Electrochemical mineralization

Basic Principles of the Electrochemical Mineralization of Organic Pollutants for Wastewater Treatment... 

The aim of the present work is to elucidate the basic principles of the electrochemical mineralization (EM) using some model organic pollutants. The following points will be treated ... 

Thermodynamically, the electrochemical mineralization (EM) of any soluble organic compound in water should be achieved at low potentials, widely before the thermodynamic potential of water oxidation to molecular oxygen (1.23 V/SHE under standard conditions) as it is given by (1.1) ... 

In contrast to these promising thermodynamic data, the kinetics of the electrochemical mineralization is very slow and in practice it can be achieved close to the thermodynamic potentials only in very limited cases. In fact, only platinum-based electrodes can allow EM of simple Ci organic compounds. A typical example is the use of Pt-Ru catalyst in the electrochemical mineralization of methanol. 

In this section, a kinetic model of electrochemical mineralization of organics (RH) on BDD anodes under electrolysis regime is presented. In this regime, as reported in Sect. 1.4, electrogenerated hydroxyl radicals (1.20) are the intermediates for both the main reaction of organics oxidation (1.21) and the side reaction of oxygen evolution (1.22). 

The consequence of this last assumption is that the rate of the mineralization reaction is independent on the chemical nature of the organic compound present in the electrolyte. Under these conditions, the limiting current density for the electrochemical mineralization of an organic compound (or a mixture of organics) under given hydrodynamic conditions can be written as (1.23)... 

From (1.25) and (1.27) and at given time t during electrolysis, we can relate the limiting current density of the electrochemical mineralization of organics with the COD of the electrolyte (1.28) ... 

Intermediates Formed During the Electrochemical Mineralization Process Using BDD... 

It has been found, that the amount and nature of intermediates formed during the electrochemical mineralization of organics on BDD anodes depends strongly on the working regime. In fact, electrolysis under conditions of current limited control... 

Electrical Energy Consumption in the Electrochemical Mineralization Process... 

As it has been shown in Sect. 1.8, the specific energy consumption for the electrochemical mineralization of organics decreases strongly with increasing average current efficiency (EOI) and reaches a minimum value at EOI = 1. In order to work... 

More recently, Bonfatti et al. (1999) have verified that the reactivity of glucose at Ti/Pt electrodes was acceptable in all current densities, slightly higher at 600A m-2 however, the electrochemical mineralization was low, particularly over a long electrolysis time, due to the accumulation of intermediates, mainly glucaric acid, which resisted further attack at the platinum electrode. The situation improved by increasing the temperature to 56°C. 

The electrochemical conversions of solid compounds and materials that are in direct contact with electrolyte solutions or liquid electrolytes (ionic liquids), belong to the most widespread reactions in electrochemistry. Such conversions take place in a wide variety of circumstances, including the majority of primary and secondary batteries, in corrosion, in electrochemical machining, in electrochemical mineral leaching, in electrochemical refining (e.g., copper refining), and in electrochemical surface treatments (e.g., the anodization of aluminum). 

Electrochemical Reactor Design for the Oxidation of Organic Pollutants, Fig. 1 (a) Direct electro-oxidation, (b) Electrochemical mineralization, (c) Indirect electrochemical oxidation... 

In electrochemical mineralization, oxygen atoms are transferred from water to the organic pollutant R via the strong oxidizing hydroxyl radicals (E° = 2.74 V/SHE) produced by water discharge (Fig. lb) ... 

Kapalka K, Foti G, Comninellis Ch (2010) Basic principles of the electrochemical mineralization of organic pollutants for wastewater treatment. In Comninellis Ch, Chen G (eds) Electrochemistry for the environment. Springer, New York... 

Secondly, additives based on fluorinated alcohols turned out to be beneficial for the lifetime of the intermediate radical species [12, 13]. It is anticipated that the known stabilization of intermediates causes a strongly enhanced lifetime, reducing the electrochemical mineralization by over-oxidation. 

In conclusion, in the actual state of the art, electrochemical mineralization of organic pollutants with cogeneration of electrical energy is not feasible, due to the lack of active electrocatalytic anode material. Bioelectrocatalysis is a new and active field and can overcome this problem as has been demonstrated recently in the development of biofuel cells. Nevertheless, this technology is yet in its infancy. 

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