Preparation Of Granular Palygorskite Adsorbent And Its Performance On Heavy Metal Ions Removal From Aqueous Solution

Heavy metal pollution is becoming more and more serious, reseachers are looking for cost-effective adsorbent to remove heavy metal ions in wastewater recently. Palygorskite, also known as the Attapulgite, is increasingly drawing environmental worker’s attention due to its abundant sources, low cost, simple regeneration and high removal rate for heavy metal ions treatment.The adsorption mechanism and effects of influencing factors of original palygorskite adsorbing heavy metal ions were explored. And different modification methods of palygorskite were also studied to improve its adsorption performance. However, in former studies, palygorskite were existed as powder, which was difficult to separate palygorskite-metal ion mixture from the treated water by filtration and clarification. To overcome the defect of powdered palygorskite, this study take palygorskite as main material, granular palygorskite adsorbent was prepared successfully after mixing, shaping and roasting. Batch reactors were used to investigate the effects of preparation process parameters and the adsorption properties of Cu(II) and Pb(II) by granular palygorskite adsorbent. The main research results were as follows:(1) XRD analysis and BET analysis were used to characterize granular palygorskite adsorbents. Diffraction peak intensity of palygorskite decreased gradually with the calcination temperature increased. Palygorskite diffraction peaks almost disappeared over 800 "C. And during the process of calcination temperature increased, specific surface area and pore volume of adsorbents correspondingly decreased. The specific surface area value showed a downward trend with the dosage of sodium alginate increased.(2) When the calcination temperature was 600 "C, with the increase of sodium alginate dosage, the removal rate of Cu(II) and Pb(II) by granular palygorskite adsorbent increased; When the ratio of palygorskite : sodium alginate:water=100:9:77(g:g:ml), the removal rate of Cu(II) and Pb(II) decreased while the calcination temperature increased.(3) Water quality showed significant impact on adsorbing Cu(II) and Pb(II). 1) With the increased of the initial concentration, the removal rate of Cu(II) and Pb(II) decreased, while the quantity adsorbed increased significantly; 2) With the increased of pH value, the removal rate increased correspondingly; 3) When solution temperature increased from 5 "C to 40 " C, equilibrium adsorption capacity increased gradually.(4) With the time going on, the quantity adsorbed increased significantly, and tended to equilibrium after a certain time. The studies of kinetics showed that the adsorption process of granular palygorskite adsorbent could be described well by diffusion model.(5) According to the results of thermodynamics analysis, !H>0 indicated the adsorption was an endothermic process, which meant that elevating temperature could promote the adsorption of Cu(II) and Pb(II) by granular palygorskite adsorbent; !S>0 indicated that under normal temperature, randomness of the system was increased.(6) Adsorption isotherm was fitted with Langmuir adsorption isotherm model, Freundlich adsorption and D-R isotherm model respectively. The results showed that the adsorption process of granular palygorskite adsorbent could be described well by Langmuir adsorption isotherm model.In summary, some preparation process parameters were chosen to make palygorskite granule, which had overcomed the defect of powdered palygorskite. And granular palygorskite showed better adsorption performance on Cu(II) and Pb(II), which provided certain theoretical support for preparation of granular palygorskite adsorbent and removal of heavy metals in water.