The sonochemical treatment with RECAM® RE.70 is based on its catalytic action within a specific solution coupled with the sonochemical effect, or rather the application of the ultrasounds to chemical reactions involving oxide reduction.
The ultrasound treatment method is based on the propagation of pressure waves at high or medium frequencies, in a fluid, and works through the creation and collapse of bubbles (cavitation). The cavitation bubbles collapse adiabatically in microseconds. This leads to the formation of hot spots characterized by a pressure of hundreds of atmospheres and by a temperature of thousands of °C, generating an environment with strongly oxidizing conditions via the production of hydroxyl radicals and hydrogen peroxide.
The reactor, based on the application of the ultrasound radiation for the creation of the cavities, is classified as a sonochemical reactor. In the presence of these extreme conditions, the molecules trapped within the bubbles (water and solute vapours) reach an excited state and dissociate themselves. During the process, RECAM®-ultrasound treatment is used in order to oxidize the organic substance and to remove the volatile component, especially the ammonia.
Indeed, volatile components are inclined to move into the cavitation bubbles and they are degraded by pyrolysis reactions that occur within the bubbles. Non-volatile components are inclined to accumulate in the liquid phase where they are degraded by oxidation reactions with the hydroxyl radicals. The ammonia is principally removed by thermal reactions that occur within the bubbles and this is due to the volatile nature of the ammonia.
The use of RECAM® RE.70 is effective or accelerating the sonochemical reactions. The effect is based on the synergy of ultrasound and surface chemistry, i.e. enhancement of the oxidative power of ultrasound by increased surface area of the catalyst, and the formation of OH• on RE.70 by heterogeneous nucleation of the bubbles. RECAM® RE.70 is not only effective in silent reactions but also more so in sonolytic reactions of recalcitrant compounds. Enhanced
efficacy of RE.70 under ultrasonic irradiation is based on enhanced mass transport of the reactants to the RE.70 surface, where ultrasound increases surface defects and the number of active sites while inducing a continuous cleaning action. Moreover the chemical reactions at the RE.70 surface produce H2O2 and gaseous hydrogen to promote decolorization and mineralization of the dyes and reductive cleavage of azo bonds.
The reactions which develop during the treatment are the following, where ))) represents the ultrasound radiation:
|
H2O + RE.55 ))) → • OH + •H + RE.55 (RECOVERED) O2 + ))) → 2O O + H2O → 2•OH •H + O2 → •OOH O2 → 2•O O2 + •O → O3 •O + •O2H → •OH + O2 •O + H2O → 2•OH 2•OH → H2O2 2•OH → H2O• + O• 2HOO• ↔ H2O2+ O2 |
 |
contaminant + •OH + ))) → degraded contaminant contaminant + •OOH + RE.55 ))) → degraded contaminant contaminant + H2O2 + ))) → degraded contaminant |
Sonochemical treatment with RECAM® is particular cost-effective for hydrophobic contaminants.
Main parameters that affect the sonochemical process with RECAM® are listed in the Table below.
Parameter |
General consideration |
Typical value |
|
Power |
By increasing the power, it boosts the unite number of cavity volume and the removal efficacy. |
10÷75 kW/m3 |
|
Frequency |
The process can be used with perceptible frequencies (100Hz), low frequencies (20kHz) or high frequencies (1,6MHz). The differences in terms of conditions are obvious. With high frequencies the wavelength, the temporal cycle, the bubbles dimension and their service life are much lower. Thus, the bubbles density for a unite of volume is higher. This influences the mass transfer to the bubbles and, consequently the energy release, the water hydrolysis and the degradation mechanisms. |
100 kHz |
|
pH |
In an acid environment the free ammonia percentage available for the nanoiron-ultrasound reaction is very low. In the presence of pH values that are higher than 10, 95% of the total ammonia is present as free ammonia. |
> 8 |
|
Dissolved oxygen |
Oxigenation increases the concentration of cavitation bubbles within the solution, speeding up the cavitation and the pyrolysis but decreasing the cavitation bubble dimension. |
> 5 mg/l |
|
Temperature of the process |
The removal efficiency of the process decreases with the increase of the temperature because it constitutes a limiting factor for the collapse of the cavitation bubbles. With moderate temperature values, the contaminants are present in gaseous form (not in steam form) and the efficiency is higher. |
40÷70 °C |
|
Reaction time |
The best reaction time derives from a right balance between the best removal efficiency of the contaminant and the economic sustainability of the energy consumption. |
0,1÷1,0 hours |
|
RE.55 dosage |
The catalytic effect of RECAM® RE.55 affects the efficiency of entire process and reduces the reaction time and energy consumption. |
0,01÷0,20 kg/m3 |
