以兩種光度法測試酸礦水溶氧的可行性研究

Abstract

酸礦水的溶氧是難以光度法來測定的，這是由於酸礦水中含有大量的溶解態鐵物種，會干擾碘的呈色，使得測值被錯估。為了解決這個問題，在樣水進行醃氧之前，先行加入過量的過錳酸鉀，將樣水中所有的亞價離子氧化成鐵三價離子，再加入草酸以及氟化鉀來消除過錳酸鉀及鐵三價離子的干擾，最後樣水在酸化後即可用分光光度計在波長456nm測定，在本篇論文中，此修正法稱為去鐵前處理光度法。但在此還有另一個更為簡便的光度法，不需使用草酸及氟化鉀，利用一試劑反加的步驟來扣除鐵三價離子所造成的信號，此法稱為反加試劑扣除法。此兩種方法皆可應用在測定礦區酸礦水的溶氧，且其結果與傳統的滴定法與校正良好的溶氧探針一致。

Oxygen in acidic mine water is difficult to measure by colorimetry because such water contains high amount of dissolved iron which interferes. Both ferric and ferrous ions produce excess molecular iodine and triiodide thus leading to overestimated results. To solve this problem, a modified colorimetric method is proposed in which the sample is added with permanganate prior to the pickling procedure and all ferrous ions are converted to ferric ions. The sample was further treated with K2C2O4 and KF to remove the interference of permanganate and ferric ions. After acidification iodine and triiodide are formed and the color of the final solution was measured at 456 nm. Another simplified procedure was also compared by neglecting the addition of KF. Excess iodine generated due to ferric ions is compensated by a parallel sample that is pickled with the same reagent but in reverse order. The methods have been applied to measure the oxygen in the run-off water from an abandoned mining area, and the results are in agreement with data obtained by modified titration method and a well-calibrated oxygen sensor.