The Solidification/Stabilization And Phytoremediation Of Arsenic Contaminated Soils

Arsenic(As) soil pollution is a worldwide environmental problem, some traditional technology of arsenic soil pollution has been difficult to meet the current situation of pollution, and there are some questions which were complex process, the low efficiency, high cost, secondary pollution, and so on. Therefore, we need a more efficient technology about removing arsenic.In order to address the current difficulty of arsenic contamination soil, this stud y focuses on the controlling of arsenic by combining stabilization/solidification(S/S) technology which target to high concentration(>500 mg As /kg soil) contaminates soils with phytoremediation which target to low concentration(<50 mg As /kg soil). For stabilization/solidification treatment, cement was used as a curing material, fly ash and sand as auxiliary curing material, two indicators include compressive strength and arsenic leaching rate were used to examine the optimal conditions for curing cement. At the same time, three traditional arsenic uptake plants Zeamays L., Pteris vittata L. and Ophiopogon japonicus were selected to enrich arsenic fro m contaminated soils of a arsenic concentration of 10 mg/L and 50 mg/L, arsenic adsorption and growth conditions of the three plants were researched, and then the suitable plant can be determined. Four conclusions were achieved from the study was presented as follows.(1) The optimum compositions and their mixture proportion in the cementing materials for arsenic contaminated soils were Portland Cement(PC), fly ash and river sand at a ratio of 50%: 35%: 7.5%: 7.5%, in which water/ cementing materials(W/ C) was 0.35. The best strength of the solidified samples was 8.5 MPa which was enough to meet the requirements of the landfill. The solidified samples have the possibility to be used for partition walls in a landfill.(2) The biggest concentration of the arsenic leaching from the samples was 220 μg/L even when the solidified crushed to a particle size of less than 0.2 mm. which was far below the criteria of arsenic leaching toxic standard(5 mg/L) in < Identification standards for hazardous wastes – Identification for extraction toxicity >(GB50833 — 2007). Take the fact that in practice it is difficult to break the solidified to such a small particle diameter as 0.2 mm in to consideration, the solidifying and stabilizing was energy saving and it won’t bring the second pollution.(3) Zeamays L., Pteris vittata L. and Ophiopogon japonicus had some sort of As adsorption capacity and the As accumulation in the three plants reached 10- 20 mg/kg when planted in As contaminated soils for 20 days. The highest arsenic content of Pteris vittata L. always accumulated in the root. There was a little difference of the arsenic content between stem and leaf. Therefore, the highest arsenic absorption mainly in the roots of Pteris vittata L., thus weak transportation arsenic ability of the part up away from the roots could be supposed. The alpine environment of northeast of China makes some injury to Pteris vittata L. and then affecting the adsorption of arsenic from contaminated soils.(4) Ophiopogon japonicus had the largest arsenic adsorption capacity in three selected plants, but it is not an ideal plant for arsenic enrichment due to its low biomass and weak growth ability. Zeamays L. had some sort of As adsorption capacity and had some advantages such as short growth cycle, low cost, thus it was appropriate to be applied in the contaminated sites in the alpine regions by continuously seeded and harvested.