Preparation Of Modified Humic Acid Based Adsorbent By Cross-Linking And The Research Of Its Properties

With the development of social industrialization and the smelting of heavy metals,more and more heavy metals have been used in various industrialized production processes,and a large amount of heavy metal wastewater has emerged,resulting in the entry of heavy metals into the ecological environment in the form of ions.The circulation of ecosystems and their continuous migration,transformation,and enrichment not only cause serious pollution damage to the natural environment,but also is a visible and long-term threat to human survival.Therefore,the study of the economical and efficient heavy metal wastewater treatment technology has gradually become a research hotspot in recent years.In this paper,Shaanxi Huangling weathered coal is used as raw material.Based on the purpose of secondary utilization of resources,experimental analysis and research were conducted to prepare a modified humic acid-based resin adsorbent.The preliminary investigation of the resin on hexavalent chromium(Cr(VI))aims to explore an adsorbent with excellent adsorption performance for the treatment of heavy metal wastewater.The experiment firstly extracted humic acid(HA)from weathered coal samples,including two steps of activation pretreatment and alkali dissolution acid precipitation.The concentration of hydrochloric acid,activation time,alkali concentration,solid-liquid ratio and boiling water bath time were selected as the main influencing factors of orthogonal experiment to determine the best extraction conditions for humic acid.The result was as follows: hydrochloric acid concentration was 18 %,activation time was 25 min,lye concentration was 0.8 mol/L,solid-liquid ratio was 1:12,boiling water bath time was 60 min.Under this condition,it was verified by repeated experiments that the highest extraction rate of humic acid was 48.17 %.To improve the water-soluble characteristics of humic acid,the extracted humic acid was modified by high temperature calcification method to prepare insoluble humic acid(IHA).The optimum high temperature temperature in the modification process was determined by thermogravimetric analysis,and then select high temperature time,Ca Cl2 solution concentration,soaking timeof Ca Cl2 solution,and Na NO3 solution concentration as the main influencing factors of the modification to the orthogonal experiments and the optimal conditions for preparation of insoluble humic acid were as follows: high temperature was 330°C,high temperature duration was 90 min,Ca Cl2 concentration was 2mol/L,Ca Cl2 soak time was 120 min,concentration of Na NO3 solution used during washing was 1 mol/L.Under these conditions,the yield of IHA can reach up to 74.21 %.Finally,a modified humic acid-based resin(IHA-PAA)was synthesized by a cross-linking method through a set of orthogonal experiments,and the effect of the synthesis conditions on the adsorption of IHA-PAA was investigated using the Cr(VI)adsorption amount as an indicator.The synthesis experiments showed that the optimal conditions for preparing IHA-PAA were: monomer ratio IHA:AA was 3:40,MBA amount was 0.5 %,KPS amount was 0.5 %,and Na OH neutralization degree was 60 %.The adsorption of hexavalent chromium by IHA-PAA prepared under this condition can reach0.749 mg/g.In order to investigate the influence of external factors,the p H,initial concentration and time,adsorbent dosage,temperature,stirring speed and particle size were selected as the main influencing factors in the experiment,and the adsorption effect HA,IHA,and IHA-PAA under various conditions were studied and analyzed.The results showed that under the same influencing factors,the adsorption effect of IHA-PAA was better than that of HA and IHA,and the acid-alkaline resistance and temperature resistance of IHA-PAA were all improved.Isothermal adsorption experiments were performed on IHA-PAA.The data fitting results showed that the Freundlich adsorption isotherm model can better describe the adsorption behavior of Cr(VI)on IHA-PAA;adsorption kinetics experiments were performed on IHA-PAA,and data fitting results show that the pseudo-first-order kinetic model can describe the adsorption kinetics of Cr(VI)with IHA-PAA under low concentration conditions,and the pseudo-second-order kinetic model can describe the adsorption kinetics under high concentration conditions.The structures of HA,IHA,and IHA-PAA adsorbents were characterized by infrared spectrum and scanning electron microscope,and the performance differences of HA,IHA,and IHA-PAA were compared and analyzed.The results showed that compared with HA,the hydrophilic groups in IHA such as hydroxyl groups were reduced and the hydrophobicity was increased,which increased its insolubility and was beneficial to its individual application and avoided the water pollution.Compared with IHA,the hydrophilicity of IHA-PAA increased for the increase of C=O absorption peaks,and adsorption properties was enhanced because the amount of phenolic hydroxyl groups,alcoholic hydroxyl groups,and carboxyl groups increased.These changes improve its adsorption properties and indicated that IHA-PAA was a polymer of humic acid and acrylic acid,which is advantageous for its use in water treatment.SEM showed that the surface of the modified IHA is roughened and loosely layered,and the dispersed uniform spherical particles were loaded,and the number of adsorption sites increased.The IHA-PAA formed more cluster-like protrusions and was arranged in an orderly manner.And there were more pore structures between the clusters,which significantly increased the surface area and specific surface area,thereby improving the adsorption performance.