Hanlie Hong

A mechanistic study of ciprofloxacin removal by kaolinite

As one of the most important soil components, kaolinite plays a vital role in transport and retention of ionizable contaminants in soils of warm and wet climate. Ciprofloxacin (Cip) is a second generation fluoroquinolone (FQ) antibiotic of high use. It has high aqueous solubility under high and low pH conditions and higher stability in soil system. In this study, the interactions between Cip and kaolinite in aqueous solution were investigated by batch experiments, XRD and FTIR analyses. Quantitative correlation between the exchangeable cations desorbed and Cip adsorbed confirmed experimentally that cation exchange was the dominant mechanism of Cip adsorption on kaolinite. Fitting of experimental data to the cation exchange model resulted in a selectivity coefficient of 27, suggesting a strong affinity of Cip on negatively charged kaolinite surfaces. At the adsorption maximum 190-200 Å(2) was available per Cip molecule, much larger than the Cip molecule area, confirming charge-limited instead of surface-limited Cip adsorption. The invariable d-spacing after uptake of different amounts of Cip suggested that the adsorption of Cip was on the external surfaces of kaolinite. As solution pH increased beyond 8, the amount of Cip adsorption decreased significantly and reached close to zero at pH 11. The high adsorption rate constant due to surface adsorption instead of intercalation and the wide distribution of kaolinite in different soils suggest that the fate and transport of Cip may be governed by the transport of colloidal sized clays.

An FTIR investigation of hexadecyltrimethylammonium intercalation into rectorite

Rectorite is an interstratified clay mineral made at 1:1 ratio of an orderly arrangement of a nonswelling component illite and a swelling component smectite. Due to the presence of two distinct types of components, it is of great interest to study the adsorption of long chain alkylammonium in rectorite. In this study, we conducted batch experiments and used X-ray diffraction (XRD) and Fourier Transform infrared (FTIR) spectroscopy to characterize the interlayer configuration of intercalated long chain hexadecyltrimethylammonium (HDTMA) in rectorite. The FTIR results showed that a monomer-like intercalation with extensive gauche conformers was formed at surfactant loading less than the cation exchange capacity (CEC) of the mineral. At a higher surfactant loading the CH2--symmetric and anti-symmetric vibrations shifted to lower frequencies, suggesting a more ordered all-trans surfactant interlayer configuration. The thermogravimetric and derivative of thermogravimetric analayses showed a high pyrolysis temperature for the monomer-like gauche conformers and lower pyrolysis temperature for the all-trans configuration of the intercalated HDTMA. The XRD analysis confirmed the monomer-like conformation with a d-spacing of 25.2 angstroms at the low surfactant intercalation and a vertical all-trans configuration with a d-spacing of 49.5 angstroms at an HDTMA intercalation of 3.20 CEC. In addition to conformation analyses of intercalated surfactant in the interlayer using FTIR, the absorbance measured by peak height at 1470, 2850, and 2917 cm(-1) increased linearly with surfactant loading, providing a faster, yet efficient method to quantify the amount of surfactant adsorbed.

Desorption of ciprofloxacin from clay mineral surfaces

Desorption from soil clay components may affect the transport and fate of antibiotics in the environment. In this study, ciprofloxacin (CIP) desorption from a kaolinite and a montmorillonite was investigated under different pHs, different concentrations of metal cations of various valencies (Na(+), Ca(2+) and Al(3+)) and a cationic surfactant hexadecyltrimethylammonium (HDTMA), and different desorption cycles. Desorption of CIP from kaolinite and montmorillonite was strongly pH-dependent and desorption isotherms were well fitted with the Langmuir equation. The percentage of CIP desorbed increased with increasing initial CIP loadings, desorbing cation concentrations, and desorption cycles. Comparatively, CIP was more readily desorbed from kaolinite than from montmorillonite. Moreover, the hysteresis index values were all negative, suggesting that the presence of metal cations and HDTMA in solution promoted CIP desorption from clay minerals, owing to cation exchange. The XRD analyses indicated that desorption of CIP occurred from both external and interlayer surfaces of montmorillonite. Formation of Al-CIP complex on solid surface and then detachment of Al-CIP from the solid surface may contribute to the higher CIP desorption by Al(3+) in comparison to Na(+) and Ca(2+).

Retardation of chromate through packed columns of surfactant-modified zeolite.

In this study, zeolite aggregates with particle size < 0.4, 1.4-2.4, and 3.6-4.8 mm were modified by the cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide to a surfactant loading level of 80, 130, and 250 mmol kg(-1), respectively. The modified and unmodified zeolites were subjected to column tests to study the chromate transport and retardation as affected by particle size. At an input concentration of 11-15 mg L(-1), unmodified zeolite did not retard chromate transport for all three particle size ranges. In contrast, the observed retardation factor for chromate, defined as the number of pore volumes passed when the output concentration equals to half of the input concentration, was 55, 50, and 500 for the columns packed with 3.6-4.8, 1.4-2.4, and < 0.4 mm modified zeolite, respectively. Prolonged tailing of chromate desorption from the modified zeolite was the most striking feature after the feeding solution was switched from chromate to water at full breakthrough. Monitoring of HDTMA and counterion bromide concentration in the effluent revealed that slow but persistent desorption of HDTMA and bromide occurred throughout the transport experiment, which resulted in stripping off of the upper layer of the surfactant bilayer formation on zeolite. The change of HDTMA surfactant surface configuration from bilayer to monolayer resulted in a loss of functionality to absorb and immobilize chromate on the modified zeolite surfaces.

OLIGOCENE CLAY MINERALOGY OF THE LINXIA BASIN: EVIDENCE OF PALEOCLIMATIC EVOLUTION SUBSEQUENT TO THE INITIAL-STAGE UPLIFT OF THE TIBETAN PLATEAU

The clay mineral content of the Oligocene sediments in the Linxia Basin has been investigated using X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The clay mineral assemblages are mainly mixed-layer illite-smectite (I-S), illite, kaolinite and minor palygorskite in the early-Middle Oligocene deposits, mixed-layer I-S, illite and kaolinite in the Middle Oligocene deposits, mainly illite and chlorite (usually >50–70 vol.%), mixed-layer I-S, and trace to minor palygorskite in the late Oligocene sediments, respectively. The mineral assemblage indicates a warm and seasonally humid climate in the Middle Oligocene, with an episode of warm and dry conditions in the early stage of the Middle Oligocene, and a trend of temperature decrease and more arid conditions in the late Oligocene. Climate evolution in the Oligocene corresponds with the significant elevation change in central Tibet since late Oligocene, and therefore, suggests that tectonic-forced cooling of climate took place in Linxia in the northeast margin of the Tibetan Plateau. The ubiquitous mixed-layer I-S and carbonates throughout the Oligocene sediments reflect relatively small fluctuations in climate conditions during the epoch. The changes in clay mineral components and feldspars in the late Oligocene suggest a variation in the source of clastic materials, which probably reflects an increase in erosion of soils and poorly weathered parent rock in more elevated or high-relief source areas during this period of tectonic uplift.

Removal of diphenhydramine from water by swelling clay minerals.

Frequent detection of pharmaceuticals in surface water and wastewater attracted renewed attention on studying interactions between pharmaceuticals and sludge or biosolids generated from wastewater treatment. Less attention was focused on studying interactions between pharmaceuticals and clay minerals, important soil and sediment components. This research targeted on investigating interactions between diphenhydramine (DPH), an important antihistamine drug, and a montmorillonite, a swelling clay, in aqueous solution. Stoichiometric desorption of exchangeable cations accompanying DPH adsorption confirmed that cation exchange was the most important mechanism of DPH uptake by the swelling clay. When the solution pH was below the pK(a) of DPH, its adsorption on the swelling clay was less affected by pH. Increasing solution pH above the pK(a) value resulted in a decrease in DPH adsorption by the clay. An increase in d(001) spacing at a high DPH loading level suggested interlayer adsorption, thus, intercalation of DPH. The results from this study showed that swelling clays are a good environmental sink for weak acidic drugs like DPH. In addition, the large cation exchange capacity and surface area make the clay a good candidate to remove cationic pharmaceuticals from the effluent of wastewater treatment facilities.

Influence of chain lengths and loading levels on interlayer configurations of intercalated alkylammonium and their transitions in rectorite.

There have been extensive studies on intercalation of alkylammonium into swelling clay minerals for the purpose of surface charge determination of the clay minerals, as well as their interlayer configurations in the clay minerals. The most accepted findings are that the intercalated alkylammonium molecules adopted horizontal monolayer, bilayer, pseudotrilayer, and vertical paraffin-like configurations in the interlayer space of the swelling clay minerals depending on the chain length and loading level of the alkylammonium used. This study examined the interlayer configurations of intercalated alkyltrimethylammonium and their transition structure as a function of alkylammonium inputs and chain lengths. As the amount of alkylammonium intercalation increased, the bilayer configuration of the intercalated alkylammonium was absent during a transition from a horizontal monolayer to a pseudotrilayer intercalation. Instead, the transition structure involved a mixed layer made of rectorite intercalated with one layer and rectorite intercalated with pseudotrilayer of alkylammonium molecules. When intercalated in horizontal monolayer, the alkylammonium molecules took a random, more gauche-like arrangement. On the other hand, as alkylammonium molecules adopted a pseudotrilayer, particularly the vertical paraffin-like arrangement, a more ordered all-trans configuration was achieved. As layer charge is one of the most important properties of swelling clay minerals, commonly determined by intercalation of n-alkylammonium ions, the identification of mixed-layer transition structure in this study may suggest a need for further investigations on principles of layer charge determination of swelling clays by the alkylammonium method.

FTIR and XRD investigations of tetracycline intercalation in smectites

Due to swelling, smectite minerals are capable of intercalating many organic molecules in their interlayer space. Tetracycline (TC) is a group of antibiotics used extensively in human and veterinary medicine. The great aqueous solubility and long environmental half life of TC mean that the study of interactions between swelling clay minerals and TC are of great importance in TC transport and retention in subsurface soils. In the present study, the intercalation of TC molecules at different levels into smectites was investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The shift of the FTIR bands of amide I and II in comparison to crystalline TC suggested a strong interaction between the amide groups and the clay surfaces. The band at 1455 cm−1 remained the same after TC intercalation into SAz-1, SWy-2, and SYn-1, suggesting that complexation was not a dominant mechanism of TC uptake by these minerals. With cation exchange as the major mechanism of TC intercalation into these minerals, simultaneous removal of H+ from solution protonated the TC molecules and provided a positive charge to interact with negatively charged mineral surfaces even in neutral to slightly alkaline conditions. The increase in interlayer distance after intercalation by TC, as revealed by XRD, suggested a tilted orientation of the intercalated TC molecules in both twisted conformation in acidic condition and extended conformation in alkaline condition.

CLAY MINERALOGY ACROSS THE P-T BOUNDARY OF THE XIAKOU SECTION, CHINA: EVIDENCE OF CLAY PROVENANCE AND ENVIRONMENT

The provenance of clays in shaley intervals across the Permian-Triassic boundary (PTB) in the Xiakou section was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), and the results suggest that the layers have three different provenances. The layer P267-b has a loose texture with an oriented arrangement of detrital clay particles, consisting mainly of illite and minor chlorite with irregular outlines or ragged edges. The dehydroxylation reaction of the clays in this layer is characterized by an intense overlapping endothermic effect at ∼600°C, produced by mixed-layer illite-smectite (I-S) consisting of a mixture of cis-vacant (cv)and trans-vacant (tv) octahedral sheets derived from weathering of detrital illite. Layer P259-b shows a more condensed texture with a dark color, and is composed mainly of I-S and minor illite and chlorite. Evidence for alteration of detrital materials to clay mineral aggregates was observed under SEM. Similar to layer P267-b, an intense dehydroxylation reaction occurs at ∼600°C, indicating clays consisting of a mixture of tv and cv sheets and, therefore, that the sediments were derived from a mixture of terrigenous and volcanic sources, combining the texture and the clay-mineral composition of those sediments. However, the undisturbed lamination and relatively small grain size in this bed indicate a low-energy depositional environment. The clay-mineral compositions of the other layers are mainly of I-S with minor amounts of illite and chlorite. Their endothermic dehydroxylation reaction, however, occurs mainly at ∼660°C, indicating that cv sheets are dominant in the clays, and thus, are derived from smectites of volcanic origin. Observations by SEM show that clay minerals grow at the expense of detrital materials, confirming the diagenetic alteration of volcanic ashes in marine sediments. Illite and chlorite are the detrital clay minerals in the clay layers across the PTB in the Xiakou section. The presence of detrital illite and chlorite in the sediments means that an arid climate prevailed in the region during the end-Permian and early Triassic period.

The early-Eocene climate optimum (EECO) event in the Qaidam basin, northwest China: clay evidence

Abstract Clay mineralogy and its palaeoclimatic interpretation of the early-Eocene (~53.3-49.70 Ma) sediments at Lulehe, Qaidam basin, northwest China, were investigated using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The interval of ~53.3–49.70 Ma, including the early-Eocene climate optimum (EECO) with isotopic events, was the transition period of ‘‘greenhouse’’ to ‘‘icehouse’’. Climate changes during the episode were documented in the sediments and were expressed by the proportion of clay species and clay indices, as well as by the proportion of non-clay minerals, gypsum, halite and calcite. Our results suggest that a warm and humid climate prevailed over the period ~53.3–52.90 Ma, followed by a warm and seasonally dry and humid climate in the period ~52.90–51.0 Ma and a subsequently warm and humid climate in the period ~51.0–49.70 Ma. Three warmer and more humid intervals were observed at 52.7, 51.0 and 50.5 Ma based on clay indices. The climate evolution in the Qaidam Basin during the period derived from the clay mineralogical study is in good agreement with the early Eocene global climate change, and the warm and seasonally dry and humid episode in the early Eocene in Qaidam basin is a regional response to the global early-Eocene climate optimum.