Bioleaching of heavy metals from dewatered sludge by Acidithiobacillus ferrooxidans

The feasibility of bioleaching for removal of heavy metals from dewatered sewage sludge using an iron‐oxidizing bacterium Acidithiobacillus ferrooxidans was investigated. The influence of seven process parameters including cell adaptation, total amount and particle size of the sludge, initial concentrations of Fe²⁺ and At ferrooxidans, and addition of inorganic nutrients and sulfur were evaluated in terms of the solubilization of Zn, Cu and Cr. When sludge‐adapted cells, addition of inorganic nutrients and lower sludge content were involved, higher yields of metal extraction were obtained. However, higher initial concentrations of At ferrooxidans and Fe²⁺, fine particle size of the sludge and S addition did not improve the metals' solubilization during an experimental period of 7 days. As a result of a long‐term (40 days) bioleaching experiment, 42% of Zn (1300–1648 mg kg^?1), 39% of Cu (613–774 mg kg^?1) and 10% of Cr (37–44 mg kg^?1) in the sludge were leached into the solution. The results indicate that a bioleaching process conducted under operationally optimal conditions can be effectively employed for the removal of heavy metals from sewage sludge before land application. Copyright © 2005 Society of Chemical Industry     

Heavy metals removal from solution by polyaniline/palygorskite composite

Batch adsorption experiments were carried out to remove heavy metal ions such as Cu (II), Ni (II), Cd (II), and Cr (VI) from single‐metal solutions using a polyaniline/palygorskite (PP) composite. Different parameters affecting the adsorption capacity such as contact time and pH of the solution have been investigated. The structural characteristics of the PP composite were studied in this work. Atomic absorption spectroscopy was used for the measurement of heavy metal contents, and the adsorption capacity (q_e) calculated were 114 mg Cu (II) g^?1, 84 mg Ni (II) g^?1, 56 mg Cd (II) g^?1, and 198 mg Cr (VI) g^?1 under optimal conditions. The removal of the metal ions from solutions was assigned to chelation, ionic exchange, and electrostatic attraction. Data from this study proved that the novel organic/inorganic composite presents great potential in the recovery and elimination of noble or heavy metal ions from industrial wastewater. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Nickel and cobalt sorption on anaerobic granular sludges: kinetic and equilibrium studies

The kinetics and equilibria of sorption of the divalent metal ions cobalt and nickel onto anaerobic granular sludge are described. Single component and binary equimolar systems were studied at different pH values (pH 6, 7 and 8). The kinetic modelling of metal sorption by anaerobic granular sludge has been carried out using Lagergren equations. On fitting the experimental kinetic data both in first‐ and pseudo‐second‐order equations, the regression analysis of a pseudo‐second‐order equation gave a higher r² value, indicating that both external mass transfer and intra‐particle diffusion are involved in the sorption process. The experimental isotherm data were analysed using the Langmuir, Freundlich and Redlich–Peterson equations. The Redlich isotherm, a combination of the Langmuir and Freundlich equations, was found to have the highest regression correlation coefficients at pH 7. At pH 8, the Langmuir mechanism dominated for cobalt and nickel adsorption. In contrast, at pH 6, the Freundlich equation gave a better correlation coefficient which suggests a more heterogeneous adsorption at that pH. The maximal adsorption capacity of the granular sludge, as determined by the Langmuir equation, for cobalt or nickel in single systems (8.92 mg g^?1 Co TSS; 9.41 mg g^?1 Ni TSS, pH 7) compared with binary systems (8.06 mg g^?1 Co TSS; 8.43 mg g^?1 Ni TSS, pH 7) showed no great difference in the accumulation of these metals onto granular sludge. Copyright © 2004 Society of Chemical Industry     

Low temperature one‐step synthesis of poly(barbituric acid) functionalized magnetic nanoparticles for removal of heavy metal ions

Poly(barbituric acid) functionalized magnetic nanoparticles with excellent adsorption behavior were facilely synthesized through one‐step chemical oxidation polymerization method by using sodium borohydride as the reducing agent. Structure, morphology, and magnetism of the products were thoroughly investigated by means of FTIR, FESEM, EDX, X‐ray photoelectron spectra, thermogravimetric analyzer–differential scanning calorimetry, and vibrating sample magnetometer. The products were of a sphere‐shaped nanostructure with the saturation magnetization value of 7.5 emu g^?1, which make them reusable for adsorption application. Removal capability for heavy metal ions were systematically evaluated using Pd (II) and Cu (II) ions as the models. The maximum sorption capacities by applying the Langmuir equation were calculated to be 166.6 mg/g for Cu (II) and 142.8 mg/g for Pb (II). A recycle test revealed that the PBA‐MNPs have above 87.1% for Cu (II) and 82.69% for Pb (II) ion desorption efficiency after the three regeneration cycle process. All the above experimental results demonstrated that barbituric acid‐based material could be used as a possible adsorbent for the efficient removal of heavy metals from aqueous solution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40957.     

Performance assessment of a UASB–anoxic–oxic system for the treatment of tomato‐processing wastes

An upflow anaerobic sludge blanket (UASB)–anoxic–oxic system was used to achieve biochemical oxygen demand, NH₄ and total suspended solids (TSS) criteria of 15, 1 and 15 mg dm^?3 at 1.17 days of system hydraulic retention time during treatment of tomato‐processing waste. The incorporation of an anoxic tank was found to affect the improvement in sludge‐settling characteristics, as reflected by about 25–33% reduction in the sludge volume index, along with final effluent TSS and soluble biochemical oxygen demand concentrations of 13 and 9 mg dm^?3, respectively, which met the discharge criteria. Despite incomplete denitrification, sludge settleability was very good (sludge volume index < 60 cm³ g^?1) owing to reduction in volatile suspended solids/TSS ratio from 0.75 to 0.6 as a result of higher alkalinity in the UASB effluent. Also in this study, phosphorus release was observed in the anoxic tank, predominantly due to abundance of acetic acid in the UASB effluent. A phosphate release of 5.4 mg P dm^?3 was observed in the anoxic tank with subsequent P uptake in the following aerobic stage. Copyright © 2006 Society of Chemical Industry     

Batch and fixed‐bed column adsorption of Cu(II), Pb(II) and Cd(II) from aqueous solution onto functionalised SBA‐15 mesoporous silica

Functionalised SBA‐15 mesoporous silica with polyamidoamine groups (PAMAM‐SBA‐15) was successfully prepared with the structure characterised by X‐ray diffraction, nitrogen adsorption–desorption, Fourier transform infrared spectra and thermogravimetric analysis. PAMAM‐SBA‐15 was applied as adsorbent for Cu(II), Pb(II) and Cd(II) ions removal from aqueous solution. The effects of the solution pH, adsorbent dosage and metal ion concentration were studied under the batch mode. The Langmuir model was fitted favourably to the experimental data. The maximum sorptive capacities were determined to be 1.74 mmol g^?1 for Cu(II), 1.16 mmol g^?1 for Pb(II) and 0.97 mmol g^?1 for Cd(II). The overall sorption process was fast and its kinetics was fitted well to a pseudo‐first‐order kinetic model. The mean free energy of sorption, calculated from the Dubinin–Radushkevich isotherm, indicated that the sorption of lead and copper, with E > 16 kJ mol^?1, followed the sorption mechanism by particle diffusion. The adsorbent could be regenerated three times without significant varying its sorption capacity. A series of column tests were performed to determine the breakthrough curves with varying bed heights and flow rates. The breakthrough data gave a good fit to the Thomas model. Maximum sorption capacity of 1.6, 1.3 and 1.0 mmol g^?1 were found for Cu(II), Pb(II) and Cd(II), respectively, at flow rate of 0.4 mL min^?1 and bed height of 8 cm, which corresponds to 83%, 75% and 73% of metallic ion removal, respectively, which very close to the value determined in the batch process. Bed depth service time model could describe the breakthrough data from the column experiments properly. © 2012 Canadian Society for Chemical Engineering     

Biosorption of heavy metals from aqueous solution using modified activated carbon: comparison of linear and nonlinear methods

BACKGROUND: Biosorption of heavy metals from aqueous solution by modified activated carbon with Phanerochaete chrysosporium immobilised in Ca‐alginate beads was investigated using a batch system and comparison of linear and nonlinear methods. RESULTS: The amount of Cu(II), Zn(II) and Pb(II) ion sorption by the beads was as follows: activated carbon with P. chrysosporium immobilised in Ca‐alginate beads (ACFCA) (193.4, 181.8, 136.6 mg g^?1) > activated carbon immobilised in Ca‐alginate beads (ACCA) (174.8, 162.0, 130.7 mg g^?1) > P. chrysosporium (F) (148.8, 125.6, 120.4 mg g^?1) > activated carbon (AC) (138.8, 112.3, 109.3 mg g^?1) > plain Ca‐alginate beads (PCA) (125.4, 105.2, 98.2 mg g^?1). The widely used Langmuir and Freundlich isotherm models were utilised to describe the biosorption equilibrium process. CONCLUSION: The results of this study suggest that the immobilisation of modified activated carbon with P. chrysosporium in Ca‐alginate beads is suitable for a batch system. The isotherm parameters were estimated using linear and nonlinear regression analyses. The surface charge density of the biosorbents varied with the pH of the medium; the maximum biosorption of heavy metal ions on the biosorbents was obtained when the pH was between 5.6 and 7.4. Copyright © 2008 Society of Chemical Industry     

Dried waste activated sludge as biosorbents for metal removal: adsorptive characterization and prevention of organic leaching

Dried waste activated sludge was used for copper removal from simulated waste water in this study. Unconditioned activated sludge (UAS) bound up to 35 mg Cu g^?1, although there was significant leaching of organic material. Organic and copper leaching from the UAS increased significantly as the pH was reduced. Immobilization of UAS by sodium and calcium alginate was utilized in order to overcome the leaching problems, but reduced the adsorption capacity. Based on metal removal and organic leaching, calcium alginate‐conditioned UAS (CACAS) was found to be the most suitable sorbent for copper removal. Kinetic experiments showed that copper removal by both sodium alginate‐conditioned UAS (SACAS) and CACAS was faster than that by activated carbons, but slower than most of the other biosorbents described in the literature. FTIR spectroscopy identified a number of atomic groupings and structures in UAS relevant to copper adsorption. It suggested that hydrogen ions are replaced with copper ions. The Freundlich equation fitted the experimental isotherms better than the Langmuir equation. A computational model based on adsorption isotherm, external mass transfer and diffusion processes successfully described the kinetics of copper ion removal and suggested that the biosorption kinetics was controlled by mass transfer. © 2002 Society of Chemical Industry     

Heavy Metals Precipitation in Sewage Sludge

Abstract

There is a great need for heavy metal removal from strongly metal‐polluted sewage sludges. One of the advantages of heavy metal removal from this type of sludge is the possibility of the sludge disposal to landfill with reduced risk of metals being leached to the surface and groundwater. Another advantage is the application of the sludge as soil improver. The use of chemical precipitation to remove dissolved heavy metals from sewage sludge implies a high cost for chemicals. This work shows, for real sewage sludge for the first time that the addition of NaOH as first precipitating agent considerably saves the addition of Na₂S, that is one of the most effective metal precipitating agents and also expensive. After solubilization of heavy metals by chemical leaching with previous aeration, the next step was the separation of the sludge solids from the metal‐rich acidic liquid (leachate) by centrifugation and filtration. Afterwards, the filtered leachate was submitted to the application of NaOH and Na₂S, separately and in combination, followed by filtration. The results showed that when iron and aluminium are present in the leachate, adsorption and/or coprecipitation of Cr, Pb, and Zn with Fe(OH)₃ and Al(OH)₃ might occur at increasing pH conditions. The combination of hydroxide and sulfide precipitation was able to promote an effective removal of heavy metals from leachate. Applying NaOH at a pH of 4–5 as a first precipitation step, followed by filtration and further addition of Na₂S to the filtered liquid at pH of 7–8 as a second precipitation step, decreased considerably the dosage of the second precipitant (almost 200 times), compared to when it was solely applied. This has practical applications, as the claimed costs drawbacks of H₂S addition is considerably reduced by the addition of the less expensive NaOH. The best removal efficiencies obtained were: Pb: ～100%, Cr: 99.9%, Cu: 99.7%, and Zn: 99.9%.     

Control of filamentous organisms in food‐processing wastewater treatment by intermittent aeration and selectors

Various measures were tested at a full‐scale wastewater treatment plant to control sludge bulking by type 0041 and 0675 filamentous microorganisms, instigated by highly variable wastewater loadings from a food‐processing facility. Intermittent aeration on a 1‐h on 1‐h off basis was found to effect a marginal improvement in sludge settling characteristics, as reflected by about an 11–36% reduction in the Sludge Volume Index (SVI) to 118 cm^?3 g^?1. At BOD loadings of 1500 kg d^?1 which marginally exceeded the design capacity of the plant of 1200 kg d^?1, SVI rose sharply to 230 cm^?3 g^?1 in less than a week. The anoxic selector effected a reduction in SVI to 170 cm^?3 g^?1 within 3 weeks of operation at temperatures of 8–12 °C. The aerobic selector was most effective, reducing SVIs further to 79 cm^?3 g^?1 in 2 weeks. Sludge settleablity was found to be inversely proportional to the aerobic selector food‐to‐microorganism ratio. The optimum aerobic selector loading was found to be 1.8–2.7 kgBOD₅ kgMLVSS d^?1, with corresponding SVIs in the range of 80–120 cm^?3 g^?1. © 2003 Society of Chemical Industry     

Mode of action of ferric and ferrous iron salts in activated sludge

BACKGROUND: Both ferric iron Fe(III) and ferrous iron Fe(II) salts are commonly used for chemical phosphorus removal (CPR) in the activated sludge (AS) process but only a few studies have compared Fe(III) and Fe(II) salts regarding their effect on the physical and biological properties of AS. In this research, the units of a continuous flow laboratory‐scale AS plant were dosed with Fe(III) and Fe(II) salts at a concentration of 25 mg Fe dm^?3 feed and changes in the AS properties were measured as Fe accumulated or washed out during startup, normal operation and withdrawal of dosing. RESULTS: The morphological characteristics of the flocs showed marked differences depending on the type of ion used. Fe(II) dosed flocs were more compact, less filamentous and smaller in size than Fe(III) dosed flocs. The settleability index of the Fe(II) dosed sludge was lower than that of the Fe(III) dosed sludge. The activity of ammonium (NH₄⁺‐N) and nitrite (NO₂^?‐N) oxidizing bacteria was found to be affected by the accumulation of Fe relating products into the sludge. CONCLUSIONS: Fe(II) was a more effective flocculent than Fe(III) and this was attributed to its ability to form stronger ionic bonds with the flocs prior to its oxidation to Fe(III). A hypothesis explaining the mode of action of Fe(II) is proposed. Floc surface properties were enhanced, this being beneficial to the morphological characteristics and settleability with further implications for the operation of AS. However, the effect may be reversed at high Fe contents. Copyright © 2010 Society of Chemical Industry     

Evaluation of the Efficiency of a Combined Adsorption–Ultrafiltration System for the Removal of Heavy Metals,Color, and Organic Matter from Textile Wastewater

In this work an ultrafiltration (UF) membrane system was investigated for the treatment of textile wastewater. UF membranes were assisted by activated sludge and minerals, which were employed as sorbents, to remove Cu(II), Pb(II), Zn(II), Ni(II), color, and organics. Significant variations were observed in metal removal efficiencies among the textile wastewater samples of different origin, even at the same pH (= 6) due to the presence of different compounds in wastewater. At the examined pH range (5.63–9.21), the dominant mechanism for copper and lead removal was the formation of insoluble metals due to precipitation and complexation of metal ions with wastewater compounds, including adsorption of metals on suspended solids and colloidal matter. The adsorption process of metals on minerals and activated sludge was the dominant process for nickel and zinc removal at low pH, while precipitation/complexation prevailed at higher pH. The examined adsorption-UF system could produce a treated effluent having low metal concentrations that could be safely discharged into municipal sewers. COD removal ranged from 76%–92% for the five textile wastewater samples. The color removal accomplished was significant (45%–70%), and depended on the type of dye.     

Interference of EDTA in the treatment of metal plating wastewater by biosorption

BACKGROUND: The applicability of biosorption for the treatment of metal plating wastewater is adversely affected by the presence of complexing agents. To investigate this limitation on the removal of copper(II) onto peat, batch and column experiments were carried out using EDTA as the model complexing agent. The influence of pH and copper(II):EDTA mass ratios were evaluated for copper(II) concentrations between 5 and 100 mg Cu(II) dm^?3. RESULTS: EDTA negatively affected the copper(II) uptake of peat for pH > 5. Batch and column experiments showed that copper(II)‐EDTA complexes were not sorbed by peat. The leaks of copper(II) detected from the beginning of the column operation matched the copper(II)‐EDTA concentration in the feed solutions. To overcome the interference of EDTA, a novel approach based on the combination of peat + activated carbon was proposed. Nearly complete removal of copper(II) was maintained over 70 h in the treatment of a solution containing 20 mg Cu(II) dm^?3 with 11% of copper(II)‐EDTA complexes. CONCLUSION: A new mass transport model coupling copper(II) speciation in the feed and mass transfer rate‐controlled process simulated the copper(II) breakthrough curves in the presence of EDTA and could be used to successfully predict the breakthrough point. This work demonstrated that biosorption can also be applied for the treatment of wastewater containing complexing agents with the proper combination of sorbent materials. © 2012 Society of Chemical Industry     

The use of 3,3′,4′,5‐tetrachlorosalicylanilide as a chemical uncoupler to reduce activated sludge yield

To determine whether chemical additions can be used to reduce sludge production in biological wastewater treatment, 3,3′,4′,5‐tetrachlorosalicylanilide (TCS) was added to activated sludge cultures as a metabolic uncoupler. Batch tests confirmed that TCS is an effective chemical uncoupler in reducing the sludge yield at concentrations greater than 1.0 mg dm^?3; a TCS concentration of 1.0 mg dm^?3 reduced sludge yield by approximately 50%. Substrate removal capability and effluent nitrogen concentration were not affected adversely by the presence of TCS when dosed every other day in a range of 2.0–3.6 mg dm^?3 during the 40‐day operation of activated sludge batch cultures. Such sludge growth reduction was associated with the enhancement of microbial activities in terms of the specific oxygen uptake rate and dehydrogenase activity. Sludge settleability of the treated and control samples was qualitatively comparable and not significantly different. Filamentous bacteria continued to grow in sludge flocs only in the control reactor at the end of the 40‐day trial. These results suggest that TCS treatment of activated sludge systems may reduce excess sludge yield. Copyright © 2003 Society of Chemical Industry     

High power generation with simultaneous COD removal using a circulating column microbial fuel cell

BACKGROUND: A circulating column microbial fuel cell (MFC) with Cu anode and Au? Cu air cathode was used for power generation and chemical oxygen demand (COD) removal from synthetic wastewater. The column was operated in repeated‐fed batch mode using acclimated anaerobic sludge. The contents of the column MFC were circulated while the feed wastewater was fed to the reactor in fed‐batch mode. Effects of feed COD concentration and COD loading rate on voltage difference, power density and percentage COD removal were investigated. RESULTS: The highest voltage difference (650 mV), power density (40 W m^?2) were obtained with a feed COD of 6400 mg L^?1, yielding 45% COD removal with a COD loading rate of nearly 90 mg h^?1. Low COD loadings (<90 mg h^?1) caused substrate limitations, and high loadings (>90 mg h^?1) resulted in inhibition of COD removal and power generation. The highest percentage COD removal (50%) was obtained with feed COD content of 10.35 g L^?1 or a COD loading rate of 145 mg h^?1. CONCLUSION: The power densities obtained with the circulating column MFC were considerably higher than those reported in the literature due to elimination of mass transfer limitations by the high circulation rates, proximity of electrodes and small anode surface area used in this study. Further improvements may be possible with optimization of the operating parameters. Copyright © 2009 Society of Chemical Industry     

Preparation of gel resins and removal of copper and lead from water

A series of gel resins were prepared by polymerizing glycidyl methacrylate (GMA) and 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) and functionalizing with ammonia (NH₃) and tetraethylenepentamine (TEPA). The aminated gel resins were then used as an adsorbent for the removal of heavy metal ions (Cu²⁺ and Pb²⁺). These gel resins containing amino groups and chelating amino groups had excellent adsorptive properties for Cu²⁺ and Pb²⁺. The adsorption process reached equilibrium in 40 min, and the adsorption capacities of Cu²⁺ and Pb²⁺ were 75.0 mg g^?1 and 266.6 mg g^?1 for the NH₃‐aminated gel resins and 57.5 mg g^?1 and 330.6 mg g^?1 for the TEPA‐aminated gel resins, respectively. After five adsorption–desorption processes, the adsorption capacities only decreased slightly. Thus, these aminated gel resins can be used as effective adsorbents for aqueous heavy metal ions (Cu²⁺ and Pb²⁺). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44466.     

High‐rate clarification of municipal wastewaters: a brief appraisal

Pilot‐plant studies on the treatment of three wastewaters (biological aerated flooded filter (BAFF) backwash water, post‐primary settling tank effluent and BAFF effluent) have been conducted using a ballasted sedimentation process (ACTIFLO^®) coupled with ferric chloride and polyaluminium chloride (PACl) coagulants. The response of the process to shock loads of high solids concentrations was also investigated. Results showed over 80% turbidity, 70% suspended solids, and 50% COD removals to be achievable at rise rates in excess of 80 m h^?1 and dose rates of 10–20 mg dm^?3 Fe. Slightly improved performance was attained using PACL at half the weight concentration (but about the same molar concentration) as that of Fe. No pH adjustment was necessary and process performance was not significantly influenced by changes in hydraulic loading rate. Effluent quality was largely unaffected by shock organic loads provided coagulant dosing was commensurately increased. Non‐ideal flow through the plant was apparent from the measured residence time, which was ～25% less than that calculated for plug flow. Clarification data were comparable to those reported for other high‐rate clarification (HRC) processes, with somewhat improved performance in terms of hydraulic retention time and coagulant use. Copyright © 2004 Society of Chemical Industry     

Effects of butyric acid stress on anaerobic sludge for hydrogen production from kitchen wastes

BACKGROUND: Anaerobic digestion is an alternative technology to achieve the dual benefits of hydrogen production and waste stabilization from kitchen wastes. In this work, the butyric acid stress on anaerobic sludge was investigated in order to improve the tolerance of sludge against organic acids, and to enhance hydrogen accumulation. RESULTS: The tolerance of butyric acid in anaerobic sludge increased with the stress concentration, however, it decreased at concentrations greater than of 4.0 g L^?1. The maximum hydrogen yield reached 63.72 mL g^?1 VS at 4.0 g L^?1 stress, representing an increase of 114% compared with the control group. The concentration of volatile solids (VS) of the sludge and SCOD increased steadily with time up to 20 h. At 4.0 g L^?1 butyric acid stress, the maximum activity of β‐glucosidase, BAA‐hydrolysing protease and dehydrogenase enzyme were 14912.1 µmol PNP g^?1 TS h^?1, 134.14 µmol NH₄‐N g^?1 TS h^?1 and 7316.42 µg TF g^?1 TS h^?1, which were 2.78, 1.90 and 2.01 times that of the control, respectively. CONCLUSIONS: The feasibility of butyric acid stress on anaerobic sludge to increase hydrogen production from kitchen wastes was demonstrated. Remarkably, 4.0 g L^?1 butyric acid stress was found to be favorable for improving the tolerance of butyric acid in sludge as well as hydrogen yield in the experiment. Copyright © 2010 Society of Chemical Industry     

A modified cellulose adsorbent for the removal of nickel(II) from aqueous solutions

A series of adsorption studies was carried out on a glycidyl methacrylate‐ modified cellulose material functionalised with imidazole (Cellulose‐g‐GMA‐Imidazole) to assess its capacity in the removal of Ni(II) ions from aqueous solution. The study sought to establish the effect of a number of parameters on the removal of Ni(II) from solution by the Cellulose‐g‐GMA‐Imidazole. In particular, the influence of initial metal concentration, contact time, solution temperature and pH were assessed. The studies indicated a Ni(II) uptake on the Cellulose‐g‐GMA‐Imidazole sorbent of approximately 48 mg g^?1 of nickel from aqueous solution. The adsorption process fitted the Langmuir model of adsorption and the binding process was mildly endothermic. The kinetics of the adsorption process indicated that nickel uptake occurred within 400 min and that pseudo‐second order kinetics best describe the overall adsorption process. Nickel(II) adsorption, recovery and re‐adsorption studies indicated that at highly acidic pH values the adsorbent material becomes unstable, but in the range pH 3–6, the adsorbent is stable and shows limited but significant Ni(II) recovery and re‐adsorption capability. Copyright © 2006 Society of Chemical Industry     

Amidinothiourea-linked covalent organic framework for the adsorption of heavy metal ions

For the first time, a novel amidinothiourea-linked covalent organic framework (COF) (TpAt) has been successfully synthesized by the condensation between 1,3,5-triformylphloroglucinol and amidinothiourea via vacuum solvothermal reaction, and was further utilized for the adsorption of metal ions from aqueous solution. The effects of initial concentration, pH and contact time on the adsorption process were investigated. As a result, the TpAt COF showed maximum binding capacities as high as 95.44, 100.76 and 99.08 mg g^–1 for Cr(III), Cd(II) and Cu(II) within 180 min at the initial concentration of 100 mg L^–1, respectively. The isotherms of metal ions onto TpAt could be described by the Freundlich isotherm equation, and the adsorption kinetics followed the pseudo-second-order model. The TpAt could be reused for more than five adsorption–elution cycles, whilst basically maintaining its original adsorption performance and the structural integrity of the COF layers. The robust adsorption efficiency can be attributed to the coordination between metal ions and N, O and S atoms in the TpAt framework. The TpAt COF represents an ideal candidate for the removal of heavy metal ions in environmental pollution treatment. © 2021 Society of Industrial Chemistry.