| Boron and its compounds have been very widely used in industry and agricultural fields as important raw materials.In recent years,boron ore resources are increasingly exhausted.However,the salt lake brines rich in boron resources has not been utilized effectively.Salt lake brines contain many valuable elements such as potassium,magnesium,lithium and boron.For producing high quality magnesium and lithium products from brines,boron need to be separated because it is harmful for the products quality.The separation of boron from brines is of great meaning for the comprehensive utilization of salt lake brines.The target of this thesis is deep separation of boron,for this purpose,a extraction-adsorption hybrid method is used to remove boron and a new type chitosan/zirconium composite beads are prepared for the adsorption of boron.The main contents are organized as follows.Firstly,a solvent extraction-resin adsorption combined method was developed to recover boron from brine of salt lake brine after acid precipitation of boron.The mixed solvents of n-decyl alcohol,iso-octyl alcohol,2-ethyl-1,3-hexanediol,tributyl phosphate and aviation kerosene were used as extractant,the D564 resin was used as adsorbent.The effects of pH value,phase ratio,extraction stages on extraction process and the effect of pH of brine after first stage extraction,resin dosage on boron adsorption were investigated,the adsorption isotherm and kinetics were investigated,the stripping and elution process were optimized as well.The results show that the extractant exhibits high extraction performance towards boron in brine,the pH value has a significant effect on the boron extraction and best extraction result can be obtained when pH value is 2,the reduction of boron concentration is not obvious when the phase ratio and extraction stage value are further increased after 3.The best p H value for boron adsorption from brine is 7.The adsorption kinetics and adsorption isotherm data are fitted well with pseudo-second-order rate model and Langmuir model,respectively.The concentration of boron can reduce to 1.0 mg/L or less when resin dosage is6g/?100m L brine?using the extraction-adsorption hybrid method.The proper stripping agent and eluent are 0.1 mol/L NaOH and 0.5 mol/L HCl,respectively.Secondly,the CTS-Zr composite has been prepared through coordination reaction between Zr4+and chitosan.The CTS-Zr composite was characterized by scanning electron microscope?SEM?and Fourier transform infrared spectroscopy?FT-IR?.The effects of pH vale,initial boron concentration,contact time,temperature and co-existing ions Cl-,NO3-?SO42-on adsorption performance were also investigated systematically.The results demonstrate that prepared adsorbent could maintain high boron adsorption efficiency in a pH value range of 2 to 7.The equilibrium adsorption behavior of boron on the CTS-Zr composite had a good agreement with the Langmuir isotherm model,and the maximum adsorption capacity was calculated as 21.1 mg/g with pH value of 7.The uptake kinetics was fitted well with the pseudo-second order rate equation,the adsorption process was controlled by film diffusion.The adsorption process included not only physical adsorption but also inner-sphere complexation between boric acid and hydroxyl on the surface of Zr?OH?4.The common coexisting anions almost had no negative effect on the boron adsorption.The results of adsorption thermodynamics of boron on CTS-Zr indicate the exothermic and not spontaneous nature of the adsorption process.The boron adsorbed on CTS-Zr particles was regenerated with an efficiency of96.3%using a distilled water of pH 12,and the adsorption efficiency was not significantly reduced after three adsorption-desorption cycles.The relatively higher boron adsorption capacity indicated that the CTS-Zr composite had a potential application for boron adsorption from brine. |
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