![]() ![]() ![]() To determine the effect of these surface structure variations on sorption properties, the chromium (VI) ion sorption on synthesized and modified TCP samples was studied as a function of shaking time. TCP samples were modified in their morphology and particle size by varying the milling time and then compared to the corresponding parameters of the sample prepared by the continuous precipitation method. High-energy ball milling was employed to pulverize tribasic calcium phosphate (TCP) powders to create a fresh surface. 1315 In this paper, the continuous precipitation method was used to synthesize calcium phosphate with highly purified monobasic ammonium phosphate and calcium nitrate. Though tribasic calcium phosphate (TCP) can be synthesized through precipitation from aqueous solutions containing calcium and phosphate ions, 10 other methods (hydroxyapatite) have been reported: high temperature solid-state reactions 11 or the calcination of animal bones, 12 where calcium is supplied as aqueous solutions of CaCl 2, Ca(NO 3) 2, CaC0 3 or Ca(CH 3COO) 2, and the phosphates are supplied as aqueous solutions of (NH 2)HPO 4, NH 4H 2PO 4, KHPO 4, N 2HPO 4, o NaH 2PO 4. This structure exhibits high stability under reducing and oxidizing conditions and very low water solubility (K sp< 10" 40) under alkaline conditions. 8,9 Tribasic calcium phosphate (TCP), adopting the hydroxyapatite structure Ca 5(PO 4) 3(OH), is structurally arranged in a hexagonal system with space group P6/m and characterized by a 6-fold c-axis perpendicular to three equivalent a-axis at 120° to each other. Tribasic calcium phosphate (TCP) is a sparingly soluble mineral with a strong affinity for radionuclides and heavy metals sorption and has therefore been proposed as an adsorbent for radioactive and non-radioactive waste. Ball milling is now a well known method in the nanocrystalline and amorphous powder mass production and was applied to the powders tribasic calcium phosphate in order to boost their sorption properties. 7 Producing these materials in a nanocrystalline form can improve their properties because the high density of defects and interfaces can enhance adsorption. It is well known that fresh surfaces and cracks are created by the ball milling of metals and intermetallic compounds. 5,6 The exchange capacity is most likely connected to structural and morphological changes of the powder surface, i.e. 1-4 However, this literature indicates thatthe actual exchange capacities of amorphous phosphates do not exceed half of the theoretical value calculated for the corresponding crystalhne ion exchangers. Numerous amorphous and crystalhne metallic phosphates have already been synthesized and studied as selective sorbents for the removal of lanthanide, actinide and heavy metal cations from aqueous solutions. Keywords: Ball milling Tribasic calcium phosphate Chromium (VI) ion Sorption XRD SEM This increasing Cr(VI) sorption may be due to the presence of the Fe atoms found in the milled TCP samples. ![]() An increase of Cr(VI) ion sorption with milling time was observed with a maximum chromium sorption of 14.0 x 10 -4meq/g. Fe atoms were found in the milled TCP samples as XRD and EDS techniques revealed. ![]() In TCP samples with a milling time of 5 and 10 h, the specific surface values also diminished to 16.81 and 15.11 m 2/g, respectively. The specific surface area of the prepared TCP prepared sample was 60.55 m 2/g and unexpectedly decreased to 12.57 m 2/g for samples where milling time was 15 hrs. The materials obtained were characterized by X-ray diffraction, SEM, particle size and specific surface area. ball milling effect on the sorption properties of tribasic calcium phosphate (TCP) is presented. * Instituto Nacional de Investigaciones Nucleares. THE BALL MILLING EFFECT ON TRIBASIC CALCIUM PHOSPHATE AND ITS CHROMIUM (VI) ION SORPTION PROPERTIESį. ![]()
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