All chemicals used here are of reagent grade and used without further purification. Iron vitriol Fe_SO₄∙7H₂O, ferric chloride FeCl₃∙6H₂O, Sodium hypochlorite NaClO (10%, w/v), ammonium hydroxide (25%, w/v), sulfuric acid H₂SO₄ and sodium hydroxide NaOH were purchased from Sinopharm Chemical Reagent Co. Ltd., China. Goldmine waste-solid was obtained from Zhejiang Province Suichang Gold Mine Co. Ltd., China. The chemical composition of the goldmine waste-solid is CaO: 32.46%, MgO: 1.41%, Fe₂O₃: 20.75%, Al₂O₃: 3.26%, SiO₂: 14.11%, ZnO: 2.16%, CuO: 0.22%, PbO: 0.11%, Na₂O: 1.59%, SO₃: 15.37%.

The industrial dyes effluent was obtained from Zhejiang Runtu Co. Ltd., China. The main parameters (average values) of samples were: pH < 1, COD = 13,000 mg/L.

Raw goldmine waste-solid was pre-treated by acid-washing process, in which 20 g goldmine was mixed with 20 mL H₂SO₄ solution and stirred for 2 hours. Then the goldmine waste-solid was filtered off, washed repeatedly with distilled water and dried at 80˚C in vacuum for 2 hours. The obtained 20 g pretreated goldmine waste-solid was added to 20 mL 0.1 M FeSO₄ solution and stirred for 12 h under 50˚C. After the solid phase being isolated and washed with deionized water, the solid phase was added to 30 mL 0.1 M NaOH solution and stirred for 4 h. Then the modified goldmine solid was washed and dried at 80˚C. After that the solid was heated to 600˚C with a speed of 10˚C/min, and kept for 6 h in muffle furnace (Nabertherm Industrial Furnaces Ltd. Co). Upon cooling, the solid was broken to powders for the following use.

The experiment using NaClO as oxidant was done as follows: 100 mL industrial dyes effluent was added into Erlenmeyer flasks. Then various amount of NaClO (1.0 mL, 2.0 mL, 3.0 mL, 4.0 mL, 5.0 mL) was added to each flask by droplet and all suspensions were stirred at 30˚C for 2 hr. After being filtered, the COD value of industrial dyes effluent was measured by K₂Cr₂O₇ method. And the reduction of COD before and after oxidation was calculated.

Fenton reaction in the treatment of industrial dyes effluent was done as follows: 30 mmol/L FeSO₄ and 100 mL dyes effluent were added into Erlenmeyer flasks individually. Then different amount of H₂O₂ (1.0 mL, 2.0 mL, 3.0 mL, 4.0 mL, 5.0 mL) was added to each flask by droplet and all suspensions were stirred at 30˚C for 2hr. After being filtered, COD of the industrial effluent was determined and the reduction before and after stirring was used to calculate the removal rate in the Fenton reaction.

The experiments for Nano-Fe₂O₃/goldmine complex as the heterogeneous catalyst in Fenton-like reaction were done as follows: 3.0 g nano-Fe₂O₃/goldmine complex and 100 mL dyes effluent were added into Erlenmeyer flasks individually. Then various amount of NaClO (1.0 mL, 2.0 mL, 3.0 mL, 4.0 mL, 5.0 mL) was added to each flask by droplet and all suspensions were stirred at 30˚C for 2 hr. After being filtered, COD of the industrial effluent was determined and the reduction before and after stirring was used to calculate the removal rate in the Fenton-like reaction.

Relationship between the degradation effect and the dosage of NaClO in the treatment process was given in Figure 1. It can be seen that when the content of NaClO increased from 10 to 50 (mL/L), the COD removal efficiency increased slowly from 6.2% to 35.4%, while the color removal rate show a little higher disposal ability. It is reasonable that with the increased addition of oxidants more NaClO would join the oxidation reaction of dyes components, then much higher COD removal efficiency could be obtained.

In Figure 2, effects of homogeneous catalyzed Fenton reactions are investigated based on the results of COD and color removal, respectively. Being kept the concentration of FeSO₄ equivalent to 30 mmol/L, degradation of industrial dyes was studied under various in feed H₂O₂ concentration. And a linear enhancement of oxidation capacity was observed for COD and color with increased H₂O₂ addition. Since the removal efficiency of COD is lower than that of color during the oxidation reaction, a conclusion can be got that mineralization of dyes components in wastewater is more difficult when compared with the damage of chromophore.

Influence of NaClO concentration on heterogeneous Fenton-like processes for dyes degradation is given in Figure 3. By varying concentration of oxidant from 10 to 50 mL/L, COD removal efficiency of industrial dyes ef-

fluent was in the range of 16.9% - 75.5%. Being compared with the results treated by NaClO and Fenton reaction, it is clear that almost 2 times larger COD removal efficiency was achieved in the Fenton-like reaction when NaClO was used as oxidant in AOPs.