| Boric acid, as an important boron compound, has been widely used in various industries including cutting-edge technologies field. Massive wastewater containing boron was discharged from the industrial processes. Adsorption technique shows an efficient method for removal or recovery of boron from aqueous solutions as it provides advantages of high boron recovery, renewable adsorbents and easy operation. The key to the adsorption process is the selection of adsorbents with high adsorption capacity, acceptable mechanical strength and regeneration capability. This work was aimed to prepare an organic-inorganic hybrid material functionalized with N-Methyl-D-Glucamine (NMDG) for boron recovery or removal from aqueous solutions such as from salt lake brine and desalinize sea water.In this thesis, we developed the methods for preparing a spherical hybrid material for boron adsorption by sol-gel reactioa Firstly, we explored the synthetic procedure for the precursor denoted as W by the ring-opening reaction of N-Methyl-D-glucamine (NMDG) and (3-glycidoxypropyl)-trimethoxysilane (GPTMS) in N,N-dimethyformamide. The reaction was conducted at 80℃ until an ivory white waxy solid substance formed after 6 h, and the resultant was extracted by Soxhlet extraction with methanol. Subsequently, the possibility of the sol-gel reaction involving hydrolysis and cross-linking poly condensation of W and tetramethoxysilane (TMOS), was investigated by dissolving in 50% aqueous methanol solution in an autoclave under pH 2. Then, we proposed a technique known as inverse suspension polymerization for preparing bead hybrid adsorbent. The mixture obtained by hydrolysis and polycondensation reacted at 80℃ for 12 hours in the autoclave utill the formation of viscous sol, which was dispersed in the dispersion solvents composed of homogeneous phase of liquid paraffin with Span80 at a speed of 400 rpm and 80℃ for 72 hours. Afterward, the transparent beads with the diameter of 1-3 mm were filtered off, and washed with n-hexane, ethanol and deionized water successively, and then dried at 30 ℃. Finally, the bead adsorbents were obtained and stored for the adsorption experiments.In order to ameliorate the spherical shape of the boron adsorbent for industrial application, factors on inverse suspension polymerization have been investigated to determine the optimal process parameters. We concluded that the optimal conditions include the concentration of Span80 dispersant of 20 mg/L, the sol dissolved in oil phase with the ratio being 1:10. Besides, the time of sol prepolymerization in an autoclave was suggested to be 12 h. After that, the time of sequent dispersion reaction using three leaf-type impeller at a speed of 400rpm should be at least 65 hours. Under these optimal parameters, the product of transparent sphere around 1-2 mm was obtained.In the end of this thesis, we evaluated the prepared boron adsorbent. Boron adsorption by this hybrid bead and the boron-selective commercial resin Amberlite 743 has been examined.(1) The boron acid adsorption process by the spherical hybridized adsorbent is an exothermic reaction. The adsorption isotherm of the hybrid adsorbent fit the Langmuir fitting result well (R= 0.99877). The spherical hybrid adsorbent exhibits a remarkably high capability of boron removal, with the maximum adsorption amount of 1.99 mmol/g, much higher than many other organic-inorganic adsorbents, included the contrast material Amberlite 743 resin (1.24 mmol/g). Equilibrium boron adsorption amount increased with the solution pH in the range of 2-10 and decreased with the further increasing pH above 10. The equilibrium adsorption amount was slightly sensitive to the solution ionic strength. However, MgCl2 promoted the boron adsorption amount obviously, beneficial for the boron separation from brine, seawater and other solution containing Mg2+. The used adsorbent could be eluted by hydrochloric acid and had good regeneration properties.(2) More important, the NMDG density of the spherical hybrid adsorbent could be controlled during preparation, and promote boron adsorption capacity further. The hybrid beads prepared with W ratio in the sol of 20%,50%,80% would have organic content of 35.4%,51.5%,69.8%, with NMDG density of 0.17 mmol/g,0.59 mmol/g,1.154 mmol/g, which could achieve a boron adsorption capacity of 0.25 mmol/g,0.78 mmol/g,1.17 mmol/g in the acid conditions, and of 0.32 mmol/g,0.88 mmol/g,1.63 mmol/g under alkaline conditions correspondingly.(3) The complex mechanism of chemical adsorption and the mierocellular structure of the bead adsorbent(<< 20°A) is confirmed by combining methods, included BET, MS and XRD. Moreover, MS directly indicates the complex ratio of NMDG functional group and Boron compound being 1:1,32, and 2:1. |
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