The Adsorptive Capacity of Vapor-Phase Mercury Chloride onto Powdered Activated Carbon Derived from Waste Tires

Abstract

Injection of powdered activated carbon (PAC) upstream of particulate removal devices (such as electrostatic precipitator and baghouses) has been used effectively to remove hazardous air pollutants, particularly mercury-containing pollutants, emitted from combustors and incinerators. Compared with commercial PACs (CPACs), an alternative PAC derived from waste tires (WPAC) was prepared for this study. The equilibrium adsorptive capacity of mercury chloride (HgCl₂) vapor onto the WPAC was further evaluated with a self-designed bench-scale adsorption column system. The adsorption temperatures investigated in the adsorption column were controlled at 25 and 150 °C. The superficial velocity and residence time of the flow were 0.01 m/sec and 4 sec, respectively. The adsorption column tests were run under nitrogen gas flow. Experimental results showed that WPAC with higher Brunauer–Emmett–Teller (BET) surface area could adsorb more HgCl₂ at room temperature. The equilibrium adsorptive capacity of HgCl₂ for WPAC measured in this study was 1.49 × 10^?1 mg HgCl₂/g PAC at 25 °C with an initial HgCl₂ concentration of 25 μg/m³. With the increase of adsorption temperature ≤150 °C, the equilibrium adsorptive capacity of HgCl₂ for WPAC was decreased to 1.×34 10^?1 mg HgCl₂/g PA≤C. Furthermore,WPAC with higher sulfur contents could adsorb even more HgCl₂ because of the reactions between sulfur and Hg²⁺ at 150 °C. It was demonstrated that the mechanisms for adsorbing HgCl₂ onto WPAC were physical adsorption and chemisorption at 25 and 150 °C, respectively. Experimental results also indicated that the apparent overall driving force model appeared to have the good correlation with correlation coefficients (r) >0.998 for HgCl₂ adsorption at 25 and 150 °C. Moreover, the equilibrium adsorptive capacity of HgCl₂ for virgin WPAC was similar to that for CPAC at 25 °C, whereas it was slightly higher for sulfurized WPAC than for CPAC at 150 °C.     

Determination of the adsorptive capacity and adsorption isotherm of vapor-phase mercury chloride on powdered activated carbon using thermogravimetric analysis

This study investigated the use of thermogravimetric analysis (TGA) to determine the adsorptive capacity and adsorption isotherm of vapor-phase mercury chloride on powdered activated carbon (PAC). The technique is commonly applied to remove mercury-containing air pollutants from gas streams emitted from municipal solid waste incinerators. An alternative form of powdered activated carbon derived from a pyrolyzed tire char was prepared for use herein. The capacity of waste tire-derived PAC to adsorb vapor-phase HgCl2 was successfully measured using a self-designed TGA adsorption system. Experimental results showed that the maximum adsorptive capacities of HgCl2 were 1.75, 0.688, and 0.230 mg of HgCl2 per gram of powdered activated carbon derived from carbon black at 30, 70, and 150 degrees C for 500 microg/m3 of HgCl2, respectively. Four adsorption isotherms obtained using the Langmuir, Freundlich, Redlich-Peterson, and Brunauer-Emmett-Teller (BET) models were used to simulate the adsorption of HgCl2. The comparison of experimental data associated with the four adsorption isotherms indicated that BET fit the experimental results better than did the other isotherms at 30 degrees C, whereas the Freundlich isotherm fit the experimental results better at 70 and 150 degrees C. Furthermore, the calculations of the parameters associated with Langmuir and Freundlich isotherms revealed that the adsorption of HgCl2 by PAC-derived carbon black favored adsorption at various HgCl2, concentrations and temperatures.     

Enhanced mercuric chloride adsorption onto sulfur-modified activated carbons derived from waste tires

A number of activated carbons derived from waste tires were further impregnated by gaseous elemental sulfur at temperatures of 400 and 650 degrees C, with a carbon and sulfur mass ratio of 1:3. The capabilities of sulfur diffusing into the micropores of the activated carbons were significantly different between 400 and 650 degrees C, resulting in obvious dissimilarities in the sulfur content of the activated carbons. The sulfur-impregnated activated carbons were examined for the adsorptive capacity of gas-phase mercuric chloride (HgC1) by thermogravimetric analysis (TGA). The analytical precision of TGA was up to 10(-6) g at the inlet HgCl2 concentrations of 100, 300, and 500 microg/m3, for an adsorption time of 3 hr and an adsorption temperature of 150 degrees C, simulating the flue gas emitted from municipal solid waste (MSW) incinerators. Experimental results showed that sulfur modification can slightly reduce the specific surface area of activated carbons. High-surface-area activated carbons after sulfur modification had abundant mesopores and micropores, whereas low-surface-area activated carbons had abundant macropores and mesopores. Sulfur molecules were evenly distributed on the surface of the inner pores after sulfur modification, and the sulfur content of the activated carbons increased from 2-2.5% to 5-11%. After sulfur modification, the adsorptive capacity of HgCl2 for high-surface-area sulfurized activated carbons reached 1.557 mg/g (22 times higher than the virgin activated carbons). The injection of activated carbons was followed by fabric filtration, which is commonly used to remove HgCl2 from MSW incinerators. The residence time of activated carbons collected in the fabric filter is commonly about 1 hr, but the time required to achieve equilibrium is less than 10 min. Consequently, it is worthwhile to compare the adsorption rates of HgCl2 in the time intervals of < 10 and 10-60 min.     

Determination of the Adsorption Isotherm of Vapor-Phase Mercury Chloride on Powdered Activated Carbon Using Thermogravimetric Analysis

Abstract

This study investigated the use of thermogravimetric analysis (TGA) to determine the adsorptive capacity and adsorption isotherm of vapor-phase mercury chloride on powdered activated carbon (PAC). The technique is commonly applied to remove mercury-containing air pollutants from gas streams emitted from municipal solid waste incinerators. An alternative form of powdered activated carbon derived from a pyrolyzed tire char was prepared for use herein. The capacity of waste tire-derived PAC to adsorb vapor-phase HgCl₂ was successfully measured using a self-designed TGA adsorption system. Experimental results showed that the maximum adsorptive capacities of HgCl₂ were 1.75, 0.688, and 0.230 mg of HgCl₂ per gram of powdered activated carbon derived from carbon black at 30, 70, and 150 °C for 500 µg/m³ of HgCl₂, respectively. Four adsorption isotherms obtained using the Langmuir, Freundlich, Redlich-Peterson, and Brunauer–Emmett–Teller (BET) models were used to simulate the adsorption of HgCl₂. The comparison of experimental data associated with the four adsorption isotherms indicated that BET fit the experimental results better than did the other isotherms at 30 °C, whereas the Freundlich isotherm fit the experimental results better at 70 and 150 °C. Furthermore, the calculations of the parameters associated with Langmuir and Freundlich isotherms revealed that the adsorption of HgCl₂ by PAC-derived carbon black favored adsorption at various HgCl₂ concentrations and temperatures.     

Preparation of sulfurized powdered activated carbon from waste tires using an innovative compositive impregnation process

The objective of this study is to develop an innovative compositive impregnation process for preparing sulfurized powdered activated carbon (PAC) from waste tires. An experimental apparatus, including a pyrolysis and activation system and a sulfur (S) impregnation system, was designed and applied to produce sulfurized PAC with a high specific surface area. Experimental tests involved the pyrolysis, activation, and sulfurization of waste tires. Waste-tire-derived PAC (WPAC) was initially produced in the pyrolysis and activation system. Experimental results indicated that the Brunauer-Emmett-Teller (BET) surface area of WPAC increased, and the average pore radius of WPAC decreased, as water feed rate and activation time increased. In this study, a conventional direct impregnation process was used to prepare the sulfurized PAC by impregnating WPAC with sodium sulfide (Na2S) solution. Furthermore, an innovative compositive impregnation process was developed and then compared with the conventional direct impregnation process. Experimental results showed that the compositive impregnation process produced the sulfurized WPAC with high BET surface area and a high S content. A maximum BET surface area of 886 m2/g and the S content of 2.61% by mass were obtained at 900 degrees C and at the S feed ratio of 2160 mg Na2S/g C. However, the direct impregnation process led to a BET surface area of sulfurized WPAC that decreased significantly as the S content increased.     

Adsorption characteristics of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solution on powdered activated carbon

The removal of 2,4-dichlorophenoxyacetic acid (2,4-D), one of the most commonly used phenoxy acid herbicides, from aqueous solution was studied by using acid-washed powdered activated carbon (PAC) as an adsorbent in a batch system. Adsorption equilibrium, kinetics, and thermodynamics were investigated as a function of initial pH, temperature, and initial 2,4-D concentration. Powdered activated carbon exhibited the highest 2,4-D uptake capacity of 333.3 mg g(-1) at 25 degrees C and an initial pH value of 2.0. Freundlich, Langmuir, and Redlich-Peterson isotherm models were used to express the equilibrium data of 2,4-D depending on temperature. Equilibrium data fitted very well to the Freundlich equilibrium model in the studied concentration range of 2,4-D at all the temperatures studied. Three simplified models including pseudo-first-order, pseudo-second-order, and saturation-type kinetic models were used to test the adsorption kinetics. It was shown that the adsorption of 2,4-D on PAC at 25, 35, and 45 degrees C could be best fitted by the saturation-type kinetic model with film and intraparticle diffusions being the essential rate-controlling steps. The activation energy of adsorption (EA) was determined as--1.69 kJ mole(-1). Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of adsorption (deltaG degrees, deltaH degrees, and deltaS degrees) were also evaluated.     

Preparation of Sulfurized Powdered Activated Carbon from Waste Tires Using an Innovative Compositive Impregnation Process

Abstract

The objective of this study is to develop an innovative compositive impregnation process for preparing sulfurized powdered activated carbon (PAC) from waste tires. An experimental apparatus, including a pyrolysis and activation system and a sulfur (S) impregnation system, was designed and applied to produce sulfurized PAC with a high specific surface area. Experimental tests involved the pyrolysis, activation, and sulfurization of waste tires. Waste-tire-derived PAC (WPAC) was initially produced in the pyrolysis and activation system. Experimental results indicated that the Brunauer-Emmett-Teller (BET) surface area of WPAC increased, and the average pore radius of WPAC decreased, as water feed rate and activation time increased. In this study, a conventional direct impregnation process was used to prepare the sulfurized PAC by impregnating WPAC with sodium sulfide (Na₂S) solution. Furthermore, an innovative compositive impregnation process was developed and then compared with the conventional direct impregnation process. Experimental results showed that the compositive impregnation process produced the sulfurized WPAC with high BET surface area and a high S content. A maximum BET surface area of 886 m²/g and the S content of 2.61% by mass were obtained at 900°C and at the S feed ratio of 2160 mg Na₂S/g C. However, the direct impregnation process led to a BET surface area of sulfurized WPAC that decreased significantly as the S content increased.     

碳基材料对污水厂尾水和太湖水体中CDOM的吸附特征

采用颗粒活性炭、粉末活性炭和碳纳米管3种典型碳基材料来吸附太湖水和污水厂尾水中的有机物,考察碳基材料对水中有色可溶性有机物(CDOM)的吸附特征。基于荧光光谱和平行因子分析(PARAFAC),提取出C1(腐殖酸类)、C2(色氨酸类蛋白)和C3(酪氨酸类蛋白)3个PARAFAC荧光组分。粉末活性炭和碳纳米管具有发达的中孔孔隙结构,对水中大分子有机物具有较高的吸附容量,颗粒活性炭微孔结构发达反而不利于吸附水中腐殖酸等大分子有机物。粉末活性炭对水中有机物具有最高的吸附速率,对太湖水中荧光组分C1、C2和C3 的吸附速率分别为0.278、0.358和0.359 min-1,颗粒活性炭的吸附速率明显低于粉末活性炭和碳纳米管。研究结果揭示了水中复杂混合有机物的吸附特征,为吸附工艺参数的优化提供技术参考。     

Crystalline hydrous ferric oxide: an adsorbent for chromium(VI)-contaminated industrial wastewater treatment.

Synthetic crystalline hydrous ferric oxide (CHFO) (particle size 0.14 to 0.29 mm) has been used systematically for adsorptive chromium(VI) removal from contaminated water. Batch experiments were performed as a function of pH, contact time, solute concentration, and regeneration of adsorbents. Column experiments were performed for breakthrough points in the presence and absence of other ions and treatment of industrial effluent. The optimum pH range was 2.0 to 4.0. The adsorption kinetic data could be described well by both second-order and pseudo-first-order models. The isotherm adsorption data at 30 +/- 2 degrees C obeyed the Langmuir model best. The monolayer adsorption capacity was 35.7 mg/g. Chromium(VI)-rich CHFO could be regenerated up to 89 +/- 1% with 2.0 M sodium hydroxide. Regenerated column reuse showed a decrease (10 to 12%) in breakthrough capacity. Finally, the CHFO- (dried at 300 degrees C) packed column was used for the recovery (98.5 +/- 1.0%) of chromium(VI) from contaminated industrial waste effluent of Hindustan Motor Limited (Hooghly, West Bengal, India).     

硅酸镁/PES复合膜吸附材料的制备及其对亚甲基蓝的吸附

采用共混法制备了硅酸镁/聚醚砜（PES）复合膜吸附材料,通过傅氏转换红外线光谱分析仪（FT-IR）和 扫描式电子显微镜（SEM）等手段对膜的结构进行表征,研究了复合膜的吸附性能、机械性能和热稳定性。考察了时间、溶液平衡浓度和pH等对亚甲基蓝吸附的影响。结果表明,综合机械性能和吸附性能考虑,硅酸镁含量为19%时的复合膜最佳。25℃条件下,对亚甲基蓝的吸附6 h达到平衡,最大吸附量为1.85 mg/cm2;25℃条件下,弱酸或碱性条件时有利于复合膜对亚甲基蓝的吸附。     

应对南方某水厂土霉嗅味的活性炭技术

粉末活性炭（PAC）是应对季节性嗅味问题的主要处理技术,选择合适的活性炭、确定投加条件等因素对于水厂的高效运行等具有重要意义。针对南方某水厂存在的季节性嗅味问题,选择了国内9种常用PAC（包括3种煤质炭,3种木质炭,3种椰壳炭）,对其吸附能力及处理成本进行比较,同时对该水厂在用PAC的处理效果、原有预氧化工艺（预加次氯酸钠及高锰酸钾）的影响等条件进行评价。结果表明：9种PAC中碘值为1 030 mg·g-1的椰壳炭吸附能力最强,对150 ng·L-1的2-甲基异崁醇（2-MIB）吸附容量为6.2 ng·mg-1。水厂的预氧化工艺会显著降低PAC对2-MIB、土臭素（GSM）的吸附效果（分别降低29.5%、31.6%）。综合处理效果和经济成本后,碘值为800 mg·g-1的煤质炭对该水厂水源条件下的嗅味问题处理效果最优,在将2-MIB浓度由150 ng·L-1处理至嗅阈值以下时,水的活性炭处理成本为0.3 元·t-1。     

Adsorption of chloridazon from aqueous solution on modified kerolite-rich materials

The adsorption of chloridazon (5-amine-4-chloro-2-phenylpyridazin-3(2H)-one) on kerolite samples heated at 110 degrees C (K-110), 200 degrees C (K-200), 400 degrees C (K-400), 600 degrees C (K-600) and acid-treated with H(2)SO(4) solutions of two different concentrations (0.25 and 0.5 M) (K-0.25 and K-0.5, respectively) from pure water at 25 degrees C has been studied by using batch and column experiments. The adsorption experimental data points were fitted to the Freundlich equation in order to calculate the adsorption capacities (K(f)) of the samples; K(f) values ranged from 184.7 mg kg(-1) (K-0.5) up to 2253 mg kg(-1) (K-600). This indicated that the heat treatment given to the kerolite greatly increases its adsorption capacity for the herbicide whereas the acid treatment produces a clear decrease in the amount of chloridazon adsorbed. The removal efficiency (R) was also calculated; R values ranging from 52.8% (K-0.5) up to 88.3% (K-600). Thus, the results showed that the 600 degrees C heat-treated kerolite was more effective in relation to adsorption of chloridazon and it might be reasonably used in removing this herbicide from water.     

Effects of ionic strength and temperature on adsorption of atrazine by a heat treated kerolite

The adsorption of 6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (atrazine) on a heat treated kerolite sample at 600 degrees C (K-600) from pure water solution at 10 degrees C, 25 degrees C and 40 degrees C has been studied. The influence of the presence of 0.1 M KCl in the medium was also investigated for a better understanding of variables affecting the adsorption of this herbicide. The experimental adsorption data points were fitted to the Langmuir equation in order to calculate the adsorption capacities (Xm) of the samples; Xm values range from 2.3x10(3) mg kg-1 (pure water solution at 40 degrees C) up to 15.2x10(3) mg kg-1 (0.1 M KCl solution at 10 degrees C). The adsorption data were also fitted to the Freundlich equation in order to clarify the influence of the presence of 0.1 M KCl on atrazine adsorption. The parameter K10 obtained from this equation (adsorption capacity at an equilibrium solution concentration of atrazine equal to 10 mg l-1) shows clearly that the presence of 0.1 M KCl in the medium tends to increase the adsorption of atrazine in the range of temperature studied. The adsorption experiment also showed that the lower temperature, the more effective the adsorption of atrazine from both, pure water and 0.1 M KCl solutions. The values of the removal efficiency (R) obtained ranged from 39% at 40 degrees C (pure water solution) up to 93% at 10 degrees C (0.1 M KCl solution).     

Entrained-flow adsorption of mercury using activated carbon

Bench-scale experiments were conducted in a flow reactor to simulate entrained-flow capture of elemental mercury (Hg0) by activated carbon. Adsorption of Hg0 by several commercial activated carbons was examined at different C:Hg ratios (by weight) (350:1-29,000:1), particle sizes (4-44 microns), Hg0 concentrations (44, 86, and 124 ppb), and temperatures (23-250 degrees C). Increasing the C:Hg ratio from 2100:1 to 11,000:1 resulted in an increase in removal from 11 to 30% for particle sizes of 4-8 microns and a residence time of 6.5 sec. Mercury capture increased with a decrease in particle size. At 100 degrees C and an Hg0 concentration of 86 ppb, a 20% Hg0 reduction was obtained with 4- to 8-micron particles, compared with only a 7% reduction for 24- to 44-micron particles. Mercury uptake decreased with an increase in temperature over a range of 21-150 degrees C. Only a small amount of the Hg0 uptake capacity is being utilized (less than 1%) at such short residence times. Increasing the residence time over a range of 3.8-13 sec did not increase adsorption for a lignite-based carbon; however, increasing the time from 3.6 to 12 sec resulted in higher Hg0 removal for a bituminous-based carbon.     

表面活性剂对多壁碳纳米管吸附Pb~(2+)的影响

多壁碳纳米管(MWNT)在吸附有毒气体和重金属离子方面具有极高的应用价值.针对MWNT对水溶液中Pb2+的净化吸附进行了研究,从吸附量,吸附速率、动力学角度考察了表面活性剂、Pb2+浓度对MWNT吸附Pb2+的影响.结果表明,司班-60、吐温-20、阿拉伯树胶等表面活性剂的加入,促进了MWNT在溶液中的分散,导致在Pb2+摩尔浓度为3～18 mmol/L的Lang-muir和Freundlich等温吸附方程中的吸附常数(K)变大,使得MWNT对Pb2+的吸附速率和平衡吸附量都得到提高;随着溶液中Pb2+浓度的增大,MWNT对其吸附量渐至饱和,随后由于Pb2+的位阻作用.吸附量下降;在这3种表面活性剂中,由于司班-60具有相对较小的分子量,其分散的MWNT在Pb2+摩尔浓度为14 mmol/L时,吸附量最大,为230 mg/g.     

Adsorption behavior of reactive dye in aqueous solution on chemical cross-linked chitosan beads

A batch system was applied to study the adsorption of reactive dye (reactive red 189) from aqueous solutions by cross-linked chitosan beads. The ionic cross-linking reagent sodium tripolyphosphate was used to obtain more rigid chitosan beads. To stabilize chitosan in acid solutions, chemical cross-linking reagent epichlorohydrin (ECH), glutaraldehyde and ethylene glycol diglycidyl ether was used and ECH shows a higher adsorption capacity. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms at different particle sizes and isotherm constants were determined. The Langmuir model agrees very well with experimental data and its calculated maximum monolayer adsorption capacity has very large value of 1802-1840 (g/kg) at pH 3.0, 30 degrees C. The kinetics of the adsorption with respect to the initial dye concentration, temperature, pH, ionic strength, and wet/dry beads were investigated. The pseudo-first-order, second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The dynamical data fit well with the second-order kinetic model, except for the dry beads fitting better with the first-order model. The adsorption capacity increases largely with decreasing solution pH or with increasing initial dye concentration. Thermodynamic parameters such as change in free energy (deltaG(0)), enthalpy (deltaH(0)), entropy (deltaS(0)) and activation energy were also determined. The adsorption mechanism is shown to be the electrostatic interactions between the dye and chitosan beads. The desorption data shows that the removal percent of dye RR 189 from the cross-linked chitosan beads is 63% in NaOH solutions at pH 10.0, 30 degrees C. The desorbed chitosan beads can be reused to adsorb the dye and to reach the same capacity as that before desorption.     

Adsorptive conversion of nitrogen dioxide from etching vent gases over activated carbon

Some metal etching operations emit limited flow rates of waste gases with reddish-brown NO₂ fume, which may cause visual and acidic-odor complaints, as well as negative health effects. In this study, tests were performed by passing caustic-treated waste gases vented from Al-etching operations through columns packed either with virgin or regenerated granular activated carbon (GAC) to test their adsorptive conversion performance of NO₂ in the gases. The gases contained 5–55 ppm NO₂ and acetic and nitric acids of below 3 ppm. Exhausted carbon was regenerated by scrubbing it with caustic solution and water, and dried for further adsorption tests. Results indicate that with an (empty bed residence time (EBRT) of 0.15 sec for the gas through the GAC-packed space, around 60% of the influent NO₂ of 54 ppm could be removed, and 47% of the removed NO₂ was converted by and desorbed from the carbon as NO. GAC used in the present study could be regenerated at least twice to restore its capacity for NO₂ adsorption. Within EBRTs of 0.076–0.18 sec, the adsorptive conversion capacity was linearly varied with EBRT. In practice, with an EBRT of 0.20 sec, a conversion capacity of 0.80 kg NO₂ (kg GAC)^?1 with an influent NO₂ of 40 ppm can be used as a basis for system design.

Implications: Some metal etching operations emit waste gases with reddish-brown (yellow when diluted) NO₂ fume which may cause visual and acidic-odor complaints, as well as negative health effects. This study provides a simple process for the adsorptive conversion of NO₂ in caustic-treated waste gases vented from metal-etching operations through a GAC column. With an EBRT of 0.20 sec, a conversion capacity of 0.80 kg NO₂ (kg GAC)^?1 with an influent NO₂ of 40 ppm can be used as a basis for system design. Saturated GAC can be regenerated at least twice by simply scrubbing it with aqueous caustic solution.     

聚合氯化铝污泥对磷的吸附动力学及热力学

聚合氯化铝污泥（polyaluminium chloride sludge,PACS）是指以聚合氯化铝（PAC）为混凝剂的城镇给水厂在生产过程中所产生的污泥。采用批量吸附实验考察了PACS对磷的吸附动力学及热力学行为。结果表明,吸附反应发生1 h后,PACS对磷的吸附量达到平衡吸附量的75%～90%,随后PACS对磷的...     

Adsorptive separation of cadmium from aqueous solutions and wastewaters by riverbed sand

Application of riverbed sand for the adsorptive separation of cadmium(II) from aqueous solutions has been investigated. Removal increased from 26.8 to 56.4% by decreasing the initial concentration of cadmium from 7.5 x 10(-5) to 1.0 x 10(-5)M at pH 6.5, 25 degrees C temperature, agitation speed of 100 rpm, 100 microm particle size and 1.0 x 10(-2) NaClO4 ionic strength. Process of separation is governed by first order rate kinetics. The value of rate constant of adsorption, k(ad), was found to be 2.30 x 10(-2)per min at 25 degrees C. Values of coefficient of mass transfer, beta L, were calculated and its value at 25 degrees C was found to be 1.92 x 10(-2)cm/s. Values of Langmuir constant were calculated. Values of thermodynamic parameters delta G0, delta H0 and delta S0 were also calculated and were recorded as -0.81 kcal/mol, -9.31 kcal/mol and -28.10 cal/mol at 25 degrees C. pH has been found to affect the removal of cadmium significantly and maximum removal, 58.4%, has been found at pH 8.5. Process can be used for treatment of cadmium(II) rich wastewaters.     

Fluoride removal performance of a novel Fe-Al-Ce trimetal oxide adsorbent

A trimetal oxide was developed as a fluoride adsorbent by coprecipitation of Fe(II), Al(III) and Ce(IV) salt solutions with a molar ratio of 1:4:1 under alkaline condition. The material retained amorphous structure and maintained relatively stable fluoride adsorption performance at calcination temperatures lower than 600 degrees C. The optimum pH range for fluoride adsorption was 6.0-6.5 and the adsorbent also showed high defluoridation ability around pH 5.5-7.0, which is preferable for actual application. A high fluoride adsorption capacity of 178 mg g(-1) was acquired under an equilibrium fluoride concentration of 84.5 mg l(-1), adsorbent dose of 150 mg l(-1) and pH 7.0. The adsorption isotherm could be better described by the two-site Langmuir model than the one-site model, suggesting the existence of two types of active sites on the adsorbent surface. Coexistence of high concentrations of phosphate or arsenate only led to partial inhibition of fluoride adsorption, which further suggests the existence of heterogeneous adsorption sites. Sulfate and chloride did not affect fluoride adsorption, and nitrate influenced it only when the concentration of NO(3)(-)-N exceeded 50 mg l(-1). A high desorption efficiency of 97% was achieved by treating fluoride loaded Fe-Al-Ce oxide with NaOH solution at pH 12.2. A column experiment using the adsorbent fabricated into 1mm pellets was performed at an initial fluoride concentration of 5.5 mg l(-1), space velocity of 5h(-1) and pH of 5.8, and 2240 bed volumes were treated with the effluent fluoride under 1.0 mg l(-1).