| China has an abundance of brine resources,which are mainly used for producing potash fertilizer and the residual brines contain a lot of magnesium.Generally,these magnesium resources are discharged locally or into the salt lake remotely,and evaporated into bischofite whose mainly component was MgCl2·6H2O.The above treatments not only lead to the waste of magnesium resources,but also damage the surrounding ecology and environment.Therefore,it is an increasing demand to make the best use of bischofite resources from salt lake.However,it is a good direction for preparing magnesium hydroxide using these magnesium resources.In this paper,magnesium hydroxide was synthesized through a cathodic electrodeposition method with the bischofite as raw material.Meanwhile,the valuable elements in bischofite were concentrated and reused.Then the modified preparation of magnesium hydroxide was carried out.At last,the modified product was applied to the dyes adsorption and modified magnesium oxide preparation.The results are as follows:(1)The thermodynamics and electrochemical behaviors showed it is feasible to prepare magnesium hydroxide by electrodeposition methods.Through designing and building the experimental device,it demonstrated that the magnesium hydroxide had a good filtration performance.Through the optimization of process conditions,the optimum conditions were as follows:the electrolyte concentration was 0.5mol/L,the electrolysis temperature was 40?,the pole distance was 4cm,the current density was 0.05A/cm2 the electroly sis time was 4h,the solution pH was 6.Under these conditions,the current efficiency of preparing magnesium hydroxide was 88.29%,the power consumption was 7353k Wh/t,and the initial shedding time of magnesium hydroxide was 7.9min.(2)This paper investigated the effects of process conditions and impurities of bischofite from salt lake on the properties of magnesium hydroxide prepared by electrodeposition,proposed the pretreatment of bischofite solution with a little magnesium hydroxide slurry,and then prepared high purity magnesium hydroxide.Under the above optimum conditions,the purity of the obtained product was 99.1%,the whiteness was 95.3,and the distribution of the product particles was uniform.Moreover,the enrichment and extraction of valuable elements such as K,Na and Li in the brucite were realized by the cyclic electrolysis experiment.(3)This paper studied the modified preparation in specific surface area of magnesium hydroxide by adding graphene.The results showed that the graphene provided a frame and the magnesium hydroxide uniformly grew on the surface of it.Also,the specific surface area of modified magnesium hydroxide had 5 times as lager as pure magnesium hydroxide.Lastly,by varying process conditions,it could controllably synthesize modified magnesium hydroxide with different specific surface area varied from 100m2/g to 600m2/g.(4)The modified magnesium hydroxide exhibited better adsorption properties for dyes wastewater.When the amount of adsorbent was l0mg,the graphene content was 1%,the adsorption time was 30min,the initial concentration of dye was 1000mg/g,the stirring speed was 500r/min and the pH value of the system was 2,the adsorption capacity of Congo red onto modified magnesium hydroxide could reach 1986.43mg/g.Compared with pure magnesium hydroxide,the adsorbed amount improved by 4 times.Besides,the isothermal adsorption equilibrium,thermodynamic analysis and kinetics data showed that the adsorption was a spontaneous,randomness increased and endothermic physical adsorption process.Furthermore,it proved that the adsorbent had an excellent regeneration performance.(5)The modified magnesium oxide was prepared by the calcination of modified magnesium hydroxide.The results showed that the modified magnesium oxide had uniform particle size,regular crystal structure and good dispersion properties when the calcined temperature was higher than 600 ?.Meanwhile,the decomposition of magnesium hydroxide could cause the reaction between graphene with its superficial oxygen-containing functional groups.Thus,the graphene with a lower defect and thinner layer was obtained.The thermal decomposition kinetic equation of magnesium hydroxide and modified magnesium hydroxide were obtained by thermal decomposition kinetics analysis:Magnesium hydroxide:d?/dt=4.13×109 exp(-15648/T)(1-?)Modified magnesium hydroxide:d?/dt=1.27×108 exp(-13132/T)(1-?)... |
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