Effects of pristine and engineered biochars of pistachio-shell residues on cadmium behavior in a cadmium-spiked calcareous soil

Abstract

ABSTRACTUtilization of biochars (BCs) surfaces as suitable substrates for placement of nanoscale zero-valent iron (nZVI) not only can increase the stability of nZVI, but also can improve biochar sorption mechanisms for various pollutants in the environment. In this research, pistachio-shell residues (R), pistachio-shell residues biochar (B), and pistachio-shell residues biochar coated by nZVI (BN) were applied to a Cd-spiked (200 mg Cd kg−1 soil) calcareous soil at three levels (0.5, 2, and 4%). After the incubation process (90 d), the soil cadmium (Cd) behavior was examined using desorption kinetic and sequential extraction experiments. The results showed that application of BN was more effective compared with the other two amendments in decreasing Cd desorption. Reduction of Cd mobility from 70.8% in the unamended sample to 60.2, 50.8 and 41.7% in the R, B, and BN treated samples, respectively, showed the high effectiveness of BN in Cd stabilization, as compared to B and R. The existence of ion exchange, surface complex formation, surface precipitation or co-precipitation processes as possible mechanisms by BCs, along with possible processes of adsorption and surface complex formation from nZVI, leads to higher efficiency in Cd stabilization using engineered BCs compared to pristine BCs.