Geo-environmental and mechanical behaviors of As(V)and Cd (Ⅱ)co-contaminated soils stabilized by goethite nanoparticles modified biochar

Goethite nanoparticles modified biochar(FBC)could address the weak effectiveness of conventional biochar commonly to process heavy metal(loids)(HMs)co-contamination with different charges.However,few studies have focused on the change of soil mechanical properties after stabilization.In this study,FBC was synthesized to stabilize simultaneously arsenic(As(V))(anions)and cadmium(Cd (Ⅱ))(cations)in co-contaminated soils.Batch adsorption,leaching toxicity,geotechnical properties and micro-spectroscopic tests were comprehensively adopted to investigate the stabilization mechanism.The results showed that FBC could immobilize As(V)mainly through redox and surface precipitation while stabilizing Cd (Ⅱ)by electrostatic attraction and complexation,causing soil agglomeration and ultimately making rougher surface and stronger sliding friction of contaminated soils.The maximum adsorption capacity of FBC for As(V)and Cd (Ⅱ)was 31.96 mg g^(−1) and 129.31 mg g^(−1),respectively.Besides,the dosages of FBC required in contaminated soils generally were approximately 57%higher than those in contaminated water.FBC promoted the formation of small macroaggregates(0.25-2 mm)and the shear strengths of co-contaminated soils by 21.40%and 8.34%,respectively.Furthermore,the soil reutilization level was significantly improved from 0.14-0.46 to 0.76-0.83 after FBC stabilization according to TOPSIS method(i.e.,technique for order preference by similarity to an ideal solution).These findings confirm the potential of FBC in immobilizing As(V)and Cd (Ⅱ)of co-contaminated soils and provide a useful reference for green stabilization and remediation of HMs co-contaminated sites.

Biochar alleviates metal toxicity and improves microbial community functions in a soil co-contaminated with cadmium and lead

Soil amendment with biochar alleviates the toxic effects of heavy metals on microbial functions in single-metal contaminated soils.Yet,it is unclear how biochar application would improve microbial activity and enzymatic activity in soils co-polluted with toxic metals.The present research aimed at determining the response of microbial and biochemical attributes to addition of sugarcane bagasse biochar(SCB)in cadmium(Cd)-lead(Pb)co-contaminated soils.SCBs(400 and 600°C)decreased the available concentrations of Cd and Pb,increased organic carbon(OC)and dissolved organic carbon(DOC)contents in soil.The decrease of metal availability was greater with 600°C SCB than with 400°C SCB,and metal immobilization was greater for Cd(16%)than for Pb(12%)in co-spiked soils amended with low-temperature SCB.Biochar application improved microbial activity and biomass,and enzymatic activity in the soils co-spiked with metals,but these positive impacts of SCB were less pronounced in the co-spiked soils than in the single-spiked soils.SCB decreased the adverse impacts of heavy metals on soil properties largely through the enhanced labile C for microbial assimilation and partly through the immobili-zation of metals.Redundancy analysis further confirmed that soil OC was overwhelmingly the dominant driver of changes in the properties and quality of contaminated soils amended with SCB.The promotion of soil microbial quality by the low-temperature SCB was greater than by high-temperature SCB,due to its higher labile C fraction.Our findings showed that SCB at lower temperatures could be applied to metal co-polluted soils to mitigate the combined effects of metal stresses on microbial and biochemical functions.

Effects of biochars on the bioaccessibility of phenanthrene/pyrene/zinc/lead and microbial community structure in a soil under aerobic and anaerobic conditions

The immobilization of co-contaminants of organic and inorganic pollutants by biochar is an efficient remediation strategy. However, the effect of biochar amendments on the bioaccessibility of the co-contaminants in dry versus flooded soils has rarely been compared. In batch experiments, bamboo-derived biochar（BB） had a higher sorption capacity for phenanthrene（Phe）/pyrene（Pyr）/zinc（Zn） than corn straw-derived biochar（CB）, while CB had a higher sorption capacity for lead（Pb） than BB. After 150 days of incubation, the amendments of 2% CB, 0.5% BB and 2% BB effectively suppressed the dissipation and reduced the bioaccessibility of Phe/Pyr by 15.65%/18.02%, 17.07%/18.31%and 25.43%/27.11%, respectively, in the aerobic soils. This effectiveness was more significant than that in the anaerobic soils. The accessible Zn/Pb concentrations were also significantly lower in the aerobic soils than in the anaerobic soils, regardless of treatments.The Gram-negative bacterial biomass and the Shannon–Weaver index in the aerobic soil amended with 2% CB were the highest. The soil microbial community structure was jointly affected by changes in the bioaccessibility of the co-contaminants and the soil physiochemical properties caused by biochar amendments under the two conditions. Therefore, dry land farming may be more reliable than paddy soil cultivation at reducing the bioaccessibility of Phe/Pyr/Zn/Pb and enhancing the soil microbial diversity in the short term.