Effect of palygorskite thermal transformation on the ceramic valorization of clayey sludge

The disposal of clayey sludge generated from aggregate washing in quarries and from the dredging of hydraulic infrastructures (dams and irrigation canals) has significant environmental impacts and represents an additional economic burden for the aggregate industry and related sectors. This study investigates three types of sludge originating from an aggregate quarry, a dam, and an irrigation canal. These sludges were characterized through particle size distribution, plasticity limits, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). Carbonate and organic matter contents were determined by calcimetry and loss on ignition at 500 °C and 950 °C. The sludges are composed mainly of quartz, feldspars, and clay minerals, with illite as the predominant clay mineral. Their low to moderate plasticity restricts direct application in ceramic production. To enhance shaping and mechanical performance, a palygorskite-rich clay was incorporated at 10–40 wt%. Brick specimens were produced and fired between 800 and 1050 °C. The findings reveal that increasing palygorskite content enhances plasticity and flexural strength, producing homogeneous bricks without deformation or cracking. Although shrinkage, mass loss, water absorption capacity, and apparent porosity slightly increase with increasing palygorskite content, all other values remain within international standards. Above 950 °C, pronounced mineralogical and microstructural transformations occurred. Increasing the firing temperature reduces porosity and water absorption due to the formation of a glassy phase, thereby enhancing mechanical performance. These findings highlight the potential of clayey sludge as a sustainable and environmentally friendly raw material for brick manufacturing and traditional ceramic production.