Remediation of cadmium contamination in paddy soils by washing with chemicals: selection of washing chemicals.
The efficiencies of neutral salts, strong acids, and chelates were tested for extracting cadmium (Cd) from three paddy soils. The higher the selectivity of the cations of the added neutral salts toward soil adsorption sites, the lower the pH in the extracts and the more soil Cd could be extracted. In addition, soil carbon and nitrogen contents and mineral composition were closely associated with the amount of Cd extracted. Calcium chloride and iron(III) chloride were selected as wash chemicals to restore Cd-contaminated paddy soils in situ. Washing with calcium chloride led to the formation of Cd chloride complexes, enhancing Cd extraction from the soils. The washing also substantially decreased soil levels of exchangeable and acid-soluble Cd, which are the major forms of bioavailable Cd for rice (Oryza sativa L.). The optimum conditions for in situ soil washing were also determined for calcium chloride.
Makino
Tomoyuki
T
National Institute for Agro-Environmental Sciences, 3-1-3, Kannondai, Tsukuba, Ibaraki 305-8604, Japan. michiai@affrc.go.jp <michiai@affrc.go.jp>
Sugahara
Kazuo
K
Sakurai
Yasuhiro
Y
Takano
Hiroyuki
H
Kamiya
Takashi
T
Sasaki
Kouta
K
Itou
Tadashi
T
Sekiya
Naoki
N
D000143:Acids; D000383:Agriculture; D002104:Cadmium; D002122:Calcium Chloride; D002614:Chelating Agents; D005591:Chemical Fractionation; D002712:Chlorides; D052918:Environmental Restoration and Remediation / Q000379:methods*; D005290:Ferric Compounds; D006863:Hydrogen-Ion Concentration; D012275:Oryza; D012987:Soil / Q000032:analysis; D012989:Soil Pollutants
D000143:Acids; D002614:Chelating Agents; D002712:Chlorides; D005290:Ferric Compounds; D012987:Soil; D012989:Soil Pollutants; D002104:Cadmium; D002122:Calcium Chloride; C024555:ferric chloride