Alkali-Hydrothermal Synthesis of Acicular Tobermorite Using Natural Mineral K-Feldspar Powder

Abstract

This research reports a new economical method of preparing acicular tobermorite as well as high-valuable KOH obtained. Acicular tobermorite was hydrothermally synthesized at 180∼250°C for 4∼8 h using the K-feldspar powder and CaO chemical firstly while the filtrate could be used to prepare KOH. The K-feldspar powder used is from Luonan county of Shaanxi province in China. The XRD analysis indicated that the main phase is microcline with the content of 91%. The chemical analysis showed that the main chemical components of the K-feldspar powder are SiO₂ 64.53%, Al₂O₃ 16.70% and K₂O 14.75% in mass.

The micrographs of the synthesized samples at the condition of different water/solid ratios, hydrothermal treated temperature and time were investigated. It is concluded that the well-crystallized tobermorite was formed with the acicular shape when the synthesized parameters were as follows. nCa/n(Si+Al) = 0.83, Water/Solid(in mass) = 20, T = 250°C and t = 8h. The synthesized well-crystalline tobermorite sample was characterized by the use of chemical analysis, powder X-ray diffraction and scanning electron microscope. It is shown that the synthesized sample is acicular with the diameter of around 0.2∼0.5 µm.

Keywords:

• K-feldspar; alkali-hydrothermal process; acicular tobermorite; KOH

Acknowledgments

The authors give thanks to Ms. Long Mei, Wang Junling and Liang Shuping for the chemical analysis.

Funding

The authors are grateful for the funds from China Geological Survey Project (12120113087700) and the Fundamental Research Funds for the Central Universities (2652014017, 2652015016, 2652015015).