Application of activated carbon in water treatment

According to statistics, the industrial waste water discharged from China every year is about 8 × 108m3, which contains not only highly toxic components such as cyanide, but also metal ions such as chromium, zinc and nickel. There are many methods of wastewater treatment, mainly including chemical precipitation, electrolysis and membrane treatment. This paper introduces the activated carbon adsorption method. The surface area of activated carbon is huge and it has high physical and chemical adsorption functions. Therefore, activated carbon adsorption is widely used in wastewater treatment. It has the characteristics of high efficiency and good effect.

Activated carbon

Activated carbon is a kind of specially treated carbon with numerous tiny pores and huge surface area. The surface area of each gram of activated carbon is 500-1500 square meters. Activated carbon has strong physical and chemical adsorption functions, and also has detoxification. Detoxification is to use its huge area to absorb the poison in the micropores of activated carbon, so as to prevent the absorption of the poison. At the same time, activated carbon can combine with a variety of chemicals, thus preventing the absorption of these substances.

Classification of activated carbon

There are many kinds of activated carbon used in production. Generally made into powder or granule.

The powdered activated carbon has strong adsorption capacity, easy preparation and low price, but it is difficult to regenerate and cannot be reused.

Granular activated carbon is more expensive, but it can be reused after regeneration, and the working conditions are better when it is used, and the operation and management are convenient. Therefore, granular activated carbon is widely used in water treatment [1].

activated carbon adsorption 

Activated carbon adsorption refers to the adsorption of one or more substances in water by the solid surface of activated carbon, so as to achieve the purpose of purifying water quality.

Factors affecting the adsorption of activated carbon

Adsorption capacity and adsorption speed are the main indicators of adsorption process. Adsorption capacity is measured by adsorption capacity. The adsorption speed refers to the mass of adsorbed substance per unit weight of adsorbent in unit time. In water treatment, the adsorption speed determines the contact time between wastewater and adsorbent.

The adsorption capacity of activated carbon is related to its pore size and structure. Generally speaking, the smaller the particles are, the faster the pore diffusion speed is, and the stronger the adsorption capacity of the activated carbon is.

The pH value and temperature of sewage also have influence on the adsorption of activated carbon. Generally, activated carbon has higher adsorption capacity in acidic condition than in alkaline condition. The adsorption reaction is usually exothermic, so low temperature is favorable for the adsorption reaction.

Of course, the adsorption capacity of activated carbon is related to the concentration of sewage. At a certain temperature, the adsorption capacity of activated carbon increases with the increase of equilibrium concentration of adsorbed substances.

Application of activated carbon in sewage treatment

Due to the high requirement of activated carbon for water pretreatment and the high price of activated carbon, activated carbon is mainly used to remove the micro pollutants in wastewater treatment, so as to achieve the purpose of deep purification.

Treatment of chromium containing wastewater with activated carbon

Chromium is a large amount of metal raw material in electroplating. Hexavalent chromium in wastewater exists in different forms with different pH values.

Activated carbon has a very developed microporous structure and a high specific surface area. It has a very strong physical adsorption capacity and can effectively adsorb Cr (Ⅵ) in wastewater. There are a large number of oxygen-containing groups on the surface of activated carbon, such as hydroxyl (- OH), carboxyl (- COOH), etc., which have electrostatic adsorption function and produce chemical adsorption on Cr (Ⅵ). It can be used to treat Cr (Ⅵ) in electroplating wastewater. The adsorbed wastewater can meet the national discharge standard.

The results show that the mass concentration of Cr (Ⅵ) in the solution is 50mg / L, pH = 3, and the adsorption time is 1. At 5h, the adsorption performance of activated carbon and the removal rate of Cr (Ⅵ) were the best.

Therefore, the process of using activated carbon to treat chromium containing wastewater is the result of the physical adsorption, chemical adsorption and chemical reduction of Cr (Ⅵ) in solution by activated carbon. Activated carbon has stable adsorption performance, high treatment efficiency, low operating cost and certain social and economic benefits in the treatment of chromium containing wastewater.

Treatment of cyanide containing wastewater with activated carbon

In industrial production, cyanide or by-product cyanide is used in wet extraction of gold and silver, production of chemical fiber, coking, synthetic ammonia, electroplating, gas production and other industries, so a certain amount of cyanide containing wastewater must be discharged in the production process.

Activated carbon has been used to purify wastewater for quite a long time, and there are more and more reports about its application in the treatment of cyanide containing wastewater. However, due to the small adsorption capacity of cn_and HCN on the activated carbon, it is generally 3mgcn / GAC ~ 8mgcn / GAC (different varieties), which is not cost-effective.

Treatment of wastewater containing mercury with activated carbon

Activated carbon has the ability to adsorb mercury and compounds containing mercury, but its adsorption capacity is limited, so it is only suitable for the treatment of wastewater with low mercury content. If the concentration of mercury is high, it can be treated by chemical precipitation first. After treatment, the concentration of mercury is about 1mg / L, and it can reach 2-3mg / L when the concentration is high. Then active carbon is used for further treatment.

Treatment of phenol wastewater with activated carbon

Phenolic wastewater is widely sourced from petrochemical plants, resin plants, coking plants and oil refining and chemical plants. The results show that the adsorption performance of activated carbon for phenol is good, the increase of temperature is not conducive to adsorption, so that the adsorption capacity is reduced, but the time to reach adsorption equilibrium is shortened. The amount of activated carbon and adsorption time have the best value. Under the acidic and neutral conditions, the removal rate does not change much. Under the strong alkaline condition, the phenol removal rate drops sharply. The stronger the alkaline condition, the worse the adsorption effect.

Treatment of methanol wastewater with activated carbon

Activated carbon can adsorb methanol, but its adsorption capacity is not strong, so it is only suitable for the treatment of wastewater with low methanol content. work