NOVELTY - The crystallization system has a crystallization reaction tank (10) including a top input port (11) and a bottom output port (12). A pH value/fluoride detecting section (40) is provided with a pH meter (41) and a fluoride meter (42) which are electrically connected by wires and controlled by a control device. A first passage (43) of pH meter is communicated with a bottom of the lower reaction space of the crystallization reaction tank, and a second passage (44) of a fluoride meter is communicated with a top of the lower reaction space.    USE - Crystallization system for producing sodium aluminum fluoride cryolite from hydrofluoric acid waste for manufacturing semiconductor integrated circuit (IC), thin-film transistor LCD panel and solar cell.    ADVANTAGE - The factor affecting the cryolite purity during the operation process is effectively controlled, thus purity is improved for recycle process. The quality of cryolite is improved.    DETAILED DESCRIPTION - A dispersing plate (13) is arranged in inside of crystallization reaction tank, and is formed with dispersing apertures. A control plate (14) is located above the dispersing plate and formed with control apertures. A sodium aluminate tank is electrically controlled with the control device, and is provided with a batch dosing control section (201) through which sodium aluminate flows from the sodium aluminate tank (20) to the upper dosing space of the crystallization reaction tank. A high concentration hydrofluoric acid waste tank (30) is electrically controlled with the control device, and is provided with a batch dosing control section (301) through which high concentration hydrofluoric acid waste is transported from the high concentration hydrofluoric acid waste tank to the lower reaction space of the crystallization reaction tank. The first passage is provided with a metering pump (431), a flow rate control valve (432), and a ball valve (433) which are arranged between the metering pump and the crystallization reaction tank, and between the metering pump and the pH meter, respectively. A clear water input section (46) is provided with a flow rate control valve (461) for controlling amount of clear water to be inputted. A second passage is provided with a backflow control valve (441). A fluoride meter is provided with a third passage having a discharge control valve (451) and a ball valve (452) for controlling the discharge of aqueous waste. The metering pump, the two flow rate control valves the three ball valves, and the discharge control valve of the pH value/fluoride detecting section are electrically controlled by the control device. A discharge control section is connected to a dehydrator (50) and a low concentration hydrofluoric acid waste tank (60) to separate cryolite and low concentration hydrofluoric acid waste. The dehydrator is electrically controlled to operate by the control device, and is communicated with the discharge control section of the crystallization reaction tank. A low concentration hydrofluoric acid waste tank is electrically controlled by the control device to collect the low concentration hydrofluoric acid waste discharged from the dehydrator. An anti-overflow base (70) is provided an anti-overflow element (71) that comprises a leak detector (72) and a discharge valve (73) that are electrically controlled by the control device. The dispersing apertures are arranged along radial lines extending radially from a center of the dispersing plate, the control apertures are arranged along radial lines extending radially from a center of the control plate. The control plate is provided with positioning apertures which are aligned and connected to the positioning apertures of dispersing plate by fasteners. An INDEPENDENT CLAIM is included for a method for operating crystallization system for producing sodium aluminum fluoride cryolite from hydrofluoric acid waste, involves using the control device to set parameters, after all parameters are set. The dispersing plate and the control plate are set to meet flow rate requirement of the sodium aluminate, so as to control the flow rate of the sodium aluminate flowing into the lower reaction space. The batch dosing control section of the high concentration hydrofluoric acid waste tank is turned on to introduce high concentration hydrofluoric acid into the lower reaction space of the crystallization reaction tank. The batch dosing control section of the sodium aluminate tank is turned on to introduce sodium aluminate into the upper dosing space of the crystallization reaction tank, after the high concentration hydrofluoric acid waste tank is introduced into the crystallization reaction tank. A fifth step is turned on the pH value/fluoride detecting section, to introduce the water sample from the crystallization reaction tank into the pH value/fluoride detecting section. The pH value/fluoride concentration of the water sample is detected. The water sample is reintroduced back into the crystallization reaction tank. The determination is made whether reaction ends or not based on the pH value, and the fluoride concentration detected, if the reaction does not end. The pH value/fluoride detecting section is turned off. The micro adjustment of the dosing of the sodium aluminate is carried out. A micro amount of sodium aluminate is introduced into the crystallization reaction tank, based on the set parameters. The cryolite is dehydrated and collected. The discharging of low concentration hydrofluoric acid waste is carried out, and the discharge control section of the crystallization reaction tank is turned off.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the crystallization system for producing sodium aluminum fluoride cryolite from hydrofluoric acid waste.    Crystallization reaction tank (10)    Top input port of crystallization reaction tank (11)    Bottom output port of crystallization reaction tank (12)    Dispersing plate (13)    Control plate (14)    Sodium aluminate tank (20)    High concentration hydrofluoric acid waste tank (30)    PH value/fluoride detecting section (40)    PH meter (41)    Fluoride meter (42)    First passage of pH meter (43)    Second passage of fluoride meter (44)    Clear water input section (46)    Dehydrator (50)    Low concentration hydrofluoric acid waste tank (60)    Anti-overflow base (70)    Anti-overflow element (71)    Leak detector (72)    Discharge valve (73)    Batch dosing control sections (201,301)    Metering pump of first passage (431)    Flow rate control valve of first passage (432)    Ball valve of first passage (433)    Backflow control valve of second passage (441)    Discharge control valve of fluoride meter (451)    Ball valve of fluoride meter (452)    Flow rate control valve of clear water input section (461)