Original Research Paper Parametric investigation on anhydrous sodium metaborate (NaBO 2 ) synthesis from concentrated tincal Aysel Kantürk Figen, Sabriye Pis ßkin * Department of Chemical Engineering, Yildiz Technical University, Istanbul 34210, Turkey article info Article history: Received 18 November 2009 Received in revised form 27 January 2010 Accepted 30 January 2010 Key words: Anhydrous sodium metaborate Concentrated tincal Parametric investigation Sodium borohydride Crystalline phase abstract In this study, anhydrous sodium metaborate (NaBO 2 ), an industrial and technologically important boron compound, synthesis from concentrated tincal (CT) was carried out. Experiments with different temper- ature and time were performed in the parametric investigation to map out the reaction mechanism. Crys- talline phase characterization of metaborates products indicates that anhydrous NaBO 2 synthesis from CT occurred at 400 °C with 5 h of reaction conditions. At the end of synthesis, the obtained anhydrous NaBO 2 product can be used in many fields without having the calcination step due to the advantages of this method. Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. 1. Introduction In some field of study, boron minerals are being used as the ores. Especially after refinement into pure chemical compounds, they are used widely. In the world, Turkey, USA, and Russia have important boron mines. In terms of total reserve basis, Turkey has a share of 72.20%; the other important country USA has 6.8%. With a share of 72.20%, Turkey has total boron reserves of 851 mil- lion tons on the basis of B 2 O 3 content [1]. Currently, boron minerals and compounds have gained increas- ing importance, especially in R&D of hydrogen energy storage tech- nologies. Hydrogen can be stored safely as a chemical in the boron minerals/compounds in the form of sodium borohydride (NaBH 4 ). NaBH 4 , which is a known reducing agent, has attracted more atten- tion as an anodic fuel in a fuel cell or as a hydrogen storage med- ium due to its high hydrogen storage capability (10.6 wt%). NaBH 4 can generate hydrogen gas according to the following hydrolysis reaction (Eq. (1)). The reaction can be controlled in an aqueous medium through pH and the use of a catalyst [2–4]. NaBH 4 þ 2H 2 O ! 4H 2 þ NaBO 2 þ Q ð217 kJÞ ð1Þ In a review article, a convenient hydrogen generation technol- ogy based on NaBH 4 and H 2 O as hydrogen carriers has been sum- marized. The NaBH 4 hydrolysis behavior is discussed in detail and it is considered that hydrogen generation from NaBH 4 hydrolysis is a feasible technology to supply hydrogen for the Proton Exchange Membrane Fuel Cells (PEMFC). However, they highlight many engi- neering problems to be solved such as catalyst durability, mist elimination, crystallization of borates, thermal management, and NaBH 4 production cost, and so on [5]. In another article, recent advances in the development of the direct borohydride fuel cell (DBFC) technology are reviewed. It is concluded that the BH 4  electro-oxidation is determined by the catalyst used and BH 4  concentration at the catalytic sites. Hydro- gen evolution during the DBFC operation can be suppressed by: (1) using a composite catalyst or a hydrogen storage alloy as the anode catalyst via a quasi 8-electron reaction; (2) using metals with high hydrogen over-potential, such as Au and Ag as the anode catalyst via an intrinsic 8-electron reaction; and/or (3) modifying and opti- mizing fuel composition [6]. Literature on anhydrous sodium metaborate (NaBO 2 ) used as sources of boron in the production of the NaBH 4 methods are avail- able. Therefore, the use of anhydrous NaBO 2 in the energy field and the importance of both commercial borates class are growing grad- ually. Recently, some methods of synthesizing NaBH 4 from anhy- drous NaBO 2 such as ball-milling synthesis [7,8] and thermal synthesis [9–13] have been developed. Thermal synthesis is a pro- duction method by which NaBH 4 is formed through chemical reac- tion of borates with metals and hydrogen by heating up to approximately 600 °C. It is also noted that NaBH 4 can be prepared by calcining the 4NaH–NaBO 2 –2SiO 2 ternary mixture. It is found that NaBH 4 is suc- cessfully synthesized under Ar, instead of H 2 atmosphere at approximately 480 °C as predicted in [14]: 0921-8831/$ - see front matter Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2010.01.012 * Corresponding author. Tel.: +90 2123834551; fax: +90 2124828071. E-mail addresses: akanturk@yildiz.edu.tr (A.K. Figen), piskin@yildiz.edu.tr (S. Pis ßkin). Advanced Powder Technology 21 (2010) 513–520 Contents lists available at ScienceDirect Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt