Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc...Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc- culation with polyaluminum chloride. The compensatory effect of slow-mixing on coagulation performance fol- low!ng inadequate_or excessive rapid-mi_xing was also examined. It is found that slowTmixing intensity has a more marked positive ettect on charge neutralization coas;ulatlon tlaan on sweep tlocculatlon. llle optimal root-mean- square velocity gradient, G, for slow-mixing is 15 s-＇ for both coagulation mechanisms, and charge neutralization coagulation requires a longer slow-mixing duration. The optimal slow-mixing duration, based on residual turbidity,is longer than the time to tbrm the largest mean Ilocs. The optimal product of G and mixing duration, GT, lbr slow-mixing during charge neutralization coagulation （13500） are higher than that during sweep flocculation （4500） and both are less than the range of values recommended by the American Water Works Association （24000-84000）.The optimal GT value under various slow-mixing conditions increases with G. Appropriate extension＇of slow-mixing duration during charge neutralization coagulation can improve coagulation performance after an inadequate or excessive rapid-mixing duration, but during sweep flocculation, appropriate shortening of slow-mixing duration after an excessive rapid-mixing or appropriate extension of slow-mixing duration after an inadequate rapid-mixing is favorable.展开更多
Coagulation mechanisms of polyaluminum chloride(PACl) at various dosages were studied using a conventional jar test at different final and initial pH values during treating kaolin suspension. The optimal final pH and ...Coagulation mechanisms of polyaluminum chloride(PACl) at various dosages were studied using a conventional jar test at different final and initial pH values during treating kaolin suspension. The optimal final pH and dosages for PACl were obtained based on residual turbidity and zeta potential of flocs. The coagulation zones at various PACl dosages and solution p H values were developed and compared with those of alum. It is found that the optimal mechanism under acidic condition is charge neutralization, while alkaline condition will facilitate the coagulation of PACl. Both charge neutralization coagulation and sweep coagulation can achieve high coagulation efficiency under the alkaline condition ranging from final p H 7.0 to 10.0. Stabilization, charge neutralization destabilization, restabilization and sweep zones occur successively with increasing PACl dosages with the final p H values fixed at 7.0 and 8.0, but restabilization zone disappears at final p H 10.0. When the final p H is not controlled and consequently decreases with increasing PACl dosage, no typical sweep zone can be observed and the coagulant efficiency decreases at high PACl dosage. It seems that the final pH is more meaningful than the initial p H for coagulation. Charge neutralization coagulation efficiency is dominated by zeta potential of flocs and PACl precipitates. The charge neutralization and sweep coagulation zones of PACl are broader in the ranges of coagulant dosage and p H than those of alum. The results are helpful for us to treat water and wastewater using PACl and to understand the coagulation process of PACl.展开更多
Copper oxide nanomaterials have been extensively applied and can have serious impacts when discharged into the aquatic environment, especially when complexed with humic acid(HA) to form composite contaminants.As an in...Copper oxide nanomaterials have been extensively applied and can have serious impacts when discharged into the aquatic environment, especially when complexed with humic acid(HA) to form composite contaminants.As an innovative recycled coagulant aid,Enteromorpha polysaccharides(Ep) were associated with polyaluminum chloride(PACl)(denoted as PACl-Ep) to simultaneously remove CuO nanoparticles, Cu2+and HA in this study.The influence of different Al species coagulants(AlCl3, PAClb and PAClc) and water pH on coagulation performance, floc properties and reaction mechanisms was investigated in detail.Results showed that in the three PACl-Ep systems, PAClb-Ep gave the highest removal efficiencies for turbidity and Cu2+, and the best UV254 removal effect was reached by using PAClc-Ep.Higher contents of Alb and Alc contributed to great coagulation performance because of their stronger bridging and sweeping effects.For all the Al species coagulants, alkalescent conditions were more conducive to removing Cu and HA compared to acidic conditions.Additionally, smaller and more agminated flocs with great recovery ability were formed by PAClb-Ep and PAClc-Ep systems(bridging and enmeshment effects cooperated with the chelated reticular structure formed by the Ep and Al species).Similarly,due to the increased hydrolysis and hydroxide precipitates, flocs formed under the condition of alkalescence were smaller, denser and stronger compared with weakly acidic conditions.展开更多
Compared with traditional aluminum salts, polyaluminum chloride （PACI） has better coagulation-flocculation performance in turbidity removal. However, it is still inferior to organic polymers in terms of bridging fun...Compared with traditional aluminum salts, polyaluminum chloride （PACI） has better coagulation-flocculation performance in turbidity removal. However, it is still inferior to organic polymers in terms of bridging function. In order to improve the aggregating property of PACl, different composite PACl flocculants were prepared with various organic polymers. The effect of organic polymer on the distribution or Al（Ⅲ） species in composite flocculants was studied using ^27TAl NMR and Al-ferron complexation methods. The charge neutralization and surface adsorption characteristics of composite flocculants were also investigated. Jar tests were conducted to evaluate the turbidity removal efficacy of organic polymer modified composite flocculants. The study shows that cationic polymer and anionic polymer have significant influences on the coagulation-flocculation behaviors of PACl. Both cationic and anionic polymers can improve the turbidity removal performancc of PACl but the mechanisms arc much different： cationic organic polymer mainly increases the charge neutralization ability, but anionic polymer mainly enhances the bridging function.展开更多
A method of direct contact membrane distillation （DCMD） with a self-made hollow polyvinylidene fluoride membrane was applied to prepare high concentration polyaluminum chloride （PACl） with high Alb content based o...A method of direct contact membrane distillation （DCMD） with a self-made hollow polyvinylidene fluoride membrane was applied to prepare high concentration polyaluminum chloride （PACl） with high Alb content based on chemical synthesis. The permeate flux and Al species distribution were investigated. The experimental results showed that the permeate flux decreased from 14 to 6 kg/（m2·hr） at the end of the DCMD process, which can be mainly attributed to the formation of NaCl deposits on the membrane surface. The Alb content decreased slightly, only from 86.3% to 84.4%, when the DCMD experiment finished, correspondingly the Alc content increased slightly from 7.2% to 8.5%, and the Ala content remained at 7% during the whole DCMD process. A PACl with Alb content of 84% at total aluminum concentration 2.2 mol/L was successfully prepared by the chemical synthesis-DCMD method.展开更多
A novel membrane distillation concentration method was used m prepare high concentration polyaluminum chloride （PAC1） with high content of AID or Ale. 2.52 mol/L PACl1 with 88% Alb and 2.38 mol/L PACl2 with 61% Ale ...A novel membrane distillation concentration method was used m prepare high concentration polyaluminum chloride （PAC1） with high content of AID or Ale. 2.52 mol/L PACl1 with 88% Alb and 2.38 mol/L PACl2 with 61% Ale were successfully prepared. Three coagulants, AlCl3, PACl1 and PACl2 were investigated on their hydrolysis behavior and speciation under different conditions. The effects of pH and dilution ratio on Al species distribution were investigated by ferron assay. Experimental result showed that pH had a significant effect on Al species distribution for the three coagulants. Dilution ratio had little effects on Alb and Alc distribution in whole dilution process except the beginning for PACl1 and PACl2. The results indicated that transformation of Al depends largely on their original composition. AlCl3 was the most unstable coagulant among these three coagulants during hydrolysis process. PACl1 and PACl2 with significant amounts of highly charged and stable polynuclear aluminum hydrolysis products were less affected by the hydrolysis conditions and could maintain high speciation stability under various conditions.展开更多
A direct contact membrane distillation（DCMD）process was applied to prepare high concentration polyaluminum chloride（PACl）with high Alc content.The changes in total Al concentration（AlT）and Al species distributio...A direct contact membrane distillation（DCMD）process was applied to prepare high concentration polyaluminum chloride（PACl）with high Alc content.The changes in total Al concentration（AlT）and Al species distribution were investigated.The results showed that AlT increased but the flux decreased with operating time during the DCMD process.The Alc content increased from 65%to 81%while the Alb content decreased from 34% to 18%,and the Ala content was almost 1%in the process.2.1 mol·L 1PACl with 81%Alc was successfully prepared by DCMD method.Thus the DCMD is an effective method for preparing high concentration PACl with high Alc content.展开更多
The effects of polyaluminum chloride（PACl） hydrolysis prior to coagulation on both the coagulation zone and coagulation performance of a kaolin suspension were investigated by a novel jar test named the ＂reversed c...The effects of polyaluminum chloride（PACl） hydrolysis prior to coagulation on both the coagulation zone and coagulation performance of a kaolin suspension were investigated by a novel jar test named the ＂reversed coagulation test＂.The tests showed that PACl hydrolysis prior to coagulation decreased the performance of charge neutralization coagulation in the case of short-time slow mixing（10 min;G = 15 sec-1） and increased the optimal dosage for charge neutralization and sweep coagulation.Moreover,the hydrolysis time had insignificant effects on the size and zeta potential of PACl precipitates and the residual turbidity of the raw water.However,PACl hydrolysis prior to coagulation and the size of PACl precipitates had a negligible effect on the performance of sweep coagulation.The results imply that,in practice,preparing a PACl solution with deionized water,rather than tap water or the outlet water from a wastewater treatment unit,can significantly save PACl consumption and improve the performance of charge neutralization coagulation,while preparing the PACl solution with tap or outlet water would not affect the performance of sweep coagulation.In addition,the optimal rapid mixing intensity appears to be determined by a balance between the degree of coagulant hydrolysis before contacting the primary particles and the average size of flocs in the rapid mixing period.These results provide new insights into the role of PACl hydrolysis and will be useful for improving coagulation efficiency.展开更多
Considering that Fe,Al elements in bauxite residue are active components for water purification,an effective polyaluminum ferric chloride(PAFC)coagulant derived from bauxite residue,with Fe2O3 content>5.1%,Al2O3%&g...Considering that Fe,Al elements in bauxite residue are active components for water purification,an effective polyaluminum ferric chloride(PAFC)coagulant derived from bauxite residue,with Fe2O3 content>5.1%,Al2O3%>6.5%,basicity>65%,was successfully prepared.The effect of as-prepared PAFC on the zeta potential for printing and dyeing wastewater was investigated.Comparing with polyferric chloride(PFC)and polyferric sulfate(PFS)for printing and dyeing wastewater treatment,prepared bauxite residue-based PAFC exhibited the optimal performance in the aspects of chromaticity and chemical oxygen demand(COD)removal rate.Furthermore,the combination of bauxite residue-based PAFC and PFS for synergy coagulation of such wastewater demonstrated an obvious positive effect.With the proportion between as-prepared PAFC and PFS to be 2.5:1,the COD of treated wastewater could be further reduced to meet the national level A standard of China,providing a promising route to solve the problem of substandard printing and dyeing sewage outfall by a simple coagulation strategy.展开更多
Polyaluminum chloride was synthesized with a membrane reactor,in which NaOH was added into AlCl 3 solution through the membrane’s micropores to reduce the NaOH droplets size.The content of the most efficient species ...Polyaluminum chloride was synthesized with a membrane reactor,in which NaOH was added into AlCl 3 solution through the membrane’s micropores to reduce the NaOH droplets size.The content of the most efficient species increased to about 80%.The process characteristics in the reaction （i.e.,flow velocity,pressure drop）,and membrane fouling and cleaning were investigated.The evolution of both flow velocity and pressure drop during the reaction were related to changes in species distribution and solution viscosity.The process characteristics were well interpreted in terms of the Bernoulli equation.After reaction,the membranes were recovered by cleaning with diluted hydrochloride acid.This study is crucial for process design and scale-up of membrane reactors.展开更多
The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test metho...The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test method. The experimental results showed that the interaction between polysilicic acid characterized negative charge and hydrolyzed aluminum species result in a decrease of the charge neutralizing ability of PASiC, compared to PAC. The decrease has a close relationship with the basicity ( B ) and Al/Si molar ratio in PASiC. The less the B value and the Al/Si molar ratio, the lower the charge neutralizing ability of PASiC is. In contrast, the preparation technique for PASiC affects the charge-neutralization of PASiC to a smaller extent. In addition, compared with PAC, PASiC may enhance aggregating efficiency and give better coagulating effects.展开更多
In this paper a polyaluminum chloride solution with high Al13 content was prepared and used as raw material for preparation ofγ-Al2O3.The texture and crystalline phase of the prepared alumina samples were characteriz...In this paper a polyaluminum chloride solution with high Al13 content was prepared and used as raw material for preparation ofγ-Al2O3.The texture and crystalline phase of the prepared alumina samples were characterized by energy dispersive X-ray spectroscopy(EDX) ,X-ray diffraction,transmission electron microscope(TEM) and nuclear magnetic resonance(NMR) analyses.The effects of alkaline solution and calcination temperature were investigated.The results showed that alkaline solution including NH3·H2O and NaOH had little effect on the alumina sample formation.The impurities of NH4Cl and NaCl in solution can be removed through repeated washing by EDX analysis.Calcination temperature had a significant effect on alumina crystal phase.The alumina sample can transform completely toγ-Al2O3 in the subsequent heating from 600°C to 800°C.It is very interesting that Al13 can be existed inγ-Al2O3 phase even after calcinations.The results indicate that polyaluminum chloride with high Al13 content is an effective material to prepareγ-Al2O3.展开更多
Al 13 or Alb is usually regarded as the most efficient species of polyaluminum chloride(PAC), the performance flocculant for water treatment. This paper was intended to report a new method to synthesize PAC with hig...Al 13 or Alb is usually regarded as the most efficient species of polyaluminum chloride(PAC), the performance flocculant for water treatment. This paper was intended to report a new method to synthesize PAC with high content Al b, by using the membrane reactor. NaOH solutions were managed to permeate slowly through the micropores of ultrafiltration membrane into AlCl 3 solutions under the suitable transmembrane pressure(TMP). Meanwhile NaOH drops size was limited to nano scale, resulting in dramatical reduction of the characteristic diffusion time and great increment of contact interface between the strong base and Al ions in solution to favor the formation of Al(OH) - 4, the precursor of Al 13 , so few precipitates and much Al b are produced. When the initial concentration of AlCl 3/NaOH is 0 40/2 0 (mol/L), MWCO =10000, TMP =0 0085 MPa, T =305 K and B (molar ratio of OH -/Al 3+ )=2 25, the quantity of Al b attains about 80%. The results of 27 Al NMR determination showed that the Al 13 content is equal to Al b content. And our PAC product has shown better flocculation effects than the commercial product.展开更多
A polyaluminium chloride solution with high Al 13 content self-prepared was used as material for preparing the spherical γ-Al 2 O 3 by the sol-gel and oil-drop method. Polyethylene glycol with different molecular mas...A polyaluminium chloride solution with high Al 13 content self-prepared was used as material for preparing the spherical γ-Al 2 O 3 by the sol-gel and oil-drop method. Polyethylene glycol with different molecular mass was used as surfactant to investigate the effect on property of γ-Al 2 O 3 . The physical property was characterized by 27 Al NMR (nuclear magnetic resonance) spectra, X-ray diffraction, FT-IR (Fourier transform infrared spectroscopy) and TG-DTA (thermogravimetric-differential thermal analysis). The results showed that surface area, pore volume and pore size of γ-Al 2 O 3 all increased with the increase of polyethylene glycol molecular mass in the experimental research range, and polyethylene glycol 10000 was the most suitable pore forming additive. γ-Al 2 O 3 with surface area of 339 m 2 ·g 1 , pore volume of 0.59 cm 3 ·g 1 and pore diameter of 6.9 nm were obtained at 450 °C.展开更多
Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the poten...Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the potential solution of using polyaluminum chloride(PAC)in the water jet.The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area.The experimental results showed that the optimal PAC dose was found to be 0.75 g/L.Compared with the test conditions without the addition of PAC,the presence of PAC leads to a reduction in volume,lower characteristic turbidity,smaller diffusion velocity,and shorter settling time of the plume.This indicates that PAC inhibits the entire development process of the plume.The addition of PAC leads to the flocculation of mm-sized particles,resulting in the formation of cm-sized flocs.The flocculation of particles decreases the rate of erosion on the seabed by around 30%.This reduction in erosion helps to decrease the formation of plumes.Additionally,when the size of suspended particles increases,it reduces the scale at which they diffuse.Furthermore,the settling velocity of flocs(around 10^(-2) m/s)is much higher that of compared to sediment particles(around 10^(-5) m/s),which effectively reduces the amount of time the plume remains in suspension.展开更多
In this paper,cement and dechlorinated Polyaluminum Chloride Residue(PACR)have been used to prepare a net slurry and mortar specimens.Two hydration activity indicators have been used to quantitatively analyze the dech...In this paper,cement and dechlorinated Polyaluminum Chloride Residue(PACR)have been used to prepare a net slurry and mortar specimens.Two hydration activity indicators have been used to quantitatively analyze the dechlorinated PACR hydration activity.In particular,the effect of dechlorinated PACR content on the compressive strength of mortar has been assessed by means of compressive strength tests.Moreover,X-ray diffraction(XRD)and scanning electron microscopy(SEM)have been employed to observe the microstructure of the considered hydration products.The following results have been obtained.The 28th day activity index of the dechlorinated PACR is 75%,and therefore it meets the criterion for the use of active admixture.The increase in the content of the dechlorinated PACR tends to reduce the compressive strength of mortar specimens,however,it is beneficial to its later strength growth.When the content is not greater than 10%,the strength remains unchanged,otherwise,it decreases.The PACR does not form a new crystalline phase in the cement slurry,and the dechlorinated PACR remains active until the age of the 28th day.The inclusion of the PACR mainly deteriorates the early strength of the cement slurry,but it promotes the production of hydration products in the cement slurry after the 7th day.展开更多
基金Supported by the National High Technology Research and Development Program of China (2009AA063901)the Special Funds for Technological Development of Research Institutes from the Ministry of Science and Technology of China(2010EG111022, 2011EG111307)+1 种基金the Budding Program (2011A-12-L)the Program for Innovative Research Team(IG201204N) of Beijing Academy of Science and Technology
文摘Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc- culation with polyaluminum chloride. The compensatory effect of slow-mixing on coagulation performance fol- low!ng inadequate_or excessive rapid-mi_xing was also examined. It is found that slowTmixing intensity has a more marked positive ettect on charge neutralization coas;ulatlon tlaan on sweep tlocculatlon. llle optimal root-mean- square velocity gradient, G, for slow-mixing is 15 s-＇ for both coagulation mechanisms, and charge neutralization coagulation requires a longer slow-mixing duration. The optimal slow-mixing duration, based on residual turbidity,is longer than the time to tbrm the largest mean Ilocs. The optimal product of G and mixing duration, GT, lbr slow-mixing during charge neutralization coagulation （13500） are higher than that during sweep flocculation （4500） and both are less than the range of values recommended by the American Water Works Association （24000-84000）.The optimal GT value under various slow-mixing conditions increases with G. Appropriate extension＇of slow-mixing duration during charge neutralization coagulation can improve coagulation performance after an inadequate or excessive rapid-mixing duration, but during sweep flocculation, appropriate shortening of slow-mixing duration after an excessive rapid-mixing or appropriate extension of slow-mixing duration after an inadequate rapid-mixing is favorable.
基金Supported by the Special Funds of Technological Development for Scientific Research Institutes from the Ministry of Science and Technology of China(2010EG111022,2011EG111307,2012EG111122)the Program for Overseas Talents(OTP-2013-015)the Program for Innovative Research Team(IG201204N)from Beijing Academy of Science and Technology
文摘Coagulation mechanisms of polyaluminum chloride(PACl) at various dosages were studied using a conventional jar test at different final and initial pH values during treating kaolin suspension. The optimal final pH and dosages for PACl were obtained based on residual turbidity and zeta potential of flocs. The coagulation zones at various PACl dosages and solution p H values were developed and compared with those of alum. It is found that the optimal mechanism under acidic condition is charge neutralization, while alkaline condition will facilitate the coagulation of PACl. Both charge neutralization coagulation and sweep coagulation can achieve high coagulation efficiency under the alkaline condition ranging from final p H 7.0 to 10.0. Stabilization, charge neutralization destabilization, restabilization and sweep zones occur successively with increasing PACl dosages with the final p H values fixed at 7.0 and 8.0, but restabilization zone disappears at final p H 10.0. When the final p H is not controlled and consequently decreases with increasing PACl dosage, no typical sweep zone can be observed and the coagulant efficiency decreases at high PACl dosage. It seems that the final pH is more meaningful than the initial p H for coagulation. Charge neutralization coagulation efficiency is dominated by zeta potential of flocs and PACl precipitates. The charge neutralization and sweep coagulation zones of PACl are broader in the ranges of coagulant dosage and p H than those of alum. The results are helpful for us to treat water and wastewater using PACl and to understand the coagulation process of PACl.
基金supported by the Taishan Scholar Program (No.ts 201511003)the National Natural Science Foundation of China (No.51478250).
文摘Copper oxide nanomaterials have been extensively applied and can have serious impacts when discharged into the aquatic environment, especially when complexed with humic acid(HA) to form composite contaminants.As an innovative recycled coagulant aid,Enteromorpha polysaccharides(Ep) were associated with polyaluminum chloride(PACl)(denoted as PACl-Ep) to simultaneously remove CuO nanoparticles, Cu2+and HA in this study.The influence of different Al species coagulants(AlCl3, PAClb and PAClc) and water pH on coagulation performance, floc properties and reaction mechanisms was investigated in detail.Results showed that in the three PACl-Ep systems, PAClb-Ep gave the highest removal efficiencies for turbidity and Cu2+, and the best UV254 removal effect was reached by using PAClc-Ep.Higher contents of Alb and Alc contributed to great coagulation performance because of their stronger bridging and sweeping effects.For all the Al species coagulants, alkalescent conditions were more conducive to removing Cu and HA compared to acidic conditions.Additionally, smaller and more agminated flocs with great recovery ability were formed by PAClb-Ep and PAClc-Ep systems(bridging and enmeshment effects cooperated with the chelated reticular structure formed by the Ep and Al species).Similarly,due to the increased hydrolysis and hydroxide precipitates, flocs formed under the condition of alkalescence were smaller, denser and stronger compared with weakly acidic conditions.
文摘Compared with traditional aluminum salts, polyaluminum chloride （PACI） has better coagulation-flocculation performance in turbidity removal. However, it is still inferior to organic polymers in terms of bridging function. In order to improve the aggregating property of PACl, different composite PACl flocculants were prepared with various organic polymers. The effect of organic polymer on the distribution or Al（Ⅲ） species in composite flocculants was studied using ^27TAl NMR and Al-ferron complexation methods. The charge neutralization and surface adsorption characteristics of composite flocculants were also investigated. Jar tests were conducted to evaluate the turbidity removal efficacy of organic polymer modified composite flocculants. The study shows that cationic polymer and anionic polymer have significant influences on the coagulation-flocculation behaviors of PACl. Both cationic and anionic polymers can improve the turbidity removal performancc of PACl but the mechanisms arc much different： cationic organic polymer mainly increases the charge neutralization ability, but anionic polymer mainly enhances the bridging function.
基金supported by the National High Technology Research and Development Program (863) of China (No.2007AA06Z339, 2009AA062901, 2008AA06A414)the National Natural Science Foundation of China (No.50978245, 21076219)
文摘A method of direct contact membrane distillation （DCMD） with a self-made hollow polyvinylidene fluoride membrane was applied to prepare high concentration polyaluminum chloride （PACl） with high Alb content based on chemical synthesis. The permeate flux and Al species distribution were investigated. The experimental results showed that the permeate flux decreased from 14 to 6 kg/（m2·hr） at the end of the DCMD process, which can be mainly attributed to the formation of NaCl deposits on the membrane surface. The Alb content decreased slightly, only from 86.3% to 84.4%, when the DCMD experiment finished, correspondingly the Alc content increased slightly from 7.2% to 8.5%, and the Ala content remained at 7% during the whole DCMD process. A PACl with Alb content of 84% at total aluminum concentration 2.2 mol/L was successfully prepared by the chemical synthesis-DCMD method.
基金supported by the National Natural Science Foundation of China (No 50708109, 20577061,40673003)the National Hi-Tech Research and Develop-ment Key Program (863) of China (No 2007AA06Z339)the Special Fund from the State Key Laboratory of Environmental Aquatic Chemistry (No 09Y02ESPCR,09Z01ESPCR)
文摘A novel membrane distillation concentration method was used m prepare high concentration polyaluminum chloride （PAC1） with high content of AID or Ale. 2.52 mol/L PACl1 with 88% Alb and 2.38 mol/L PACl2 with 61% Ale were successfully prepared. Three coagulants, AlCl3, PACl1 and PACl2 were investigated on their hydrolysis behavior and speciation under different conditions. The effects of pH and dilution ratio on Al species distribution were investigated by ferron assay. Experimental result showed that pH had a significant effect on Al species distribution for the three coagulants. Dilution ratio had little effects on Alb and Alc distribution in whole dilution process except the beginning for PACl1 and PACl2. The results indicated that transformation of Al depends largely on their original composition. AlCl3 was the most unstable coagulant among these three coagulants during hydrolysis process. PACl1 and PACl2 with significant amounts of highly charged and stable polynuclear aluminum hydrolysis products were less affected by the hydrolysis conditions and could maintain high speciation stability under various conditions.
基金Supported by National Natural Science Foundation of China（50708109 21076219） the National High Technology Research and Development Key Program of China（2007AA06Z339 2009AA062901）
文摘A direct contact membrane distillation（DCMD）process was applied to prepare high concentration polyaluminum chloride（PACl）with high Alc content.The changes in total Al concentration（AlT）and Al species distribution were investigated.The results showed that AlT increased but the flux decreased with operating time during the DCMD process.The Alc content increased from 65%to 81%while the Alb content decreased from 34% to 18%,and the Ala content was almost 1%in the process.2.1 mol·L 1PACl with 81%Alc was successfully prepared by DCMD method.Thus the DCMD is an effective method for preparing high concentration PACl with high Alc content.
基金the Special Fund for the Technical Development of Scientific Research Institutionsfinanced by the Ministry of Science and Technology of the People's Republic of China(Nos.2011EG111307 and 2012EG111122)the Program for Overseas Talents of the Beijing Academy of Science and Technology(No.OTP-2013-015)
文摘The effects of polyaluminum chloride（PACl） hydrolysis prior to coagulation on both the coagulation zone and coagulation performance of a kaolin suspension were investigated by a novel jar test named the ＂reversed coagulation test＂.The tests showed that PACl hydrolysis prior to coagulation decreased the performance of charge neutralization coagulation in the case of short-time slow mixing（10 min;G = 15 sec-1） and increased the optimal dosage for charge neutralization and sweep coagulation.Moreover,the hydrolysis time had insignificant effects on the size and zeta potential of PACl precipitates and the residual turbidity of the raw water.However,PACl hydrolysis prior to coagulation and the size of PACl precipitates had a negligible effect on the performance of sweep coagulation.The results imply that,in practice,preparing a PACl solution with deionized water,rather than tap water or the outlet water from a wastewater treatment unit,can significantly save PACl consumption and improve the performance of charge neutralization coagulation,while preparing the PACl solution with tap or outlet water would not affect the performance of sweep coagulation.In addition,the optimal rapid mixing intensity appears to be determined by a balance between the degree of coagulant hydrolysis before contacting the primary particles and the average size of flocs in the rapid mixing period.These results provide new insights into the role of PACl hydrolysis and will be useful for improving coagulation efficiency.
基金Project(BE2015628)supported by Jiangsu Province Science and Technology Support Program,China
文摘Considering that Fe,Al elements in bauxite residue are active components for water purification,an effective polyaluminum ferric chloride(PAFC)coagulant derived from bauxite residue,with Fe2O3 content>5.1%,Al2O3%>6.5%,basicity>65%,was successfully prepared.The effect of as-prepared PAFC on the zeta potential for printing and dyeing wastewater was investigated.Comparing with polyferric chloride(PFC)and polyferric sulfate(PFS)for printing and dyeing wastewater treatment,prepared bauxite residue-based PAFC exhibited the optimal performance in the aspects of chromaticity and chemical oxygen demand(COD)removal rate.Furthermore,the combination of bauxite residue-based PAFC and PFS for synergy coagulation of such wastewater demonstrated an obvious positive effect.With the proportion between as-prepared PAFC and PFS to be 2.5:1,the COD of treated wastewater could be further reduced to meet the national level A standard of China,providing a promising route to solve the problem of substandard printing and dyeing sewage outfall by a simple coagulation strategy.
基金supported by the National Natural Sci-ences Foundation of China(No.50072042,20676016,21076024)
文摘Polyaluminum chloride was synthesized with a membrane reactor,in which NaOH was added into AlCl 3 solution through the membrane’s micropores to reduce the NaOH droplets size.The content of the most efficient species increased to about 80%.The process characteristics in the reaction （i.e.,flow velocity,pressure drop）,and membrane fouling and cleaning were investigated.The evolution of both flow velocity and pressure drop during the reaction were related to changes in species distribution and solution viscosity.The process characteristics were well interpreted in terms of the Bernoulli equation.After reaction,the membranes were recovered by cleaning with diluted hydrochloride acid.This study is crucial for process design and scale-up of membrane reactors.
文摘The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test method. The experimental results showed that the interaction between polysilicic acid characterized negative charge and hydrolyzed aluminum species result in a decrease of the charge neutralizing ability of PASiC, compared to PAC. The decrease has a close relationship with the basicity ( B ) and Al/Si molar ratio in PASiC. The less the B value and the Al/Si molar ratio, the lower the charge neutralizing ability of PASiC is. In contrast, the preparation technique for PASiC affects the charge-neutralization of PASiC to a smaller extent. In addition, compared with PAC, PASiC may enhance aggregating efficiency and give better coagulating effects.
基金Supported by National Natural Science Foundation of China（50708109 40673003） the Scientific Research Foundation for the Returned Overseas Chinese Scholars State Education Ministry（ITLXHG2009071702） the Special Fund from the State Key Laboratory of Environmental Aquatic Chemistry（09Y02ESPCR）
文摘In this paper a polyaluminum chloride solution with high Al13 content was prepared and used as raw material for preparation ofγ-Al2O3.The texture and crystalline phase of the prepared alumina samples were characterized by energy dispersive X-ray spectroscopy(EDX) ,X-ray diffraction,transmission electron microscope(TEM) and nuclear magnetic resonance(NMR) analyses.The effects of alkaline solution and calcination temperature were investigated.The results showed that alkaline solution including NH3·H2O and NaOH had little effect on the alumina sample formation.The impurities of NH4Cl and NaCl in solution can be removed through repeated washing by EDX analysis.Calcination temperature had a significant effect on alumina crystal phase.The alumina sample can transform completely toγ-Al2O3 in the subsequent heating from 600°C to 800°C.It is very interesting that Al13 can be existed inγ-Al2O3 phase even after calcinations.The results indicate that polyaluminum chloride with high Al13 content is an effective material to prepareγ-Al2O3.
文摘Al 13 or Alb is usually regarded as the most efficient species of polyaluminum chloride(PAC), the performance flocculant for water treatment. This paper was intended to report a new method to synthesize PAC with high content Al b, by using the membrane reactor. NaOH solutions were managed to permeate slowly through the micropores of ultrafiltration membrane into AlCl 3 solutions under the suitable transmembrane pressure(TMP). Meanwhile NaOH drops size was limited to nano scale, resulting in dramatical reduction of the characteristic diffusion time and great increment of contact interface between the strong base and Al ions in solution to favor the formation of Al(OH) - 4, the precursor of Al 13 , so few precipitates and much Al b are produced. When the initial concentration of AlCl 3/NaOH is 0 40/2 0 (mol/L), MWCO =10000, TMP =0 0085 MPa, T =305 K and B (molar ratio of OH -/Al 3+ )=2 25, the quantity of Al b attains about 80%. The results of 27 Al NMR determination showed that the Al 13 content is equal to Al b content. And our PAC product has shown better flocculation effects than the commercial product.
基金Supported by the National Natural Science Foundation of China (21076219)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry (ITLXHG2009071702)
文摘A polyaluminium chloride solution with high Al 13 content self-prepared was used as material for preparing the spherical γ-Al 2 O 3 by the sol-gel and oil-drop method. Polyethylene glycol with different molecular mass was used as surfactant to investigate the effect on property of γ-Al 2 O 3 . The physical property was characterized by 27 Al NMR (nuclear magnetic resonance) spectra, X-ray diffraction, FT-IR (Fourier transform infrared spectroscopy) and TG-DTA (thermogravimetric-differential thermal analysis). The results showed that surface area, pore volume and pore size of γ-Al 2 O 3 all increased with the increase of polyethylene glycol molecular mass in the experimental research range, and polyethylene glycol 10000 was the most suitable pore forming additive. γ-Al 2 O 3 with surface area of 339 m 2 ·g 1 , pore volume of 0.59 cm 3 ·g 1 and pore diameter of 6.9 nm were obtained at 450 °C.
基金supported by the National Natural Science Foundation of China(Nos.52225107,U2106224,U1906234,51822904,and U1706223)the Fundamental Research Funds for the Central Universities(No.202041004)
文摘Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the potential solution of using polyaluminum chloride(PAC)in the water jet.The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area.The experimental results showed that the optimal PAC dose was found to be 0.75 g/L.Compared with the test conditions without the addition of PAC,the presence of PAC leads to a reduction in volume,lower characteristic turbidity,smaller diffusion velocity,and shorter settling time of the plume.This indicates that PAC inhibits the entire development process of the plume.The addition of PAC leads to the flocculation of mm-sized particles,resulting in the formation of cm-sized flocs.The flocculation of particles decreases the rate of erosion on the seabed by around 30%.This reduction in erosion helps to decrease the formation of plumes.Additionally,when the size of suspended particles increases,it reduces the scale at which they diffuse.Furthermore,the settling velocity of flocs(around 10^(-2) m/s)is much higher that of compared to sediment particles(around 10^(-5) m/s),which effectively reduces the amount of time the plume remains in suspension.
基金Henan Science and Technology Key Project,Research on Key Technology and Performance of Polyaluminum Chloride Residue(PACR)Concrete Preparation(202102310253)National Natural Science Foundation Project“Carbonization Strengthening of Recycled Coarse Aggregate and Its Influence on Mechanical Properties of Recycled Concrete Materials and Structures”(U1904188).
文摘In this paper,cement and dechlorinated Polyaluminum Chloride Residue(PACR)have been used to prepare a net slurry and mortar specimens.Two hydration activity indicators have been used to quantitatively analyze the dechlorinated PACR hydration activity.In particular,the effect of dechlorinated PACR content on the compressive strength of mortar has been assessed by means of compressive strength tests.Moreover,X-ray diffraction(XRD)and scanning electron microscopy(SEM)have been employed to observe the microstructure of the considered hydration products.The following results have been obtained.The 28th day activity index of the dechlorinated PACR is 75%,and therefore it meets the criterion for the use of active admixture.The increase in the content of the dechlorinated PACR tends to reduce the compressive strength of mortar specimens,however,it is beneficial to its later strength growth.When the content is not greater than 10%,the strength remains unchanged,otherwise,it decreases.The PACR does not form a new crystalline phase in the cement slurry,and the dechlorinated PACR remains active until the age of the 28th day.The inclusion of the PACR mainly deteriorates the early strength of the cement slurry,but it promotes the production of hydration products in the cement slurry after the 7th day.
