[Salinity change and its impact on heavy metals during beach soil leaching and desalination]

The salinity ion in soil pore water and the heavy metal content in soil as well as the heavy metal speciation were investigated in various stages of desalination during an experiment of leaching beach soil. Results show that salinity ion including Na+, K+, Mg2+, Ca2+, Cl- and SO4(2-) decreased by 80.3%, 73.5%, 86.6%, 90%, 81.8%, 98.2%. respectively compared to pre-leaching. The amount of total salt decreased by 81.6%. However, the main chemical compound in pore water was NaCl throughout the leaching experiment. The pH value of pore water increased with leaching time. Besides, the reductions of heavy metals after leaching were: Cd 26.6%, Pb 22.8%, Cu 16.9%, Cr 7.9%, Zn 9.1%. The concentrations of Pb, Cr, Cu, Zn and Cd in carbonate bound form decreased by 77.8%, 61.7%, 68.4%, 67.1% and 7.1% respectively. The contents of Cd and Pb bound to Fe-Mn oxide decreased by 49.1%, 23.5% respectively. The different mobility of salinity ions in the pore water resulted in the proportion change of each ion. Meanwhile the Eh value of the soil changed in the leaching process. All these factors resulted in the change of heavy metal speciation and the removal of heavy metals in the soil.