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2段階溶出モデルによる黄鉄鉱の酸化・溶解速度の評価

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Title: 2段階溶出モデルによる黄鉄鉱の酸化・溶解速度の評価
Other Titles: Evaluation of Pyrite Dissolution Rates by Two-step Leaching Model
Authors: 五十嵐, 敏文1 Browse this author →KAKEN DB
井筒, 崇文2 Browse this author
岡, 泰道3 Browse this author
Authors(alt): Igarashi, Toshifumi1
Izutsu, Takafumi2
Oka, Yasumichi3
Keywords: pyrite
oxidation
leaching model
拡散
diffusion
Issue Date: 10-Oct-2002
Publisher: 日本応用地質学会
Journal Title: 応用地質
Volume: 43
Issue: 4
Start Page: 208
End Page: 215
Publisher DOI: 10.5110/jjseg.43.208
Abstract: 2種類の粉砕した黄鉄鉱試料に対する酸化・溶解速度を評価するために,好気的条件下でのバッチ溶出試験を行い,溶出水のpH,酸化生成物である鉄イオンや硫酸イオン濃度の変化を測定した.その結果,溶出水pHは黄鉄鉱の種類,固液比,溶出期間に依存し,溶出水pHの低下とともに電気伝導度,鉄イオン濃度,硫酸イオン濃度が上昇した.化学形態分析によれば,鉄はFe(II)イオンとして,イオウは硫酸イオンとして溶出した.Fe(II)イオンや硫酸イオンの溶出速度に関しては,2種類の試料どちらに対しても溶出初期においては,固相濃度に関する一次反応によって溶出することが明らかになった。溶出期間の増加とともに,いったん溶出水濃度が一定になった1つの試料に対しては,その後溶出期間の1/2乗で溶出水中のFe(II)イオンや硫酸イオン濃度が増加することがわかった.これは,黄鉄鉱内部における拡散が溶出速度を律速することを示唆している.すなわち,溶出初期においては黄鉄鉱表面からの溶出が,その後黄鉄鉱酸化物層を通しての拡散という2段階の溶出機構によって黄鉄鉱の酸化・溶解反応が進行することが見出された.ここで見積られた拡散係数がおよそ10^<-10>cm^2/sという低い値であったことから,黄鉄鉱の酸化・溶解に伴う影響は溶出初期に大きいことが予想された.また,黄鉄鉱の粒径が小さくなるとともに,pHが低下し,電気伝導度,Fe(II)イオン濃度,硫酸イオン濃度が上昇したが,溶出速度に顕著な相違は認められなかった.
Batch leaching experiments in aerated conditions for two different types of crushed pyrite were carried out by measuring changes in pH and concentrations of Fe and SO_4 for leachate. The results showed that leachate pH depended on the solid-liquid ratio and leaching period as well as the pyrite used, and that the electric conductivities and the concentrations of Fe and SO_4 increased with the decrease in leachate pH. The chemical forms of iron and sulfur in the leachate were identified as ferrous ions and sulfate ions, respectively. The concentration changes observed illustrated that the initial leaching rates of ferrous and sulfate ions from both pyrite samples were demonstrated by a first-order reaction with respect to the solid-phase concentration. This indicates that the initial dissolution process was governed by a surface reaction. On the other hand, the subsequent dissolution of one of the samples was expressed by a function of the square root of the leaching period, suggesting that the rate-determining process was diffusion in the crushed pyrite sample. These two different mechanisms were found to affect the dissolution rate of pyrite. Therefore, the initial leaching may be expected to be more critical to the chemical properties of leachate than the following leaching, due to the estimated diffusion coefficient within the pyrite being as low as 10^<-16> cm^2/s. In addition, the diameter of the crushed pyrite affected the chemical properties of the leachate, but not the leaching rate.
Type: article
URI: http://hdl.handle.net/2115/52644
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 五十嵐 敏文

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