Basic characterization, separation of heavy metals from harbor sediments and the potential uses
Contaminated sediments in the harbors remain being a significant issue during dredging operations. Numerous methods have been suggested in recent years for remove, treating and beneficial uses of harbor sediments. In this research, the basic characteristics and the geochemistry of metals in the sediments were studied, and which were subjected to pH-dependent leaching test, percolation test and column test. The results of experimental leaching tests of harbor sediments are compared with computer calculations, the LeachXS expert system. This computer program allows to predict the metal concentrations and the pH of leaching solution at equilibrium, along with the minerals that precipitate and the organic characteristics react with the metal ions forming into stable organic metal compounds. The result of laboratory research showed that the content of heavy metals contaminants is primarily governed by the grain size. The optimum separation process was approached through hydrocyclone separation and sieving. The sediments might be classified as a clean sand product (d ≧ 63 µm) of 26.1% which could be directly reused, and a contaminated fine sediment with silt and clay fraction (d < 63 µm) of 73.9%. Heavy metal contaminants tend to adsorb on the fine sediments, and thus further treatments such as chemical washing and stabilization/modification are needed before deposition and recycling. Results from the chemical washing (extraction) technique showed that under 0.01M EDTA and H2SO4 as reagents with a sediment/reagent ratio of 1/10, contact time of 30 minutes, the Cu removal efficiency was 30.7% and 32.6%, respectively; the Zn removal efficiency was 12.6% and 36.8%, respectively. Besides that, stabilization/modification processes (adding with soil amelioration products) can make the heavy metal containing sediment to be low-matrix leachability and which might be reused as construction material. Thus, this research projects might provide a basic understanding, and the statistic correlation among the sediment characteristics, metal concentration and the possible controlling factors.
Sediments, leaching tests, hydrocyclone separation