Study of the Stabilization Process for Arsenic-Contaminated Soil and Mine Tailing around Abandoned Mines Using Lime (CaO) and Limestone (CaCO3)

Abstract

The main objective of this study is to evaluate the efficiency of lime (CaO) and limestone (CaCO3) in immobilizing arsenic (As) from contaminated soils and mine tailing. As-contaminated surface soil was collected at the farmland around the Samkwang abandoned mine in Korea and its initial As concentration was 41.0 mg/kg. Mine tailing were collected at the pithead of the Ilkwang abandoned mine in Korea and As concentration of mine tailing was 4119.5 mg/kg. Batch experiments were performed to investigate the decrease of arsenic extraction rate from contaminated farmland soil by amendments (lime and limestone). Various amounts of amendment (0, 0.1, 0.5, 1, 2, 5, and 10 wt% of soil) were used in the experiments. From the results of the batch experiment, the arsenic removal efficiency increased with the increase of amendments added in the soil, suggesting that the addition of lime and limestone was very effective in decreasing the leaching rate of arsenic from the soil. With the addition of 2 wt% granulated lime (2 ~ 5 mm in diameter), the leaching rate of As decreased by more than 80 % and decreased by more than 95 % with 5 wt% of granulated lime. In the case of adding 2 and 5 wt% of granulated limestone, As concentration of leached solution decreased by more than 75 and 85 %, respectively. For only limestone addition, the pH of extracted solution maintained at lower than pH 7. However, the pH of solution increased to higher than pH 10 with the addition of lime. Column experiments were also performed to investigate the decrease of the arsenic extraction rate from soil and mine tailing. For a physical model of As leaching from the contaminated soil, the acryl column (15 cm in diameter and 100 cm in height) was desibned. For the column experiment of mine tailing, the glass column (5 cm in diameter and 15 cm in height) was used. The lower and the upper part of each column consisted of dense lattice screen plates and the drain system for injection and extraction of artificial rainfall. For the experiment of As stabilization, granulated lime and limestone were homogeneously mixed with contaminated soil (or mine tailing) and they were packed in the column. Deionized water, titrated with HCl at pH 5.5 ~ 6.0, was used as the artificial rainfall for the column experiments. The artificial rainfalls were injected from the top of large column at 100 ml/min or bottom of glass column at 2 ml/min. Extracted solutions were drained out from the bottom of large column or top of glass column and were analyzed on ICP/OES to investigate the decrease of the amount of As in drained solution. From the results of the acryl column experiments for soils, with the addition of 1 wt% granulated lime, As concentrations in drained solution decreased by 97 %, compared to the result of the experiment without the amendment. When 2 wt% granulated limestone was added, As concentrations in drained solution decreased by 91 %. With the mixed amendment (1 wt% of lime + 2 wt% of limestone) As concentration of leached solution decreased by 96 %. From the result of the glass column experiments for mine tailing, with the addition of 1 wt% granulated lime, As concentrations in the drained solution decreased by 60 %, compared with that of experiment without the amendment. As concentration of leached solution decreased by 84 % with 2 wt% granulated limestone. For the experiments without an amendment and only with limestone, pH value of the drained solution maintained lower than 8. However, the pH of solution increased to higher than 10 with lime, suggesting that it is harmful for the agricultural usage and it might increase As leaching from the solution. Results investigated that limestone is more useful than lime in decreasing As leached from the contaminated soil and mine tailing because of low pH increase and low cost.

Key words : stabilization, amendment, soil contamination, mine tailing, arsenic, CaO, CaCO3