pH-dependent leaching behaviour and other performance properties of cement-treated mixed contaminated soil

Portland cement has been widely used for stabilisation/solidification （S/S） treatment of contaminated soils. However, there is a dearth of literature on pH-dependent leaching of contaminants from cement-treated soils. This study investigates the leachability of Cu, Pb, Ni, Zn and total petroleum hydrocarbons （TPH） from a mixed contaminated soil. A sandy soil was spiked with 3000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel, and treated with ordinary Portland cement （CEM I）. Four different binder dosages, 5%, 10%, 15% and 20% （m/m） and different water contents ranging from 13%-19% dry weight were used in order to find a safe operating envelope for the treatment process. The pH-dependent leaching behaviour of the treated soil was monitored over an 84-day period using a 3-point acid neutralisation capacity （ANC） test. The monolithic leaching test was also conducted. Geotechnical properties such as unconfined compressive strength （UCS）, hydraulic conductivity and porosity were assessed over time. The treated soils recorded lower leachate concentrations of Ni and Zn compared to the untreated soil at the same pH depending on binder dosage. The binder had problems with Pb stabilisation and TPH leachability was independent of pH and binder dosage. The hydraulic conductivity of the mixes was generally of the order, 10-8 m/sec, while the porosity ranged from 26%--44%. The results of selected performance properties are compared with regulatory limits and the range of operating variables that lead to acceptable performance described.

Simultaneous removal of Pb and MTBE by mixed zeolites in fixed-bed column tests

The co-contamination of metals and organic pollutants,such as Pb and methyl tert-butyl ether(MTBE),in groundwater,has become a common and major phenomenon in many contaminated sites.This study evaluated the feasibility of their simultaneous removal with permeable reactive barrier(PRB)packed with mixed zeolites(clinoptilolite and ZSM-5)using fixed-bed column tests and breakthrough curve modeling.The effect of grain size on the permeability of PRB and removal efficacy was also assessed by granular and power clinoptilolite.The replacement of granular clinoptilolite by powder clinoptilolite largely reduced the breakthrough time but increased the saturation time nearly fourfold.The column adsorption capacity of clinoptilolite powders almost tripled that of clinoptilolite granules(130.6mg/g versus 45.3 mg/g)due to higher specific surface areas.The minimum thickness and corresponding longevity of PRB were calculated as 7.12 cm and 321.5 min when 5%of granular clinoptilolite was mixed with 5%ZSM-5 and 90%sand as mixed PRB reactive media compared with 10.86 cm and 1230.2 min for the application of powder clinoptilolite.This study is expected to provide theoretical support and guidance for the practical application of mixed adsorbents in PRBs.