Kinetics of sorptive removal of fluorine onto modified diatomite
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DATSKO, Tatiana, ZELENTSOV, Veaceslav. Kinetics of sorptive removal of fluorine onto modified diatomite. In: Materials Science and Condensed Matter Physics, Ed. 7, 16-19 septembrie 2014, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2014, Editia 7, p. 142.
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Materials Science and Condensed Matter Physics
Editia 7, 2014
Conferința "Materials Science and Condensed Matter Physics"
7, Chișinău, Moldova, 16-19 septembrie 2014

Kinetics of sorptive removal of fluorine onto modified diatomite


Pag. 142-142

Datsko Tatiana, Zelentsov Veaceslav
 
Institute of Applied Physics, Academy of Sciences of Moldova
 
Disponibil în IBN: 5 martie 2019


Rezumat

In the last decades the sorption methods became more and more attractive at the purification of natural and wastewater from different dissolved toxic substances thanks to their availability simplicity of implementation selectivity and efficiency. This report describes the investigation of fluorine removal from model solution on moldavian diatomite modified by structure-chemical method with aluminosilicate (DMA). The modification procedure consists in subsequent processing of diatomite sample with alkali solution at heating, solutions of aluminum salt and ammonia, washing and drying in air and in oven at 1100C. Specific surface area and sorption pore volume of the obtained sorbent were 81.2 m2 / g and 0.106 cm3 / g, respectively. Adsorption ability of the sorbent DMA with respect to fluorine has been studied: adsorption equilibrium and kinetics. Adsorption equilibrium was performed in batch conditions. The fluorine adsorption isotherms and kinetic curves have been obtained for model fluorine solution with initial fluorine concentration 2- 10mg F/l – the average value from 30natural aqueous sources of Moldova. It has been shown that the maximum adsorption capacity of the sorbent with respect to fluorine achieved in the pH range 4, 85 – 5, 50 and is 22mg/g at the initial fluorine concentration 10 mgF/l and sorbent doze 0.5g/l. The isotherms were fitted to Freundlich and Henry models, the parameters of the equations were obtained and it was shown that the first model more adequately described the fluorine adsorption experimental data (R2 = 0.9971). The kinetic curves have been obtained and it has been shown that the adsorption process is fast enough – more than 90% of fluorine is removed at the first 2-5 minutes of adsorption. In order to examine the controlling mechanism of the sorption process of F ions on diatomite at 20oC, three kinetic models were used: Intraparticle diffusion model of Weber-Morris [1], a k t C t d 0.5 Pseudo-first order model Lagergren [2], at = am(1- ·exp-k1·t) Pseudo-second order model Mackay and Ho [3] /(1 ) 2 akatka ttm am and at are the amounts of F ions adsorbed at equilibrium and at time t, respectively (mg/g), k1 (min-1), is the rate constant of the pseudo-first order kinetics k2 [g/(mg min)] is the rate constant of the pseudo-second order kinetics kd [g/mg min0.5] is the intraparticle diffusion rate constant C is a constant that gives an idea about the effect of boundary layer thickness. The equations parameters have been determined and it has been shown that Pseudo-second order model is the best for fitting to experimental kinetic curves, indicating the chemical character of interaction of fluorine with active sites of the sorbent surface. It is also noted that the mechanism of fluorine removing is controlled by intraparticle diffusion and superficial adsorption.