EARTH

[31001-12-05] Creation of amorphous ettringite using low temperature dehydration and influence of dehydration temperature on the boron removal amount

○Shungo Hobo¹, Giuseppe Granata¹, Chiharu Tokoro¹, Yoshiyuki Tanaka², Takeshi Nakamura² (1. Waseda University, 2. Sumitomo Metal Mining Co., Ltd.)

Chairman: Granata Giuseppe （Waseda University）, Richard Alorro (Curtin University)

Keywords:boron, wastewater treatment, amorphous, ettringite

Boron is one of the most important elements in modern industry, in particular in semiconductor manufacturing where it is used as doping agent. Because boron is toxic and difficult to remove from wastewaters, the development of an efficient technology for boron removal is highly anticipated.
Among the possible removal methods, the co-precipitation was found capable of determining higher removal performances compared to the adsorption method. In co-precipitation, the method using ettringite as co-precipitating and adsorbing agent seems to be promising. However, the adsorption of boron by previously synthesized ettringite must be improved in order to achieve efficient removal processes.
One of the latest improvement implies the use of ettringite upon amorphization at 175℃ to increase the adsorption capacity towards boron. However, because the use of high temperatures in wastewater treatment dramatically affect the process sustainability, the use of lower temperatures is desirable.
In this research, we studied the production of amorphous ettringite with high adsorption capacity at temperatures lower than 100℃ and we investigated the influence of the dehydration temperature on boron removal performances.
In spite of literature data showing the impossibility of amorphization below 100℃, our results showed that the ettringite dehydrated in the temperature range 75-95℃ became amorphous and efficient for boron removal. In particular, the ettringite sample dehydrated at 75℃ showed a removal efficiency equivalent to samples dehydrated at 175℃.