Projects / Programmes
Utilization of secondary lead slag as a secondary raw material for the production of lead
| Code |
Science |
Field |
Subfield |
| 1.04.00 |
Natural sciences and mathematics |
Chemistry |
|
| Code |
Science |
Field |
| 1.04 |
Natural Sciences |
Chemical sciences |
secondary raw materials, lead, secondary lead slag, separation
Researchers (10)
Organisations (2)
Abstract
The lead-acid battery is still the most widely used battery in many application fields. Its most important property is the ease of the recycling with 99 % of all lead-acid batteries being recycled today. Spent lead-acid batteries are crushed and drained of sulfuric acid, followed by removal of plastics by flotation. The obtained battery paste is than desulfurized with either sodium carbonate or sodium hydroxide and processed in a reduction furnace, where the paste is treated with iron scrap, anthracite, and silica fluxes resulting in the elemental lead and slag that is discarded to different landfills and stockpiles. However, such slags contain large amounts of useful elements like Pb (?22 %), followed by Zn and Cu, but also contain certain highly migratory toxic elements, such as Pb, Zn and Cd. In order to reduce the quantities of toxic waste and reach the zero waste goal in EU, we should strive to develop adequate technologies for the separation and reprocessing of these wastes. Slovene producer MPI-Reciklaža d.o.o. is using a proprietary process for the recycling of lead-acid batteries and produces around 10.500 ton of lead slag annually. The goal of the project is to sufficiently reprocess the lead slag, so that it can be used again in their lead-acid battery recycling process. Preliminary analyses show that their slag also contains Na2SO4, anthracite and scrap iron that are ingredients in the recycling process as well as around 10 % of Pb and 3.6 % of Zn. In order to reach the goal, Na2SO4, anthracite and scrap iron should be removed from the slag and the remaining Zn, Cu and Fe should be leached out if necessary to prepare the lead concentrate suitable for re-use in their lead-acid battery recycling process. However, no such process was developed yet. Only pyrometallurgical methods were implemented for the recycling of such slags, but this processes require high temperatures and consume huge amounts of energy together with a significant amount of non-renewable resources and are as such prohibitive. Different hydrometallurgical processes based on citrates, acetic acid, hydrochloric acid and nitric acid were also studied, but they are unable to cover the full separation spectrum required for this type of waste. In order to solve this problem, we propose in this project to test the combined approach using both chemical and physical separation techniques. Na2SO4 will be dissolved, concentrated and removed from the solution by exploitation of its huge difference in solubility between 30 and 10°C. In the next step, anthracite particles of different sizes will be removed by the use of density difference and specialized jig, spiral and Mozley gravity separators. After that the remaining slag stream will be crushed and scrap iron together with magnetic iron oxides will be removed by magnetic separators. If the lead concentrate obtained through these steps will reach the criteria for use in the lead-acid battery recycling process, it will be used as obtained. If not, other, more intricate measures will be tested, including the hydrometallurgical extraction, cementation and electrowinning of the elements Cu, Zn and Fe. The main goal of the proposed project is to produce lead concentrate from the slag, suitable for returning to the lead-acid recycling process. Besides the lead concentrate, three additional products will be retrieved. Anthracite could be pelletized and used as reducer in the same process. Retrieved scrap Fe will be cleaned of iron oxides by attrition scrubber and returned to the process. Na2SO4 obtained in the first step is used in detergents and paper production, and could be sold as a separate product. Reprocessing of the slag will significantly improve the yield of the recycling process as well as reduce the environmental risk represented by the leachable toxic elements present in the landfilled slag and as such be an important step toward the zero waste production.
