Modification Mechanism Of Amphoteric-cationic And Amphoteric-anionic Modified Clays And Its Adsorption To Phenanthrene And Cr(?)

The studies of organic and heavy metal pollutants adsorption on organic-modified clay have great significance and application prospects for reducing the activity of pollutants in soil environment, avoiding pollutants into the food chain, and protecting the ecological environment and human health. Bentonite(2:1 type clay) and kaolin(1:1 type clay) were chosen as clay matrix and simultaneously modified by amphoteric modifier(Dodecyl dimethyl betaine, BS-12) and cationic modifier(Dodecyl trimethyl ammonium bromide, DTAB), or BS-12 and anionic modifier(Sodium tetradecyl sulfate, STS) to explore the modification mechanism, surface characteristics, adsorption for organic and heavy metal pollutants, and practical application of amphoteric-composite modified clays under different clays and composite modifier type. The modification mechanisms of BS-12 on clays, DTAB and STS on BS-12 modified clays were studied and the structure of BS-12+DTAB and BS-12+STS modified clays were characterized by total organic carbon(TOC) contents, specific surface area(SBET), X-ray diffraction(XRD), Fourier transformed infrared spectrum(FTIR), thermogravimetric(TG) and scanning electron microscope(SEM). The adsorption characteristics of phenanthrene and Cr(?) on BS+DT and BS+ST) [Short for BS-12+DTAB and BS-12+DTAB] modified clays were studied. 200%BS(Bentonite modified by BS-12 with modified ratio of 200% CEC of Bentonite) and 100%BS+100%DT(Bentonite simultaneously modified by BS-12 and DTAB all with modified ratio of 100% CEC of bentonite) modified bentonites were chose to enhance the Cr(?) adsorption capacity of Lou soil, also 200%BS modified bentonite and biochar were composited to improve the adsorption capacity of phenanthrene and Cr(?) for Lou soil. This doctoral thesis aimed to establish the structure-function relationship among composite modified mechanism, surface characteristics, and adsorption effect, and also provide a theoretical basis and application basis for amphoteric-composite modified clays.The results achieved in this paper are as follows:(1) Ion exchange and hydrophobic modification coexisted in the process of bentonite and kaolin modified by BS-12, and BS bentonite(BS-12 modified bentonite) and BS kaolin(BS-12 modified kaolin) modified by DTAB and STS. Hydrophobic modification began to appear when the ion exchange mode proceeds into a certain degree. The hydrophobic modification began to appear at BS-12 modification ratios of 42.20% and 29.11% CEC for bentonite and kaolin, respectively. After 101.42% and 59.77% CEC of bentonite and kaolin, hydrophobic modification was stronger than ion exchange and became the main modification mechanism. 25%BS(Ion exchange mode), 50%BS(Hydrophobic beginning mode) and 100%BS(Hydrophobic dominant mode) bentonites began to appear hydrophobic bonding at DTAB modification proportion of 30.40%, 17.26% and-3.34% CEC respectively. And 15%BS(Ion exchange mode), 30%BS(Hydrophobic beginning mode) and 60%BS(Hydrophobic dominant mode) kaolins began to appear hydrophobic modification at DTAB modification proportion of 16.80%, 7.63% and 0.68% CEC, respectively. 25%BS, 50%BS and 100%BS bentonites began to appear hydrophobic bonding at STS modification proportion of 15.93%,-1.86% and-1.71% AEC, respectively. 15%BS, 30%BS and 60%BS kaolins began to appear hydrophobic bonding at STS modification proportion of-6.50%,-4.00% and 1.50% AEC, respectively. Our results indicated that CEC is the detrimental factor for the hydrophobic beginning and hydrophobic dominant when clay modified by BS-12, and for the hydrophobic beginning when BS bentonites and BS kaolins modified by DTAB. AEC decided the turning proportion of hydrophobic beginning when BS bentonites and BS kaolins modified by STS.(2) TOC content of BS bentonites and BS kaolins all showed BS-12 hydrophobic dominant mode > hydrophobic beginning mode > ion exchange mode, and SBET decreases with the increasing of BS-12 modification ratio. Interlayer spacing(d001) of BS bentonites increased with the BS-12 modification ratio, while that of BS kaolins had no significant distinction under different modification mode. The results indicated that bentonite was modified by BS-12 through intercalating modification, and only the surface of kaolin was modified by DTAB.TOC content of BS+DT modified bentonites(BS+DT bentonites) and BS+DT modified kaolins(BS+DT kaolins) all increased with the increasing modification ratio of DTAB. SBET of the BS+DT bentonites decreased and SBET of the BS+DT kaolins increased first and then decreased, the d001 increased on 25%BS+DT and 50%BS+DT bentonites while no difference on 10%BS+DT bentonites and BS+DT kaolins. The results also confirmed that DTAB modified BS bentonite were through intercalating modification, and only the surface of kaolin was modified by DTAB.With the increase of STS modification proportion, TOC content and d001 increased, SBET decreased of 25%BS+ST bentonites and BS+ST kaolins, while TOC content decreased first and then increased, SBET increased first and then decreased of 50%BS+DT and 100%BS+DT bentonites, and d001 had no changes on 50%BS+DT and 100%BS+DT bentonites and BS+ST kaolins. Researches showed that the STS on BS bentonite and BS kaolin surface were all outer surface modification.(3) IR spectra confirmed that bentonite and kaolin were successfully modified by BS-12, DTAB and STS. Weightless rate of BS bentonites and BS kaolins all presented BS-12 hydrophobic dominant mode > hydrophobic beginning mode. With the increasing BS-12 modification ratio, loose degree increased on BS bentonite surface, and layer stripping number increased on BS kaolin surface.With the increasing modification ratio of DTAB, weightless rate of BS+DT bentonites and BS+DT kaolins under the same BS-12 modification mode(hydrophobic dominant mode) all increased, and surface flatness was higher on BS+DT bentonites and the accumulation degree of lamella was higher on BS+DT kaolins.With the increase of STS modification proportion, the organic degree and fragmentation degree were higher on BS+ST bentonites under BS-12 hydrophobic dominant mode and ion exchange mode respectively, layer stripping number and surface flatness increased on BS+ST kaolins under BS-12 hydrophobic dominant mode and ion exchange mode respectively.(4) Adsorption ability of phenanthrene on BS bentonites and BS kaolins all showed BS-12 hydrophobic dominant mode > hydrophobic beginning mode > ion exchange mode. Adsorption isotherms of BS bentonites and BS kaolins were synergistic adsorption and distributive adsorption, respectively. The phenanthrene adsorption of BS bentonites and BS kaolins was determined by their TOC content.Adsorption ability of phenanthrene on 25%BS+DT and 50%BS+DT bentonites, BS+DT kaolins all increased with the increasing of DTAB modification ratio, and adsorption ability of phenanthrene on 100%BS+DT showed no significant difference between different DTAB modification ratios. Different mode of BS bentonites were modified by DTAB, the Adsorption isotherms of changed from distributive adsorption to saturated adsorption. Adsorption isotherms of BS+DT kaolins were all distributive adsorption. TOC content was still the determinant of phenanthrene adsorption on BS+DT bentonites and BS+DT kaolins.Adsorption isotherms of BS+ST kaolins were all distributive adsorption. With the increasing modification ratio of STS, adsorption ability of phenanthrene on BS+ST bentonites and BS+ST kaolins all increased. AEC of clay was the determinant of phenanthrene adsorption on BS+ST bentonites and BS+ST kaolins.(5) Adsorption ability of Cr(?) on BS bentonites showed BS-12 hydrophobic dominant mode > hydrophobic beginning mode > ion exchange mode. Adsorption isotherms of BS bentonites were synergistic adsorption(Ion exchange mode), distributive adsorption(Hydrophobic beginning mode) and saturated adsorption(Hydrophobic beginning mode), respectively. Adsorption ability of Cr(?) on BS kaolins were no significant difference and the adsorption isotherms all showed distributive adsorption.Cr(?) adsorption ability on BS+DT bentonites and BS+DT kaolins all showed DTAB hydrophobic dominant mode > hydrophobic beginning mode > ion exchange mode. Adsorption isotherms of BS+DT bentonites were synergistic adsorption(Ion exchange mode), distributive adsorption(Hydrophobic beginning mode) and saturated adsorption(Hydrophobic beginning mode), respectively. The adsorption isotherms of BS+DT kaolins showed distributive adsorption.The modification mode of BS+ST bentonites and BS+ST kaolins changed from BS-12 ion exchange mode to BS-12 hydrophobic dominant mode,the total Cr adsorption isotherms also changed form saturated adsorption to distributive adsorption. Under the same BS-12 modification mode, total Cr adsorption amount of BS+ST bentonites and BS+ST kaolins all increased with the increasing STS modification proportion.(6) Adsorption capacities of Cr(?) on B100B/100 D Lous(Lou soil mixed with B100B/100D) and B200 B Lous(Lou soil mixed with B100B/100D) increased with the increasing proportion of B100B/100 D and B200 B, and the adsorption capacities were 1.52~5.12 times higher than raw Lou soil. B200 B Lous showed higher adsorption capacity of Cr(?) than B100B/100 D Lous.CS1:2(Mass ratio, biochar : B200 B = 1 : 2), CS1:1(Biochar : B200 B = 1 : 1) and CS2:1(Biochar : B200 B = 2 : 1) all enhanced the Cr(?) adsorption amount of Lou soil. At the same adding proportion, Cr(?) adsorption amount increased with the increasing of CS ratio in compound adsorbent. Phenanthrene adsorption presented CS1:2 Lou > CS2:1 Lou > CS1:1 Lou > L-CK(raw Lou soil) at the adding amount of compound adsorbent at 2% and 5%, while showed CS1:2 Lou > CS1:1 Lou > CS2:1 Lou > L-CK when adding 10% of the compound adsorbent. The higher ratio of B200 B in compound adsorbent, the better phenanthrene adsorption was, and phenanthrene adsorption amount on 10% CS1:2 Lou was 13.00-fold higher than that of L-CK. The higher ratio of biochar in compound adsorbent, the better Cr(?) adsorption was, and Cr(?) adsorption amount on 10% CS2:1 Lou was 13.61-fold higher than that of L-CK. Lou soil mixed with B200 B and biochar composites have practical applications in the adsorption of phenanthrene and Cr(?).