| Humic acid is a kind of natural chelating polymer material. It not only has a porous network structure like cellulose, but also contains many polar functional groups, such as carboxyl, phenolic hydroxyl, alcoholic hydroxyl group, quinone group, and enol group, etc. For metal ions, humic acid can show acid, ion exchange and complexation chelating, etc. This is because that humic acid molecule has the various of carboxyl, hydroxyl, phenol group, and other aliphatic, they can form complexes with metal ions or metal oxides, which can realize the adsorption of metal ions.At present, the separation methods of iron and aluminum mainly include physical method and chemical method in domestic. Technological process of physical method is simple, the cost is low, but it is only applicable to simple structure of iron and aluminum inlay, scope of application is limited. In the chemical method, the effect of resin separation is better. However, these resins need to be compounded, the synthetic conditions of different resin are different, some synthetic conditions even are not easy to control. At the same time, a large number of studies showed that:different metals have different properties, the adsorption capacity of humic acid on different metal ions would be different. Therefore, the application value of natural humic acid chelate material in this regard is worth to research and development. This article attempted to humic acid applied the separation experiment of iron and aluminum, explored separation performance of humic acid on iron and aluminum.This study focused on lignite humic acid on the separation performance of iron and aluminum ions, and compared with the separation performance of synthetic salicylic acid chelating resin. The detailed research contents are as follows:(1) Preparation of humic acid and salicylic acid chelating resin material:By using the method of alkali soluble and acid analysis, humic acid was extracted from lignite, it was also tested by FTIR analysis method. Chloromethylation crosslinked polystyrene and 5-aminosalicylic acid (ASA) carried on nucleophilic substitution reaction, producing salicylic acid type chelating resin, which was tested by FTIR analysis method.(2) The separation experiment of humic acid on iron and aluminum:First by single ion adsorption experiments of iron and aluminum, they explored the adsorption feasibility of humic acid on iron and aluminum ions. Then, under the conditions of changing the pH and adsorption temperature and constant adsorption time, the adsorption experiments of humic acid on mixed iron and aluminum ions were carried on. The adsorption masses of aluminum and iron could be obtained by under different conditions. Experimental data showed that:In adsorption experiment of single ions, the maximum absorptive capacities of humic acid on iron and aluminum were 0.7917 mg/g and 1.5656 mg/g, respectively. In adsorption experiment of the mixed ions, the maximum absorptive capacities of humic acid on iron and aluminum were 0.6900mg/g and 1.1896 mg/g, respectively. When the solution pH was 0.5, adsorption time was 1 h and adsorption temperature was 308 K, the largest separation ratio of aluminum and iron could reach 3.08.(3) The contrast of iron and aluminum separation experiment of humic acid and salicylic acid chelating resin:From adsorption experiments of the above two kinds of absorbents to single metal ions in solution and iron and aluminum ions mixed solution, respectively, we could get the effects of two kinds of adsorbent on adsorption of iron and aluminum single ion, the separation ability of mixed iron and aluminum ion. In the experiment of single ion, adsorption effect of salicylic acid was better than humic acid. In the mixed iron and aluminum ions experiments, selective separation ability of humic acid was better than salicylic acid. The separation ratio of salicylic acid chelate chelating resin was as high as 0.15, the separation ratio of humic acid was as high as 3.08.(4) The optimization of the separation process conditions of humic acid on iron and aluminum:Through the response surface method to optimize process conditions of the humic acid on iron and aluminum separation process conditions, we could known that pH had a great impact on adsorption effects of two kinds of ions. The optimal process conditions of humic acid to separation of iron and aluminum ions mixed solution were that:solution pH for 0.5, adsorption time for 0.5 h, adsorption temperature for 338k. Under the condition of the experiment, the adsorption mass of humic acid on iron was 0.5035 mg/g, the adsorption mass of humic acid on aluminum was 2.0991 mg/g. In the process condition, the adsorption amount of iron was smaller and the adsorption amount of aluminum was larger, it can make the separation ratio was 4.17.(5) The theoretical analysis of iron and aluminum separation properties of humic acid:By the adsorption isothermal experiments of humic acid on iron and aluminum ion, we drawn the sorption isotherms of iron and aluminum ions, respectively, getting relevant experimental datas. Then using the Langmuir model and Freundlich model for fitting the experimental data, respectively, we could judge the adsorption behaviors of humic acid on iron and aluminum ions are much more suitable for the Langmuir model. Finally, from the equations of adsorption model and thermodynamic calculation, we could get enthalpy, entropy and gibbs free energy of the adsorption of humic acid on iron and aluminum ions. Then we carried on the analysis of thermodynamic theory. The analysis results showed that the adsorption of the humic acid on iron ions was spontaneous, increasing of entropy and endothermic reaction. The adsorption of the humic acid on aluminum ions was spontaneous, and exothermic reaction. Preliminary speculation:the adsorption processes of humic acid on iron and aluminum were very complex adsorption processes containing physical adsorption and chemical adsorption process.(6) The characterizations of products:Using FTIR, scanning electron microscope, energy spectrometer and the ICP to characterize the adsorption materials, we got the content change of the metal ions in the adsorption materials. Further, the situations of adsorbent material adsorbed Fe-Al metal ions were analyzed. |
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