Characterization of phosphorus engineered biochar and its impact on immobilization of Cd and Pb from smelting contaminated soils

Abstract

Biochar has been used as an amendment to immobilize toxic metals (TMs) and increase nutrient content in the contaminated soil. In this study, Ca(H2PO4)2-engineered swine manure biochar (PSMB) and swine manure biochar (SMB) were prepared and investigated to evaluate their effects on the availability of toxic metals (Cd and Pb) and soil nutrient content in Fengxian (FX)- and Kunming (KM)-contaminated soils through incubation experiment. The soil samples were collected at 0–20 cm depth from two contaminated farmlands close to abandoned Pb smelters, which are located in FX and KM. Swine manure was obtained from the rural hog lot in Yangling, China. Each biochar (SMB and PSMB) was mixed with the air-dried soil samples (FX and KM) at a dosage of 1% and 3% w/w, respectively. Then, a portion of 3 kg of the mixture was placed in plastic pots and incubated for 30 days in a greenhouse. After the soil incubation experiment, pot experiments were performed in a greenhouse of Northwest A&F University, Yangling, China. Adding PSMB at a rate of 3% maximally decreased the concentrations of DTPA-extractable Cd (34.02 and 47.73%) and Pb (18.70 and 24.58%) in FX and KM soil. The BCR data revealed that the percentage of acid-soluble Cd and Pb fraction in FX and KM soils remarkably decreased whereas the percentages of residual Cd fraction and reducible Pb fraction in FX and KM soils significantly increased in all the biochar-amended soils compared with control. To confirm these results, a pot experiment was conducted to investigate the effects of amendments on growth and uptake of toxic metals in Chinese cabbage (Brassica rapa L. spp. pekinensis). The results showed that the addition of PSMB3% significantly (P < 0.05) increased the biomass of plants and reduced the absorption of toxic metals in plant. The results revealed that the dry biomass increased and the absorption of toxic metals decreased in plants. All treatments of biochar were beneficial and application of PSMB 3% was most effective in enhancing plant biomass and reducing the accumulation of toxic metals in the plants.