Comparative study on the passivation of heavy metals in soil among curing agent based on blast furnace slag, calcium oxide and phosphate

A comparative study on the passivation of available heavy metals in soil was carried out among the traditional curing agent calcium agents, including calcium oxide, calciun dihydrogen phosphate, and a new heavy metal curing agent HMS. The main raw material of HMS was blast furnace slag and the new curing agent was prepared under the effect of activator. The results indicate that the optimal additive amount of HMS、calcium oxide and calcium dihydrogen phosphate are obtained when the mass ratio of curing agent to soil is 1:4. The best passivation effect on content of available Pb achieved by the soil treated by calcium dihydrogen phosphate is 97.05%, the best passivation effect on content of available Zn and Cd achieved by the soil treated by calcium oxide is respectively 80.41%, 74.74% and that the second passivation effect on content of available Zn、Pb and Cd achieved by the soil treated by HMS is respectively 46.12%, 53.26% and 65.64% when the soils is treated by three curing agents under their optimum mix amount, mass ratio between the liquid and solid is 0.28:1(L/kg), curing temperature is 25℃ and curing time is 28d. Compared with the original soil, the soil pH value is increased by 3.64 and 0.99 with calcium oxide and HMS treatment for 28 d, respectively, and is decreased by 4.85 with calcium dihydrogen phosphate treatment for 28 d. HMS has the most balanced recovery effect on the contaminated soil. Therefore, it is the most ideal one of three curing agents in this experiment and can attain the purpose of waste control by waste. Finally, the passivation mechanism of three curing agents is discussed.