The improvement in properties and environmental safety of fired clay bricks containing hazardous waste electroplating sludge: The role of Na2SiO3

The introduction of electroplating sludge in the manufacturing of clay brick can be considered a feasible method to consume it, while physical-mechanical performances would degrade significantly and the potential leachability of heavy metals remain. This study proposed an alternative to remedy these negative impacts by adding Na2SiO3. The addition of Na2SiO3 decreased water absorption and promoted compressive strength substantially. Water absorption of bricks fired at 1050 °C for 3 h decreased from 6.05 to 0.56% and compressive strength increased dramatically from 22 to 46 MPa with the adding amount of Na2SiO3 raising from 0 to 20 wt%. The porosity analysis demonstrated the apparent porosity, surface area, pore volume, and pore size decreased significantly, especially at 1050 °C. The mineralogical phase analysis showed the Na2SiO3 reacted with quartz and formed albite, and the albite played an important role in decreasing porosity and enhancing mechanical property. Additionally, Na2SiO3 decreased the leachability of heavy metals, it was mainly due to the decrease in water absorption, surface area, pore volume, and pore size. Prolonging the firing time can also decrease water absorption and enhance compressive strength in the presence of Na2SiO3. These results proved that the addition of Na2SiO3 is a feasible strategy for enhancing the properties and environmentally safe of fired bricks when solid waste was introduced to produce bricks or ceramics.