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Combined neutralization-adsorption system for the disposal of hydrothermally altered excavated rock producing acidic leachate with hazardous elements

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Title: Combined neutralization-adsorption system for the disposal of hydrothermally altered excavated rock producing acidic leachate with hazardous elements
Authors: Tatsuhara, Takeshi Browse this author
Arima, Takahiko Browse this author
Igarashi, Toshifumi Browse this author →KAKEN DB
Tabelin, Carlito Baltazar Browse this author →ORCID
Keywords: Hydrothermally altered rock
Arsenic
Heavy metals
Neutralization
Adsorption
Issue Date: 22-Jun-2012
Publisher: Elsevier B.V.
Journal Title: Engineering Geology
Volume: 139-140
Start Page: 76
End Page: 84
Publisher DOI: 10.1016/j.enggeo.2012.04.006
Abstract: Hydrothermally altered rock excavated in a tunnel project produces acidic leachate containing hazardous elements that include arsenic (As), lead (Pb), copper (Cu) and zinc (Zn). To mitigate this problem, this paper evaluated a combined neutralization-adsorption system that used readily available and cheap reagents like calcium carbonate (CaCO3) and partly-weathered volcanic ash. Batch neutralization experiments showed that CaCO3 was effective in raising the pH of the leachate around neutral while the batch adsorption experiments illustrated that the volcanic ash sample collected near the tunnel project area was highly capable of adsorbing arsenate (As[V]), Pb, Cu and Zn. Under column conditions, the amount of hazardous elements released from the rock increased by several folds and their breakthrough curves had flushing-out trends. The mechanisms of As and heavy metals release probably include the dissolution of soluble phases and pyrite oxidation. Addition of CaCO3 in the column experiments based on estimates from the batch results underestimated the amount of neutralizer needed to adjust the effluent pH to around 8, resulting only in slight increase of the pH. Nevertheless, the presence of CaCO3 drastically reduced the amount of hazardous elements released from the altered rock especially during the initial stages of the column experiments. Combining neutralization and adsorption effectively reduced the amount of As and heavy metals in the effluent throughout the duration of the column experiments, which is attributed to the slight neutralizing effect of volcanic ash that raised the pH around circumneutral as well as its rich Al and Fe oxyhydroxide/oxide contents. The combined system immobilized the hazardous elements through a combination of co-precipitation and adsorption reactions and showed potential as an alternative method for the disposal of altered rocks producing acidic leachate.
Type: article (author version)
URI: http://hdl.handle.net/2115/49832
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: Tabelin, Carlito Baltazar

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