Author: Alberto Bergamaschini, STC Srl
Nowadays, the most critical aspects in the Used Lead Acid Battery recycling field are related to the environmental compliance and the relevant environmental management costs.
Permitted emission levels are constantly under revision by Environmental Authorities and disposal costs in landfills for the hazardous waste (slag) generated by the pyrometallurgical process are remarkably increasing. That’s why the lead paste desulphurization process has become so crucial: this hydrometallurgical process, in fact, allows a drastic reduction of SOx emissions in the furnace flue gas by 90%, reduction of lead in the slags and a consequent higher lead recovery yield, reduction of slags produced due to a lower amount of iron addition in the charge for Sulphur sequestration, lower energy consumption due to a reduction of temperatures in the furnace and reduced process cycle duration with consequent higher productivity due to the increased space available for the charge in the furnace.
However, for STC Srl, Mesagne, Italy, this is not enough! The need to develop an alternative desulphurization process to the ones already available on the market arose about 3 years ago. The company wanted to propose the lead paste desulphurization technology via Ammonium Carbonate (the most recent and the most efficient one) to one of its clients but immediately realized that due to its high price, volatility and toxicity, it was necessary to look for other valid options.
For this reason, thanks to the great R&D team and to the incredible support and wide knowledge of Prof. Renato Guerriero, President of the company at that time, STC decided to push itself beyond the limits and actually discovered that it was possible to implement an even more efficient desulphurization process starting from a very cheap amino compound, easy to find, to treat and to handle: UREA. The U4Lead system is based on a well-defined and innovative STC process protected by National and International (PCT) patent and it has been successfully installed and commissioned in the ULAB recycling plant realized by STC of our Nigerian client Green Recycling Industries Ltd. based in Agbara, Ogun State.
All the advantages of the traditional desulphurization are maintained and in many cases furtherly improved considering that this process ensures a higher degree of conversion of the lead sulphate into lead carbonate (more than 97%, is achieved) and that it is faster than using other chemicals thus allowing reduction of reactors volume. Furthermore, the desulphurization level obtained is higher than the traditional processes (0,2-0,3% of Sulphur remaining) and it leads to a further reduction of slag generation (only 5-6% on Pb produced!) and associated lead losses. A drastic reduction of Iron usage in the charge, fuel and oxygen consumption is also obtained and, with Urea, there are no undesired side-reactions during desulphurization such as formation of double salts. UREA is normally cheaper than other reagents, it is worldwide largely available and it does not involve any environmental, pollution and safety problems for workers related to transport, storage and handling.
The final by-product obtained is ammonium sulphate and can be easily used and sold as fertilizer in liquid or crystals form: the selling price is normally higher than sodium sulphate.
The possibility to desulphurize the lead paste via UREA has been verified for the first time in the World on industrial scale in our client’s plant and, after the first initial tuning, the technology confirmed the excellent results already obtained in the lab scale testing.
The process can be easily implemented and integrated also into existing plants and further technical results and specifications of the unit will be presented during the GDMB Lead Expert Committee on 29th October 2020.