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Ice-Bentonite Powder Mixing Method to Improve the Homogeneity of Compacted Bentonite in An Initial Sample Preparation Stage

Published online by Cambridge University Press:  01 January 2024

Yu Peng
Affiliation:
Key Laboratory of Mechanics on Disaster and Environment in Western China (Lanzhou University), Ministry of Education, Lanzhou 730000, China
Huyuan Zhang*
Affiliation:
Key Laboratory of Mechanics on Disaster and Environment in Western China (Lanzhou University), Ministry of Education, Lanzhou 730000, China
Bingzhuo Yang
Affiliation:
Key Laboratory of Mechanics on Disaster and Environment in Western China (Lanzhou University), Ministry of Education, Lanzhou 730000, China
Xuewen Wang
Affiliation:
Key Laboratory of Mechanics on Disaster and Environment in Western China (Lanzhou University), Ministry of Education, Lanzhou 730000, China
Xianxian Shao
Affiliation:
Key Laboratory of Mechanics on Disaster and Environment in Western China (Lanzhou University), Ministry of Education, Lanzhou 730000, China
Ping Liu
Affiliation:
Key Laboratory of Mechanics on Disaster and Environment in Western China (Lanzhou University), Ministry of Education, Lanzhou 730000, China
*
*E-mail address of corresponding author: zhanghuyuan@lzu.edu.cn

Abstract

Bentonite is considered as an ideal buffer/backfill material for preparing an engineering barrier for high-level radioactive waste (HLW) disposal. During initial sample preparation, the tendency of wet bentonite powder to gather into large agglomerates and the water to be spread unevenly in the traditional water content adjustment process decreases the homogeneity of compacted bentonite. The main purpose of this study was to solve this problem by applying a new wetting method, which mixes ice powder with bentonite powder (the ice-bentonite mixing method). This new method was used to adjust the water distribution in Gaomiaozi County, China (GMZ) bentonite powder and was compared to the traditional spray method. The screening method was used to separate macro-agglomerates (≥ 0.25 mm) from the water and bentonite mixture. The properties, the content of the various size agglomerates in loose mixtures, and the heterogeneity defects observed in compacted bentonite were compared. An index (P) was defined to quantitatively evaluate the water distribution in a loose bentonite/water mixture. Macro-agglomerates in loose mixtures produced heterogeneities in water content, density, and shrinkage. By using the ice-bentonite mixing method, fewer macro-agglomerates were formed and a homogeneous distribution of water was produced in the compacted bentonite. A homogeneous water distribution had the tendency to decrease the number of shrinkage cracks after the drying process and to maintain high mechanical strength in the compacted bentonite. Although the production of ice powder was laborious, the ice-bentonite mixing method has workability advantages: (i) a high mixing efficiency, (ii) a low mass loss rate, and (iii) a small deviation between measured water content and target water content. The low thawing efficiency of ice-bentonite mixtures can be solved by using a microwave-assisted thawing method. This research can improve the sample preparation method used to produce compacted buffer/backfill materials for HLW disposal.

Type
Article
Copyright
Copyright © Clay Minerals Society 2016

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Footnotes

This paper is published as part of a special section on the subject of ‘Clay and fine particle-based materials for environmental technologies and clean up,’ arising out of presentations made during the 2015 Clay Minerals Society-Euroclay Conference held in Edinburgh, UK..

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