Removal of copper from water by electrocoagulation process—effect of alternating current (AC) and direct current (DC)

Purpose and aim

In general, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of copper from water using magnesium alloy as anode and cathode.

Materials and methods

Magnesium alloy of size 2.0 dm² was used as anode and as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. Copper adsorbed magnesium hydroxide coagulant was characterized by SEM, EDAX, XRD, and FTIR.

Results

The results showed that the optimum removal efficiency of copper is 97.8 and 97.2 % with an energy consumption of 0.634 and 0.996 kWh/m³ at a current density of 0.025 A/dm², pH of 7.0 for AC and DC, respectively. The adsorption of copper is preferably fitting the Langmuir adsorption isotherm for both AC and DC respectively. The adsorption process follows the second-order kinetics model with good correlation. Temperature studies showed that adsorption was endothermic and spontaneous in nature.

Conclusions

The magnesium hydroxide generated in the cell removes the copper present in the water, reducing the copper concentration to less than 1 mg/L, making it safe for drinking. The results of the scale-up study show that the process was technologically feasible.     

Oxidized multiwalled carbon nanotubes as adsorbent for the removal of manganese from aqueous solution

A batch adsorption process was applied to investigate the removal of manganese from aqueous solution by oxidized multiwalled carbon nanotubes (MWCNTs). In doing so, the thermodynamic, adsorption isotherm, and kinetic studies were also carried out. MWCNT with 5–10-nm outer diameter, surface area of 40–600 m²/g, and purity above 95 % was used as an adsorbent. A systematic study of the adsorption process was performed by varying pH, ionic strength, and temperature. Manganese-adsorbed MWCNT was characterized by Raman, FTIR, X-ray diffraction, XPS, SEM, and TEM. The adsorption efficiency could reach 96.82 %, suggesting that MWCNT is an excellent adsorbent for manganese removal from water. The results indicate that second-order kinetics model was well suitable to model the kinetic adsorption of manganese. Equilibrium data were well described by the typical Langmuir adsorption isotherm. Thermodynamic studies revealed that the adsorption reaction was spontaneous and endothermic process. The experimental results showed that MWCNT is an excellent manganese adsorbent. The MWCNTs removed the manganese present in the water and reduced it to a permissible level making it drinkable.     

Recovery of hydrogen and removal of nitrate from water by electrocoagulation process

The present study provides an optimization of electrocoagulation process for the recovery of hydrogen and removal of nitrate from water. In doing so, the thermodynamic, adsorption isotherm, and kinetic studies were also carried out. Aluminum alloy of size 2 dm² was used as anode and as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. The results show that a significant amount of hydrogen can be generated by this process during the removal of nitrate from water. The energy yield calculated from the hydrogen generated is 3.3778 kWh/m³. The results also showed that the maximum removal efficiency of 95.9 % was achieved at a current density of 0.25 A/dm², at a pH of 7.0. The adsorption process followed second-order kinetics model. The adsorption of NO ₃ ^? preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. Thermodynamic studies showed that adsorption was exothermic and spontaneous in nature. The energy yield of generated hydrogen was ~54 % of the electrical energy demand of the electrocoagulation process. With the reduction of the net energy demand, electrocoagulation may become a useful technology to treat water associated with power production. The aluminum hydroxide generated in the cell removes the nitrate present in the water and reduced it to a permissible level making the water drinkable.     

Graphene—a promising material for removal of perchlorate (ClO4 −) from water

A batch adsorption process was applied to investigate the removal of perchlorate (ClO₄ ^?) from water by graphene. In doing so, the thermodynamic adsorption isotherm and kinetic studies were also carried out. Graphene was prepared by a facile liquid-phase exfoliation. Graphene was characterized by Raman spectroscopy, Fourier-transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscope, and zeta potential measurements. A systematic study of the adsorption process was performed by varying pH, ionic strength, and temperature. The adsorption efficiency of graphene was 99.2 %, suggesting that graphene is an excellent adsorbent for ClO₄ ^? removal from water. The rate constants for all these kinetic models were calculated, and the results indicate that second-order kinetics model was well suitable to model the kinetic adsorption of ClO₄ ^?. Equilibrium data were well described by the typical Langmuir adsorption isotherm. The experimental results showed that graphene is an excellent perchlorate adsorbent with an adsorbent capacity of up to 0.024 mg/g at initial perchlorate concentration of 2 mg/L and temperature of 298 K. Thermodynamic studies revealed that the adsorption reaction was a spontaneous and endothermic process. Graphene removed the perchlorate present in the water and reduced it to a permissible level making it drinkable.     

Biosorption of copper(II) from aqueous solutions by pre-treated biomass of marine algae Padina sp

Biosorption of heavy metals can be an effective process for the removal and recovery of heavy metal ions from aqueous solutions. The biomass of marine algae has been reported to have high uptake capacities for a number of heavy metal ions. In this paper, the adsorption properties of a pre-treated biomass of marine algae Padina sp. for copper(II) were investigated. Equilibrium isotherms and kinetics were obtained from batch adsorption experiments. The biosorption capacities were solution pH dependent and the maximum capacity obtained was 0.80 mmol/g at a solution pH of about 5. The biosorption kinetics was found to be fast, with 90% of adsorption within 15 min and equilibrium reached at 30 min. The effects of light metal ions on copper(II) uptake were studied and the presence of light metal ions did not affect copper(II) uptake significantly. Fixed-bed breakthrough curves for copper(II) removal were also obtained. This study demonstrated that the pre-treated biomass of Padina sp. could be used as an effective biosorbent for the treatment of copper(II) containing wastewater streams.     

Use of carbonised beet pulp carbon for removal of Remazol Turquoise Blue-G 133 from aqueous solution

Carbonised beet pulp (BPC) produced from agricultural solid waste by-product in sugar industry was used as adsorbent for the removal of Remazol Turquoise Blue-G 133 (RTB-G 133) dye in this study. The kinetics and equilibrium of sorption process were investigated with respect to pH, temperature and initial dye concentration. Adsorption studies with real textile wastewater were also performed. The results showed that adsorption was a strongly pH-dependent process, and optimum pH was determined as 1.0. The maximum dye adsorption capacity was obtained as 47.0 mg g^?1at the temperature of 25 °C at this pH value. The Freundlich and Langmuir adsorption models were used for describing the adsorption equilibrium data of the dye, and isotherm constants were evaluated depending on sorption temperature. Equilibrium data of RTB-G 133 sorption fitted very well to the Freundlich isotherm. Mass transfer and kinetic models were applied to the experimental data to examine the mechanisms of adsorption and potential rate-controlling steps. It was found that both external mass transfer and intra-particle diffusion played an important role in the adsorption mechanisms of dye and adsorption kinetics followed the pseudo second-order type kinetic model. The thermodynamic analysis indicated that the sorption process was exothermic and spontaneous in nature.     

改性二次锶渣吸附去除废水中的磷

以改性二次锶渣为吸附剂,研究了吸附时间、吸附剂投加量、磷初始浓度和pH值对废水中磷去除效果的影响。结果表明,当总磷浓度为10mg／L,pH为7、二次锶渣投加量为15g／L时,90min内就可使废水中磷的去除率达到95％以上,总磷浓度低于污水综合排放标准的一级标准;改性二次锶渣对磷的吸附符合Langmuir等温吸附模型及准二级动力学模型。     

铁基膨润土对水中磷酸根的吸附热力学及动力学研究

采用铁盐改性制得铁基膨润土,研究了其对水中磷酸根的吸附性能及影响因素,结果表明,通过对膨润土的改性提高了磷的去除率,含磷废水初始pH值的大小对磷的去除率影响不大,初始浓度越低越有利于磷的去除。磷的去除率随改性膨润土的投加量增大而提高,随温度升高而增大。进一步研究表明,改性膨润土对磷的吸附是吸热反应,其吸附等温线可采用Langmuir等温吸附方程拟合;改性膨润土对磷的吸附是快速吸附,在20 min内,磷去除率达70%以上,符合准二级吸附动力学模型。     

改性钢渣吸附氨氮和磷的特性研究

利用钢渣与氢氧化铝以4∶3质量配比混合,在700℃下进行2 h煅烧,得到改性钢渣。通过批次吸附实验,研究了改性钢渣在不同初始pH值、振荡时间和温度下对水溶液中氨氮和磷酸根的吸附情况,进而分析了改性钢渣对氨氮和磷酸根的吸附等温线、热力学和动力学特性。结果表明,改性钢渣脱氮除磷能力比原钢渣显著增强,且最适pH值为4～8。改性沸石对氨氮和磷酸盐的吸附均符合Langmuir等温吸附方程,氨氮(以N计)最大吸附量在10、20和30℃下分别为1.67、2.59和3.24 mg/g,磷酸根(以P计)的最大吸附量在10、20和30℃下分别为1.02、1.19和1.37 mg/g。热力学参数ΔG0、ΔH0和ΔS0表明,该吸附是一个自发、吸热、熵增型反应过程,且磷的吸附是化学吸附为主,氨氮的吸附是以离子交换吸附和物理吸附为主。改性钢渣对磷和氨氮的吸附动力学符合伪二级方程(R2>0.999)。     

污泥活性炭对次甲基蓝废水的吸附

立足于污泥的资源化,利用化学活化法制得的污泥基活性炭,处理次甲基蓝染料废水.考察了污泥活性炭的粒径以及染料废水的pH值对染料脱色效果以及活性炭的吸附量的影响,并对吸附过程进行等温吸附线和吸附动力学分析.结果表明,在本研究的范围内,污泥活性炭的粒径越小、染料废水的pH值越高,则污泥活性炭对染料废水的吸附效果越好.当粒径在200目以上时,去除率及吸附量分别为88.2％和136.7 mg/g;当pH值为11时,去除率和吸附量分别为90.4％和91.9 mg/g.污泥活性炭对次甲基蓝染料的吸附脱除符合Langmuir吸附等温线和Lagergren准二级动力学方程.     

镇江斜发沸石对氨氮的吸附动力学及热力学研究

采用静态平衡法,开展了镇江斜发沸石对水中氨氮的吸附动力学和热力学研究.结果表明,吸附量随反应温度升高而增加,斜发沸石对氨氮吸附符合Freundlich等温线方程,对氨氮吸附实验数据与准二级动力学模型拟合更好(R2＞0.998),热力学参数吸附焓变△H=18.26 kJ/mol,熵变△S=0.0632 kJ/kmol,对...     

煤气发生炉炉渣改性和吸附性能

以工业中生产煤气时产生的煤气炉炉渣为原料,采用手工分选法将炉渣中的炭及残渣分离,再采用酸碱浸渍方法对炉渣残渣进行改性,研究了改性后的炉渣残渣及炉渣中分离出的炭对溶液中苯酚的吸附性能。吸附实验结果表明,分离炭的吸附性能最好,其次为碱改性炉渣残渣和酸改性炉渣残渣,未改性炉渣残渣吸附性能最差。改性的炉渣残渣及分离炭对苯酚吸附过程符合二级吸附动力学模型。吸附等温线研究表明,改性炉渣残渣及分离炭对苯酚的吸附符合Lang-muir吸附等温式。     

改性粉煤灰对糖蜜废水的吸附效果及机理

采用改性粉煤灰(MCFA)吸附糖蜜废水中的有机污染物,对吸附行为和机理进行了考察和分析。结果表明,MCFA投加量为30 g/L及pH为5.0的优化条件下,COD去除率为88.6%,饱和吸附量为89.7 mg COD/g MCFA。准二级方程能更好地描述糖蜜废水在MCFA上的吸附动力学。颗粒内扩散方程结果表明孔扩散并非唯一的速度控制步骤。吸附平衡表明,Freundlich等温线最符合吸附模式,为优惠吸附。D-R模式中的吸附自由能Ea值推断更可能是物理吸附而不是化学吸附。吸附热力学参数ΔG0(<0)、ΔH0(5.130 kJ/mol)和ΔS0(19.936 J/(mol.K))表明MCFA对糖蜜废水的吸附过程为可行的,自发性的吸热反应。     

粉煤灰微波改性及其对Cr~（6＋）的吸附特性

将粉煤灰（fly ash,FA）微波辐照制得微波改性粉煤灰（MFA）,选择用H2SO4、NaOH和Ca（OH）2对MFA进行化学改性制得微波化学改性粉煤灰（MMFA）,结果表明,用2 mol/L NaOH并按与MFA的质量体积比为1∶4制得的MMFA对Cr6＋的吸附去除效果最好,与原灰相比,去除率显著增强。研究了NaOH改性MMFA对废水中Cr6＋的吸附性能。动力学研究结果表明,MMFA对Cr6＋的吸附动力学符合二级吸附动力学速率方程,吸附受颗粒内扩散过程控制。热力学研究结果表明,在25、35和45℃下MMFA对Cr6＋的等温吸附行为均可用Langmuir方程、Freundlich方程和线性方程描述,所得热力学参数吸附自由能（ΔG）、吸附焓（ΔH）和吸附熵（ΔS）均为负值,说明MMFA对Cr6＋的吸附过程为自发进行的放热吸附过程。     

铁碳微电解-Fenton法预处理苯胺基乙腈生产废水的动力学研究

通过采用铁碳微电解-Fenton法预处理苯胺基乙腈生产废水的实验研究,分析了处理过程的COD降解动力学;同时研究了单纯活性炭吸附和微电解过程中COD去除率的变化。结果表明,铁碳微电解的初期COD降解过程近似符合一级反应动力学,并且得到微电解与活性炭吸附对铁碳微电解降解COD的关系式;Fenton反应中通过研究有机物浓度和过氧化氢初始浓度与反应进程的关系,建立了反应动力学模型;单纯吸附实验COD去除率在24h内快速下降,而微电解在相应时间内COD去除率波动较小,为实际应用提供了数据经验和理论依据。     

铁碳微电解-Fenton法预处理苯胺基乙腈生产废水的动力学研究

通过采用铁碳微电解-Fenton法预处理苯胺基乙腈生产废水的实验研究,分析了处理过程的COD降解动力学;同时研究了单纯活性炭吸附和微电解过程中COD去除率的变化。结果表明,铁碳微电解的初期COD降解过程近似符合一级反应动力学,并且得到微电解与活性炭吸附对铁碳微电解降解COD的关系式;Fenton反应中通过研究有机物浓度和过氧化氢初始浓度与反应进程的关系,建立了反应动力学模型;单纯吸附实验COD去除率在24 h内快速下降,而微电解在相应时间内COD去除率波动较小,为实际应用提供了数据经验和理论依据。     

Adsorptive removal of an acid dye by lignocellulosic waste biomass activated carbon: equilibrium and kinetic studies

Chemically prepared activated carbon material derived from palm flower was used as adsorbent for removal of Amido Black dye in aqueous solution. Batch adsorption studies were performed for the removal of Amido Black 10B (AB10B), a di-azo acid dye from aqueous solutions by varying the parameters like initial solution pH, adsorbent dosage, initial dye concentration and temperature with three different particle sizes such as 100 μm, 600 μm and 1000 μm. The zero point charge was pH 2.5 and the maximum adsorption occurred at the pH 2.3. Experimental data were analyzed by model equations such as Langmuir, Freundlich and Temkin isotherms and it was found that the Freundlich isotherm model best fitted the adsorption data and the Freundlich constants varied from (K_F) 1.214, 1.077 and 0.884 for the three mesh sizes. Thermodynamic parameters such as ΔG, ΔH and ΔS were also calculated for the adsorption processes and found that the adsorption process is feasible and it was the endothermic reaction. Adsorption kinetics was determined using pseudo first-order, pseudo second-order rate equations and also Elovich model and intraparticle diffusion models. The results clearly showed that the adsorption of AB10B onto lignocellulosic waste biomass from palm flower (LCBPF) followed pseudo second-order model, and the pseudo second-order rate constants varied from 0.059 to 0.006 (g mg⁻¹ min) by varying initial adsorbate concentration from 25 mg L⁻¹ to 100 mg L⁻¹. Analysis of the adsorption data confirmed that the adsorption process not only followed intraparticle diffusion but also by the film diffusion mechanism.     

利用钢渣对聚驱采油废水进行深度处理

利用钢渣对模拟聚驱采油废水进行深度处理,依靠吸附作用去除水中的HPAM。考察了钢渣粒径、搅拌速度、pH以及吸附时间对HPAM去除率的影响,进行了吸附等温线和吸附热力学分析,并对钢渣进行了吸附再生实验。当搅拌速度为250r／min,pH为2～10,吸附时间为90rain,钢渣粒径为10-16目、投加量为100g／100mL时,HPAM的去除率可达到84％以上。钢渣对HPAM的吸附符合Langmuir等温式,吸附自由能变和吸附焓的结果都表明,该吸附属于物理吸附。吸附之后的钢渣可以通过600℃焚烧得到再生,再生后仍可保持良好的吸附性能。     

天氧污泥对问二氯苯的吸附性能

为了研究灭活厌氧污泥和活性厌氧污泥对问二氯苯（m-DCB）的吸附,考察了吸附平衡时间、吸附动力学、吸附等温线、吸附热力学、污泥投加量和pH对吸附m-DCB的影响。结果表明,2种污泥对m-DCB的吸附在1h内达到平衡。应用伪一级、伪二级反应动力学对实验数据进行验证,表明厌氧污泥吸附m-DCB更符合伪二级反应动力学模型。2种污泥对m-DCB的吸附都可以用Langmuir和Freundlich吸附模型拟合,但Langrnuir吸附模型的拟合结果要好于Freundlich模型,且活性厌氧污泥的吸附性能显著高于灭活厌氧污泥。从吸附热力学上看,该吸附为放热反应,低温有利于吸附反应的进行。pH值对2种污泥吸附m-DCB的影响很小。     

改性玉米秸秆吸附Cu^2＋的动力学和热力学

本研究用ZnCl2作为活化剂,使用功率640W的微波照射4min的方法制备改性玉米秸秆。考察投加量、pH、吸附时间对吸附性能的影响,并对等温吸附特征、吸附动力学和热力学进行了系统研究。结果表明：投加量为0．2g,pH为6,改性玉米秸秆对Cu^2＋具有很好的吸附效果,吸附在8h后达到平衡。该吸附过程符合Langmuir及Freundlich等温吸附模型和准二级动力学方程,其反应的吉布斯自由能△G〈0,为自发反应过程。