Polyaluminum Chloride Solution Research Articles

Physicochemical characterization and flocculation performance evaluation ofPAC/PMAPTACcomposite flocculant

AbstractA novel inorganic–organic composite flocculant was prepared with polyaluminum chloride (PAC) and poly(methacrylamido propyl trimethyl ammonium chloride) (PMAPTAC). To understand the physicochemical characterization of PAC/PMAPTAC and evaluate its flocculation efficiency, the interactions of PAC and cationic polymer were investigated, then the characterization and flocculation performance of PAC/PMAPTAC and PAC/Poly‐dimethyldiallylammonium chloride (PDMDAAC) were compared. The results showed that there were obvious interactions between PAC and cationic polymer in composite flocculant. The cationic polymer chain exhibited a coiled state in PAC solution, and the curly degree of PMAPTAC chain was lower than that of PDMDAAC due to the intermolecular association of methyl of PMAPTAC. The cationic polymer enhanced the charge neutralization ability of PAC and changed the aluminum hydrolysis polymerization species of PAC from low and medium polymeric species to high‐polymeric species. The flocculation sedimentation experiments turned out that the charge neutralization and bridging ability of PAC/PMAPTAC was higher than that of PAC/PDMDAAC, and the increase of molecular weight or content of PMAPTAC in PAC/PMAPTAC could enhance the charge neutralization and adsorption bridging ability simultaneously. The enhanced effects may come from the exist of polymer and the interactions between PAC and cationic polymer in composite flocculant.

Synthesis of beta zeolite with mesopores from a milk containing precursor and its performance in naphthalene isopropylation

The synthesis of micro-/mesoporous beta zeolite by employing a solid precursor was described and its activity in the isopropylation of naphthalene was tested. The precursor was prepared by spray-drying of a homogenous mixture of silica sol, polyaluminum chloride solution and acidophilus milk, the presence of the latter induced formation of mesopores. The volume of mesopores of the synthesized beta zeolites ranged from 0.13 to 0.6 cm3/g and strongly depended on the concentration of tetraethylammonium hydroxide (TEAOH) in the reaction mixtures at the hydrothermal synthesis. Micro-/mesoporous beta zeolites exhibit positive effects of mesopores on the naphtalene conversion in its isopropylation by isopropyl alcohol, by improving the availability of active sites. With an increasing volume of mesopores, the conversion of naphthalene proportionally increases from 12 up to 27% for the volume of mesopores 0.6 cm3/g, while the selectivity to isopropylnaphthalene decreases from 92 to 55–66% for beta zeolites with 0.15–0.45 cm3 of mesopores/g, followed by selectivity increase up to mesopore volume 0.6 cm3/g reaching 81% at conversion 27%. A yield of isopropylnaphthalene is increasing in the whole range, particularly when the volume of mesopores exceeds 0.4 cm3/g. A zeolite with the highest volume of mesopores provides 1.8 times higher yield of isopropylnaphthalene then a microporous beta zeolite without mesopores. The increasing conversion of naphthalene is accompanied by a decrease in the selectivity to isopropylnaphthalene for zeolites with a low volume of mesopores, but an increasing selectivity to isopropylnaphthalene in the case of zeolites with a volume of mesopores above 0.4 cm3/g. This unusual effect can be explained by the mesoporosity of zeolites. Mesopores improve the availability of active centers, so they react faster, but the by-products are also formed faster and later undesired reactions run more easily as active centers are gradually blocked by by-products. Zeolites with the largest pores provide not only better availability of active centers, but the reaction products can also leave the zeolitic phase more easily and undesirable reactions have less chance to occur. This method of micro/mesoporous beta zeolite synthesis is advantageous for its low cost.

Hydrolysis of polyaluminum chloride prior to coagulation: Effects on coagulation behavior and implications for improving coagulation performance

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 (10min; G=15sec−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.

Organics removal and protein recovery from wastewater discharged during the production of chondroitin sulfate

Bentonite, chitosan and polyaluminum chloride (PAC) were applied to treat wastewater discharged during the production of chondroitin sulfate and recover protein dissolved in the wastewater. The results showed that the combination of pH 9.00, 3-4 mL chitosan solution, 2 g of bentonite and 5 mL of 8% PAC solution per 100 mL of wastewater with a 4.0 h flocculation time were the optimal conditions for the recovery of protein and removal of total organic carbon (TOC) from wastewater. A pilot-scale test also was conducted, and 130 kg (dry weight) of sediment was obtained from 1.1 m(3) of discharged wastewater. This sediment contained abundant amino acids (proteins comprised 61% of the total sediment), after the recovery of protein, the dissolved TOC concentration in wastewater was decreased by approximately 80% and the residual wastewater could be readily disposed using a traditional activated sludge process.

The formation mechanism of Al 13 and its purification with an ethanol–acetone fractional precipitation method

The formation mechanism of Al 13 is discussed via the investigation of the distribution and transformation of Al 13 in the precipitate and in the solution during the preparation of polyaluminum chloride (PACl). After the NaOH is injected into the AlCl 3 solution, the monomeric Al a species reacts with OH − immediately to form the high-molecular-weight Al c species, which may exist either in the solution or in the precipitate, depending on the system temperature and the rate of base injection. Subsequently, the Al c species reacts with Al a to generate the medium-molecular-weight Al b species, i.e., Al 13. The Al 13 species can be separated and purified from PACl solutions with an ethanol–acetone fractional precipitation method. The results from ferron assay and liquid- and solid-state 27Al NMR show that the purity and the extraction yield of the extracted Al 13 depend on the initial Al 13 concentration. A higher Al 13 content in the initial PACl solution leads to higher Al 13 purity and to a higher extraction yield. A maximum purity of 99.5% for Al 13 can be achieved by the described ethanol–acetone precipitation method.

Purification and characterization of Al13 species in coagulant polyaluminum chloride

Nano-Al13 was separated and purified by four methods to investigate its characteristic, and was analyzed by Al-Ferron timed complexation spectrophotometer, 27Al-NMR (nuclear magnetic resonance), and transmission electron microscopy (TEM). Coagulation efficiency of nano-Al13, polyaluminum chloride (PAC), and AlCl3 in synthetic water were also investigated by jar test. The dynamic process and aggregation state of kaolin suspensions coagulating with nano-Al13, PAC, and AICl3 were also investigated. The experimental results indicated that the efficiency of gel column chromatography method was the highest for separating PAC solution with low Al concentration. Ethanol and acetone method was simple and could separated PAC solution with different Al concentrations, while silicon alkylation white block column chromatography method could separate PAC solution only with low Al concentration. The SO4(2-)/Ba2+ displacement method could separate PAC solution with high Al concentration, but extra inorganic cation and anion could be introduced into the solution during the separation. The coagulation efficiency and dynamic experimental results showed that nano-Al13 with a high positive-charged species was the main species of electric neutralization in coagulation process, and it could reduce the turbidity and increase the effective particles collision rate efficiently in coagulation process. Its coagulation speed and the particle size of coagulant formed were of greatest value in this study.

Separating method and dynamic processes of Nano-Al13

In order to investigate the characteristics of pure Nano-Al13, Nano-Al13 was separated and purified from a series of poly-aluminum chloride (PAC) solutions which had the same Al13 percentage but different total Al concentrations, by using column chromatography, ethanol-acetone resolving and SO2− 4/Ba2+ displacement. The Al13 species yield was characterized by Al-ferron timed complexation spectrophotometry and 27Al-NMR (nuclear magnetic resonance). The coagulation efficiency of Nano-Al13, PAC and AlCl3 in synthetic water was also investigated by Jar tests. The dynamic process and aggregation state of kaolin suspensions coagulating with Nano-Al13, PAC and AlCl3 were similarly investigated using a photometric dispersion analyzer 2000 (PDA2000). The experimental results indicated that the ethanol-acetone resolving method was simple and could separate the PAC solution at different concentrations, while column chromatography could separate PAC solutions at low concentrations. The SO4 2−/Ba2+ displacement method could separate PAC solutions at high concentrations. However, extra inorganic cation and anion could be added in the solution during separation. The coagulation efficiency and dynamic experimental results showed that Nano-Al13 with high positive-charged species was effective in removing turbidity and color. The dynamic process results showed that Nano-Al13 also had the best recovery capability after shearing compared with PAC and AlCl3 because the Nano-Al13 conformation is more effective in charge neutralization.

Characterization and separation of Al13 species using gel-filtration chromatography

A polyaluminum chloride (PAC) sample was prepared using a slow alkaline titration method. The Bio-Gel P-100 gel column chromatographic technique was used to separate and characterize the various forms of aluminum present in the prepared PAC solution. The effluents from a gel column were monitored using online chemical method: Al-Ferron timed complexation spectrophotometry and by 27Al nuclear magnetic resonance (NMR) spectroscopy. Effects of different experimental conditions such as eluent flow rate, ionic strength and pH on separation of Al13 were investigated. Experimental results indicated that molecule size exclusion was not the only parameter affecting the column chromatographic separation efficiency of Al13 but molecule charge as well. Reducing the eluent flow rate, increasing the ionic strength and suitable pH resulted in increase in the separation efficiency. Experimental results clearly indicated that by varying the experimental conditions, it is possible to produce pure Al13 species using a gel column chromatographic technique.