All chemicals were of pure grade and were used without further purification. Amaranth Red purchased from Fisher Scientific company chemical manufacturing division Fair town, New Jersey (molecular weight = 604.47, l_max = 520 nm). The chemical structure and uv-vis spectrum of amaranth red dye is given in Figure 1. FeCl₃, NaCl, NaNO₃ and Na₂CO₃ were purchased from Merck. Hydrogen peroxide solution (35%) was of analytical grade. All solutions were prepared using bidistilled water. Stock solutions of dye (1 mM), FeCl₃ (10mM) were prepared in 0.01 M of HCl. All experiments were performed at pH below 3.

The kinetic measurements were carried out spectrophotometrically using 292 Cecil spectrophotometer was equipped with constant temperature cell holder attached to thermostatic controlled bath with temperature stabil- ity of ±0.1˚C. The reactants were thermostated for 15 min, then mixed thoroughly and quickly transferred to an absorption cell. The progress of the reaction was monitored at 520 nm. The pH of the reaction was adjusted using Griffin pH-meter fitted with a combined glass calomel electrode.

Advanced oxidation processes are powerful alternative methods of wastewater treatment. This method based on the production of powerful oxidant, HO^. (E = 2.8 V versus NHE). These radicals are capable to degrade recalci- trant organic compounds under mild experimental conditions [10] . The general mechanism of Fenton reaction [11] is

Then, Fe³⁺ ions can be reduced by excess H₂O₂ to form Fe²⁺ ions and more HO^. radicals. Second reaction is called Fenton-like [12] allowing Fe²⁺ regeneration leading to catalytic mechanism (reactions, 2 - 6),

As clear from above mechanism the amount of HO^. depends on the pH of solution. The effect of pH was stu- died in pH range of 2 - 3. The results showed that increasing pH from 2 to 2.6 ± 0.1 increases the observed rate constant, k_obs, from 0.45 × 10⁻³ s⁻¹ to 8.9 × 10⁻³ s⁻¹ (Figure 3). The drastic decrease in the rate of decolorization at pH = 2 is attributed to drastic reduction of hydroxyl radicals resulted from the stabilization of hydrogen pe- roxide. Also Figure 3 showed that increasing pH above 2.6 decreases the observed rate constant. Therefore, the optimal pH value for the decolorization of amaranth is 2.6. This is in agreement with earlier results [8] [11] -[15] . These studies showed that there is optimum pH value (pH = 3).

No reaction was observed between amaranth and hydrogen peroxide in absence of ferric ions. Ferric ion con- centration shows acceleration effect on the decolorization rate of amaranth. Keeping temperature at 35˚C, [dye] = 5 ´ 10⁻⁵ mol∙dm⁻³ and [H₂O₂] = 5 ´ 10⁻³ mol∙dm⁻³ using different concentrations of ferric chloride namely, 1 - 3.75 ´ 10⁻⁴ mol∙dm⁻³, the decolorization rate increased by increasing ferric ions concentrations. This is attri- buted to increase HO^. concentrations. Above that concentration the rate decreased, Figure 4. This could be at-

tributed to the increasing in [Fe³⁺] increases [Fe²⁺] which scavenging the HO^. [8] [15] . Maximum rate at [Fe³⁺] = 3.75 ´ 10⁻⁴ mol×dm⁻³, almost, 95% color removed was observed. Khataee et al. [16] reported that increasing the concentration of Fe³⁺ ions increases the decolorization rate of brilliant blue and maximum rate was at [Fe³⁺] = 2 ´ 10⁻⁴ mol∙dm⁻³.

The effect of hydrogen peroxide concentration on the rate of decolorization of amaranth studied at pH equals 2, [dye] = 5 ´ 10⁻⁵ mol×dm⁻³ and [Fe³⁺] = 5 ´ 10⁻⁴ mol×dm⁻³. Figure 5 showed that the decrease in dye concentra- tion as function of time was dependent of hydrogen peroxide concentration. Increases of hydrogen peroxide concentrations in range of 5 - 25 ´ 10⁻³ mol∙dm⁻³ increases the rate constant of decolorization from 0.5 ´ 10⁻³ to 2 ´ 10⁻³ s⁻¹. This is due to the increase of HO^. radicals [8] [15] . Plot of lnk_obs versus ln[H₂O₂] yields straight line with slope of unity indicates the reaction is first order in hydrogen peroxide.

The effect of initial dye concentration of aqueous solution of amaranth on Fenton-like process was investigated since pollutant concentration is important parameter in wastewater treatment. Increasing the initial amaranth concentration from 2 to 4 × 10⁻⁵ mol∙dm⁻³ did not show any effect on the decolorization rate, Figure 6. Also

Figure 6 shows that increasing the concentration of dye above (4 × 10⁻⁵ mol∙dm⁻³) decrease the rate of decolo- rization. This attributed to relatively lower of HO^. results from the increasing of amaranth concentration while concentration of H₂O₂ and Fe³⁺ remains the same. The obtained results were in good agreement with earlier re- ported [11] [13] -[15] .

The variation of the temperature in range of 298 - 308 K increases the rate of decolorization of amaranth. No optimal temperature in this study was detected as opposed to the literature reports [17] [18] in which 30˚C are stated as optimal temperature for Fenton oxidation. Another optimal temperature, 50˚C was reported on decolo- rization of some dyes by Fenton-like reaction [8] . The activation energy was calculated from Arrhenius plot and Eyring equation and was found to be 104.79 kJ∙mol⁻¹. The other thermodynamic parameters are given in Table 1. As observed from Table 1 positive value of ΔS* indicates reaction is favor. The ΔH* positive value indicates that the process is endothermic.

Inorganic anions occur naturally in waste water (e.g.) or may be added to facilitate the dyeing (e.g. Cl⁻ and). The presence of inorganic anions in textile wastewaters plays an important role in the oxidation kinetics of different dyes. Inorganic anions may induce or reduce the rate of oxidation.