報告書番号

T87106

タイトル（和文）

各種元素の土壌中移行機構（その３）－浸透水のｐＨ変化を考慮した元素の土壌内輸送モデル－

タイトル（英文）

TRANSPORT OF SOLNTES FROM COAL ASH THROUGH SOIL -EFFECTS OF PH IN INTERSTITIAL WATER ON SOLUTE TRANSPORT THROUGH SOIL-

概要 （図表や脚注は「報告書全文」に掲載しております）

石炭灰溶出元素の土壌内移動速度を予測する輸送モデルを作成した。石炭灰溶出水は通常アルカリ性であり，土壌内を浸透する過程で中和される。元素の移動速度は浸透水のｐＨに大きく依存する為，この輸送モデルでは移動速度に及ぼすｐＨの影響を考慮している。この輸送モデルを用いて土壌カラム実験結果を解析し，元素の移動速度に及ぼすｐＨの影響を考察した。得られた主な結果は以下の通りである。■ホウ素と硫酸イオンの硫黄は，土壌内における移動速度がアルカリ性溶液の移動速度に比べて十分に大きいため，中和に起因するｐＨ変化の影響を受けなかった。■Ｍｏ■は，流出水中の濃度が添加溶液中の濃度よりも一時的に高くなる特異な現象を示した。この現象は，Ｍｏ■は中性土壌によく吸着するが，アルカリ性土壌には殆ど吸着しないことに起因している。■Ｃｒ■についてもＭｏ■と同様の現象が予測されたが，流出水中の濃度が添加溶液中の濃度より

概要 （英文）

IN ORDER TO ESTIMATE MOVEMENT OF SOLUTES LEACHED FROM COAL ASH IN THE SOIL,SOLUTE TRANSPORT MODELS WERE DEVELOPED THROUGH LABORATORY EXPERIMENTS. EACH MODEL IS COMPOSED OF A ONE-DIMENTIONAL CONVECTIVE-DISPERSIVE EQUATION AND AN ADSORPTION EQUATION. MOST COAL ASH FROM COAL-FIRED POWER PLANTS IN JAPAN PRODUCE STRONGLY ALKALINE LEACHATES. THIS ALKALINITY IS EXPECTED TO BE NEUTRALIZED BY THE UNDERLYING,UNSATURATED SOIL LAYER DURING THE INFILTRATION OF LEACHATE. THE MODELS ESTIMATE THE EFFECT OF PH IN INTERSTITIAL WATER ON ADSORPTION OF SOLUTES BY SOIL. MOVEMENT OF ALKALINE LEACHATE SOLUTES IN NEUTRAL SOIL LAYERS WAS EXAMINED THROUGH SOIL-COLUMN EXPERIMENTS,AND THE RESULTS WERE ANALYZED USING THE MODELS. THE MAIN RESULTS ARE AS FOLLOWS: (1)CHANGES IN PH OF INTERSTITIAL WATER DUE TO NEUTRALIZATION OF ALKALINE LEACHATE BY SOIL DID NOT CAUSE CHANGES IN THE INFILTRATION VELOCITY OF BORON AND SULFATE THROUGH SOIL,BECAUSE THEY MOVE THROUGH THE NEUTRAL SOIL LAYER EXTREMELY RAPIDLY COMARED TO THE ALKALINE LEACHATE FRONT. (2)MOLYBDENUM CONCENTRATION IN EFFLUENT FROM SOIL-COLUMNS EXCEEDED THAT OF THE INPUT LEACHATE WHEN THE ALKALINE LEACHATE FRONT REACHED THE BOTTOM OF THE COLUMNS. THIS PHENOMENON CAN BE EXPLAINED BY THE STRONG ADSORPTIN OF MOLYBDENUM BY NEUTRAL SOIL AND WEAK ADSORPTION BY ALKALINE SOIL,THUS MOLYBDENUM ADSORBED BY NEUTRAL SOIL WAS DESORBED WHEN THE ALKALINE LEACHATE FRONT MOVED DOWNWARD. (3)THE MODELS ALSO PREDICTED THE SAME PHENOMENON FOR CHROMIUM(6),HOWEVER,CHROMIUM CONCENTRATION IN EFFLUENT DID NOT INCREASE WHEN THE ALKALINE LEACHATE FRONT REACHED THE BOTTOM OF THE COLIMNS. THIS RESULT SUGGESTS THAT REDUCTION OF CHROMIUM(6) TO CHROMIUM(3) OCCURRED WHEN CHROMIUM(6) MOVED THROUGH SOIL.

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