Production of pure lead oxide through the STC process allows the use of parts of these oxides in the paste preparation for the production of new batteries. For the complete replacement of the BARTON oxide a further step that permits to reduce parts of the lead oxide into metal is necessary in order to obtain a correct mixing of lead and lead oxide. The reduction of lead oxide to metal can be achieved in different ways.
STC prefers a direct reduction of the lead oxide through the use of hydrogen.
The chemical reaction studied since the beginning of last century starts at a very low temperature (less than 200°C). At this temperature part of the oxide is directly reduced into metal with water production.
PbO + H2 → Pb + H2O
The STC process is carried out just below lead fusion temperature (ca. 300°C), in order to avoid the melting of the obtained metal powder. STC has developed a fluidized bed pilot reactor for the reduction of these lead oxides. This process is patent pending.
The use of hydrogen in this process is due to the necessity of obtaining the reduction at a temperature lower than the lead fusion one. Instead of hydrogen, methane or water gas (H2 + CO) can be used to obtain a complete reduction of the oxide into metal. In this case the operative temperatures are higher than 500°C. This process, together with the hydrometallurgical STC process to convert lead paste into lead oxide, makes it possible to obtain pure metal lead and may potentially replace the rotative furnaces with advantages for the environment:
- less gaseous emissions and slag;
- energetic consumption is lower.
The production of metal through direct reduction of lead oxide by hydrogen or methane is one of the most studied technologies in the last years and many scientists see the future of the lead recycling sector in this technology.