Optimization of Fe and Mn Removal from Coal Acid Mine Drainage (AMD) with Waste Biomaterials: Statistical Modeling and Kinetic Study

The main characteristics of coal acid mine drainage (AMD) are a low pH and high concentrations of sulfate and different metallic ions. Response surface methodology using the central composite rotatable design (CCRD) model was used to optimize the parameters for AMD remediation with aquaculture farming waste [shrimp shell (SS) and mussel byssus (MB)]. SS was chosen due to its high chitin (a metal sorbent) and calcium carbonate (an acidity neutralizing agent) content, and MB because of its potential synergistic effect for the treatment. The coefficient of determination and standard error results from the analysis of variance have shown the model to be adequate. The predicted values were in good agreement with the experimental values. The best experimental conditions established from the statistical study were 136 rpm, 11.46 g L −1 SS and 71.6 g L −1 MB. CCRD can efficiently be applied for modeling the AMD remediation with biomaterials and is an economical way of obtaining the maximum amount of information in a short period of time with the fewest number of experiments. Additionally, five kinetic models, i.e., pseudo-first-order, pseudo-second-order, intraparticle diffusion, Bangham and Elovich equation, were tested to investigate the adsorption mechanisms. The kinetic studies revealed that a 200 min contact time is sufficient to transform AMD into water suitable for non-potable reuse. The pseudo-second-order model provided the best fitting of the experimental data, indicating a chemical adsorption mechanism. This research shows the suitability of the proposed treatment, and the information is valuable for designing a low-cost remediation process for AMD. Graphical Abstract