Response Surface Optimization of Quarry Pit Soil Washing and Fe Dissolution Kinetics

Environmental pollution by quarry mining activities has proven to be harmful, mitigating these pollution levels by soil washing may not be effective for all pollution sites. Therefore, it is necessary to optimize these processes and identify the leaching mechanism. Quarry site soil sample was obtained from quarry pit. Physicochemical properties; specific gravity, particle size, porosity, elemental composition and pH were determined. The optimum leaching conditions were obtained following response surface methodology (RSM) approach using central composite design. Four (4) factors, particle size, time, agitation rate and solvent concentration were studied in twenty (20) experiments. Following optimization, the highest dissolution rate was observed to be 82 % with the reaction conditions of agitation rate (175 rpm), time (35 mins) and particle size (335 mm). The model’s P-values were less than 0.05 while the correlation regression (R2) value of 0.7169 was obtained. The rate constants for the surface chemical reaction process (Ks) and the diffusion-controlled process (Kd) of Fe ranged from 0.007053-0.008023 min-1 for (Ks), and 0.730567-0.912173 min-1 for (Kd). The dissolution process was identified to be influenced by the diffusion-controlled mechanism having a rate constant value of > 0.9. The findings of this study will be helpful in mine reclamation and revision of soil washing protocol in the study area.