Abstract: Hydroxylamine hydrochloride was used to improve the activity of heavy metals in soil, and its strengthening effect on washing efficiency of heavy metals in soil by citric acid was investigated. Based on the single factor experiment, the multi-factor experiment was designed with the response surface model method. The relationships between heavy metal washing efficiency and citric acid dosage, hydroxylamine hydrochloride dosage, liquid-solid ratio were fitted. The reaction conditions were optimized, and the heavy metal washing efficiency and environmental risk reduction rate were used to evaluate the treatment results. The results show that, compared with single treatment with 5 g·L^-1 citric acid, addition of 10 g·L^-1 hydroxylamine hydrochloride significantly improved the washing efficiency of heavy metals, of which the Pb washing efficiency increased by 36.2%. When both the dosage of citric acid and hydroxylamine hydrochloride were 8 g·L^-1, the liquid-solid mass ratio was 12∶1, and the shaking time was 2 h, the washing efficiency of Cu, Zn, Pb, and Cd were 55.8%, 58.3%, 47.1% and 47.9%, respectively; and the environmental risk reduction rates were 87.8%, 85.9%, 38.2% and 90.7%, respectively. The removal rates of the weak acid extracted components of four heavy metals were between 37.6% and 86.2%, the removal rates of the reducible components were between 49.4% and 80.4%, and the contents of heavy metal in residues were significantly increased.

Key words: heavy metal, citric acid, hydroxylamine hydrochloride, environmental risk reduction, toxicity characteristic leaching procedure (TCLP), chemical specification