以菱水鎂鋁石移除水溶液之鉻酸根與磷酸根陰離子

Abstract

利用吸附移除自然環境中之污染物是種常用的處理方法，菱水鎂鋁石(HT)具有類似水鎂石構造(brucite-like)之帶正電荷層，因此被認為是種有潛力的陰離子吸附劑。本研究目的在了解HT移除水溶液中鉻酸根與磷酸根離子之影響因子及移除效果。研究中分別在不同條件下之進行吸附實驗。等溫吸附實驗結果套入Langmuir等溫吸附方程式而得鉻酸根與磷酸根離子之最大單層吸附量分別為0.042與0.146 mmol g-1。不同pH值之動力吸附結果顯示pH值5時HT可移除溶液中49 %之鉻酸根或81 %之磷酸根離子，吸附量會隨著pH上升而減少。在添加不同劑量HT之動力吸附實驗中，雖然移除效果會隨著HT劑量增加而增加，但HT之單位吸附量則會下降，可能因為HT在溶液中聚集成塊而減少了吸附位置。將動力吸附結果套入五種動力學方程式，以Elovich方程式最適合用來描述鉻酸根與磷酸根離子在HT上之吸附現象。競爭實驗結果顯示HT溶液中含有少量磷酸根離子即可抑制鉻酸根離子在HT上之吸附，但鉻酸根離子對磷酸根離子之吸附影響並不大。從X光近邊緣結構( X-ray Absorption Near-Edge Structure )分析結果顯示鉻酸根離子在吸附於HT時不會產生價數變化，延伸X光吸收精細結構(Extended X-ray Absorption Fine Structure)結果發現鉻有可能與構造中心的鋁產生鍵結而吸附。

The adsorption is a common treatment to remove pollutants from natural environments. Hydrotalcite(HT) consists of brucite-like positively layers is considered as a potential anion sorbent.The aims of this study were to understand the influence of adsorption factors of chromate and phosphate adsorb on HT and investigate the removal effects. The sorption maximum of chromate and phosphate on HT were 0.042 and 0.146 mmol g-1 which calculated from Langmuir equation, respectively. The kinetics sorption indicate that chromate and phosphate anion were removed 49% and 81% by HT from solution at pH 5. In the different kinetic sorption of pH, the sorption amounts of chromate and phosphate were increased with decreasing pH. In the different kinetic sorption of different amounts of sorbents, chromate and phosphate sorbed by HT increased with increasing the quantity of sorbents, but the HT sorption amount per weight was decreased, thus suggested that HT particles in the suspension was aggregated, reducing the active sorption sites. The kinetic data was fitted with five kinetic models and showed the Elovich equation was suitable for describing the sorption behavior of chromate and phosphate on HT. The competition research showed that HT was prefer to sorb phosphate than chromate. Sorb of chromate on HT decreased with increasing phosphate.According to X-ray absorption near-edge structure (XANES) analysis result, Cr(VI) were not be reduced into Cr(III) when sorb on HT. On the hand,extended X-ray absorption fine structure (EXAFS) analysis showed that chromate bond with aluminum in the structure of HT.