Evaluation of heavy metals stability and phosphate mobility in the remediation of sediment by calcium nitrate.

Abstract

The injection of oxidants is one of the useful remediation technologies for eliminating hydrogen sulfide (H2 S) and ammonia (NH3 / ) in aquatic sediments. In the current work, the impact of calcium nitrate injection on the release of heavy metals associated with phosphate was evaluated in a column test of sediment with overlying water at a volume ratio of 1:1 for 131days. Sulfide was significantly oxidized by calcium nitrate, as its amount was reduced substantially by 85% from the 20th to the 30th day, with a decrease in the oxidation-reduction potential to -68mV and a simultaneous increase in pH to 9.83. Over 50% of the mobile Zn, Pb, and Cu were reprecipitated in the sediment when the phosphate was partially released. It is proposed that the heavy metal immobilization was related to the phosphate content in the pore water due to the precipitation of heavy metals and phosphorus on the surface of Fe hydroxide particles after oxidation. This is supported by chemical fraction analysis of the heavy metals in the sediment, which indicated increased residual fractions of heavy metals. Our results provide an insight into the remediation of sediment by oxidation with a self-stabilization of heavy metals and phosphate. PRACTITIONER POINTS: Effective removal of sulfide after calcium nitrate injection was achieved. Metal immobilization was related to the phosphate content in pore water. Over 50% of mobile Zn, Pb, and Cu might be reprecipitated in sediment. Oxidizable fraction of heavy metal predominantly transformed to its residual fraction.