磷酸根及重金屬離子在針鐵礦上之吸附平衡

Adsorption Equilibria of Phosphate and Heavy Metal Ions onto Goethite

鍾瑞嬰(Jui-Yin Chung)

指導教授 ： 莊瑞鑫

元智大學/工程學院/化學工程與材料科學學系/碩士(2003年)

摘要

針鐵礦（Goethite，a-FeO·OH）為一水合鐵氧化物，普遍存在於熱帶及亞熱帶環境土壤中，是土壤中最穩定的（氫）氧化態。本實驗自行合成針鐵礦探討重金屬－銅、鋅及磷酸根於針鐵礦表面之吸附情形，實驗變因有溶液濃度、pH 值與溫度，並控制背景離子強度為 0.1 mol/L NaNO3。
研究結果顯示，在重金屬吸附方面，吸附量隨 pH 值增加、溫度升高而增加，吸附過程屬於吸熱反應， pH值高者，吸附熱較小，因為pH值高者在相同條件（同一溫度、相同初始濃度）下，比較容易吸附，所以所需的反應吸附熱也就較小。 Cu2+ 的吸附量大於Zn2+ 。在等溫吸附方面，兩金屬吸附模式皆符合 Langmuir 等溫式；Cu2+ 與Zn2+ 在 35 ℃、pH 5.0時，最大吸附量分別為82與25 mmol/kg。
在雙成分金屬系統中，對於吸附量本來就比較低的Zn2+，在競爭後其吸附量更低。而Cu2+的吸附量卻比由Langmuir competitive model計算所得之理論值要高。
在針鐵礦吸附磷酸根方面，磷酸根吸附量隨pH值降低、溫度升高而增加；吸附過程也是屬於吸熱反應。在較低的pH值下，吸附熱較小，因為pH值低者在相同條件（同一溫度、相同初始濃度）下，吸附比較容易發生，因此反應所需的吸附熱也就較小。吸附模式符合 Langmuir 等溫式。在 35 ℃、pH 2.5 時針鐵礦對磷酸根的最大吸附量為 200 mmol/kg 。
在磷酸根與 Cu2+ 共存的系統中，磷酸根的存在有助於針鐵礦對Cu2+ 的吸附；而Cu2+ 也使磷酸根在高pH值的吸附量增加，此雙成分系統為協同吸附。

關鍵字

針鐵礦 ； 磷酸根 ； 重金屬離子 ； 吸附平衡

並列摘要

Goethite [a-FeO·OH], a kind of hydrated iron(III) oxide, was often encountered on the tropical and subtropical areas, and was the most stable (hydro-) oxidation state in soil. This study investigated the adsorption equilibria of single heavy metal－copper(II), zinc(II), and phosphate, as well as the competitive adsorption equilibria of binary copper(II) zinc(II) as well as binary phosphate and copper(II) onto synthesized goethite. All experiments were carried out at different temperatures (15~35℃), initial adsorbate concentrations, and pH values. The ionic strength was maintained at 0.1 mol/L of NaNO3.
The amounts of heavy metals adsorbed decreased with decreasing pH, but increased in the case of single phosphate. In addition, the amounts of both heavy metals and single phosphate adsorbed increased as temperature was increased. All adsorption processes were endothermic. At a given equilibrium pH, the adsorption isotherms of single phosphate and heavy metals could be well described by the Langmuir equation.
In the binary─copper(II)/zinc(II) system, the amounts of znic(II) adsorbed was decreased. However, in the binary copper(II)/phosphate system, the amounts of copper(II) and phosphate adsorbed were enhanced.

並列關鍵字

Goethite ； Phosphate ； Heavy Metal Ions ； Adsorption equilibria

參考文獻

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