Highlights

• Chicken manure biochar was modified by sulfur, hydroxyapatite and MnFe₂O₄ respectively.

• The maximum Cd²⁺ adsorption capacity of modified biochar significantly increased.

• Sulfur modified biochar decreased the concentration of Cd in shoots of brassica chinensis.

Biochar is thought to be good sorbent for heavy metal and exploring ways to increase the efficiency of heavy metal adsorption by biochar is of great importance. Chicken manure biochar was modified with sulfur, hydroxyapatite and MnFe₂O₄ respectively.

Figure 1 Graphic abstract

The Cd²⁺ adsorption isotherms of sulfur modified chicken manure biochar (SCMB), hydroxyapatite modified chicken manure biochar (HCMB) and MnFe₂O₄ modified chicken manure biochar (FMCMB) was better fitted by Freundlich model, while the Cd²⁺ adsorption by pristine chicken manure biochar (CMB) was well fitted by Langmuir model. The maximum Cd²⁺ adsorption capacity of SCMB, HCMB, FMCMB and CMB was 188.20, 111.53, 109.94 and 19.65 mg·g^-1 respectively. Quantitative analysis of Cd²⁺ adsorption mechanism by biochar showed that the contribution of ion exchange for Cd²⁺ adsorption of CMB accounted for 58%, while SCMB, HCMB and FMCMB decreased to only 12%, 8% and 4% respectively. Meanwhile, the contribution of precipitation, complexion and metal-Cπ coordination for Cd²⁺ adsorption increased after modification.

Figure 2 Contribution of different adsorption mechanisms of different biochar to Cd²⁺ adsorption. Figure (a) is the adsorption contribution value; Figure (b) is the adsorption contribution rate

Pot experiment showed that application of SCMB significantly increased soil pH value, decreased the bioavailable Cd in soil and Cd uptake by brassica chinensis shoots, suggesting that SCMB can be a potential material for the safety use of Cd contaminated agricultural soil.

Table 1 pH value and concentration of DTPA-extractable Cd in soil and Cd concentration in plant tissue (Values are mean ± standard deviation. Values followed by different letters within a column indicate significant difference (P<0.05) at LSD test)

posted by Sun Lijuan from Eco-environment  Protection Research Institute