In the present thesis, a study has been performed of remediating mine tailings around abandoned mine contaminated with high concentrations of arsenic and heavy metals using techniques of soil washing and stabilization sequentially. The soil washing was applied to removing arsenic, whereas the stabilization was to minimizing the mobility of the heavy metals remained in soils after the washing.
The optimal conditions in the type and concentration of washing reagent, mixing ratio of soil and washing reagent, and washing time were derived through the removal experiment of arsenic using the soil-washing technique. Results showed that the most effective washing reagents to remove arsenic from soils were phosphoric acid (65% efficiency) and oxalicacid (72%), while the oxalic acid (89%) was the most effective for removal of the heavy metals containing Cu. The economical and efficient washing concentration was 0.25M and the suitable washing time was 90 minutes. The optimal mixing ratio of soil and washing reagent was 1:20 (mass/vol) in viewpoint of minimization of wastewater produced after the washing, in addition to the washing effectiveness. Although the mixture of washing reagents did not help in removal of arsenic, it lead to much elevated synergy effect in removing Cu and Zn, compared to the single reagent.
Over 80% of heavy metals were removed from the wastewater through the natural sedimentation for 30 days with no additive, whereas most of arsenic (over 70%) remained. The adjustment of pH at 9-10 in the wastewater enabled over 99% of arsenic to be sedimentated.
By performing the stabilization, with 10wt% of calcium phosphate (CaHPO4) for 14 days, of heavy metals remained in soils after the washing, high treatment efficiencies were obtained asfollows: Pb (99.7%), Cd (87.1%), Cu (97.9%), Zn (99.4%).
In the adsorption/desorption experiments of arsenic, a column of diameter 2.5cm and length 10cm was used and the arsenic concentration and flow rate were respectively 0.39-0.42mmol/L as As and 1.0-2.9mL/min. The experiments were performed in an oxidized condition for the case of As(V) and in a reduced condition for that of As(III). As(V) reached a quasi-equilibrium state when the solution passed through the column was over 900mL (9 hours) for the adsorption and 500mL (6 hours) for the desorption. On the other hand, As(III) reached a quasi-equilibrium state when the solution was over 390mL (3.5 hours) for the adsorption and 400mL (2.5 hours) for the desorption. In addition, the adsorption and desorption for As(V) proceeded more slowly than for As(III).