Adsorption Characteristics and Mechanisms of Walnut Shell Biochar on Pb2+and Zn2+
In order to further find more effective Pb2+,Zn2+ adsorption materials and realize resource utilization of agricultural and forestry wastes,in this study,walnut shell was used as raw material to produce biochar at 600℃by limited oxygen cracking method.The effects of biochar dosage,initial solution pH value,adsorption time,adsorption temperature and initial concentration on the adsorption of Pb2+and Zn2+were investigated.The adsorption of Pb2+ and Zn2+ by walnut shell biochar was characterized by FTIR.At the same time,three typical isotherm adsorption models and three commonly used adsorption kinetic models were used to analyze and discuss the adsorption effect.The results show that the optimal pH value of Pb2+ adsorption by walnut shell biochar is 5,the dosage is 0.1 g/L,the adsorption equilibrium is reached at 720 min,and the maximum adsorption capacity is 27.172 mg/g.Theoptimal pH valueof walnut shell biochar for Zn2+ is 6,the dosage is 0.2 g/L,the adsorption equilibrium is reached at 480 min,and the maximum adsorption capacity is 10.8 mg/g.The adsorption process of Pb2+ by walnut shell biochar can be well fitted by Elovich kinetic equation and Langmuir-Freundlich isotherm equation,indicating that the adsorption process is a diffusion-limited heterogeneous chemisorption process.However,the adsorption process of Zn2+ by walnut shell biochar can be better fitted by Elovich kinetic equation and Freundlich isotherm adsorption equation,which indicates that the adsorption of Zn2+ is heterogeneous multilayer adsorption.The adsorption mechanisms of Pb2+and Zn2+by biochar are mainly coordination and electrostatic attraction.
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