Adsorption Isotherm, Kinetic and Thermodynamic Modelling of <i>Bacillus subtilis</i>ATCC13952 Mediated Adsorption of Arsenic in Groundwaters of Selected Gold Mining Communities in the Wassa West Municipality of the Western Region of Ghana

This study investigated Bacillus subtilis ATCC13952 as an adsorbent for arsenic in groundwater. Batch experiments were used to determine the effect of contact time, adsorbent dose, arsenic (III) concentration, pH, and temperature on the process. The percentage of arsenic (III) removed was high at a contact time of four days, 3.0 mL of Bacillus subtilis ATCC13952, pH 8 and temperature of 35°C. The kinetics of the process showed the Elovich kinetics model as the best fit for the process. This indicates that arsenic removal was by chemisorption. The analysis of the nonlinear equilibrium isotherms and the error functions showed the Langmuir isotherm as best fit for the process. Mechanistic study of the process indicated bulk diffusion to be the rate-determining step. Thermodynamically, the process was favourable, spontaneous and feasible. When the community water samples were treated with the Bacillus subtilis ATCC13952 at the optimum contact time, adsorbent dose, pH and temperature, 99.96% - 99.97% of arsenic was removed across all sampling points within the studied communities. Hence, the results show that Bacillus subtilis ATCC13952 is an efficient adsorbent for arsenic in aqueous systems and the organism appears to hold the key to purging the environment of arsenic contamination.

Water Adsorption Isotherms of Amaranth (Amaranthus caudatus) Flour

Water sorption isotherms are unique for individual food materials and can be used directly to predict shelf life and determine proper storage conditions. In this context, the aim of this study was to determine the moisture adsorption isotherms of amaranth flour at 15℃, 25℃ and 35℃ in a range of water activity from 0.1 to 0.9. Experimental data were modeled using five equations commonly applied in the foods field. The goodness of the fit for each isotherm model was evaluated through the coefficient of determination, the variance due to error and the confidence interval of the estimated parameters. All models can predict the adsorption isotherms of amaranth flour, but the GAB equation gives a better understanding of the observed sorption behavior. Estimated adsorption monolayer water contents ranged from 6.4 g to 7.2 g of water per 100 g of dry material. It was observed by a weak dependence of water activity with temperature. For ensuring microbiological stability, water content in amaranth flour should not be higher than 13 g of water per 100 g of dry material.

CO_2 isothermal adsorption models of coal in the Haishiwan Coalfield

Since the capacity of CO2 adsorption of coal is a key factor in coal and CO2 outbursts,an experimental study was carried out on CO2 isothermal adsorption with high-pressure volumetry with dry coal samples from the No.2 coal seam in the Haishiwan Coalfield.Four different equations(Langmuir,BET,D-R and D-A) were used to fit the experimental data.We discuss adsorption mechanisms.The results show that the amount of CO2 adsorption increases rapidly under low relative pressure,i.e.,the ratio of equilibrium pressure and saturated vapor pressure,which indicates that molecular layer adsorption or micropore filling may occur in coal.No clear equilibrium state was observed on the isothermal adsorption curves under relative pressure(P /P0 ) ranging from 0 to 0.8.The fitted results show that the accuracy of the D-A equation is highest with n=1.Micropores are more developed in coal by comparing the BET equation with a pressure mercury injection method on the surface area.The D-A equation(n=1) provides the best fit.By comparing the calculated specific surface area of the BET equation and the mercury intrusion method,it is found that micropore adsorption of CO2 occupies a dominant position.

Adsorption of K^+ from an aqueous phase onto an activated carbon used as an electric double-layer capacitor electrode

The adsorption capacity and absorption rate for electrolyte onto activated carbon are important parameters used to characterize activated carbon electric double-layer capacitor electrodes. In this paper the pore structure of typical commercial activated carbons, and various Mn-doped activated carbons prepared on a laboratory scale, are described. The pore structure was character-ized by N2 adsorption/desorption isotherms. Isotherms for K+ adsorption onto these activated carbons from the aqueous phase were also obtained. The experimental, equilibrium K+ adsorption data were fitted to the Langmuir, Freundlich or Temkin equations. Adsorption of K+ onto the activated carbons was measured and plotted as a function of time. The adsorption kinetic data were modeled by either pseudo-first or pseudo-second order equations. The Elvoich equation, a liquid film diffusion and an intra-particle diffusion model were used to fit the kinetic data. The results indicate that the adsorption of K+ onto activated carbon is influenced by many factors including pore size distribution, specific surface area and the surface chemistry of the activated carbons. The Temkin equation best describes the equilibrium adsorption data. The pseudo-second order model exactly describes the whole adsorption process, which is controlled by both liquid film and intra-particle diffusion.

Adsorption of Phenol by Activated Carbon Prepared from Waste Rice Straw by Chemical Activation with (NH_4)_2HPO_4

Activated carbons,RS-1,RS-2,and RS-3,prepared from rice straw with(NH4)2HPO4 activation were used as adsorbents for removing phenols from aqueous solutions.The maximum adsorption capacities of phenol for RS-1,RS-2,and RS-3 were 163.9,172.9,and 200.0 mg/g,respectively.The equilibrium data were analyzed by the Langmuir,Freundlich,and Temkin models.It displayed that Langmuir isotherm fitted to the results best.The dimensionless parameter RL indicated the favorable nature of the adsorption of phenol.Otherwise,the kinetic rates were well explained by pseudo-second-order model.According to the results,activated carbon derived from waste rice straw can be a high-performance adsorbent for wastewater treatment.

Adsorption of Cu(Ⅱ) from Aqueous Solution Using Activated Carbon Modified with Nitric Acid

The objective of the presented work was to assess the adsorption processes of Cu(Ⅱ) from aqueous solution onto a granular activated carbon (GAC) and a modified activated carbon (MAC) with nitric acid. Available surface functional groups, pH of the isoelectric point (pHIEP), and Fourier transform infrared spectroscopes were obtained to characterize the GAC/MAC. Factors influencing Cu(Ⅱ) adsorption such as adsorbent dosage, pH of solution, and contact time of the adsorption onto the MAC/GAC had been investigated in a batch experiment. Experimental equilibrium data had been obtained and modelled using both Freundlich and Langmuir classical adsorption isotherms and the data fitted better to Langmuir isotherm. It was found that nitric acid modification increased the Cu(Ⅱ) adsorption capacity to 90.9 mg/g, which was higher than the unmodified carbon by 41%. Two simplified models including pseudo-first-order and pseudo-second-order equations were selected to follow the adsorption processes.

Valorization of Mango Peels as Low-Cost Biosorbent in Methylene Blue Adsorption:Kinetic and Equilibrium Study

Mango peels,which constitute a significant proportion of urban waste,have been modified with phosphoric acid for use as a biosorbent in the removal of methylene blue from wastewater.The characterization of the obtained biosorbent showed that cellulose is the primary constituent followed by lignin and hemicellulose.The high water content and the low value of ash content indicate that the studied biosorbent is a porous material containing a low proportion of inorganic,inert,amorphous and unusable part for biosorbent production.The zero charge point(pHpzc)assessment showed that the overall surface charge of the biosorbent is negative and therefore plays a key role in the adsorption process.The adsorption of methylene blue by mango peels biosorbent is a two-step process:a rapid first step in which over 90%methylene blue is removed in less than 10 min followed by a slowdown of the adsorption rate when approaching the adsorption equilibrium.Among pseudo-first,pseudo-second order and intraparticle diffusion kinetics models studies,pseudo-second order was the best applicable to describe methylene blue adsorption,suggesting a two-step mechanism:the transfer of methylene blue molecules from the solution to the mango peels biosorbent surface,followed by the interaction between adsorbates and surface.The equilibrium adsorption data were analyzed by Langmuir,Freundlich and Temkin isotherms models.Among them,Langmuir was the best model to describe adsorption,indicating the existence of homogeneous distribution of adsorption sites on mango peels biosorbent surface and a mono-layer adsorption of methylene blue molecules.The low value of Temkin’s constant B relative to the interaction energy between methylene blue molecules and the surface of the biosorbent shows that the adsorption involved is a physisorption process.

Adsorption of Cr(III) from an Aqueous Solution by Chitosan Beads Modified with Sodium Dodecyl Sulfate (SDS)

This study is to prepare chitosan beads modified with sodium dodecyl sulfate (SDS) to effectively remove Cr(III) from an aqueous solution. The characterizations of SDS-chitosan by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Fourier transform-infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) proved the successful synthesis of the adsorbent. The adsorption of Cr(III) on the SDS material was investigated by varying experimental conditions such as pH, contact time and adsorbent dosage. The maximum adsorption capacity of SDS-chitosan for Cr(III) was estimated to be 3.42 mg?g-1. The results of adsorption kinetics and isothermal models show that the adsorption process conforms to the pseudo-second-order and Langmuir isotherm models, indicating that the adsorption is single-layer chemical adsorption. Thermodynamic analyses indicate that the adsorption of Cr(III) is an endothermic reaction. These results show that the new adsorbent has obvious application prospect to eliminate Cr(III).

ADSORPTION MECHANISM OF SOME BIVALENT HEAVY METAL CATIONS IN SOLUTIONS USING MONTMORILLONITE

The frontier orbital energies of montmorillonite molecule and[Me(H_(2)O)_(6)]^(2+)(Me=Cu^(2+),Zn^(2+),Co^(2+)and Ni^(2+))were calculated by INDO method.Results showed that the chemical interaction between montmorillonite molecule and[Cu(H_(2)O)_(6)]^(2+)or[Zn(H_(2)O)_(6)]^(2+)was possible.The experimental results of powder X-ray diffraction and isothermal adsorption supported the above-mentioned calculation results.

Kinetic and Thermodynamic Study of the Elimination of Remazol Black on Activated Carbon Based on Ricinodendron heudelotii Shells

Activated carbon made from the shells of Ricinodendron heudelotii was used to remove the remazol black dye in aqueous solution. The results of the characterization of this carbon revealed that it is microporous, with a basic global surface (0.337 mmol/L) and a specific surface of 612 m2/g. The prepared carbon therefore has excellent adsorbent properties. Kinetic and thermodynamic studies were carried out to describe the adsorption mechanism of remazol black on this carbon. It appears from this study that the pseudo-second-order kinetic model is the best suited to describe this adsorption phenomenon with an equilibrium time of 200 min. The adsorption equilibrium study revealed that Langmuir and Freundlich models can help to describe the adsorption process. We note that the optimum pH and optimum mass for the removal of 20 mg/L of remazol black are 3 and 0.25 g, respectively. This carbon made it possible to eliminate more than 98% of the remazol dye in aqueous solution. The thermodynamic study revealed that the adsorption is of the physisorption type, spontaneous and endothermic.

Influence of mineral species on oil-soil interfacial interaction in petroleum-contaminated soils

The mineral species in soils vary in a wide variety of places,thus resulting in the petroleumcontaminated soil(PCS)with complex characters.Thus,the research on the effect of mineral species on oil-soil interactions in PCS takes on a critical significance.In this study,the desorption and adsorption behaviors of aromatic hydrocarbons(Ar)on two minerals surfaces were examined.Meanwhile,the interfacial forces between minerals and Ar were studied and the sources of these forces were analyzed.Moreover,molecular dynamics(MD)simulations were conducted to gain insight into the interfacial interaction mechanisms.As revealed by the results of this study,in comparison with Qs-Ar(quartz sand,Qs),Mnt-Ar(montmorillonite,Mnt)contaminants required higher temperature and activation energies for thermal desorption(201.95 kJ·mol^(-1)vs.127.82 kJ·mol^(-1))The above difference was generated since the adhesive forces between Ar and Mnt surfaces were greater than those between Ar and Qs.As indicated by the analysis of the adhesion force sources,the van der Waals forces were responsible for facilitating oil adhesion to mineral surfaces,even though the electrostatic force prevented oil-mineral adhesion.Furthermore,the hydrophobic forces facilitated adhesion in 3 nm.The MD results demonstrated that compared with the Qs system,there existed larger binding energies between Ar and Mnt,a lower diffusion coefficient for Ar on the Mnt surface,as well as more significant adsorption of Ar on Mnt.In general,the different mineral species affect the strength of the interaction at the oil-soil interface,which is a guideline for proposing targeted oil-soil separation measures.

Mesoporous tablet-shaped potato starch aerogels for loading and release of the poorly water-soluble drug celecoxib

In this study,after determination of the optimal values of the effective parameters in the synthesis using experimental design software,tablet-shaped potato starch aerogels were synthesized at the optimal condition in order to be used as a drug carrier.The celecoxib,as the model drug,was loaded into the aerogel matrix during the solvent exchange step.FTIR(Fourier Transform Infrared Spectroscopy),FESEM and HRTEM(Transmission Electron Microscopy)analyses showed that celecoxib has been successfully loaded into aerogel matrix.Also,XRD analysis showed that most of the celecoxib has been loaded in amorphous form.In vitro studies were performed in both simulated gastric and intestinal fluids.The release kinetics showed that the loaded celecoxib dissolved faster than crystalline celecoxib.At rotational speed of 100 r·min^-1,about 26%and 50%and at rotational speed of 50 r·min^-1,about 20%and 42%drug was released during the first 30 min of soaking in the simulated gastric fluid and simulated intestinal fluid,respectively.The release of the mentioned drug was increased up to 60%and 98%at a rotational speed of 100 r·min^-1 and up to 46%and 93%at a rotational speed of 50 r·min^-1 at the end of 5 h in the simulated gastric fluid and simulated intestinal fluid,respectively.It could be concluded that potato starch aerogels can be very useful in many drug delivery applications along with conventional micronization techniques.Modeling of release data showed that the release kinetics follows the Korsmeyer Peppas model,which considers phenomena of matrix erosion and drug diffusion.

Adsorptive Removal of Fluoride from Water by Heat-Treatment Waterworks Alum Sludge

Alum sludge( AS) is a world-wide by-product generated in the drinking water treatment process when aluminum salts are used as coagulant. Its high Al content makes it a potential adsorbent for flouride removal from water. A high performance adsorbent was fabricated via heat treatment of AS and batch adsorption experiments were carried out to investigate its flouride adosroption performance. The results indicated that AS treated at 300℃( AS300) for 1 h had the highest adsorption capacity for fluoride( 52. 9% fluoride removal). The adsorption of fluoride by AS300fitted better the Langmuir isotherm model than the Freundlich model. The maximum fluoride adsorption capacity of AS300increased from 4. 0 to 9. 3 mg /g sludge when reaction temperature increased from 15 to 35 ℃. Thermodynamic parameters showed that the adsorption of fluoride by AS was spontaneous and endothermic.Hence higher temperature was favorable for fluoride adsorption.The adsorption process followed the pseudo-second-order equation.In addition,the fluoride adsorption on AS300 decreased from 4. 3 to2. 5 mg /g sludge when the solution initial pH increased from 4. 0 to9. 0,which meant that adsorption capacity was greatly dependent upon the initial pH of the solution. The results provide new insight into the resource utilization of AS for fluoride removal.

Curcumin Extract as a Green Inhibitor of Leaching from Aluminum Cookware at Quasi-Cooking Conditions

Curcumin aqueous extract is used successfully as a green corrosion inhibitor at quasi-cooking conditions (90℃) to inhibit leaching from Aluminum cook wares in solutions containing vegetables or meat. Aluminum cook wares were bought from the market from four countries and cut to make the Aluminum samples. Six types of vegetables and three kinds of meat were chosen. Each type of vegetable and meat was used to prepare 30% w/v aqueous solutions. Three methods were used in the present study: Gravimetric method, Atomic Absorption and FTIR. Gravimetric method was applied to determine the leaching rate and the corrosion inhibition efficiency with/without NaCl. The effect of Curcumin concentration, Tab water, immersion time, alloying elements was investigated. There was a good consistency between Gravimetric and Atomic Absorption methods. The adsorption of Curcumin on the aluminum surface was in accordance with Langmuir isotherm. The values of the adsorption constant (Kads) and the free energy of adsorption (Gadso) were calculated and discussed. FTIR spectrum indicated that Curcumin coordinated with Al3+ resulting in the formation of Al3+-Curcumin complex on the metal surface. Using a small amount of Curcumin decreased leaching from Aluminum cook wares into food by 60% - 80% depending about the type of food.

Activated Carbon Based on Acacia Wood (<i>Auriculeaformis</i>, Côte d’Ivoire) and Application to the Environment through the Elimination of Pb²⁺Ions in Industrial Effluents

The objective of this study is to develop carbon, that of Acacia auriculeaformis through its activation in order to eliminate lead in an aqueous medium. A series of activated carbon has been prepared by chemical activation with phosphoric acid, sodium hydroxide and sodium chloride. The determination of the physico-chemical properties of the prepared carbon guided the choice of phosphoric acid activated carbon as the best adsorbent for the elimination of lead(II) in an aqueous solution. Pb2+ adsorption tests in batch mode have shown that the adsorption capacity is influenced by various parameters such as mass, pH, concentration of Pb2+ ions and contact time linked to the medium and the adsorbent. Adsorption isotherms, kinetic models and thermodynamics have been used to describe the adsorption process. The equilibrium data for activated charcoal correspond well to the model of Freundlich, Langmuir, Temkin and Kiselev. The kinetic adsorption data proved to be better described by the pseudo-second order model with external and intraparticle diffusion which are two decisive steps in the adsorption process of Pb2+ ions. Thermodynamics and adsorption isotherms predict a spontaneous exothermic surface reaction, of the chemisorption type, with ion retention in orderly monolayers on the heterogeneous surface of the adsorbent. Tests carried out with this adsorbent material have contributed to the elimination of the Pb2+ ions contained in an industrial effluent with a reduction rate reaching 42.52% against 85.90% in a synthetic solution.

Comparative study of natural chemical for enhanced oil recovery: Focus on extraction and adsorption at quartz sand surface

In chemical enhanced oil recovery(CEOR),it is very important to utilize the excessive usage of chemicals.A great opportunity lies in adopting natural surfactants,since it is cheaper,ecosystem friendly,and less toxic than their counterpart synthetic surfactants.Despite the availability of natural surfactant sources,it is yet very early to decide on their applicability.Therefore,this research focuses on natural-saponin extracted from different raw materials available in the Middle East and their interaction with quartz-sand.A special focus was given to the adsorption isotherm models to describe the interaction with the reservoir rocks.Three raw materials were investigated are fenugreek,sugar beet leaves and chickpeas.The main extraction method employed was the chemical extraction using the soxhelet.The study used Uv–vis spectrometer to investigate the micellization behaviour and the consequent adsorption on quartz-sand.The presence of triterpenoid saponin is found dominant in all the sample,the intensity and purity differed according to the raw material source.Tthe critical micelle concentration(CMC)was at a close range of 4–5.5 wt%in all the samples.The highest adsorption was obtained by sugar beet leaves which is 192 g/kg.It is 25%and 37%higher than the Fenugreek and chickpeas,respectively.Increasing the salinity resulted in adsorption reduction between 2%and 56%.For the adsorption isotherms,it showed good agreement with the Langmuir model fitting.The remarkable finding is that the sugar beet leaves heterogeneous model seems to be valid by Frendluich and Halsey isotherms.

Experimental Study of the Adsorption-Induced Coal Matrix Swelling and Its Impact on ECBM

Carbon dioxide(CO_2) enhanced coalbed methane(ECBM) is an effective method to improve methane(CH_4) production and this technology has already been used to increase gas production in several field trials worldwide. One major problem is the injection drop in the later period due to permeability decrease caused by coal matrix swelling induced by CO_2 injection. In order to quantify the swelling effect, in this work, coal samples were collected from the Bulli coal seam, Sydney Basin and adsorption tests with simultaneous matrix swelling measurement were conducted. The adsorption and swelling characteristics were analyzed by measuring the adsorption mass simultaneously with the strain measurement. Then experiments were conducted to replicate the ECBM process using the indirect gravity method to obtain the swelling strain change with CO_2 injection. The results show that the coal adsorption capacity in CO_2 is almost two times greater than that in CH_4, and nitrogen adsorption is the least among these gases. A Langmuir-like model can be used to describe the strain with the gas pressure and the swelling strain induced by gas adsorption has a linear relationship with gas adsorption quantity. Moreover, swelling strain increase was observed when CO_2 was injected into the sample cell and the swelling strain was almost the sum of the strains induced by different gases at corresponding partial gas pressure.

Estimating soil ammonium adsorption using pedotransfer functions in an irrigation district of the North China Plain

Extensive use of chemical fertilizers in agriculture can induce high concentration of ammonium nitrogen(NH4^(+)_(-)N) in soil. Desorption and leaching of NH4^(+)_(-)N has led to pollution of natural waters. The adsorption of NH4^(+)_(-)N in soil plays an important role in the fate of the NH4^(+)_(-)N. Understanding the adsorption characteristics of NH4^(+)_(-)N is necessary to ascertain and predict its fate in the soil-water environment, and pedotransfer functions(PTFs) could be a convenient method for quantification of the adsorption parameters. Ammonium nitrogen adsorption capacity, isotherms, and their influencing factors were investigated for various soils in an irrigation district of the North China Plain. Fourteen agricultural soils with three types of texture(silt, silty loam, and sandy loam) were collected from topsoil to perform batch experiments. Silt and silty loam soils had higher NH4^(+)_(-)N adsorption capacity than sandy loam soils.Clay and silt contents significantly affected the adsorption capacity of NH4^(+)_(-)N in the different soils. The adsorption isotherms of NH4^(+)_(-)N in the 14 soils fit well using the Freundlich, Langmuir, and Temkin models. The models’ adsorption parameters were significantly related to soil properties including clay,silt, and organic carbon contents and Fe^(2+) and Fe^(3+) ion concentrations in the groundwater. The PTFs that relate soil and groundwater properties to soil NH4^(+)_(-)N adsorption isotherms were derived using multiple regressions where the coefficients were predicted using the Bayesian method. The PTFs of the three adsorption isotherm models were successfully verified and could be useful tools to help predict NH4^(+)_(-)N adsorption at a regional scale in irrigation districts.

Adsorption of Rhodamine B from Aqueous Solution onto Heat-Activated Sepiolite

The heat-activated sepiolite,which was prepared using sepiolite by thermal treatment at different temperatures,was used as an absorbent for the removal of rhodamine B(RhB) from aqueous solutions.The structure and morphology of the as-prepared samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM) techniques,respectively.The adsorption capacity of RhB onto the heat-activated sepiolite has been examined with pH,adsorbent dosage,contact time,initial dye concentration,and temperature.Kinetic studies showed that the equilibrium was attained within 40 min,and the kinetic data were well described by the pseudo-second-order kinetic model.Besides,the experimental data(R 2 >0.999) fitted the Freundlich model better than the Langmuir model.The as-prepared sample showed higher adsorption capacity(8.33 mg/g) for the removal of RhB than that of sepiolite,which could be attributed to more adsorption sites caused by appropriate heat treatment.The adsorbent can be well regenerated by calcination at 400 ℃ for 2 h and regenerated sepiolite did not exhibited significant loss of adsorption activity after five recycles.

Adsorption of 1,3-propanediol from synthetic mixture using polymeric resin as adsorbents

The aim of this work was to separate 1,3-PDO from a synthetic mixture using polymeric resins,Amberlite XAD-7 and XAD-16 resins.The equilibrium adsorption of 1,3-PDO onto two polymeric resins were investigated in binary and tertiary systems.Experimental results of binary component adsorption equilibrium indicated that the adsorption capacity(q)of 1,3-PDO at 160 g/L onto XAD-7 and XAD-16 was 835.96 and 584.61 mg 1,3-PDO/g dry resin,respectively.The adsorption isotherms were closely predicted by the Langmuir-Freundlich model among the two isotherm model tested.The value of n of 1,3-PDO adsorbed on XAD-7 are much higher than those on XAD-16.This result suggested that XAD-7 resin has a higher affinity for the 1,3-PDO adsorption than XAD-16 resin.Moreover,the value of adsorption capacity of 1,3-PDO in the binary and tertiary component were compared at the same conditions.In the tertiary system,although the selectivity of 1,3-PDO from XAD-7 was approximately six times higher than XAD-16,the adsorption capacity of 1,3-PDO at 160 g/L onto XAD-16 was higher than XAD-7.Interestingly,the reusability of XAD-7 and XAD-16 resins in the three cycle times shows a slight loss of adsorption capacity.Furthermore,the investigation about desorption by an ethanol/water mixture at 50%(V/V)indicated that the desorption yield of 1,3-PDO from XAD-7 was lower than XAD-16 resin for both the binary and tertiary component.This was due to the more favorable adsorption characteristics of XAD-7 resin than XAD-16 resin.