Abstract: This paper introduces the sources, existing forms, pollution characteristics and hazards of mercury in water. The different treatment methods of mercury-containing wastewater are reviewed. Finally, some suggestions are put forward to control the pollution of mercury-containing wastewater. Key words: mercury; source; pollution characteristics; treatment of mercury-containing wastewater Mercury is a kind of volatile toxic heavy metal element, which is the only metal in liquid form at room temperature and atmospheric pressure. It is silver-white, chemically stable, insoluble in acid and soluble in alkali, and evaporates at room temperature. Mercury has the characteristics of low melting point, large specific gravity, high boiling point, good electrical conductivity and even expansion coefficient. It has been widely used in industry, agriculture, science and technology, transportation, medicine, health and defense. More compounds of mercury vapor and mercury are highly toxic, especially methylmercury. Mercury is a persistent, easily migratory and highly bioaccumulative chemical. Various forms of mercury in the environment can be transformed into highly toxic methylmercury under certain conditions [2]. Mercury can also be transported over long distances, Long-distance settlement, easily lead to cross-border pollution has become a regional issue, the United Nations Environment Program has been listed as a global pollutant. 1, the source of mercury in water, there are morphological and harmful. China is a country where primary mercury production exists. The demand for primary mercury is very large and widely used in our country. However, the exploitation of mercury mine poses huge environmental risks. China's mercury production, use and emissions status is not optimistic. The sources of mercury in water are mainly due to the improper application of mercury treatment or the production of mercury mines, gold mines, chlor-alkali plants, aromatherapy recovery precious metals, non-ferrous metal smelters, pesticide plants, batteries, fluorescent tubes and thermometers. , Pharmaceuticals, cosmetics, hospital laboratories, etc. also have a certain amount of mercury-containing wastewater emissions, mercury-containing pollutants mainly exist in the sediment near the sewage outfall and suspended solids. In addition to inorganic mercury mercury in waste water, but also in the form of various organic compounds exist. Any form of mercury in the environment (metallic mercury, inorganic divalent mercury, arylmercury and alkylmercury, etc.) can be converted to highly toxic methylmercury under certain conditions. Methylmercury has methylmercury (Hg + -CH3) and dimethylmercury (CH3-Hg-CH3). In 1967, Swedish scholars S. Jensen and Jerndov pointed out that anaerobic bacteria in the freshwater body sediments can methylate inorganic mercury and form methylmercury and dimethylmercury. Japanese scholars found that in the water with acetic acid, acetaldehyde, methanol, ethanol, alcohol and other organic compounds coexist, after UV, sunlight generated methyl free radical mercury chloride mercuric chloride [3]. 2, mercury hazards in the water environment. In the 1950s, Minamata disease, one of the eight major public hazard cases that shocked the world, was caused by methylmercury in wastewater discharged from an acetaldehyde plant. The wastewater was discharged into Minamata Bay, and methylmercury was enriched in the fish. Long-term Meal containing methylmercury fish, causing the body's central nervous system lesions. The Japanese Minamata disease caused a total of 5,172 people and 730 deaths. In 1972, 459 deaths from mercury poisoning occurred in Iraq in the treatment of seeds with methylmercury and ethylmercury fungicides [1]. Studies have shown that elemental mercury and organic mercury compounds may cause harm to the kidneys and the immune system, and methylmercury can pose a threat to the nervous system and cardiovascular and cerebrovascular diseases. Methylmercury has the ability of enrichment in the food chain and eventually enters the human body, which has an impact on human health. Therefore, the harm of mercury pollution in the water environment is causing more and more concern. 3, mercury in wastewater control technology At present, mercury-containing wastewater treatment methods are: precipitation, electrolysis, ion exchange, activated carbon adsorption and combined process. (1) precipitation method: Precipitation is divided into two kinds of coagulation and precipitation precipitation. The principle of coagulation and sedimentation is to add coagulant (lime, iron salt and aluminum salt) into the mercury-containing waste water to form hydroxide flocs under the weak alkaline conditions of pH 8-10, Mercury coprecipitation. Iron salt generally better than aluminum. Sulfidation precipitation method is reported more of a precipitation method. In this method, sodium sulfide is put into a mercury-containing waste water to utilize the strong affinity of Hg2 + and S2- to generate mercuric sulfide with a very small solubility to remove mercury from the solution. Wu Xiuying, etc. [4] sodium sulfide treatment of mercury-containing waste water plant in Qingdao battery test and production test, the results show that the mercury content in wastewater is lower than the national standard, the effect is better, the chemical stability of sediment, small and medium chemical Industry promotion. Vulcanization precipitation method is widely used in the United States and other countries chlor-alkali plant mercury pollution control. This method is suitable for the treatment of different concentrations of different types of mercury salts, mercury ion concentration should be the preferred chemical precipitation method. It is reported that precipitation of mercury removal rate of up to 95% -99.9%. The inadequacies of the method: (1) easily lead to water hardening, wastewater containing low concentration of mercury is not thoroughly treated, easily lead to secondary pollution. (2) Due to the influence of precipitant, environmental conditions and process control parameters, the effluent concentration is difficult to meet the emission standards and therefore needs further treatment. (2) electrolysis method Electrolysis is the use of metal electrochemical properties, under the action of direct current, the mercury compounds dissociate into mercury ions in the anode, the cathode reduced to metallic mercury, and remove mercury in wastewater. This method is suitable for the treatment of high concentration inorganic mercury wastewater. The disadvantage of this method is that the concentration of mercury in water can not be lowered very low, the power consumption is high, the investment cost is high, mercury vapor is easy to be generated and the secondary pollution is formed. (3) ion exchange method
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