| There is a large number of leachate generating from landfill. Once the pollutant transport into soil and groundwater, it will directly threaten human health. Thus laying liners on the bottom of the landfill is necessary, which prevent leachate flowing out of the landfill and groundwater entering into the landfill.The use of natural clay as a landfill liner continues to expand due to its low cost. But natural clay liners are easy to be eroded and drying shrinkage which affects the permeation and attenuation. Domestic and foreign scholars have made untiring researches on the bottom liner, but the results are not ideal. Therefore, study a new liner has a great significance.The feasibility of bentonite, zeolite and red mud as landfill liner is studied. According to the geotechnical engineering test method and criterion, the particle size, moisture content, dry density and hydraulic conductivity of the three materials were measured. The effects of moisture content and dry density on the hydraulic conductivity of these materials were investigated in order to provide basis for liner design. Under the conditions of maximum dry density and optimum moisture content, hydraulic conductivity of the three materials were 2.54×10-7、7.84×10-7 and 2.81×10-7 cm/s respectively and were all larger than 10-7cm/s which is the maximum limit permitted by liner standards.Two batches of column tests were carried out in this paper using practical leachate as penetrant. In the first batch of test, three kinds of monolayer mineral liner were designed with thicknesses of 2cm using bentonite, zeolite and red mud respectively. The results showed that hydraulic conductivities of the three liners were all more than 10-7cm/s, and attenuation was not efficient. In the second batch of test, five different kinds of liner were designed. Column 1, 2 and 3 were monolayer liners as in the first batch, but the thickness increased to 4cm. And column 4 (red mud+bentonite+zeolite from top to down) and 5 (red mud+ zeolite +bentonite from top to down) were multilayer liners composed of three materials with thicknesses of 4cm. The results showed that average hydraulic conductivities of the five liners were 1.88×10-8、5.17×10-7、4.36×10-7、1.04×10-7 and 1.38×10-8cm/s, average attenuation rate of ammonium-nitrogen were 91.35%、60.93%、99.46%、99.20% and 98.92%. The removal rates of COD and electrical conductivity in column 1, 3, 4 and 5 were 42.09% and 52.36%, 44.09% and 30.64%, 77.68% and 41.39%, 49.91% and 34.97%, and pH was equivalent with leachate. Among the two batches of tests, COD, pH and electrical conductivity in two red mud liners were much higher than leachate. Therefore, red mud was not suitable to use as liner material individually. But red mud had high strength which could ensure liner integrity.Compared with the two batches of test, when the thickness of bentonite and zeolite monolayer liner increased, permeability and attenuation capability became better. As a whole, properties of multilayer liner were superior to monolayer liner, not only could keep liner integrity and have equivalent pH with leachate, but also had a good permeability and attenuation which reached the best level of monolayer liner, even better. |
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