STUDY ON TRACE ELEMENTS LEACHING FROM FLY ASH ON SUBSURFACE ENVIRONMENT POLLUTION

摘要

The impact of fly ash leaching on the subsurface environment was studied. In order to assess their leachability, a laboratory column leaching experiment was used to determine the potential mobility of Cd, Cu, Pb, Zn. Experiments were conducted at PH values 2,4,6,8,10,12. The following L/S (Liquid-to-Solid) ratios of the leaching test were used: 50:1, 40:1, 30:1, 20:1, and 10:1.The results show that PH of the solution and liquid-to-solid ratios have a strong influence on leaching behavior of trace elements. For most of the trace elements, aqueous phase concentrations increase at lower PH and leach more into the extracts at low PH values than at neutral and high PH values. Trace elements concentrations were greater at higher L/S and increased as the L/S increased. A numerical model for variably saturated flow and trace elements transport has been developed. Solutions to the coupled model are accomplished by implicit finite difference method. Taking trace element Cd as an example, the dynamic characteristics of migration and transformation of trace elements Cd leaching from fly ash was analyzed. The subsurface pollution range has a trend of increasing with time longer, and trace elements concentration values increase at the same location. Trace element Cd concentrations are much higher in the vicinity of fly disposal site than that far away from the disposal sites. The concentrations of trace element Cd in the groundwater exceed the maximum allowable drinking water concentration values. It provides theoretical evidence for quantitative assessment soil-water quality of trace elements transport on environment pollution.