2024-12-17
With the continuous changes in electronic information technology, the semiconductor technology industry has increasingly become the "heart" of development and is increasingly widely used in national economic production and life. However, the semiconductor industry is a high water-consuming industry. The more advanced the process manufacturing, the higher the requirements for its surface cleanliness, and the greater the water consumption and wastewater discharge.
For example, a semiconductor company in Beijing and a semiconductor company in Taiwan consume 1346x104㎡3 and 7000x104㎡ of water respectively, while the per capita water resources in China are 2300m2 , which is equivalent to the total domestic water consumption of a town with a population of 250,000 and 1.3 million respectively.
If the wastewater generated in semiconductor manufacturing is recycled, it will not only reduce the demand for water resources and production costs, but also reduce the emission of pollutants and the load on the environment. Shanqing Environment shared the treatment process of semiconductor wastewater containing fluorine, nitrogen, phosphorus, organic matter, heavy metal ions and acid and alkali , as well as the advantages of different processes in removing pollutants from semiconductor wastewater .
Characteristics and classification of semiconductor wastewater
1.1 Wastewater characteristics
(2) The strong color, high COD, high volatile organic compound content, and rich in heavy metal ions , toxic organic matter, and corrosive substances such as hydrofluoric acid make the biological degradation performance of wastewater low, and it is not suitable for treatment using traditional activated sludge method.
(3) Fluoride ions ( F - ) and fulvic acid substances can react with heavy metal ions to form stable complexes, and heavy metal ions are easy to interact with organic matter, silicate and other substances, so the pollutants in wastewater are complex and diverse.
Therefore, it is crucial to select the process and divert the treatment according to the wastewater quality type.
1.2 Wastewater classification and treatment
1.2.1 Treatment of fluoride-containing wastewater
Semiconductor fluoride-containing wastewater mainly comes from the diffusion and CMP processes in the chip manufacturing process . The current industrial applications of fluoride-containing wastewater removal methods mainly include chemical precipitation, adsorption, membrane separation , etc.
Figure 1 Fluoride-containing wastewater treatment process and its advantages and disadvantages
a.Chemical precipitation is suitable for the treatment of high-concentration fluoride-containing wastewater. Compared with other precipitants , calcium salts are relatively cheap and - The reaction generates insoluble CaF₂ . Therefore, the calcium salt precipitation method is most widely used in fluoride-containing wastewater in the semiconductor industry .
b.There are two adsorption methods: direct adsorption and electrosorption. Electrosorption, also known as capacitive deionization technology, is a method that uses charged electrodes to adsorb ions and charged particles in wastewater, so that pollutants are enriched and concentrated on the electrode surface to achieve the purpose of water purification . Traditional adsorbents in direct adsorption, such as activated carbon and clay, have problems such as low adsorption capacity, poor selectivity, secondary pollution to the environment, and poor effluent quality .
c.Membrane separation methods mainly include electrodialysis and reverse osmosis. Electrodialysis is to use the electrodes to apply a current on both sides of the selective permeable membrane to generate a potential difference, which promotes the selective permeation of anions and cations through the membrane. Reverse osmosis is to use the pressure difference on both sides of the membrane to filter water molecules and F -Method of separation.
1.2.2 Treatment of nitrogen-containing wastewater
Nitrogen-containing wastewater mainly comes from ammonia water and ammonium fluoride used in the etching process, and mainly exists in the form of ammonia nitrogen. At present, the main treatment methods for ammonia nitrogen wastewater include air stripping , adsorption, neutralization, breakpoint chlorination, biological method, etc.
picture 2 Ammonia nitrogen wastewater treatment process and its advantages and disadvantages
a.There are two types of stripping methods: air stripping and steam stripping. Compared with air stripping, steam stripping has a higher ammonia nitrogen removal rate, which can reach more than 90%, and is suitable for wastewater with higher concentrations .
b.The adsorption method is generally only applicable to low-concentration ammonia nitrogen wastewater. In high-concentration ammonia nitrogen wastewater, it is often coordinated with other processes to carry out deep denitrification treatment .
c.The breakpoint chlorination denitrification process can be used for a single denitrification process or for the deep treatment of a denitrification process.
1.2.3 Treatment of phosphorus-containing wastewater
mainly comes from aluminum etching liquid in the production process. It exists in the form of PO₄³ - . The treatment methods for phosphorus-containing wastewater include chemical precipitation, biological method, adsorption method, crystallization method and ion exchange method.
picture 3 Phosphorus-containing wastewater treatment process and its advantages and disadvantages
( 1) Traditional adsorbents have problems such as high replacement cost and low adsorption capacity. Recently, many scholars have prepared high-performance adsorbents by chemically modifying low-cost industrial waste .
( 2) Compared with chemical precipitation, the precipitate produced by crystallization precipitation has a higher secondary utilization value and can be used as plant fertilizer. At the same time , it can also show good removal performance for phosphorus.
1.2.4 Treatment of organic wastewater
And CMP process in production , and mainly contains solvents such as isopropyl alcohol, propylene glycol monomethyl ether acetate, acetone, xylene, etc., with high COD and low biodegradability. At present, the main treatment methods for organic wastewater include biological methods and advanced oxidation methods.
(1)bioreactors and chemical and biological combined methods are often used to treat wastewater.
( 2) The advanced oxidation treatment (AOP) process is considered to be the best method for treating organic wastewater due to its fast oxidation rate and high mineralization efficiency.
Figure 4 Organic wastewater treatment process and its advantages and disadvantages
1.2.5 Treatment of heavy metal wastewater
Heavy metal wastewater in semiconductors mainly comes from electrochemical plating ( ECP ) and CMP processes, mainly copper and cobalt, which mainly exist in the form of complexes formed by chelating agents. The main treatment methods for complexed heavy metal wastewater include adsorption, chemical precipitation, ion exchange, oxidation-reduction, etc.
Figure 5 Heavy metal wastewater treatment process and its advantages and disadvantages
( 1) Chelate precipitation is a method of removing heavy metals by using heavy metal chelating agents (such as amino and dithiocarboxyl groups) to form insoluble salts with heavy metals.
( 2) Advanced oxidation method uses strong oxidative free radicals to destroy the strong chemical bonds between heavy metal ions and certain functional groups in the ligand to release heavy metal ions.
( 3) Adsorption methods include co-removal of heavy metals and organic acids and heavy metal extraction. Organic acid co-removal technology is a process of removing pollutants from wastewater by adsorbing the entire complex onto an adsorbent .
1.2.6 Acid and alkali wastewater treatment
The semiconductor manufacturing process will discharge a large amount of acidic or alkaline substances , which will make the pH value of the wastewater too low or too high , which is easy to cause harm to the environment . At present, the treatment of this type of wastewater usually adopts three-stage neutralization technology to adjust the pH value. Value is 6.0-7.5 rear emission.
The semiconductor industry is a high water consumption industry, and wastewater recycling is one An effective way to solve the water crisis in the semiconductor industry , At present, due to cost and technical issues , wastewater with relatively good water quality can be recycled, while wastewater with relatively complex water quality can be recycled. one Generally discharged after treatment .