In situ immobilisation of toxic metals in soil using Maifan stone and illite/smectite clay

Abstract

Clay minerals have been proposed as amendments for remediating metal-contaminated soils owing to their abundant reserves, high performance, simplicity of use and low cost. Two novel clay minerals, Maifan stone and illite/smectite clay, were examined in the in situ immobilisation of soil metals. The application of 0.5% Maifan stone or illite/smectite clay to field soils significantly decreased the fractions of diethylenetriaminepentaacetic acid (DTPA)-extractable Cd, Ni, Cr, Zn, Cu and Pb. Furthermore, reductions of 35.4% and 7.0% in the DTPA-extractable fraction of Cd were obtained with the Maifan stone and illite/smectite clay treatments, respectively, which also significantly reduced the uptake of Cd, Ni, Cr, Zn, Cu and Pb in the edible parts of Brassica rapa subspecies pekinensis, Brassica campestris and Spinacia oleracea. Quantitatively, the Maifan stone treatment reduced the metal uptake in B. rapa ssp. Pekinensis, B. campestris and S. oleracea from 11.6% to 62.2%, 4.6% to 41.8% and 11.3% to 58.2%, respectively, whereas illite/smectite clay produced reductions of 8.5% to 62.8% and 4.2% to 37.6% in the metal uptake in B. rapa ssp. Pekinensis and B. campestris, respectively. Therefore, both Maifan stone and illite/smectite clay are promising amendments for contaminated soil remediation.

Figure 1

Effects of Maifan stone and illite/smectite clay on the concentrations of toxic metals in the edible parts of Brassica rapa spp. pekinensis. Error bars represent standard deviations, and the means with different letters are significantly different from each other (p < 0.05).

Figure 2

Effects of Maifan stone and illite/smectite clay on the concentrations of toxic metals in the edible parts of Brassica campestris. Error bars represent standard deviations, and the means with different letters are significantly different from each other (p < 0.05).

Figure 3

Effects of Maifan stone on the concentrations of toxic metals in the edible parts of Spinacia oleracea. Error bars represent standard deviations, and the means with different letters are significantly different from each other (p < 0.05).