應用多硫化鈣整治六價鉻污染土壤及地下水技術之建立-操作參數及衍生物穩定性之研究

Technique of apply calcium polysulfide to remediate heavy metals-contaminated soil and groundwater - operating parameters and immobility of derived species

劉資祺(Liu Tz-Ci)

指導教授 ： 程淑芬

朝陽科技大學/理工學院/環境工程與管理系/碩士(2018年)

摘要

目前國內地下水重金屬污染以六價鉻的案例最多，六價鉻具有高毒性及高移動性，若能將其還原成三價鉻，三價鉻是人體必需之微量元素，不僅毒性降低，也會形成移動性較低的三價鉻沉積物如Cr(OH)3。
對於六價鉻，許多場址都採用化學還原穩定法。藉由化學還原反應降低污染物毒性或以形成沉澱物的方式降低重金屬移動性減少地下水中重金屬濃度；然而，化學還原穩定法在現地應用時，所形成的衍生物在地下環境中的穩定性，一直備受質疑，其原因為還原劑停止施用後，地下環境會隨著當地之水文、地質特性逐漸恢復原來情況，原本地下水可能是富含氧，偏向弱酸性，地質中可能存在一些鐵、錳等氧化物都可使藉由化學還原、沉澱之重金屬再度地釋出，而無法真正達到化學穩定的功效。
多硫化鈣近年在國外應用於處理鉻鐵礦砂殘渣，證實有還原六價鉻的處理能力。此外，國外多個六價鉻污染場址也嘗試以多硫化鈣進行處理，皆顯示對六價鉻的還原及穩定具有顯著的成效。
本研究使用去離子水、地下水及污染場址水樣配製六價鉻水樣，使用市售及自製多硫化鈣進行批次試驗。以石英砂、砂土及紅土進行管柱試驗。實驗結果顯示：多硫化鈣對六價鉻的還原相當快速，而低pH值水樣條件有利於多硫化鈣還原六價鉻；水樣溶氧的多寡並不影響多硫化鈣還原六價鉻的效果。自製多硫化鈣對六價鉻的還原效果比市售多硫化鈣佳，在濃度100 mg L-1的六價鉻溶液中，市售多硫化鈣需添加莫耳比18：1對六價鉻之去除率達到95 %以上，而自製60分鐘多硫化鈣添加莫耳比9：1對六價鉻之去除率將近100 %。管柱試驗結果，石英砂、砂土及紅土於12週內總鉻溶出濃度均低於第二類水體管制標準（0.5 mg L-1）。

關鍵字

六價鉻 ； 化學還原穩定法 ； 多硫化鈣 ； 製備多硫化鈣 ； 操作條件 ； 沉澱物穩定性

並列摘要

Currently, heavy metal contamination of groundwater is dominated by hexavalent chromium, a highly toxic and mobility. Hexavalent chromium can be reduced to trivalent chromium, which is easily suspended with less mobility, and conducive to sedimentation, such as chromium hydroxide. Trivalent chromium is an essential element of the human body, it is less toxic than hexavalent chromium.
Many hexavalent chromium polluted sites use chemical reduction method for remediation. However, the stability of sediment produced by chemical reduction was questioned, the reason is the physical conditions of groundwater are restored to the past condition. Heavy metals may be released by iron-manganese oxide and acidic groundwater. That is the chemical precipitation in question.
Calcium polysulfide has been applied in recent years to treat chromite ore processing residue in other countries, that confirmed the ability to reduce hexavalent chromium. In addition, multiple hexavalent chromium contaminated sites have also been tried with calcium polysulfide, it also shows significant effect on the reduction and stabilization of hexavalent chromium.
This study used deionized water, groundwater and contaminated water samples to prepare hexavalent chromium solution. Batch tests were conducted using commercially available calcium polysulfide and lab-prepared calcium polysulfides. Quartz sand, sand and clay for column test. The result shows calcium polysulfide reduction of hexavalent chromium quite quickly. Low pH conditions favor the reduction of hexavalent chromium by calcium polysulfide. Dissolved oxygen does not affect the effect of calcium polysulfide reduction of hexavalent chromium. Lab-prepared calcium polysulfide reduction of hexavalent chromium better than the commercially available calcium polysulfide. The hexavalent chromium removal rate of commercially available calcium polysulfide is as hight as 95 % when the molar ratio of applied dose is 18:1. The hexavalent chromium removal rate of lab-prepared boiled for 60 min calcium polysulfide is as hight as 100 % when the molar ratio of applied dose is 9:1. Column test results show that the concentrations of total chromium dissolved in quartz sand, sand and clay within 12 weeks were lower than the second type of water control standards.

並列關鍵字

hexavalent chromium ； chemical reduction stabilization ； calcium polysulfide ； preparation of calcium polysulfide ； operating conditions ； stability of the precipitate

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