Study Of The Key Parameter On Controling Recycling Technology Of Aviation Chemical Milling Solution

From characteristics and hazards of chemical milling solution about heat treatment in a certain aircraft factory in Chengdu, this paper has a brief introduction to the structure and nature of aluminum ions of the chemical milling solution, and treatment technology and related application status has been described. Single factor experiments of reaction parameters on dilution crystallization have been done and found the best regulatory parameters. On this basis, it carried out the method named efficient crystallization point.At the same time, it explains its mechanism and determines optimal processing parameters of the method. Finally, based on the theory of the above experiment, we carried out the design and commissioning of the circulating processing system on chemical milling solution. And in best regulatory parameters of the dilution crystallization, we verified that efficient crystallization point can be used to fast crystallization in practical engineering.(1) In the dilution crystallization conditions, when the pre-treatment, we need to use pure water to dilute chemical milling solution and the sludge of chemical milling solution which seriously affect the subsequent crystallization reaction effect must filter. regulating different regulation parameters of the crystallization reaction makes removaling of aluminum ion in crystallization reaction to achieve the best, the best regulation parameters:dilution multiple is 1.0, industrial aluminum hydroxide seed, adding 1.0 times the amount of seed, mechanical stirring rate of 50 r/min, the reaction temperature is 30 ℃. Under optimum conditions, the six days aluminum ion removal rate can reach 50%.(2) The mechanism of crystallization efficient point method is studied. By IR analysis, infrared spectra of time point in induction period dose not have absorption peak in 640cm-1 and 880cm-1, but infrared spectras of time point in rapid crystallization period and time point in limit crystallization period have 880cm-1 absorption peaks which has a functional group capable of accelerating the crystallization of the reaction. It proves the cause that the average daily removal rate of concentration of aluminum ion in rapid crystallization point and the limit point are greater than the induction point; aluminum ions of chemical milling solution, after the induction period, transform mononuclear tetrahedral aluminum ion (Al(OH)4-) in the crystallization process. Compared with other adding times of chemical milling solution, the crystallizations of rapid crystallization point which have more clear angular crystal and more active sites can accelerate crystallization reaction by analyzing SEM. Aluminum hydroxide crystals of rapid crystallization point are pure gibbsite crystals by XRD. The crystals can be used repeatedly as a kind of pure seed to treat chemical milling solution(3)For the method of efficient crystallization point, amount of processing cycles and endurance parameters were determined. Determine ratio of efficient crystallized chemical milling solution and old chemical milling solution is 2:1 when it has the best treatment. The removal rate of aluminum ion in three days can reach 34.38%, and the average daily removal rate of concentration of aluminum ion is about 3.30 g/L·d; In the conditions of cycle period of three days and strong endurance, it can be recycled more than at least six times. When the cycle time to the sixth times, it still has a good crystal effect and the removal rate of aluminum ion can reach 34.6% in a cycle time.(4)At the optimal regulation parameters of dilution crystallization, efficient crystallization point method has been used to crystal fast in practical engineering applications. By debugging and running twice, in each cycle, the removal rate of aluminum ion in chemical milling solution circulation system is about 35%.it not only reach the requirement to the removal rate of aluminum ion (20%) in the technical contract but also stable operation. Metallurgical testing and physical and chemical properties of chemical milling quality testing are in line with aviation chemical milling quality standards. It also meets the production needs. And in best regulatory parameters of the dilution crystallization, we verified that efficient crystallization point can be used to fast crystallization in practical engineering.