有機酸與鋁離子對纖鐵礦與針鐵礦形成的影響

本研究以適當比率的有機酸與鋁離子加入Fe(上標 2+)溶液中(0.1M, 20mL)，模擬森林土壤中薄膠層的纖鐵礦與針鐵礦的形成，合成過程中溶液維持在pH 6.0並通以N2(25 mL/min)，鋁／鐵莫耳比越高越容易形成針鐵礦，當鋁／鐵莫耳比為0-0.005時生成纖鐵礦；鋁／鐵莫耳比為0.01-0.04則生成纖鐵礦及針鐵礦；鋁／鐵莫耳比為0.05-0.25時生成針鐵礦；當鋁／鐵莫耳比為0.5時，結果產生紅棕色膠體物質，以X-射線繞射鑑定可知其為非結晶性礦物。合成過程中加入少量有機酸根（醋酸／鐵或草酸／鐵莫耳比為0.005-0.1，檸檬酸／鐵莫耳比為0.001-0.05）於Fe(上標 2+)溶液時，皆生成纖鐵礦；當檸檬酸／鐵莫耳比為0.1時，則雖經8小時溶液仍呈橙黃色澄清液。將鋁加入纖鐵礦合成體系中，會促使生成纖鐵礦和少量的針鐵礦，酸性土壤中的可交換性鋁，是促使這些鋁取代鐵礦物生成之主因。

關鍵字

纖鐵礦；針鐵礦；薄膠層；鋁；有機酸

並列摘要

For simulating lepidocrocite and goethite formation in placic horizons of forest soils, Al(superscript 3+) and organic acids in suitable proportions were added to Fe(superscript 2+) solutions (0.1 M, 20 mL). The solution was constantly bubbled with N2(25 mL/min), and pH was maintained at 6.0. Increasing molar ratios Al/Fe in the solutions increased the amounts of goethite in the precipitates. Lepidocrocite formed at Al/Fe ratios=0-0.005; a mixture of lepidocrocite and goethite formed in solutions with Al/Fe ratios=0.01-0.04; geothite formed at Al/Fe ratios of 0.05-0.25; while in a solution with an Al/Fe molar ratio of 0.5, reddish-brown precipitates of X-ray noncrystalline formation occurred. Adding low quantities of organic acids to Fe(superscript 2+) solutions (e. g., acetic acid/Fe and oxalic acid/Fe molar ratios of 0.005-0.1 and citric acid/Fe molar ratios of 0.001-0.05) produced lepidocrocite precipitates. However a citric acid/Fe molar ratio of 0.1 remained as a clear orange-yellow solution at the end of an 8-h reaction period. Al added to the synthetic system of lepidocrocite initiated the formation of lepidocrocite and goethite. Exchangeable Al of soil acidity was the major factor in the formation of Al-substituted goethite and Al-substituted lepidocrocite.

並列關鍵字

lepidocrocite ； goethite ； placic horizon ； aluminum ； organic acid

國際替代計量

有機酸與鋁離子對纖鐵礦與針鐵礦形成的影響

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