Electroflocculation kinetics of humic acid removal from boiler make-up water using Al-base electrodes

Abstract

Many coal-fired power plants have undergone a "heating transformation." This transformation measure significantly increases the boiler make-up water required by the power plant, and the make-up water source contains humic acid (HA) organic matter. HA will cause problems such as corrosion、scaling of thermal equipment and increaseing the difficulty of water treatment. The kinetics of electroflocculation were investigated in this study using an experimental device designed to treat HA from boiler make-up water, which is made of plexiglass and has a capacity of 1.2 L. The alloy plates are placed parallel to each other and perpendicular to the horizontal plane as the anode and cathode and are connected to the DC power supply through a wire. Three parameters were investigated: current density, initial pH, and electrode distance. The experimental results show that electroflocculation has a better removal effect on HA. The reaction rate constants of the three electrodes (Al–Zn–In, 6061 alloy, and Al) were 0.07994, 0.04282, and 0.03174 min−1. When the pH was 5, the current density was 100A·m−2, and the spacing between the electrodes was 3 cm, the highest rate constant of 0.10249 min−1 was observed for Al–Zn–In, and the removal rate of HA was 93.3% in 30 min. The SEM and EDS analyses were performed on the electrode and precipitated before and after electroflocculation. The doping of Al–Zn–In with In and Zn helps maintain the electrode surface's activation state during electroflocculation. The electroflocculation effect and anti-passivation ability of the three metals are Al–Zn–In＞6061 alloy＞Al. Al–Zn–In is expected to replace aluminum plates due to its resistance to passivation and superior electroflocculation effect.