Using shell to enhance the phosphorus adsorption capability of aluminum-based drinking water treatment residue-dominant sintered ceramsite

Al-based drinking water treatment residue (DWTR) is an inevitable byproduct of potable production that can provide skeletal components to make sintered ceramsite for water treatment. However, sintering promotes Al aging and decreases its adsorption capability. This study proposes and verifies a strategy for using shell, a common natural Ca-based material, to enhance P adsorption by Al-based DWTR-dominant ceramsite. The results showed that the shell mainly acted as an expanding component, and thermolysis of CaCO3 to form CaO was the main expanding mechanism, further enhancing the coupling effect of Fe, K, and Si for sintering. This mechanism led to a reduction in the cylinder compressive strength with increasing shell proportions and an increase in the broken rate and cylinder compressive strength with increasing temperature. However, all DWTR shell-based ceramsites are non-hazardous. Importantly, the shell increased the P adsorption capacity of the ceramsite by approximately two orders of magnitude and caused the adsorbed P to remain as HCl-extractable and residual P. A logistic equation (r2 = 0.923, n = 10) was established for the cylinder compressive strength to Si, K, Fe, and Ca in ceramsite and loss on ignition in raw materials to provide a potential reference for ceramsite production.