Summary
In addition to its use as a flame retardant, antimony is also used as a catalyst in PET production and in the glass and ceramics industry. Despite its critical availability, future demand for ATO is forecast to grow by more than 4%.
Recycling streams containing antimony either enter the lead route directly or take a detour via copper recycling. The antimony is finally removed from the lead in lead refining by selective oxidation. This produces a complex mixed oxide which contains many other heavy metal oxides in addition to lead and antimony and is therefore difficult to recycle.
In the first part of the project the selectivity of lead refining was increased by reducing the partial pressure of oxygen. In the second part, a volatilization process for the mixed oxides obtained in the first step was optimised in order to obtain as little lead in the condensate as possible. It was shown that in the Pb-Sb-O ternary system, a minimum Sb2O3 content of 38 wt.% at 700 °C volatilization temperature and 65 wt.% at 900 °C is sufficient to produce a condensate containing less than 1000 ppm lead. Additionally, the influence of accompanying oxides on the volatilization tendency of Sb2O3 was investigated. It was found that Cao is not suitable as it inhibits Sb2O3 activity by up to 65%.
The produced recyclates were tested for their suitability as flame retardants in PVC products. While they turned out to be almost identical to the primary product in terms of processability and flame-retardant effect, the laboratory tests already showed large colour deviations due to the impurities contained. For this reason, the use in color-critical products must be excluded up to now.
