Preparation of high concentration polyaluminum chloride with high content of Alb or Alc

A novel membrane distillation concentration method was used to prepare high concentration polyaluminum chloride (PACl) with high content of Al_b or Al_c. 2.52 mol/L PACl₁ with 88% Al_b and 2.38 mol/L PACl₂ with 61% Al_c 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 Al_b and Al_c 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.     

Al(Ⅲ) speciation distribution and transformation in high concentration PACl solutions

Effects of Al(Ⅲ) concentration and pH on the speciation of Al(Ⅲ) in polyaluminum chloride (PACl) solutions especially on the Al13 fraction were investigated. A series of PACl samples were prepared over the range of Al(Ⅲ) concentration from 0.01 to 2.0 mol/L with the B (OH/Al ratio) value from 1.0 to 2.5 by forced hydrolysis of AlCl3. The samples were characterized by ferron assay,pH and 27Al NMR. It was shown that the Al(Ⅲ) concentration had a dramatic effect on the hydrolysis processes and the species distribution of PACl was in relate to the decrease of pH. The fraction of Al species, Alb (or Al13) decreased and Alc increased with increase of total Al(Ⅲ) concentration. Under the condition of Al(Ⅲ) 2.0 mol/L, B = 2.5, the pH value was 2.73 and no Al13 could be detected. During diluting and aging, the species distribution evolved. The Al13 could then be detected again and the amounts increased with time. If the diluted samples were concentrated by freeze dry at -35℃ or heating at 80℃, the pH value and Al13 content would decrease with the increased concentration. It demonstrated that the key factor for formation of Al13 in concentrated PACl was pH value.     

Al(Ⅲ) speciation distribution and transformation in high concentration PACl solutions

Effects of Al（Ⅲ） concentration and pH on the speciation of Al（Ⅲ） in polyaluminum chloride （PACl） solutions especially on the Al13 fraction were investigated. A series of PACl samples were prepared over the range of Al（Ⅲ） concentration from 0.01 to 2.0 mol/L with the B （OH/Al ratio） value from 1.0 to 2.5 by forced hydrolysis of AICl3. The samples were characterized by ferron assay, pH and 27^Al NMR. It was shown that the Al（Ⅲ） concentration had a dramatic effect on the hydrolysis processes and the species distribution of PACl was in relate to the decrease of pH. The fraction of Al species, Alb （or Al13） decreased and Al0 increased with increase of total Al（Ⅲ） concentration. Under the condition of Al（Ⅲ） 2.0 reel/L, B = 2.5, the pH value was 2.73 and no Al13 could be detected. During diluting and aging, the species distribution evoIved. The Al13 could then be detected again and the amounts increased with time. If the diluted samples were concentrated by freeze dry at -35℃ or heating at 80℃, the pH value and Al13 content would decrease with the increased concentration. It demonstrated that the key factor for formation of Al13 in concentrated PACl was pH value.     

Effect of in-situ formed Al hydrates through long-term aging on enhanced particle destabilization by PACl coagulation

Aging of polyaluminum chloride (PACl) coagulants could significantly influence hydrolyzed Al speciation ruling coagulation performance. The goal of this study was to investigate Al species transformation through long-term aging and its impact on coagulation performance. Two kinds of commercial coagulants (PACl-1 and PACl-2) were stored for in-situ aging tests in six months to evaluate Al species variation with time and the performance of coagulation with natural turbid waters. The results showed that CaSO₄ precipitation easily occur in a commercial PACl coagulant with time as it contains SO₄^2? and Ca²⁺. It also activates the precipitation of gibbsite Al(OH)₃ in PACl with aging. Through 180 days aging, both monomeric Al (Al_a) and polymeric Al (Al_b) substantially transform into colloidal Al (Al_c) and precipitated for both PACl coagulants. At low turbidity (10 NTU), PACl-1 has a superior turbidity reduction rate than PACl-2, while PACl-2 performs a little better turbidity reduction at high turbidity (1000 NTU) regardless of aging time. With aging time, an obvious decrease in turbidity reduction for PACl-1 coagulation is observed at low turbidity of 10 NTU, while the improvement in turbidity reduction for PACl-2 coagulation by enhanced sweep flocculation can be achieved as Al_b mostly transform into Al_c after 150 days aging. It is concluded that dominant in-situ formed Al_c after a long time hydrolysis can improve PACl coagulation efficiency in turbidity reduction by enhanced sweep flocculation, especially for low turbidity water, but the increase in preformed Al_c in PACl would worsen particle destabilization after aging.     

Chemical species distribution and transformation in polyaluminum chemical solutions

The hydrolysis polymerization precipitation process of Al(III) was studied with pH titration method, and the prepared polyaluminum solutions were characterized by various experimental methods: acid depolymerization, timed complex-colorimetric procedure, ultrafiltration, X-ray diffraction and infrared absorption spectrum. The results showed that the chemical species transformation and distribution of Al(III) in the hydrolysis-polymerization process depended on B=(OH/Al) ratio, pH and other factors. By their structures, the chemical species can be divided into three categories of monomeric (Ala), polymeric (Alb), sol or gel precipitates (Alc) and the polymeric species may be further divided into three groups such as linear low polymer (Alb1), linear high polymer (Alb2) and high polymer with cyclic structure (Alb3). The nominal molecular weight of polymeric species obtained by ultrafiltration was about 1000-50000 and most of them failed into a range around 10000. A scheme for the chemical speciation model     

聚合铝形态分布特征及转化规律

采用多种实验方法,对Al(Ⅲ)的水解—聚合—沉淀反应特征及其转化规律、形态分布及规范分子量大小进行了研究,同时应用X-射线衍射光谱仪和红外光谱仪对聚合铝形态进行了表征。由研究结果似可推断,Al(Ⅲ)水解—聚合过程的形态转化过程为线型→环型→体型。其聚合形态分布取决于翔/铝比值或pH值以及其它因素。在一定羟/铝比值时,聚合铝溶液中可划分为三种类型的形态分布。提出了相应的形态转化模式来表达聚合铝的形态及转化规律。     

Interaction of PACIs with sulfate

This article discusses the influential factors on Al13 separation considering the interaction of sulfate with various polyaluminum chloride (PACI). The experimental results showed that the basicity (B = [OH]/[Al]), the concentration of PACI and Al/SO4 ratio exhibited significant roles in the PACI-sulfate reaction. It indicated that different species in various PACI underwent different reaction pathway with sulfate. The Alc, colloidal species,formed precipitation quickly with sulfate, while Alb, oligomers and polymers, underwent slow crystallization. And Ala,monomers, reacted with sulfate to form soluble complexes. The kinetic difference of reaction made it possible to realize the separation of Alb and further purification. The decrease of Ala resulted in the limit of ferron method wasalso mentioned.     

化学沉淀分离-置换法提纯Al13的工艺研究

采用AlCl₃溶液和Na₂CO₃粉末在不同温度下制备了不同浓度的聚合氯化铝(PACl). 以选定的中等浓度、高Al₁₃含量的PACl为原液,研究了Al₁₃与硫酸盐沉淀反应过程中SO₄/Al摩尔比、反应体系起始总铝浓度的影响以及Al₁₃硫酸盐与Ba(NO₃)₂置换反应过程中的Ba/SO₄摩尔比、超声、温度等因素的影响. 实验结果表明,在制备温度为50℃条件下,浓度在0.4～0.6　mol/L范围的PACl含有较高的Al₁₃. 沉淀分离反应的最佳SO₄/Al摩尔比为0.6∶1;生成的 Al₁₃硫酸盐沉淀物为正四面体状晶体. 在Al₁₃硫酸盐与Ba(NO₃)₂溶液置换反应过程中,Ba/SO₄的最佳摩尔比为1∶1,反应温度及超声作用对置换反应的影响较小;提高Ba(NO₃)₂的起始浓度可以得到相应较高浓度的纯化Al₁₃溶液. 所得Al₁₃纯度的统计平均值为92.1％.     

Al13形态在混凝中的作用机制

从铝的水解形态转化角度考察了铝盐在高碱度和高有机物浓度水体中的混凝行为.结果表明,铝盐的混凝效能是与混凝过程中的Al₁₃含量成正比.高投药量时氯化铝(AlCl₃)既可以有效调节水体pH值又能在混凝过程中原位水解产生较多的Al₁₃形态,因而混凝效能要高于聚合氯化铝(PACl).在铝盐混凝中,调节pH值到6～7之间可以控制铝形态分布从而达到提高混凝效能和减少残留铝的目的.在调节pH值强化混凝的方法中使用传统铝盐的效果要好于无机高分子絮凝剂.     

聚合氯化铝中Al_(13)形态水解稳定性的研究

采用聚丙烯酰胺凝胶柱层析法分离纯化聚合氯化铝(PAC)中的Al13形态,并采用Al-Ferron逐时络合比色法对比研究了Al13形态、PAC和Al13三种样品水解稳定性。研究结果表明Al13形态无论是对于稀释倍数、介质的pH值和水解时间都具有较高的水解稳定性,是给水和废水处理中的一种较为有效的Al形态。     

A novel method to synthesize polyaluminum chloride with a membrane reactor

Al13 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 Alb, by using the membrane reactor. NaOH solutions were managed to permeate slowly through the micropores of ultrafiltration membrane into AlCl3 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 AI ions in solution to favor the formation of Al(OH)4^-, the precursor of AI,3, so few precipitates and much Alb are produced. When the initial concentration of AlCl3/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 Alb attains about 80%. The results of ^27Al-NMR determination showed that the Al13 content is equal to Alb content. And our PAC product has shown better flocculation effects than the commercial product.     

新型絮凝剂聚合氯化铝钙中铝形态表征及钙含量测定

以Al2O3和CaCO3为原料经高温焙烧酸溶制备工艺合成新型高效絮凝剂——聚合氯化铝钙。采用Al-Ferron逐时络和比色法研究产品中的铝形态;络合滴定法研究钙含量。结果表明:焙烧工艺对钙含量的影响较大,酸溶工艺对钙含量的影响较小。在最佳配比条件下,生成的Alb为最佳;焙烧温度提高Ala、Alc含量减小,Alb含量增大;增长酸溶反应时间Alb含量减少;增加酸用量,Ala、Alc含量减少,Alb含量增大。     

Synchronous removal of CuO nanoparticles and Cu2+ by polyaluminum chloride-Enteromorpha polysaccharides: Effect of Al species and pH

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, PACl_b and PACl_c) and water pH on coagulation performance, floc properties and reaction mechanisms was investigated in detail. Results showed that in the three PACl-Ep systems, PACl_b-Ep gave the highest removal efficiencies for turbidity and Cu²⁺, and the best UV₂₅₄ removal effect was reached by using PACl_c-Ep. Higher contents of Al_b and Al_c 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 PACl_b-Ep and PACl_c-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.     

Preparation of high concentration polyaluminum chloride by chemical synthesis-membrane distillation method with self-made hollow fiber membrane

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 Al_b 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 Al_b content decreased slightly, only from 86.3% to 84.4%, when the DCMD experiment finished, correspondingly the Al_c content increased slightly from 7.2% to 8.5%, and the Al_a content remained at 7% during the whole DCMD process. A PACl with Al_b content of 84% at total aluminum concentration 2.2 mol/L was successfully prepared by the chemical synthesis-DCMD method.     

聚合氯化铝镁钛的制备及结构表征

为提高铝基复合混凝剂的混凝效果,以AlCl₃、MgCl₂、TiCl₄为原料,通过共聚反应制备出无机复合高分子混凝剂PCAMT（聚合氯化铝镁钛）,并探究其混凝机理.采用Ferron（高铁试剂）逐时络合比色法、红外光谱、X-射线衍射谱图、扫描电镜与能谱分析（SEM-EDS）、Zeta电位对产物的Al形态、结构形貌、组成及混凝机理进行分析.结果表明:①采用单因素试验法获得最佳合成条件,即反应温度为60 ℃,Mg/Al（摩尔比,下同）为0.5,Ti/Al（摩尔比,下同）为0.5,OH/（Al+Mg+Ti）（摩尔比,下同）为0.6.②形态分析表明,反应温度、Mg/Al、Ti/Al,OH/（Al+Mg+Ti）对Al的形态分布均存在影响.随着反应温度的升高,n（Ala）（Ala在Al的水解聚合形态中所占摩尔分数,下同）先减后增,n（Alb）（Alb在Al的水解聚合形态中所占摩尔分数,下同）先增后减,n（Alc）（Alc在Al的水解聚合形态中所占摩尔分数,下同）逐渐减小;随着Mg/Al的增大,n（Ala）先减后增,n（Alb）、n（Alc）为先增后减的趋势;随着Ti/Al的增大,n（Ala）逐渐增加,n（Alb）逐渐减少,n（Alc）先增后减;随着OH/（Al+Mg+Ti）的增大,n（Ala）逐渐减少,n（Alb）、n（Alc）逐渐增加.③通过红外光谱、X-射线衍射,确定了PCAMT的结构组成,表明PCAMT是一种—OH桥联的铝镁钛复杂无定型聚合物,含有Al—OH—Mg与Ti—O—Ti新基团以及形成了Mg_1.5Ti_1.25O₄、Mg_1.2Ti_1.8O₅、Al₃Ti₅O₂等共聚物.④扫描电镜与能谱结果表明,PCAMT呈紧凑的空间立体网状形貌结构,利于发挥吸附架桥、网捕卷扫作用.⑤由PCAMT投加量对Zeta电位的影响分析可知,低投药量的混凝过程中起主导作用的是电中和作用,高投药量PCAMT处理原水的混凝机制以吸附架桥和网捕卷扫作用为主.研究显示,AlCl₃、MgCl₂和TiCl₄通过共聚反应,可生成具有更高聚合度的无定型共聚物PCAMT,利于电中和、吸附架桥和网捕卷扫,具有较好的混凝效果.      

Hydrolyzed AI（Ⅲ） clusters： Speciation stability of nano-All3

Pure nano-Al13 and aggregates at various concentrations were prepared to examine the particle size e ect of coagulation with inorganic polymer flocculant. The property and stability of various species formed were characterized using Infrared, 27Al-NMR, photo correlation spectroscopy (PCS), and Ferron assay. Results showed that concentration and temperature exhibited di erent roles on the stability of Al13. The quantity of Alb species analyzed by ferron assay in the initial aging period corresponded well with that of Al13, which has been confirmed in a dimension range of 1–2 nm by PCS. Al13 solutions at high concentrations (0.5–2.11 mol/L) were observed to undergo further aggregation with aging. The aggregates with a wide particle size distribution would contribute to the disappeared/decreased Al13 basis on the 27Al-NMR spectrum, whereas a part of Al13 would still remain as Alb. At low concentrations, Al13 solution was quite stable at normal temperature, but lost its stability quickly when heating to 90°C.     

高Al13纳米聚合氯化铝的结构表征及混凝效果

采用AlCl36H2O和Na2CO3制备了聚合氯化铝(PAC),并采用SO42-/Ba2+沉淀-置换法分离提纯了其中的纳米Al13形态,应用27Al-NMR和XRD等现代实验技术对其中的Al13形态进行了分析表征,27Al-NMR结果表明,分离提纯后样品中的Al13含量明显高于PAC,XRD结果表明,Al13的衍射峰出现在2q角为5~25之间;混凝烧杯实验表明,纳米级PAC较传统的混凝剂AlCl3、Al2(SO4)3和PAC具有更好的除浊、脱色效果.     

Hydrolyzed Al(Ⅲ) clusters: Speciation stability of nano-Al13

Pure nano-Al13 and aggregates at various concentrations were prepared to examine the particle size effect of coagulation with inorganic polymer fiocculant. The property and stability of various species formed were characterized using Infrared, 27Al-NMR,photo correlation spectroscopy (PCS), and Ferron assay. Results showed that concentration and temperature exhibited different roles on the stability of Al13. The quantity of Alb species analyzed by ferron assay in the initial aging period corresponded well with that of Al13, which has been confirmed in a dimension range of 1-2 nm by PCS. Al13 solutions at high concentrations (0.5-2.11 mol/L)were observed to undergo further aggregation with aging. The aggregates with a wide particle size distribution would contribute to the disappeared/decreased Al13 basis on the 27Al-NMR spectrum, whereas a part of Al13 would still remain as Alb. At low concentrations,Al13 solution was quite stable at normal temperature, but lost its stability quickly when heating to 90°C.     

聚合氯化铝中纳米Al13形态的混凝效应

采用聚丙烯酰胺凝胶柱层析法分离纯化聚合氯化铝(PAC)中的Al13形态,用透光率脉动检测技术并结合絮凝效能和Zeta电位测定结果,对纳米Al13形态以及PAC、AlCl3絮凝过程中絮集物形成和增长的变化差异作了对比性研究.结果表明,混凝剂的不同铝形态分布在混凝过程中起着十分重要的作用.Al13形态是在絮凝过程中起电中和作用的主要形态,可以大大增加颗粒间的有效碰撞率,其凝聚速度和所形成絮集物颗粒大小在实验条件下呈现最大值.而对于PAC,其Alc含量较高,可起到吸附架桥和网捕卷扫作用,所以在低投加量表现出较快的絮体增长速率.     

无机-有机复合混凝剂处理夏季引黄水库水的对比研究

合成了具有不同Fe(Al)/聚二甲基二烯丙基氯化铵(PDMDAAC)质量比的无机-有机复合混凝剂PFC-PDMDAAC和PAC-PDMDAAC,并对夏季引黄水库水进行混凝处理.考察了复合比例、投药量、pH值和投加方式对浊度、有机物和叶绿素-a的去除效果;并通过混凝过程中形成絮体的Zeta电位的变化分析了2种混凝剂的混凝机理.结果表明,无机-有机复合混凝剂处理夏季引黄水库水的效果好于2种单独成分的复配使用;复合比例对PFC-PDMDAAC和PAC-PDMDAAC处理夏季引黄水库水的效果影响较大,Fe(Al)/PDMDAAC质量比为4:1,投药量为4mg/L时混凝效果最好;与无机混凝剂相比,复合混凝剂的最佳pH值范围较广,可在5.0~8.0的pH值范围内取得良好的混凝效果;2种混凝剂相比,PAC-PDMDAAC对浊度和叶绿素-a的去除效果较好,而PFC-PDMDAAC对有机物的去除效果更佳.