In the model analysis of variance, the correlation coefficient of quadratic regression equations of uranium removal efficiency was R2 = 0.7629, which indicated that the model very well fit the actual situation. The F value of 3.58 implied that the model was significant. There was only a 2.99% chance that a model F value this large could occur because of noise. Values of Prob > F less than 0.0500 indicated that the model terms were significant. In this situation, A and A2 were significant model terms. A negative Pred R2 of –0.7962 implied that the overall mean was a better predictor of response than the current model. “Adeq precision” measures the signal-to-noise ratio. A ratio greater than 4 was desirable. The ratio of these uranium removal experiments was 7.747, which indicated an adequate signal. This model can be used to navigate the design space.
The actual and predicted uranium removal efficiency and the response surface plots for relative uranium removal efficiency are plotted in Fig. 2 and Fig. 3, respectively. Fig. 3 depicts the change in uranium removal efficiency due to pH, ultrasonic reaction time, and dosage of zero-valent iron, plotted for the situation in which the ultrasonic power is 500 W.