Preparation Of Polyhydroxy Group Functionalized Boron-chelating Resins And Their Application In Boron Adsorption

Boron and boron compounds are very important basic chemicals. There are more than 300 different applications about boron. In recent years, there is a sharp growth in domestic demand for boron products with the annual average growth rate of consumption more than 10%. However, the amount of domestic boron products is in short supply. More than 70% of boron products consumed in China need to be imported from abroad. Recovering boron from the abundant resources containing boron like salt lake brine is an indispensable way to reduce shortage of boron products in China. Meanwhile, animals and plants are extremely sensitive to boron in the environment. Excessive boron in soil or water has a harmful effect on their growth. Removing boron from industrial effluents, irrigation water and drinking water is necessary to protect eco-environment. Developing the technologies for boron recovery or removal from aqueous solution is of great significance. With advantages of strong adaptability, high selectivity, large adsorption capacity, easy operation and regenerability, boron adsorption by boron-chelating resins is the most promising method for boron recovery or removal. In this work, several boron-chelating resins decorated with polyhydroxy structures were prepared from functional monomers such as salicylic acid and its derivatives, amino propanediol, N-Methyl-D-glucamine (NMDG), aiming to obtain high-efficiency boron adsorbents.Firstly, salicylic acid(SA),2,4-dihydroxybenzoic acid(DHBA), catechol (CT), mandelic acid(MA) and gallic acid(GA) were individually used as aromatic functional monomers in the preparation of the boron-chelating resins denoted as SA-BCR, DHBA-BCR, MA-BCR, GA-BCR, CT-BCR, SA-CT-BCR, respectively, through inverse suspension polymerization technique. SA-BCR was characterized by FT-IR, BET and acid -base titration. Adsorption behavior of boric acid on SA-BCR was studied in batch mode. It was found that adsorption isotherm of boric acid on SA-BCR was correlated well with Langmuir model. The saturated boron capacity Qm(fit) was calculated to be 0.560 mmol/g, and the corresponding availability of functional group Af(fit) was 25.0%. PS-ASA resin was prepared from porous chloromethyl polystyrene(CMPS) functionalized by aminosalicylic acid(ASA). Its maximum adsorption capacity was measured to be 0.234 mmol/g, and its Af(exp) was calculated to be 14.5%. The results showed that resins functionalized by salicylic acid or its derivatives could adsorb boric acid by chelation reaction with salicylic acid. The unsatisfactory adsorption uptake demonstrated it is necessary to modify the functional structure to enhance boron adsorption capacity.Secondly, two boron-chelating resins denoted as PS-3-APD and PS-2-APD containing aliphatic 1,2-diols and 1,3-diols were prepared from CMPS functionalized by 3-amino-1,2-propanediol (3-APD) and 2-amino-1,3-propanediol (2-APD). The resins were characterized by FT-IR, EA, MIP and LPS. It was confirmed that the functional monomers were successfully grafted onto the polymer matrix. The results of static boron adsorption experiment on PS-APDs indicated that the optimal boron capacity could be obtained when pH was ranged from 9.15 to 9.20. The presence of foreign ions such as Na+, Mg+, Ca+ would deteriorate the adsorption performance. Kinetic studies showed that both reisns adsorbed boric acid from aquesous solutions very quickly and that their kinetic curves could be fitted well with pseudo second order model. Boron adsorption isotherms on both resins were correlated well with Langmuir model. The maximum boron capacity of PS-3-APD and PS-2-APD fitted by Langmuir equation was calculated to be 0.730 mmol/g and 0.868 mmol/g. Their availability of functional group Af(exp) were 25.2% and 28.7%. Both adsorption capacity and functional group availability of PS-2-APD were higher than that of PS-3-APD. The result showed that 1,3-diols had a stronger chelation on boric acid than 1,2-diols.In the end, the performance of PS-NMDG that was prepared from CMPS functionalized by N-methyl-D-glucamine was compared with commercial resin Amberlite-743. PS-NMDG and Amberlite-743 resins were characterized by FT-IR, EA, MIP and LPS. Their adsorption properties were studied in batch mode. The results showed that both of PS-NMDG and Amberlite-743 could maintain a high adsorption capacity in a wide pH range. Both of adsorption process could reach equilibrium in 100 min. The kinetic curves could be better fitted with pseudo second order model. Adsorption isotherms were correlated well with Langmuir model. Qm(fit) were calculated to be 1.609 mmol/g and 1.040 mmol/g, and Af(exp) were 60.4% and 51.4%. The presence of Na+, Mg2+, Ca2+ had no obvious influence on adsorption performance. Their adsorption capacity could remain above 90% of initial adsorption capacity after 5 cycles.N-methyl-D-glucamine which belongs to aliphatic polyols with a long chain can adsorb boric acid efficiently compared with salicylic acid, its derivatives and amino propanediol. Boron adsorbent prepared from NMDG has a bright application prospective. This study may offer helpful guidance in development of novel high-performance boron adsorbents.