How Lead Dioxide (pbo2) Anode is Used in Textile Wastewater Treatment?

How Lead Dioxide (pbo2) Anode is Used in Textile Wastewater Treatment?

Electrochemical methods offer an environmentally friendly way of removing toxic inorganic or organic species via redox reactions. These methods may be a good option for textile wastewater treatment, since they are easy to implement, versatile, and can lead to high organic and color removals; their main drawbacks regarding the use of electrical energy and the poor current efficiencies attained at low pollutant concentrations. However, the use of adequate anode materials, coupled with optimized operation conditions, tends to minimize these problems.

The electrochemical oxidation of pollutants can occur in two ways: directly, when the organic pollutant is oxidized by electron transfer directly to the electrode, or indirectly when this electron transfer is mediated by some electroactive species (an oxidant generated at the anode). The most common electrogenerated oxidants in indirect oxidation processes are the hydroxyl radical (•OH), from the oxidation of water; Cl2, HOCl, and OCl- (frequently referred to as active chlorine), from the oxidation of chloride ions.

According to the nature of the interaction between the hydroxyl radical and anode materials, they are classified from high (boron-doped diamond BDD) to low (dimensionally stable anodes DSA) oxidation power anodes; in this classification, lead dioxide (PbO2) is a medium oxidation power anode. The electrochemical oxidation mediated by active chlorine is commonly used with medium to low oxidation power anodes in order to increase the pollutant oxidation rate and the process current efficiency. Indeed, it has been shown that oxidation rates comparable to those on BDD anodes are obtained when using PbO2 or DSA (medium or low oxidation power) anodes in the presence of chloride ions. When using active chlorine, it might be essential to have the solution pH under control in order to improve the pollutant removal efficiency, since pH dictates the predominant chlorine species in the electrolyzed solution. Thus, different pH conditions were reported as the best ones for color and organic removals. The possible formation of undesirable chloro-organic derivatives is a known drawback of electrooxidation processes in chloride-containing solutions.  

PbO2 film anodes are interesting materials for the electrochemical degradation of pollutants due to their medium to high oxidation power, easiness of preparation, and low cost. The PbO2 film electrochemical performance and stabilization are influenced by the presence of doping species, electrodeposition conditions, and substrate preparation.