Adsorption of phosphate from aqueous solution by sludge biochar
In this paper,the adsorption characteristics of phosphate by sludge biochar(SDBC)were investigated with batch equilibrium method using SDBC prepared from residual sludge(RS)of a wastewater treatment plant.The effects of factors such as dosage of SDBC and pH of solution on phosphate adsorption by SDBC were investigated,and the conditions affecting phosphate adsorption were optimized by response surface methodology(RSM).The mechanism of phosphate adsorption by SDBC was investigated by combining the experimental results with the characterization data.The results showed that the kinetics of phosphate adsorption on SDBC conformed to the Elovich(R2=0.984)equation,which indicated that the phosphate adsorption on SDBC was a non-homogeneous diffusion process with multiple reactions acting together.The Langmuir(R2=0.980)and Langmuir-Freundlich(R2=0.979)equations could well describe the phosphate adsorption on SDBC,and the maximum adsorption capacity estimated from the Langmuir equation was 4.508mg/g.The Langmuir-Freundlich model was fitted with a small homogeneous phase index n(1.143),indicating that the adsorption sites on SDBC were not uniformly distributed,and there were interaction forces between SDBC and phosphate.The optimal initial pH value for phosphate adsorption on SDBC is 4.0～5.0.The optimal dosage for phosphate adsorption on SDBC is 8g/L.The optimum conditions for phosphate adsorption by SDBC were obtained by RSM analysis with a dosage of 5g/L,an initial phosphate concentration of c0 of 10mg/L,and a pH of 5.0.The possible mechanisms of phosphate adsorption by SDBC included electrostatic adsorption,co-precipitation,replacement,ligand exchange,and pore filling.
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