Mechanism Insights Into Co-removal Of Combined Pollutants Involving Heavy Metals And Organic Acids With Series Of Amine Decorated Resins

Combined pollutants involving heavy metal ions(HMIs)and organic acids(OAs)widely exist in electroplating,breeding wastewaters and urban domestic sewage as well as.large area of surface/ground water in China.Most of OAs like chelating agent and pharmaceuticals tend to complex with HMIs and form various species,making their environmental behaviors more complicate.The combined pollutants are harder to remove and give great threat to human health and ecological safety.With the increasingly stringent environmental requirement,it is urgent to intensively control both HMIs and OAs.The traditional control technologies as the combination of coagulating sedimentation and reduction-oxidation etc.,have the drawbacks like long processes,secondary pollution and high cost.Thus,it is necessary and significant to develop novel integrated and reusable technologies for the co-removal of HMIs and OAs.Coadsorption,a relative simple,green and recyclable method,is very attractive to co-remove HMIs and OAs.Several adsorbents with abundant amine groups showed superior adsorption capacities to both HMIs and OAs,and synergistic co-removal toward them at a certain range,indicating that these kinds of adsorbents had great potential to co-remove HMIs and OAs.However,the previous reports provided limited information about the structure-function relationship and mechanisms during the coremoval as well as the application feasibility of these adsorbents which is significant to guild the designation and application of the integrated technique for the HMI-OA combined pollution.In this thesis,series amine resins were synthesized and their adsorption properties and mechanisms in co-removal of HMIs and OAs from three typical HMI-OA combined systems were systematically studied.In addition,the corresponding integrated processes involving co-removal and recovery of HMI-OA were also developed and evaluated.Eight polyamine resins(PSA,PSB,PSC,PSD,PAMA,PAMB,PAMC and PAMD)and two aminoacetic resins(PS-AC and PAM-AC)were synthesized.The nitrogen content of polyamine resins were 11%?22%and increased with the length of polyamines,while the oxygen contents of aminoacetic resins were 20%-40%,2-3 times of those in-the corresponding precursor resins.PAMD,PAM-AC and PSA were the optimum resins for the co-removal of carboxyl-complex combined pollutants(Cu and citric acid,CA were the representatives),hydroxyl-complex combined pollutants(Cu and tetracycline,TC were the representatives)and weakly-complex combined pollutants(Cu and sulfamethoxazole,SMZ were the representatives),respectively.The adsorption of Cu and CA onto polyamine resins was all synergistic and their total adsorption amounts were positively related with amine contents of resins.The adsorption of Cu and TC was synergistic by aminoacetic resins and higher adsorption amounts were obtained for resins with more functional groups.Cu and SMZ could be effectively co-remove by polyamine resins and the co-removal was synergistic at a certain range.Under pH range(3?7),PAMD can synergistically remove Cu and CA.In binary system,the saturation adsorption capacity of Cu by PAMD was 5.07 mmol/g,2.86 times of that in sole system,while CA capacity also increased by 9.1%to 3.58 mmol/g.The total adsorption amount of PAMD toward Cu and CA was 2.0?7.9 times of those of commercial resins(D113,D001,D201 and S984).The interaction mechanism was further studied with preloading tests,Visual MINTEQ calculations and various characterizations such as XANES.The synergistic co-removal was mainly attributed to the contributions of both neutral and positively charged amine sites in which cationic or neutral species(Cu2+and CuHL0)coordinated with neutral amine sites,and anionic complex species(CuL-and Cu2L22-)interacted with protonated amine sites via electrostatic attraction.The adsorption proportion of the four main species was approximately 1:2:4:1 at equalmolar ratio of Cu and CA concentrations.Cu and CA could be recovered completely by 1 mol/L HCl with high concentrate ratios(31.6 and 27.9 folds for Cu and CA,respectively).With the presence of high concentration of inorganic salts,the total adsorption-amounts of Cu and CA onto PAMD slightely decreased by less than 19.2%.Besides,other carboxyl-complex combined pollutants could be also synergistically removed by PAMD with a total adsorption amount up to 4.8 mmol/g.TC adsorption onto PAM-AC markedly enhanced by one order of magnitude along with the increasing concentration of coexistent Cu,while Cu uptake also slightly increased by 15%in the copresence of TC.The total adsorption amount of Cu and TC onto PAM-AC was 1.3?8.7 times of those onto commercial resins(D113,S984 and XAD-4).Based on results of preloading tests and UV-Vis,FTIR,XPS characterizations,"dcomplexing-bridging" was demonstrated to be the leading mechanism for the synergistic co-removal of Cu and TC.The introduce of carboxyl groups improved the affinity of resin towards Cu in[Cu-TC]complex,resulting in the decomplexing of[CuTC]complex and the release of free TC.Cu coordinated with amine groups([N-Cu]stuctrure)further participated in bridging interaction with free TC at a bridging stoichiometric ratio(Cu:TC)of 2:1.TC and Cu could be sequentially recovered with 0.01 mol/L NaOH followed by 1.0 mol/L HCl with the concentration ratio of 3.5 folds for TC and 23.2 folds for Cu.Besides,PAM-AC could stably co-remove Cu and TC from vairous water environments.The coexistence of Pb,Zn,Ni and Cd could also facilitate TC removal onto PAM-AC by 3 to 17 times.PSA exhibited high adosorption capacities for both Cu and SMZ,and synergistic co-removal towards them at low concentrations.The total adsorption amounts reached 1.4?8.9 times of those onto commercial resins(D001,S984,D201 and XAD-4).According to the results in preloading tests,FTIR and XPS characterizations and DFT optimization,the co-adsorption properites of Cu and SMZ onto PSA were resulted from the comprehensive contributions of site competition,site enhancement and site bridging.In detail,Cu and SMZ directly competed for the same-NH20 sites through coordination and hydrogen bond,respectively(site competition).The electrostatic interaction between SMZ" and-NH3+ shielded part of the positive charges and thus freed more amine groups available for Cu2+ coordination(site enhancement).The enrichment of Cu in resin-phase enhanced its complexation ability with SMZ,resulting in the formation of ternary complex(-N-Cu-SMZ)to offer new adsorption sites for SMZ(site bridge).In binary systems,the saturation adsorption capacities of Cu and SMZ onto PSA were 1.481 and 1.190 mmol/g,respectively.1.077 mmol/g of them was-N-CuSMZ ternary complex and the bridging stoichiometric ratio(Cu:SMZ)was possiblely 1:1.Furthermore,SMZ and Cu could be sequentially recovered with 1 mol/L NaClO3 followed by 1.0 mol/L HCl with the concentration ratio of 5.8 folds for SMZ and 18.2 folds for Cu.Coexistent inorganic salts significantly improved Cu adsorption by 42,7%whereas suppressed SMZ uptake by 19.2%.The influence of humic acid on their adsorption was negligible.Other weakly-complex combined polutants such as Cu and sulfamerazine,p-nitrophenol and hydroquinone etc.could be also simultaneously removed by PSA.In summary,PAMD,PAM-AC and PSA showed high capacity,good antiinterference and recyclability in synergistic co-removal of carboxyl-complex,hydroxyl-complex and weakly-complex combined pollutants,respectively,which implies wide applicative potential of them in integrated treatment for wastewater containing HMI-OA combined pollutants.