In 1993 the 62,940 tons of municipal solid waste(MSW) and 55,969 tons of industrial non-hazardous waste were generated daily in Korea and 81.6% and 31.4% of each waste were disposed of by landfill. But there are almost one thousand of unsanitary landfills in Korea. Thus there has been many associated problems such as the pollution from uncontrolled landfills, the shortage of new landfill sites and little availability of cover material.
Recently the concept of landfill mining is being adopted and tested in Korea to utilize landfilled area and to recover the recyclable materials in it. The soils in the old landfill waste may be reused as the cover material of new landfill. In addition to this recycling, the landfill mining is a good way to remediate uncontrolled landfill and to prevent soil and groundwater pollution. And the purpose of this study is to estimate the adsorption capacity of heavy metals by old landfill soil, and to assess the possibility of usage as the cover material of new landfill. The adsorption capacity of old landfill soil was compared with that of the cover material of Kimpo new landfill site in Seoul Metropolitan area.
The chemical characteristics such as cation exchange capacity(CEC), organic carbon content, weight loss from ignition, heavy metal leaching and physical characteristics of soil texture were investigated. Lead(Ⅱ) and chromium(Ⅲ) are used for the adsorption experiments of two pH values of 4 and 7. The Langmuir and Freundlich isotherms were used to analyze the adsorption characteristics of lead and chromium.
Soil portion of the wastes in old HwaMyung and SukDae landfill in Pusan city which is the second biggest city in Korea is 74 ∼ 83% and that of old NanJi landfill was 26 ∼ 95%. Old landfill soil has higher pH values of 6.62 ∼ 8.17 than cover material of Kimpo new landfill site, and has the huge alkalinity of $5\times10^6\sim10\times10^6$ $CaCO_3$ mg/kg soil.
In leaching test, Pb and Cr concentrations of old landfill soil are 0.28 ∼ 1.40mg/l and below 0.18mg/l, respectively, and safely below the limit values(Standard : Pb ＜ 3ppm and Cr ＜ 1.5ppm) of hazardous waste. Organic content of old landfill soil is 1.6 ∼ 3.8% and higher than that of the cover material of Kimpo landfill site of 0.14 ∼ 0.22%. The CEC of old landfill soil is 4.9 ∼ 16.4 meq/100g, and also higher than new cover soil of Kimpo landfill(6.8meq/100g).
Adsorption experiment of Pb and Cr at pH=4 showed that Kn value of old landfill soil and the cover material of Kimpo landfill were 1.64 ∼ 11.8 and 1.45, respectively, which says that old landfill soil has better adsorption capacity than cover material.
From these results, it has been found that old landfill soil is better adsorbent than the cover material, and in case of reusing the old landfill soil, 52 ∼ 65% volume reduction of cover material for new landfill site is expected if and only if the geotechnical criteria of design and operation of sanitary landfill are met.
