Preparation of non-sintered sludge based material and mechanism of phosphorus adsorption

The non-sintered materials were prepared using sludge as raw materials, and four influencing factors were selected, including the mass ratio of silt/cement, the amount of activator, the amount of sodium silicate and the curing time, to determine the optimal preparation conditions by the Box-Behnken(BB) response surface method. The adsorption performance was evaluated by isothermal adsorption, adsorption kinetics and intragranular diffusion model, and the adsorption mechanism of phosphate was explored by characterization methods. The results showed that the optimal preparation conditions of the non-sintered materials were as follows:the mass ratio of silt/cement was 2.48, the amount of activator was 12.95%, the amount of sodium silicate was 1.4%, the curing time was 13 days, the predicted value of the breakage rate was only 2.32%, and the predicted value of phosphorus adsorption capacity was 0.582 mg/g. The adsorption process was in line with the Langmuir model, the quasi-second-order kinetic model and the intragranular diffusion model. The non-sintered materials adsorbed phosphorus by chemical precipitation and ligand exchange, with low environmental risk and high economic benefit.