Abstract
Little is known about the exact mechanism of cadmium (Cd) immobilization by phosphate (P) in arable soil containing low Cd concentration. This study was designed to describe this mechanism in detail. We determined the phosphorus (P) addition rate allowing Cd to precipitate as Cd minerals in Cd-contaminated arable soils and identified the main species of Cd minerals formed by the reaction of Cd and P, using the chemical equilibrium model MINTEQ. To determine the amount of Cd adsorption to soil adsorbed P, 0 –10,000 mgPL−1 of K2HPO4 solution was reacted with soil, then the P adsorbed soil was reacted with a CdCl2 solution (500 mg Cd L−1). Cadmium might not precipitate as Cd minerals such as Cd3(PO4)2 and CdCO3 with a recommended application rate of P fertilizer in field scale. Cadmium might be immobilized by Cd2+ adsorption instead of precipitation under a low P application system. Phosphate adsorption increased the negative charge of soil and Cd adsorption. The contributions of the increase in pH- and P-induced negative charges to the total increase in the soil negative charge were 93.2 and 6.8%, respectively. The increase in Cd adsorption caused by P adsorption was mainly attributed to the increase in pH-induced negative charge.
Highlights
Various remediation technologies have been applied to cadmium (Cd)-contaminated arable soils to make the crops grown in these soils suitable for human consumption [1,2,3,4,5,6]
The immobilization of Cd with P compounds in soils is caused by various mechanism: (i) the formation of Cd minerals such as Cd3(PO4)2; (ii) Cd2+ adsorption induced by P; (iii) cation exchange; and (iv) surface complexation
Ruangcharus et al Appl Biol Chem (2020) 63:36 containing low Cd concentration, by estimating (1) the P addition rate under which Cd could precipitate as a Cd-P mineral and identify the main species of Cd minerals formed by the reaction of Cd and P; (2) the contribution of negative charge induced by P to C d2+ adsorption in soil
Summary
Various remediation technologies have been applied to cadmium (Cd)-contaminated arable soils to make the crops grown in these soils suitable for human consumption [1,2,3,4,5,6]. In a previous study [4], we suggested that Cd might not be precipitated as Cd-P minerals under 1,600 mg P kg−1 of P addition in soil containing low Cd concentration (total Cd: 5.57 mg kg−1). The soil used for the P and Cd adsorption test was used to determine the contribution of pH-induced negative charge in the soil.
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