重金属一般是指密度大于4.5 g/cm3的金属，主要包括汞、镉、铅、铬、钒、锰、铜、锌及镍等有毒重金属元素。重金属是地壳的重要构成元素，广泛地分布于自然界中，并在自然环境中迁移、转化、循环。水体中的重金属主要来自两部分：自然源和人为源。通过自然循环进入水体中的重金属浓度一般较低，不会影响人体健康，人为源是造成水体重金属污染的主要原因。由于一些人为因素，大量的重金属向环境中排放并不断累积，使其远远超过了环境的本底含量，从而造成了严重的重金属污染。采矿、冶金、石油化工、电子生产、制革等工业生产过程中均会产生含重金属离子的废水和废渣，其中冶金和采矿是最重要的重金属污染源。水体流经被重金属污染的土壤及含重金属的大气沉降物排入水中，也能使水中重金属含量急剧升高，进一步加剧水体重金属污染。
Heavy metals generally refer to metals with a density greater than 4.5 g / cm3, mainly including mercury, cadmium, lead, chromium, vanadium, manganese, copper, zinc and nickel. Heavy metals are important elements in the earth's crust. They are widely distributed in nature and migrate, transform and circulate in the natural environment. Heavy metals in water mainly come from two parts: natural source and man-made source. The concentration of heavy metals entering the water body through natural circulation is generally low, which will not affect human health. Anthropogenic source is the main cause of heavy metal pollution in water body. Due to some human factors, a large number of heavy metals are discharged into the environment and accumulated continuously, which makes them far beyond the background content of the environment, thus causing serious heavy metal pollution. Waste water and waste residue containing heavy metal ions will be produced in the process of mining, metallurgy, petrochemical, electronic production, tanning and other industrial production processes. Metallurgy and mining are the most important sources of heavy metal pollution. Water flowing through the soil polluted by heavy metals and atmospheric deposition containing heavy metals into the water, can also make the content of heavy metals in the water increase sharply, and further aggravate the heavy metal pollution of water body.
重金属在水中不断的迁移转化，形态也可能发生变化，并有可能被水中胶体物质等吸附，浓度随着pH和水温的变化不断变化。但是重金属不能被生物降解，因此水中重金属的总量不会减少。进入水中的重金属部分被水生生物所摄取，并在食物链中放大，而且有可能转化成毒性更大的形态，最后富集在人体内;直接饮用含重金属的水或者食用含重金属的水浇灌的农作物也会使重金属进入人体内。重金属能够使蛋白质结构发生不可逆转的改变，蛋白质的功能也随之丧失，从而影响人体的正常代谢活动，导致各种疾病的发生和机体紊乱。世界八大公害事件中的水俣病和骨痛病都是由于重金属中毒引起的。其中，水俣病是工厂排放废水中汞所引起的，汞被水生生物食用后在体内转化成甲基汞，甲基汞的毒性是汞毒性的100倍，而且甲基汞更容易溶于脂肪，主要侵犯中枢神经系统。
With the continuous migration and transformation of heavy metals in water, their forms may change, and they may be adsorbed by colloidal substances in water. The concentration of heavy metals changes with the change of pH and water temperature. However, heavy metals can not be biodegraded, so the total amount of heavy metals in water will not be reduced. Some of the heavy metals in the water are absorbed by aquatic organisms and amplified in the food chain, and may be transformed into more toxic forms and finally enriched in the human body; drinking water containing heavy metals directly or eating crops irrigated with water containing heavy metals will also cause heavy metals to enter the human body. Heavy metals can cause irreversible changes in protein structure and protein function, thus affecting the normal metabolic activities of human body, leading to the occurrence of various diseases and disorders of the body. Minamata disease and osteodynia disease are all caused by heavy metal poisoning. Among them, Minamata disease is caused by mercury in wastewater discharged from factories. Mercury is converted into methyl mercury in vivo after being eaten by aquatic organisms. The toxicity of methyl mercury is 100 times that of mercury. Moreover, methylmercury is more easily soluble in fat and mainly invades the central nervous system.
3.重金属废水常见的处理方法
3. Common treatment methods of heavy metal wastewater
处理含重金属废水的传统方法有：化学沉淀法、离子交换法、膜分离法、吸附法、生物法等。
The traditional methods of treating wastewater containing heavy metals include chemical precipitation, ion exchange, membrane separation, adsorption and biological methods.
3.1化学沉淀法
3.1 chemical precipitation method
化学沉淀法是向废水中加入与作用机理相适应的反应剂，使水中溶解状态的重金属离子转化成不溶于水的金属化合物，再将其从水中分离出去的方法。该方法技术成熟、操作简单、处理成本低等优点，但容易造成二次污染，其最主要的影响因素是pH。难溶盐沉淀法又包括硫化物沉淀法、碳酸盐沉淀法、钡盐沉淀法，其主要优点是处理后的废水pH大约是7~9，不用再进行中和处理，而且还可以回收废水中的重金属，具有一定的经济效益。铁氧体法主要是在含有重金属离子废水中加入铁盐或亚铁盐，形成铁氧体，通过吸附、包裹和夹带作用使重金属离子形成复合铁氧体沉淀析出。该方法处理条件温和、处理量大、处理效果明显、能回收磁性材料，在工业上得到了广泛的应用。

Chemical precipitation method is to add the reaction agent suitable for the mechanism of action to the wastewater, so that the dissolved heavy metal ions in water can be transformed into insoluble metal compounds, and then separated from the water. This method has the advantages of mature technology, simple operation and low treatment cost, but it is easy to cause secondary pollution, and the main influencing factor is pH. The insoluble salt precipitation method includes sulfide precipitation method, carbonate precipitation method and barium salt precipitation method. Its main advantage is that the pH value of the treated wastewater is about 7 ~ 9, and there is no need for neutralization treatment. Moreover, the heavy metals in the wastewater can be recovered, which has certain economic benefits. The ferrite method is mainly to add iron salt or ferrous salt to the wastewater containing heavy metal ions to form ferrite. Through adsorption, encapsulation and entrainment, the heavy metal ions form composite ferrite precipitation. This method has been widely used in industry due to its mild treatment conditions, large amount of treatment, obvious treatment effect and recovery of magnetic materials.
3.2离子交换法
3.2 ion exchange method
离子交换法是利用离子交换剂中的可交换基因与废水中的重金属离子交换能力的不同来分离的方法。常用的离子交换剂有阳离子交换树脂、阴离子交换树脂、螯合树脂、腐殖酸树脂等。离子交换法可对废水中的重金属离子选择性的分离，通过再生回收再生液，可实现重金属离子的回收，还具有交换容量大、吸附-再生可逆性好等优点，但适用范围有限，且容易造成二次污染。
Ion exchange method is a method to separate the exchangeable genes in ion exchanger and heavy metal ion exchange ability in wastewater. The commonly used ion exchangers are cation exchange resin, anion exchange resin, chelating resin, humic acid resin, etc. Ion exchange method can selectively separate heavy metal ions from wastewater, and the recovery of heavy metal ions can be realized through regeneration and recovery of regeneration solution. It also has the advantages of large exchange capacity and good reversibility of adsorption regeneration, but its application scope is limited and it is easy to cause secondary pollution.
3.3膜分离法
3.3 membrane separation method
膜分离法是利用一种特殊的半透膜，在外界压力作用下，不改变溶液的化学形态使溶质和溶剂进行分离和浓缩的方法。根据膜的不同可以分为扩散渗析、电渗析、反渗透、液膜、纳滤、超滤等。膜分离技术具有能耗低、无相变、操作简单、无二次污染、分离产物易回收等优点，目前已在国内外重金属废水处理中得到了广泛的应用。Hafez等利用反渗透膜对废水中的铬进行的回收处理试验中对铬的平均回收量高达99.8%。但是膜分离法存在膜组件价格贵、膜污染等问题亟待解决。
Membrane separation is a method that uses a special semi permeable membrane to separate and concentrate solute and solvent without changing the chemical form of solution under external pressure. According to the different membrane can be divided into diffusion dialysis, electrodialysis, reverse osmosis, liquid membrane, nanofiltration, ultrafiltration and so on. Membrane separation technology has the advantages of low energy consumption, no phase change, simple operation, no secondary pollution and easy recovery of separation products. At present, it has been widely used in the treatment of heavy metal wastewater at home and abroad. Hafez et al. Used reverse osmosis membrane to recover chromium from wastewater. The average recovery of chromium was up to 99.8%. However, there are some problems in membrane separation, such as high price of membrane module and membrane pollution.
3.4吸附法
3.4 adsorption method
吸附法是利用多孔性吸附剂表面的各种活性基团与废水的重金属离子形成离子键或共价键将重金属离子吸附于吸附剂表面，从而达到吸附金属离子的目的。活性炭是传统常用的吸附剂，具有巨大的比表面积，对重金属的吸附能力强、去除率高。姜玉娟[8]在利用活性炭吸附处理络合镍重金属废水的试验中，镍离子的去除率达到95.65%。近年来，对吸附法的研究主要是寻找更加廉价、高效的吸附剂。国内外许多研究发现生物材料对重金属也有很好的吸附能力，如香蕉皮、木桔叶、花生壳、褐
Adsorption method is to use various active groups on the surface of porous adsorbent to form ionic bond or covalent bond with heavy metal ions in wastewater to adsorb heavy metal ions on the surface of adsorbent, so as to achieve the purpose of adsorption of metal ions. Activated carbon is a traditional adsorbent, which has a large specific surface area, strong adsorption capacity and high removal rate of heavy metals. Jiang Yujuan [8] in the experiment of using activated carbon to treat the wastewater containing heavy metal complex nickel, the removal rate of nickel ion reached 95.65%. In recent years, the research of adsorption method is mainly to find more cheap and efficient adsorbents. Many studies at home and abroad have found that biomaterials have good adsorption capacity for heavy metals, such as banana peel, kumquat leaf, peanut shell, brown