Several methods of heavy metal wastewater treatment

　　Heavy metal wastewater pollution is a more prominent type of water pollution in China. Because with the long-term accumulation of heavy metals that cannot be treated, their toxicity is harmful to the natural environment and human body without any benefit. At the same time, it is very difficult to effectively remove heavy metals from wastewater. Therefore, for a long time, how to remove heavy metals in water and effectively recover and utilize heavy metal wastewater has been an important content of environmental protection departments. In practice, there are many methods to treat heavy metals in wastewater, including adsorption method, chemical precipitation method, etc. Here are some details.

1. Adsorption method

In the treatment of heavy metal wastewater, adsorption method is very common. Its principle is to use special materials to adsorb heavy metal ions in wastewater, so as to achieve the purpose of treating heavy metals in water. Common adsorbents include resin, zeolite, diatomite, chitosan adsorbent, activated carbon, etc.

Among many inorganic adsorbents, activated carbon is the most commonly used and easily available. Its surface is distributed with a large number of pore structures, which can efficiently adsorb metal substances, mainly through chemical reaction interaction, to achieve the purpose of adsorbing heavy metals in wastewater. Cationic resin and anionic resin are two forms of resin. By chelating the amino, carboxyl, hydroxyl and other reactive substances contained in the resin with the heavy metal ions in the wastewater, they form a substance that is insoluble in water and relatively stable, so that the heavy metal substances in the wastewater can be easily removed.

Biosorbents can be obtained through production and processing of biological materials. Algae and bacteria are common biosorbents. The adsorption capacity of biological adsorbent is generally affected by environmental factors, such as temperature, humidity (Value and microbial cell surface structure, etc.) In the practical application of biological adsorbent in removing heavy metals from wastewater, it is not only energy-saving, environmental protection, good treatment effect, but also very simple to operate. More importantly, most of these adsorbents can be recycled, so this method is widely used. However, in the practical application of biological adsorbent to remove heavy metals from wastewater

In the process, due to the influence of various factors, there will be some difficulties that can not be grasped. In addition, the price of biological adsorbent is relatively expensive, so it is not commonly used. Therefore, at present, the most important step in the treatment of heavy metals in wastewater by adsorption is to develop an adsorbent with high efficiency, low price, energy conservation, environmental protection and pollution-free.

2. Membrane separation method

Membrane separation is one of the treatment technologies for heavy metals in wastewater. It uses pressure as the driving force to separate, purify and concentrate, which depends on the selection of membrane. In practice, electrodialysis, ultrafiltration, reverse osmosis, dialysis, etc. are most commonly used, and sometimes liquid membrane technology and natural dialysis technology are also used.

Microfiltration and ultrafiltration are selected according to the pore size under a certain pressure difference. The operation interval of nanofiltration is between ultrafiltration and reverse osmosis. At this time, the material remains about 1nm. When using the reverse osmosis method, it is necessary to select a permeable semi permeable membrane material, so that the solvent can penetrate to obtain the desired substances and effectively remove the heavy metals in the wastewater. When electrodialysis membrane separation method is used to treat heavy metals in wastewater, it is not only simple and convenient to operate, but also energy-saving and environmental friendly. It does not need to occupy too much space. The most important thing is that it is easy to separate the required substances, the water quality after treatment is good, and the system operates stably, so it is not easy to have problems. However, there are still problems such as poor stability, difficult cleaning and high heating cost.

3. Chemical precipitation method

The chemical precipitation method mainly involves adding chemical substances to the heavy metal wastewater to react with the metal, and there will be water insoluble sediments. These sediments can be removed after a certain period of precipitation and filtration.

The so-called neutralization precipitation method is mainly to add an appropriate amount of alkali into the heavy metal wastewater, and after the reaction, hydroxide or carbonate will be formed. As long as these two substances are removed, the purpose of heavy metal treatment can be achieved. The second is the co precipitation method. Its principle is to apply the preparation that can polymerize heavy metals to the waste water. After reaction, the substances produced are insoluble in water. Next, these substances can be cleared to remove heavy metals. The other is sulfide precipitation method. The main method is to add sulfide containing precipitation agents to the heavy metal wastewater, in which sulfur ions are separated from heavy metals

The sub reaction forms a sediment that is insoluble in water, and then the heavy metals are separated by filtration.

The chemical precipitation method for the treatment of heavy metal wastewater has the advantages of wide removal range, high efficiency, economy and simplicity. However, this method is not suitable for the treatment of low concentration heavy metal wastewater, and its effect is easily affected by the environment and precipitators.

4. Electrochemical method

The so-called electrochemical method is to remove heavy metals in water through electrolysis principle, which can be divided into electrocoagulation, micro electrolysis and electro reduction methods. Electroflocculation is a series of processes, in which the anode is eroded to produce cations, and then hydrolyzed and polymerized under direct current. The formation of complex and hydroxide precipitates can cause the agglomeration of heavy metals in wastewater. Microelectrolysis utilizes innumerable tiny primary cells formed by the potential difference between iron and carbon particles. These fine cells conduct electrochemical reaction and flocculation in aqueous solution containing acid electrolyte under the action of low voltage DC, forming

To form relatively stable flocculent to remove heavy metal ions from wastewater. The principle of the electro reduction method used to treat heavy metal wastewater is that heavy metal ions migrate to the cathode through electrostatic attraction, and the reduction reaction takes place on the cathode surface to precipitate.