pH and Particle Structure Effects on Silica Removal by Coagulation

Hermosilla, Daphne; Ordóñez, Ruth; Blanco, Laura; Fuente, Elena; Blanco, Ángeles

doi:10.1002/ceat.201100527

Cited by 45 publications

(25 citation statements)

References 27 publications

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“…This fact can be explained by the competition between silica and the organic matter (mainly anionic) for the neutralizing capacity of the coagulant. This reverse relationship has also been described by D. Hermosilla et al (2012) [10]. Higher dosages of the coagulants were always more efficient in COD removal, however, the effect of high dosages on COD removal was more evident at pH 8.3 and 9.5, while at pH 10.5 it was less significant.…”

Section: -Results and Discussionsupporting

confidence: 72%

“…Previous studies have demonstrated that coagulation with aluminum salts is effective for the treatment of deinked paper mill effluents; however, the required dosages and the conductivity of the treated waters were very high [10]. Therefore, the process was neither economically nor chemically feasible.…”

Section: Introductionmentioning

confidence: 99%

“…Besides, when treated water is reused in other process stages, as the process conditions can change significantly, scaling problems could appear once again. Regarding corrective methods, there are many silica removal techniques proposed in the literature, but these are usually carried out during softening processes or by coagulation at high pH [10,11]. These techniques enable the treatment of large volumes of water with high removal rates at low costs, which is a prerequisite for its use in papermaking applications .…”

Section: Introductionmentioning

confidence: 99%

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Silica removal from newsprint mill effluents with aluminum salts

Latour

Miranda

Blanco

2013

Chemical Engineering Journal

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The main obstacle for the implementation of reverse osmosis (RO) in a treatment chain to reuse the effluent of a newsprint mill as fresh water is the high silica content of the water, which produces severe scaling on the membrane, thus, limiting its recovery. Coagulation is one of the preferred methods to reduce silica concentration. Five aluminum based coagulants have been tested at five dosages (500-2500 ppm) and three pHs (8.3, 9.5 and 10.5). All products showed their best efficiency at the highest dosage and pH, with the exception of alum, that was more efficient at intermediate dosages. A combination of a polyaluminum nitrate sulphate with a cationic quaternary polyamine (PANS-PA2), was the most efficient and versatile coagulant. It removed 97% of silica (5 ppm residual silica) at the optimal conditions (pH 10.5, 2500 ppm) and it was very efficient (76% silica removal) at pH 8.3, avoiding the need of any pH adjustment, and minimizing the conductivity and pH increase of the treated waters as well as obtaining some removal of the organic colloidal matter (≈25%).

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Section: -Results and Discussionsupporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Silica removal from newsprint mill effluents with aluminum salts

Latour

Miranda

Blanco

2013

Chemical Engineering Journal

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“…When the concentration of soluble silica exceeds its solubility, it precipitates on the membrane surface alone or with other products. In the case of colloidal silica, fouling occurs due to the accumulation of the colloids formed in the bulk solution, and accumulates on the membrane surface [16,17].Although there are many silica removal techniques proposed in the literature [18], it is usually carried out during softening processes or by coagulation at high pH [2,4,5,19,20].Coagulation with aluminum-based salts is very effective at ambient temperature, but high dosages (2500-5000 mg/L) are required to achieve high removal rates and the use of hybrid coagulants which increases considerably the treatment cost [4]. On the other hand, when silica removal is carried out during softening, it is necessary to ensure that enough hardness is present in the water.…”

mentioning

confidence: 99%

“…Although there are many silica removal techniques proposed in the literature [18], it is usually carried out during softening processes or by coagulation at high pH [2,4,5,19,20].…”

mentioning

confidence: 99%

Silica removal with sparingly soluble magnesium compounds. Part I

Latour

Miranda

Blanco

2014

Separation and Purification Technology

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The main bottleneck in the treatment and reuse of effluents from deinking paper mills that employ reverse osmosis (RO) is the high silica content, which causes membrane fouling that limits the recovery of the treatment. Silica removal with magnesium compounds enables to treat large volumes of water with high removal efficiencies at low cost. Although soluble magnesium compounds are efficient, their use is limited since they increase the conductivity in the treated waters. Therefore the use of sparingly soluble magnesium compounds might be a promising alternative. Three sparingly soluble magnesium compounds (MgO, Mg(OH)2 and (MgCO3)4·Mg(OH)2·5H2O) were studied in this paper at three pHs (10.5, 11.0 and 11.5) and five dosages (250-1500 mg/L) at ambient temperature (~20ºC). Only 40% silica removal was obtained, which is not high enough to work at regular RO recoveries without scaling problems. To increase silica removal, the slurries of sparingly soluble compounds were pre-acidified with concentrated sulphuric acid and tested at the same conditions. In this case, high removal rates were obtained (80-86%) at high pH (11.5), even at ambient temperature. These removal rates would allow working at 75-80% recovery in RO units without scaling problems. This pre-acidification, together with the use of Ca(OH)2 as pH regulator limited the increase of the conductivity of the treated waters to only 0.2 mS/cm. Additionally, the use of Ca(OH)2 instead of NaOH as pH regulator increased the chemical oxygen demand removal from 15% to 25%.Keywords: silica removal, magnesium, softening, pre-acidification, membrane, fouling, effluent reuse, paper recycling 2 1.-INTRODUCTIONPaper industry is one of the leading industries in water management and sustainable water use. Although different alternatives have been developed to optimize the use of water in papermaking, there are still some unresolved aspects that limit their implementation at industrial scale. The closure of water loops through the internal reuse of water is limited by the accumulation of contaminants, especially dissolved and colloidal material (DCM), which affects the paper machine runnability and the final product quality [1]. To further reduce water consumption it is therefore necessary to treat and reuse the paper mill effluents. Membrane treatments, such as ultrafiltration (UF) and reverse osmosis (RO) [2,3], allow to produce the water quality required to reuse the effluent. However, effluents from deinking paper mills are characterized by high silica content, ranging from 50 to 250 mg/L as SiO2 [2,4,5]. This makes the removal of silica a key factor for the reuse of the effluent to work on the RO membrane at recoveries higher than 20% [3] without scaling problems. Membrane fouling caused by silica is a bottleneck as silica scaling in RO membranes is severe and, once it is formed, it is very difficult to remove by chemical cleaning [6,7]. This scaling causes decline in water production rates, low permeate quality, unsteady-state operation conditions, higher ener...

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