Phosphate sludge-based ceramics: Microstructure and effects of processing factors

International audienceThe potential use of clay amended phosphate sludge in lightweight aggregates manufacturing was assessed. For this purpose, the microstructure of heated blends was examined with X-ray diffraction, thermal analysis and scanning electron microscope and impedance spectroscopy, and their physical properties were followed as a function of heating temperature, soaking time and clay content. For the latter study, the full factorial design was used. The results showed that phase neoformation involved the breakdowns of the clay minerals and lime of carbonates. Moreover, the sintering process was significant as the clay content exceeded 5 wt% and 900< T< 1000 degrees C. In such a condition, the sintering was chiefly controlled by melt. The results of the full factorial design showed that the increase of one of the processing factors affected positively water absorption, density and compressive strength. These effects were mainly linked to the conjugate formations of calcaluminosilicate and viscous phase. The results also pointed out that the effects of the interactions between the factors on the measured properties were almost negligible. By using the full factorial design, the optimum values of the physical properties were evaluated

Effects of long-term storage of phosphate sludges on their physicochemical properties, the distribution and mobility of heavy metals, and acid generation

Some phosphate sludges (Ps) were collected in 2009, 2014, and 2018. Results of their analyses by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM-SED), differential thermal and thermogravimetric analyses (TG-DTA) and X-ray fluorescence spectrometry (XRF) confirmed that the Ps are highly carbonated. Descriptive and exploratory statistical procedures for heavy metals (HM) concentrations and chemical parameters were performed and revealed the differences between the Ps of three different ages. The results indicate that there are three sources responsible for the behavior of Ps over years: common origin and accumulation of HIM and solar radiation exposure. The sequential extraction shows that the residual fractions of Cd, Ni, Zn, Pb, and Cr were predominant The mobility factor was quite low and did not change over the years, except for Cd. The net acid generation pH for the three samples was greater than 4.5 classifying the Ps as non-acid-generating