Sludge Ceramsite Research Articles

Stabilization of heavy metals in sludge ceramsite

This paper attempts to investigate the stabilization behaviours of heavy metals in ceramsite made from wastewater treatment sludge (WWTS) and drinking-water treatment sludge (DWTS). Leaching tests were conducted to find out the effects of sintering temperature, (Fe 2O 3 + CaO + MgO)/(SiO 2 + Al 2O 3) (defined as F/SA ratios), pH, and oxidative condition. Results show that sintering exhibits good binding capacity for Cd, Cr, Cu, and Pb in ceramsite and leaching contents of heavy metals will not change above 1000 °C. The main crystalline phases in ceramsite sintered at 1000 °C are kyanite, quartz, Na–Ca feldspars, sillimanite, and enstatite. The main compounds of heavy metals are crocoite, chrome oxide, cadmium silicate, and copper oxide. Leaching contents of Cd, Cu, and Pb increase as the F/SA ratios increase. Heavy metals in ceramsite with variation of F/SA ratios are also in same steady forms, which prove that stronger chemical bonds are formed between these heavy metals and the components. Leaching contents of heavy metals decrease as pH increases and increase as H 2O 2 concentration increases. The results indicate that when subjected to rigorous leaching conditions, the crystalline structures still exhibit good chemical binding capacity for heavy metals. In conclusion, it is environmentally safe to use ceramsite in civil and construction fields.

Stabilization/Solidification of Heavy Metals in Sludge Ceramsite and Leachability Affected by Oxide Substances

To investigate stabilization of heavy metals in ceramsite made from wastewater treatment sludge (WWTS) and drinking water treatment sludge (DWTS), leaching tests were conducted to find out the effect of SiO2:Al2O3, acidic oxides (SiO2 and Al2O3), Fe2O3: CaO:MgO, and basic oxides (Fe2O3, CaO, and MgO) on the binding ability of heavy metals. Results show that as ratios of SiO2: Al2O3 decrease, leaching contents of Cu and Pb increase, while leaching contents of Cd and Cr first decrease and then increase; under the variation of Fe2O3:CaO:MgO (Fe2O3 contents decrease), leaching contents of Cd, Cu, and Pb increase, while leaching contents of Cr decrease. Acidic and basic oxide leaching results show that higher contents of Al2O3, Fe2O3, and MgO are advantageous to improve the stability of heavy metals, while the binding capacity for Cd, Cu, and Pb is significantly reduced at higher contents of SiO2 and CaO. The solidifying efficiencies of heavy metals are improved by crystallization, and the main compounds in ceramsite are crocoite, chrome oxide, cadmium silicate, and copper oxide. These results can be considered as a basic understanding for new technologies of stabilization of heavy metals in heavily polluted WWTS.

Solidification and leaching behaviours of Cr 6+ in sludge ceramsite

Making lightweight ceramsite with sewage sludge is a new effective approach for disposal of sludge. However, there is a concern as to whether the heavy metals such as Cr 6+ in sewage sludge can be solidified in ceramsite after sintering. The configuration of Cr 6+ in ceramsite was analyzed by X-ray diffraction (XRD) and leaching tests were conducted to determine the effects of sintering temperature, pH and H 2O 2 concentration on the stabilization of Cr 6+ in ceramsite. The results show that leaching of Cr 6+ changes little at temperatures above 900 °C, and both pH and H 2O 2 concentration have some effects on the leaching of Cr 6+. Leaching test results indicate that Cr 6+ is stabilized in ceramsite and cannot be easily released to the environment again as secondary pollution, which eliminates the concern for its application. XRD analysis of ceramsite sintered at 1000 °C reveals that the main compounds of Cr 6+ in ceramsite are Cr 2O 3 and FeCrO 4. The test results provides a better understanding of the factors that affect the mobility of Cr 6+, and show it is a safe way to make ceramsite with sludge as an additive.

Effect of sintering temperature on the characteristics of sludge ceramsite

In order to investigate the effect of sintering temperature on the characteristics of sludge ceramsite and find an optimal sintering temperature, dried sewage sludge, clay, and water glass were mixed at ratios of dried sewage sludge/clay = 33% and water glass/clay = 15%. Then these mixtures were heated to 850, 900, 950, 1000, 1100, and 1200 °C for production of sludge ceramsite. The sludge ceramsite were characterized by DTA-TGA, SEM-EDS, XRD, and XRF. The results indicate that the differences in thermal behaviours are caused by the compositional and structural variations; the ceramsite sintered at 1000 °C has more uniformly distributed finer pores (0.5 μm < pore size < 10.0 μm), while the ceramsite sintered at other temperatures has less pores and rougher surfaces. The main crystalline phases of ceramsite are quartz and kyanite below 1000 °C; kyanite is the main crystalline phase at 1000 and 1100 °C, and most of the crystalline phases are mullite at 1200 °C. It is therefore concluded that sintering temperature has a significant effect on the characteristics of sludge ceramsite, and that 1000 °C is the optimal sintering temperature.