EARTH

[1901-09-06] Synthesis of ettringite using various gypsum as a raw material and its anion removal ability

○Mitsuru Hirao¹, Mitsuaki Matsuoka¹, Norihiro Murayama¹ (1. Kansai University)

Chairman：Naoki Hiroyoshi（Hokkaido University）

Keywords:Ettringite, Gypsum, Adsorbent, Boron

The effective use of by-products in large quantities such as desulfurization gypsum and phoshogypsum is required. Ettringite is well-known as one of cement hydrates and it is expected to be used as a functional material having anion removal ability. We focus on the application of by-product gypsum to a raw material of ettringite. In this case, the hydration state of CaSO₄ is considered to be important factor to synthesize ettringite effectively. It is of concern to establish the synthesis method of ettringite using various gypsum for adsorbent and to clarify their anion removal abilities to dilute aqueous solution. The purpose of this study is to investigate the synthesis condition of ettringite from gypsum, especially from the viewpoint of formation speed of ettringites and their anion removal abilities. CaSO₄･2H₂O or CaSO₄ was used for calcium and sulfate ion sources to form ettringite. Whereas NaAlO₂, crystalline and amorphous Al(OH)₃ was used as an aluminum source, respectively. Phoshogypsum was used as raw material of ettringite synthesis. The removal tests of boron in dilute solution (1ppm) were conducted using ettringite synthesized under various conditions.
The Ca precipitation percentage in a ettringite synthesis process using CaSO₄ was slightly higher than that using CaSO₄･2H₂O, due to the difference in solubility or reactivity of CaSO₄. When NaAlO₂ was used, the formation speed of ettringite was found to be the highest among all products synthesized from various aluminum sources. In using phosphogypsum for ettringite synthesis, it was considered that calcium dissolution was a little reduced by the presence of impurity components such as magnesium and iron in phoshogypsum. The ettringites obtained from NaAlO₂ and Al(OH)₃ showed 17% and 11% of boron removal, respectively. We will report more detailed results and other anion removal abilities using ettringites under various synthesis conditions in our presentation.