重金屬在蛇紋岩土壤中的釋出動態

The release dynamics of heavy metals in serpentine soils

蘇映菁(Ying-Ching Su)

指導教授 ： 許正一

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2015年)

https://doi.org/10.6346/NPUST.2015.00147

摘要

蛇紋岩和其風化後之土壤含有高濃度的重金屬，包括鎳、錳、鉻及鈷等。本論文採取台灣東部及奧地利的蛇紋岩土壤，進行不同離子強度及無機酸(鹽酸、硝酸及硫酸)與有機酸(醋酸、草酸及檸檬酸)萃取，並根據酸雨不
同強度，探討酸種類、濃度及pH值對土壤中鎳、錳、鉻、鈷釋出之影響，以了解鎳、錳、鉻、鈷的釋出動態。
研究結果顯示，重金屬釋出濃度會隨著離子強度增加而增加，在相同濃度下，溶液pH值為4時，重金屬明顯有較高的釋出濃度。無機酸與有機酸萃取實驗中，隨著酸溶液濃度的提升，重金屬的釋出率也隨之增提高，兩個土樣中的鎳、錳、鉻、鈷分別在以10 mM硫酸(pH 2.37)(鎳：278 mmol/m2/d、錳：1030 mmol/m2/d、鉻：96.4 mmol/m2/d、鈷：81.7 mmol/m2/d)及10 mM檸檬酸(pH 2.97) (鎳：523 mmol/m2/d、錳：642 mmol/m2/d、鉻：131 mmol/m2/d、鈷：128 mmol/m2/d)萃取條件下有最高的釋出率，原因是硫酸含有兩個質子，檸檬酸含有三個羧基，其螯合重金屬能力較強，顯示配位基和質子數量會增加蛇紋岩土壤中鎳、錳、鉻、鈷的釋出率。比較酸萃取土壤中重金屬的釋出率依序為檸檬酸>草酸>硫酸>鹽酸≈醋酸≈硝酸。

關鍵詞：重金屬、蛇紋岩土壤、萃取、酸雨

關鍵字

重金屬 ； 蛇紋岩土壤 ； 萃取 ； 酸雨

並列摘要

Serpentine soils are enriched with Ni, Mn, Cr and Co. This study used two soil samples from eastern Taiwan and Austria derived from serpentines for the extraction procedures with different inorganic (hydrochloric acid, nitric acid, and sulfuric acid) and organic acids (acetic acid, oxalic acid, and citric acid) containing various ionic strengths and concentrations. Based on the intensity of acid rain, this study discussed the effects of acid rain and pH on Ni, Mn, Cr and Co release from the soils. The aim of this study was to evaluate the release dynamics of these metals from the serpentine soils
under acid rain simulated by these acids.
The experimental results demonstrated that the increase of ionic strength in acid increased the released concentration of Ni, Mn, Cr and Co into the soil solution. As for the extraction of different inorganic and organic acids, the metal release rate increased along with the concentration of all acids for Ni, Mn, Cr and Co. The highest rate was found by using 10 mM sulfuric acid in terms of inorganic acid extraction (Ni: 278 mmol/m2/d, Mn: 1030 mmol/m2/d, Cr: 96.4 mmol/m2/d, and Co: 81.7 mmol/m2/d), while the highest release rate occurred with 10 mM citric acid in organic acid extractions (Ni: 523 mmol/m2/d, Mn: 642 mmol/m2/d, Cr: 131 mmol/m2/d, and Co: 128 mmol/m2/d). We estimated the reason why sulfuric acid and citric acid in the extraction revealed the highest rate of release is that sulfuric acid has two protons (H+) and citric acid has three carboxyl groups, and thus showing a stronger ability to trap heavy metals from the soils. Ligands and protons enhanced the release of Ni, Mn, Cr and Co from the serpentine soils and increased the risk to the surrounding environments. Summarizing extractions, Ni, Mn, Cr and Co release rates increase in the order of nitric acid ≈ acetic acid ≈ hydrochloric acid < sulfuric acid < oxalic acid < citric acid.

Keywords: heavy metal, serpentine soil, extraction, acid rain.

並列關鍵字

heavy metal ； serpentine soil ； extraction ； acid rain

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