Simulation study on geochemical reaction of PRB in treating acid mine drainage

With the rapid development of industry, the demand for mineral resources also increases. Acid mine drainage(AMD)produced in the mining process is seriously harmful to the surrounding environment. The Permeable Reactive Barrier(PRB)utilizes the natural hydraulic gradient to intercept the pollution plume by placing reactive materials under it, and this technology has become one of the means to effectively deal with AMD. In order to study the effect of chemical reaction blockage in the PRB on its lifespan, a box device with a scale of 60 cm×15 cm×20 cm was built to simulate the process of limestone PRB for AMD treatment. Based on the data obtained from the box experiment, a new geochemical algorithm was developed using the chemical reaction transport model theory to describe the chemical reactions that may occur during the PRB treatment of AMD. Through the coupled simulation of MODFLOW and RT3D,the maximum lifetime of PRB to effectively treat pollutants is predicted. The results show that(1) The acid neutralization ability of limestone in the PRB and its removal effect on total iron and Al³⁺ in acid wastewater are effectively simulated, and the chemical blocking process of the PRB system is well reflected.(2) The simulation results are in good agreement with the actual values. The maximum errors between the measured and predicted pH values of the effluent at three different locations in the inlet area, the middle area and the outlet area are 0.38,0.30 and 0.29 respectively. The maximum errors between the actual value and the predicted value of the total iron concentration are 1.570,0.120 and 0.124 mg/L respectively. The maximum error between the actual value and the predicted value of Al³⁺ concentration is 1.010,0.374 and 0.160 mg/L respectively.(3) The prediction results show that the total iron and Al³⁺ contents in the effluent of this laboratory-scale PRB device are the lowest in the first 30 days, and the removal effect is the best, and the removal capacity gradually weakens with time. With reference to the limit of groundwater quality standard, it is judged that the limestone PRB can effectively treat total iron with a maximum life of 132 days, and effectively treat Al³⁺ with a maximum life of 63 days.