Permanent disposal of Cs ions in the form of dense pollucite ceramics having low thermal expansion coefficient

A promising method for removal of Cs ions from water and their incorporation into stable crystal structure ready for safe and permanent disposal was described. Cs-exchanged X zeolite was hot-pressed at temperature ranging from 800 to 950 °C to fabricate dense pollucite ceramics. It was found that the application of external pressure reduced the pollucite formation temperature. The effect of sintering temperature on density, phase composition and mechanical properties was investigated. The highest density of 92.5 %TD and the highest compressive strength of 79 MPa were measured in pollucite hot-pressed at 950 °C for 3 h. Heterogeneity of samples obtained at 950 °C was determined using scanning electron microscopy. The pollucite hot-pressed at 950 °C had low linear thermal expansion coefficient of ∼4.67 × 10−6 K−1 in the temperature range from 100 to 1000 °C. © 201

Ultrasound and shacking-assisted water-leaching of anions and cations from fly ash

Two mechanical extraction techniques were used for the extraction of environmentaly interesting components of coal fly ash: shaking, during which the extraction process lasted from 6 up to 24 h, and sonication that lasted from 15 up to 60 min, using water as extractant. The concentration of anions in fly ash extracts was determined by ion chromatography, while atomic absorption spectrometry was used for determination of: As, Pb, Cd, Ni, Cr, Zn, Cu, Fe, Mn and Al. The ultrasonication yielded slightly higher amounts of extracted anions as well as Pb, Al, Mn and Fe cations, while shaking-assisted extraction was more efficient for the Cr, As, Zn and Ni ions. The changes in pH value, particle size distribution within colloid solution, zeta potential and conductivity during ultrasound-assisted extraction were measured in order to explain changes that occur on the surface of fly ash particles contacting water and different processes (adsorption, ion exchange and flocculation) that develop under natural conditions. Principal Component Analysis was used for assessing the effect of observed process parameters. It is essential to evaluate quantity of these elements leachable from coal fly ash into the surface waters in natural conditions in order to prevent contamination of the environment

Thermal Induced Phase Transformation of Cs-Exchanged LTA framework zeolite

Cesium aluminosilicate phases are of great interest as possible hosts for 137Cs immobilization in radioactive waste management. Cs+ exchanged forms of two synthetic zeolites (4A and 3A) were prepared by standard procedure, and content of exchanged ions was determined by ion chromatography. Obtained samples were investigated by differential thermal gravimetry TG/(DTG) and SEM/EDS analysis. All samples were annealed in the range of 600–1500 °C. High temperature phase transformations of Cs+ exchanged zeolites (LTA) were investigated. Based on data obtained by XRD analysis of the samples, it was concluded that above 1000 °C Cs-LTA (4A and 3A) frameworks recrystallized in a pollucite phase

Synthesis, characterization and application of magnetite-based adsorbents for the phosphate removal from water

Predmet istraživanja ove doktorske disertacije je sinteza i karakterizacija adsorbenata na bazi magnetita i ispitivanje njihovih adsorptivnih karakteristika za uklanjanje fosfatnih jona iz vode. Sintetisani su nanočestični prahovi magnetita, kompoziti magnetita i ugljeničnog kriogela i modifikovan je prirodni filtracioni materijal na bazi silicijum-dioksida (tuf) oblaganjem nanočesticama magnetita. Hidrotermalna sinteza uz dodatak polietilen glikola (PEG) pokazala se kao pogodan metod za dobijanje mezoporoznog magnetita velikog kapaciteta uklanjanja fosfata i potencijala za magnetnu separaciju i ponovno korišćenje. Prahovi magnetita sintetisani su bez PEG-a i u prisustvu PEG 400 i 20.000 pri različitim odnosima PEG/voda. Analizirana je kristalna struktura, morfologija, magnetne, teksturalne i kiselo-bazne osobine dobijenih prahova. Uloga PEG-a je bila ključna za formiranje pora, a odnos PEG/voda je bio glavni faktor za povećanje specifične površine i mezoporoznosti magnetita. Na povećanje adsorpcionog kapaciteta za fosfate uticalo je povećanje specifične površine i zapremine pora. Najbolji rezultati su postignuti korišćenjem PEG 20.000, pri odnosu PEG/voda = 3:1. Mezoporozni prah magnetita (prečnika najzastupljenijih pora 11 nm), čestica nano veličina (<10 nm) bio je 9 puta efikasniji od neporoznog praha dobijenog sintezom bez korišćenja PEG-a (maksimalni adsorpcioni kapacitet po Langmuir-u, qm = 26,2 prema 3,0 mg/g). Zavisnost adsorpcije od pH vrednosti rastvora, bila je u skladu sa promenama zeta potencijala magnetita. Pomeranje izoelektrične tačke i tačke nultog naelektrisanja u suprotnim smerovima potvrdilo je specifičnu adsorpciju fosfata na magnetitu putem zamene površinskih hidroksilnih i sulfatnih grupa. Kompoziti magnetit/ugljenični kriogel su sintetisani u cilju dobijanja adsorbenta za istovremenu adsorpciju organskih supstanci i fosfata. Ispitan je uticaj oksidacije kriogela i dodatka hlorovodonične kiseline u rastvor gvožđe(II) i gvožđe(III) jona, pre ko-precipitacije, na adsorpcioni kapacitet kompozita za fosfatne jone. Najbolji rezultati u uklanjanju fosfata su postignuti sa kompozitom sintetisanim sa oksidisanim kriogelom i dodatkom HCl. Prirodni filtracioni materijal tuf (granulacije 0,6-1,9 mm) modifikovan je oblaganjem nanočesticama magnetita. Modifikacija je uticala na povećanje poroznosti, dok je specifična površina uvećana za 35%. Šaržni eksperimenti su pokazali da je tuf modifikovan magnetitom (MMT) 4-5 puta efikasniji u uklanjanju fosfata od nemodifikovanog tufa. Maksimalni adsorpcioni kapaciteti na osnovu Langmuir-ovog modela iznosili su 0,45 i 1,91 mg/g za tuf i MMT, redom. Unutarčestični kinetički model se pokazao kao najpodesniji za opisivanje adsorpcije fosfata na MMT. Rezultati adsorpcije u koloni su potvrdili rezultate ispitivanja u šaržnim uslovima, pri čemu je efikasnost adsorbenta MMT bila 6 puta veća nego nemodifikovanog tufa.The aim of this study was the synthesis and characterization of magnetite-based adsorbents and the investigation of their adsorptive properties for the phosphate removal from water. The nanoparticulate magnetite powders, magnetite composites based on carbon cryogel were synthesized and the natural filtration material, silica-based tuff, was modified by coating with magnetite nanoparticles. Poly(ethylene) glycol (PEG)-assisted hydrothermal synthesis proved as a convenient route for fabrication of mesoporous magnetite with enhanced capacity for phosphate removal, excellent potential for magnetic separation and good reusability. Powders were synthesized in PEG-free or - assisted conditions (PEGs 400 and 20,000 at varied PEG/water ratio), and characterized in terms of crystalline structure, magnetic, morphological, textural, and acid–base properties. PEG acted as a powerful pore-forming agent, the PEG/water ratio being the key factor in developing the surface area and mesoporosity of magnetite. Uptake capacity for phosphates increased with an increase in surface area and pore volume. PEG 20,000 at a PEG/water ratio of 3:1 gave the best result. This mesoporous (the maximum of the pore size distribution 11 nm), nano-scale (<10 nm) magnetite was ca. 9 times more efficient than nonporous micrometric powder derived from PEG-free synthesis (Langmuir maximum capacity, qm = 26.2 vs. 3.0 mg/g). The adsorption was pH-dependent, in accord with variations in zeta potential of magnetite. Opposite shifts of isoelectric point and point of zero charge confirmed specific adsorption of phosphates at water/magnetite interface which proceeded via replacement of surface hydroxyls and sulfates. The magnetite /carbon cryogel composites were synthesized in order to improve the already existing properties for adsorption of organic pollutants with a new possibility of application for phosphate removal. The addition of hydrochloric acid in the solution of iron (II) and iron (III) ions, as well as the effect of surface oxidation of cryogel on the adsorption capacity of obtained composites were investigated. The best phosphate adsorption results were achieved with magnetite composite synthesized with oxidized cryogel and HCl addition. Natural filtration material tuff (0.6-1.9 mm grain fraction) was modified by coating with nano-sized magnetite. This modification changed pore structure and specific surface area. Specific surface area was increased by cca 35%. Batch experiments proved that magnetite modified tuff (MMT) was 4-5 times more efficient in removal of phosphates than tuff before modifying. The maximum adsorption capacities of phosphate obtained by the Langmuir equation were 0.45 and 1.91 mg g-1 for tuff and MMT, respectively. The intra-particle diffusion model was the most suitable for describing the adsorption process of phosphate onto MMT. Fixed-bed column data corroborated batch results, i.e. MMT was 6 times superior in phosphate adsorption than tuff

Synthesis, characterization and application of magnetite-based adsorbents for the phosphate removal from water

Predmet istraživanja ove doktorske disertacije je sinteza i karakterizacija adsorbenata na bazi magnetita i ispitivanje njihovih adsorptivnih karakteristika za uklanjanje fosfatnih jona iz vode. Sintetisani su nanočestični prahovi magnetita, kompoziti magnetita i ugljeničnog kriogela i modifikovan je prirodni filtracioni materijal na bazi silicijum-dioksida (tuf) oblaganjem nanočesticama magnetita. Hidrotermalna sinteza uz dodatak polietilen glikola (PEG) pokazala se kao pogodan metod za dobijanje mezoporoznog magnetita velikog kapaciteta uklanjanja fosfata i potencijala za magnetnu separaciju i ponovno korišćenje. Prahovi magnetita sintetisani su bez PEG-a i u prisustvu PEG 400 i 20.000 pri različitim odnosima PEG/voda. Analizirana je kristalna struktura, morfologija, magnetne, teksturalne i kiselo-bazne osobine dobijenih prahova. Uloga PEG-a je bila ključna za formiranje pora, a odnos PEG/voda je bio glavni faktor za povećanje specifične površine i mezoporoznosti magnetita. Na povećanje adsorpcionog kapaciteta za fosfate uticalo je povećanje specifične površine i zapremine pora. Najbolji rezultati su postignuti korišćenjem PEG 20.000, pri odnosu PEG/voda = 3:1. Mezoporozni prah magnetita (prečnika najzastupljenijih pora 11 nm), čestica nano veličina (<10 nm) bio je 9 puta efikasniji od neporoznog praha dobijenog sintezom bez korišćenja PEG-a (maksimalni adsorpcioni kapacitet po Langmuir-u, qm = 26,2 prema 3,0 mg/g). Zavisnost adsorpcije od pH vrednosti rastvora, bila je u skladu sa promenama zeta potencijala magnetita. Pomeranje izoelektrične tačke i tačke nultog naelektrisanja u suprotnim smerovima potvrdilo je specifičnu adsorpciju fosfata na magnetitu putem zamene površinskih hidroksilnih i sulfatnih grupa. Kompoziti magnetit/ugljenični kriogel su sintetisani u cilju dobijanja adsorbenta za istovremenu adsorpciju organskih supstanci i fosfata. Ispitan je uticaj oksidacije kriogela i dodatka hlorovodonične kiseline u rastvor gvožđe(II) i gvožđe(III) jona, pre ko-precipitacije, na adsorpcioni kapacitet kompozita za fosfatne jone. Najbolji rezultati u uklanjanju fosfata su postignuti sa kompozitom sintetisanim sa oksidisanim kriogelom i dodatkom HCl. Prirodni filtracioni materijal tuf (granulacije 0,6-1,9 mm) modifikovan je oblaganjem nanočesticama magnetita. Modifikacija je uticala na povećanje poroznosti, dok je specifična površina uvećana za 35%. Šaržni eksperimenti su pokazali da je tuf modifikovan magnetitom (MMT) 4-5 puta efikasniji u uklanjanju fosfata od nemodifikovanog tufa. Maksimalni adsorpcioni kapaciteti na osnovu Langmuir-ovog modela iznosili su 0,45 i 1,91 mg/g za tuf i MMT, redom. Unutarčestični kinetički model se pokazao kao najpodesniji za opisivanje adsorpcije fosfata na MMT. Rezultati adsorpcije u koloni su potvrdili rezultate ispitivanja u šaržnim uslovima, pri čemu je efikasnost adsorbenta MMT bila 6 puta veća nego nemodifikovanog tufa.The aim of this study was the synthesis and characterization of magnetite-based adsorbents and the investigation of their adsorptive properties for the phosphate removal from water. The nanoparticulate magnetite powders, magnetite composites based on carbon cryogel were synthesized and the natural filtration material, silica-based tuff, was modified by coating with magnetite nanoparticles. Poly(ethylene) glycol (PEG)-assisted hydrothermal synthesis proved as a convenient route for fabrication of mesoporous magnetite with enhanced capacity for phosphate removal, excellent potential for magnetic separation and good reusability. Powders were synthesized in PEG-free or - assisted conditions (PEGs 400 and 20,000 at varied PEG/water ratio), and characterized in terms of crystalline structure, magnetic, morphological, textural, and acid–base properties. PEG acted as a powerful pore-forming agent, the PEG/water ratio being the key factor in developing the surface area and mesoporosity of magnetite. Uptake capacity for phosphates increased with an increase in surface area and pore volume. PEG 20,000 at a PEG/water ratio of 3:1 gave the best result. This mesoporous (the maximum of the pore size distribution 11 nm), nano-scale (<10 nm) magnetite was ca. 9 times more efficient than nonporous micrometric powder derived from PEG-free synthesis (Langmuir maximum capacity, qm = 26.2 vs. 3.0 mg/g). The adsorption was pH-dependent, in accord with variations in zeta potential of magnetite. Opposite shifts of isoelectric point and point of zero charge confirmed specific adsorption of phosphates at water/magnetite interface which proceeded via replacement of surface hydroxyls and sulfates. The magnetite /carbon cryogel composites were synthesized in order to improve the already existing properties for adsorption of organic pollutants with a new possibility of application for phosphate removal. The addition of hydrochloric acid in the solution of iron (II) and iron (III) ions, as well as the effect of surface oxidation of cryogel on the adsorption capacity of obtained composites were investigated. The best phosphate adsorption results were achieved with magnetite composite synthesized with oxidized cryogel and HCl addition. Natural filtration material tuff (0.6-1.9 mm grain fraction) was modified by coating with nano-sized magnetite. This modification changed pore structure and specific surface area. Specific surface area was increased by cca 35%. Batch experiments proved that magnetite modified tuff (MMT) was 4-5 times more efficient in removal of phosphates than tuff before modifying. The maximum adsorption capacities of phosphate obtained by the Langmuir equation were 0.45 and 1.91 mg g-1 for tuff and MMT, respectively. The intra-particle diffusion model was the most suitable for describing the adsorption process of phosphate onto MMT. Fixed-bed column data corroborated batch results, i.e. MMT was 6 times superior in phosphate adsorption than tuff

Multifunctional use of magnetite-coated tuff grains in water treatment: Removal of arsenates and phosphates

Natural filtration material tuff (T) was modified by coating with nano-sized magnetite. The grain fraction of 0.6–1.9 mm was submitted to hydrothermal synthesis of magnetite. Thus formed magnetite modified tuff (MMT) was characterized in terms of Fe-content, N2 adsorption- desorption isotherm, SEM, zeta potential-pH analyses and adsorption behavior towards phosphates/arsenates in batch and column conditions. Elemental analysis showed that 36.54 mg g−1 of magnetite was attached to the porous tuff grains. This modification changed pore structure and specific surface area. An increase of cca 35% in Sp value was obtained. Batch experiments proved that MMT was 4-5 times more efficient in removal of phosphates/arsenates than non-modified T. The maximum sorption capacities of phosphates calculated based on Langmuir equation were 0.45 and 1.91 mg g−1, while those for arsenate were 0.551 m g−1 and 2.36 mg g−1 for T and MMT, respectively. The intra-particle diffusion model was the most suited for describing the adsorption process of phosphate and arsenate onto MMT. Fixed-bed column data corroborated batch results, i.e. MMT was 6 times superior in contaminant adsorption than T. Modification with magnetite improved T potential for usage in water treatment applications: its filtration ability remained unchanged, while adsorption capacity for phosphates/arsenates removal was improved. © 2019 The Society of Powder Technology Japa

Procena rizika za potencijalno opasne supstance iz letećih pepela dobijenih sagorevanjem uglja i otpadnog uglja

Lignite and coal waste used as feed fuels in thermal power plants (TPPs) and semi-industrial fluidized bed boiler (FBB), as well as their representative fly ashes (FAs), were examined. Fly ashes were compared employing anions and cations content in correspondent water extracts, trace elements and polycyclic aromatic hydrocarbon concentrations, as well as health risk assessments of substances known to be of concern for public health. Fluoride and sulfate contents in water extracted FAs are far below the legislation limits for waste, classifying all investigated FAs as non-hazardous. Among investigated trace elements, Cd content is the lowest, while Mn content is the highest. The highest enrichment ratios are noticed for As, Pb, Hg, Cu, V and Cr. The results indicate that total PAHs content is elevated in FA from the combustion of coal waste (AFB), with fluoranthene prevailing. The cancer risk of As and the non- -cancer risk of As and Ni in some FAs surpass their respective permissible limits. The incremental lifetime cancer risk of an adult population indicates a potential PAHs risk in AFB, whereas all other fly ashes are within safe limits.U ovom radu, ispitivana su goriva (lignit i otpadni ugalj) koja se koriste u termoelektranama i poluindustrijskom postrojenju sa fluidizovanim slojem, kao i leteći pepeli dobijeni njihovim sagorevanjem. Leteći pepeli su upoređeni na osnovu: sadržaja anjona i katjona u njihovim vodenim ekstraktima, koncentracije elemenata u tragovima i policikličnih aromatičnih ugljovodonika (PAH), kao i procene zdravstvenog rizika koji potiče od prethodno pomenutih potencijalno opasnih supstanci. Sadržaj fluorida i sulfata u vodenim ekstraktima letećih pepela daleko je ispod zakonski dozvoljenih granica za otpad, na osnovu čega se mogu svrstati u bezopasne. Od ispitivanih elemenata u tragovima, sadržaj Cd je najniži, dok je koncentracija Mn najviša. Najveće obogaćenje pepela u odnosu na odgovarajući ugalj, primećeno je za As, Pb, Hg, Cu, V i Cr. Na osnovu dobijenih rezultata pokazano je da je ukupni sadržaj PAH najveći za leteći pepeo dobijen sagorevanjem otpadnog uglja. Među ispitivanim PAH, najvišu koncentraciju ima fluoranten. Rizici koji potiču od arsena (među kancerogenim elementima), kao i arsena i nikla (među nekancerogenim elementima), premašuju dozvoljene granične vrednosti. Vrednost procenjenog rizika od raka kod odrasle populacije u slučaju PAH, pokazuje da za leteći pepeo dobijen sagorevanjem otpadnog uglja postoji potencijalni rizik, dok su vrednosti za ostale pepele unutar dozvoljenih granica

Adsorption of Candida rugosa lipase onto alumina: Effect of surface charge

The impact of the surface charge of alumina support on the adsorption of Candida rugosa lipase has been investigated in terms of zeta potential of the adsorption partners. Lipase adhered onto alumina with similar efficiency under both repulsive and attractive electrostatic conditions, shifting the zeta potential of the support towards that of the enzyme. The behavior was explained by a heterogeneous distribution of the surface charge of the lipase molecule. Special emphasis in this study was placed on the effect of immobilization on enzyme kinetics and principal reasons for enzyme immobilization: improvement in stability and potential for reuse. The enzyme affinity was not altered by its adsorption onto alumina, while Vmax of the lipase decreased. Thermostability of adsorbed lipase was improved. Significant potential for reuse was found. [Projekat Ministarstva nauke Republike Srbije, br. III 43004 i br. III 45012

Mn-Fe Layered Double Hydroxide Modified Cellulose-Based Membrane for Sustainable Anionic Pollutant Removal

This study aimed to investigate the adsorption of As(V), phosphate, and textile dye Acid Green 25 (AG-25) on layered double hydroxides Mn-Fe_LDH and corresponding membranes (wCell/Mn-Fe_LDH). The wCell membrane, derived from waste tobacco boxes, was formed by cross-linking of epoxy and amino modified cellulose fibers with epoxy modified Mn-Fe_LDH and lysine as cross-linker. Structural and morphological analyses were conducted for Mn-Fe_LDH and wCell/Mn-Fe_LDH. The batch system explored pH, contact time, temperature, and initial concentration effects on wCell/Mn-Fe_LDH adsorption efficiency. Adsorption capacities of 82.71, 106.9, and 130.3 mg g−1 were achieved for As(V), phosphate, and AG-25, respectively, indicating effective anionic species removal. Kinetic analysis suggested intraparticle diffusion as the rate-limiting step. Thermodynamic parameters and ionic strength effects indicated a physisorption mechanism for AG-25 and surface complexation for As(V) and phosphate. Biodegradation experiments after five adsorption/desorption cycles revealed the membrane’s decomposition, with phosphate’s strong bonding releasing essential elements valuable for soil fertilization. Effluent wastewater treatment demonstrated low environmental impact through the formation of insoluble As(V) salts and photocatalytic dye degradation

Tailoring of magnetite powder properties for enhanced phosphate removal: Effect of PEG addition in the synthesis process

This study demonstrates that PEG-assisted hydrothermal synthesis provides a convenient and eco-friendly route to fabrication of mesoporous magnetite with enhanced capacity for phosphate removal, excellent potential for magnetic separation and good reusability. Adsorption of phosphate onto 4 laboratory prepared magnetite powders was investigated in a systematic manner. Powders were synthesized in poly(ethylene) glycol-free or assisted conditions (PEGs 400 and 20,000 at varied PEG/water ratio), and characterized in terms of crystalline structure, and magnetic, morphological, textural, and acid-base properties. PEG acted as a powerful pore forming agent, the PEG/water ratio being the key factor in developing the surface area and mesoporosity of magnetite. Uptake capacity for phosphates increased with an increase in surface area and pore volume. PEG 20,000 at a ratio of 3:1 gave the best result. This mesoporous (D-max = 11 nm), nano-scale ( lt 10 nm) magnetite was ca. 9 times more efficient than nonporous micrometric powder derived from PEG-free synthesis (Langmuir maximum capacity, q(m) = 26.2 vs. 3.0 mg g(-1)). The adsorption was pH-dependent, in accord with variations in zeta potential of magnetite. Opposite shifts of isoelectric point and point of zero charge confirmed specific adsorption of phosphates at water/magnetite interface which proceeded via replacement of surface hydroxyls and sulfates