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Antimikrobni materijali na bazi hidroksiapatita su potencijalno atraktivni za širok spektar primena u medicini. Monofazni srebro-, bakar- i cink-dopirani hidroksiapati (MxCa10-x(PO4)6(OH)2, M = Ag, Cu ili Zn, 0,002 ≤ x ≤ 0,04) su sintetizovani korišćenjem metode neutralizacije. Ova metoda se sastoji od rastvaranja oksida metala (Ag2O, CuO ili ZnO) u rastvoru H3PO4, i sporog dodavanja rastvora u suspenziju Ca(OH)2 radi homogene raspodele dopantnog jona.Kvantitativna elementala analiza je pokazala da su joni srebra, bakra i cinka u potpunosti ugradili u hidroksiapatit. Rendgenostrukturna analiza je pokazala da su svi dopirani uzorci veoma slične strukture sa čistim hidroksiapatitom i u skladu su sa ASTM podacima (kartica 9-432). Svi difrakcini pikovi su oštri i dobro razdvojeni, što ukazuje da je dobijeni monofazni i dobro iskristalisani hidroksiapatiti. Posmatranja transmisionim elektronskim mikroskopoma su pokazala da su morfologije čestice sintetisanih hidroksiapatita veoma slične, nepravilnog oblika i nano veličine. Prosečna dužina čestica u svim uzorcima je oko 70 nm i oko 15-25 nm u prečniku. Antimikrobna aktivnost uzorka su testirani na mikroorganizme koji mogu da izazovu infekcije vezane za implantate: Staphilococcus aureus, Escherichia coli i Candida albicans. Rezultati antimikrobnih testova su pokazali da svi dopirani uzorci hidroksiapatita imaju antimikrobnu aktivnost. Antimikrobna efikasnost materijala je u funkcija vrste i količine dopantnog jona. Aktivnost je najviše izraženo sa uzorcima hidroksiapatita dopiranih jonima srebra. Antimikrobno dejstvo uzoraka dopiranog sa najvećom količinom srebra na ćelije mikroorganizama je posmatrana pomoću mikroskopa atomskih sila. Studije su pokazale da dopirani uzorak hidroksiapatita stvara značajne morfološke promene na ćelijama mikroorganizama koje mogu biti uzrok njihove smrti. Test hemolize je izveden na srebro- i cink-dopirane uzorke kako bi se ispitala njihova hemokompatibilnost. Stepen hemolize uzoraka je bio m, Antimicrobial materials based on hydroxyapatite are potentially attractive in a wide variety of medical applications. Monophase silver-, copper- or zinc-doped hydroxyapatite (MxCa10−x(PO4)6(OH)2; M = Ag, Cu or Zn; 0.002 ≤ x ≤ 0.04) were synthesized using a neutralization method. This method consists of dissolving metal oxide (Ag2O, CuO or ZnO) in a solution of H3PO4, and the slow addition of a solution to the suspension of Ca(OH)2 was applied for the purpose of homogenous distribution of dopant ions.The quantitative elemental analysis showed that the silver, copper and zinc ions fully incorporated into the hydroxyapatite. X-ray diffraction analysis showed that all doped samples are very similar in structure to pure hydroxyapatite and in accordance with ASTM data (Card 9-432). All of the diffraction peaks were sharp and well resolved, indicating the obtained monophase and well crystallized hydroxyapatite. Observation of transmission electron microscopy showed that the morphology of the synthesized hydroxyapatite particles are very similar, irregular shaped and nano sized. The average length of particles in all samples is about 70 nm and about 15–25 nm in diameter. Antimicrobial activities of the samples were tested for microorganisms that can cause implant-related infections including: Staphylococcus aureus, Escherichia coli and Candida albicans. The results of antimicrobial tests demonstrate that all doped hydroxyapatite samples showed antimicrobial activity. Antimicrobial efficacy of these materials is a function of types and quantities of dopant ions. The activity is most pronounced with the silver-doped hydroxyapatite samples. Antimicrobial effects of silver-doped samples with the most silver on microorganism’s cells are observed by the atomic force microscope. The studies show that a silver-doped hydroxyapatite sample causes considerable morphological changes of microorganism cells which might be the cause of cells’ death. A hemolysis test was performed on silve

Antimikrobni materijali na bazi hidroksiapatita su potencijalno atraktivni za širok spektar primena u medicini. Monofazni srebro-, bakar- i cink-dopirani hidroksiapati (MxCa10-x(PO4)6(OH)2, M = Ag, Cu ili Zn, 0,002 ≤ x ≤ 0,04) su sintetizovani korišćenjem metode neutralizacije. Ova metoda se sastoji od rastvaranja oksida metala (Ag2O, CuO ili ZnO) u rastvoru H3PO4, i sporog dodavanja rastvora u suspenziju Ca(OH)2 radi homogene raspodele dopantnog jona. Kvantitativna elementala analiza je pokazala da su joni srebra, bakra i cinka u potpunosti ugradili u hidroksiapatit. Rendgenostrukturna analiza je pokazala da su svi dopirani uzorci veoma slične strukture sa čistim hidroksiapatitom i u skladu su sa ASTM podacima (kartica 9-432). Svi difrakcini pikovi su oštri i dobro razdvojeni, što ukazuje da je dobijeni monofazni i dobro iskristalisani hidroksiapatiti. Posmatranja transmisionim elektronskim mikroskopoma su pokazala da su morfologije čestice sintetisanih hidroksiapatita veoma slične, nepravilnog oblika i nano veličine. Prosečna dužina čestica u svim uzorcima je oko 70 nm i oko 15-25 nm u prečniku. Antimikrobna aktivnost uzorka su testirani na mikroorganizme koji mogu da izazovu infekcije vezane za implantate: Staphilococcus aureus, Escherichia coli i Candida albicans. Rezultati antimikrobnih testova su pokazali da svi dopirani uzorci hidroksiapatita imaju antimikrobnu aktivnost. Antimikrobna efikasnost materijala je u funkcija vrste i količine dopantnog jona. Aktivnost je najviše izraženo sa uzorcima hidroksiapatita dopiranih jonima srebra. Antimikrobno dejstvo uzoraka dopiranog sa najvećom količinom srebra na ćelije mikroorganizama je posmatrana pomoću mikroskopa atomskih sila. Studije su pokazale da dopirani uzorak hidroksiapatita stvara značajne morfološke promene na ćelijama mikroorganizama koje mogu biti uzrok njihove smrti. Test hemolize je izveden na srebro- i cink-dopirane uzorke kako bi se ispitala njihova hemokompatibilnost. Stepen hemolize uzoraka je bio, Antimicrobial materials based on hydroxyapatite are potentially attractive in a wide variety of medical applications. Monophase silver-, copper- or zinc-doped hydroxyapatite (MxCa10−x(PO4)6(OH)2; M = Ag, Cu or Zn; 0.002 ≤ x ≤ 0.04) were synthesized using a neutralization method. This method consists of dissolving metal oxide (Ag2O, CuO or ZnO) in a solution of H3PO4, and the slow addition of a solution to the suspension of Ca(OH)2 was applied for the purpose of homogenous distribution of dopant ions. The quantitative elemental analysis showed that the silver, copper and zinc ions fully incorporated into the hydroxyapatite. X-ray diffraction analysis showed that all doped samples are very similar in structure to pure hydroxyapatite and in accordance with ASTM data (Card 9-432). All of the diffraction peaks were sharp and well resolved, indicating the obtained monophase and well crystallized hydroxyapatite. Observation of transmission electron microscopy showed that the morphology of the synthesized hydroxyapatite particles are very similar, irregular shaped and nano sized. The average length of particles in all samples is about 70 nm and about 15–25 nm in diameter. Antimicrobial activities of the samples were tested for microorganisms that can cause implant-related infections including: Staphylococcus aureus, Escherichia coli and Candida albicans. The results of antimicrobial tests demonstrate that all doped hydroxyapatite samples showed antimicrobial activity. Antimicrobial efficacy of these materials is a function of types and quantities of dopant ions. The activity is most pronounced with the silver-doped hydroxyapatite samples. Antimicrobial effects of silver-doped samples with the most silver on microorganism’s cells are observed by the atomic force microscope. The studies show that a silver-doped hydroxyapatite sample causes considerable morphological changes of microorganism cells which might be the cause of cells’ death. A hemolysis test was performed on silv

U ovom radu izučavani su mehanizmi sorpcije teških metala korišćenjem dve forme minerala apatita: sintetičkog hidroksiapatita (HAP) i prirodnog apatita iz ležišta Lisina kod Bosilegrada (LA). Karakterizacija materijala je izvršena korišćenjem metode difrakcije x-zraka. Utvrđeno je da je sintetički apatit (HAP) čist hidroksiapatit molekulske formule Ca10(PO4)6(OH)2, dok je prirodni apatit (LA) smeša minerala kvarca, muskovita i fluorapatita. Mehanizmi sorpcije izučavani su korišćenjem teorijskog modela stabilnosti čvrste faze, kao i eksperimentalnim proučavanjem sorpcije olova iz vodenog rastvora. Teorijski matematički model stabilnosti čvrste faze baziran je na izračunavanju jon-jon interakcionih potencijala. Ovaj model upotrebljen je za procenu stabilnosti čvrste faze nastale reakcijom zagađujućih materija sa prirodnim i sintetičkim apatitom. Primenjeni model omogućava preliminarni izbor najpogodnijeg aditiva za imobilizaciju teških metala u zagađenom zemljištu ili podzemnim vodama sa stanovišta stabilnosti novonastale čvrste faze. Detaljno su razmotreni sledeći sistemi: Cd/HAP, Pb/HAP, Pb/prirodni apatiti i As/HAP. Na osnovu prikazanih rezultata predloženi su dominantni mehanizmi u procesima sorpcije zagađujućih materija u ispitivanim sistemima. U radu su izvršena eksperimentalna ispitivanja i modelovanje kinetike sorpcije olova iz vodenih rastvora korišćenjem prirodnog i sintetičkog apatita na tri temperature. Za modelovanje eksperimentalnih podataka korišćeni su kinetički modeli pseudo-prvog i pseudo-drugog reda. Utvrđeno je da model pseudo-drugog reda dobro opisuje kinetiku sorpcije olova u oba ispitivana sistema. Takođe su izvršena eksperimentalna ispitivanja adsorpcionih izotermi olova na hidroksiapatitu i prirodnom apatitu. Za analizu sorpcionih podataka korišćeno je pet modela adsorpcionih izotermi. Na osnovu primene ANOVA statističke analize utvrđeno je da Freundlich-ova adsorpciona izoterma najbolje opisuje eksperimentalne podatke u oba sistema. Analiza s, In this work, the mechanisms of heavy metal sorption by two forms of mineral apatite were studied. The materials used include synthetic hydroxyapatite (HAP) and natural apatite from Lisina ore deposit (LA). The materials were characterized by x-ray diffraction. It was shown that synthetic apatite is pure hydroxyapatite, with molecular formula Ca10(PO4)6(OH)2, while natural apatite is a mixture of three minerals: quartz, muscovite and fluorapatite. The mechanisms were investigated using theoretical model of the solid matrix/impurity system stability as well as by experimental investigations of dissolved Pb sorption by HAP and LA. The theoretical model of the solid matrix/impurity system stability is based on ion-ion interaction potential calculation. This model was used to estimate the stability of the solid phase obtained by the reaction of heavy metals with synthetic and natural apatite. The applied model can be used for pre-selection of the most suitable amendment for heavy metal immobilization in polluted soils and ground water, based on the stability of the newly formed solid phase. The following systems were investigated in detail: Cd/HAP, Pb/HAP, Pb/natural apatites and As/HAP. Based on the results obtained, the dominant mechanisms involved in reactions in the investigated systems were suggested. In this work, experimental investigations and modeling of the kinetics of Pb sorption by natural and synthetic apatites were carried out at three temperatures. Two kinetic models were used: pseudo-first and pseudo-second order model. It was concluded that pseudo-second order model describes the kinetics of the processes in both systems best. Experimental investigations of the sorption isotherms were also carried out. Five sorption isotherms were used to model the experimental results. Using ANOVA statistical analysis it was concluded that Freundlich isotherm model described both systems with the greatest accuracy. Based on the analysis of all the results obtained, it

In this work, the mechanisms of heavy metal sorption by two forms of mineral apatite were studied. The materials used include synthetic hydroxyapatite (HAP) and natural apatite from Lisina ore deposit (LA). The materials were characterized by x-ray diffraction. It was shown that synthetic apatite is pure hydroxyapatite, with molecular formula Ca10(PO4)6(OH)2, while natural apatite is a mixture of three minerals: quartz, muscovite and fluorapatite. The mechanisms were investigated using theoretical model of the solid matrix/impurity system stability as well as by experimental investigations of dissolved Pb sorption by HAP and LA. The theoretical model of the solid matrix/impurity system stability is based on ion-ion interaction potential calculation. This model was used to estimate the stability of the solid phase obtained by the reaction of heavy metals with synthetic and natural apatite. The applied model can be used for pre-selection of the most suitable amendment for heavy metal immobilization in polluted soils and ground water, based on the stability of the newly formed solid phase. The following systems were investigated in detail: Cd/HAP, Pb/HAP, Pb/natural apatites and As/HAP. Based on the results obtained, the dominant mechanisms involved in reactions in the investigated systems were suggested. In this work, experimental investigations and modeling of the kinetics of Pb sorption by natural and synthetic apatites were carried out at three temperatures. Two kinetic models were used: pseudo-first and pseudo-second order model. It was concluded that pseudo-second order model describes the kinetics of the processes in both systems best. Experimental investigations of the sorption isotherms were also carried out. Five sorption isotherms were used to model the experimental results. Using ANOVA statistical analysis it was concluded that Freundlich isotherm model described both systems with the greatest accuracy. Based on the analysis of all the results obtained, it, U ovom radu izučavani su mehanizmi sorpcije teških metala korišćenjem dve forme minerala apatita: sintetičkog hidroksiapatita (HAP) i prirodnog apatita iz ležišta Lisina kod Bosilegrada (LA). Karakterizacija materijala je izvršena korišćenjem metode difrakcije x-zraka. Utvrđeno je da je sintetički apatit (HAP) čist hidroksiapatit molekulske formule Ca10(PO4)6(OH)2, dok je prirodni apatit (LA) smeša minerala kvarca, muskovita i fluorapatita. Mehanizmi sorpcije izučavani su korišćenjem teorijskog modela stabilnosti čvrste faze, kao i eksperimentalnim proučavanjem sorpcije olova iz vodenog rastvora. Teorijski matematički model stabilnosti čvrste faze baziran je na izračunavanju jon-jon interakcionih potencijala. Ovaj model upotrebljen je za procenu stabilnosti čvrste faze nastale reakcijom zagađujućih materija sa prirodnim i sintetičkim apatitom. Primenjeni model omogućava preliminarni izbor najpogodnijeg aditiva za imobilizaciju teških metala u zagađenom zemljištu ili podzemnim vodama sa stanovišta stabilnosti novonastale čvrste faze. Detaljno su razmotreni sledeći sistemi: Cd/HAP, Pb/HAP, Pb/prirodni apatiti i As/HAP. Na osnovu prikazanih rezultata predloženi su dominantni mehanizmi u procesima sorpcije zagađujućih materija u ispitivanim sistemima. U radu su izvršena eksperimentalna ispitivanja i modelovanje kinetike sorpcije olova iz vodenih rastvora korišćenjem prirodnog i sintetičkog apatita na tri temperature. Za modelovanje eksperimentalnih podataka korišćeni su kinetički modeli pseudo-prvog i pseudo-drugog reda. Utvrđeno je da model pseudo-drugog reda dobro opisuje kinetiku sorpcije olova u oba ispitivana sistema. Takođe su izvršena eksperimentalna ispitivanja adsorpcionih izotermi olova na hidroksiapatitu i prirodnom apatitu. Za analizu sorpcionih podataka korišćeno je pet modela adsorpcionih izotermi. Na osnovu primene ANOVA statističke analize utvrđeno je da Freundlich-ova adsorpciona izoterma najbolje opisuje eksperimentalne podatke u oba sistema. Analiza s

Natural apatites represent a cost effective soil amendment, which can be used for in situ reduction of lead bioavailability and mobility. In our previous work, we selected Lisina apatite (LA) as a promising natural mineral for lead immobilization based on theoretical predictions. This study investigated the adsorption equilibrium and kinetics of aqueous Pb sorption onto Lisina apatite and synthetic hydroxyapatite (HAP) at different temperatures. XRD analysis indicated that LA consists of three minerals: fluorapatite, quartz and muscovite. After reaction with a Pb solution, only FA peaks were changed, confirming that fluorapatite present in LA is responsible for Pb sorption. Sorption experiments confirmed that both LA and HAP are effective in Pb removal. Langmuir, Freundlich, Temkin, Koble-Corrigan and Redlich-Peterson isotherm models were applied to experimental data. The kinetics of the sorption process on both minerals was well characterized by the pseudo-second order reaction rate. Results indicate that Pb immobilization by HAP is a two-step process: the first rapid phase, possibly surface complexation and secondary dissolution of HAP and precipitation of pyromorphite. The sorption of Pb by Lisina apatite is also a two-step process, but the reaction mechanisms are more complicated and need further research as the results indicate that different mechanisms dominate at different temperatures. The values of thermodynamic equilibrium constants and Gibbs free energy were also calculated. The values of AG obtained confirm the feasibility of both HAP and LA as effective sorbents of the Pb ion. (C) 2010 Elsevier B.V. All rights reserved.

Contamination of the environment with toxic metals, such as lead (Pb), represents a serious concern for human health. Most of the studies on Pb stabilization were performed using various phosphorus-containing amendments that can reduce Pb mobility and bioavailability by the sorption and precipitation of new, stable pyromorphite-type minerals, presenting very low solubility and bioaccessibility. However, the presence of competing ions, such as zinc (Zn), can reduce stabilization efficacy. The role of chemical composition on the stability of immobilization products of Pb and Zn by the addition of hydroxyapatite (HAP) Or fluoroapatite (FAP) has been examined in this paper. In this analysis we used a theoretical criterion which is based on calculation of the ion-ion interaction potential, representing the main term of the cohesive energy of the matrix/pollutant system. It has been demonstrated that the stability of the HAP matrix decreases and that the stability of the FAP matrix increases with the Pb immobilization in the presence of Zn. The results of this analysis point out FAIR as an advantageous amendment for the immobilization of Pb in the presence of Zn. (C) 2008 Elsevier Ltd. All rights reserved.

In this work, mineral apatite was investigated for the remediation of lead contamination. Two different apatite minerals were used: synthetic apatite, Ca10(PO4)6(OH)2 (hereafter denoted as HAP) and natural apatite from Lisina, near Bosilegrad, Serbia (hereafter denoted as LA). Phosphate ore from Lisina deposit consists of 43.3 % apatite in the form of fluorapatite, Ca10(PO4)6(F)2. Sorption properties of HAP and LA were investigated. The results show that both of these minerals are effective in lead removal from the water solution. Sorption capacity of HAP obtained in this experiment is 0.216 mmol Pb/g HAP, while the value for LA is 0.162 mmol Pb/g LA. Modeling of these systems was conducted using Visual Minteq computer program. The values obtained from the computer simulation were compared to experimental values.

The effect of pH, contact time, initial metal concentration and presence of common competing cations, on hydroxyapatite (HAP) sorption properties towards Ph2+, Cd2+, Zn2+, and Sr2+ ions was studied and compared using a batch technique. The results strongly indicated the difference between the sorption mechanism of Pb2+ and other investigated cations: the removal of Pb2+ was pH-independent and almost complete in the entire pH range (3-12), while the sorption of Cd2+, Zn2+ and Sr2+ generally increased with an increase of pH; the contact time required for attaining equilibrium was 30 mm for Pb 2+ versus 24h needed for other cations; maximum sorption capacity of HAP sample was found to be an order of magnitude higher for Pb2+ (3.263 mmol/g), than for Cd2+ (0.601 mmol/g), Zn (2+) (0.574 mmol/g) and Sr2+ (0.257 mmol/g); the selectivity of HAP was found to decrease in the order Ph2+ gt Cd2+ gt Zn2+ gt Sr2+ while a decrease of pHpzc, in respect to the value obtained in inert electrolyte, followed the order Cd2+ gt Zn2+ gt Ph2+ gt Sr2+; neither of investigated competing cations (Ca2+, Mg2+, Na+ and K+) influenced Pb2+ immobilization whereas the sorption of other cations was reduced in the presence of Ca2+, in the order Sr2+ gt Cd2+ gt Zn (2+). The pseudo-second order kinetic model and Langmuir isotherm have been proposed for modeling kinetic and equilibrium data, respectively. The sorption of all examined metals was followed by Ca2+ release from the HAP crystal lattice and pH decrease. The ion exchange and specific cation sorption mechanisms were anticipated for Cd2+, Zn2+ and Sr2+, while dissolution of HAP followed by precipitation of hydroxypyromorphite (Pb-10(PO4)(6)(OH)(2)) was found to be the main operating mechanism for Pb 2+ immobilization by HAP, with the contribution of specific cation sorption.

Several approaches for immobilization of arsenic (As) based on the transformation of its soluble forms (compounds) into highly insoluble arsenate apatite Ca5(AsO4)3 OH have been proposed. These immobilization techniques are successfully applied in treatment of industrial waste containing As. Quite the contrary, treatment of soil contaminated with As by apatite amendments, instead of immobilization of this toxic element, increases its mobility and bioavailability. The mechanism underlying these opposite effects still remains elusive. Here, the stability analysis of different calcium arsenates: Ca5(AsO4)3OH, Ca4(AsO4)2, Ca3(AsO 4)2 Ca5H2(AsO4) 2 and CaHAsO4 was performed, which is based on the calculation of the ion-ion interaction potential (HIP). It has been demonstrated earlier that IIIP, representing the main term of the cohesive energy, is a suitable parameter for assessment of mineral stability. According to the results of this analysis, arsenate apatite with IIIP value of -0.578 Ry represents the most stable chemical form among analyzed compounds. Based on this finding, we proposed a mechanism of formation of arsenate apatite in the presence of hydroxyapatite. This mechanism can explain the suitability of this approach for the treatment of industrial waste and its limitations for in situ treatment of soil and water contaminated with As.

Primena hidroksiapatita (HAP-a) u raznim oblastima nauke i tehnologije vrlo je raznovrsna a fizičko-hemijska svojstva prahova moraju se prilagoditi specifičnoj nameni. U ovom radu ispitan je uticaj promena parametara neutralizacionog postupka sinteze (temperature, koncentracije i brzine dodavanja reaktanata, brzine mešanja, vremena starenja taloga i prisustva inertne atmosfere) na svojstva HAP-a, primenom Plackett-Burmanovog eksperimentalnog dizajna. Primenom statističkog softvera izvršeno je poređenje apsolutnih vrednosti efekata parametara sinteze na odgovore sistema kao što su hemijski sastav, kristaličnost, specifična površina i tačka nultog naelektrisanja uzoraka. Utvrđeno je da promena temperature i vremena starenja taloga imaju najviše uticaja na na strukturna i površinska svojstva HAP-a

Primena hidroksiapatita (HAP-a) u raznim oblastima nauke i tehnologije vrlo je raznovrsna a fizičko-hemijska svojstva prahova moraju se prilagoditi specifičnoj nameni. U ovom radu ispitan je uticaj promena parametara neutralizacionog postupka sinteze (temperature, koncentracije i brzine dodavanja reaktanata, brzine mešanja, vremena starenja taloga i prisustva inertne atmosfere) na svojstva HAP-a, primenom Plackett-Burmanovog eksperimentalnog dizajna. Primenom statističkog softvera izvršeno je poređenje apsolutnih vrednosti efekata parametara sinteze na odgovore sistema kao što su hemijski sastav, kristaličnost, specifična površina i tačka nultog naelektrisanja uzoraka. Utvrđeno je da promena temperature i vremena starenja taloga imaju najviše uticaja na na strukturna i površinska svojstva HAP-a.

Addition of an amendment or reagent to soil/sediment is a technique that can decrease mobility and reduce bioavailability of uranium (U) and other heavy metals in the contaminated site. According to data from literature and results obtained in field studies, the general mineral class of apatites was selected as a most promising amendment for in situ immobilization/ remediation of U. In this work we presented theoretical assessment of stability of U(VI) in four apatite systems (hydroxyapatite (HAP), North Carolina Apatite (NCA), Lisina Apatite (LA), and Apatite H) in order to determine an optimal apatite soil amendment which could be used for in situ remediation of uranium. In this analysis we used a theoretical criterion which is based on calculation of the ion-ion interaction potential, representing the main term of the cohesive energy of the matrix/ pollutant system. The presented results of this analysis indicate (i) that the mechanism of immobilization of U by natural apatites depends on their chemical composition and (ii) that all analyzed apatites represent, from the point of view of stability, promising materials which could be used in field remediation of U-contaminated sites. (c) 2005 Elsevier B.V. All rights reserved.

Physicochemical properties of hydroxyapatite (HAP) synthesized by neutralization method are heavily dependent on the process variables. A Plackett-Burman two-level experimental design was therefore, chosen to screen a large number of variables and to determine their effect on HAP characteristics. The sorption of cadmium ions on HAP was studied as well. Of six selected variables (temperature, mixing speed, reactant concentration, addition rate, presence of inert atmosphere and aging time), temperature has shown the strongest influence on HAP structural and sorption properties. Smaller crystallites, lower crystallinity and higher specific surface area lead to higher sorption of cadmium ions. Room temperature and no aging are preferable conditions for the synthesis of HAP with the highest sorption efficiency.

Apatites are well known matrix for heavy metal immobilization and remediation of ground water and contaminated soils. In this work, capacities of different synthetic hydroxyapatite (HAP) samples for Pb, Cd, Sr and Zn sorption were analyzed, from single metal solutions and their equimolar mixture. Initial concentration of each metal in single metal solutions and total metal concentration in the mixture was 10(-2) mol/dm(3). Initial pH was adjusted to 5.0 +/- 0.1. After 24 h equilibration of HAP samples with heavy metal solutions (solid/liquid ratio 1:200), the concentration of metals and of Ca2+ released from crystal lattice, as well as the final pH values were measured. The selectivity of all samples, regardless of the differences in their compositions, crystallinities, specific surface areas, points of zero charge and sorption capacities, was as follows: Pb gt Cd gt Zn gt Sr. The same order was obtained for both single metal solutions and their mixture. In all cases, the sorption was followed by a decrease in final pH values, which are lower than the pH(PZC) values obtained by equilibration of HAP samples with an inert electrolyte (KNO3). A linear relationship between the amount of metals sorbed and Ca2+ released from HAP was observed. Also, a correlation between sorption capacities and physicochemical properties of HAP samples was found.

The in situ (in place) immobilization of toxic metals, using inexpensive "reactive" amendments, is considered as a simple and cost-effective approach for the treatment of soils, contaminated by the presence of heavy metals, when these soils are difficult or costly to be removed and treated ex situ. Several application studies have demonstrated that the stabilization of contaminated soils and groundwaters by the addition of apatite minerals has the potential to be a successful and widely applicable remediation strategy for the case of Pb, Cd, as well as for other toxic metals, existing in polluted soils. On the other hand, the specific immobilization mechanism(s) of these toxic metals remains rather elusive. The present work involves an interdisciplinary theoretical and experimental approach, designed to gain at the fundamental (molecular) level the understanding of respective mechanisms, considering the immobilization of Pb and Cd by the addition of apatites. The theoretical analysis of stability, regarding the apatite/Pb or apatite/Cd systems and the relevant results of sorption experiments, pointed out two different mechanisms for the immobilization of Pb or Cd by the use of apatites. The possible practical consequences of these findings for the selection/application of natural apatites for the remediation of contaminated soils by the presence of heavy metals have been also discussed.

Sorption of different ionic species, especially heavy metals, on calcium-hydroxyapatite Ca10(PO4)6(OH)2, (HAP) and other apatite minerals plays an important role in environmental chemistry and practical applications of these materials. As HAP particles exhibit pH dependent surface charge, and the percent of various heavy metals hydrolytic species depend on pH, it is evident that pH significantly influences sorption processes. ...

Sorption capacities and kinetics of toxic heavy metals sorption by synthetic, wellcharacterized, hydroxyapatite (HAP) was studied using the batch technique. Initial concentration of Pb2+, Zn2+, Cd2+ and Sr2+ solutions, obtained from their nitrate salts, was 2. 10-3 mol/dm3 for kinetic experiments. The effect of initial metal concentration (10-4-10-2 mol/dm3 for Zn2+, Cd2+ and Sr2+ and 10-4-5. 10-2 mol/dm3 for Pb2+) on the amounts of retained heavy metals was examined in order to calculate sorption capacities. Initial pH values, in all batches were adjusted to 5.0 ±0.1. Suspensions of HAP and individual metal solutions were equilibrated on a horizontal shaker, at the solid to solution ratio of 1:200, at room temperature (20±1o C). The suspensions were filtrated and analyzed for residual heavy metal concentration, final pH and the amount of Ca2+ released into the solution at different time intervals (from 5 minutes up to 2 days) for kinetic and at 24 h for equilibrium studies. Sorption of all examined metals was followed by Ca2+ release from crystal lattice of HAP, indicating ion-exchange or dissolutionprecipitation mechanisms. The isotherm data were found to be well fitted by linear Langmuir equation. The sorption of Pb2+ was found to be the most rapid in respect to other cations (for equilibrium, a contact time of approximately 30 minutes was required for Pb2+ and 24 hours for Cd2+, Zn2+, and Sr2+). In order to determine the sorption mechanisms and rate constants, two most widely used kinetics models in sorption processes (pseudo-first and pseudo-second order equations) have been applied to experimental data. According to correlation coefficients and calculated values of equilibrium concentrations, the pseudo-second order model was found to be more appropriate, suggesting that the rate limiting step in heavy metal sorption on HAP involves valence forces through sharing or exchange of electrons between the sorbent and sorbates.

Apatites are well known matrix for heavy metal immobilization and remediation of ground water and contaminated soils. In this work, capacities of different synthetic hydroxyapatite (HAP) samples for Pb, Cd, Sr and Zn sorption were analyzed, from single metal solutions and their equimolar mixture. Initial concentration of each metal in single metal solutions and total metal concentration in the mixture was 10-2 mol/dm3 . Initial pH was adjusted to 5.0 ± 0.1. After 24 h equilibration of HAP samples with heavy metal solutions (solid/liquid ratio 1:200), the concentration of metals and of Ca2+ released from crystal lattice, as well as the final pH values were measured. The selectivity of all samples, regardless of the differences in their compositions, crystallinities, specific surface areas, points of zero charge and sorption capacities, was as follows: Pb > Cd > Zn > Sr. The same order was obtained for both single metal solutions and their mixture. In all cases, the sorption was followed by a decrease in final pH values, which are lower than the pHPZC values obtained by equilibration of HAP samples with an inert electrolyte (KNO3). A linear relationship between the amount of metals sorbed and Ca2+ released from HAP was observed. Also, a correlation between sorption capacities and physicochemical properties of HAP samples was found.

Selection of solid matrix for immobilization of nuclear waste and of geological sites for its disposal represents a complex and consuming task. Previously, we demonstrated that the ion-ion interaction potential (HIP), representing the main term of the cohesive energy, can be used for estimation of stability of solid matrix/impurity systems. Here we demonstrated a strong correlation between the weathering properties of minerals and their IIIP. Based on these results we proposed a simple theoretical criterion which can be used for assessment of the long term stability of solid matrix for immobilization of radioactive and toxic metals. This criterion was applied in analysis of stability of autunites and some possible practical consequences of results obtained for immobilization of uranium by apatite are discussed.

Two hydroxyapatite (HAP) samples of different crystallinity were studied as a nickel immobilization matrix. Sorption isotherms were obtained by batch equilibration method, in the concentration range 1. 10-4 – 8. 10-3 mol/dm3 . Low crystalline sample has sorption capacity of 0.212 mmol/g, and due to its higher specific surface area and lower Ca/P ratio it was found to be better sorbent for Ni2+ than crystalline HAP (0.092 mmol/g).

Surface properties of synthetic well-crystallized hydroxyapatite were investigated. Points of zero charge (pH(PZC)) for different solid to solution ratios were determined by the batch equilibration technique, using KNO3 as a background electrolyte. It has been found that the decrease in solid to solution ratio from 1:100 to 1:500 leads to a decrease in pH(PZC) from 6.1 to 4.1, respectively. Sorption of Cd2+ ions is not influenced by the initial pH value in the investigated range (5-7), while sorption of Sr2+ -ions, determined in the wider pH range (4.5-11.5), depends only on the initial pH higher than 10, i.e. final pH values higher than 4.5. Negative surface charge established when pH of the solution is higher than pH,, leads to a more effective cation sorption. (C) 2000 Elsevier Science B.V. All rights reserved.

The results of coprecipitation and sorption of strontium by amorphous and crystalline hydroxyapatite are presented. Coprecipitation experiments, performed over a wide range of experimental conditions, have confirmed that strontium is incorporated into hydroxyapatite by the isomorphous substitution of calcium. Adsorption on the surface of well crystallized hydroxyapatite follows a Langmuir adsorption isotherm with a monolayer capacity of 1.5x10(-4) mol g(-1).

In spite of good adsorption characteristics of activated carbon for molecular iodine, from water solution, problems arising due to complexity of chemistry of iodine and hydrolysis as well as influences of other relevant factors in water solutions which easily change the equilibrium concentrations toward domination of species with lower absorbability. Sorption of hypoiodus acid as predominant chemical form of iodine in neutral and weak alkaline solution within the range of micro concentrations has been studied in great details. In the experiments sorption of hypoiodous acid from water solutions on activated carbon with surface area of 1000 m(2)/g, under static and dynamic conditions, has been performed Isotherms on various temperatures (25 degrees C, 50 degrees C, 70 degrees C) hm been obtained. Parameters of the sorption are determined and mechanism of adsorption of hypoiodous acid molecules on activated carbon has been discussed.

The sorption of radioactive strontium by poorly crystalline hydroxyapatite (HA) obtained by the transformation of amorphous calcium phosphate (ACP) at initial pH 10.8, was investigated, Morphological analysis, performed by transmission electron microscopy, has demonstrated that the solid phase consists of nanometer size ultra-micro particles connected into spherical aggregates. A maximum sorption capacity, determined as the asymptote of the sorption isotherm was Gamma = (3.8 +/- +/- 0.3). 10(-2) mol Sr/mol P. Based on this result and the structural conditions, a possible theoretical explanation for the incorporation of a strontium ion into the apatite lattice has been proposed.

In spite of good adsorption characteristics of activated carbon for molecular iodine, from water solution, problems arising due to complexity of chemistry of iodine and hydrolysis as well as influences of other relevant factors in water solutions which easily change the equilibrium concentrations toward domination of species with lower absorbability. Sorption of hypoiodus acid as predominant chemical form of iodine in neutral and weak alkaline solution within the range of micro concentrations has been studied in great details. In the experiments sorption of hypoiodous acid from water solutions on activated carbon with surface area of 1000 m(2)/g, under static and dynamic conditions, has been performed Isotherms on various temperatures (25 degrees C, 50 degrees C, 70 degrees C) hm been obtained. Parameters of the sorption are determined and mechanism of adsorption of hypoiodous acid molecules on activated carbon has been discussed.