Preparation And Curing Properties Of Magnesia-based Matching Curing Agent

Soil heavy metal pollution has been an environmental problem absorbing more and more attention, while curing stabilization technology gets universal attention because of its cheapness and efficiency. This paper used simulate soil as the research object and then used a magnesia-based curing agent prepared with bentonite, diatomite and magnesia to reduce the Pb2+, Cd2+ leaching toxicity. By the orthogonal experiment method, this research considered the leaching toxicity and soil pH changes before and after curing to study the key factors influencing the curing and work out the optimal curing agent. The structures of the optimal curing agent and soil before and after curing were characterized by SEM. On this basis,by the batch equilibrium method, curing of Pb,Cd on the curing agent was studied as a fimction of pH, calcium ion strength,temperature, contact time, the removal comparison and competition removal. The conclusions were listed as follow:1、Analysisof the orthogonal experiment showed that the main factors in the soil curing of Pb2+,were the dosage of magnesia, the dosage of bentonite and the dosage of diatomite,which the dosage of magnesia influenced the most. The main factors in the soil curing of Cd2+ were the dosage of magnesia and the dosage of bentonite, which the dosage of diatomite influenced the least. And the orders in curing of Pb2+, Cd2+ were the same,like the dosage of magnesia>the dosage of bentonite>the dosage of diatomite. And finally the result indicated the optimal curing agent composed of magnesia, bentonite and diatomite in the quality proportion 0.3:1.4:0.7 when curing agent and soil in the quality proportion 1:100.The testing of SEM showed that the surface of the curing agent and the soil after curing rough, full of adsorption sites and pores, but the surface of the soil before curing smooth.^ I^ I2、Pb, Cd simulation solution experiments showed that initial pH and calcium ion strength affected tiie curing. Curing of Pb2+,Cd2+ on the curing agent increased with increasing initial pH from 2 to 3 and tended to be stable at pH 3-6. However, Pb2+、Cd2+ curing decreased with increasing calcium ion strength from 0.00 to 0.30 molL-13、The thermodynamics and kinetics experiments results showed that the curing of of Pb2+ followed the pseudo-second-order kinetic model, the isothermal data obeyed the Langmuir model better compared to Freundlich model and Tempkin model, and the maximum Pb2+ adsorption capacity of matching curing agent was 96.2mg·g-1 at 30℃, 114.9mg·g-1 at 40℃ and 151.5mg·g-1 at 50℃. The apparent thermodynamic parameters indicated that the adsorption of Pb2+ was spontaneous, endothermic and entropically unfavorable physisorption. However, the curing of Cd2+ was precipitation. The maximum Cd+ curing capacity of matching curing agent was 203.2mg·g-14、The removal comparison experiments showed that bentonite and diatomite promoted the Pb2+ curing effect of magnesia, but not for Cd2+. The competition removal experiments showed that the removal efficiency of Pb2+ was greater than that of Cd2+, because Pb2+ hydrated radius was smaller and Pb(OH)2 was amphoteric hydroxide. Mixing bentonite, diatomite and magnesia could get the electrostatic forces, van der Waals force, ion exchange and the chemical precipitation together to cure heavy metal.