Background Production of stone-based mineral wool, which is used for insulation, requires large quantities of energy and raw materials. The production process also results in large volumes of municipal and industrial waste that could serve as raw materials and energy sources. The project's aim was to use waste materials – such as spent pot-lining (hazardous waste), sewage sludge ash, dry sewage sludge and carbogrit – for producing stone wool. A further objective was to enable stone wool production units to use locally produced waste materials as a partial substitution for current energy sources. Objectives The project set out to test use of waste fractions as ingredients in stone wool manufacturing at five locations (Denmark, France, two in Germany, and the United Kingdom): carbogrit (used blasting sand made of dried sewage sludge) was tested in Denmark; sewage sludge ash was tested in France and at one German location; dried sewage sludge was tested in the second German location; and spent pot-lining was tested in the UK. In each case, seven steps were taken: Process analysis and description: laboratory tests of materials and comprehensive descriptions of the chemical and mechanical processes that would make it possible to use the waste product in stone wool production; Engineering: technical calculations and design of the equipment for realising the usage of the waste product (the equipment used was to vary between the project’s tasks, depending on the waste material in question, and on the melting technology at the plant using the waste product); Purchasing: purchase of the equipment according to the design and specifications established during the engineering phase; Construction: mounting of the equipment at the plants applying the waste materials in their production processes; Tuning and analysis: process optimisation and tuning of the stone wool production process after partly replacing the existing raw materials with waste product including deposit tests, emission tests and fly ash composition analysis; Test series: a series of production tests to demonstrate that the new process with a share of waste products replacing raw materials (stone) and energy (coke) is competitive in terms of quality and cost efficiency; Documentation: documentation of the new processes and the results of the test programme; Independent analyses: to assess the environmental net impact of using the waste materials.Results The project implemented three of the five waste testing tasks / locations. In the UK, spent pot liner, a waste fraction from the aluminium industry, was successfully used as an ingredient in a process using a cupola furnace. Use of this material reduced energy costs but other environmental impacts were neutral. The injection of sewage sludge ash in a cupola furnace in Germany also proved technically feasible. Use of the carbogrit waste fraction in a cupola furnace in Denmark was also a success. In two locations, however, work could not be finalised because of risk of explosion that became evident during the project (use of dried sewage sludge in a cupola furnace in Germany), and because of administrative difficulties in obtaining raw materials (sewage sludge ash in France). A Life Cycle Analysis (LCA) was completed based on the three successful trial series. All trials show that using waste will result in some energy savings and that raw material used did not compromise environmental targets. The LCA indicated that the processes are environmentally neutral. Specifically, the use of spent pot liner showed the most beneficial environmental impacts, while the use of sewage sludge ash reduced the amount of waste sent to landfill. The processes developed during the successful tests can be applied in several plants producing insulation materials, that the beneficiary runs in several EU countries. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).