Natural Clay Mineral Research Articles

Thermocatalytic Conversion of Plastics into Liquid Fuels over Clays.

Recycling polymer waste is a great challenge in the context of the growing use of plastics. Given the non-renewability of fossil fuels, the task of processing plastic waste into liquid fuels seems to be a promising one. Thermocatalytic conversion is one of the methods that allows obtaining liquid products of the required hydrocarbon range. Clays and clay minerals can be distinguished among possible environmentally friendly, cheap, and common catalysts. The moderate acidity and the presence of both Lewis and Brønsted acid sites on the surface of clays favor heavier hydrocarbons in liquid products of reactions occurring in their pores. Liquids produced with the use of clays are often reported as being in the gasoline and diesel range. In this review, the comprehensive information on the thermocatalytic conversion of plastics over clays obtained during the last two decades was summarized. The main experimental parameters for catalytic conversion of plastics according to the articles’ analysis, were the reaction temperature, the acidity of modified catalysts, and the catalyst-to-plastic ratio. The best clay catalysts observed were the following: bentonite/spent fluid cracking catalyst for high-density polyethylene (HDPE); acid-restructured montmorillonite for medium-density polyethylene (MDPE); neat kaolin powder for low-density polyethylene (LDPE); Ni/acid-washed bentonite clay for polypropylene (PP); neat kaolin for polystyrene (PS); Fe-restructured natural clay for a mixture of polyethylene, PP, PS, polyvinyl chloride (PVC), and polyethylene terephthalate (PET). The main problem in using natural clays and clay minerals as catalysts is their heterogeneous composition, which can vary even within the same deposit. The serpentine group is of interest in studying its catalytic properties as fairly common clay minerals.

Antimicrobial activity of chitosan film containing nanocomposite of Trachyspermum ammi (ajwain) seed oil loaded Halloysite nanotubes against foodborne pathogenic microorganisms

Ajwain seed oil (ASO) is a volatile organic compound possessing antimicrobial properties against a wide range of microorganisms. Halloysite nanotubes (Hal) are aluminosilicate natural clay minerals with about 200–2000 nm in length and diameters between 10-50 nm. The structure of Hal allows a sustained release of antimicrobial agents to microbial cells which can be beneficial in the food packaging field. In this work, we loaded ASO into Sodium hydroxide (NaOH) treated Hal and further incorporated it with chitosan to develop an innovative antimicrobial food packaging nanocomposite film. The developed nanocomposite films were characterized by UV–visible spectroscopy, Fourier transform infrared spectroscopy, Raman Spectroscopy, Differential scanning calorimetry, Field emission scanning electron microscopy and X-ray diffraction. The antimicrobial properties of the developed nanocomposites were studied against two bacterial strains (Escherichia coli and Bacillus mojavensis) and two fungus strains (Aspergillus niger and Aspergillus flavus) potential food spoilage microorganisms. The nanocomposite (ASO-NaOH-Hal) prevented the growth of Esherichia coli up to 99%, Bacillus mojavensis up to 95%, Aspergillus niger about 97%, and Aspergillus flavus about 97% at concentrations of 5 mg/ml, 7 mg/ml, 5 mg/ml and 5 mg/ml, respectively. And the chitosan film containing ASO-NaOH-Hal presented a clear zone of inhibition against the above-mentioned bacterial strains and inhibited the growth of fungus on the tomato's surfaces therefore, this nanocomposite film could find application in the food packaging field owing to its antimicrobial and antioxidant properties.

Halloysite-based aerogels by bidirectional freezing with mechanical properties, thermal insulation and flame retardancy

Halloysite (Hal) is a natural nanotubular clay mineral with the characteristics of low price and easy availability. The aerogels prepared by Hal are low thermal conductivities, good thermal stabilities and low flammability, which have great application prospects in the field of thermal insulation with flame retardancy. However, they typically suffer from inferior mechanical property and difficulty of mechanically resilient or flexible. Herein, aerogels with anisotropic mechanical properties were prepared by bidirectionally freezing aqueous suspensions of Hal with a small proportion of chitosan (CS). The directionally aligned porous structure gave the aerogels prominent strength in the direction of lamellar orientation, and superelasticity in the vertical direction. The Hal-based aerogels showed good performance in the combination of thermal insulation and flame retardancy. The thermal equilibrium temperatures of Hal/CS aerogels at 50 °C and 100 °C are 27.5 °C and 35.2 °C, respectively. They also remained unscathed after 180 s of burning in a candle flame. The present study provided a versatile method for design and fabrication aerogels for high-performance thermal insulation materials and had significance in the high-value utilization of Hal mineral resources.

Preparation of highly hydrophobic sepiolite for efficient oil removal

Oil spill cleanup has aroused increasing concern in environmental protection, which makes the development of a low-cost absorbent with good hydrophobicity to be a task of high practical significance. In this work, a novel and highly hydrophobic absorbent based on natural clay minerals was prepared and used for oil removal from water. The originally hydrophilic sepiolite was modified by tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMS) through a one-pot direct modification. The pristine and modified sepiolite (MS) were characterized for hydrophobicity, morphology, and composition. The results showed that the modify agent was successfully grafted onto the sepiolite surface, improved the roughness and disaggregation of fibers. And MS exhibited higher contact angle compared to the pristine sample. The diesel oil removal efficiency of MS was significantly higher compared to pristine sepiolite. The surface roughness and high hydrophobic properties played important role in the retention of oil from water. This study presented a facile method to produce promising absorbent based on clay minerals with excellent properties for oil spill cleanup.

Controlling oxygen vacancies of CoMn2O4 by loading on planar and tubular clay minerals and its application for boosted PMS activation

A representative transition metal oxide (TMO), CoMn2O4 (CMO), is recognized as an effective peroxymonosulfate (PMS) activator with disadvantages like limited reactive sites and metal leakage. Herein, novel catalysts were synthesized by anchoring CMO on kaolinite (Kln) and halloysite (Hal) matrixes, two natural clay minerals with lamellar and tubular structures, for PMS activation in pharmaceutical degradation. Hal and Kln helped to control the crystallinity of CMO spontaneously with induce oxygen vacancies (OVs), which significantly enhanced the working efficiency. The reaction rate constants of Hal/CMO and Kln/CMO towards OFX degradation were nearly triple and twice that of bare CMO, respectively, with a 60% decrease in metal usage. The formation of OVs provided additional active sites for the reaction and accelerated the electron transfer. CMO/Hal and CMO/Kln exhibited better stability and durability than CMO, while CMO/Kln showed higher structural stability with lower metal leaching after 3 rounds of reaction. The higher crystallinity of CMO/Kln resulted in less OVs, but higher structural stability. The universal applicability of CMO/Hal and CMO/Kln were verified by using three other pharmaceuticals as probes. This work shed light on the modification of TMO catalysts by introducing clay mineral substrates for the efficient and ecofriendly remediation of pharmaceuticals in wastewater.

Acceleration of the Dehydrogenation of d-Glucose to 2-Keto-d-gluconate in Aqueous Amino Acid via Hydrated Stacked Clay Nanosheets

The assembly of discrete active species to form periodical nanostructures is essential in realizing low-cost artificial enzymes that mimic natural enzymatic functions in extraordinary bio(chemo)selective reactions. In this study, we developed artificial bifunctional glucose/gluconic acid dehydrogenase from naturally abundant resources: l-aspartic acid (Asp) and montmorillonite (a subgroup of smectite natural clay minerals). β-d-Glucose (Glc) was dehydrogenated to 2-keto-d-gluconate (2-KGA) at 25 and 30 °C in an aqueous acidic solution (pH = 3, 4, and 5). The reaction involved sequential steps that yielded d-gluconic acid (GA) as an intermediate. The second step of the dehydrogenation (GA to 2-KGA) occurred at a higher rate than the first (Glc to GA), which is comparable to the natural process. A negatively charged carboxylate in Asp was required for the dehydrogenation, which donates an electron pair (COO:-) to the hydroxyl group bonded to the C(1)-position of Glc. The acidic sites in clay served as coenzymatic sites (electron acceptor), promoting the Glc dehydrogenation as the Glc reduced by Asp approached the clay coenzymatic sites. The active coenzymatic structures were developed in 48 h (induction period) through the rearrangement of the adsorbed Asp and Glc molecules on montmorillonite in water (intermediate structure). The spontaneous assembling of the intermediate structures facilitated the one-pot dehydrogenation of Glc to 2-KGA via periodic "hydrated stacked layers" comprising clay nanosheets, Asp, and Glc. The facile synthetic route proposed here is inexpensive and would be beneficial without using both GDH and GADH enzymes bound to a cell membrane.

Kaolinite nanoscroll significantly inhibiting polysulfide ions shuttle in lithium sulfur batteries

The shuttling effect of polysulfide ions is an important reason that hinders the commercial application of lithium‑sulfur batteries. The natural clay mineral halloysite has good adsorption performance and hollow tubular structure, which can absorb and accommodate enough sulfur, while the flake kaolinite can roll to form a halloysite-like structure. The effect of acid-modified halloysite and kaolinite nanoscrolls as sulfur carriers on the performance of lithium‑sulfur batteries was studied in this paper. As a result, both acid-modified halloysite and kaolinite nanoscrolls could effectively adsorb polysulfide ions, while kaolinite nanoscrolls were more conducive to the migration and diffusion of Li+ due to its thinner wall (about 5 nm), thus exhibiting faster reaction kinetics and higher sulfur utilization, and had better rate performance and cycle stability. The application of clay minerals in the field of energy has always been unpromising. This research work makes full use of the characteristics of clay minerals and broadens its application, providing a basis for the design of clay minerals and a possible modification direction for their application in lithium‑sulfur batteries.

Natural-clay-reinforced hydrogel adsorbent: Rapid adsorption of heavy-metal ions and dyes from textile wastewater.

In this study, two natural clay minerals were combined with hydrogels to study the influence of natural adsorbents on the adsorption performance of hydrogels. Here, we separately doped bentonite and vermiculite and discussed their mechanical properties and adsorption properties. It was found that the compressive performance of the hydrogel added with clay increased by 21.6% and the swelling performance decreased or increased to varying degrees. Regarding the adsorption performance of hydrogels, it can be seen from the adsorption Langmuir isotherm model that the adsorption capacity of clay-hydrogels is improved to varying degrees (6.6%-15.8%) compared with non-clay-hydrogels, and clay-hydrogels have different degrees of improvement (6.6%-15.8%). The hydrogel has a removal efficiency of more than 95% for low concentrations of heavy-metal ions and dyes. In addition, the clay-hydrogel has low cost and is easy to prepare, and can be recycled many times. Therefore, the material is of great significance for the treatment of pollutants. PRACTITIONER POINTS: The effect of natural clay on the adsorption performance of hydrogels was studied. Clay can enhance the compression and adsorption properties of hydrogels. The adsorption mechanism and adsorption capacity of clay hydrogels were evaluated.

Anisotropic Elastic Properties of Montmorillonite With Different Layer Charge Densities and Layer Charge Distributions Through Molecular Dynamic Simulation

The knowledge of the anisotropic elastic properties of clay minerals is of crucial importance for the exploration and development of shale oil and gas. Montmorillonite (MMT) is a common natural clay mineral with different layer charge densities and layer charge distributions due to different geological conditions. Therefore, it is important to understand the currently poorly known effect of layer charge density and layer charge distribution on the anisotropic elastic properties of MMTs. This work aims to obtain such knowledge by studying the anisotropic elastic properties of different MMTs under stratigraphic conditions through molecular dynamic simulations. We showed that the in-plane compressional coefficients C11, C22 and C12 decrease with the increasing layer charge density for MMTs with different layer charge distributions, and the MMTs with the layer charges distributed on the two tetrahedral (T) sheets were found to have the smallest C11, C22 and C12. We also showed that the out-of-plane compressional coefficients C33, C13 and C23 of the MMTs with the layer charges distributed in the two T sheets decrease, while those with the layer charges in the octahedral (O) sheet increase and those with layer charges distributed in both the O sheet and the T sheets do not vary much with the increasing layer charge density. The variations of the anisotropic compressional elastic coefficients with different layer charge densities and layer charge distributions were found to be a result of the impact of the density and distribution of layer charges on the molecular interactions within the MMT layer. We further demonstrated that the layer charge density and layer charge distribution do not influence significantly the shear coefficients C44, C55, and C66. The results revealed the mechanisms of how the density and distribution of layer charges affect the anisotropic elastic properties of MMTs and will contribute to the more successful exploration and development of unconventional resources in MMT bearing shale reservoirs.

Facile synthesis and optical study of organic-inorganic lead bromide perovskite-clay (kaolinite, montmorillonite, and halloysite) composites

The organic-inorganic hybrid perovskite methylammonium lead bromide nanocrystals are an important class of light-emitting materials. However, their poor stability under humid conditions hampers their practical applications. Herein, for the first time, MAPbBr3 NCs have been successfully assembled with various clays, such as kaolinite, montmorillonite, and halloysite for synthesizing MAPbBr3@clay composites. The bare MAPbBr3 NCs and all the synthesized MAPbBr3@clay composites show green emission ranging from 531 to 540 nm and an average lifetime spanning between 0.91 and 1.03 ns. These composite materials offer improved thermal stability up to 250 °C and luminescence properties under humid conditions for more than one month. These materials open up a new insight into obtaining stable nanocrystals with natural clay minerals.

Nanotubular Polyaniline/Reduced Graphene Oxide Composite Synthesized from a Natural Halloysite Template for Application as a High Performance Supercapacitor Electrode

AbstractPolyaniline (PANI) is a promising material for developing high‐performance supercapacitors, and adopting some specific templates to design one‐dimensional nanostructured PANI electrode is considered to be a key strategy to enable high performance supercapacitors. Here, the nano‐tubular PANI(HNTs) were successfully achieved by using the natural tubular halloysite as hard template with low cost, and the PANI(HNTs) were further compounded with reduced graphene oxide (rGO) to prepare a binder‐free, self‐supporting PANI(HNTs)‐rGO composite electrode. The characterization tests of Infrared, Raman and XRD diffraction proved that PANI (HNTs) and PANI (HNTs)‐rGO composite material were successfully synthesized. SEM and TEM verified the nanotubular structure of PANI(HNTs) and the three‐dimensional network structure of PANI(HNTs)‐rGO. Owing to the rGO’ positive effect on the PANI(HNTs) electrode, the composite electrode exhibited excellent specific capacity performance of 762 F g−1, 660 F g−1, 595 F g−1, 545 F g−1 and 493 F g−1 at current densities of 1 A g−1, 2 A g−1, 5 A g−1, 10 A g−1, and 20 A g−1, respectively. This work prove that natural clay minerals have good application prospects in the design of nanostructured electrodes of conductive polymers (CPs) or other electrode materials for energy storage devices.

Evolution of Black Talc upon Thermal Treatment

Black talc is a natural silicate clay mineral with a typical 2:1 layered structure, low electrical conductivity, large specific surface area, and high thermal stability. The world’s largest black talc mine, with known reserves of one billion tons, is located in China’s Jiangxi province. Due to the restriction of its color, the application of black talc is only limited to ceramic raw materials, coating filler, waterproof materials, and other low-end application industries. Thermal treatment is a common method of clay mineral modification. It is vital to examine the structural and physical changes of black talc during calcination in order to prepare black-talc-based composites and to broaden their applications. This work discusses the evolution of black talc upon thermal treatment (30–1000 °C) and the corresponding structural changes. The thermal stability of minerals was analyzed via thermogravimetric (TG) analysis and thermogravimetry–mass spectrometry (TG-MS). The decomposition of minerals during calcination consists of four processes: dehydration, organic carbon decomposition, dihydroxylation, and phase transformation. In situ FTIR and in situ XRD were employed to track changes in black talc in real time during thermal treatment. At 800 °C, black talc was found to begin to go through dihydroxylation, and the crystallinity index decreased significantly. The XRD pattern of samples at 950 °C (T950) showed the reflection of the enstatite structure, and the relative crystallinity index was 27.3%, indicating that the mineral had undergone phase transformation. In addition, the Brunauer–Emmet–Teller (BET), laser particle size analyzer, Zeta potential, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques were used to systematically characterize the physicochemical properties of minerals at different temperatures. The results show that black talc’s particle size and specific surface area increase with the calcination temperature. The surface charge changes, and more amorphous SiO2 and MgO appear, indicating that thermal treatment could induce structural changes and activate the surface of black talc.

An Environmentally Friendly Soil Amendment for Enhancing Soil Water Availability in Drought-Prone Soils

Applying soil amendments plays a critical role in relieving water stress in arid and semiarid areas. The natural clay mineral attapulgite (ATP) can be utilized to adjust the balance of water and soil environment. In this study, we investigated four different particle size distribution typical soils in the Loess Plateau: (1) lou soil (LS), (2) dark loessial soil (DS), (3) cultivated loess soil (CS), (4) sandy soil (SS). Five ATP application rates (0, 1%, 2%, 3%, and 4%) were selected to test the effect of ATP on the soil water retention curve, soil saturated hydraulic conductivity, and soil structure. The results showed that applied ATP significantly increased the soil clay content, and the relative change of SS with 3% ATP applied increased by 53.7%. The field water holding capacity of LS, DS, CS, and SS with 3% ATP applied increased by 8.9%, 9.6%, 18.2%, and 45.0%, respectively. Although applied ATP reduced the saturated hydraulic conductivity, the values of CS and SS were opposite when the amount of ATP applied was >3%. The relative change in the amount of 0.25–1 mm soil water-stable aggregates of SS was 155.9% when 3% ATP was applied. Applied ATP can enhance soil water retention and soil stability, which may improve limited water use efficiency and relieve soil desiccation in arid and semiarid areas or similar hydrogeological areas.

Prospects for the use of natural clay minerals in animal husbandry (review)

This review presents the current state in the field of the use of natural clay minerals in the feeding of farm animals and poultry. The analysis of some feed additives containing natural clay minerals is carried out and the advantages of their use are also characterized. The characteristics of the properties of natural minerals presented in this review are given.

Interlayer Cation-Controlled Adsorption of Carbon Dioxide in Anhydrous Montmorillonite Clay

Widely available natural layered expandable clay minerals (smectites) can sorb carbon dioxide in their interlayer space under specific conditions and hence may show potential for gas separation or carbon sequestration processes. This work presents experimental adsorption and desorption measurements of gaseous, sub-critical carbon dioxide (p = 0.1 bar up to 20 bar, T = −20 °C up to 300 °C) on well-characterized anhydrous smectite (Wyoming montmorillonite) and focuses on the effect of the interlayer cation (size). Using seven alkali and alkaline-earth metal cations and three quaternary ammonium cations, a wide range of ionic radii are studied. Physisorption of CO2 in the interlayer space is confirmed via infrared spectroscopy measurements. The results show that optimally sized interlayer cations─comparable to the thickness of a carbon dioxide monolayer─open the interlayer space to make it easily accessible for CO2 up to 1.7 mmol g–1. In particular, Cs-exchanged and tetramethylammonium-exchanged montmorillonite facilitate the rapid sorption of carbon dioxide even at ambient pressure and temperature. These results provide valuable insights into the applicability of widely available natural adsorbent clays for carbon capture and sequestration for the mitigation of climate change.

High Sorption and Selective Extraction of Actinides from Aqueous Solutions.

The selective elimination of long-lived radioactive actinides from complicated solutions is crucial for pollution management of the environment. Knowledge about the species, structures and interaction mechanism of actinides at solid–water interfaces is helpful to understand and to evaluate physicochemical behavior in the natural environment. In this review, we summarize recent works about the sorption and interaction mechanism of actinides (using U, Np, Pu, Cm and Am as representative actinides) on natural clay minerals and man-made nanomaterials. The species and microstructures of actinides on solid particles were investigated by advanced spectroscopy techniques and computational theoretical calculations. The reduction and solidification of actinides on solid particles is the most effective way to immobilize actinides in the natural environment. The contents of this review may be helpful in evaluating the migration of actinides in near-field nuclear waste repositories and the mobilization properties of radionuclides in the environment.

Guidelines to Study the Adsorption of Pesticides onto Clay Minerals Aiming at a Straightforward Evaluation of Their Removal Performance

Natural and modified clay minerals have been extensively used for the adsorption/desorption of organic substances, especially pesticides, from waters and wastewater, aiming at pollution control and more efficient use of the herbicides through controlled release. While natural clay minerals efficiently remove organic cations such as paraquat and diquat, the adsorption of anionic or neutral species demands surface chemical modification with, for instance, quaternary ammonium salts containing long alkyl chains. Basic pesticides, on the other hand, are better absorbed in clay minerals modified with polycations. Kinetic studies and adsorption/desorption isotherms provide the parameters needed to evaluate the clay mineral’s adsorptive performance towards the pollutant target. However, the direct comparison of these parameters is complicated because the experimental conditions, the analytical techniques, the kinetic and isotherm models, and the numerical fitting method differ among the various studies. The free-energy-related Langmuir constant depends on the degree of site occupation; that is, it depends on the concentration window used to construct the adsorption isotherm and, consequently, on the analytical technique used to quantify the free concentrations. This paper reviews pesticides’ adsorption on natural and modified clay minerals and proposes guidelines for designing batch adsorption/desorption studies to obtain easily comparable and meaningful adsorption parameters. Articles should clearly describe the experimental conditions such as temperature, contact time, total concentration window, the solution to adsorbent ratio, the analytical technique, and its detection and quantification limits, besides the fitting models. Research should also evaluate the competitive effects of humic substances, colloidal inorganic particles, and ionic strength to emulate real-world adsorption experiments.

Oleophobic modification of clay minerals to improve encapsulation ratios of shape-stabilized phase change materials: A universal method

Liquid-solid phase change materials (PCMs) show reversible storage and release of latent heat, which has attracted extensive interests in applications for thermal energy storage. However, stubborn leakage issue may cause corrosion and extra thermal resistance. The non-wettability of melted paraffin on the oleophobic surface of diatomite has been reported by authors earlier, and the result showed that the encapsulation ratio (84.5%) of diatomite@paraffin shape-stabilized PCM greatly increased. Here, in order to prove this method equally applicable to other PCMs and porous natural clay minerals, diatomite and sepiolite were oleophobically modified to encapsulate melted stearic acid and paraffin, to form shape-stabilized PCMs. The results showed that the encapsulation ratios of 67.8% and 56.6% for diatomite@stearic acid and sepiolite@paraffin were higher than that reported in the references (28.9% and 36.8%). In addition, the encapsulation ratios of diatomite-based shape-stabilized PCMs can be also increased using different PCMs, such as n-octadecane and polyethylene glycol via the same approach. Therefore, this is a universal method for improving encapsulation ratios of shape-stabilized PCMs.

CO2 Methanation Over Ni-Sepiolite Catalysts

In this study, it was aimed to develop new catalysts to increase the conversion of environmentally harmful carbon dioxide gas to methane which is a valuable fuel. By using a natural clay mineral sepiolite (SEP) as support material; 6-8% (weight-weight) Ni-containing catalysts were prepared by impregnation. Catalysts were characterized by XRD and FT-IR analysis. Reaction conditions of catalytic hydrogenation of carbon dioxide for methane production were determined as: H2/CO2 = 4 molar ratio, the temperature range of 300-600°C at atmospheric pressure. The output gas mixture was analyzed using the µGC. The activities of the catalysts were determined in terms of carbon dioxide conversion and methane selectivity. 6%Ni/SEP and 8%Ni/SEP provided 65.76% and 68.42% carbon dioxide conversion at 400°C, respectively. In addition, both catalysts exhibited high methane selectivity at 300 and 400°C (>98%).

The relation between nanotube diameter, length and surface area and pore volume of multi-walled spiral halloysite nanotubes: A theoretical study

Halloysite (Hal) is a natural clay mineral with nanotube structure. Due to their outstanding specific surface area, loading capacity and selective adsorption ability, Hal have been widely used in the fields of catalysis, adsorption, drug loading and releasing. However, the loading ability of Hal from different halloysite deposits still varies in a large range. The relation between the microstructure properties of Hal and the intrinsic parameters such as length (L), inner/outer diameter (Dinner/Douter) of halloysite nanotubes (HNTs) is still obscure. In this study, we constructed the atomic structures of several multi-walled spiral HNTs with diameters (10–40 nm) in the range of the real size of Hal, and calculated their specific surface area (S) and pore volume (V) to compare with experimental results. By comparing the difference between the calculated values and the theoretical values (based on simple mathematics), the relation between the S/V of HNTs and its Dinner/Douter and L is established using modified equations. The equations were applied to deduce the theoretical values of the specific surface area and pore volumes of HNTs in a wide range of inner/outer diameter (10–200 nm) and length (100–5000 nm). Notably, while the experimental surface area are highly consistent with the theoretical values, the experiment pore volume are mostly lower than the theoretical values, which indicates that the lumen space of HNTs from different deposits are blocked in different degrees by the associated minerals and impurities. It is expected that, in addition to traditional physicochemical purifications, the removal of lumen impurities can help to revive the lumen loading ability of HNTs upto their theoretical limits.