| Boron and its compounds have a wide range of uses. At present, the main raw materials for producing boric acid are ascharite in China. However, the ascharite resources were increasingly drying up in recent years.China has abundant boron resources in brines, it has a great development value, at the same time for recycling magnesium to prepar high quality magnesium chemical products from brine, boron need to be separated from brine because it is harmful for magnesium chemical products. If boron can be recyled during the separation process, it can achieve the purpose for comprehensively utilization of brine resource.Ion-exchange method is used to separate and enrich boron from brine in this paper. Comparing the ability such as boron adsorption, desorption, selectivity and stability of resin and other factors, the batch adsorption experiments were carried out in synthetic boric acid solutions to choose the most suitable one from three kinds of resins D403, D564and XSC-700under controlled conditions (initial boron concentration, volumes of resin, pH, contact time, temperature, and the behavior of foreign ions). The results showed that the maximum adsorption capacities are6.6,7.1,7.31mg-mL-1of D403, D564, XSC-700under appropriate conditions. Mg2+, K+, Na+, Li+and other metal ions has little effect on resin D403, D564, XSC-700. Deionized water is difficult to wash down boron which was adsorbed on the resin and is easy to wash down Mg+, K+, Na+, Li+and other metal ions. Desorption experiment results showed that acid solution facilitates the desorption reaction, under suitable conditions, the boron desorption rate was more than95%using hydrochloric acid and sulfuric acid solution. In comparison of three kinds of resin, the boron adsorption capacity of XSC-700is better than D403, D564resin under appropriate conditions, and it has better selectively ability, mechanical, chemical and thermal stability.The study was performed to investigate the boron adsorption onto the resin XSC-700in Lop Nor Saline Lake bittern.The results showed that, XSC-700resin can effectively extract boron and has a good selective adsorption.The technology is simple and convenient and not bring the secondary pollution. The maximum adsorption capacities for XSC-700are6.16mg-mL-1under appropriate conditions. After adsorption, loaded resin can be effectively separate boron and other ions by washing with deionized water. It has important significance in the following preparation of boric acid.On static experimental data, Kinetics and thermodynamics were studied. The adsorption process is analyzed using pseudo-first-order kinetic model, pseudo-second-order kinetic model and intrapartical diffusion model and the adsorption kinetics is found to preferably obey the pseudo-second-order model. With temperature increasing, the reaction rate increased, the activation energy is calculated to6.527kJ/mol. In addition, equilibrium data are fitted to Langmuir and Freundlich isotherm equations and the equilibrium data are found to be well represented by Langmuir isotherm equation. Using thermodynamic formula to calculate AG, AS and AH during adsorption process, the results showed that△G was less than0, and with temperature increasing, the absolute value of AG increased which means the reaction process of XSC-700resin adsorbing boron can be spontaneous, while at the same time, we can see the absolute value of AG increased not greatly, so although increasing temperature is better for boron adsorption, but the impact is not great, AH is greater than0which means that the adsorption of boron is an endothermic reaction, AS is greater than0which means that the adsorption is an entropy increase process.The effects of flow rate, initial boron concentration and the bed volume of resin on boron adsorption were investigated in column-mode experiments. The experimental results showed the breakthrough capacity of XSC-700decreased with flow rate and initial boron concentration increasing. The appropriate condition was the flow rate1.5mL·min-1, resin volume100mL and initial boron concentration370-620mg·L-1.The dynamic desorption results showed that when the velocity is lower, the desorption peak is narrower and higher, the effect of desorption is better, while the desorption time is longer, work efficiency is reduced. The appropriate desorption condition was desorption velocity5～10mL·min-10.5mol·L-1HC1120-140mL, desorption time14-24min. After desorption, the water washing experimental results showed that200mL water can wash resin to weakly acidic to neutral. Resin transformation experiment results demonstrated that when the flow rate was4mL·min-1,0.5mol·L-1NaOH is above40mL, the resin can be completely transformation. After transconformation, the water washing experimental results showed that200mL water can wash resin to weakly acidic to neutral.When the amount of resin is expanded to2000mL, that the appropriate experimental conditions was the flow rate120mL·min-1, penetration time66.7min which can handle brine volume8000mL. After adsorption,3600-4000mL deionized water can basically washing down the other ions which adsorbed onto the resin. It can be desorbed with2800mL0.5moL·L-1HCl under the flow rate of160mL-min-1. It can wash down the residual desorption solution with4000mL water. When using800mL0.5mol·L-1NaOH to transite the resin, the appropriate transconformation flow rate is80mL·min-1. When the volume of water is about4000mL, it can wash down the residual alkali solution to avoid the reaction with Mg2+in brine in the subsequent adsorption process.The resin was tested for cycle test. The adsorption rates of cycle test result under no transformation process is slightly lower than the the cycle test result under transformation process, but can be basically stable at around95%. However, the washing rates of cycle test result under no transformation process is higher than the the cycle test result under transformation process. XSC-700in expanding production has good cycle performance.Based on the results of Enlarged laboratory experiment and the scale of treatable5.68m3brine each time in the trial experiment, it can be calculated the qulity of required resin is1.3ton, pilot plant process parameters were adjusted, the appropriate condition is that adsorption flow rate is (countercurrent)5.68m3·h-1, the adsorption time is60min.; Using2.112m0.5mol·L-1hydrochloric to wash loaded resin, the flow rate is6.336m3·h-1, and the desorption time was20min,0.5mol·L-1sodium hydroxide the0.5952m3resin transformation velocity (countercurrent)3.5712m3·h-1, the transconformation time is10min after washing; after every step,1.448m3water is used to wash the resin twice, the flow rate (downstream) is29.76m3·h-1, and the washing time is3min. Loop experimental results of the pilot test in this condition either not transformed or transformed resin showed that the adsorption and desorption rates remained stable. It illustrated that resin has a good cycle performance.The washing rate in the washing process of the resin under notransformation is lower than the resin under transformation.By evaporating the boron concentrated eluate, boric acid was crystallized in pure form as confirmed by XRD and ICP analysis technique. The IR diagrams of old and new resin showed that the functional structure exchange capacity and water content has not changed which indicated that the resin has better stability, and can be repeatedly used. |
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