Optimization of preparation conditions for biochar derived from water hyacinth by using response surface methodology (RSM) and its application in Pb2+ removal

In this study, response surface method (RSM) was adopted to optimize the preparation conditions of water hyacinth biochar. The interaction on Pb2+ adsorption performance between the three basic preparation conditions of heating time (X-1), heating temperature (X-2) and heating rate (X-3) were designed by Box-Behnken Design (BBD). The results showed that the mathematical model can fit the experimental data well. The significance of a single factor affecting followed by X-2 > X-3 > X-1, and the interactive items as follows: X1X2 > X2X3 > X3X1. Through the analysis of variance and the numerical expectation function method, the optimal heating time is 2.65 h, heating temperature is 433 degrees C, and heating rate is 19.96 degrees C/min. The water hyacinth biochar was prepared under optimized conditions (OWHBC) to adsorb 50 mg/L Pb2+ solution. The actual experiment value of adsorption capacity (q) for Pb2+ was 24.94 mg/g, the predicted value of the model was 24.95 mg/g, and the error was only 0.02%. The maximum theoretical adsorption capacity (Q(m)) obtained with the Langmuir model were 195.24 mg/g for WHBC (prepared at center values of preparation conditions from single-factor experiments: 3 h, 400 degrees C, and 20 degrees C/min) and 251.39 mg/g for OWHBC, respectively. Through the determination of pH and specific surface area of biochar before and after optimization, it is proved that the RSM is feasible to optimize the preparation conditions of biochar. The results showed that RSM could optimize the preparation conditions of water hyacinth biochar and improve the adsorption ability of OWHBC to Pb2+.