Study On Preparation And Adsorption Properties On The Heavy Metal Ions Of Chitosan/geopolymer Permeable

With the rapid development of industrial society,the problem of resources is becoming more and more prominent,so the resource utilization of waste is the key research direction of China’s sustainable development road.While the industry has brought many conveniences to society,the damage to the environment has gradually affected the normal life and future development of human beings,among which the problem of heavy metal pollution is particularly prominent and is a thorny issue facing the world.Geo-polymer（GP）is an inorganic gelling material mainly prepared from silicate raw materials by alkali excitation,with a three-dimensional mesh structure.It is a new type of green cementitious material with lower energy consumption,lower emission,and better stability in the preparation process.In this paper,slag/fly ash base polymer permeable material was prepared with industrial solid waste slag and fly ash as raw materials and water glass as alkali exciter,and the effects of different material ratios and preparation processes on its mechanical properties were investigated.For the problem of poor toughness and brittleness of geopolymer,organic polymer material carboxymethyl chitosan（CMCS）was added to toughen and modify it,and SEM,FT-IR,and multifunctional NMR microstructure analysis and imaging systems were used to study the modification mechanism;the modification of the adsorption properties of geopolymers by carboxymethyl chitosan was investigated,and the static adsorption properties of CMCS/GP composites prepared under optimal conditions were studied by integrating the mechanical and adsorption properties of CMCS/GP composites,and the adsorption mechanism was analyzed by thermodynamic and kinetic models.Finally,the geopolymer permeable material’s adsorption of heavy metal ions was simulated in the practical application.The following conclusions were obtained:（1）The best material ratio for the preparation of slag/fly ash-based matrix polymer was determined through orthogonal experiments:40%slag,40%water glass,and 0.3 water-solid ratios;the preparation process was:adding water glass with a modulus of 1.4 to the powder,stirring and mixing well,and then placing it in a 60°C curing oven for 14 d.The compressive strength of the prepared slag/fly ash-based matrix polymer was 78.61 MPa and the flexural strength was 9.65 MPa.The compressive strength of the slag/fly ash-based polymer was 78.61MPa and the flexural strength was 9.65 MPa.（2）The effect of carboxymethyl chitosan on the mechanical properties and water permeability of the geopolymer permeable materials was investigated.The results showed that the addition of 0.2 wt%carboxymethyl chitosan increased the compressive strength of the geopolymer by 22.7%and the flexural strength by 33.3%,reaching 86.12 MPa and 11.01 MPa respectively,the permeability coefficient reached 0.13.The modification mechanism was analyzed by SEM,FT-IR,and NMR,and it was found that the amino,hydroxyl,and carboxyl groups in the macromolecule of carboxymethyl chitosan The amino,hydroxyl,and carboxyl groups in carboxymethyl chitosan were found to form hydrogen bonds with the hydrolysis products of fly ash and slag,and then polymerized into a more dense three-dimensional cross-linked mesh structure,which effectively improved the internal pore structure of the geopolymer and realized the toughening modification of the geopolymer.However,when the amount of carboxymethyl chitosan is too much,carboxymethyl chitosan macromolecules wrapped around slag and fly ash particles will hinder their hydrolysis and form a large number of harmful pores,resulting in the degradation of the mechanical properties of the geopolymer.（3）The modification of the adsorption performance of the geopolymer by carboxymethyl chitosan was investigated.The results showed that the removal rate and adsorption amount of Pb²⁺in the solution by the geopolymer after adding 0.2 wt%of carboxymethyl chitosan increased by 33.9%and 34.3%respectively compared with the blank sample.The EDS analysis revealed that the improvement of the adsorption performance of the geopolymer was mainly manifested by the formation of a more dense three-dimensional mesh structure between the C-S-H gel and carboxymethyl chitosan and the high adsorption performance of carboxymethyl chitosan itself.（4）The static adsorption performance of CMCS/GP was investigated and its adsorption mechanism was analyzed.The results showed that the adsorption of Pb²⁺by CMCS/GP was by the Langmuir isotherm model and the quasi-secondary kinetic model,indicating that its adsorption was mainly favorable adsorption of a single molecular layer,and the whole adsorption process was mainly chemisorption and included physical adsorption;at p H equal to5,the temperature of 30℃,adsorbent mass in the range of 0.08-0.1 g,and the initial concentration of ions was 120mg/L,the adsorption reached saturation after 20 h.At this time,the removal rate of Pb²⁺by the CMCS/GP was about 96%,and the equilibrium adsorption amount was about 64 mg/g.（5）The adsorption of heavy metal ions by geopolymer permeable materials was simulated during the practical application,and the adsorption performance of bulk CMCS/GP permeable materials on Pb²⁺was investigated.The results showed that the adsorption of Pb²⁺by CMCS/GP permeable material was mainly concentrated in the first 7 d.The geopolymer permeable material with 0.2 wt%carboxymethyl chitosan had better adsorption performance on Pb²⁺,and the removal rate of 30 d could reach 98.64%.