Preparation Of MgO Material From Magnesite Tailings And Its Properties

As the shortage of global resource, the environmental pollution is more and more serious, it isurgently necessary for us to furthest recycle resources. In this paper, industrial tailings containingmagnesium (hereinafter referred to as Mg), after being calculated of their components, grinded intopowder and burned appropriately, were taken as the raw material to produce MgO expansive agent.After treatment with magnesite tailings, nanometer MgO was prepared by homogeneous precipitationmethod. The paper focused on the research of the process of producing MgO expansive agent andnanometer MgO, the expansion character of MgO expansive agent in paste, mortar and concrete, andhydration expansion mechanism and hydration dynamics of MgO, the paper established a primaryhydration model of MgO.Using the tailings containing Mg as raw material, the concrete MgO expansive agent of ecotypewas produced, moreover, the character of the expansive agent and the physical character of the pasteblended with the expansive agent were both studied. The standard water consumption of the pasteincreased with the increase of expansive agent ratio, meanwhile, the setting time was prolonged. Thepaste and mortar with the expansive agent expanded fast in the early period, but slowly in the late.With the extension of the setting time, the expansion become bigger; the more the hydration productwas, the bigger theexpansion would be. MgO could effectively refine the pore structure of the paste,increase the ratio of the harmless hole and decrease that of the harmful hole and improve themicrostructure of paste. The reasonable adding of the fly ash can effectively prevented the MgOfrom expanding or shrinking too much.Using the tailings of light roasting magnesite and dolomite as raw material, while ammonia wateras the precipitant, so the nanomter MgO powder of cubic structure could be acquired in the method ofhomogeneous precipitation. The average diameter of the calculated sample is46.88nm. Besides,applications of the nanometer MgO in antibacterial material, catalyst and chemical adsorbentwerediscussed in this paper.The\influence of pH value and maintenance temperature on the degree of MgO hydrating wasanalyzed. In the strong alkaline condition, the ion concentration of the resolution was high in the earlystage and a lot of Mg(OH)2crystal nucleuses were formed in the resolution, MgO hydrated intoMg(OH)2quickly; as the maintenance temperature increasing, the hydration of the MgO becomestronger. When the pH value was12and maintenance temperature was60℃,79.9%of MgO wouldbe hydrated within24h. The hydration degree of MgO in different temperatures and setting times could be calculated with the dynamics equation of solid-phase reaction, and the hydration dynamicsequation of MgOwas G3k=[1-(1-α)1/]2=Kt. The apparent activation energy(E) of MgO in the hydrationreaction in cement was calculated as59.8kJ/mol. Combining the hydration expansion mechanism, adynamics model of MgO was built, which further explained the hydrating process of the MgOexpansive agent: MgO hydrated faster in the early period, but with the extension of the setting time,more and more MgOwas hydrated into Mg(OH)2which gradually covered the MgO particles, so thatthe area of MgO which contacts water molecules was reduced. Therefore, MgO expanded slowly andmildly to compensate the contraction after the stable expansion period.