Effect of moisture condition on the immobilization of Cd in red paddy soil using passivators

ABSTRACT

In this study, the immobilization of cadmium (Cd) was evaluated in red paddy soil amended with four different passivators (biochar, lime (CaO), calcium dihydrogen phosphate (Ca(H₂PO₄)₂) and zeolite (modified with NaOH)) for three moisture regimes (70% water-holding capacity (WHC), continuous flooding (CF) and wetting-drying cycle (WDC)). The results showed that: the pH of the soil was obviously influenced by the moisture regimes and decreased in the general order of CF > WDC > 70% WHC, and the addition of lime and Ca(H₂PO₄)₂ could obviously enhance and reduce the values to some extent, respectively. Flooding condition could enhance soil pH and increase the content of free Fe-oxides, amorphous Fe-oxides and water-soluble organic/inorganic carbon in paddy soil. The efficiency in decreasing the exchangeable Cd of different moisture regimes followed the order: CF > 70%WHC > WDC. CF combined with lime was the most effective treatment for reducing exchangeable Cd. The transformation of Cd fractions mainly occurred between the acid-extractable and reducible fractions in the immobilization experiments. The most effective passivator is Ca(H₂PO₄)₂, and CF is the most favorable regime in promoting the transformation of Cd in red paddy soil from acid-extractable to reducible fraction.

KEYWORDS:

• Cadmium
• red paddy soil
• immobilization
• moisture regime
• biochar

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the GDAS’s Special Project of Science and Technology Development [2017GDASCX-0830], the National Natural Science Foundation of China [Nos. 41701320, 41501298, 51521006], the High-level Leading Talent Introduction Program of Guangdong Academy of Sciences [2060599], the SPICC Program (The Scientific Platform and Innovation Capability Construction Program of GDAS), [2016GDASPT-0105 and 0304], the Innovation-driven Development Capability Construction Program of GDAS [2017GDASCX-0106] , Construction of Innovative Talents for Pollution Control and Management of Heavy Metals in Farmland [2016B070701015], and Key R&D Program of Science and Technology of Hunan Province in China [No. 2015SK2004].