Evaluation of nickel stabilization in a calcareous soil amended with biochars using mathematical adsorption models

Abstract

ABSTRACT Batch adsorption experiments were performed to investigate the effect of different biochars (corn straw biochar (S-CSB), wheat straw biochar (S-WSB), rice husk biochar (S-RHB) and licorice root pulp biochar (S-LRB) each at 3% w/w) application on the kinetics, isotherms and thermodynamic parameters of nickel (Ni) adsorption onto a calcareous soil. The kinetics of Ni adsorption as a function of time was evaluated by seven different kinetic models. Also, the equilibrium adsorption data of Ni were analyzed by the Freundlich, Langmuir, and Temkin adsorption models. Two-constant rate model was best for the description of Ni adsorption kinetic and the S-CSB had the greatest adsorption rate of Ni (a = 841.5 (mg Ni kg−1 h−1)b and b= 0.030 [(mg Ni kg−1)]−1) among all the soil treatments. The Freundlich isotherm model had the best fit for the Ni equilibrium adsorption data, indicating multilayer adsorption. The maximum adsorption capacity of Ni (Qm) was increased by the addition of all the biochars to the soil and the highest amount was observed in S-CSB treatment (1.683 mg Ni g−1). This was mainly attributed to the CSB properties such as high amounts of CaCO3 and phosphorus. The Ni adsorption process onto the calcareous soil was endothermic, spontaneous and irreversible in nature according to the thermodynamic parameters (ΔG, ΔH and ΔS). In conclusion, it seems that the S-CSB was the best treatment for Ni immobilization in the calcareous soil.