Effect of sludge from oil refining industry or sludge from pomace oil extraction industry addition to clay ceramics

• SOI and SPOEI could be used as raw materials in clay bricks.
• Incorporating 5 wt.% of SOI or 10 wt.% of SPOEI barely alters properties of clay.
• The addition of waste is limited to 10 wt.% for SOI and 20 wt.% for SPOEI.
• SOI and SPOEI are pore formers in bricks improving thermal conductivity.
• Waste bricks met the UNE standards and can thus be used as green construction materials.

This work studies mixing sludge from oil refining industry (SOI) or sludge from pomace oil extraction industry (SPOEI) with clay in order to produce lightweight bricks for civil construction. Applied sludges and clay were previously characterized in terms of chemical and mineralogical composition and thermal behavior. Ceramic bricks were produced with different quantities of sludge (0–30 wt.%) as raw material, with conformed bricks being fired at 950 °C. In order to determine optimal mixing, physical, mechanical, thermal and chemical properties of bricks were assessed. Results indicated that the type and proportion of waste are important parameters in determining brick quality. Increasing content of SOI or SPOEI resulted in a loss of brick compressive strength and thermal conductivity, due to decreasing bulk density and increasing water absorption. Incorporating 5 wt.% of SOI or 10 wt.% of SPOEI barely alters properties of clay (control bricks). However, additions exceeding 10 wt.% of SOI or 15 wt.% of SPOEI led to bricks with low compressive strength due to increasing porosity caused by their content in organic substances, which, during combustion, act as pore forming agents, increasing clay porosity and providing energy support during a brick firing process. Leaching tests, performed according to TCLP standards on substituted brick samples, showed that the quantities of heavy metals leached from crushed bricks were within the regulatory limits.