Heavy Metal Removal from Water by Adsorption Using Pillared Montmorillonite

Removal of Cu^2＋, Cr^3＋ and Cd^2＋ from aqueous solutions by adsorption on montmorillonite modified by sodium dodecylsulfate （SDS） and hydroxy-alumino-silicate （HAS） was investigated. Experiments were carried out as a function of solution pH, solute concentration, and time. The Langmuir model was adopted to describe the single-solute adsorption isotherm, in which the Langmuir parameters were directly taken from those obtained in single-solute systems. The kinetics of metal ions adsorption was examined and the pseudo-first-order rate constant was finally evaluated.

Comments on“Adsorption behavior of heavy metal ions by carbon nanotubes grown on microsized Al_2O_3 particles”

Recently, Hsieh and Horng [1] published the paper entitled as above. In section 3 results and discussion, the authors mentioned the first and the second order kinetic models without any quotations. In fact these two kinetic models have been published [2-5]. In order to distinguish a kinetics model based on the ad- sorption capacity of a solid from the one based on the concentration of a solution, Lagergren＇s first-order rate equation has been called pseudo-first-order [6-7]. The Lagergren＇s equation has been widely cited, but there are far more mistakes made in the quotation and in the reference section of papers, including the title, the author＇s name, journal title, year of publishing, volume, and page number [3]. In addition, the second order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat has been reported by Ho [8].

Heavy metal removal from aqueous solution using carbonaceous K_2S-impregnated adsorbent

A novel carbonaceous adsorbent for heavy metal removal was prepared from raw coal by one-step simple sulfur impregnation using K2S. Raw coal was mixed with K2S powder and then heated at 800℃ for 30 min in nitrogen to produce K2S char. The sulfur content and form in K2S char were determined, and the ability of K2S char to adsorb Zn^2＋, Cd^2＋ and Pb^2＋ was examined. The K2S impregnation was effective at impregnating sulfur into coal, especially in the form of elemental, thiophenic and sulfatic sulfur. The sulfur content of K2S char was higher than those of raw coal and pyrolysis char. The Zn^2＋ removal in 2.4 mmol/L of Zn^2＋ solution by K2S char was higher than raw coal with the removal rate of 100%. K2S char adsorbed Pb^2＋ and Cd^2＋ in 24 mmol/L of Pb^2＋ and Cd^2＋ solution with the removal rate of 97% and 35%, respectively. The elution extents of adsorbed Pb^2＋ and Cd^2＋ were zero in distilled water and 27% in 0.1 mol/L HCl solution. These results indicated that an effective adsorbent for heavy metal ions was prepared from coal using K2S sulfur impregnation, and that the adsorbed metals were strongly retained in K2S char.

Synthesis of activated carbons from black sapote seeds,characterization and application in the elimination of heavy metals and textile dyes

Many different techniques may be used to remove industrial pollutants from wastewater. Adsorption using activated carbon has been reported to be an effective method. This work proposes the use of a vegetable residue(black sapote seeds) as a raw material for its synthesis. These carbons were chemically activated using phosphoric acid and carbonized at 673 and 873 K. Adsorption isotherms were constructed for the textile dyes on the carbons, and this data was treated using Langmuir’s equation to quantitatively describe the adsorption process. The synthesized carbons were characterized using FTIR, EA, SEM, Nitrogen adsorption(specific surface areas of 879 and 652 m2·g-1), and their points of zero charge(2.1 and 2.3). It was possible to adsorb both heavy metals and textile dyes present in aqueous solutions and wastewaters using these activated carbons. Heavy metals were adsorbed almost completely by both carbons. Cationic dyes where adsorbed(58–59.8 mg·g-1) in greater amounts compared to anionic dyes(10–58.8 mg·g-1). The amount of anionic dyes adsorbed increased almost 30% by changing the pH of the solutions. One of the carbons was thermally regenerated on three occasions without losing its adsorption capacity and it was proved in a flow system.

Study on Functional and Structure Properties of Soluble Dietary Fiber Modified by Extrusion-expansion Technology from Peanut Shells

[Objectives] This study was conducted to investigate the feasibility of using modified peanut dietary fiber as a functional food ingredient. [Methods]Using peanut shells as a test material,the process parameters of soluble dietary fiber( SDF) modified by extrusion and expansion were studied,and the functional and structural characteristics of SDF before and after modification were discussed. [Results] The optimum conditions were as follows: screw speed 200 rpm,temperature 130 ℃ and moisture content 20 %,and the SDF extraction yield was 22. 3%. The modified SDF showed BCmax values of( 378. 5 ± 5. 3),( 278. 3 ± 3. 2)and( 167. 2 ± 2. 5) μmol/g and BCmin of( 30. 4 ± 1. 3),( 63. 4 ± 3. 7) and( 71. 3 ± 4. 2) μmol/L,for Pb,As and Cu,respectively,indicating that the adsorption to the three heavy metals was enhanced. The modified SDF had a porous network like honeycomb and swelled structure. [Conclusions]Therefore,it is feasible to modify SDF by extrusion and expansion.

Selective targeted adsorption and inactivation of antibiotic-resistant bacteria by Cr-loaded mixed metal oxides

Herein we provide a novel high-efficiency nanocomposite for bacterial capture based on mixed metal oxides(MMOs)with deleterious chromium properties.With both the layer structure of layered double hydroxides(LDHs)and the magnetic properties of Fe,MMOs enrich the location of ionic forms on the surface,providing a good carrier for adsorption of the heavy metal Cr(VI).The capacity for adsorption of Cr(VI)by MMOs can be as high as 98.80 mg/g.The prepared Cr(VI)-MMOs achieved extremely expeditious location of gram-negative antibiotic-resistant E.coliNDM-1 by identifying lipid bilayers.Cr-MMOs with a Cr loading of 19.70 mg/g had the best bactericidal effect,and the concentration of E.coliNDM-1 was decreased from~10^(8) to~10^(3) CFU/mL after 30 min of reaction.The binding of nitrogen and phosphorus hydrophilic groups to chromate generated realistic models for density functional theory(DFT)calculations.The specific selectivity of MMOs toward bacterial cells was improved by taking Cr(VI)as a transferable medium,thereby enhancing the antibacterial activity of Cr-MMOs.Under the combined action of chemical and physical reactions,Cr(VI)-MMOs achieved high capacity for inactivation of bacteria.Moreover,the metallic elements ratio in Cr-MMOs remained stable in their initial valence states after inactivation.This guaranteed high removal efficiency for both heavy metals and bacteria,allowing recycling of the adsorbent in practical applications.

Comparative Evaluation of Calcium, Magnesium, Copper and Zinc Removal by Wood Ash, Sodium Carbonate and Sodium Hydrogen Phosphate

Remediation via adsorption process has been proven to be one of the best water treatment technologies globally. Many adsorbents, including agricultural wastes, have been considered for the removal of a variety of pollutants from water. However, most of the studies reported in the literature used metal concentrations below 1000 ppm. It is also known that initial metal concentrations in polluted aqueous solutions, as well as metal and adsorbent type, are some of the factors that affect metal removal. Therefore, this project examined the remediation of water contaminated by 1000 ppm of lead, zinc, copper, magnesium, and calcium ions using wood ash, sodium hydrogen phosphate (dibasic), and sodium carbonate (dibasic). Comparative analysis of the results showed the order of order of metal removal by the adsorbents as: dibasic phosphate (Ca > Cu > Pb > Zn > Mg);dibasic Carbonate (Pb ~ Ca > Zn > Cu > Mg);Wood ash (Mg > Cu > Zn > Pb > Ca). These results suggest that metal and adsorbent type as well as the inherent chemical properties of these metal cations may contribute to the varying binding affinity of the metals to the adsorbent ligand(s) and thus, affect the extent of metal removal. It is equally worthy to note that wood ash more effectively removed hardness metals (Mg and Ca) from water than the inorganic phosphate and carbonate ions.

New insight into adsorption characteristics and mechanisms of the biosorbent from waste activated sludge for heavy metals

The adsorption characteristics and mechanisms of the biosorbent from waste activated sludge were investigated by adsorbing Pb2＋and Zn2＋in aqueous single-metal solutions. A p H value of the metal solutions at 6.0 was beneficial to the high adsorption quantity of the biosorbent. The optimal mass ratio of the biosorbent to metal ions was found to be 2. A higher adsorption quantity of the biosorbent was achieved by keeping the reaction temperature below 55°C. Response surface methodology was applied to optimize the biosorption processes, and the developed mathematical equations showed high determination coefficients（above 0.99 for both metal ions） and insignificant lack of fit（p = 0.0838 and 0.0782 for Pb2＋and Zn2＋, respectively）. Atomic force microscopy analyses suggested that the metal elements were adsorbed onto the biosorbent surface via electrostatic interaction. X-ray photoelectron spectroscopy analyses indicated the presence of complexation（between –NH2,-CN and metal ions） and ion-exchange（between –COOH and metal ions）. The adsorption mechanisms could be the combined action of electrostatic interaction, complexation and ion-exchange between functional groups and metal ions.

Predicting heavy metals' adsorption edges and adsorption isotherms on MnO_2 with the parameters determined from Langmuir kinetics

Although surface complexation models have been widely used to describe the adsorption of heavy metals, few studies have verified the feasibility of modeling the adsorption kinetics,edge, and isotherm data with one p H-independent parameter. A close inspection of the derivation process of Langmuir isotherm revealed that the equilibrium constant derived from the Langmuir kinetic model, KS-kinetic, is theoretically equivalent to the adsorption constant in Langmuir isotherm, KS-Langmuir. The modified Langmuir kinetic model（MLK model） and modified Langmuir isotherm model（MLI model） incorporating p H factor were developed. The MLK model was employed to simulate the adsorption kinetics of Cu（II）, Co（II）, Cd（II）, Zn（II） and Ni（II） on MnO2 at pH 3.2 or 3.3 to get the values of KS-kinetic. The adsorption edges of heavy metals could be modeled with the modified metal partitioning model（MMP model）, and the values of KS-Langmuir were obtained. The values of KS-kinetic and KS-Langmuir are very close to each other, validating that the constants obtained by these two methods are basically the same. The MMP model with KS-kinetic constants could predict the adsorption edges of heavy metals on MnO2 very well at different adsorbent/adsorbate concentrations. Moreover, the adsorption isotherms of heavy metals on MnO2 at various pH levels could be predicted reasonably well by the MLI model with the KS-kinetic constants.

Preparation and properties of chitosan–metal complex：Some factors influencing the adsorption capacity for dyes in aqueous solution

Chitosan–metal complexes have been widely studied in wastewater treatment, but there are still various factors in complex preparation which are collectively responsible for improving the adsorption capacity need to be further studied. Thus, this study investigates the factors affecting the adsorption ability of chitosan–metal complex adsorbents, including various kinds of metal centers, different metal salts and crosslinking degree. The results show that the chitosan–Fe（ Ⅲ） complex prepared by sulfate salts exhibited the best adsorption efficiency（100%） for various dyes in very short time duration（10 min）, and its maximum adsorption capacity achieved 349.22 mg/g. The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan–metal complex. SO4^（2-） ions not only had the effect of crosslinking through electrostatic interaction with amine group of chitosan polymer, but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process.Additionally, the p H sensitivity and the sensitivity of ionic environment for chitosan–metal complex were analyzed. We hope that these factors affecting the adsorption of the chitosan–metal complex can help not only in optimizing its use but also in designing new chitosan–metal based complexes.

Metal cation removal by P（VC-r-AA） copolymer ultrafiltration membranes

A series of amphiphilic copolymers containing poly（vinyl chloride-r-acrylic acid） （P（VC-r-AA）） was synthesized and used to prepare membranes via a non-solvent induced phase separation method. The prepared membranes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and water contact angle and zeta potential measurements. The copolymer P（VC-r-AA） chains did not dissolved in a coagulation bath, indicating that the AA segments were completely retained within the membrane. Enriching degree of AA segments in surface layer was 2 for copolymer membrane. In addition, the introduction of AA segments made the membrane electronegative and hydrophilic so that the membrane was sensitive to the solution pH. The fouling resistance, adsorption of Cu（II）, Cr（III） and Ce（IV） ions and the desorption properties of the membranes were also determined. The copolymer membranes exhibited good antifouling performance with a fouling reversibility of 92%. The membranes also had good adsorption capacities for Cu（II）, Cr（III） and Ce（IV） ions. The optimal pH for Cu（II） adsorption was 6 and the copolymer membrane has potential applications for low concentration Cu（II） removal.

Structures, Stabilities and Work Functions of Alkali-metal-adsorbed Boron α1-Sheets

In this study, we employed the density functional theory method to simulate Li-, Na- and K-adsorbed boron α1-sheets（al-BSTs）. After optimizing possible structures, we investigated their thermodynamic stabilities, barriers for metal atom diffusion on the substrate, and work functions. The computed results indicate that the work function of α1-BST decreases significantly after the adsorption of Li, Na and K. Furthermore, under high hole coverage, these alkali-metal-adsorbed α1-BSTs have lower work functions than the two-dimensional materials of greatest concern and the commonly used electrode materials Ca and Mg. Therefore, the Li-, Na- and K-adsorbed α1-BSTs are potential low-work-function nanomaterials.

Experimental determination of Cd^2＋ adsorption mechanism on low-cost biological waste

Carbonate shells have an astonishing ability in the removal of Cd^2＋ in a short time period with emphasis on being a low cost adsorbent. In the present study, the sorption capacity of carbonate shells was studied for Cd^2＋ in batch experiments. The influence of different carbonate shell sizes and physico-chemical factors were evaluated and the results were analyzed for its correlation matrices by using Predictive Analytics Software （PASW）. The miner- alogy state of aqueous solution regarding the saturation index was simulated using PHREEQC to identify the Cd^2＋ uptake mechanism. The Cd uptake rates were calculated as well as Ca^2＋, HCO3- concentration, pH, ambient humidity and temperature were measured. Cd2＋ removal of 91.52% was achieved after 5 h adsorption. The adsorption efficiencies were significantly influenced by pH as they increased with the increase of pH from acidic solution （5.50±0.02） to slightly alkaline （7.60±0.05）. In addition, the mineralogy state of aqueous solution calculated from PHREEQC confirmed that the increment of Ca^2＋ and HCO3- concentrations in solution was attributed to the dissolution of carbonate shells. Moreover, the ion exchange adsorption mechanism of Cd^2＋ toward Ca^2＋ was identified as the process involved in Cd^2＋ uptake.

Preparation of Mg,N-co-doped lignin adsorbents for enhanced selectivity and high adsorption capacity of As(Ⅴ) from wastewater

Among various environmental problems,water pollution has drawn more and more attention.To develop an adsorbent with enhanced selectivity and high capacity for As(V)oxyanion,a novel lignin-based adsorbent was prepared by doping with N and modifying with Mg^(2+),using thiethylenetetramine(TETA)and MgCl_(2) as the source of N and Mg^(2+),respectively.N-doped lignin(NL)shows a high selectivity for As(Ⅴ),which is further enhanced by modifying with Mg^(2+)(MNL).MNL shows an excellent reusability.The adsorption isotherms and kinetics of MNL for As(Ⅴ)follow Langmuir isotherms model and pseudo-second-order kinetics model,respectively.The adsorption of MNL for As(Ⅴ)achieved a maximum adsorption capacity of 687.46 mg g^(−1) and the equilibrium was established within 30 min.This study offers a novel idea on the recycle of the waste of paper industry and provides a new technology for As(Ⅴ)adsorption from wastewater.

Removal of Pb(Ⅱ) from aqueous solution by hydrous manganese dioxide:Adsorption behavior and mechanism

Hydrous manganese dioxide （HMO） synthesized by redox of potassium permanganate and hydrogen peroxide was used as an adsorbent for Pb（Ⅱ） removal.The specific surface area,pore volume and BJH pore diameter of the HMO were 79.31m2/g,0.07cm3/g and 3.38 nm,respectively.The adsorption equilibrium at 298K could be well described by the Langmuir isotherm equation with q max value of 352.55mg/g.The negative values of G and the positive values of H and S indicated the adsorption process was spontaneous and endothermic.The pseudo second-order equation could best fit the adsorption data.The value of the calculated activation energy for Pb（Ⅱ） adsorption onto the HMO was 38.23 kJ/mol.The uptake of Pb（Ⅱ） by HMO was correlated with increasing surface hydroxyl group content and the main adsorbed speciation was PbOH＋.The final chemical state of Pb（Ⅱ） on the surface of HMO was similar to PbO.HMO was a promising candidate for Pb（Ⅱ） removal from aqueous solution.

Rapid adsorption of toxic Pb(Ⅱ) ions from aqueous solution using multiwall carbon nanotubes synthesized by microwave chemical vapor deposition technique

Multiwall carbon nanotubes（MWCNTs） were synthesized using a tubular microwave chemical vapor deposition technique, using acetylene and hydrogen as the precursor gases and ferrocene as catalyst. The novel MWCNT samples were tested for their performance in terms of Pb（Ⅱ）binding. The synthesized MWCNT samples were characterized using Fourier Transform Infrared（FT-IR）, Brunauer, Emmett and Teller（BET）, Field Emission Scanning Electron Microscopy（FESEM） analysis, and the adsorption of Pb（Ⅱ） was studied as a function of p H,initial Pb（Ⅱ） concentration, MWCNT dosage, agitation speed, and adsorption time, and process parameters were optimized. The adsorption data followed both Freundlich and Langmuir isotherms. On the basis of the Langmuir model, Qmaxwas calculated to be 104.2 mg/g for the microwave-synthesized MWCNTs. In order to investigate the dynamic behavior of MWCNTs as an adsorbent, the kinetic data were modeled using pseudo first-order and pseudo second-order equations. Different thermodynamic parameters, viz., ΔH0, ΔS0and ΔG0were evaluated and it was found that the adsorption was feasible, spontaneous and endothermic in nature. The statistical analysis revealed that the optimum conditions for the highest removal（99.9%） of Pb（Ⅱ） are at p H 5, MWCNT dosage 0.1 g, agitation speed 160 r/min and time of 22.5 min with the initial concentration of 10 mg/L. Our results proved that microwave-synthesized MWCNTs can be used as an effective Pb（Ⅱ） adsorbent due to their high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.

Evaluation of Ce(Ⅲ) and Gd(Ⅲ) adsorption from aqueous solution using CTS-g-(AA-co-SS)/ISC hybrid hydrogel adsorbent

CTS-g-（AA-co-SS）/ISC hybrid hydrogel adsorbent with crosslinked network structure and superior adsorption performance for rare-earth metal ions was successfully synthesized in aqueous solution by a simple one-step free-radical grafting polymerization reaction among acrylic acid（AA）, sodium p-styrenesulfonate（SS） and chitosan（CTS） using illite/smectite clay（ISC） as the inorganic additive. The structure of the as-prepared CTS-g-（AA-co-SS）/ISC hydrogel adsorbent was characterized, and the reaction parameters such as AA/SS molar ratio and ISC content were optimized, and the effects of pH values, initial concentration and contact time on the adsorption performance for Ce（Ⅲ） and Gd（Ⅲ） were systematically evaluated. It was found that the maximum adsorption capacities of the hydrogel adsorbent toward Ce（Ⅲ） and Gd（Ⅲ） reached 174.05 and 223.79 mg/g, respectively, and the adsorption quickly achieved equilibrium within 15–20 min. The adsorbed Ce（Ⅲ） and Gd（Ⅲ） could be easily desorbed for recovery, and the used adsorbent was able to be regenerated for reuse. After five adsorption-desorption cycles, the regenerated adsorbent could still retain the adsorption capacities that were close to the initial value. The adsorption process was well described by pseudo-second-order kinetic mode and the Langmuir isotherm model, and the chemical complexation between ions and –COO~–was mainly responsible for the high adsorption capacity. As a whole, the hybrid hydrogel adsorbent was potential to be used for the adsorption and recovery of Ce（Ⅲ） and Gd（Ⅲ） from water.

Synthesis of linear low-density polyethylene-g-poly(acrylic acid)-co-starch/organo-montmorillonite hydrogel composite as an adsorbent for removal of Pb(Ⅱ) from aqueous solutions

The purpose of this work is to remove Pb（II） from the aqueous solution using a type of hydrogel composite. A hydrogel composite consisting of waste linear low density polyethylene, acrylic acid, starch, and organo-montmorillonite was prepared through emulsion polymerization method. Fourier transform infrared spectroscopy（FTIR）, Solid carbon nuclear magnetic resonance spectroscopy（CNMR））, silicon-29 nuclear magnetic resonance spectroscopy（Si NMR））, and X-ray diffraction spectroscope（（XRD） were applied to characterize the hydrogel composite. The hydrogel composite was then employed as an adsorbent for the removal of Pb（II） from the aqueous solution. The Pb（II）-loaded hydrogel composite was characterized using Fourier transform infrared spectroscopy（FTIR））,scanning electron microscopy（SEM））, and X-ray photoelectron spectroscopy（（XPS））. From XPS results, it was found that the carboxyl and hydroxyl groups of the hydrogel composite participated in the removal of Pb（II）. Kinetic studies indicated that the adsorption of Pb（II）followed the pseudo-second-order equation. It was also found that the Langmuir model described the adsorption isotherm better than the Freundlich isotherm. The maximum removal capacity of the hydrogel composite for Pb（II） ions was 430 mg/g. Thus, the waste linear low-density polyethylene-g-poly（acrylic acid）-co-starch/organo-montmorillonite hydrogel composite could be a promising Pb（II） adsorbent.

The synthesis of MOF derived carbon and its application in water treatment

In recent years,since water pollution has aroused great public concern,various carbon materials have already been widely applied for water treatment.In this respect,tremendous effort has been made to provide different synthesis methods of carbon materials.Among all carbon materials,metal-organic framework(MOF)derived carbon has always been favored as it possesses several appealing merits such as high specific surface area,large pore volume,and outstanding chemical stability.This review presents the latest development of MOFs as templates and precursors for the fabrication of various carbon materials,including porous carbon,nanocarbon,and graphene,which are pyrolyzed at different temperatures.The article also emphasizes on their future trends and perspectives on the application of water treatment.