Abstract
In this study, preparation of Eichhornia crassipes stem biochar (ECSBC) was optimized and applied for the removal of Cd2+ from aqueous solution. To obtain the best adsorption capacity of ECSBC, the response surface methodology (RSM) was used to optimize the preparation conditions of ECSBC (OECSBC). The interactions among heating time (X1), heating temperature (X2) and heating rate (X3) were designed by Box-Behnken Design (BBD) experiments. The software gave seventeen runs experiment within the optimal conditions towards two response variables (removal rate and adsorption capacity for Cd2+). The results showed that the mathematical model could fit the experimental data very well and the significance of the influence factors followed the order as heating temperature (X2) > heating rate (X3) > heating time (X1), and the influence of interaction term is: X1 and X2 (heating time and heating temperature) > X2 and X3 (heating temperature and heating rate) > X1 and X3 (heating time and heating rate). Based on the analysis of variance and the method of numerical expected function, the optimal conditions were heating time of 2.42 h, heating temperature of 393 °C, and heating rate of 15.56 °C/min. Under the optimum conditions, the predicted the maximum removal rate and adsorption capacity were 85.2724% and 21.168 mg/g, respectively, and the experimental value of removal rate and adsorption capacity for Cd2+ were 80.70% and 20.175 mg/g, respectively, the deviation from the predicted value were 5.36% and 4.69%. The results confirmed that the RSM can optimize the preparation conditions of ECSBC, and the adsorption capacity of OECSB was improved.
Highlights
Biochar (BC), a carbon-rich solid which is defined as “a solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment” and produced from various feedstocks, such as wood biomass, animal manure, crop residues, and solid wastes[1,2]
Lot of studies have used Eichhornia crassipes as adsorbent for heavy metal removal[31,32,33,34], while no study has been reported on preparation conditions of biochar which from Eichhornia crassipes stem for the adsorption of heavy metals from aqueous solutions by using an optimization method, for instance Box-Behnken design (BBD), a subset of response surface methodology
When the heating time increased to 5 h, the removal rate and adsorption capacity of Cd2+ were 96.8% and 9.68 mg/g, respectively
Summary
Biochar (BC), a carbon-rich solid which is defined as “a solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment” and produced from various feedstocks, such as wood biomass, animal manure, crop residues, and solid wastes[1,2]. Many scholars have done a lot of research on the components and structural characteristics of biochar under various pyrolysis conditions These results show that heating temperature, heating time and heating rate are the three most important factors in the preparation of biochar[9,10,11,12]. Lot of studies have used Eichhornia crassipes as adsorbent for heavy metal removal[31,32,33,34], while no study has been reported on preparation conditions of biochar which from Eichhornia crassipes stem for the adsorption of heavy metals from aqueous solutions by using an optimization method, for instance Box-Behnken design (BBD), a subset of response surface methodology. These results showed that the response surface methodology is suitable for the optimization of conditions in the preparation process of biochar
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