Effect of the ratio of components on the characteristics of lightweight aggregate made from sewage sludge and river sediment

Previous studies shown that sewage sludge and river sediment can be used to produce lightweight aggregate (LWA). Control of the ratio of components in the LWA production process is important. In this study, we investigated the effect of mass ratio (K) of basic (Fe2O3, CaO, and MgO) and acidic (SiO2 and Al2O3) oxides on the characteristics of LWA. The studies show that LWA with lowest water absorption, the lowest solubility in hydrochloric acid and the highest grain density, the highest bulk density can be obtained when K in the range of 0.15-0.3, the properties of LWA in accordance with the standard of GB/T 17431.2-1998, China. When K was fixed at 0.2, the mass ratio of SiO2:Al2O3 in the range of 4:1-1:1 and the mass ratio of Fe2O3:CaO:MgO in the range of 5:2.2:1-1.7:1.9:1 resulted in LWA with the desired physical properties, the maximum compressive strength can reach 17.07 MPa. The heavy metals experiments show that the leaching content (Cd, Cr, Cu and Pb) is closely related to a variation in K ratio, heavy metals can existed as stable crystalline compounds in LWA, and exhibiting excellent heavy metals solidification ability even it subjected to destruction, which indicates that stronger chemical bonds are formed between these heavy metals and the components through heat-induced transformation to the crystalline state. Investigations indicate that K can be a useful parameter to optimize LWA qualities.