Research progress on hazards and treatment technology of mine wastewater

Acid-base neutralization is the most commonly used traditional method to treat acid mine wastewater. It has the advantages of simple process, convenient operation and low operating cost, but it also has some disadvantages such as serious scaling, large amount of sediment and easy to cause secondary pollution. In the treatment of acid mine wastewater, in order to improve the treatment effect, the neutralization method is often combined with oxidation method and other methods.

2.2 Coagulation sedimentation method

Coagulation sedimentation method is to destroy the stability of colloids by adding coagulant to wastewater, so that fine suspended particles and colloidal particles aggregate into larger particles and settle, so as to achieve the purpose of wastewater purification. Commonly used coagulants are alum, aluminum chloride, polyaluminum chloride (PAC), polyferric sulfate (PFs), polyferric chloride (PFC), polyacrylamide (PAM) and so on.

As a basic water purification method, coagulation sedimentation method is widely used in the treatment of various sewage. Its main mechanism is that the colloid is destabilized and condensed into floc by adsorption bridge, sediment net trapping and compression double electric layer. In view of different mine wastewater, coagulation sedimentation method, adsorption method and chemical oxidation method are often composed of different treatment processes. Yan Qun et al. adopted the coagulation sedimentation and activated carbon adsorption process to treat the beneficiation wastewater of a lead-zinc mine in Panxi area of Sichuan Province, which not only reduced the concentration of heavy metal ions in the wastewater, but also solved the problem of high CODcr in the wastewater. The beneficiation index of the treated wastewater can be equivalent to that of fresh water after reuse. Sun Shuiyu et al. studied the purification treatment and reuse of wastewater from a lead-zinc sulfide ore flotation plant in Jiangsu province, and the results showed that: with coagulation sedimentation and chemical oxidation process, all the indicators of effluent can meet the national discharge standard, but the treatment cost is high; The treatment cost is low, the content of suspended solids and heavy metals in the effluent is up to the standard, the chemical oxygen demand and foaming property are reduced to a certain extent, and the reuse effect of the treated wastewater is comparable to that of domestic tap water.

2.3 Chemical oxidation method

Chemical oxidation is one of the effective methods to completely remove pollutants from wastewater. Through chemical oxidation, the liquid or gaseous inorganic matter and organic matter can be converted into a slightly toxic, non-toxic substance, or it can be converted into a form that is easy to separate, to achieve the purpose of reducing COD, BOD and toxicity of wastewater. Chemical oxidants commonly used in wastewater treatment include ozone, sodium hypochlorite, hydrogen peroxide, Fenton reagent and so on.

Chemical oxidation method can oxidize refractory organic matter to small molecular organic matter and improve the biodegradability of wastewater. Zhao Yonghong et al. conducted an experimental study on xanthate removal from water by bleaching powder oxidation method. When the addition amount of bleaching powder was 15 mg/L, the pH value was 3, and the oxidation time was 3 h, xanthate solution with a concentration of 10 mg/L could be completely degraded. The experimental results show that xanthate and No. 2 oil in mineral processing wastewater can be effectively decomposed by ozone. When the oxidation time is 5 min, the removal rate of xanthate and No. 2 oil reaches more than 99%.

2.4 Constructed wetland method

Since Kickuth proposed the "root zone theory" in 1972, constructed wetland technology has entered the field of water pollution control as a unique new sewage treatment technology. In 1974, the first constructed wetland system for sewage treatment was built in Othfrensen, West Germany, and since then, constructed wetland technology has gained rapid development because of its superior performance. In recent years, constructed wetland technology, as an alternative to traditional sewage treatment technology, has been widely used in the treatment of domestic sewage, industrial wastewater and agricultural wastewater.

Constructed wetland is a natural biological sewage treatment system, which is a practical technology combining sewage treatment and utilization. Its core is a composite ecosystem of matrix, microorganism and plant. The physical, chemical and biological synergies of this composite system are utilized. The wastewater can be purified by filtration, adsorption, precipitation, dissolution, complexation, ion exchange, plant absorption and microbial decomposition. Suspended matter and organic pollutants in mine wastewater can be removed through the filtration of matrix, the interception of wetland plants, the adsorption of plant root biofilm, the feeding of wetland organisms and the degradation of microorganisms, etc., while heavy metal ions in mine wastewater can be removed through the adsorption of fillers and chemical reactions. Although the matrix generally cannot chemically react with the heavy metals in the wastewater to form precipitation, it can transform the heavy metals into a low toxic state through complexation.