Kinetics and isotherm modeling of azoxystrobin and imidacloprid retention in biomixtures

The paper reports the kinetics and adsorption isotherm modeling for imidacloprid (IMIDA) and azoxystrobin (AZOXY) in rice straw (RS)/corn cob (CC) and peat (P)/compost (C) based biomixtures. The pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich and intraparticle diffusion models were used to describe the kinetics. The adsorption data were subjected to the Langmuir and the Freundlich isotherms. Results (r(Adj)(2) values) suggested that the modified Elovich model was the best suited to explain the kinetics of IMIDA sorption while different models explained AZOXY sorption kinetics in different biomixtures (PFO in RS + C and RS + P; PSO in CC + P and Elovich in CC + C). Biomixtures varied in their capacity to adsorb both pesticides and the adsorption coefficient (K-d) values were 116.8-369.24 (AZOXY) and 24.2-293.4 (IMIDA). The Freundlich isotherm better explained the sorption of both pesticides. Comparison analysis of linear and nonlinear method for estimating the Freundlich adsorption constants was made. In general, r(Adj)(2) values were higher for the nonlinear fit (AZOXY = 0.938-0.982; IMIDA = 0.91-0.970) than the linear fit (AZOXY = 0.886-0.993; IMIDA = 0.870-0.974) suggesting that the nonlinear Freundlich equation better explained the sorption. The rice straw-based biomixtures performed better in adsorbing both the pesticides and can be used in bio-purification systems.