If secondary zinc resources are to be recycled, it is necessary to carry out research on the recycling of SZO. A large amount of secondary zinc resources are produced in industrial production every year, a large part of which is SZO. SZO is a kind of secondary zinc resource.
The proportion of secondary zinc resources as raw materials for industrial production is increasing after years of research. Zinc has excellent recycling performance, and the utilization of secondary zinc resources has attracted more and more attention. The analysis results of the initial residue and the leached residue indicated that lead was transferred from PbCl 2 to PbCO 3 and that ZnFe 2O 4 was not leached in the NH 3-NH 4HCO 3-H 2O system.
mol −1, while the order of reaction with respect to total ammonia concentration was 1.53 and the liquid/solid ratio was 2.26. The apparent activation energy of the reaction was estimated to be 11.04 KJ The kinetics of leaching were modeled using the shrinking core model of constant-size particles, and the rate-controlling step was determined to be the diffusion through the product layer. Zinc extraction is promoted by the addition of ammonium bicarbonate to a NH 3–H 2O system, and the maximum recovery of zinc could be close to 80% at the optimum leaching conditions of a stirring rate of 400 rpm, an ammonia/ammonium ratio of 7:3, a total ammonia concentration of 4 mol/L, and a liquid/solid ratio of 7 mL/g for 30 min at 35 ☌. In this study, the production feasibility and rationality of a cleaner zinc recovery process using SZO and a hydrometallurgical method were described. The various processing techniques for polymer composite manufacturing have been discussed.Secondary zinc oxide (SZO), which comes from the zinc industry, is an important secondary resource of zinc and other valuable metals. The reason for improved properties has also been explored through synergistic effect. Improved properties in terms of mechanical, thermal, gas barrier, optical and special effects have been discussed in this chapter considering their uses in aerospace applications. Different dimensions of the fillers are confined to achieve superior properties in composites. Nowadays, polymer composites are replacing the other materials widely in aerospace applications. Various fillers including nanofillers reinforce the pristine polymer keeping in contact with its original properties. 
Filled systems circumvent these shortcomings with improved properties without additional cost. Often, there is a trade-off between the requirement and actual properties of pure materials. Polymeric materials, being light weight, are replacing the conventional metal and ceramics, especially in an aerospace application. The requirement of materials for aerospace industries includes light weight, high reliability, durability against corrosion, vacuum, radiation, fatigue and passenger safety.
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