Regulation and Mechanism of a Dregs Biochar Matrix Combined with Maifanite on a Soil-Ryegrass System

Abstract

An indoor pot experiment and isothermal adsorption experiment were used to examine the regulation of soil-ryegrass system treatments. For the treatments, Banlangen dregs were selected as a raw material alongside two kinds of biochar (BC300, BC500) prepared by pyrolysis at 300℃ and 500℃ under anoxic conditions. Fe was modified by BC500 (Fe-BC500), which was then combined with maifanite (MFS) as a passivating agent[BC500:MFS (1:1) and Fe-BC500:MFS (1:1)]. Surface pore distribution (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) were used in the analyses. The results showed that treatment with BC300, BC500, Fe-BC500, MFS, BC500:MFS (1:1), and Fe-BC500:MFS (1:1) significantly reduced the Cu and Cd content (2% content in soil) of ryegrass (P<0.05) and significantly increased the biomass of ryegrass. This effect could have resulted from the enhanced chlorophyll content and root activity of the ryegrass. The effect of BC300 was better than the other treatments, which reduced the content of Cu and Cd in the roots of ryegrass by 44.78% and 63.89%, respectively, and in the aboveground biomass by 76.34% and 53.40%, respectively. The biomass of roots was also increased by 327.22%, and the aboveground biomass increased by 504.11%. The Langmuir equation produced the best fit for adsorption effects of BC300, BC500, and Fe-BC500, for which the maximum adsorption capacity for Cu was 8.02, 9.20, and 8.82 mg·g-1, respectively. The maximum adsorption capacity for Cd was 7.97, 8.51, and 7.70 mg·g-1, respectively. The Freundlich equation gave a better fit for the adsorption of MFS. In this case, the maximum adsorption capacity for Cu and Cd was 7.03 mg·g-1 and 6.10 mg·g-1, respectively. BC300 and BC500 mainly passes through their surface hydroxyl, carboxyl, carbonyl, and ester groups; Fe-BC500 mainly passes through its surface hydroxyl group and iron hydroxyl group; MFS mainly passes through its silicon hydroxyl group, hydroxyl group, and carboxyl group on the surface of NaAlSi3O8 and Al2Si2O5(OH)4 and then to repair passivated Cu and Cd contaminated soil effect. Therefore, Banlangen dregs biochar, iron-modified Banlangen dregs biochar, maifanite, and the combination of these materials can be used for the remediation of Cu and Cd contaminated soils, although the mechanism of remediation is different.