The electrolyte obtained during the recycling of lead batteries can cause serious problems to the environment if not opportunely treated.
STC has developed clean technologies for the purification and concentration of electrolyte from the recycling of lead batteries by membrane and heat pump technology.
The electrolyte from the recycling of lead batteries is a watery solution containing sulphuric acid and metals in solution. Lead is one of the principal polluting substances of the solution but there are also many other metals like copper, cadmium, tin and iron. The manifestation of calcium can be caused by presence of calcium lead alloys in the battery or by the contamination of the electrolyte due to storage in concrete containers.
STC has developed a nanofiltration plant for the purification of the electrolyte from the recycling of lead batteries through a membrane technology. In order to minimize the osmotic pressure of the solution to be purified, STC uses membranes with an opportune molecular weight cut off. The choice of the membranes is of fundamental importance. In this application STC uses membranes produced with a special glue that resists extreme chemical aggression.
The obtained sulfuric acid solution can be reused in other industrial processes or for the production of new batteries after a further purification carried out with an electrodialysis membrane process.
The sulfuric acid solution present in exhausted batteries has a concentration of ca. 15-20%. In order to be reusable in some industrial processes it is necessary to reach a higher concentration. STC has developed a heat pump evaporator that allows to concentrate the solution up to 45% in weight.
Heat pump technology does not release effluents into the atmosphere, does not need particular pretreatment and is easy to install. The thermodynamic cycle, applied to evaporate and condensate the water contained in the solution uses a common refrigerating gas that is accepted by the most severe regulations for environmental protection. The use of the heat pump technology is particularly suitable for the treatment of solutions with dangerous chemical substances as in this case.
Another advantage of the heat pump technology is the reduction of energy consumption, especially in countries where electric energy is not produced through fossil fuel.