| Humic acid(HA) which widely exists in natural water and soils, is a complexorgnic matter, which formed by the animal and plant after long-term physical,chemical and biological function. The existence of humic acid in the naturalwater will bring about a series of negative effects to humans and animals.Therefore, how to remove the humic acid in natural water is one of the hot issuesconcerned.Amine-adsorbents exhibit high adsorption capacity for humic acid inaqueous solution. In the study, attapulgite were modified by different kinds ofamino material and used for the removal of humic acid in water. Factorsaffecting the adsorption amount of humic acid on modified attapulgite were alsoinvestigated, consisting of adsorption temperature, solution pH and coexistedions.Amino functionalized attapulgite composite materials is prepared by properways to make different modified agents effectively combined to attapulgite toform a new adsorption material. Three adsorbents, such as polyaniline modifiedattapulgite, the silane coupling agents modified attapulgite and surfactantmodified attapulgite were synthesized. The surface functionalized attapulgitewere developed as the adsorbents for the removal of humic acid. Combined withthe results of adsorption tests and adsorbent characterization, the adsorptionmechanisms were advised.(1) Adsorption of HA on polyaniline modified attapulgite(ATP-PANI)ATP-PANI was prepared by the chemical precipitation, the PANI can beeffective to combine with the attapulgite surface by FITR analysis. By the analysis of BET and IEP kowns that the the surface area was65.71m2/g and theIEP of ATP-PANI was3.98.ATP-PANI showed high adsorption capcity for HA. In experimentalconditions, the maximum adsorption amount was52.19mg/g, and the adsorptionequilibrium was achieved with in200min. The adsorption amount of HA ontoATP-PANI is increasing with the increasing of temperature, and the adsorptionisotherms at different temperature can be well fitted by Langmuir model; theadsorption kinetics obeyed pseudo-second-order equation at different initialconcentrations.Solution pH has obvious influence on humic acid adsorption, in tested rangethe maximum adsorption amount was found to be at pH3.6. When pH value ishigher than3.6, the adsorption amount decreased monotonously with increasingpH. The presence of cation in the solution can improve the adsorption amount ofhumic acid and the enhanced adsorption was in the order of Ca2+＞K+≈Na+.NaOH solution was used as a desorption agent, HA adsorbed on ATP-PANIcan be effectively desorbed in NaOH. After four desorption-regenetation cycles,the adsorption amount was not significantly reduced, therefore, the regeneratedadsorbents still keep high adsorption capacity for agucous humic acid.(2) HA adsorption on silane coupling agent modified attapulgite(ATP-APTES)The results of the analysis of infrared and thermogravimetric indicate thatthe amount of ATPES effectively combinated to attapulgite is about3.56%.Though the results of the analysis of the XPS spectrogram of before and afterHA on ATP-APTES explained that, the adsorption is mainly through the surfacecoordination of HA molecules and the protonated amino groups of theadsorbents.In experimental conditions, the adsorption isotherms could be describedwell by Freundlich model and the adsorption dynamics could be fitted thepseudo-second-order equation very well. The influence of solution pH is abvious,the adsorption amount gradually reduced with the increasing of pH. The salt ionsin the solution can promote the HA adsorption onto adsorbents, and the effect ofCa2+is more obvious.(3) Adsorption of HA on surfactant modified attapulgite(ATP-CTAC)By the infrared and thermogravimetric analysises of ATP and ATP-CTAC know that the CTAC effective combination of attapulgite surface is about8.90%.In experimental conditions, the adsorption isotherms of HA on ATP-CTACcould be described by Freundlich model, and the adsorption kinetics could befitted by pseudo-second-order equation very well. HA adsorption kinetics onATP-CTAC is highly dependent on solution pH, and HA adsorption amountdecreased with the increasing pH. The presence of cations can improve theadsorption and the increased adsorption was in the order of Ca2+＞K+＞Na+. Theloaded HA adsorbent can be desorbed in0.1mol/L NaOH solution, and after fourdesorption-regeration cycles, the adsorption amount does not significantlyreduced, therefore, the adsorbent still has strong adsorption affinity for HA.Compared with the natural attapulgite, the composite material modified byorganic matters are significantly improved the adsorption capacity for HA. Andthe adsorption mechanism is maily rely on the interaction between the protonamino group of the adsorbent’s surface and HA in solution. |
PDF Full Text Request