What are the characteristics of zero discharge of polycrystalline silicon production wastewater?
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Polysilicon is a form of elemental silicon that can be used as a raw material for monocrystalline silicon. In the utilization of solar energy, polysilicon also plays a significant role, and the wastewater generated by polysilicon is also properly treated. Through research on polycrystalline silicon processing wastewater, a method for resource utilization and zero wastewater discharge has been proposed to address water pollution issues in polycrystalline silicon production. Features of the zero-discharge system for polysilicon production wastewater: 1. It can **reduce the capital investment and operating costs associated with wastewater treatment plants.** 2. Since the water quality of the effluent from the modified membrane separation and recovery system meets industrial tap water standards, with a conductivity of around 150 us/cm. As a result, the tap water used by manufacturers on a daily basis will be reduced by over 60%, leading to **lower costs for tap water and the operation of the original water supply system**, with wastewater disposal costs also being reduced by over 60%. It can **reduce the investment and operating costs associated with the construction of wastewater treatment plants.
Polysilicon belongs to the field of inorganic chemistry; therefore, the main impurity in wastewater is salts. So, the method of reuse should be the same as that used in seawater desalination. What is this zero-emission method the original poster is talking about? ? RO membrane? RO membranes can only concentrate, but they cannot achieve zero discharge, right? Zero emissions require evaporation crystallization to treat the resulting salt.
The treatment of polysilicon wastewater is not that simple, as the wastewater contains cyanides.
Cyanide? Where did this impurity come from?
After polycrystalline silicon is shaped, it must be cut into specific shapes. The silicon wafers resulting from this cutting process contain certain pollutants and impurities, which are usually removed using chemical reagents such as strong acids, concentrated alkalis, and organic solutions. After that, they are washed with high-concentration ionized water. The wastewater generated as a result contains cyanides, heavy metal ions, etc., and its treatment requires very complex processes.
The mixed acid used for pickling contains hydrofluoric acid, but I haven’t heard of cyanide being present? What is this thing called “high-concentration ionized water”? Isn’t it cleaned with high-purity water?
In the production of polysilicon or monocrystalline silicon, large amounts of hydrofluoric acid-based mixtures are used. The waste acids are classified into concentrated acids and dilute acids. Concentrated acids mainly consist of hydrofluoric acid mixtures and fluorosilicic acid, while dilute acids contain a small amount of fluoride ions as a result of washing with fresh water during the production process. The regulations for discharging such wastes vary. The methods for treating waste acids involve using calcium hydroxide or calcium chloride to absorb and remove fluoride ions, neutralizing the acidity, and then dealing with ammonia nitrogen emissions.
Please clarify how silicon is removed from wastewater.