Study On The Preparation Of Mg(OH)₂/MgO From Bischofite In Qinghai Salt Lake

Bischofite in Salt Lake is the product of the crystallization of the waste brine after the extraction of potassium chloride.In the early stage of development,there are few treatment methods for it,and most of them are discharged in situ.At present,although the research of utilization has been carried out,the efficiency of current treatment methods is generally low,which makes a large number of bischofite accumulation and flooding in the Salt Lake area.The comprehensive utilization of bischofite in the Salt Lake area is the key to realize the green cycle development of the Salt Lake area.In this paper,the technology and process of preparing magnesium hydroxide by electrodeposition were studied.The changes of physical properties of the products in electrolysis and the causes of these changes were analyzed.Magnesium oxide was prepared by calcination,and the products were characterized by SEM and XRD.Magnesium oxide was prepared by calcination,and the products were characterized by SEM and XRD.The effect and mechanism of surfactant polyethylene glycol(PEG)on the electrolytic product magnesium hydroxide were studied.When the current density is 0.040 A/cm2,the electrolyte magnesium chloride concentration is 0.35mol/l and the electrolysis temperature is 25?,the current efficiency is 88%and the energy consumption is 8500 kW·h/t.In order to study the influence of process stability and non-magnesium ion enrichment on the process behavior,an electrolysis experiment of 60 h was carried out.The BO33-concentration increased from 0.025 mg/L to 0.063 mg/L.It was found that the enrichment BO33-in the electrolyte have a negative impact on the morphology of the product.The content of BO33-in the solution could be effectively controlled by pretreatment of the electrolyte with magnesium hydroxide.When the concentration of BO33-in the solution is controlled within 0.055 mg/L,the quality of the product will not be affected.Magnesium hydroxide was prepared by calcination with magnesium hydroxide as precursor.When the calcination temperature of magnesium hydroxide is 1000? and the calcination time is 1 h,the crystallinity of the calcined product is good,the purity is over 99.6%,and the activity is moderate,the hydration rate is about 3%,which meets the industry standard of silicon steel grade magnesium oxide.The nucleation and crystal growth process of magnesium hydroxide prepared by this methode were calculated.It was found that the effect of temperature on nucleation is obvious,and the nucleation process will be promoted at high temperatures,and the surface Gibbs free energy of the nucleation process will be lower.The current density is the dominant factor controlling the nucleation process with constant temperature,and the nucleation rate constant increases with the increase of current density.In the nucleation stage,the growth rate constant decreases with the increase of time at the same temperature,indicating that the growth rate of magnesium hydroxide crystal decreases gradually in the later stage.In the study of PEG as surfactant,it is found that the lower concentration(0.4 g/L)of PEG can regulate the growth of magnesium hydroxide crystal,and the obtained magnesium hydroxide crystal growth is complete and has good dispersion.When the surfactant content is higher than 0.6 g/L,PEG will form a complex complexcomplex with Mg2+ on the electrode surface.The complex can cover the active sites on the electrode surface,which greatly hinders the electrode reaction.