Treatment method of mercury in wastewater
Activated carbon adsorption method is often used in conjunction with other methods, placed after the secondary treatment, as the advanced treatment of wastewater. For example, it can be used to treat heavy metal wastewater, mainly for removing mercury and hexavalent chromium.
After the wastewater is treated by Na2S chemical precipitation and FeSO4 coagulation, it still contains metallic mercury and its compounds (such as HgC12). The mercury content is about 1~2mg/L, which does not meet the emission standard (0.05mg/L). It needs to be further treated with activated carbon. Adsorption treatment, the adsorption treatment part is composed of three tanks.
(1) Sedimentation tank
Its function is to adjust the water volume and water quality, and to separate impurities, sand and sediment formed in the reaction in the water at the same time. The volume of the sedimentation tank is about 1 to 2 days of total wastewater.
(2) Adsorption tank
There are 2 in total, each of which can hold 2~3 days of wastewater (about 40t). Activated carbon is placed in the pool. After the wastewater is added to the No. 1 pool to 40t, it is stirred with 3~4 atmospheres of compressed air for 30 minutes, and then left to stand for 2 hours, sampling and measuring. If the mercury content is less than 0.05mg/L, it will be discharged directly, otherwise it will enter the No. 2 pool for further adsorption treatment. Generally, the emission standard can be reached after 2~3 times of adsorption treatment, and the first tank can absorb more than 95% of mercury.
The amount of compressed air is calculated according to 0.4m3/m2 (the area of the bottom of the pool).
Regeneration of activated carbon: The regeneration cycle is one year. Place the activated carbon to be activated in an activation furnace and heat it for half an hour at 1000°C. Metal mercury turns into mercury vapor (the boiling point of mercury is 357°C), and mercury compounds are also decomposed into mercury vapor. C12, etc., are then introduced into the condensation system for recovery , A part of mercury is recombined into mercury chloride in the gas phase, which can be recycled into the water sealing system, and then iron filings are added to replace the mercury.
The treatment effect of using activated carbon to treat wastewater depends on the properties and concentration of mercury in the wastewater, the type and amount of activated carbon, and the contact time between activated carbon and wastewater. Using this method to treat wastewater with high mercury content can get a high removal rate (85%~99%). For wastewater with low mercury content, although the removal rate is not high, effluent with very low mercury content can be obtained. . If the influent water contains 5-10ug/L of mercury, after treatment, the removal rate is 80%, and the effluent contains less than 2ug/L of mercury.
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