heavy metals from wastewater include the ion exchange,
chemisorption, microprecipitation, complexation and chelatation
Development of hybrid orgаnic-inorgаnic (bio)sorbents for Pb(II) removаl
No full textPromising new removal of pollutants and the improvement of existing ones make up development of new sorbents with improved sorbing properties. With this aim, this research include the development of hybrid organic-inorganic and combined (bio)sorbents. The use of biomass originated materials for cleansing of wastewaters is extensively studied. Removal of lead ions from aqueous solutions was examined with different materials: Myriophyllum spicatum, peach pits, modified apricot pits, corn cobs, bentonite, zeolite, apatite. Two materials organic and inorganic with best characteristic – capacities of removal Pb(II) were selected for development of combined (bio)sorbents. Selected mixture of 75% M. spicatum and 25% bentonite showed lead binding capacity of 45 mg/g. The main effective biding sites were identified by FTIR spectral comparison of the pure and lead (bio)sorbed material: M. spicatum, bentonite and their best mixture 75%MS-25%B. Our research is applied to the expansion of ways of updating vegetative waste products and mineral materials with the purpose of improving their ability to selectively remove ions of heavy metals and application of this hybrid organic-inorganic - (bio)sorbents is innovative, simple and low cost
Ecological and corrosion behavior of depleted uranium
No full textPoslednjih decenija se sve više govori o 'new pollutant' - osiromašenom uranijumu (OU), koji se koristi u protivtenkovskim penetratorima zbog svoje velike gustine, prodornosti i pirofornih svojstava. Procenjuje se da je za vreme NATO agresije na bivšu Jugoslaviju 1999. god., približno 10 t osiromašenog uranijuma uneto u životnu sredinu, uglavnom na poljoprivredno zemljište. U vreme tih dešavanja je bilo vrlo malo dostupnih informacija o ponašanju ekoloških sistema narušenih ostacima penetratorima sa OU. Danas, nakon četrnaest godina, sve više se susrećemo sa 'nevidljivom pretnjom' upotrebe municije sa OU, koji ima snažan radioaktivni i hemotoksični uticaj na ljudsko zdravlje. Ovaj rad pruža pregled korozionog i ekološkog ponašanja OU, zajedno sa indikatorima uticaja na životnu sredinu, sa ciljem da se istaknu oblasti koje zahtevaju dodatnu pažnju u izradi remedijacionih programa.Environmental pollution with radionuclides, particularly uranium and its decay products is a serious global problem. The current scientific studies estimated that the contamination originating from TENORM, caused by nuclear and non-nuclear technologies, has significantly increased natural level of radioactivity in the last thirty years. During the last decades all the more were talking about the 'new pollutant' - depleted uranium (DU), which has been used in anti-tank penetrators because of its high density, penetration and pyrophoric properties. It is estimated that during the Gulf War, the war in Bosnia and Yugoslavia and during the invasion of Iraq, 1.4 million missiles with depleted uranium was fired. During the NATO aggression against the ex Yugoslavia in 1999, 112 locations in Kosovo and Metohija, 12 locations in southern Serbia and two locations in Montenegro were bombed. On this occasion, approximately 10 tons of depleted uranium were entered into the environment, mainly on land, where the degree of contamination ranged from 200 to 235000 Bq/kg, which is up to 1000 times higher than the natural level. Fourteen years ago there was very little information about the behavior of ecological systems damaged by DU penetrators fired. Today, unfortunately, we are increasingly faced with the 'invisible threat' of depleted uranium, which has a strong radioactive and hemotoxic impact on human health. Present paper provides a detailed overview of the current understanding of corrosion and corrosion behavior of DU and environmental factors that control corrosion, together with indicators of environmental impact in order to highlight areas that need further attention in developing remediation programs
Chemometric Approach for Mechanical Properties Prediction during the Electromagnetic Casting Process
No full textIn this study the mechanical properties (reduction of area, S-0, tensile strength, R-m, yield strength, R-p, and elongation, A) of EN AW 7075 aluminum alloy obtained by electromagnetic casting were investigated at different operating parameters: frequency (V), field strength (T) and current intensity (I). The predictive mathematical models using Response Surface Methodology, with second order polynomial (SOP) regression models, and Artificial Neural Network model (ANN), were afterwards compared to obtained experimental results. Analysis of variance and post-hoc Tukey's HSD test at 95% confidence limit ("honestly significant differences") have been utilised to show significant differences between various samples. SOP models showed good prediction capabilities, with high coefficients of determination (r(2)), 0.531-0.977, while ANN model performed even better prediction accuracy: 0.800-0.992. The optimal samples were chosen depending on mechanical properties of the product (S-0 = 50.49mm(2), R-m = 405.75Nmm(-2), R-p = 302.49Nmm(-2), A = 6.86%), using optimal operating parameters (V = 30 Hz, I = 250 A, T = 18 x 10(-3) At)
Metallurgical processing of copper secondary raw materials
No full textPostupci prerade sekundarnih sirovina bakra uključuju dva osnovna stupnja: pripremu bakarnih otpadaka i njihovu dalju metaluršku preradu. Za pripremu bakarnih otpadaka koriste se različiti postupci u zavisnosti od vrste i kvaliteta sekundarne sirovine. Sve operacije pripreme utiču na kvalitet metalurške prerade, odnosno na kvalitet proizvoda. Za topljenje pripremljenih sekundarnih sirovina u cilju dobijanja legura na bazi bakra koriste se razni agregati: šahtne peći, konvertori, plamene lončaste i koritaste plamene peći, kratke bubnjaste peći i električne peći (elektrolučne, elektrootporne, indukcione).Procedures for copper secondary raw materials processing include two basic stages: pretreatment of the copper waste and its further metallurgical processing. For copper waste pretreatment technology, there are different applied procedures depending on the type of raw material. All operations of pretreatment are influencing the quality of metallurgical processing. For metallurgical processing of raw materials prepared for the purpose of obtaining copper and copper alloys the shaft, flaming and short-drum furnaces, converters and electric furnaces (electric resistant, electric arc and induction furnaces) are used