Evaluation of Chemical-Resistant Bentonite for Landfill Barrier Application

Abstract

耐化学性ベントナイトである多膨潤性ベントナイト(mutiswellablebentonite:MSB)の, 廃棄物処分場バリア材への適用性を実験的に検討した。MSBは塩化カルシウムや塩酸の溶液に対しても高い膨潤性を示し, 透水係数も天然ベントナイトより1オーダー以上低い値が得られたことから, 廃棄物処分場のライナーやカバーなどのバリア材に有効に適用しうることが示唆された。

Chemical compatibility of a newly developted material -multiswellable bentonite- is evaluated for the purpose of landfill barrier application. A series of liquid limit, free swell, and hydraulic conductivity tests were performed. The materials used in this study are natural bentonite and multiswellable bentonite. The permeants are distilled water, and CaCl2 and/or HCl solutions. Electrical conductivity and pH values of the effluents obtained from the hydraulic conductivity tests were measured to ensure the total chemical breakthrough. Multiswellable bentonite was found to perform better than natural bentonite does when in contact with CaCl2 and/or HCl solutions. Values of free swell and liquid limit of both bentonites decreased with the increase in concentration of CaCl2. Most specimens of multiswellable bentonite had the hydraulic conductivity one or more orders of magnitude lower than that of natural bentonite when in contact with the same concentration of CaCl2 solutions. The hydraulic conductivity values of both bentonites are higher than the requirement by the US EPA for MSW landfill clay liner (k < 10-7 cm/s) when permeated with calcium chloride solution greater than 0.3 M.