Comparison of Phosphate Materials for Immobilizing Cadmium in Soil

Abstract

A study was conducted to compare the effects of phosphate (P) materials in reducing cadmium extractability. Seven P materials (commercial P fertilizers--fused phosphate (FP), 'fused and superphosphate' [FSP], and rock phosphate [RP]; P chemicals--Ca[H(2)PO(4)](2).H(2)O, [NH(4)](2)HPO(4), KH(2)PO(4), and K(2)HPO(4)) were selected for the test. The selected P source was mixed with Cd-contaminated soil at the rate of 0, 200, 400, 800, and 1,600 mg P kg(-1) under controlled moisture conditions at 70% of water holding capacity, then incubated for 8 weeks. FP, Ca(H(2)PO(4))(2) H(2)O, KH(2)PO(4), and K(2)HPO(4) significantly decreased NH(4)OAc-extractable Cd (plant-available form) concentrations with increasing application rates. Compared to other phosphate materials used, K(2)HPO(4) was found to be the most effective in reducing the plant-available Cd concentration in soil, mainly due to the negative charge increase caused by soil pH and phosphate adsorption. Contrary to the general information, FSP and (NH(4))(2)HPO(4) increased Cd extractability at low levels of P application (<400 mg kg(-1)), and thereafter Cd extractability decreased significantly with increasing application rate. RP scarcely had an effect on reducing Cd extractability. Ion activity products of CdHPO(4), Cd(OH)(2), and CdCO(3) analyzed by the MINTEQ program were significantly increased by K(2)HPO(4) addition, but the effect of Cd-P compound formation on reducing Cd extractability was negligible. Conclusively, the P-induced alleviation of Cd extractability can be attributed primarily to Cd immobilization due to the increase in soil pH and negative charge rather than Cd-P precipitation, and therefore, alkaline P materials such as K(2)HPO(4) are effective for immobilizing soil Cd.

Effect of Phosphate Addition on Cadmium Precipitation and Adsorption in Contaminated Arable Soil with a Low Concentration of Cadmium

“…1 Cadmium solubility diagram of soil solution at different levels of phosphorus after 8 weeks of incubation at 25°C (When the solubility diagram was plotted, high and low levels of CO 2 were assumed to be 0.03 and 0.0003 atm, respectively, to determine formation of CdCO 3 at different CO 2 concentrations) an increased release of OH-groups and a concomitant increase in soil pH. The increase in pH from P addition has also been demonstrated to enhance negative charge of soil (Hong et al 2010). Our results were similar in that soil negative charge increased with P addition (Fig.…”

“…Total Cd concentration was 5.57 mg kg -1 , and Cd was the only heavy metal that exceeded South Korean national standards. The specific characteristics of the soils used in this study are given in Hong et al (2010).…”

“…adsorption to soil particles (Santillian-Medrano and Jurinak 1975;Street et al 1977;Pierzynski and Schwab 1993;Naidu et al 1994;Chen et al 1997;Mandjiny et al 1998;Boisson et al 1999;McGowen et al 2001;Seamon et al 2001;Bolan et al 2003;Hong et al 2008Hong et al , 2010Hong et al , 2014. Cadmium minerals such as Cd 3 (PO 4 ) 2 and CdCO 3 are more geochemically stable and immobile in the soil environment than Cd 2?…”

“…However, some studies have reported that Cd 2? adsorption had a greater effect than Cd precipitation in soils with inherently low concentrations of Cd (Bolan et al 2003;Hong et al 2008Hong et al , 2010Hong et al , 2014.…”

Effect of Phosphate Fertilizer and Manure in Reducing Cadmium Phytoavailability in Radish-grown Soil

“…산성비료인 용과린은 pH가 5.7이고 비 교적 적은 양의 수용성 인산 (27 P g/kg)을 함유하고 있다. 반면 알카리성 비료인 K2HPO4는 pH가 9.5이고 수용성 인 산함량(63 P g/kg)을 상대적으로 많이 함유하고 있다 (Hong et al, 2010). 용과린과 K2HPO4의 시용에 따른 토양 용액 내 카드뮴의 농도는 CdCO3, Cd3(PO4)2, Cd(OH)2, CdHPO4에 대하여 불포화상태로 존재하고 있었다 (Fig.…”