The addition of phosphates was found to decrease the rate of the decomposition of ozone in water; they accepted hydroxyl radicals
and thereby inhibited chain ozone decomposition. The presence of phosphates decreased the order of the reaction from second
for pure water to one-and-a-half. The rate constants for ozone decomposition in the presence of various phosphate concentrations
increased as pH grew from 4 to 9.
"Then , it can be suggested that the participation of the phosphates are not as radical scavengers as it was proposed in other works ( Bi´n et al . 2013 ; Morozov and Ershov 2010 ) but as a proton source for the chemical reaction : "
[Show abstract][Hide abstract] ABSTRACT: The ozone decomposition reaction is analyzed in an homogeneous reactor through in-situ measurement of the ozone depletion. The experiments were carried out at pH’s between 1 to 11 in H2PO4-/HPO42- buffers at constant ionic strength (0.1 M) and between 5 and 35 ºC. A kinetic model for ozone decomposition is proposed considering the existence of two chemical subsystems, one accounting for direct ozone decomposition leading to hydrogen peroxide and the second one accounting for the reaction between the hydrogen peroxide with the ozone to give different radical species. The model explains the apparent reaction order respect of the ozone for the entire pH interval. The decomposition kinetics at pH 4.5, 6.1 and 9.0 is analyzed at different ionic strength and the results suggest that the phosphate ions do not act as a hydroxyl radical scavenger in the ozone decomposition mechanism.
[Show abstract][Hide abstract] ABSTRACT: Decolourization of direct azo dye, direct blue 15 (DB15), by an advanced Fenton process coupled with ultrasonic irradiation (Fenton/US) was investigated. Zero-valent iron (ZVI) aggregates were used as the catalyst. A positive synergistic effect occurred when Fenton's reagent was combined with ultrasonic irradiation. Experimental results showed that the optimum conditions for decolourization were pH 3.0, Fe(0) 1g/L, H(2)O(2) 5.15×10(-3)mol/L with ultrasound density of 120W/L at 60kHz. These conditions yielded 99% decolouration of 4.7×10(-5) M DB15 (4130 ADMI) solution within 10min. DB15 decolouration follows the first-order decolouration kinetics. Although the solutions containing H(2)CO(3), Cl(-), ClO(4)(-), NO(3)(-) and SO(4)(2-) ions did not have a significant effect on the decolouration, the H(2)PO(4)(-) ion did decrease the decolouration rate. High ultrasonic input power accelerated the reaction and increased decolourization efficiency. The cost effectiveness of this process at high ultrasound density could be controlled despite the high electricity costs incurred by the process. ZVI aggregates were reusable; however, an increase in the number of times ZVI was recycled decreased the decolourization rate. This study demonstrates that a Fenton/US process can effectively decolour the direct azo dye DB15 in wastewater.
[Show abstract][Hide abstract] ABSTRACT: The decoloration of reactive azo dye, Reactive Black 5 (RB5), by an advanced Fenton process in conjunction with ultrasound (Fenton/US) was investigated. The Fenton/US process using zero-valent iron (ZVI) aggregates as catalyst could achieve synergistic degradation of RB5, as compared to Fe(0)/US and Fenton systems. A synergy factor of 22.9 based on the first-order rate constant (k) was found. The decoloration efficiency was strongly influenced by initial pH, ZVI dose, H2O2 dose, ultrasonic input power, and the presence of salts in reaction solution. Experimental results showed that the optimum conditions for the decoloration of RB5 were ZVI 1 g/L, initial pH 3.0, and H2O2 1.03 × 10−2 mol/L with acoustic power of 120 W/L at 60 kHz. These conditions yielded 99% decoloration of 5.0 × 10−4 M RB5 (ADMI 5605) solution within 10 min treatment and the operation cost was only 2.25 USD/m3. The dye solutions containing inorganic anions could retard the decoloration. The inhibitory effect of various inorganic anions on decoloration of RB5 followed the sequence of . High acoustic power accelerated the reaction rate and increased decoloration efficiency. ZVI aggregates were reusable and the decoloration efficiency did not decrease substantially with repeated use of ZVI. Findings showed that the Fenton/US process could effectively decolor the reactive azo dye RB5 in wastewater.
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