Effects of swine manure biochar on sorption equilibrium of cadmium and zinc in sandy soils
2021
Wellyton Santos de Assis | Elisamara Caldeira do Nascimento | Brenda D’Acunha | Oscarlina Lúcia dos Santos Weber | Eliana Freire Gaspar Dores | Eduardo Guimarães Couto
Swine manure is an agricultural waste that can increase soil fertility. However, this residue has a high content of heavy metals, particularly zinc (Zn) and cadmium (Cd), that are not only toxic to plants and soil organisms but they also pose a great threat to human health due to the potential accumulation of these metals through the food chain. Transforming swine manure into biochar and adding it to soils can improve the soil’s capacity to retain heavy metals. The main objective of this research was to study the capacity of sandy soils mixed with different doses of swine manure biochar (SMB) to retain Cd and Zn as well as to evaluate the sorption equilibrium of these metals. Sorption essays were performed by adding solutions of Zn (ZnCl2) or Cd (CdCl2) at different concentrations (0, 2.5, 5, 10, 50 and 100 mg L-1) to soil samples mixed with different doses of SMB (0, 0.25, 0.75, 1.5, and 3.0 % (w/w)). The data were modelled using both Langmuir and Freundlich adsorption isotherm models to describe the adsorption processes. The data were best represented by the Langmuir model (R2>0.97), indicating a mono-layer sorption to the surface. Results showed that sorption capacity of Zn and Cd increased with the dose of SMB, improving metal retention. The Langmuir constant (KL) for soil without SMB for Cd and Zn were 0.01 L mg-1 and 0.05 L mg-1, respectively. With the highest dose of SMB, KL increased to 9.86 L mg-1 and 1.26 L mg-1 for Cd and Zn, respectively. Results suggest that SMB has the potential to mitigate Zn and Cd contamination of sandy soils.
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