Assessing the impact of preload on pyrite-rich sediment and groundwater quality.

Pyrite-rich sediments would, invariably, undergo redox reactions which would lead to acidic aqueous environment containing solubilized toxic metal species. When such sediments are subjected to preload, a technique employed by geotechnical engineers to improve the load-bearing capacity of highly compressible formation, transient flow of pore water, accompanied by acidity transfer, would occur as a response. Despite the concomitant environmental and socio-economic significance, to date, there has been limited interdisciplinary research on the underpinning geotechnical engineering and geo-environmental science issues for pyrite-rich sediments under preload. In this study, we investigate the effect of pyrite-rich sediment pore water transfer under preload surcharge on the receiving environment and the impact on the groundwater speciation and quality. Sediment samples were obtained at close depth intervals from boreholes established within pristine areas and those subjected to the preload application. Soil and pore water samples were subjected to solid/solution speciation, moisture contents, soil pH and the Atterberg Limits' analyses using standard analytical techniques and methods. Standpipes were also installed in the boreholes for groundwater sampling and in situ monitoring of water quality parameters. It is shown that the imposition of preload surcharge over pyritic sediment created a reducing environment rich in SO42-, iron oxide minerals and organic matter. This reducing environment fostered organic carbon catabolism to generate excess pyrite and bicarbonate alkalinity, which would invariably impact adversely on soil quality and plant growth. These were accompanied by increase in pH, dissolved Al, Ca, Mg and K species beneath the surcharge.

In situ particle film ATR FTIR spectroscopy of poly (N-isopropyl acrylamide) (PNIPAM) adsorption onto talc.

The adsorption of poly(N-isopropyl acrylamide) (PNIPAM) onto talc from aqueous solutions has been studied using the in situ methodology of particle film attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. PNIPAM was observed to adsorb significantly onto the talc particle film at a temperature below its lower critical solution temperature (LCST). Peak shifts were seen in the adsorbed layer FTIR spectrum that match those observed when PNIPAM solution is heated above its LCST. This observation indicates that adsorption causes a conformational re-arrangement similar to that seen when PNIPAM undergoes a coil-to-globule transition, in this case presumably induced by hydrophobic interactions between PNIPAM and the talc basal plane surface. The kinetics of adsorption are seen to be complex, with potential influences of conformational rearrangement and differential adsorption kinetics for the two dominant surface regions of talc particles. The adsorbed PNIPAM was seen to be exceptionally resistant to removal, with no desorption occurring when a background electrolyte solution was flowed over the adsorbed layer. Spectra acquired of the adsorbed polymer layer heated above the LCST reveal that a further conformational rearrangement takes place for the adsorbed layer, finalizing the transition from coil-to-globule that was initiated by the interaction with the mineral surface.

Carboxymethylcellulose adsorption on molybdenite: the effect of electrolyte composition on adsorption, bubble-surface collisions, and flotation.

The adsorption of carboxymethylcellulose polymers on molybdenite was studied using spectroscopic ellipsometry and atomic force microscopy imaging with two polymers of differing degrees of carboxyl group substitution and at three different electrolyte conditions: 1 × 10(-2) M KCl, 2.76 × 10(-2) M KCl, and simulated flotation process water of multicomponent electrolyte content, with an ionic strength close to 2.76 × 10(-2) M. A higher degree of carboxyl substitution in the adsorbing polymer resulted in adsorbed layers that were thinner and with more patchy coverage; increasing the ionic strength of the electrolyte resulted in increased polymer layer thickness and coverage. The use of simulated process water resulted in the largest layer thickness and coverage for both polymers. The effect of the adsorbed polymer layer on bubble-particle attachment was studied with single bubble-surface collision experiments recorded with high-speed video capture and image processing and also with single mineral molybdenite flotation tests. The carboxymethylcellulose polymer with a lower degree of substitution resulted in almost complete prevention of wetting film rupture at the molybdenite surface under all electrolyte conditions. The polymer with a higher degree of substitution prevented rupture only when adsorbed from simulated process water. Molecular kinetic theory was used to quantify the effect of the polymer on the dewetting dynamics for collisions that resulted in wetting film rupture. Flotation experiments confirmed that adsorbed polymer layer properties, through their effect on the dynamics of bubble-particle attachment, are critical to predicting the effectiveness of polymers used to prevent mineral recovery in flotation.

Surface-functionalized diatom microcapsules for drug delivery of water-insoluble drugs.

Naturally available and biocompatible materials are potential substitutes for synthetic mesoporous materials as suitable drug carriers for the development of cost-effective drug delivery systems. This work investigates the application of a porous silica material derived from diatoms, also known as diatomaceous earth. The aim is to explore the surface functionalization of diatom microcapsules and their impact on the drug loading and release characteristics of water-insoluble drugs. Indomethacin was used as the model for poorly soluble drug. The surface modification on diatoms was performed with two organosilanes; 3-aminopropyltriethoxy silane and N-(3-(trimethoxysilyl) propyl) ethylene diamine and phosphonic acids (2-carboxyethyl-phosphonic acid and 16-phosphono-hexadecanoic acid) providing organic surface hydrophilic and hydrophobic properties. Extensive characterizations using scanning electron microscopy, X-ray photoelectron spectroscopy and differential scanning calorimetry was performed to confirm covalent grafting of monolayer aminosilane and phosphonic acid on the diatom surfaces. Differences in loading capacity of diatoms (15-24%) and release time (6-15 days) were observed which is due to the presence of different functional groups on the surface. It was found that 2-carboxyethyl-phosphonic acid, 3-aminopropyltriethoxy silane and N-(3-(trimethoxysilyl) propyl) ethylene diamine render diatom surfaces hydrophilic, due to polar carboxyl functional group (COOH) and active amine species (NH and NH2) that favor drug adsorption; better encapsulation efficiency and prolonged release of drugs, over the hydrophobic surface created by 16-phosphono-hexadecanoic acid. This work demonstrates diatom porous silica as a promising drug carrier, with possibility to further improve their performances by tailoring their surface functionalities to achieve the required drug loading and release characteristics for different therapeutic conditions.

Polymer micelles for delayed release of therapeutics from drug-releasing surfaces with nanotubular structures.

A new approach to engineer a local drug delivery system with delayed release using nanostructured surface with nanotube arrays is presented. TNT arrays electrochemically generated on a titanium surface are used as a model substrate. Polymer micelles as drug carriers encapsulated with drug are loaded at the bottom of the TNT structure and their delayed release is obtained by loading blank micelles (without drug) on the top. The delayed and time-controlled drug release is successfully demonstrated by controlling the ratio of blank and drug loaded-micelles. The concept is verified using four different polymer micelles (regular and inverted) loaded with water-insoluble (indomethacin) and water-soluble drugs (gentamicin).

A multi-drug delivery system with sequential release using titania nanotube arrays.

A multi-drug delivery system with sequential release based on titania nanotube arrays and polymer micelles as drug carriers is presented. Delivery of multiple water insoluble and soluble drugs required for combined local therapy is demonstrated.

Functionalized diatom silica microparticles for removal of mercury ions.

Diatom silica microparticles were chemically modified with self-assembled monolayers of 3-mercaptopropyl-trimethoxysilane (MPTMS), 3-aminopropyl-trimethoxysilane (APTES) and n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS), and their application for the adsorption of mercury ions (Hg(II)) is demonstrated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed that the functional groups (-SH or -NH2) were successfully grafted onto the diatom silica surface. The kinetics and efficiency of Hg(II) adsorption were markedly improved by the chemical functionalization of diatom microparticles. The relationship among the type of functional groups, pH and adsorption efficiency of mercury ions was established. The Hg(II) adsorption reached equilibrium within 60 min with maximum adsorption capacities of 185.2, 131.7 and 169.5 mg g-1 for particles functionalized with MPTMS, APTES and AEAPTMS, respectively. The adsorption behavior followed a pseudo-second-order reaction model and Langmuirian isotherm. These results show that mercapto- or amino-functionalized diatom microparticles are promising natural, cost-effective and environmentally benign adsorbents suitable for the removal of mercury ions from aqueous solutions.

Silica microcapsules from diatoms as new carrier for delivery of therapeutics.

AIM: This study explores the use of natural silica-based porous material from diatoms, known as diatomaceous earth, as a drug carrier of therapeutics for implant- and oral-delivery applications. MATERIALS & METHODS: To prove this concept, two drugs models were used and investigated: a hydrophobic (indomethacin) and hydrophilic (gentamicin). RESULTS & DISCUSSION: Results show the effectiveness of diatom microcapsules for drug-delivery application, showing 14-22 wt% drug loading capacity and sustained drug release over 2 weeks. Two steps in the drug release from diatom structures were observed: the first, rapid release (over 6 h is attributed to the surface deposited drug) and the second, slow and sustained release over 2 weeks with zero order kinetics. CONCLUSION: These results confirm that natural material based on diatom silica can be successfully applied as a drug carrier for both oral and implant drug-delivery applications, offering considerable potential to replace existing synthetic nanomaterials.

Chemical functionalization of diatom silica microparticles for adsorption of gold (III) ions.

Diatom silica microparticles from natural diatomaceous earth (DE) silica have been functionalized with 3-mercaptopropyltrimethoxysilane (MPTMS) and their application for adsorption of gold (III) ions from aqueous solutions is demonstrated. Fourier transform infrared spectroscopy (FTIR) and X-ray Photoelectron spectroscopy (XPS) analyses of the MPTMS modified diatom microparticles revealed that the silane layer with functional group (-SH) was successfully introduced to the diatom surface. The adsorption study of Au(III) ions using MPTMS-DE indicated that the process depends on initial gold (III) concentration and pH showing maximum adsorption capacity at pH = 3. The Au(III) adsorption kinetics results showed that the adsorption was very fast and followed a pseudo-second-order reaction model. The Langmuir model was used to provide a sound mechanistic basis for the theoretical of the adsorption equilibrium data. Gold recovery from MPTMS-DE structures was also investigated by using acidified thiourea solution and found to be high (> 95%). These results show that chemically modified DE microparticles can be used as a new, cost effective and environmentally benign adsorbent suitable for adsorption of gold metal ions from aqueous solutions.

Surface functionalisation of diatoms with dopamine modified iron-oxide nanoparticles: toward magnetically guided drug microcarriers with biologically derived morphologies.

Diatom silica microcapsules prepared by purification of diatomaceous earth (DE) were functionalised by dopamine modified iron-oxide nanoparticles, in order to introduce diatoms with magnetic properties. The application of magnetised diatoms as magnetically guided drug delivery microcarriers has been demonstrated.

Synthesis of self-supporting gold microstructures with three-dimensional morphologies by direct replication of diatom templates.

Diatoms (unicellular algae) form porous silica walls (frustule) with intricate, hierarchically organized three-dimensional (3D) structures with micro- to nanoscale dimensions. This paper presents the fabrication of self-supporting gold microstructures with complex 3D morphologies by using electroless gold deposition onto a diatom silica substrate, followed by the substrate removal by acid dissolution. It was demonstrated that gold diatom replicas with distinct micro- to nanoscale structures can be created by a simple and scalable process based on electroless gold deposition. Excellent catalytic properties (catalytic rate constant k = 23.5 +/- 1 x 10(-2) min(-1)) of prepared gold replica catalysts were confirmed for the reduction process of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) in the presence of NaBH(4) as the reductant. This synthetic approach is general and flexible, and it is envisaged that it can be applied for the preparation of a wide range of different metals (Pt, Pd, Ag, Ni, etc.) offering more efficient catalytic, optical, or magnetic properties.

Spectroscopic investigation of the adsorption mechanisms of polyacrylamide polymers onto iron oxide particles.

The mechanisms of high-molecular-weight polyacrylamide nonionic homopolymer and 25 mol% anionic acrylate-substituted copolymer adsorption onto iron oxide particles were investigated via DRIFT and UV-vis spectroscopies at three pH values (6, 8.5, and 11). While electrostatic interactions play an important role in charged polymer adsorption, this information is not spectroscopically available. At pH values above and below pH 8.5 (the isoelectric point for the anionic polymer), bidentate chelation and hydrogen bonding were the main adsorption mechanisms. At the isoelectric point, monodentate chelation was observed to be the main mode of adsorption, along with hydrogen bonding. For the nonionic polymer, in all cases, hydrogen bonding through the carbonyl group was the main mode of adsorption. The adsorption of both polymers conformed well to the Freundlich model, suggesting that the adsorbed polymer amount increases with increasing polymer concentration up to 7500 g/t solid, rather than approaching monolayer coverage. Spectroscopic evidence was found to suggest that hydrolysis of nonionic polyacrylamide occurs at high pH.

Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization.

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 degrees C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100-500 rpm) and time (15/60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of "honeycomb" particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20-22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5-7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.

The influence of Al(III) supersaturation and NaOH concentration on the rate of crystallization of Al(OH)3 precursor particles from sodium aluminate solutions.

The growth kinetics of colloidal Al(III)-containing particles (diameter<1000 nm), nucleated in optically clear, supersaturated sodium aluminate solutions as a precursor to Al(OH)(3) crystals, has been studied using dynamic light scattering. Two series of solutions were examined at 22 degrees C to determine the influence of Al(III) supersaturation and NaOH concentration on the initial particle growth behavior. One solution series consisted of solutions with constant Al(III) absolute supersaturation (DeltaC) of 1.48 M and [NaOH] range 1.83-4.00 M ([NaOH]/[Al(III)]=1.13-2.15) and Al(III) relative supersaturation (sigma)=3.86-10.36. The other solution series had a constant sigma of 7.55 and [NaOH] range of 1.50-4.27 M ([NaOH]/[Al(III)]=1.18-1.54) and DeltaC=0.86-3.19. The correlation between the initial particle growth rates and supersaturation (DeltaC or sigma) revealed marked anomalies over the entire supersaturation range studied. The growth rate remained substantially constant in the DeltaC range 0.86-2.55 M (for the constant sigma solution series), before increasing sharply upon a further increase of DeltaC beyond 2.55 M. The variation of the growth rate with sigma in the range 3.86-9.00 (for the constant DeltaC solution series) was remarkably weak, contrary to expectation. At higher sigma (>9.00), however, a marked increase in growth rate with increasing sigma was displayed. At constant DeltaC or sigma, the growth rate showed a strong variation with NaOH concentration, indicating that Na(+) and OH(-) species play a pivotal role in the Al(OH) precursor particles (nuclei) growth process. Furthermore, the kinetics of growth displayed by these nanosized particles are an order of magnitude slower than those observed for macroscopic gibbsite (gamma-Al(OH)(3)) crystals at similar supersaturations and temperature. The difference may be rationalized in terms of particle size and Al(OH)(3) dimorphic phase dependent solubility effects. An empirically adequate growth kinetics modeling was achieved when the growth rates were correlated with the Al(III) supersaturation (DeltaC or sigma) and the excess (free) NaOH concentration, rather than the former alone, as is commonly the case. A critical [NaOH]/[Al(III)] molar ratio of 1.27-1.35, below which the particle growth rate increased markedly and above which the rate was significantly reduced, was observed. This behavior is believed to be linked to solution speciation change that occurs at certain Al(III) and NaOH compositions.

Interfacial-chemistry mediated behavior of colloidal talc dispersions.

Interfacial chemistry and rheological behavior of talc suspensions as a function of pH, talc solid content, and type and concentration of ions have been investigated using electrokinetic measurements, rheology, settling behavior, and solution analysis. Zeta potential measurements show a strong dependence on the pH history of the talc suspension that only occurs when the surface area (solid content) of the talc is high. Particle interactions measured through dispersion yield stress measurements show a similar dependence. Talc is a magnesium silicate mineral and the dependence seen in the electrokinetic properties in this study has been attributed to Mg(II) dissolution at low pH, and has been confirmed by solution analysis. At high solid content (>20 wt%), pronounced Mg(II) ion dissolution occurs at low pH values. Formation and adsorption of electropositive Mg(II) hydrolysis products occurs at high pH (>9), and these lead to zeta potential reduction and, at high solid contents, charge reversal. Particle interactions reflect the surface chemistry behavior. Consequently, for a freshly prepared suspension at high pH, the yield stress is lower compared to after the pH has been taken to 5 and subsequently increased.

Temperature influence of nonionic polyethylene oxide and anionic polyacrylamide on flocculation and dewatering behavior of kaolinite dispersions.

Nonionic polyethylene oxide (PEO) and anionic polyacrylamide (PAM) flocculation of kaolinite dispersions has been investigated at pH 7.5 in the temperature range 20-60 degrees C. The surface chemistry (zeta potential), particle interactions (shear yield stress), and dewatering behavior were also examined. An increase in the magnitude of zeta potential of kaolinite particles, in the absence of flocculant and at a fixed PEO and PAM concentration, with increasing temperature was observed. The zeta potential behavior of the flocculated particles indicated a decrease in the adsorbed polymer layer thickness, while at the same time, however, the adsorbed polymer density showed a significant increase with increasing temperature. These results suggest that polymer adsorption was accompanied by temperature-influenced conformation changes. The hydrodynamic diameter and supernatant solution viscosity of both polymers decreased with increasing temperature, consistent with a change in polymer-solvent interactions and conformation, prior to adsorption. The analysis of the free energy (DeltaG(ads)) of adsorption showed a strong temperature dependence and the adsorption process to be more entropically than enthalpically driven. The polymer conformation change and increased negative charge at the kaolinite particle surface with increasing temperature resulted in decreased polymer bridging and flocculation performance. Consequently, the shear yield stress and the rate and the extent of dewatering (consolidation) of the pulp decreased significantly at higher temperatures (>40 degrees C). The temperature effect was more pronounced in the presence of PEO than PAM, with 40 and 20 degrees C indicated as the optima for enhanced performance of the latter and former flocculants, respectively. The results demonstrate that a temperature-induced conformation change, together with polymer structure type, plays an important role in flocculation and dewatering behavior of kaolinite dispersions.

Influence of hydrolyzable metal ions on the interfacial chemistry, particle interactions, and dewatering behavior of kaolinite dispersions.

The influence of hydrolyzable metal ions (Mn(II) and Ca(II)) adsorption on the surface chemistry, particle interactions, flocculation, and dewatering behavior of kaolinite dispersions has been investigated at pH 7.5 and 10.5. Metal ion adsorption was strongly cation type- and pH-dependent and significantly influenced the zeta potential, anionic polyacrylamide-acrylate flocculant (PAM) adsorption, shear yield stress, settling rate, and consolidation of kaolinite slurries. The presence of Mn(II) and Ca(II) ions alone led to a systematic reduction in zeta potential due to specific adsorption of positively charged metal ion-based hydrolysis products at the kaolinite-water interface. Metal ion-mediated zeta potential changes were reflected by lower dispersion shear yield stresses and improved clarification (higher settling rates) but had no detectable effect on dispersion consolidation. The adsorption of PAM was significantly improved by prior addition of the metal ions. In the presence of Mn(II) or Ca(II) ions, the flocculant adsorption density was enhanced at pH 7.5 for Mn(II) and pH 10.5 for Ca(II). Optimum flocculation conditions, involving partial rather than complete particle surface coverage by both metal ions and flocculant, were identified. As a consequence, the metal ions and flocculant acted synergistically to enhance dewatering, producing particle interactions that were more conducive to high settling rates and greater consolidation of kaolinite dispersions at pH 7.5 than 10.5.