Vermicompost Regulates Arsenic(V) Adsorption in Loam and Sandy Loam Soils

Amendments viz., vermicompost, farmyard manure, and rock phosphate may support higher arsenic(V) adsorption in loam and sandy loam soils. The present study explored arsenic(V) adsorption behavior and surface mechanisms in the vermicompost-amended loam (VC-L) and sandy loam (VC-SL) soils. The As(V) adsorption by the VC-L and VC-SL soil was found to increase from 4.9 to 32.65 µg g−1 and from 3.8 to 28.74 µg g−1, respectively, with an increase in As(V) concentration from 5 to 100 µg mL−1. The R2 and RL (adsorption parameter) values at different As(V) concentration (5–100 µg mL−1) were fitted with linear and non-linear Langmuir models with reference to equilibrium of As(V) adsorption by the VC-L and VC-SL soil. Results on adsorption kinetics showed well-fitting of linear pseudo-second order (LPSO), non-linear pseudo-first order (NLPFO) and non-linear pseudo-second order (NLPSO) kinetic models on As(V) adsorption by the VC-L and VC-SL soil supported by closer calculated qe values to experimental qe values and high R2 values. Further, results showed high As(V) retention and low mobility in the VC-L and VC-SL soil due to enriched organic soil matter and active participation of O─H, COOH, Fe─O/Fe─OH and C─O─C functional groups in As(V) adsorption via surface complexation, hydrogen bonding and electrostatic interactions. The overall results on kinetics, isotherms and IR-Spectroscopy provided mechanistic support of better surface adsorption and retention capability of the VC-L soil for As(V) as compared to the VC-SL soil. The findings may lead to vermicompost-based arsenic immobilization in arsenic contaminated soils.