Differences In Adsorption Mechanism Research Articles

Influence of pyrolysis temperature on sludge biochar: the ecological risk assessment of heavy metals and the adsorption of Cd(II).

Pyrolysis of sludge to biochar can not only reduce the sludge volume, toxic organic compound, and pathogens, but also be applied as effective adsorbents. However, the immobilization of heavy metals in the sludge and the properties of the biochar greatly rely on the pyrolysis temperature. In this paper, municipal sludge biochar (SBC) was prepared from 400 to 1000°C. Pyrolysis immobilized heavy metals in sludge and the potential ecological risk of heavy metals significantly decreased to low level at temperature above 500°C. At 700°C, the adsorption capacity of Cd(II) reached a maximum (120.24mg·g-1). The Cd(II) adsorption fitted the Pseudo-second-order model, indicating the existence of chemical adsorption. The adsorption capacity increased along with the initial pH and slowed down after pH reached 5.5. The existence of coexisting cations (Ca2+ and Na+) and anions (SO42- and NO3-) displayed different degree of inhibitory action on Cd(II) adsorption. The SEM, XRD, FTIR, and XPS analysis of sludge biochar before and after adsorption revealed that there were CdCO3, CdSO4, Cd2SiO4, Cd3(PO4)2, and Cd9(PO4)6 appearing on the surface of sludge biochar, suggesting that the adsorption of Cd(II) by SBC included co-precipitation, ion exchange, coordination with π electrons, and complexation. It was confirmed that different properties formed by pyrolysis temperature made a difference in adsorption mechanism of sludge biochar.

Comparative adsorption studies of cadmium ions on phosphogypsum and natural clay

Cadmium ions pollution and waste resulting from industrial activities are classified as serious environmental problems. In this study, we performed comparative adsorption studies of cadmium (II) on phosphogypsum (PG) and natural clay (NC) from an aqueous solution. The difference in adsorption mechanisms between phosphogypsum and natural clay was inspected using scanning electron micrographs; X-ray diffraction and Fourier transform infrared. The effects of contact time and certain factors such as the adsorbent dosage and the pH of the solution were studied. The comparative study shows that the differences in adsorption behavior come from the chemical and structural differences of the adsorbents studied. It was found that 0.73 mg·g−1 is the maximum adsorption capacity for phosphogypsum, whereas for natural clay it was 5.65 mg·g−1. Cadmium (II) removal was pH-dependent and the optimum adsorptions of phosphogypsum and clay were found at pH basic. It has been confirmed that the pseudo-second order model is best suited to the kinetics of the process studied for the two adsorbents. Overall, natural clay is a better adsorbent than phosphogypsum and this latter can be used as a potential adsorbent candidate for the removal of Cd(II) from aqueous solutions.

Different binding characteristics of ciprofloxacin to iron mineral surfaces: Thermodynamic evidence and site energy distribution analysis.

Iron minerals in soil play an important role in controlling the migration of fluoroquinolones. In this study, batch experiments were carried out to investigate interactions in ciprofloxacin (CIP) adsorption to goethite, hematite, and magnetite at pH 6.0. Thermodynamics and the site energy distribution theory (SEDT) were adopted to clarify the complexation types. Using the adsorption results, pH-dependent interactions were qualitatively elucidated. The thermodynamic data revealed the difference in adsorption mechanisms. With increasing sorbate loading, CIP adsorption to hematite and magnetite was endothermic, and both enthalpy change and entropy change decreased; however, CIP sorption to goethite showed opposite characteristics. The higher adsorption capacity and affinity of CIP to hematite and magnetite than those to goethite were caused by their higher site energy of the highest occurring frequency (E0 * ) and the temperature-dependent average site energy, respectively. The E0 * on the surface of goethite was about 17-19kJ mol-1 , where E0 * values of hematite and magnetite were 20-26kJ mol-1 . When temperature increased from 289.15 to 308.15 K, the high- and low-energy site densities for three iron minerals changed by -32 to 167% and by -36 to 223%, respectively. The different thermodynamic and SEDT results indicated that CIP adsorption mechanisms to goethite and hematite/magnetite were mainly outer- and inner-sphere complexation, respectively. The findings of this study reveal the adsorption mechanisms and are helpful in evaluating the transport of antibiotics in soils containing typical iron minerals.

Adsorption model identification for chromium (VI) transport in unconsolidated sediments

Transport of hexavalent chromium, Cr (VI), in groundwater is largely influenced by adsorption and desorption processes. Sediment types can result in substantial difference in adsorption mechanisms. The goal of this work is to explore the adsorption mechanism of Cr (VI) within sediments with different properties and to identify the controlling factors. In this paper, Cr (VI) adsorption onto six different natural unconsolidated sediments (two loamy sands, two sandy loams, one loam, and one silty loam clay) collected from a typical fluvial aquifer in Qiqihar, China, was assessed with batch and column experiments. Equilibrium adsorption capacities and kinetic rates were quantified with batch experiments. Potential controlling effects of pH, solid/solution ratio, grain size, and clay mineral content on adsorption capacities were also analyzed. Adsorption kinetics was evaluated with Elovich, pseudo first- and second-order models, and equilibrium properties were assessed with Henry, Freundlich, and Langmuir isotherms. Model adequacy was discriminated with selection criteria of Akaike information criterion (AIC), modified Akaike information criterion (AICc), Bayesian information criterion (BIC), and Hannan information criterion (HIC). Adsorption and desorption of Cr (VI) onto and from the collected sediment samples under flow conditions were investigated with column experiments. Key results suggest that irreversible chemical adsorption is the dominant mechanism for Cr (VI) adsorption onto the sediment samples. Grain sizes and clay mineral contents are the controlling factors for adsorption capacity. Fine-grained sediments with high clay mineral contents present the highest Cr (VI) adsorption capacity. Chromium (VI) presents high retention on loam and silty loam clay, and high mobility on loamy sand. Results from this study may provide important insight for understanding the transport behaviors of Cr (VI) in shallow aquifers.

Different surface complexation patterns of gatifloxacin at typical iron mineral/water interfaces

Gatifloxacin (GAT), a new generation fluoroquinolone antibiotic, is widely used in the world but its environmental behavior has been rarely studied. In this study, the adsorption and desorption characteristics of GAT interacting with goethite and hematite at pH 6.0 ± 0.1 were investigated by batch experiments combining with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The results indicated that the total desorption ratio of GAT from goethite (70.8–84.8%) after three desorption steps was far higher than that from hematite (7.8–39.4%). In GAT adsorption onto goethite and hematite, a strong dependence on ionic strength was only observed for goethite. These all suggested that outer-sphere complexation was the main mechanism of GAT adsorption onto goethite while inner-sphere complexation dominated the adsorption onto hematite. No evidence for inner-sphere coordination was found at the goethite surface in this study under our conditions. Due to the difference in adsorption mechanisms, the pH at point of zero charge (pHpzc) of hematite increased by about 1.0 unit after adsorption in relation to the pristine hematite, but the increase of goethite pHpzc was less than 0.3 unit. ATR-FTIR observations indicated that the surface hydration-shared ion pairs involving in strong hydrogen-bond interactions were predominant in GAT adsorption onto goethite. However, a bridging bidentate surface complex with hematite was most likely formed. Our results are helpful to advance understanding of the importance of comparatively strong ionic hydrogen-bonding interactions for adsorption processes of fluoroquinolones at the goethite/water interface. The findings of this study suggest that soils with goethite as the main mineral compositions may have very limited retention ability for GAT under field conditions.

Similarities and differences in adsorption mechanism of dichlorvos and pymetrozine insecticides with coconut fiber biowaste sorbent

In this study, the similarities and differences of the adsorption mechanisms between dichlorvos and pymetrozine and coconut fiber biowaste sorbent (CF-BWS) were investigated. CF-BWS was produced using the slow pyrolysis process at 600 °C for 4 h. HCl acid modification was used to improve the specific surface area. The properties of CF-BWS were analyzed by SEM, FT-IR, BET, and pHpzc. The adsorption kinetics of dichlorvos and pymetrozine on the CF-BWS were well explained by the pseudo-second-order model. The adsorption isotherms for both insecticides were followed the Langmuir isotherm. The difference in molecular structures and surface chemistry caused the difference in adsorption mechanisms of both insecticides. The pore-filling and the hydrophobic interactions were the key mechanisms for both insecticide adsorptions. However, the π–π electron donor–acceptor interaction played the major role in the pymetrozine adsorption but hardly impacted on the adsorption of dichlorvos. The hydrogen bonding mechanism was pronounced in the pymetrozine adsorption, but it had little influence on the dichlorvos adsorption. The CF-BWS is exhibited as an excellent material for the removal of both pollutants and has high potential to be used further as the adsorbent in water treatment process.

Heavy metal adsorption with zeolites: The role of hierarchical pore architecture

Zeolites have been widely used for heavy metal removal due to their high cation exchange capacity and surface sorption properties. However, the empirically determined adsorption capacity trend of Pb2+ > Cu2+ > Ni2+ was not well understood. Herein, we discovered that the adsorption of Ni2+ by zeolites was greatly influenced by hierarchical pore geometry, while the adsorption of Pb2+ or Cu2+ was dependent on cation exchange determined by the framework composition. This difference in adsorption mechanisms is manifested through the systematic study of heavy metal adsorption using low-silica LTA and FAU zeolites with different mesopore architectures and compositions. Synthesizing mesoporous zeolite A of MLTA-P using proline mesoporogen considerably enhanced the Ni2+ adsorption capacity to more than twice of that of conventional zeolite A synthesized without organics, while the adsorption capacities for Cu2+ and Pb2+ were almost unaltered at ∼170 and 510 mg/g. The study on the effect of zeolite synthesis time and adsorbate pH value revealed the significant influence of zeolite crystallinity, surface hydroxyl group, and hierarchical pore architecture on the Ni2+ uptake. The MLTA-P zeolite showed higher stability against pH variation in acid range and remarkably enhanced uptake in alkaline conditions, reaching 218 mg/g at a pH of 11. The full characterization of the adsorbent by scanning electron microscopy and X-ray photoelectron spectroscopy indicated the involvement of the surface reaction forming Ni phyllosilicate nanosheet species during the nickel metal removal process in which transport limitation played a crucial role. The uptake kinetics and isotherms could be perfectly reflected by a pseudo-second-order rate equation and the Langmuir model, confirming the nature of chemisorption.

Strengthened floatation of molybdite using oleate with suitable co-collector

The difference in flotation and adsorption mechanism of mixed sodium oleate (NaOl)/dodecylamine (DDA) and NaOl/cetyl pyridinium chloride (CPC) collectors on molybdite was comparative studied through micro-flotation, fluorescence emission spectroscopy, zeta potentials measurement, adsorption tests and FTIR measurement. The flotation results show that the best flotation of molybdite for 2 × 10−4 M NaOl, CPC and DDA is achieved at pH 7, 8 and 10, with corresponding mineral recovery of 64.3%, 40.9% and 44.5%, respectively. It is found that the collecting ability of single collector on molybdite is in the order of NaOl > CPC > DDA. For mixed system, molybdite recoveries with NaOl are improved by co-adsorbed DDA from about 75% to 95% with increasing DDA dosage, while no improvement is found in the case of mixed NaOl/CPC collectors. Fluorescence emission spectroscopy investigation displays the critical hemimicelle concentration (CHC) and critical micelle concentration (CMC) of NaOl are 2 × 10−4 M and 2 × 10−3 M, respectively. A larger micro-polarity of molybdite in mixed NaOl/DDA than that of mixed NaOl/CPC collectors is found. The adsorbed amount of DDA increase with the increasing DDA dosage due to the extra adsorption of DDA cations between the adjacent adsorbed NaOl ions, which leads to the less negative zeta potentials (from about −60 mV to −30 mV) of molybdite surface for mixed NaOl/DDA collectors. Above phenomenon and corresponding explanation are further confirmed by FTIR findings. Suggested models are presented to interpret the difference in adsorption mechanism of mixed NaOl/DDA and NaOl/CPC collectors on molybdite.

Comparative study on phosphate adsorption by inorganic and organic adsorbents from a diluted solution

Technology of phosphate adsorption from a diluted solution is important in the field of water supply or waste water treatment. Although a number of adsorbent for phosphate is developed up to date, there have been little studies on the survey of their phosphate uptakes in the same criteria. Such approach enables us to clarify the factors that improve the phosphate selectivity.Phosphate uptakes from a diluted NaH2PO4 solution (CP=3 mg-P/L) were studied using 63 kinds of inorganic and organic adsorbents. Schwertmannite type hydrous iron oxide (Sch-1), Mg-Al type layered double hydroxide (MgAl-1), activated magnesium oxide (aMgO), Fe-Al type double hydroxide (FeAl-2), Ce2(CO3)3·8H2O, and La(OH)3 showed large phosphate uptakes above 20 mg-P/g. Sch-1 and MgAl-1 had high adsorption rates and large phosphate uptakes of 15 and 9 mg-P/g, respectively, even at CP=0.01 mg-P/L. The influence of excess bicarbonate ion (2mM NaHCO3) in the solution was small for the iron-containing adsorbents, while was marked for the other adsorbents. This difference could be partly explained by the difference in adsorption mechanism: ion exchange or dissolution-precipitation. The phosphate uptakes by different kinds of hydrous iron oxide showed that schwertmannite types had good phosphate adsorptivity independent of preparation method. Control of the state of sulfate ions in the adsorbent may be important for improving the phosphate adsorptivity by SO42−/phophate ion exchange. A future subject is to improve the reusability of adsorbent, since the 2nd adsorptions after phosphate desorption did not show satisfactory phosphate uptakes.

Adsorbate Pairing on Oxide Surfaces: Influence on Reactivity and Dependence on Oxide, Adsorbate Pair, and Density Functional

Open-shell molecules on metal oxide surfaces frequently display cooperative adsorption mechanisms, where pairs of adsorbates are significantly more stable than the isolated species. In this work, density functional theory is used to investigate the cooperative adsorption of OH—H and NO2—NO on rocksalt BaO(100), rutile TiO2(110), fluorite CeO2(111), and tetragonal PdO(101) surfaces. The OH and NO2 adsorbates are considered to be located at the metal sites, whereas H and NO are situated on the oxygen sites. Despite differences in adsorption mechanisms, the pairing is found to be consistently exothermic. The pairing is most pronounced on BaO(100) and weakest on PdO(101). OH and H form more stable pairs than do NO2 and NO. In all cases except CeO2(111), the hybrid HSE06 functional predicts a stronger pairing than the semilocal PBE functional. The absolute pairing energy is a convoluted measure of charge transfer energies, electrostatic interactions, and ionic relaxations, which is analyzed in detail using a thermodynamic cycle. Adsorbate pairing has marked effects on the reactivity, which is exemplified by studying the reaction of CO with OH on CeO2(111).

Chromatographic retention and thermodynamics of adsorption of dipeptides on a chiral crown ether stationary phase

The enantioselective adsorption of several dipeptides on the crown ether-based stationary phase ChiroSil RCA(+) was studied by means of the linear chromatography method. The retention of analytes was measured with acidified water-methanol mobile phases with varied concentration of methanol (from 60 to 90%, v/v) at different temperatures. Thermodynamic characteristics of adsorption were determined and analyzed applying extrathermodynamic relationships. A considerable difference in adsorption mechanisms of dipeptides with a chiral and achiral N-terminal fragment was proved. An explanation to this fact was proposed assuming that the enantiorecognition of the dipeptides of the first type occurred through the interaction of side groups of the N-terminus with the chiral cavity formed by the crown ether ring. The enantiorecognition of the dipeptides of the second type occurs through the interaction of the C-terminal residue with the side groups of the crown ether moiety. The study also demonstrates how extrathermodynamic concepts can be used for obtaining additional information about retention mechanisms from a limited amount of chromatographic data.

Differences in adsorption mechanisms of heavy metal by two different plant biomasses: reed and brown seaweed

The adsorption of Pb(II) by two different biomaterials, reed (Phragmites australis) and brown seaweed (Sargassum horneri) biomass pretreated with CaCl(2), were compared in an attempt to explain the differences in adsorption performance between the two biosorbents. A very interesting characteristic was found in their individual adsorption performances; the Pb(II) adsorption capacity of brown seaweed (Q(max)=0.45 mmol/g) was much higher than that of reed (Q(max)=0.05 mmol/g), but its adsorption affinity (b=112 L/mmol) was much lower compared with that of reed (b=471 L/mmol). To elucidate the mechanism, the elemental components, ion exchange phenomenon and roles of functional groups of these two biosorbents were compared. The higher Pb(II) adsorption by brown seaweed could be due to its richness in total functional groups and calcium contents on its surface. In contrast, the functional complexity, higher zeta potential and pK(a) value (deprotonation state) of reed are believed to lead to its high adsorption affinity.

Carbon nanotube self-assembly with lipids and detergent: a molecular dynamicsstudy

The dispersion of carbon nanotubes (CNTs) in aqueous media is of potential importance ina number of biomedical applications. CNT solubilization has been achieved viathe non-covalent adsorption of lipids and detergent onto the tube surface. Weuse coarse-grained molecular dynamics to study the self-assembly of CNTs withvarious amphiphiles, namely a bilayer-forming lipid, dipalmitoylphosphatidylcholine(DPPC), and two species of detergent, dihexanoylphosphatidylcholine (DHPC) andlysophosphatidylcholine (LPC). We find that for a low amphiphile/CNT ratio, DPPC,DHPC and LPC all wrap around the CNT. Upon increasing the number of amphiphiles, atransition in adsorption is observed: DPPC encapsulates the CNT within a cylindricalmicelle, whilst both DHPC and LPC adsorb onto CNTs in hemimicelles. Thisstudy highlights differences in adsorption mechanism of bilayer-forming lipids anddetergents on CNTs which may in the future be exploitable to enable enhancement ofCNT solubilization whilst minimizing perturbation of cell membrane integrity.

Arsenate adsorption by Mg/Al–NO 3 layered double hydroxides with varying the Mg/Al ratio

Arsenate is one of the main contaminants threatening water supplies all over the world. Layered double hydroxides (LDHs) have large surface areas and high anion exchange capacities, so they may be used to develop rapid and cost-effective methods for scavenging As from contaminated water. In order to enhance arsenate adsorption of layered double hydroxides, it is essential to have a fundamental understanding of the interactions between arsenate and LDHs. In this study, the effects of layer charge density and interlayer nitrate orientation of Mg/Al–NO 3 LDHs on the preferential adsorption of arsenate were investigated. Mg/Al–NO 3 LDHs with a Mg:Al ratio of 2:1, 3:1 and 4:1 were synthesized, using a constant-pH co-precipitation method. The adsorption maxima of As on 2:1, 3:1 and 4:1 LDHs were 1.56, 1.08 and 0.36 mmol g − 1 , respectively, following the order of their layer charge densities. In addition, nitrate orientation in the LDHs plays a significant role in determining arsenate adsorption. The low arsenate adsorption of 4:1 LDH relative to its anion exchange capacity resulted from the low degree of access arsenate has to the interlayer space, so that arsenate adsorption largely occurred on the external surface of the material. The accessibility of the interlayer of 4:1 LDH to arsenate was restricted by the small basal spacing as a result of the parallel orientation of the interlayer nitrate with respect to the hydroxide sheets. Conversely, interlayer nitrate with an orientation perpendicular to the hydroxide sheets in 2:1 and 3:1 LDHs can be exchanged for arsenate more readily. Consequently, these two LDHs exhibit greater arsenate adsorption capacity, because arsenate can be adsorbed on both their external and interlayer surfaces. The arsenate adsorption of the LDHs also was highly dependent upon the type and concentration of competing anions. The negative effect of the competing anions on arsenate adsorption by various LDHs generally followed the order H 2PO 4 − > HCO 3 − > SO 4 2− > F − > Cl −. Due to the difference in adsorption mechanism, the arsenate adsorption of 4:1 LDH is subject to the negative impact of competing anions to a greater extent than those of 3:1 and 2:1 LDH. These results demonstrated that the preferential adsorption of arsenate by LDHs is dependent upon the nitrate orientation in these materials, as a consequence of changing layer charge density. The selective retention of arsenate for wastewater treatment can be maximized by controlling the orientation of interlayer nitrate in Mg/Al–NO 3 LDHs.

Electrochemical behavior of CO, CO 2 and methanol adsorption products formed on Pt–Rh alloys of various surface compositions

CO, CO 2 and methanol adsorption/electro-desorption processes have been studied on Pt–Rh alloy electrodes with various surface compositions and on the pure Pt and Rh electrodes. Pt–Rh alloys are slightly more tolerant to poisons from these molecules’ adsorption compared to pure Pt and Rh. The values of electrode coverage by the adsorption products and the values of the average electron-per-site ( eps) parameter obtained from stripping voltammetry suggest some differences exist between the adsorption layers formed depending on the adsorbing molecule, the electrode's surface composition and the adsorption conditions. The observations could be rationalized by considering the differences in adsorption mechanisms of CO, CO 2 and methanol and by taking the adsorption products to be uniquely bridge-bonded and on-top-bonded CO. There is no direct correlation between the average eps parameter and the stability of the adsorption layer. Adsorption layers formed on an electrode with a given surface composition and characterized by the same value of the average eps parameter can have different potential stability, if they were formed by different molecules or under different conditions.

Effects of solution conditions and surface chemistry on the adsorption of three recombinant botulinum neurotoxin antigens to aluminum salt adjuvants

Botulinum neurotoxin (BoNT) is a biological warfare threat. Protein antigens have been developed against the seven major BoNT serotypes for the development of a recombinant protein vaccine. This study is an evaluation of adsorption profiles for three of the recombinant protein antigens to aluminum salt adjuvants in the development of a trivalent vaccine against BoNT. Adsorption profiles were obtained over a range of protein concentrations. The results document that charge-charge interactions dominate the adsorption of antigen to adjuvant. Optimal conditions for adsorption were determined. However, potency studies and solution stability studies indicated the necessity of using aluminum hydroxide adjuvant at low pH. To improve the adsorption profiles to AlOH adjuvant, phosphate ions were introduced into the adsorption buffers. The resulting change in the adjuvant chemistry led to an improvement of adsorption of the BoNT antigens to aluminum hydroxide adjuvant while maintaining potency. Competitive adsorption profiles were also determined, and showed changes in maximum adsorption from mixed solutions compared to adsorption from individual protein solutions. The adsorption profiles for each protein varied due to differences in adsorption mechanism and affinity for the adjuvant surface. These results emphasize the importance of evaluating competitive adsorption in the development of multivalent vaccine products.

Intraparticle diffusion and adsorption of arsenate onto granular ferric hydroxide (GFH).

Porous iron oxides are being evaluated and selected for arsenic removal in potable water systems. Granular ferric hydroxide, a typical porous iron adsorbent, is commercially available and frequently considered in evaluation of arsenic removal methods. GFH is a highly porous (micropore volume approximately 0.0394+/-0.0056 cm(3)g(-1), mesopore volume approximately 0.0995+/-0.0096 cm(3)g(-1)) adsorbent with a BET surface area of 235+/-8 m(2)g(-1). The purpose of this paper is to quantify arsenate adsorption kinetics on GFH and to determine if intraparticle diffusion is a rate-limiting step for arsenic removal in packed-bed treatment systems. Data from bottle-point isotherm and differential column batch reactor (DCBR) experiments were used to estimate Freundlich isotherm parameters (K and 1/n) as well as kinetic parameters describing mass transfer resistances due to film diffusion (k(f)) and intraparticle surface diffusion (D(s)). The pseudo-equilibrium (18 days of contact time) arsenate adsorption density at pH 7 was 8 microg As/mg dry GFH at a liquid phase arsenate concentration of 10 microg As/L. The homogeneous surface diffusion model (HSDM) was used to describe the DCBR data. A non-linear relationship (D(S)=3.0(-9) x R(p)(1.4)) was observed between D(s) and GFH particle radius (R(P)) with D(s) values ranging from 2.98 x 10(-12) cm(2)s(-1) for the smallest GFH mesh size (100 x 140) to 64 x 10(-11) cm(2)s(-1) for the largest GFH mesh size (10 x 30). The rate-limiting process of intraparticle surface diffusion for arsenate adsorption by porous iron oxides appears analogous to organic compound adsorption by activated carbon despite differences in adsorption mechanisms (inner-sphere complexes for As versus hydrophobic interactions for organic contaminants). The findings are discussed in the context of intraparticle surface diffusion affecting packed-bed treatment system design and application of rapid small-scale column tests (RSSCTs) to simulate the performance of pilot- or full-scale systems at the bench-scale.

Retention of organic compounds on carbon adsorbents

Liquid adsorption chromatography of organic compounds (aromatic hydrocarbons, acids, phenol, anisole, benzaldehyde and acetophenone) was studied at 293 K on two carbon stationary phases. Acetonitrile, acetonitrile—water (2:3) and n-heptane were used as mobile phases. Capacity factors and Henry's constants of adsorption equilibrium of aromatic compounds were calculated from the values of their retention volumes. The influence of the chemical structure of organic compounds, the surface structure of the stationary phases and the nature of the mobile phases on retention parameters was established. The differences in adsorption mechanism of organic compounds on hydroxylated and modified silica and carbon stationary phases are discussed.

アルキル硫酸塩あるいはアルキルベンゼン, スルフォン酸塩を捕収剤として用いたときの黄鉄鉱, 黄銅鉱の浮遊性について

The collecting action of alkyl sulfate or alkylbenzene sulfonate against pyrite was studied from the view point of the separation of chalcopyrite from pyrite. The results were summarized as follows.1. Pyrite floated in acidic pulp, even in the case where only frother was used, because pyrite surface was oxidized to hydrophobic elemental sulphur. The pH region where pyrite floated extended towards more alkaline side, as the addition of this type of collectors increased. But, pyrite did not float above pH 8, even by the addition of the appreciable amounts of these collectors2. The native floatability of chalcopytite was varied by the difference of the method of preparation of mineral samples. Chalcopyrite which was dried in vacuum after wet grinding floated perfectly below pH 12 by using frother alone. While, chalcopyrite after wet grinding did not float above pH 10, but, it floated in pH value of about 12 by the addition of small amounts of this type of collectors.3. There was no substantial difference in adsorption mechanism of these collectors between pyrite and chalcopyrite. The amounts of adsorption decreased with increasing pH when pH exceeded a certain value below which the adsorption amounts of collectors remained constant. Also, in the case of constant pH value, the amounts of adsorption rapidly increased at critical concentration of collector through the formation of hemimicelles.4. The floatability of pyrite increased remarkably even in the collector concentration less than that of hemimicelle formation.From the above results, it was concluded that the role of this type of collector was to enhance the difference in native floatabilities of chalcopyrite and pyrite by collector adsorption, thus making it possible to separate chalcopyrite from pyrite at lower pH value than in xanthate flotation. This will be regarded as one of the characteristics of the flotation in which alkyl sulfate type collector is used.