Experimental study to improve the mechanical properties of iron tailings sand by using MICP at low pH

Abstract

The disposal of iron tailings sand and the reinforcement of tailings ponds are research hot spots locally and abroad. A disposal method without environmental pollution is the key. In this paper, the characterization of a low-pH bacterial solution was discussed, and an microbially induced calcium carbonate precipitation (MICP) spray treatment using a low-pH bacterial solution was proposed to improve the mechanical properties of iron tailings sand. First, a beaker test was carried out to determine the CaCO3 content, changes in pH and bioflocculation generation time of different concentrations of the low-pH bacterial solution. The results showed that the low-pH bacterial solution can lead to more CaCO3 precipitates and a longer bioflocculation generation time than conventional solution. Then, the deactivation pH and bioflocculation generation time were defined and quantified. We discovered that the deactivation pH was not related to the concentration of the bacterial solution but was related to the nutrient supply. The pH of the bacterial solution after the reaction was not related to the pH before the reaction and was stable at approximately 7. The bioflocculation generation time varied with the concentration and pH of the bacterial solution. Second, the biocementation effect was evaluated by permeability tests, water retention tests, raindrop erosion resistance tests, strength tests, wind erosion resistance tests, durability tests, scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. These tests indicated that MICP spray treatment using the low-pH bacterial solution had a much better biocementation effect than conventional treatment. Third, the influence of components in iron tailings sand on the MICP spray treatment was analyzed by comparison with quartz sand. Due to the existence of CaO, a better cementation effect was obtained in iron tailings sand than in quartz sand. This indicated that this method is especially suitable for the solidification of iron tailings sand to suppress dust and reinforce tailings ponds.