Ferric iron chloride (FeCl<3>) was selected as a promising washing chemical to extract CA from paddy soils based on a screening test with various chemicals. The primary mechanism of CA extraction by FeCl<3> was proton release coupled with hydroxide generation, as Fe hydroxide is a sparingly-soluble compound. Washing with FeCl<3> led to the formation of CA-chloride complexes, enhancing CA extraction from the soil. We developed a new three-step soil washing method to remediate CA-contarninated paddy fields with FeCl<3>. The method was comprised of 1) chemically washing the field soil with a FeCl<3> solution in situ;2) washing the treated soil with water to eliminate residual CA and FeCl<3>;and 3) on-site treatment of wastewater using a portable wastewater treatment system. Concentrations of CA in the treated water were below Japans environmental quality standard (0.01mg(Cd)·L<-1>), and CA removal efficiency from a paddy soil was approximately 45％ suggesting the effectiveness of our soil-wash method inremediating CA- contaminated paddy fields.
Cadmium chemical speciation paddy soil rice soil washing
Tomoyuki Makino Y Maejima Y Sakurai H Takano T Kamiya T Itouc N Sekiya K Kondo
Soil Environmental Division, National Institute for Agro-Environmental Sciences(IAES), Tsukuba, 305- Soil Environmental Division, National Institute for gro- Environmental Sciences (NIAES), Tsukuba, 30 Soil Environmental Division, National Institute for Agro-Environmental Sciences (NIAES), Tsukuba, 30 Research & Development Center, Taiheiyo Cement Corp, Sakura, 285-8655, Japan Depertment of Environment Conservation, Nagano Agricultural Research Center, Suzaka, 382-0072, Japan