Recycling of Waelz slag and waste foundry sand in red clay bricks

Foundry sand and Waelz slag have been used to replace clay in the production of red clay bricks. These are both problematic wastes in Northern Spain that are currently landfilled. A semi-scale industrial trial incorporating 20–40 weight percent additions to bricks has been completed. Trial samples have been compared with control bricks containing no waste additions. The physico-chemical, mechanical and environmental properties have been evaluated. Incorporating Waelz slag and foundry sand in the mix allows the production of more resource efficient, lower cost bricks. Performance benefits included improved extrusion properties during forming, lower water absorption of the sintered brick due to reduced connected porosity, significant reductions in CO2 and NOx emissions during firing and improvements in potential leachability of some pollutants in relation to samples containing only Waelz slag or foundry sand. However, it is necessary to limit the addition of Waelz slag to less than 30 wt.% in order to meet regulatory leaching limits for Mo. Other physico-chemical and mechanical parameters were not significantly affected by the addition of these industrial by-products.

► Reusing both Waelz slag and foundry sand in red clay bricks has been studied. ► Reductions of porosity and CO2 and NOx emissions during production were found. ► Other physico-chemical and mechanical properties were not significantly affected. ► Environmental behaviour of the new bricks during service and end life was assessed. ► Decreasing mobility of pollutants in relation to samples with only slag or sand.