Accumulation of dissolved and colloidal material in papermaking—Application to simulation

Miranda, Rubén; Blanco, Ángeles; Negro, Carlos

doi:10.1016/j.cej.2008.09.014

Cited by 39 publications

(34 citation statements)

References 13 publications

(11 reference statements)

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“…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.…”

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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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Silica removal with sparingly soluble magnesium compounds. Part I

Latour

Miranda

Blanco

2014

Separation and Purification Technology

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“…This is in accordance with how the issue has sometimes been approached in the literature. 15,16 During regular operation, the residence time of fibers through each circuit would be less than 1 h and even less than 2 h for all three loops. However, because of the various dewatering stages and recirculation of water, the mean residence time of stickies, especially microstickies, would be higher.…”

Section: Introductionmentioning

confidence: 99%

Time Variations of Macrostickies and Extractable Stickies Concentrations in Deinking

MacNeil

Miranda

Monte

et al. 2010

Ind. Eng. Chem. Res.

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The stickies content, both macrostickies and stickies extractable in a solvent, was determined for samples taken at short time intervals from deinking lines, producing deinked pulp for newsprint production. The study was carried out at three mills on different continents, with each having a different source of recycled paper as raw material. The short-term variations in extractable stickies in the incoming raw material were quite extreme, with differences of 100% being seen within hours. Despite this, the final deinked pulp contained fewer sudden variations and had no correlation to the incoming stickies content. While the raw material appeared to affect the incoming stickies content, a well-optimized deinking line was able to buffer the raw material variability, and the final stickies content was more dependent on the deinking process. This result was seen for the two mills examined for this phenomenon, despite a different raw material supply. Macrostickies were found to exhibit the same tendencies, although with smaller and less sudden variations. However, the variations of macrostickies and extractable stickies never correlated, even when both were measured for the same pulp fraction, thus confirming that solvent extraction is not an appropriate method for the determination of macrostickies and is more a reflection of microstickies.

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“…The minimum water quality requirements that must be met in this process in order to avoid scaling, corrosion [24], biofouling, losses in retention aid efficiencies, and runnability problems in the paper machine [5] are shown in Table 1. Furthermore, water quality criteria must also consider health risks derived from the spread out of process water as aerosols that may reach workers.…”

Section: Introductionmentioning

confidence: 99%

“…Although water is recycled within the mill at a high level, a total closure of the water circuit is not recommended for graphic papers as there are some technical limitations due to the accumulation of contaminants inside the circuits (salts, dissolved and organic matter, micro-contaminants and microorganisms), which affect the production process and the paper quality [4,5].…”

Section: Introductionmentioning

confidence: 99%