The Fundamental Kinetic Characteristics of Aqueous Dissolution of Chloride and Fluoride Salts from Secondary Aluminium Dross

Abstract

The salt content in the secondary dross obtained beside the recovered aluminium by the hot processing of the primary melting dross hinders further utilization of this material. Secondary dross samples obtained from the industrial hot processing of the primary dross generated by the melting of aluminium alloy scrap were leached with water at room temperature with different Liquid/Solid (L:S) ratios. Vessel filling (the relative volume occupied by the sludge) in the shaking bottles required further consideration in the interpretation of the results. Samples taken regularly within 15 minutes during vigorous shaking showed that NaCl and KCl can be dissolved almost instantly, and completely irrespective of the parameter settings. However, the fluoride additive (CaF2) has a complex behaviour. The results suggest its relation to some side reactions indicating also the conditions of the hot process producing the examined material. The results suggest that the salt content of the secondary aluminium dross can be lixiviated within a 2 – 4 minutes virtually completely, but the L:S ratio and the a vessel filling have to be coordinated. At the lowest L:S ratio examined of 1.0, a vessel filling of max. 11% should be observed to achieve this fast salt dissolution. The same dissolution rate can be reached with double the vessel filling (i.e. smaller unit) if the L:S is also increased in this ratio.