Adsorptive removal of tetracycline from water using Fe(III)-functionalized carbonized humic acid

Humic acid (HA) was carbonized at 300, 400 and 500 °C and then functionalized with 1 wt%–12 wt% Fe(III) respectively [CHA300/400/500-Fe(III)]. Adsorption of such Fe(III)-functionalized carbonized HA as adsorbents to aqueous tetracycline (TC: 25 mg·L⁻¹) was studied. The adsorption equilibrium time for CHA400-Fe(III) to TC was 6 h faster and the adsorption removal efficiency (R_e) was two times higher than that of HA/CHA. The adsorption R_e of CHA400-Fe(III) loaded 10% iron [CHA400-(10%)Fe(III)] to TC could reach 99.8% at 8 h and still kept 80.6% after 8 cycles. The adsorption kinetics were well fitted to the pseudo-second-order equation and the adsorption isotherms could be well delineated via Langmuir equations(R² > 0.99), indicating that the homogeneous chemical adsorption of TC occurred on the adsorbents. The main adsorption mechanisms of TC were complexation Fe(III) and hydrophobic distribution. Electropositive and electronegative repulsion between TC and CHA400-(10%)Fe(III) at lowly pH(2) and highly pH(8–10) respectively, leaded to the relatively low adsorption capacity and more notable influence of ion concentration. When the pH was between 4 and 8, TC mainly existed in neutral molecules (TCH₂), so the influence of ion concentration was not obvious. The dynamic adsorption results showed that the CHA400-(10%)Fe(III) could continuously treat about 2.4 L TC(27 mg·L⁻¹) wastewater with the effluent concentration as low as 0.068 mg·L⁻¹. Our study suggested a broad application prospect of a new, effective, low-cost and environment-friendly adsorbent CHA400-(10%)Fe(III) for treatment of low-concentration TC polluted wastewater.     

Application of ultrafiltration membranes for removal of humic acid from drinking water

Humic acids are primarily a result of the microbiological degradation of surrounding vegetation and animal decay and enter surface waters through rain water run-off from the surrounding land. This often gives rise to large seasonal variations, high concentrations in the wet season and lower concentrations in the dry season. Alone humic acid is just a colour problem but when present in conventional treatment processes like chlorination, carcinogenic by-products like trihalomethane and haloacetic acid are formed. This, in addition to the demand for clean potable drinking water, has sparked extensive research into alternative processes for the production of drinking water from various natural/industrial sources. One of the major areas of focus in these studies is the use of membranes in microfiltration, ultrafiltration and nanofiltration. In this report the humic acid removal efficiency of ultrafiltration membranes with 3 kDa, 5 kDa and 10 kDa MWCO is examined. The membranes were made of regenerated cellulose and were in the form of cassette providing a 0.1 m² surface area. At first distilled and deionised water, known as milliQ water, was used as the background feed solution to which humic acid powder was added. It was found that all three membranes removed humic acid with an efficiency of approx. 90% and were capable of reducing initial concentrations of 15mg/L to below the New Zealand regulatory limit of 1.17 mg/L. The permeate flux at a transmembrane pressure of 2.1 bar was approx. 20 l/m²/h (LMH) and 40 LMH, respectively through the membranes with MWCO 3 kDa and 5 kDa. These membranes experienced significant surface fouling resulting in retentate flow rates as low as 11 litres per hour after just four runs compared to the recommended 60–90 l/h. Cleaning with 0.1 M NaOH slightly improved the retentate flow rate, but well below those obtained with fresh membranes. The 10 kDa membrane provided high retentate flow rates which evidently minimised fouling by providing a good sweeping action across the membrane surface while maintaining humic acid removal below the regulatory 1.17 mg/L level. The permeate flux through this membrane was initially high (140–180 LMH) and reduced to approx. 100 LMH after 10–12 min of operation. Increasing the initial humic acid feed concentration from 10 mg/L to 50 mg/L did not significantly decrease humic acid removal efficiency although the retentate flow rate was lower at higher concentrations. Finally the tap water was tested as the background solution and treated for the removal of humic acid. The presence of ions and other impurities in the tap water had little effect on humic acid removal. However, the permeate flux through 10 kDa membrane decreased from 100 LMH for milliQ water to 60 LMH for tap water after 20 min of operation.     

Synthesis of the cotton cellulose based Fe(III)-loaded adsorbent for arsenic(V) removal from drinking water

A novel macroporous bead adsorbent, Fe(III)-loaded ligand exchange cotton cellulose adsorbent [Fe(III)LECCA], is synthesized for selective adsorption of arsenate anions [As(V)] from drinking water in batch and column systems. As(V) adsorption on Fe(III)LECCA was independent of pH, especially in drinking water pH range. Film diffusive control mechanism will benefit As(V) exchange with Fe(III)LECCA whether in batch or in column experiments. When treating the tap water at 26.0 BV/h, the column still preserves 83% of the original saturation adsorption capacity of the As(V) aqueous solution. These results have indicated that Fe(III)LECCA has the potential to act as an adsorbent for the removal of As(V) from drinking water considering its availability, nontoxicity and cost-effectiveness.     

Adsorptive removal and oxidation of organic pollutants from water using a novel membrane

To develop an effective method to remove and mineralize trace organic pollutants, a series of composite functional membranes containing immobilized ACF (activated carbon fibre) powder (<300 mesh) and Ce³⁺-TiO₂, a combination of adsorbent and photo-catalyst on terylene (PET) filter cloth, was prepared by using a sol–gel and dip coating method. As high as 93% BPA (bisphenol A) pollutant can be separated successfully by adsorption onto the membrane in a series of batch adsorption tests, 40% removal was achieved in dynamic filtration/adsorption test, which also removed 98% koalinite suspended solids at the same time. The measured adsorption of BPA corresponds to 37.0, 70.6 and 62.2 mg (BPA)/g(ACF) for three membranes A, B and C, where the weight ratio of ACF to ACF + TiO₂ was 29.9%, 17.6% and 11.3% respectively in batch adsorption tests (50 ml solution) and 25.48 mg (BPA)/g(ACF) for membrane A after 2 h adsorption in 200 ml solution. After dynamic filtration, the total adsorption capacity was 81.0 mg (BPA)/g(ACF) for membrane A. It is noteworthy that membrane adsorption can be regenerated by UV/Fenton treatment. Order of BPA adsorption quantity is 1st > 2nd > 3rd time use for membrane C, due to loss of ACF resulted from the supersonic treatment before oxidative regeneration. Introducing TEOS in the preparation of sol–gel solution and subsequent coating to form composite membrane, improved membrane adsorption stability in UV/Fenton regeneration treatment.     

Extraction of Fe(III) from phosphoric acid by HDDNSA

A study was conducted on the stoichiometry of the reaction that takes place on the extraction of ferric ions by didodecyl naphthalene sulphonic acid (HDDNSA) from phosphoric acid solutions. The experimental results were numerically analyzed by nonlinear regression. It was found that ferric forms two compounds with HDDNSA, namely Fe(DDNSA)₃, and FeHPO₄-DDNSA. The values of the equilibrium constants of the reactions involved were also calculated.     

Characteristics of unburned carbons and their application for humic acid removal from water

Two unburned carbons (UCs) were separated from coal fly ash and their physicochemical properties were characterised using N₂ adsorption, XRD, SEM, XPS, FT-IR and potentiometric mass titration. Chemical treatments using HNO₃ and KOH were also conducted on one of the unburned carbons. The adsorption of humic acid from aqueous solution was performed on these untreated and chemically treated UCs. It was found that the UCs showed different porous structure and surface chemical properties, which influenced their adsorption behaviour. UCs exhibited high adsorption capacity for humic acid. After chemical treatment, the textural structure and surface functional groups of the unburned carbon were changed and the adsorption behaviour showed significant difference. Acid treatment did not change the surface area but reduced the functional groups while basic treatment significantly enhanced the surface area in microporous section but still reduced the surface functional groups. Particle size and pH solution will also influence the adsorption capacity. The adsorption will increase with decreasing particle size for humic acid. Higher pH solution will reduce humic acid adsorption on unburned carbon. Ionic strength will also affect humic acid adsorption showing positive effect on adsorption capacity.     

Wollastonite as adsorbent for removal of Fe(II) from water

Wollastonite was used as an adsorbent for the removal of Fe(II) at different experimental conditions. The extent of removal is favourable at low concentration and low temperature. Maximum adsorption was noted at pH 4.0. The batch adsorption kinetics has been described by a first order rate expression, and the surface mass transfer coefficients and diffusion coefficients have been calculated at different temperatures. The intraparticle transport of Fe(II) within the pores of wollastonite is found to be the rate limiting step. The applicability of the Langmuir isotherm for the present system has been tested at different temperatures. Thermodynamic parameters indicate the exothermic nature of Fe(II) adsorption on wollastonite. The variation of adsorption with pH has been explained on the basis of interaction of iron species with negatively charged constituents of adsorbent.     

Removal of reactive dyes from wastewater using Fe(III) coagulant

The coagulation-flocculation process was employed for the treatment of reactive dye wastewaters, with ferric chloride hexahydrate employed as the coagulant. The process was found to be very effective with a more than 99.5% colour removal. Typical representatives of monochlorotriazine reactive dyes, with azo and anthraquinone chromophores, were CI Reactive Red 45 and CI Reactive Green 8, which were chosen as the model dyes. In order to determine the optimum pH range and coagulant concentration, a series of jar tests was done. Further experiments were conducted using a square flocculation tank with turbine impeller applying rapid and slow mix operations. The optimisation of initial rapid mixing, which has an important role in the overall coagulation process efficiency, was carried out. The optimum combination of velocity gradient and time of rapid mix was suggested for reactive dye wastewater treatment. Sedimentation curves for both model dyes were also obtained.     

Removal of humic acid from water using adsorption coupled with electrochemical regeneration

A novel and economic waste water treatment technology comprised of adsorption coupled with electrochemical regeneration was introduced at the University of Manchester in 2006. An electrically conducting adsorbent material called Nyex? 1000 (Graphite intercalation based material) was developed for the said purpose. This adsorbent material delivered significantly lower adsorption capacity for the removal of a number of organic pollutants. With the aim to expand the scope of newly developed adsorbent material called Nyex? 2000, we studied the adsorption of humic acid followed by electrochemical regeneration. Nyex? 2000 is a highly electrically conducting material with an adsorption capacity almost twice that of Nyex? 1000 (intercalation based graphite compound) for humic acid. The adsorption of humic acid onto both Nyex? adsorbents was found to be fast enough keeping almost the same kinetics with approximately 50% of the adsorption capacity being achieved within the first twenty minutes. The parameters affecting the regeneration efficiency, including the treatment time, charge passed and current density, were investigated. The regeneration efficiency at around 100% for Nyex? 1000 & 2000 adsorbents saturated with humic acid was obtained using the charge passed of 8 and 22 Cg^?1 at a current density of 7mA cm^?2 during a treatment time of 30minutes, respectively.     

Selectively removal of Al(III) from Pr(III) and Nd(III) rare earth solution using surface imprinted polymer

Rare earth is a very important strategic resource. But, impurities, such as Al³⁺, have great influence on the properties of rare earth material. In this paper, an Al³⁺-ionic imprinted polyamine functionalized silica gel sorbent was prepared by a surface imprinting technique for selectively adsorbing Al³⁺ from rare earth solution. The adsorption and recognition properties of IIP-PEI/SiO₂ for Al³⁺ were studied in detail. The experimental results showed that IIP-PEI/SiO₂ possessed strong adsorption affinity, specific recognition ability, and excellent selectivity for Al³⁺. The adsorption isotherm data greatly obey the Langmuir model, and the adsorption was typical monolayer. The adsorption capacity could reach to 1.98 mmol g^?1, and relative selectivity coefficients relative to Pr³⁺ and Nd³⁺ are 23.47 and 22.85, respectively. Besides, IIP-PEI/SiO₂ was regenerated easily using diluted hydrochloric acid solution as eluent and IIP-PEI/SiO₂ possesses better reusability.     

Adsorptive removal of alizarin dye from wastewater using maghemite nanoadsorbents

ABSTRACT

This is an investigation of the adsorptive removal of anthraquinone dyes, resembled by Alizarin, by utilizing maghemite iron oxide (γ-Fe₂O₃) nanoparticles in aqueous media. The adsorption process was affected by several parameters such as solution pH, adsorbent amount, contact time, and temperature. After optimizing the parameters affecting the adsorption, the process was successful in removing Alizarin dye with an efficiency exceeding 95%. Best adsorption results were achieved at a pH of 11 and contact time of 60 min. The adsorption was shown to follow the Langmuir model suggesting a monolayer and homogeneous coverage. The maximum adsorption capacity (q_m ) was found to be 23.2 mg/g at pH = 11. A thermodynamic study showed that the adsorption process is exothermic and spontaneous at room temperature. The Gibbs free energy of adsorption (-6.79 kJ/mol) obtained in this study suggests a physisorption process. This finding has facilitated the regeneration of the Fe₂O₃ nanocatalyst. Both NaOH and HNO₃ at dilute levels were tested for the regeneration of the nanocatalyst. Regeneration with HNO₃ was successful up to four successive removal cycles with an efficiency >80%. Photodegradation experiments utilizing a UV light were also successful in maximizing the adsorption removal efficiency. A sorption mechanism based on the results obtained in this work is also proposed.     

Simultaneous removal of humic acid and heavy metal from aqueous solutions using charged ultrafiltration membranes

Lab-made negatively charged ultrafiltration (UF) membranes were used for simultaneous removal of humic acid (HA) and heavy metals from water. Effects of the HA/metal ratio, solution pH and ionic strength on rejection coefficients of HA and metals were investigated. The results showed that the rejection coefficients of both HA and metals increase with the increase of pH and the HA/metal ratio, and the decrease of ionic strength. This study indicated that charged UF could be an effective method for the simultaneous removal of HA and heavy metal harnessing the principle of complexation UF and electrostatic repulsion between the membrane and the HA–M complex of the same charges.     

Enhanced removal of humic acid from water by micelle-montmorillonite composites: Comparison to granulated activated carbon

Removal of humic acid (HA) from water by octadecyltrimethyl-ammonium (ODTMA) micelle–montmorillonite (MMT) composites and by granulated activated carbon (GAC) was studied in dispersion and by filtration. FTIR measurements emphasized that the ODTMA micelle–clay-mineral composite differs from the ODTMA monomer-clay-mineral one. HA adsorption by GAC in dispersion was moderately reduced from 100% initially to 75% with an increase in HA concentrations. In contrast, the fractions adsorbed by the composite increased monotonically with HA concentrations from very low adsorption up to 80%. This effect was explained by the presence of a small concentration of ODTMA monomers in dispersion, which adsorbed on the negatively charged HA and partially neutralized it, or caused charge reversal, which in turn inhibited HA adsorption by the positively charged composite. This effect was verified by mobility measurements and was found to be more pronounced at low HA concentrations. This trend of increase in HA removal with an increase in HA concentration (3 and 10 ppm) was also observed in filtration (50% and 85% removal, respectively), when employing columns of the composite mixed with sand (to improve flow). Throughout the experiment the removal of high HA concentration (10 ppm) by the composite filter remained ~ 80% whereas, the removal by the GAC filter decreased from an initial 80% removal to a complete recovery of the HA (no removal) after the passage of 20 L (200 pore volumes). Upon applying sand of higher quality in the columns the removal of low HA concentrations was nearly complete by the composite column while the GAC only slightly contributed to its removal (for a passage of 100 L (1000 pore volumes)).     

Electrocombustion of humic acid and removal of algae from aqueous solutions

This paper reports experiments involving the electrochemical combustion of humic acid (HA) and removal of algae from pond water. An electrochemical flow reactor with a boron-doped diamond film anode was used and constant current experiments were conducted in batch recirculation mode. The mass transfer characteristics of the electrochemical device were determined by voltammetric experiments in the potential region of water stability, followed by a controlled current experiment in the potential region of oxygen evolution. The average mass transfer coefficient was 5.2 × 10⁻⁵ m s⁻¹. The pond water was then processed to remove HA and algae in the conditions in which the reaction combustion occurred under mass transfer control. To this end, the mass transfer coefficient was used to estimate the initial limiting current density applied in the electrolytic experiments. As expected, all the parameters analyzed here—solution absorbance at 270 nm, total phenol concentration and total organic carbon concentration—decayed according to first-order kinetics. Since the diamond film anode successfully incinerated organic matter, the electrochemical system proved to be predictable and programmable.     

As(III) removal from drinking water using manganese oxide-coated-alumina: Performance evaluation and mechanistic details of surface binding

This paper describes the arsenite [As(III)] removal performance of manganese oxide-coated-alumina (MOCA) and its interaction with As(III) in drinking water. MOCA was characterized by XRD, SEM, EDAX, gas adsorption porosimetry, and point of zero charge (pH_pzc) measurements. Raman spectroscopy coupled with sorption experiments were carried out to understand the As(III) interaction with MOCA. As(III) sorption onto MOCA was pH dependent and the optimum removal was observed between a pH of 4 and 7.5. The Sips isotherm model described the experimental equilibrium data well and the predicted maximum As(III) sorption capacity was 42.48 mg g⁻¹, which is considerably higher than that of activated alumina (20.78 mg g⁻¹). The sorption kinetics followed a pseudo-second-order equation. Based on sorption and spectroscopic measurements, the mechanism of As(III) removal by MOCA was found to be a two-step process, i.e. oxidation of As(III) to arsenate (As(V)) and retention of As(V) on MOCA surface, with As(V) forming an inner surface complex with MOCA. The results of this study indicated that MOCA is a promising alternative sorbent for As(III) removal from drinking water.     

Removal of Cr(VI) from water using Fe(II)-modified natural zeolite

In this study, natural zeolite aggregates with the particle size of 1.4–2.4 mm were modified by Fe(II). The unmodified zeolite and Fe(II)-modified zeolite (Fe-eZ) were subjected to batch and column tests to study the Cr(VI) sorption, transport, and retardation. Modification of the natural zeolite with Fe(II) resulted in an increase in Cr(VI) sorption to 6 mmol/kg. The Cr(VI) sorption followed a pseudo-second-order kinetics with a rate of 17 mmol/g h and a rate constant of 0.7 g/mmol h. Cr(VI) removal from solution increased with an increase in ionic strength, but decreased as the solution pH increased. At a Cr(VI) input concentration of 100 mg/L, unmodified zeolite did not show any Cr(VI) retardation at all. In contrast, the observed retardation factor of Fe-eZ for Cr(VI) increased by a factor of 6. The hydraulic conductivity of the zeolite showed little change before and after Fe(II) modification and before and after Cr(VI) sorption, suggesting its good mechanical stability to be used as packing materials for permeable reactive barriers in groundwater remediation.     

High selectivity and removal efficiency of lotus root-based activated carbon towards Fe(III) in La(III) solution

Rare earth elements are an important strategic resource. However, a trace of Fe(III) impurity has serious adverse impact on the performance of rare earth materials. We synthesized a novel nitrogen-containing carbon material, AC_LR-400, using lotus root as raw materials. The AC_LR-400 was characterized by surface area analyzer, elemental analysis and FT-IR. The selectivity and removal efficiency of AC_LR-400 towards Fe(III) were also investigated. The BET specific surface area of AC_LR-400 was 68.44 m²·g^?1, and the average pore diameter was 12.54 nm. With abundant nitrogen- containing functional groups and well-developed internal pore structure, AC_LR-400 possesses strong adsorption affinity, excellent selectivity and removal efficiency for Fe(III). The adsorption capacity of AC_LR-400 towards Fe(III) could reach to 0.46 mmol·g^?1, selectivity coefficient with respect to La(III) was 8.9, and removal efficiency was 99.61%. The adsorption isotherm data greatly obey the Freundlich isotherm. In addition, AC_LR-400 can be regenerated easily and possesses better regeneration ability and reusability.     

Adsorptive removal of dibenzothiophene from petroleum distillates using pomegranate leaf (Punica granatum) powder as a greener adsorbent

In this study, adsorption performance of pomegranate leaf powder (PLP) for the removal of dibenzothiophene (DBT) from petroleum distillates is presented. Morphology and elemental composition, surface chemistry, and textural property of the PLP were checked using scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), and N₂ physi-sorption at 77?K, respectively. Model oil contained 0.1?g DBT in 100?mL hexane was used for the performance evaluation and conducted in batch mode. The results show DBT removal of 70.55%, with the adsorbent retaining about 97.81% of its capacity after fourth cycle of usage. Results from SEM-EDX and FTIR indicate that DBT was adsorbed on the surface of PLP. Adsorption isotherm data fitted onto Freundlich and Langmuir isotherms models show very good coefficient of determination (R²) values of 0.9952 (for Langmuir) and 0.9979 (for Freundlich), indicating suitability of the models to describe the process. The adsorption kinetics of DBT onto PLP follows pseudo-second-order kinetics and the experimental q_e (53.66?mg/g) values obtained is very close to the model-estimated value q_e (55.55?mg/g). The negative value of ΔG^o and the positive values of ΔH^o obtained in the thermodynamic studies indicate that adsorption of DBT onto the PLP is an endothermic and spontaneous process at the temperatures studied.     

Adsorptive removal of methyl orange using mesoporous maghemite

In this work, mesoporous maghemite (γ-Fe₂O₃) was prepared by the thermal decomposition of [Fe(CON₂H₄)₆](NO₃)₃ with the aid of cetyltrimethyl ammonium bromide (CTAB), and its adsorption ability for the removal of methyl orange (MO) from wastewater was investigated. X-Ray powder diffraction (XRD) together with nitrogen adsorption–desorption measurements show the formation of mesoporous γ-Fe₂O₃ with an average pore size of 3.5 nm and a specific surface area of 93.0 m²/g. Magnetic measurements show that the mesoporous γ-Fe₂O₃ exhibits ferrimagnetic characteristics with the coercivity of 141.5 Oe and remanent magnetization of 7.3 emu/g and has the maximum saturation magnetization of 55.2 emu/g. The adsorption of MO on the mesoporous γ-Fe₂O₃ reaches the maximum adsorbed percentage of ca. 90% within a few minutes, showing that most of MO can be removed in a short time when the mesoporous γ-Fe₂O₃ is used as an adsorbent. When the pH of MO solution is varied from 3 to 11, the adsorbed percentage of MO decreases from ca. 90 to ca. 81%, showing that the adsorption is slightly influenced by solution pH. The adsorption data for MO fit well with either Langmuir or Freundlich adsorption models. The maximum adsorption capacity of the mesoporous γ-Fe₂O₃ for MO is determined to be 385 mg/g, which suggests that the material could be an excellent magnetic adsorbent for MO.     

超声作用联合纳米腐植酸处理苯酚废水

采用静态吸附法研究了超声联合纳米腐植酸处理苯酚废水;用红外光谱(FT-IR)、扫描电镜(SEM)、比表面积测试仪(BET)对纳米腐植酸的粒径大小、形貌、比表面积及孔径等进行表征,结果表明:纳米腐植酸粒度分布均匀,平均粒径为50 nm,比表面积为110.31 m2/g,孔径为6.56 nm;考察了苯酚初始浓度、纳米腐植酸用量、超声声强及频率等因素对纳米腐植酸和超声作用协同处理苯酚废水的最佳工艺条件。实验结果表明:超声频率为20 kHz,超声声强0.2 W/cm2,苯酚初始质量浓度为100 mg/L,pH值为6.0,溶液体积100 mL,吸附温度40℃,吸附时间120min,纳米腐植酸用量为40 g/L的条件下,纳米腐植酸与超声作用协同处理苯酚废水吸附率可以达到95.7%;吸附剂纳米腐植酸对苯酚的吸附主要受颗粒内扩散所控,其再生循环使用5次后,苯酚的吸附容量仅减少18.9%。