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Materials 2014, 7(2), 1084-1096; doi:10.3390/ma7021084
Article

Silicate Removal in Aluminum Hydroxide Co-Precipitation Process

1,* , 2
,
2
 and
2
1 Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan 2 Graduate School of Creative Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
* Author to whom correspondence should be addressed.
Received: 3 December 2013 / Revised: 2 January 2014 / Accepted: 5 February 2014 / Published: 11 February 2014
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Abstract

The removal mechanisms of silicate using an aluminum hydroxide co-precipitation process was investigated and compared with an adsorption process, in order to establish an effective and validated method for silicate removal from wastewater. Adsorption isotherms, XRD and FT-IR analyses showed that silicate uptake occurred by adsorption to boehmite for initial Si/Al molar ratios smaller than two, but by precipitation of poorly crystalline kaolinite for the ratios larger than two, in both co-precipitation and adsorption processes. Silicate was removed by two steps: (i) an initial rapid uptake in a few seconds; and (ii) a slow uptake over several hours in both processes. The uptake rate in the first step was higher in the co-precipitation process than in adsorption process, presumably due to increased silicate adsorption to boehmite and rapid precipitation of kaolinite. These results suggest that silicate removal using aluminum salts could be effectively achieved if the pH adjustment and aluminum concentration are strictly controlled.
Keywords: co-precipitation; adsorption; aluminum hydroxide; boehmite; kaolinite; sorption density co-precipitation; adsorption; aluminum hydroxide; boehmite; kaolinite; sorption density
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Tokoro, C.; Suzuki, S.; Haraguchi, D.; Izawa, S. Silicate Removal in Aluminum Hydroxide Co-Precipitation Process. Materials 2014, 7, 1084-1096.

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