Rapid determination of iron concentration in wastewater using color band formation

Abstract

High concentrations of iron ions in water bodies cause odour and discolouration due to their precipitation. The total iron ion concentration is generally analysed on-site by forming coloured compounds and measuring colour intensity with spectrophotometric or visual analysis. In this work, we developed a detection tube as an alternative simple analytical method, where the total iron ion concentration is measured not by colour but by an objective parameter called the colour band length (CBL). Tiron was selected as the colouring agent since it oxidises divalent iron ions into a trivalent state and reacts with trivalent iron ions to form a 3:1 anion complex in alkaline media, giving a red colour. The coloured solution penetrates the detection tube by capillarity, and the colour band is formed by the entrapment of the hydrophobic ion pair of iron-tiron complex and quaternary ammonium ions of the adsorbent filled in the tube. The CBL was found to correlate well with the total iron ion concentration quantitatively under the optimized measurement condition, and 5 to 40 mg-FeL−1 solutions could be measured with good objectivity and precision.