Soil Washing Coupled with the Magnetic Separation to Remediate the Soil Contaminated with Metal Wastes and TPH

Batch experiments for the soil washing coupled with the magnetic separation process were performed to remediate the soil contaminated with metal and oil wastes. The soil was seriously contaminated by Zn and TPH (total petroleum hydrocarbon), of which concentrations were 1743.3 mg/kg and 3558.9 mg/kg, respectively, and initial concentrations of Zn, Pb, Cu, and TPH were higher than the 2nd SPWL (soil pollution warning limit: remediation goal). The soil washing with acidic solution was performed to remove heavy metals from the soil, but Pb and Zn concentration of the soil maintained higher than the 2nd SWPL even after the soil washing with acidic solution. The 2nd soil washing was repeated to increase the Pb and Zn removal efficiency and the Zn and Pb removal efficiencies additionally increased by only 8 % and 5 %, respectively, by the 2nd soil washing (> 2nd SPWL). The small particle separation from the soil was conducted to decrease the initial concentration of heavy metals and to increase the washing effectiveness before the soil washing and 4.1 % of the soil were separated as small particles (< 0.075 mm in diameter). The small particle separation lowered down Zn and Pb concentrations of soil to 1256.3 mg/kg (27.9 % decrease) and 325.8 mg/kg (56.3 % decrease). However, the Zn concentration of soil without small particles still was higher than the 2nd SPWL even after the soil washing, suggesting that the additional process is necessary to lower Zn concentration to below the 2nd SPWL after the treatment process. As an alternative process, the magnetic separation process was performed for the soil and 16.4 % of soil mass were removed, because the soil contamination was originated from unreasonable dumping of metal wastes. The Zn and Pb concentrations of soil were lowered down to 637.2 mg/kg (63.4 % decrease) and 139.6 mg/kg (81.5 % decrease) by the magnetic separation, which were much higher than the removal efficiency of the soil washing and the particle separation. The 1st soil washing after the magnetic separation lowered concentration of both TPH and heavy metals to below 2nd SPWL, suggesting that the soil washing conjugated with the magnetic separation can be applied for the heavy metal and TPH contaminated soil including high content of metal wastes.

자력선별과 토양세척법을 연계하여 금속폐기물과 TPH로 복합 오염된 토양 동시 정화

금속 폐기물과 TPH(total petroleum hydrocarbon: 석유계 총탄화수소)로 복합 오염된 토양을 정화하기 위하여 자력선별법을 연계한 토양세척 배치실험을 실시하였다. 오염토양의 아연과 TPH 농도는 각각 1743.3 mg/kg과 3558.9 mg/kg으로 심하게 오염되어 있었으며, 아연, 납, 구리, TPH 항목들이 '2지역 토양오염우려기준'(정화목표)을 초과하였다. 중금속 제거를 위해 1차 산세척을 실시하였으나 납과 아연은 산세척 후에도 '2지역 토양오염우려기준'을 초과하였으며, 2차 연속 세척에 의해서 아연과 납의 제거효율은 각각 8 %와 5 % 증가에 그쳐, 정화목표에 도달하지 못하였다. 오염토양의 중금속 초기농도를 줄이고 세척 효과를 높이기 위하여 세척 전 미세입자(직경 < 0.075 mm)를 선별하였으며, 오염토양의 4.1 %가 분리되었다. 미세입자 선별만으로 오염토양의 초기 아연과 납 농도는 1256. 3 mg/kg(27.9 % 감소)과 325.8 mg/kg(56.3 % 감소)으로 감소하였으나, 미세입자 선별 후 오염토양을 1차 세척한 결과 아연 농도가 '2지역 토양오염우려기준'보다 높게 나타나, 이를 만족시킬 수 있는 추가 제거방법이 필요하였다. 본 토양이 무분별한 금속폐기물 투기에 의해 오염되었다는 사실로부터, 미세입자 선별의 대안으로 자력선별법을 적용하였으며, 토양의 16.4 %가 자력선별에 의해 제거되었다. 자력선별 후 오염토양의 아연과 납 농도는 637.2 mg/kg (63.4 % 감소)과 139.6 mg/kg (81.5 % 감소)로 감소하여, 1회 토양세척과 미세입자 선별에 의한 중금속 제거 효과보다 높았다. 자력선별 후 오염토양을 산용액으로 1차 세척한 결과, 오염토양 내 모든 중금속과 TPH농도가 '2지역 토양오염우려기준'이하로 낮게 유지되어, 본 오염토양과 같이 금속폐기물을 많이 함유하고 있는 토양의 경우 자력선별법을 연계한 토양세척에 의해 중금속과 TPH를 동시에 효과적으로 제거할 수 있는 것으로 나타났다.