Study on the treatment of mine tailings pond wastewater by alkaline oxidation

Source and properties of wastewater from tailings reservoir of sulfide mine

A part of the beneficiation process wastewater in the sulfide ore dressing production is clarified and used for beneficiation production. A part of the remaining ore slurry in the ore dressing enters the tailings pond. After the sedimentation in the tailings pond, the overflow water is called tailings pond wastewater.

In addition to ores containing small amounts of useful minerals Mn, Zn, Fe and trace Pb, TI and other metal compounds such as SiO2, is added during the beneficiation xanthate, II oil and sodium hexametaphosphate separation of useful minerals and other organic matter and other The material and the ore dressing wastewater contain metals such as Mn, Zn and Fe dissolved in the ore dressing wastewater and residual mineral processing chemicals. The ore dressing wastewater is neutral (the sulfide ore is acidic, the xanthate and sodium hexametaphosphate are alkaline), and the metals such as Zn and Fe are naturally oxidized and precipitated in the tailings pond under neutral conditions, but Mn is neutral or weakly alkali. Under the condition, it is difficult to form a precipitate, and the ore dressing agent is difficult to decompose in a short time. Therefore, the main pollutant in the waste water of the tailings pond is the chemical oxygen demand formed by heavy metal ions such as Mn dissolved in water and residual chemicals.

Analysis of the properties of sodium chlorate

Sodium hypochlorite is a yellowish solution with a chlorine odor, unstable, and easy to decompose. Sodium hypochlorite solution is a strong oxidant and its chemical properties are extremely unstable, which is determined by the structure of ClO-. The valence electron pair arrangement of hypochlorite ion is tetrahedral structure, the chlorine atom is bonded by sp3 hybrid orbital and oxygen atom, and there are three unpaired lone pairs in the acid radical. Due to the high asymmetry of the valence layer electrons of the acid ion and the large ion potential (Z/r) of the central atomic chlorine, the hypochlorite is unstable and has a strong electron conversion to be more stable. The ability of the Cl2 molecule or Cl-, that is, ClO- has a strong oxidizing power.

The reaction of ClO-accumulated under acidic or basic conditions and its electrode potential are as follows:

HClO+H++e=1/2Cl2+H2O 1.63V (1)

HClO+H++2e=Cl-+H2O 1.49V (2)

ClO-+H2O+2e=Cl-+2OH- 0.89V (3)

From the formulae (1) to (3), it is known that ClO- has a strong oxidizing property in an acidic environment or in an alkaline environment, that is, a reduction reaction occurs upon decomposition of a reducing agent.

The instability of sodium hypochlorite is mainly manifested in the decomposition reaction itself when no reducing agent is present. Mainly in the presence of light, heat, acidic environment or heavy metal ions, spontaneous decomposition reaction, the main reaction equation is shown in (4)-(7)

2NaClO=2NaCl+O2 (4) 3NaClO=2NaCl+NaClO3 (5)

2HClO=2HCl+O2 (6) HClO+HCl=H2O+Cl2 (7)

Since sodium hypochlorite is mostly prepared by a method of absorbing chlorine gas by using a sodium hydroxide solution, sodium hypochlorite not only has a small degree of hydrolysis but also has good stability in a strong alkali environment.

3-time sodium chlorate alkaline oxidation method

3.1 hypochlorite alkaline oxidation process

Sodium hypochlorite alkaline oxidation method is a method for controlling the pH value of about 10 in the water treatment process, using sodium hypochlorite to oxidize heavy metals in water and difficult to decompose organic matter to form a precipitate and remove pollutants from waste water. The specific process is shown in Figure 1:

3.2 Brief description of sodium hypochlorite alkaline oxidation method

The neutralization reaction tank is added with lime to a pH value to be more alkaline, which can effectively remove metal ions such as heavy metal Mn, and add a certain amount of sodium hypochlorite in the oxidation pond, and use the strong oxidative oxidation water to oxidize heavy metals and refractory organic substances. And release some acidic substances to neutralize the hydroxide ions, reducing the pH of the wastewater to the 6-9 range. The discharged wastewater will reach the first-level standard of the second period of the Guangdong Province Water Pollutant Emission Limit Standard.

Main advantages of 4 times sodium chlorate alkaline oxidation method

1. Sodium hypochlorite alkaline oxidation treatment process is simple and easy to operate.

2. There are few types of treatment agents and a wide range of sources.

3. The process parameters are stable and the effluent quality is good.

5. Application effect of sodium hypochlorite alkaline oxidation method in wastewater treatment

In December 2014, this method was used to treat wastewater from Guangdong Guangye Yunsu Mining tailings pond. First add lime milk to adjust the pH to 9.7-10.00, fully react, add sodium hypochlorite 2kg / m?, reaction for 14min, add PAM to stir, precipitate. The pH of the treated water dropped to 6.5-8.6, the heavy metal Mn was almost completely removed, the COD could be controlled to below 65 mg/L, and the treated water reached the first-level standard requirement of the second period of the Guangdong Province Water Pollutant Emission Limit Standard.

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