Search

4th BBBB-Bled International Conference on Pharmaceutical Sciences - New Trends in Drug Discovery, Delivery Systems and Laboratory Diagnostics, Sep 29-Oct 01, 2011, Bled, Slovenia

Recently. it has come to our attention, that a polemical note by Milonjic [S.K. Milonjic, Comments on factors influencing the removal of divalent cations by hydroxyapatite, J. Hazard. Mater. 162 (2009) 1588-1589]. has been published raising several critical comments on some experimental procedures, as well as the presentation and interpretation of some data found in the cited paper by Smiciklas et al. [L. Smiciklas, A. Onjia. S. Raicevic, Dj. Janackovic, M. Mitric, Factors influencing the removal of divalent cations by hydroxyapatite, J. Hazard. Mater. 152 (2008) 876-884]. Since we have not received any prior copy of this discussion through the process involved in the acceptance of these comments, we now take the opportunity of responding. We have reviewed some scientific papers dealing with cation sorption, in order to demonstrate variety of experimental approaches used for batch sorption tests, regarding solution pH. Finally, we justified experimental methods and data interpretation methods we chose to perform in the mentioned manuscript. (C) 2009 Elsevier B.V. All rights reserved.

Several approaches for immobilization of arsenic (As) based on the transformation of its soluble forms (compounds) into highly insoluble arsenate apatite Ca-5(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: Ca-5(AsO4)(3)OH, Ca-4(AsO4)(2)(OH)(2), Ca-3(AsO4)(2) Ca5H2(AsO4)(2) and CaHASO(4) was performed, which is based on the calculation of the ion-ion interaction potential (IIIP). It has been demonstrated earlier that HIP, 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. Research Trends in Contemporary Materials Science, 8th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 04-08, 2006, Herceg Novi, Montenegro

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). Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 2004

Stability of the solid matrix - contaminant system represents a crucial parameter in selection of the appropriate natural material for in situ remediation of the environment contaminated by toxic heavy metals. We have investigated, using a calculation of cohesive energy, suitability of different natural materials which are appropriate for in situ remediation of soil and water contaminated by Pb. Based on the applied theoretical criterion we have selected a natural apatite from the Lisina deposit (Bosilegrad, Yugoslavia) as a promising solid matrix for large-scale remediation and prevention of pollution by Pb in a cost-effective manner.

Lead contamination is an environmental concern due to its effect on human health. One of the ways of remediating lead contamination is the in situ stabilization of this heavy metal. This can be achieved by converting different types of lead species into Pb-phosphates (pyromorphites), which are among the least soluble Pb-bearing solids. Synthetic hydroxyapatite (Ca5(PO4)3OH) and natural apatite can be used for this purpose. Both hydroxyapatite and some natural apatites are effective in reducing the aqueous Pb concentration to below 15 μgT1 (EPA drinking water limit). The main mechanism in the case of hydroxyapatite is its dissolution and subsequent precipitation of pyromorphites. The mechanism and the effectiveness of natural apatites depend on the type of apatite, its composition, crystallinity and presence of impurities. Apatites are also effective in reducing the Pb concentration in leachets from contaminated soils in the pH range from 6 to 10. The percentage of Pb concentration reduction is from 60 to 99.9% depending on the type of contamination and type of apatite amendment applied. These data suggest that apatites have potential to provide cost-effective in situ Pb immobilization. Ljudske aktivnosti su dovele do promene distribucije i oblika u kojem se nalaze različiti elementi, uključujući olovo. Olovo je pretvoreno iz nereaktivnog, geohemijski stabilnog oblika u rastvorljiva jedinjenja te je tako postalo dostupno za biosferu. Jedan od mogućih pristupa saniranju zagađenja olovom je promena smera ovog procesa, odnosno transformacija reaktivnih i rastvornih jedinjenja ovog metala u stabilnije oblike. Ovim procesom se olovo ne ukljanja iz životne sredine, ali se sprečava njegova akumulacija u biosferi. Jedan od materijala koji se ispituju za korišćenje u ovu svrhu je sintetički hidroksiapatit (Ca5(PO4)3OH) i prirodni apatit. Ovi materijali omogućavaju formiranje Pb-fosfata (piromorfita) koji su veoma slabo rastvorljivi i u skladu sa tim, slabo dostupni biosferi. Korišćenje obe ove vrste apatita omogućava snižavanje koncentracije olova u vodenim rastvorima ispod 15 μgT1, što je gornja granica za pijacu vodu Američke agencije za zaštitu životne sredine (EPA). U slučaju hidroksiapatita osnovni mehanizam ovog procesa je njegovo rastvaranje i taloženje piromorfita. Efikasnost prirodnog apatita mnogo zavisi od sastava minerala, stepena kristaličnosti i količine prisutnih nečistoća. Mehanizam stabilizacije olova prirodnim apatitom nije u potpunosti utvrđen. Postoje dokazi koji potvrđuju mehanizam rastvaranje apatita i taloženja piromorfita, ali potrebna su dalja istraživanja u ovoj oblasti. Apatiti su takođe efikasni u smanjivanju koncentracije rastvorljivog olova u zagađenom zemljištu u opsegu pH od 6 do 10. Ovo smanjenje se kreće od 60 do 99.9 % u zavisnosti od vrste zagađenja i primenjenog apatita. Ovi podaci ukazuju da apatiti mogu biti korišćeni za in situ stabilizaciju olova.

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 can be concluded that natural apatite from Lisina ore deposit is a promising material for heavy metal remediation in polluted soils and ground water. 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 svih dobijenih rezultata ukazuje na mogućnost primene prirodnog apatita iz ležišta Lisina, kao jeftine polazne sirovine, za remedijaciju zemljišta i podzemnih voda zagađenih teškim metalima.