The Effect Of Control Parameters On Mg?OH?₂ Preparation By Three-phase Hydration Method

Magnesium hydroxide is been widely used in environmental engineering fields,such as,wastewater treatment,flue gas desulfurization,treatment and disposal of solid waste.The preparation methods include direct precipitation method,hydrothermal method,hydration method and physical method.The traditional hydration method has the limitations of long reaction time and low hydration efficiency.In this thesis,we carried out the three-phase hydration for magnesium hydroxide,and determined suitable control parameters of three-phase hydration.A three-phase hydration equipment was designed and built with main parts of vapor generator,mixing tank and reaction.In the experiment,the hydration effect in three-phase and two-phase hydration was compared firstly.We used Shrinking core model,Semi-Empirical equation and BNG model,and chose Semi-Empirical equation to fit the MgO hydration in this paper.Secondly,the parameters of three-phase hydration reaction in the experiment was adjusted,with the pressure in range of 0.10MPa-0.20MPa,the magnesia slurry density between 5%-15%and magnesia powder as relatively high,medium and low-activity.The optimized parameters with pressure of 0.20MPa,slurry density of 5%and high-activity magnesia were selected.Then,the hydrating agents were added into the three-phase hydration system,such as Mg?CH₃COO?₂,CH₃COOH and NH₄Cl,with the aqueous solution concentration of 0.05mol/L and 0.10mol/L.Compared with pure water hydration,the hydration rate at reaction time of 30min was improved over 20%with three hydrating agents in different concentrations.Finally,the hydration products with hydrating agents were analyzed by SEM and XRD.The characteristic peaks of XRD patterns were compared and FWHM were used to calculate the average grain size,which was consistent with the SEM results of magnesium hydroxide crystals.The three-phase hydration method was introduced in this thesis for preparation of'magnesium hydroxide,which is much more effective than the traditional hydration method.At the setting experiment conditions,high reaction pressure and high temperature,low concentration of slurry,high active magnesia powder were optimally selected.The addition of hydrated agents improved the formation efficiency of magnesium hydroxide,and brought out different crystal morphology of magnesium hydroxide.