Removing Lead from Brass Scrap - Recycling of brass metal with high lead content

Important results from the project

New regulations require that brass in contact with drinking water must be nearly lead-free. The production of brass is based to 85-95% on recirculated raw material, but today´s recirculated brass has too high a lead content to be used as a starting material for lead-free brass. The goal of the project was to develop technology to clean scrap brass from lead in aim of making more recycled material usable as raw material for lead-free brass. The purification technology is based on a vacuum process and the project´s specific objective was to determine defined process paths for different forms of scrap and use the process paths as a basis for scaling up in an industrial demonstration plant. The lead purification target was achieved for certain forms of scrap in trials in pilot equipment and a technical layout for a demo facility was developed together with an identified partner. However, the investment required to realize the demo plant turned out to greatly exceed the estimate at the start of the project, and it was thus not possible to complete the scale-up within the framework of the project. The project parties therefore decided to suspend the project after the pilot trials, with the ambition to proceed with scaling up when the investment conditions become favorable.

Expected long term effects

The project was able to determine a defined process path regarding the parameters pressure, temperature and time which results in both zinc and lead being able to be separated from the brass scrap. Scrap in the form of loose turning chips was sufficiently cleaned to be used as starting material for lead-free brass. In order to increase the density of the incoming scrap material, and thus the productivity of the process, trials were also made where chips were pressed together into briquettes. The lead content then did not reach all the way down to the desired levels, but optimization of the process path and briquette structure is deemed to be able to lead to the target levels being achieved. The effect of a scaled-up process is expected to be a flexible and efficient use of recycled scrap as starting material for lead-free brass.

Approach and implementation

Tests were carried out in pilot equipment at Swerim in Luleå. The experimental equipment consisted of a vacuum oven where the lowest pressure was about 1 mBar. In the project, different temperature levels were investigated from approx. 600 C° up to 1000-1100 C°. The raw material was treated under a low pressure in solid and molten phases for different times, after which the levels of lead and zinc were measured in the treated material. After a time-consuming search process, a suitable cooperation partner regarding process and equipment in an upscaled demo plant could be identified. Together with this partner, the project developed a technical layout and basis for a demo plant based on the results of the pilot tests.