Briefly describe the purification technologies for the gaseous pollutant SO2.

The technology for removing SO2 from flue gas is known as \"flue gas desulfurization.\" There are many such technologies, which can generally be divided into two categories: wet and dry methods. The former takes advantage of the fact that SO2 is an acidic oxide, while the latter makes use of SO2’s reducibility. 1. Wet flue gas desulfurization? In the wet method, depending on the absorbent used, there are mainly the ammonia method, sodium method, calcium method, and magnesium method. 1) Ammonia method? Using ammonia water to absorb SO2 from flue gas. The intermediate products are sulfurous acid An and ammonium bisulfite. By using different methods to treat the intermediate products, by-products such as sulfuric acid an and gypsum can be recovered. 2) Sodium method: Using aqueous solutions of sodium hydroxide, sodium carbonate, or sodium sulfite as absorbents to absorb SO2 from flue gas. This method has a fast absorption rate for SO2, and its pipelines and equipment are less prone to clogging; therefore, it is widely used. The resulting sodium sulfite and sodium bisulfite absorption solutions can be discarded after harmless treatment, or processed by appropriate methods to yield by-products. 3) Calcium method: An emulsion of limestone or quicklime is used as an absorbent to absorb SO2 from flue gas; the resulting calcium sulfite is oxidized by air to form gypsum. The absorbent used in this method is inexpensive and readily available, and the large amount of gypsum recovered can be used as a building material; therefore, this method is widely adopted both domestically and internationally. 2. Dry flue gas desulfurization – a method of absorbing SO2 from flue gas using solid absorbents. The main methods include activated carbon treatment, activated manganese oxide absorption, and contact oxidation; this approach is not suitable for treating large volumes of flue gas.

Our company first uses sodium hydroxide desulfurization, and then lime is used to replace the sodium.