Study On The Preparation And Adsorption Properities Of The Alginate/Halloysite Nanotubes Hybrid Materials

In recent years, with the industrial development, the problem of dye and heavy metal pollution becomes very serious and has attracted widespread attention. To find out a simple method with high efficiency and low energy is an important research direction in the field of wastewater treatment. It is reported that both the halloysite nanotube (HNT) and alginate (Alg) have high adsorption capacity of the pollutants in the water. And these two natural materials have many advantages for water treatment, such as low cost, non poisonous and harmless, biodegradable and without secondary pollution. However, both materials use as adsorbents are limited in practice for the following reasons. On the one hand, HNT on contact with water can form a highly stable colloidal suspension, making its separation from water very difficult. On the other hand, in aqueous solution, the alginate can swell and shows poor stability.Therefore, in this research, the new porous adsorbent has been prepared by immobilizing halloysite nanotubes with alginate. The hybrid bead has both of the two materials’advantages and shows great application potency. Furthermore, the dye and heavy metal ion, which are two kinds of common environmental pollutant, have been used as the absorbates. Both the batch and column adsorption/desorption behaviors of the new adsorbent have been investigated. The main research contents are listed as follows:(1) The Alg-HNT hybrid bead has been prepared. The as-prepared product was characterized by scanning electron microscope (SEM) and Multipoint Brunauer Emmett Teller (MBET) instrument. The results showed that Alg-HNT bead has more porous structure and specific surface areas than the pure alginate (Alg) bead. The adsorption of methylene blue (MB) onto both Alg-HNT beads and Alg beads have been studied. The results showed that the Alg-HNT hybrid bead have better adsorption ability than the single material. The effects of the reaction temperature, contact time and initial concentration on the Alg-HNT bead adsorption of MB also have been studied. The maximum adsorption capacity for MB which was calculated by Langmuir model was250mg/g. The adsorption process followed pseudo-second- order and intraparticle diffusion models. Thermodynamic parameters showed the adsorption of MB was spontaneous and exothermic. The adsorption/desorption cycles were carried out in the batch conditions, and the result showed the Alg-HNT hybrid bead has good regeneration ability.(2) The research on the batch and column adsorption of neutral red (NR) onto Alg-HNT hybrid beads has been carried out. In the batch adsorption, the adsorption capacity of NR increased with the pH value, initial concentration, temperature and contact time until the equilibrium was reached. The maximum adsorption capacity for NR which was calculated by Langmuir model was201.2mg/g. The adsorption process of NR was spontaneous and exothermic, which followed pseudo-second-order and intraparticle diffusion models. In the column adsorption, as the increase of bed height and initial concentration and the decrease of flow rate, the adsorption capacity of NR onto Alg-HNT hybrid bead was increased. The experimental datas were fitted to the BDST and Thomas models.(3) The research on the batch and column adsorption of heacy metal ions (Cu(II)) onto Alg-HNT hybrid beads has been carried out. In the batch adsorption, the adsorption property was not strongly dependent on the pH value. While the adsorption capacity of Cu(II) increased with the initial concentration, temperature and contact time until the equilibrium was reached. The maximum adsorption capacity for Cu(II) which was calculated by Langmuir model was56.81mg/g. The adsorption process of Cu(II) on Alg-HNT hybrid bead was spontaneous and exothermic, which followed pseudo-second-order and intraparticle diffusion models. In the column adsorption, as the increase of bed height and initial concentration, and the decrease of flow rate, the adsorption capacity of Cu(II) onto Alg-HNT hybrid bead was increased. The experimental datas were fitted to the BDST and Thomas models. The adsorption/desorption cycles experiments were carried out under the column condition, and the bead also showed good regeneration. Furthermore, the experiment mentioned above lasted for long times, and the morphology and size of the hybrid beads packed in the column did not change.In conclusion, the composition of these two materials can enhacnce the adsorption ability and the application potency. The Alg-HNT hybrid bead has good adsorption and regeneration abilities to removal of the cationic dyes and heavy metal ions. The results of the models research would provide the theoretical framework for adsorption processes design in the application.