Ceramics from clays and by-product from biodiesel production: Processing, properties and microstructural characterization

• Glycerine from biodiesel industry can be used in the manufacture of clay bricks.
• Glycerine addition reduces bulk density and thermal conductivity.
• 10–15 wt.% additions have the optimum equilibrium between technological properties.
• Novel lightweight porous ceramics fired at 950 °C can be obtained using glycerine as raw material.

The production of biodiesel generates a by-product called glycerine which contains glycerol that cannot be re-integrated into the same manufacturing process. The ceramic bricks are an interesting option to set in their structure a wide range of by-products and residues materials and composites, sometimes serving only as a reservoir for the inert residue, and other, having a positive effect on the ceramic material or process.In the present work, the incorporation of this waste in raw clays has been studied. The raw materials: clay and glycerine was characterized by XRD, XRF, CNHS analysis, higher heating value and thermal analysis and after, using conventional moulding and sintering processing methods to prepare clay–glycerine composites, the influence of the amount of waste added to clay has been evaluated. To do this, percentages of glycerine were added to the clay from 5% to 20% and evaluated by a series of technological properties such as compressive strength, absorption and suction of water, bulk density, the study of porosity generated by adsorption–desorption isotherms of N2, thermal conductivity and finally by the compressive strength after freezing-thaw. it was considered as the maximum permissible rate of addition of glycerol 10–15% in weight, because higher additions have a strong effect on the properties of the obtained materials such as compression strength and bulk density which descending dramatically due to the large amount of porosity generated as reflected by high values of absorption and suction experiments. It was concluded that adding 5% glycerol to the ceramic paste generated plasticity in clay to achieve be moulded, with values of compressive strength of 84 MPa while gets to reduce the density apparent by almost 5%.