Granulation of gibbsite with inorganic binder and its ability to adsorb Mo(VI) from aqueous solution

In this study, we prepared a new adsorbent and evaluated its ability to adsorb Mo(VI). Gibbsite was granulated with colloidal alumina or colloidal silica. The amount of Mo(VI) adsorbed onto granular gibbsite with a binder, effect of contact time and pH on the adsorption of Mo(VI), and column experiments were investigated. The amount of Mo(VI) adsorbed was greater in the order of ST12 (colloidal silica, 12%)?相似文献   

Utilization of fly ash in adsorption of heavy metals from wastewater

The aim of this study was to assess the toxicity reduction of wastewaster after treatment with fly ash. Fly ash is a waste material which is formed as a result of coal burning in power plants, but has the potential to adsorb heavy metal ions. The present study examined the adsorption capacity of fly ash to adsorb Pb²⁺, Cu²⁺, and Zn²⁺ from waste water under different conditions of contact time, pH, and temperature. Uptake of metal ions by fly ash generally rose with increasing pH. At lower temperatures the uptake of heavy metal adsorption were enhanced. Significant reduction in Pb²⁺ (79%), Cu²⁺ (53%), and Zn²⁺ (80%) content was found after treatment with fly ash of waste water treatment. Using the microtox test toxicity of the effluent was reduced by 75% due to removal of Pb²⁺ ion by the fly ash. Data indicated that fly ash generated by power plants may be used beneficially to remove metals from waste water.     

Removal of Mo(VI) from aqueous solutions using sulfuric acid-modified cinder: kinetic and thermodynamic studies

Removal of Mo(VI) from aqueous solutions was investigated using cinder modified by sulfuric acid. Various parameters such as pH, agitation time, Mo(VI) concentration, and temperature have been studied. The maximum adsorption of Mo(VI) occurred at pH between 4.0 and 6.0. Kinetic studies showed that the adsorption generally obeyed a pseudo second-order model. The activation energy was 31.4?kJ?mol^?1, indicating that the adsorption process was governed mainly by interactions of physical nature. Furthermore, application of Langmuir and Freundlich isotherm models to the adsorption equilibrium data showed that the adsorption behavior obeyed the Langmuir model. The adsorption capacity was found to be 10.8?g Mo(VI)?kg^?1 adsorbent. Finally, thermodynamic parameters such as ΔH ⁰, ΔS ⁰, and ΔG ⁰ were also evaluated, which showed that the adsorption of Mo(VI) on the treated cinder was endothermic, entropy increasing, and spontaneous. In conclusion, the sulfuric acid-modified cinder was shown to be an inexpensive, effective, and simple adsorbent for the removal of Mo(VI) from water.     

Leaching of arsenic from coal fly ashes 2. Arsenic pre‐leaching with sodium gluconate solution

The present study deals with the development of an efficient and reliable process for safe disposal of coal fly ash to remove arsenic that has been found to be the most easily leachable and hazardous heavy metal in coal fly ash. Pre‐leaching of fly ash prior to disposal by a natural chelating agent, sodium gluconate (SG), was proposed and studied. Several operational factors influencing arsenic leachability, such as concentration of SG solution, liquid to solid ratio, pH, length of leaching time and leaching temperature were examined. Arsenic was found to leach out substantially with SG, but almost no further release was observed from the ash pre‐leached by SG. After the pre‐leaching treatment, the desirable high buffering capacity of the ash was well sustained. SG solution was effectively regenerated by activated alumina adsorption so that it could be successfully reused for multiple leaching/adsorption cycles.     

Adsorption of rhodium(III) from plating solutions by calcined gibbsite

Gibbsite calcined at 400°C (GB400) was prepared, and its ability to adsorb rhodium(III) was investigated. Optimal pH, effect of contact time, temperature, adsorption isotherms, and recovery percentage were evaluated. The optimal pH was 6.3. The adsorption equilibrium was achieved within 24 h. The adsorption rate was found to be of pseudo-first order. The experimental data were fitted to both the Freundlich (r = 0.90–0.93) and Langmuir (r = 0.94–0.96) equations. The amount of rhodium(III) adsorbed decreased with increasing temperature. Rhodium(III) being adsorbed from phosphate or sulfate plating solution was recovered using hydrochloric acid and sodium hydroxide solutions at 1, 10, and 100 mmol L^?1.     

Removal of chromium(VI) by ZnCl2 activated coir pith carbon

The adsorption of chromium(VI) onto ZnCl₂ activated carbon developed from coir pith was investigated to assess the possible use of this adsorbent. The influence of contact time, adsorbent dose, Cr(VI) concentration, pH and temperature were investigated. The two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Q ₀) was found to be 120.5?mg Cr(VI) per g of the adsorbent. The adsorption followed the second-order kinetics and was found to be maximum at pH 2.0. The pH effect and the desorption studies showed that ion exchange mechanism might be involved in the adsorption process. The effects of foreign ions such as chloride, sulphate, phosphate, selenite, molybdate, nitrate and perchlorate on the removal of Cr(VI) have been investigated. The removal of Cr(VI) from synthetic ground water was also tested. The results show that ZnCl₂ activated coir pith carbon is effective for the removal of Cr(VI) from water.     

Prevention of dioxins de novo formation by ethanolamines

Two inhibitors, triethanolamine (TEA) and monoethanolamine (MEA), were tested for their ability to prevent the de novo formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) on sinter plant fly ash. The amounts of both PCDDs and PCDFs, formed by thermal treatment of the fly ash, decreased when inhibitors were added. Up to 90% reduction of the PCDD/Fs formation was reached when 2 wt % monoethanolamine was mixed with fly ash. The temperatures tested, 325 and 400 °C, did not affect the inhibition activity. However, a longer reaction time, 4 h instead of 2 h, gave higher percentages of PCDD/Fs reduction. The laboratory results show that ethanolamines reduce the dioxins formation on sinter plant fly ash under various conditions of temperature and reaction time. Moreover, factory tests performed in parallel at a sinter plant are in good agreement with the laboratory experiments, thus confirming that the use of ethanolamine inhibitors is an appropriate technique for the prevention of dioxins emissions from sintering processes. Electronic Publication     

HDTMAB改性粉煤灰对水体中磷的吸附特性

制备了十六烷基三甲基溴化铵(HDTMAB)改性粉煤灰,研究了该改性粉煤灰对水体中磷的吸附特性,结果表明:①当HDTMAB负载量为10%时,改性粉煤灰吸附磷酸盐的效果最佳;②改性粉煤灰对磷酸盐的吸附速度很快,20min可达吸附平衡;③改性粉煤灰对磷酸盐的吸附行为能较好地符合Langmuir等温吸附模型和Freundlich等温吸附模型,但在Freundlich模式下表现为两个线性区;④pH对改性粉煤灰吸附磷酸盐的性能有显著影响,随着pH的升高对磷酸盐的吸附能力逐渐增加。     

Leaching characteristics of heavy metals during cement stabilization of fly ash from municipal solid waste incinerators

The leaching characteristics of heavy metals in products of cement stabilization of fly ash from a municipal solid waste incinerator were investigated in this paper. The stabilization of heavy metals such as Cd, Pb, Cu, and Zn in fly ash from such incinerators was examined through the national standard method in China based on the following factors: additive quantity of cement and Na₂S, curing time, and pH of leaching liquor. The results showed that as more additives were used, less heavy metals were leached except for Pb, which is sensitive to pH of the leachate, and the worse effect was observed for Cd. The mass ratio of cement to fly ash = 10% is the most appropriate parameter according to the national standard method. When the hydration of cement was basically finished, stabilization of heavy metals did not vary after curing for 1 d. The mixtures of cement and fly ash had excellent adaptability to environmental pH. The pH of leachate was maintained at 7 when pH of leaching liquor varied from 3 to 11.     

Characteristics of the stabilized/solidified municipal solid wastes incineration fly ash and the leaching behavior of Cr and Pb

Fly ash is a hazardous byproduct of municipal solid wastes incineration (MSWI). An alkali activated blast furnace slag-based cementitious material was used to stabilize/solidify the fly ash at experimental level. The characteristics of the stabilized/solidified fly ash, including metal leachability, mineralogical characteristics and the distributions of metals in matrices, were tested by toxic characteristic leaching procedure (TCLP), X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) respectively. Continuous acid extraction was utilized to extract metal ions and characterize their leaching behavior. The stabilization/solidification procedure for MSWI fly ash demonstrates a strong fixing capacity for the metals by the formation of C-S-H phase, hydrated calcium aluminosilicate and ettringite. The stabilized/solidified fly ash shows a dense and homogeneous microstructure. Cr is mainly solidified in hydrated calcium aluminosilicate, C-S-H and ettringite phase through physical encapsulation, precipitation, adsorption or substitution mechanisms, and Pb is mainly solidified in C-S-H phase and absorbed in the Si-O structure.     

Cr (VI) and Fe (III) removal using Cajanus cajan husk

Husk of tur dal (Cajanus cajan) was investigated as a new biosorbent for the removal of Fe (III) and Cr (VI) ions from aqueous solutions. Parameters like agitation time, adsorbent dosage and pH were studied at different initial Fe (III) and Cr (VI) concentrations. The biosorptive capacity of the Tur dal husk was dependent on the pH of the chromium and iron solution, with pH 2 and 2.5 respectively being optimal. The adsorption data fit well with Langmuir and Freundlich isotherm models. The practical limiting adsorption capacity (qmax) calculated from the Langmuir isotherm was 96.05 mg of Cr(VI)/ g of the biosorbent at an initial pH of 2.0 and 66.65 mg/g at pH 2.5. The infrared spectra of the biomass revealed that hydroxyl, carboxyl and amide bonds are involved in the uptake of Cr (VI) and Fe (III) ions. Characterisation of tur dal husk has revealed that it is an excellent material for treating wastewaters containing low concentration of metal ions.     

Retention characteristics of Cu2+, Pb2+, and Zn2+ from aqueous solutions by two types of low lime fly ashes

The technical feasibility of utilization of fly ash as a low-cost adsorbent for the removal of metals from water has been studied. For two types of fly ashes, the retention capacities of copper, lead, and zinc metal ions have been studied. Contact time, initial concentration, and pH have been varied and their effect on retention mechanism has been studied. The dominant mechanisms responsible for retention are found to be precipitation due to the presence of calcium hydroxide, and adsorption due to the presence of silica and alumina oxide surfaces in the fly ash. First-order kinetic plots have revealed that the rate constant increases with increase in the initial concentration and pH. Langmuir adsorption isotherms have been plotted to study the maximum adsorption capacities for metal ions considered under different conditions. X-ray diffraction studies revealed the formation of new peaks corresponding to respective metal ions precipitates under alkaline conditions.     

Removal of toxic chromium(VI) from aqueous solution by activated carbon using Casuarina equisetifolia

Highly activated carbon from the seed husk of Casuarina Casuarinas equisetifolia, a worldwide famous plant, have been prepared and tested for the removal of toxic Cr(VI) from its aqueous solution. The adsorbent was investigated for influences of initial chromium concentration (75, 100, 125, and 150 mg l^-1), pH, contact time, and quantity of carbon on removal of Cr(VI) from aqueous solution at room temperature (25±2 °C). The adsorption kinetic of Cr(VI) was studied, and the rates of sorption were found to conform to pseudo-second-order kinetics with a good correlation (R²≥0.99). The Langmuir and Freundlich models fit the isotherm data well. Furthermore, the Gibbs free energy was obtained for each system and was found to be-5.29 kJ mol^-1 for removal of Cr(IV). The negative value of Δ G° indicates the feasibility and spontaneous nature of adsorption. The results indicate that acidic pH (1.05) supported the adsorption of Cr(IV) on activated carbon. The maximum adsorption capacity of Cr(VI) on activated carbon was about 172.4 mg g^-1 at pH 1.05.     

Use of zeolitized coal fly ash in the simultaneous removal of ammonium and phosphate from aqueous solution

Discharge of wastewater containing nitrogen and phosphate can cause eutrophication. Therefore, the development of an efficient material for the immobilization of the nutrients is important. In this study, a low calcium fly ash and high calcium fly ash were converted into zeolite using the hydrothermal method. The removal of ammonium and phosphate that coexist in aqueous solution by the synthesized zeolites were studied. The results showed that zeolitized fly ash could efficiently eliminate ammonium and phosphate at the same time. Saturation of zeolite with Ca²⁺ rather than Na⁺ favored the removal of both ammonium and phosphate because the cation exchange reaction by the NH₄ ⁺ resulted in the release of Ca²⁺ into the solution and precipitation of Ca²⁺ with PO₄ ^3? followed. An increase in the temperature elevated the immobilization of phosphate whereas it abated the removal of ammonium. Nearly 60% removal efficiency for ammonium was achieved in the neutral pH range from 5.5 to 10.5, while the increase or decrease in pH out of the neutral range lowered the adsorption. In contrast, the removal of phosphate approached 100% at a pH lower than 5.0 or higher than 9.0, and less phosphate was immobilized at neutral pH. However, there was still a narrow pH range from 9.0 to 10.5 favoring the removal of both ammonium and phosphate. It was concluded that the removal of ammonium was caused by cation exchange; the contribution of NH₃ volatilization to immobilization at alkaline conditions (up to pH level of 11.4) was limited. With respect to phosphate immobilization, the mechanism was mainly the formation of precipitate as Ca₃(PO₄)₂ within the basic pH range or as FePO₄ and AlPO₄ within acidic pH range.     

Use of fly ash agglomerates for removal of arsenic

The aim of this work is to investigate the application of fly ash adsorbent for removal of arsenite ions from dilute solution (100–1,000 ppm). Experiments were carried out using material from the “Turów” (Poland) brown-coal-burning power plant, which was wetted, then mixed and tumbled in a granulator to form spherical agglomerates. Measurements of arsenic adsorption from aqueous solution were carried out at room temperature and natural pH of fly ash agglomerates, in either a shaken flask or circulating column, to compare two different methods of contacting solution with adsorbent. Adsorption isotherms of arsenic were determined for agglomerated material using the Freundlich equation. Kinetic studies indicated that sorption follows a pseudo-second-order model. Preferable method to carry out the process is continuous circulation of arsenite solution through a column.     

1,3,5-triazine-triethylenetetramine polymer: an efficient adsorbent for removal of Cr(VI) ions from aqueous solution

The synthesis of 1,3,5-triazine-triethylenetetramine (TATETA), its characterization by infrared spectroscopy and elemental analysis, and its application for removal of Cr(VI) ions from aqueous solution is reported. The effects of pH, contact time, initial concentration of Cr(VI), sorbent dose, and temperature on adsorption were investigated and optimized by batch adsorption experiments. Adsorption was highest at acidic conditions with an equilibration time of 25 min. The adsorption followed a Langmuir model, with an adsorption capacity of 303 mg g^?1, was second order in its kinetics, and exothermic and thus spontaneous.     

Biosorption of chromium(VI), nickel(II) and copper(II) ions from aqueous solutions using Pithophora algae

The biosorption of heavy metals is considered to be one of the best alternatives for the treatment of wastewater. The metal binding capacity of algae and acid-treated algae is investigated to find out the removal characteristics of Cr(VI), Ni(II) and Cu(II) ions from single metal solutions. Batch experiments are conducted and the study is extended to investigate the effect of pH, amount of adsorbent and adsorbate concentration on the extent of biosorption. The results indicate that the adsorption capacity of algae depends strongly on pH. The maximum adsorption of Cr(VI), Ni(II) and Cu(II) occurs at pH values of 2, 7 and 4.3, respectively. The adsorption process follows first-order kinetic equation. The data obtained are correlated with Freundlich and Langmuir adsorption isotherms.     

The fly ash influenced the heavy metal status of the soil and the seeds of sunflower. A case study

In this study, four cultivars of sunflower (Helianthus annuus) were grown in the sandy loam soil, supplemented with graded (v/v) quantity (0, 20, 40, 60, 80, 100%) of the fly ash, released by the combustion of the coal from the thermal power plant. The presence of fly ash in the soil increased its porosity, water holding capacity, pH, E.C., C.E.C., the content of sulphate, carbonate, bicarbonate, chloride, phosphorus, potassium, calcium and various trace elements. However, in the seeds, except Fe, Pb, Mn and Zn, and other heavy metals remained untraced up to 40% of the fly ash, above that their quantity slightly increased but the values are very much under the permissible limits.     

Concurrent adsorption and reduction of chromium(VI) to chromium(III) using nitrogen-doped porous carbon adsorbent derived from loofah sponge

• A high-efficiency N-doped porous carbon adsorbent for Cr(VI) was synthesized. • The maximum adsorption capacity of Cr(VI) reached up to 285.71 mg/g at 318K. • The potential mechanism for Cr(VI) adsorption by NHPC was put forward. • DFT analyzed the adsorption energy and interaction between NHPC and Cr(VI). To develop highly effective adsorbents for chromium removal, a nitrogen-doped biomass-derived carbon (NHPC) was synthesized via direct carbonation of loofah sponge followed by alkali activation and doping modification. NHPC possessed a hierarchical micro-/mesoporous lamellar structure with nitrogen-containing functional groups (1.33 at%), specific surface area (1792.47 m²/g), and pore volume (1.18 cm³/g). NHPC exhibited a higher Cr(VI) adsorption affinity than the HPC (without nitrogen doping) or the pristine loofah sponge carbon (LSC) did. The influence of process parameters, including pH, dosage, time, temperature, and Cr(VI) concentration, on Cr(VI) adsorption by NHPC were evaluated. The Cr(VI) adsorption kinetics matched with the pseudo-second-order model (R²≥0.9983). The Cr(VI) adsorption isotherm was fitted with the Langmuir isotherm model, which indicated the maximum Cr(VI) adsorption capacities: 227.27, 238.10, and 285.71 mg/g at 298K, 308K, and 318K, respectively. The model analysis also indicated that adsorption of Cr(VI) on NHPC was a spontaneous, endothermal, and entropy-increasing process. The Cr(VI) adsorption process potentially involved mixed reductive and adsorbed mechanism. Furthermore, computational chemistry calculations revealed that the adsorption energy between NHPC and Cr(VI) (−0.84 eV) was lower than that of HPC (−0.51 eV), suggesting that nitrogen doping could greatly enhance the interaction between NHPC and Cr(VI).     

Preparation of magnetic nanocomposite beads and optimizing the conditions for effective removal of U(VI) from aqueous solutions

Magnetic ion-imprinted polymers (IIPs) were prepared by precipitate polymerization and leached with HCl to remove uranium. Their ability to remove hexavalent uranium from wastewater effluents was studied. Batch adsorption studies to determine the optimum conditions of U(VI) removal were conducted at different levels of sample pH, sorbent amount, agitation time, and initial uranium concentration. It was observed that, under optimum conditions (i.e. pH 4, adsorbent amount of 50 mg, 45 min agitation time, and initial U(VI) concentration of 2 mg L^?1), the maximum removal of U(VI) cations was >98% and 80% for the magnetic IIP and the corresponding magnetic non-imprinted polymers (NIP), respectively. Langmuir and Freundlich isotherms were used to describe the adsorption of U(VI) onto magnetic IIP and NIP. The adsorption capacity of U(VI) was determined to be 1.06 and 0.85 mg g^?1 for the two isotherms, respectively. The order of selectivity was found to be U(VI) > Fe(III) > Pb(II). For six cycles of regeneration and reuse, the magnetic polymers maintained their stabilities with only a 4% loss in the extraction efficiency. The average extraction efficiencies of the magnetic polymers for the spiked acid mine drainage and sewage wastewater effluents were 71% and 58% for the magnetic IIP and NIP, respectively. From powder X-ray diffraction analysis, application of the Scherrer equation yielded magnetic nanoparticles of an average mean diameter of 11.9 nm. Thermo-gravimetric analysis revealed that the HCl-leached magnetic polymers had a magnetite residual weight of 5%.