COD Degradation Process of High Chloride Saline Alkaline Wastewater

In the purification process of gold, silver, platinum, palladium, selenium, tellurium, etc., copper smelting produces many process wastewaters with different media due to the use of sulfuric acid, hydrochloric acid, liquid caustic soda, and various oxidant and reducing agent substances. The common denominator is the high content of sodium and chloride salts. The process wastewater mainly comes from the processes of silver precipitation in silver separation solution and silver reduction by formaldehyde, as well as from the processes of primary copper anode slime, secondary pretreatment decontamination, silver precipitation in copper separation solution, and platinum and palladium replacement. At present, in order to ensure that the process wastewater reaches the standard after treatment, the high-salt reducing wastewater and the high-copper arsenic sodium chloride wastewater are treated separately in two systems.

After the high-salt reducing wastewater is added with nano iron powder to replace the trace amount of gold and silver, it is oxidized and clarified by blasting, and the copper is discharged after reaching the standard. After the high copper arsenic sodium chloride wastewater is concentrated, antimony and bismuth are recovered through the primary purification and secondary purification processes, and lime is added to the purified liquid to precipitate copper arsenic. After copper precipitation, the liquid enters the complex polymetallic wastewater treatment production line. By adding nano-iron powder, polyiron, flocculants and other agents, a small amount of heavy metals Cu and As in the wastewater are reduced, adsorbed, flocculated and precipitated. After concentration, pressure filtration, and liquid-solid separation, The effluent from the pressure filtration is discharged to the general external drainage pool of the factory. The content of heavy metals such as copper, arsenic, lead, zinc and cadmium in the effluent can meet the requirements of GB25467-2010, but the COD exceeds the national discharge standard.

Due to the sensitivity of environmental protection, it is difficult to consult the relevant information of other domestic copper smelting and production enterprises. According to the review data, the most researched method for COD removal in China is to use of reagent oxidation, including hydrogen peroxide oxidation, potassium permanganate oxidation, air oxidation, etc., and with the development of science and technology, chemical coagulation, electrochemical, ozone, etc. New methods and new technologies for COD treatment such as the oxidation method, biosorption method, and micro-electrolysis method have successively reported results. However, which method is suitable for high sodium salt and high chloride salt wastewater, which can achieve a good effect and low cost, needs further systematic research.

At present, there is no very effective method for the removal of chloride ions. For wastewater with high salt chloride concentration, if the amount of water is small, membrane methods can be considered for removal, such as ion exchange, electrodialysis, etc. In the laboratory Another method of removing chloride ions is to use silver ions, which can be precipitated, but the cost is extremely high.

Methods of removing COD in wastewater:

Flocculation method: small investment and simple operation. Factors such as the type of flocculant, the amount of input, the pH and COD values of raw water, and the quality of raw water will affect the effect of flocculation to remove COD. Studies have shown that using polyaluminum chloride as a flocculant and a two-stage process under the condition of pH=7 can reduce the COD content of the wastewater after desulfurization to less than 40mg/L.

Utilize jarosite mineral formation process to pre-sulfur-containing high-concentration COD wastewater: pretreatment of a high-concentration COD-containing industrial wastewater to remove a certain amount of SO4-, the optimal process conditions are pH 2.50~3.20, chlorine The optimum input amount of FeCl3·6H2O) is 50g/L. After two jarosite mineral precipitation processes, the COD removal rate of the wastewater reached 85.29%. Combined with the oxidation treatment of H2O2, the COD removal rate could reach 96%.

Recovering sodium sulfite in dye wastewater with diatomaceous earth: The research results show that the recovery rate and relative content of the crystalline sodium sulfite obtained by this method are better than the screen filtration method; the Garman equation is used to calculate the optimal use for filtering quantitative liquids. Diatomite filter aid dosage and corresponding pressure.

Adding calcium hydroxide: adding calcium hydroxide to the wastewater containing sulfurous acid to react to generate sodium hydroxide and calcium sulfite. The insoluble calcium sulfite is removed from the water by precipitation and separation, and the alkaline wastewater and the acidic wastewater are neutralized.

Fenton oxidation-biological contact oxidation process: Chen Sili and others used the Fenton oxidation-biological contact oxidation process to treat the simulated wastewater (wastewater) containing formaldehyde and urotropine, adding 2.5g/L of H2O2 (volume fraction 30%), H2O2 Under the optimal operating conditions of Fenton oxidation pretreatment with a mass concentration ratio of Fe2+ of 3.75, a reaction time of 3h, and no adjustment of the initial pH of the wastewater, the COD of the wastewater decreased from about 1000mg/L to 300mg/L, and the COD removal rate reached 72%. The original wastewater cannot be directly biochemically treated, and its BOD/COD is about 0.5 after Fenton oxidation pretreatment, which is easy to biochemically treat. The Fenton oxidation-biological contact oxidation process treats wastewater. When the biological contact oxidation residence time is 12h, the COD removal rate of wastewater is as high as 94%. After treatment, the COD of the effluent is less than 70mg/L, and the treatment effect is very good.

Ultrasonic-Fenton Reagent-Aeration Combined Treatment: The best process conditions: 100mL of wastewater with COD of 11500mg/L (initial pH=5) under the condition of ultrasonic power of 200W, irradiation for 60min, H2O2 dosage of 1.3mL, and FeSO4 dosage of 0.069 The COD removal rate reached 83%.

Urea removal of COD: urea has a significant effect on COD removal from wastewater, with a one-time removal rate of more than 81%; white precipitate is formed to synthesize useful substance methyl urea, which has good economic and environmental benefits.

Pretreatment of industrial wastewater with a small amount of Fenton reagent: Partial oxidation of refractory organics in wastewater, changing their biodegradability, solubility and coagulation properties, is beneficial to subsequent treatment. It can be seen from the experimental data that the wastewater is acidified to pH=2+aeration+Fenton reaction has a certain removal effect of COD in this wastewater, but the effect is not good; The analysis may be that the chloride ion concentration in the wastewater is high, which interferes with the detection (the raw water chloride ion concentration is as high as 30,000 mg/L).

This study focuses on the comprehensive method to obtain good governance effect, and considers the use of waste to control waste.

  • High chloride saline alkaline wastewater contains a large amount of sodium sulfite, and by using it to reduce the tellurium powder in the liquid after platinum and palladium replacement, high-grade scattered element tellurium can be obtained, and about 50% of COD can be degraded at the same time;
  • Ozone oxidizes iron trichloride carrier lime at room temperature for 5h, the optimum pH value except COD is 5~6, and the total degradation rate of COD is more than 80%;
  • Hydrogen peroxide has a certain effect on deep oxidation to reduce COD, but it should be limited;
  • Suggestion: The main reason for the difficulty in reducing COD is that the chlorine root is too high. The chlorine root emission should be reduced or recycled, such as the reduction of gold oxalic acid and other measures.

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