ENHANCING PHOSPHATE REMOVAL BY COAGULATION USING POLYELECTROLYTES AND RED MUD

Phosphate removal by chemical precipitation remains the leading technology today. In this research, phosphate removal using polyaluminium chloride (PAC) alone and in the presence of polydiallyldimethylammonium chloride (PDADMAC) and red mud were investigated. The results showed that PAC was effective in phosphate removal by coagulation via charge neutralization and adsorption of polymeric hydroxyl complexes. For synthetic wastewater, the phosphate removal efficiency reached 94.6% and for raw wastewater, the total phosphorus removal efficiency was as high as 96.6%. PDADMAC was not efficient in removing phosphate when used alone, at dosages of 0.1-0.3 mg/L, and it had little effect on enhancing phosphate removal by PAC as a coagulation aid, even when the dosage of PDADMAC was increased from 0.1 mg/L to 2 mg/L. Red mud, a by-product of bauxite processing in the alumina manufacturing industry, served as "nuclei for coagulation" resulting in large, rapid-settling flocs. When 40 mg/L red mud was added, the phosphate removal efficiency of 3.18, 4.76 and 6.35 mg Al3+/L PAC increased by 15.1, 20.5 and 13.0%, respectively. Adsorption and desorption experiments of phosphate on flocs after coagulation showed that the addition of red mud not only decreased the required PAC dosage but also enforced the phosphate adsorption on flocs.Phosphate removal by chemical precipitation remains the leading technology today. In this research, phosphate removal using polyaluminium chloride (PAC) alone and in the presence of polydiallyldimethylammonium chloride (PDADMAC) and red mud were investigated. The results showed that PAC was effective in phosphate removal by coagulation via charge neutralization and adsorption of polymeric hydroxyl complexes. For synthetic wastewater, the phosphate removal efficiency reached 94.6% and for raw wastewater, the total phosphorus removal efficiency was as high as 96.6%. PDADMAC was not efficient in removing phosphate when used alone, at dosages of 0.1-0.3 mg/L, and it had little effect on enhancing phosphate removal by PAC as a coagulation aid, even when the dosage of PDADMAC was increased from 0.1 mg/L to 2 mg/L. Red mud, a by-product of bauxite processing in the alumina manufacturing industry, served as "nuclei for coagulation" resulting in large, rapid-settling flocs. When 40 mg/L red mud was added, the phosphate removal efficiency of 3.18, 4.76 and 6.35 mg Al(3+)/L PAC increased by 15.1, 20.5 and 13.0%, respectively. Adsorption and desorption experiments of phosphate on flocs after coagulation showed that the addition of red mud not only decreased the required PAC dosage but also enforced the phosphate adsorption on flocs

Study on the hydrolysis/precipitation behavior of Keggin Al-13 and Al-30 polymers in polyaluminum solutions

The hydrolysis/precipitation behaviors of Al3+, Al-13 and Al-30 under conditions typical for flocculation in water treatment were investigated by studying the particulates' size development, charge characteristics, chemical species and speciation transformation of coagulant hydrolysis precipitates. The optimal pH conditions for hydrolysis precipitates formation for AlCl3, PAC(A113) and PAC(A130) were 6.5-7.5, 8.5-9.5, and 7.5-9.5, respectively. The precipitates' formation rate increased with the increase in dosage, and the relative rates were AlCl3 >> PAC(A130) > PACA113. The precipitates' size increased when the dosage increased from 50 mu M to 200 mu M, but it decreased when the dosage increased to 800 AM. The Zeta potential of coagulant hydrolysis precipitates decreased with the increase in pH for the three coagulants. The isoelectric points of the freshly formed precipitates for AlCl3, PAC(A113) and PAC(A130) were 7.3, 9.6 and 9.2, respectively. The Zeta potentials of AlCl3 hydrolysis precipitates were lower than those of PAC(A113) and PAC(A130) when pH > 5.0. The Zeta potential of PAC(A130) hydrolysis precipitates was higher than that of PACA113 at the acidic side, but lower at the alkaline side. The dosage had no obvious effect on the Zeta potential of hydrolysis precipitates under fixed pH conditions. The increase in Zeta potential with the increase in dosage under uncontrolled pH conditions was due to the pH depression caused by coagulant addition. Al-Ferron research indicated that the hydrolysis precipitates of AlCl3 were composed of amorphous AI(OH)3 precipitates, but those of PACA113 and PACA130 were composed of aggregates of Al-13 and Al-30, respectively. Al3+ was the most un-stable species in coagulants, and its hydrolysis was remarkably influenced by solution pH. Al-13 and Al-30 species were very stable, and solution pH and aging had little effect on the chemical species of their hydrolysis products. The research method involving coagulant hydrolysis precipitates based on Al-Ferron reaction kinetics was studied in detail. The Al species classification based on complex reaction kinetic of hydrolysis precipitates and Ferron reagent was different from that measured in a conventional coagulant assay using the Al--Ferron method. The chemical composition of Al-a, Al-b and Al-c depended on coagulant and solution pH. The Al-b measured in the current case was different from Keggin Al-13, and the high Alb content in the AlCl3 hydrolysis precipitates could not used as testimony that most of the Al3+ Was converted to highly charged Al-13 species during AlCl3 coagulation. (C) 2009 Elsevier Ltd. All rights reserved

On the acid-base stability of Keggin Al-13 and Al-30 polymers in polyaluminum coagulants

The acid-base stabilities of Al-13 and Al-30 in polyaluminum coagulants during aging and after dosing into water were studied systematically using batch and flow-through acid-base titration experiments. The acid decomposition rates of both Al-13 and Al-30 increase rapidly with the decrease in solution pH. The acid decompositions of Al-13 and Al-30 with respect to H+ concentration are composed of two parallel first-order and second-order reactions, and the reaction orders are 1.169 and 1.005, respectively. The acid decomposition rates of Al-13 and Al-30 increase slightly when the temperature increases from 20 to ca. 35 A degrees C, but decrease when the temperature increases further. Al-30 is more stable than Al-13 in acidic solution, and the stability difference increases as the pH decreases. Al-30 is more possible to become the dominant species in polyaluminum coagulants than Al-13. The acid catalyzed decomposition and followed by recrystallization to form bayerite is one of the main processes that are responsible for the decrease of Al-13 and Al-30 in polyaluminum coagulants during storage. The deprotonation and polymerization of Al-13 and Al-30 depend on solution pH. The hydrolysis products are positively charged, and consist mainly of repeated Al-13 and Al-30 units rather than amorphous Al(OH)(3) precipitates. Al-30 is less stable than Al-13 upon alkaline hydrolysis. Al-13 is stable at pH < 5.9, while Al-30 lose one proton at the pH 4.6-5.75. Al-13 and Al-30 lose respective 5 and 10 protons and form [Al-13] (n) and [Al-30] (n) clusters within the pH region of 5.9-6.25 and 5.75-6.65, respectively. This indicates that Al-30 is easier to aggregate than Al-13 at the acidic side, but [Al-13] (n) is much easier to convert to Alsol-gel than [Al-30] (n) . Al-30 possesses better characteristics than Al-13 when used as coagulant because the hydrolysis products of Al-30 possess higher charges than that of Al-13, and [Al-30] (n) clusters exist within a wider pH range

Preparation and characterization of a cost-effective red mud/polyaluminum chloride composite coagulant for enhanced phosphate removal from aqueous solutions

10.1016/j.jwpe.2015.04.003Journal of Water Process Engineering6158-16

Adsorption of -Nitrophenol onto PDMDAAC-Modified Bentonites

A novel organobentonite was prepared by modifying bentonite with poly(dimethyldiallylammonium chloride) (PDMDAAC), a harmless and cost-effective type of polycation. Zeta potential and X-ray diffraction measurements suggest that PDMDAAC was intercalated into the bentonite interlayer space. PDMDAAC—bentonite has been found to be effective for the removal of p -nitrophenol with a removal rate of 81.4% being achieved. The adsorption process was pH-dependent and was slightly decreased by the Ca 2+ and Mg 2+ ions co-existing in the solution. A dual-phase adsorption mechanism was suggested for the process. The adsorbents obtained from the regeneration of PDMDAAC—bentonite still exhibit good adsorption capacities