Mini-column Experiments Research Articles

Sorption experiments as efficient as possible: Mini-column experiments (MCE) using HPLC-ICP-MS coupling with a new data analysis approach to determine sorption parameters

To quantify retention and sorption parameters, diffusion-, batch- or column experiments are common practice. However, these are either not close to nature, extremely time-consuming or material intensive. A promising approach to eliminate these problems is the performance of mini-column experiments (MCE). Due to dynamic retention and realistic solid–liquid ratios, these are close to nature and resource-efficient. The aim of this work is to perform highly controllable MCE using a HPLC (high-performance liquid chromatography) system and HPLC-ICP-MS (inductively coupled plasma mass spectrometry) coupling. With this approach, ultra-fast sorption experiments are possible only using 100–150 mg adsorbent and 160 mL eluent. That means, sorption experiments are even more time- and cost-efficient and also more controllable than with conventional methods. The presented method is based on a newly developed MCE-HPLC-ICP-MS coupling, which was applied to investigate the sorption of Eu(III) on kaolinite and sand in 10 mM NaCl. With that it was possible to carry out dynamic sorption experiments in just 5–15 h and thus determine e.g. maximum loading capacity (qmax) in a very short amount of time. Furthermore, a quantification method for eluates of high ionic strength is presented. Here, the sorption of Cs(I) on calcium silicate hydrate (C-S-H) phases in 10 mM and 100 mM NaCl was investigated. For validation, the sorption distribution ratios (Rd) obtained were compared with those from batch experiments. These agreed very well with each other and with those from the literature. Overall, with MCE more sorption parameters can be determined much faster, more accurately and more efficient than with the conventional methods.

Development of mini column experiments (MCE) by coupling microliter flow HPLC with ICP-MS for the analysis of metal retention under conditions close to nature

The development and implementation of mini column experiments (MCE) can be of great importance to improve existing analytical methods such as highly standardised but unrealistic batch laboratory experiments or lengthy long-term diffusion experiments to study metal sorption/desorption properties. One envisaged application would be to test the retention of repository-relevant metals in claystone, which is a promising candidate for the host rock of a final repository site for high-level radioactive waste (HLW). The used MCE setup is derived from classical high performance liquid chromatography (HPLC). On this basis, coupling of MCE to ICP-MS (inductively coupled plasma mass spectrometry) detection was realised. This online separation enables the dynamic monitoring of metal sorption and desorption experiments on clay minerals (kaolinite), natural clay (Opalinus Clay) and mixtures with quartz sand in background solutions close to nature, and without the common use of metal complexing ligands, other reaction partners or buffers for the analysed metal ions. The optimised method allows the analysis of the retention of various contaminants in real groundwater solutions and compact clay samples in a reasonable amount of time and a small amount of sample. In addition, the coupling to the unspecific mass detector of ICP-MS enables the study of different radionuclides and homologues rather than the limited UV detection of a common HPLC.

Development of Mini Column Experiments (MCE) by Coupling Microliter Flow HPLC with ICP MS for the Analysis of Metal Retention Under Conditions Close to Nature

Development of Mini Column Experiments (MCE) by Coupling Microliter Flow HPLC with ICP MS for the Analysis of Metal Retention Under Conditions Close to Nature

Potential for biocolloid transport of cesium at high ionic strength

In subsurface repositories, active bacterial populations may directly influence the fate and transport of radionuclides including in salt repository systems like the Waste Isolation Pilot Plant in Carlsbad, NM. This research quantified the potential for transport and interaction between Chromohalobacter sp. and Cs in a high ionic strength system (2.6 M NaCl) containing natural minerals. Mini-column experiments showed that Chromohalobacter moved nearly un-retarded under these conditions and that there was neither association of Cs with microbes nor dolomite despite changes in bacterial metabolic phases. Growth batch experiments that monitored the potential uptake of Cs into the microbes confirmed results in column experiments where intracellular uptake of Cs by Chromohalobacter was not observed. These results show that Cs may be highly mobile if released in high ionic strength systems and/or carbonate minerals with negligible inhibition by these microbes.

An improved approach to design bioretention system media

Bioretention modified media consists of modifier, soil, sand, and organic matter (OM), which was applied to clean rainfall runoff pollutants and control flood. These should support plant growth, cost-effectiveness, local availability besides rainwater runoff and its pollution control. A modified bioretention media design approach was developed, to determine whether the modified media could compensate the deficiency of infiltration and/or purification ability for traditional bioretention soil mixing (BSM) and undisturbed soil. Taking the soil conditions of a typical area in northwest China as an example, we defined the BSM as the mixture of river sand, soil and wood chips, and the ratio was 65:30:5 by mass, and modified media are a mixture of BSM with modifiers. The characteristics of ten modifiers were tested, and the proportions of BSM and modifiers were determined though Langmuir adsorption isotherm mainly. The infiltration capacities of modified media were over 220 mm/h, and they were more than 3.4 times that of undisturbed soil. We also got the maximum adsorption capacity and longest lifespan media which were BSM + 10% water treatment residuals (WTR) for soluble reactive phosphorus (SRP), and BSM + 10% green zeolite (GZ) for ammonia though batch and mini-column experiments. Based on analytic hierarchy process (AHP), considering infiltration, water-holding adsorption, lifespan, and cost, the comprehensive performance of modified media is as follows: BSM + 10% flyash (0.2683) > BSM + 10% GZ (0.2589) > BSM + 10% WTR (0.2443) > BSM + 10% medical (0.1553) > BSM (0.0731). The results of this study will contribute to a greater understanding of adsorption mechanism of bioretention system media, contributing to the design and evaluation of bioretention efficient media.

Adsorption Characteristics of Several Bioretention-Modified Fillers for Phosphorus

To optimize the bioretention mixed fillers with better removal of phosphorus, this paper studies the adsorption characteristics of single filler and modified mixed filler through static adsorption experiments, and adopts the dynamical mini-column experiments to examine the adsorption capacities of the soil and modified mixed fillers. Results show that, in the static adsorption experiments, both water treatment residual (WTR) and fly ash exhibit good adsorption capacity when used as a single filler and modifier. Adsorption capacity increases with increasing WTR and fly ash dosage in the mixed filler. The modified mixed filler with WTR exerts a clear effect in the dynamic adsorption experiment, which is unsaturated when influent phosphorus concentration is 1 mg/L and inflow amount is equivalent to 15 years of precipitation. The adsorption capacity of WTR is 3.5–4.5 times that of other mixed fillers. Fly ash as a modifier shows a poor dynamic adsorption effect and thus must be continuously studied. In this study, WTR is recommended as a bioretention phosphorus removal additive. In engineering applications, the amount of WTR added can be controlled within 5–10% (by mass) according to influent phosphorus concentration.

Retention of neodymium by dolomite at variable ionic strength as probed by batch and column experiments

The results presented in this paper highlight the complexity of adsorption and incorporation processes of Nd with dolomite and significantly improve upon previous work investigating trivalent actinide and lanthanide interactions with dolomite. Both batch and mini column experiments were conducted at variable ionic strength. These data highlight the strong chemisorption of Nd to the dolomite surface (equilibrium Kd's > 3000 mL/g) and suggest that equilibrium adsorption processes may not be affected by ionic strength based on similar results at 0.1 and 5.0 M ionic strength in column breakthrough and equilibrium batch (>5 days) results. Mini column experiments conducted over approximately one year also represent a significant development in measurement of sorption of Nd in the presence of flow as previous large-scale column experiments did not achieve breakthrough likely due to the high loading capacity of dolomite for Nd (up to 240 μg/g). Batch experiments in the absence of flow show that the rate of Nd removal increases with increasing ionic strength (up to 5.0 M) with greater removal at greater ionic strength for a 24 h sampling point. We suggest that the increasing ionic strength induces increased mineral dissolution and re-precipitation caused by changes in activity with ionic strength that lead to increased removal of Nd through co-precipitation processes.

Understanding operational system differences for transfer of miniaturized chromatography column data using simulations

In this paper, a simulation tool was employed to identify and appropriately incorporate differences between MiniColumns and benchtop column systems. It was first demonstrated that including multi-step gradients and fraction collection into the simulations resulted in improved agreement between simulated and experimental linear gradient profiles as well as calculated first moments in the MiniColumn experiments. Step elution experiments of binary mixtures (a monoclonal antibody and one of three model proteins) were then carried out to examine comparability of the MiniColumns to the benchtop system. Although the peak shapes were qualitatively similar, peak elution began earlier in the MiniColumn system while improved separation was observed between overlapping peaks using the benchtop format. Simulations were then carried out to demonstrate that increased dispersion of the eluent breakthrough in the benchtop system could readily explain these observed differences. Importantly, by incorporating these system differences into the simulations, we were able to predict benchtop step elution performance using the parameters solely obtained from the MiniColumns. The findings presented in this paper illustrate that the appropriate consideration of system differences can facilitate the implementation of miniature chromatography columns as scale-down models for bioprocess development.

Layered Double Hydroxide and Its Calcined Product for Fluoride Removal from Groundwater of Ethiopian Rift Valley

In this study, batch experiments have been carried out to investigate the mechanism of fluoride uptake by layered double hydroxide (LDH) and calcined layered double hydroxide (CLDH). Furthermore, practical use of these synthetic minerals was studied in continuous mini-column experiments. In these column studies, groundwater from Ethiopia was tested. LDH and CLDH were synthesized with Mg/Al mole ratio of 2. From batch experimental study, LDH and CLDH have shown maximum removal capacity of 84 and 222 mg F−/g from aqueous solution, respectively. It was observed that fluoride removal was pH dependent with favorable pH range of 5–7 (max. at pH 6). The mechanism of removal is suggested to be ion exchange for LDH and a memory effect followed by surface precipitation reaction for CLDH. The presence of other anions lowered defluoridation capacity of LDH in the order of PO4 3− > SO4 2− > NO3 − ≈ Cl−. From continuous experiments at 1 mM NaHCO3, LDH showed maximum defluoridation capacity of 1.3 mg/g and CLDH up to 20 mg/g. It was also observed that increase of bicarbonate concentration to 10 mM lowered the fluoride uptake capacity of CLDH to 4 mg/g. The presence of 1 mM H4SiO4 further reduced fluoride uptake capacity to 3 mg/g. CLDH column tested with groundwater from the Rift Valley with 10.5 mg F−/L has shown maximum removal capacity of 2.2 mg F−/g. Regeneration of this column indicated that CLDH has a good potential to be re-used.

Experimental and modeling study on room-temperature removal of hydrogen sulfide using a low-cost extruded Fe2O3-based adsorbent

In order to prevent corrosion and catalyst deactivation, commercial adsorption processes for hydrogen sulfide (H2S) removal operate at relatively high temperature (350–450 °C) by ZnO adsorption. This paper reports firstly data from experimental and modeling studies of the dynamic performance of a low-cost extruded Fe2O3 -based adsorbent for H2S removal at room temperature. The H2S adsorbent containing iron (III) oxide (Fe2O3) and bentonite was prepared by hydrothermal-precipitation method and the material has been characterized by several techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), and low temperature N2 physical adsorption. The Fe2O3-based extruded adsorbent was used in a continuous fixed-bed column experiments to evaluate the efficiency for removal of H2S under the effect of various process parameters including the bed depth, the flow rate and the initial H2S concentration. The results showed that the total H2S uptake slightly increased with increasing the bed depth and the initial H2S concentration, and decreased with increasing the flow rate. In the modeling part, the dynamics of the adsorption process was modeled by two adsorption models namely, Thomas model and BDST (bed depth service time) model. The kinetic parameters obtained from the models were used to predict the breakthrough time for a larger column which contained the adsorbent about 40 times more than that in the mini column experiments. The Thomas model was the suitable model for prediction of 10 % C0 breakthrough time with an error about 4 %.

Comparison of low-cost and engineered materials for phosphorus removal from organic-rich surface water

Excess phosphorus (P) in lakes and rivers remains a major water quality problem on a global scale. As a result, new materials and innovative approaches to P remediation are required. Natural materials and waste byproduct materials from industrial processes have the potential to be effective materials for P removal from surface water. Advantages of natural and waste byproduct materials include their low-cost, abundant supply, and minimal preparation, especially compared with engineered materials, such as ion exchange resins and polymeric adsorbents. As a result, natural and waste byproduct materials are commonly referred to as low-cost materials. Despite the potential advantages of low-cost materials, there are critical gaps in knowledge that are preventing their effective use. In particular, there are limited data on the performance of low-cost materials in surface waters that have high concentrations of natural organic matter (NOM), and there are no systematic studies that track the changes in water chemistry following treatment with low-cost materials or compare their performance with engineered materials. Accordingly, the goal of this work was to evaluate and compare the effectiveness of low-cost and engineered materials for P removal from NOM-rich surface water. Seven low-cost materials and three engineered materials were evaluated using jar tests and mini-column experiments. The test water was a surface water that had a total P concentration of 132–250 μg P/L and a total organic carbon concentration of 15–32 mg C/L. Alum sludge, a byproduct of drinking water treatment, and a hybrid anion exchange resin loaded with nanosize iron oxide were the best performing materials in terms of selective P removal in the presence of NOM and minimum undesirable secondary changes to the water chemistry.

Monod kinetics rather than a first-order degradation model explains atrazine fate in soil mini-columns: Implications for pesticide fate modelling

Pesticide transport models commonly assume first-order pesticide degradation kinetics for describing reactive transport in soil. This assumption was assessed in mini-column studies with associated batch degradation tests. Soil mini-columns were irrigated with atrazine in two intermittent steps of about 30 days separated by 161 days application of artificial rain water. Atrazine concentration in the effluent peaked to that of the influent concentration after initial break-through but sharply decreased while influx was sustained, suggesting a degradation lag phase. The same pattern was displayed in the second step but peak height and percentage of atrazine recovered in the effluent were lower. A Monod model with biomass decay was successfully calibrated to this data. The model was successfully evaluated against batch degradation data and mini-column experiments at lower flow rate. The study suggested that first-order degradation models may underestimate risk of pesticide leaching if the pesticide degradation potential needs amplification during degradation.

Removal and recovery of phosphate from municipal wastewaters using a polymeric anion exchanger bound with hydrated ferric oxide nanoparticles

A new type of ion exchange media which is highly selective for phosphate, and can be easily regenerated has been investigated. The media consists of hydrated ferric oxide nanoparticles dispersed within the pore structures of polymeric anion exchanger beads. The media combines the durability and mechanical strength of ion exchange resins with the high sorption capacity of ferric oxide for phosphate. The media was trialled in fixed bed mini column experiments with real final effluent from two UK sewage treatment works, one with treatment based on chemical precipitation with iron chloride salts into an activated sludge process (population >250,000), and one based on trickling filter treatment with no specific phosphorus removal process (population <10,000). Results show that the media has high capacity for removing phosphate, reaching capacity at 4000 and 1300 bed volumes for the chemical precipitation and trickling filter works respectively, with performance greatly exceeding that of a standard anion exchanger, Amberlite IRA-410. Also trialled was the media's ability to elute the phosphorus after breakthrough, with the aim of recovering and processing it into a useful product. A one step regenerative process using a single solution containing 4% NaOH and 2% NaCl was passed through the resin bed and the phosphorus concentration of each bed volume leaving the column analysed. 80% of the phosphorus was eluted in the first bed volume. Subsequent tests investigated the performance of the media after successive partial regenerations of one bed volume of the NaOH/NaCl solution. There was no loss of performance observed after ten regeneration cycles, and levels of eluted phosphate were consistently high. These results suggest that the media has high potential for the removal and recovery of phosphate from wastewater streams. Additionally, the small volume of regenerant required translates to a very small operational footprint.

Hydrous ferric oxide as an adsorbent in water treatment: Part 2. Adsorption studies

The mechanism of arsenic adsorption onto hydrous granular ferric oxide is discussed in detail. The effect of arsenic speciation and complexation with the granular ferric hydroxide surface is discussed in relation to batch equilibration studies. Despite the complex nature of the binding mechanism, a Langmuir model provided a satisfactory fit of the data. Mini-column experiments have shown the effective sorption of arsenic from water in the pH range 7–8 and confirmed efficient elution using dilute mineral acid. Granular ferric hydroxide can be used for the removal of trace As(V) from water, eluted and recycled and moreover, the release of iron from the adsorbent was found to be negligible under appropriate operating conditions.

Virus removal within a soil infiltration zone as affected by effluent composition, application rate, and soil type

The column studies presented in this paper simulated the infiltrative surface of onsite wastewater systems where effluent is applied and where a biomat may form. Two bacteriophages, MS-2 and PRD-1, were used as surrogates for human pathogenic enteric viruses during two tracer tests. A vacuum manifold was used to simulate the drainage effects of an underlying unsaturated soil profile, allowing for the collection of percolate samples at 4 cm immediately below the infiltrative surface. The impact of effluent applied (septic tank effluent (STE) or a simulated ground water), soil type (medium sand or sandy loam), hydraulic loading rate (5 or 25 cm/day) and method of application (four equivalent daily doses or 24 equivalent micro-doses per day) on the removal of viruses were investigated. These unsaturated mini column experiments demonstrated that the removal of viruses within an infiltrative surface zone (of ∼4 cm) generally improved over time under the conditions studied. An exception occurred in sand-filled columns dosed with STE where the removal of PRD-1 decreased after a period of effluent application. Statistical analysis conducted on the calculated percent removal demonstrated that the quality of the effluent applied to the infiltrative surface is important for removal of MS-2 and PRD-1. Hydraulic loading rate also proved important in the removal of viruses. At the time of tracer test 2, columns dosed at the higher HLR (25 cm/day) had higher percent removals for both MS-2 and PRD-1. Soil type altered the removal of PRD-1 at the time of the second tracer test, at which time sandy loam had higher removal rates for PRD-1. No significant differences were observed between columns dosed four times daily and those dosed 24 times daily for either bacteriophage at either of the tracer test time points. These data suggest that over a relatively short period of operation the infiltrative surface of soil based wastewater treatment systems can achieve much higher removal then initially measured shortly after startup.

Comparative Adsorption of Nitrophenols on Macroporous Resin and Newly-Synthesized Hypercrosslinked Resin

The comparative adsorption of o-nitrophenol, m-nitrophenol and p-nitrophenol onto a macroporous polymeric adsorbent (Amberlite XAD-4) and a hypercrosslinked polymeric adsorbent (NJ-8) was investigated. Adsorption equilibrium isotherms were measured by batch equilibration over the temperature range 283-323 K, and two kinds of isotherm model (Langmuir and Freundlich) provided the best fit of the experimental data. The adsorption capacity for each adsorbate on NJ-8 was ca. twice that on Amberlite XAD-4, which is explained by the micropore structure and stronger donor-acceptor interaction of NJ-8 resin. Mini-column experiments showed that NJ-8 resin exhibited the longest breakthrough time. The enthalpy of adsorption was estimated from the temperature dependence of adsorption.

THE INFLUENCE OF ACTIVE CARBON OXIDATION ON THE PREFERENTIAL REMOVAL OF HEAVY METALS

Oxidized active carbons were prepared by employing air- and acid-oxidation methods. Weakly acidic surface-functional groups were incorporated on the carbon surface. The distribution of functional groups varied with the oxidation techniques used. Metal sorption characteristics of oxidized active carbons were measured in both batch and minicolumn experiments. The materials preferentially adsorbed lead and copper over nickel and cadmium. Furthermore, a variable selectivity of oxidized carbons toward copper and lead was found to be based on the means by which the carbon was oxidized. Through alteration of oxidation treatment conditions and employment of different oxidizing agents, the selectivity behavior of the materials was controlled. Possible mechanisms of metal sorption are discussed.

Purification of metal plating rinse waters with chelating ion exchangers

A wide range of chelating ion exchangers was tested for their abilities to remove Zn, Ni, Cu and Cd from solutions simulating waste effluents from the metal-plating industry. The task was to reduce metal discharges to the environment so that metal-plating shops could keep up with the modern, more stringent regulations of waste effluents. The resins were tested by batch and mini-column experiments. Decontamination factors (DFs) as high as 700 and capacities up to 3.3 meq/mL were measured at the 5% breakthrough (BT) point in mini-column tests. Complexing agents, especially cyanide, considerably reduced the performance of the resins with only a few exceptions. Ammonium seemed to improve the ion-exchange performance of some chelating resins and capacities higher than the theoretical values, given by the manufacturer, were measured. Comparative experiments between chelating, strong acid and weak acid ion-exchange resins showed that the advantage of chelating exchangers over strong and weak acid exchangers is a very low metal BT level, even as low as 2 μg/L, which is very important, especially in the end-of-pipe polishing.

Removal of Cadmium Using Electrochemically Oxidized Activated Carbon

A wood-based activated carbon, AUG WHK, was oxidized electrochemically to enhance its metal binding capacity and subsequently studied for the removal of cadmium ions from aqueous solution. Treated adsorbents were characterized by N2 adsorption at 77K before and after oxidation, and a quantitative determination of weak-acid surface groups was carried out by direct titration. The BET surface area decreased considerably after oxidation ; however, the total amount of oxygen-containing surface groups was 3.36 times higher compared to the untreated adsorbent. Batch equilibrium tests indicated that the oxidized material has 16.5 times higher sorption capacity for cadmium than conventional activated carbon. Equilibrium isotherms were determined at pH4, 5 and 6 and showed that there was a slight increase in cadmium uptake with increase in pH. The experimental data were fitted by Langmuir and Freundlich isotherms and it was found that the Freundlich isotherm fitted better in all the cases. Overall, the results indicated a rapid adsorption rate with over 96% fractional uptake of metal occurring in the first 12 minutes. Small-scale mini-column experiments were performed and indicated that breakthrough occurred after about 140 bed volumes (BV) of feed solution, containing 1mM Cd at pH6, was passed at 10BV h-1 for oxidized WHK, whereas breakthrough was instantaneous for the unoxidized sample.

Preparation, characterisation and sorptive properties of polymer based phosphorus-containing carbon

A novel phosphorus-containing carbonaceous sorbent has been prepared by pyrolysis of phosphorylated phenol-formaldehyde resin. The surface properties of the material have been characterised by nitrogen adsorption–desorption isotherms and MAS NMR-P 31 spectrometry. The ion-exchange properties of the carbon were assessed by pH-titration and electrophoretic mobility measurements. Sorption studies were performed in batch and mini-column experiments and indicated high affinity towards lead(II) over copper(II), nickel(II) and cadmium(II) for solutions containing these metals (in the mg/l and μg/l range) although the rate of sorption was relatively slow. The sorption affinity series for metal ions studied coincides with the solubility products of the corresponding metal phosphates and stability constants of pyrophosphate complexes in aqueous solutions. Elution using conventional mineral acids yields good heavy metal recovery and effective adsorbent regeneration.