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Measurement of pitch deposition by impinging jet microscopy: Effect of divalent salts.

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Lee, R and Stack, KR and Lewis, T and Garnier, G and Richardson, DE and Van de Ven, TGM (2010) Measurement of pitch deposition by impinging jet microscopy: Effect of divalent salts. In: 64th Appita Annual Conference & Exhibition, 18‐21 April 2010, Melbourne, Australia.

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Abstract

Papermakers for many years have had to contend
with the wood resins that are released during pulping
and papermaking. As paper mills reduce water
consumption by further process loop closure, there is
potential for the problems to increase. Accumulated
organic and inorganic material can lead to deposits
on machinery, poor process control, loss in
efficiency, and lower product quality. There are a
number of factors, which have an impact on the
deposition tendencies of colloidal particles as a result
of different inorganic materials or salts. Along with
the valency of the salt, the concentration of salt, the
properties of the colloidal particles, and the chemical
nature of the surface are important. Variations in
colloidal stability and deposition are observed even
for salts of the same valency.
With the use of impinging jet microscopy (IJM) the
deposition of pitch on to hydrophobic and
hydrophilic model surfaces was measured and the
effect on the rate of deposition was quantified with
changing cation. On both model surfaces the pitch
deposition was seen to be slightly faster when
calcium at 800 mg/L was present than magnesium at
the same concentration. This concentration is around
twice the critical coagulation concentration. The
concentration of calcium in process water in some
paper mills can be 200 – 300 mg/L. With further
process loop closure this could rise to levels being
investigated in this study. The concentration of
magnesium would normally be much lower than this
unless magnesium based alkalis were to be used.
The rate of deposition onto the model hydrophobic
surface was far greater (up to a 2.5 times) than on the
hydrophilic surface for both salts. Contact angle
measurements inferred that in the air-surface
environment the hydrophobicity of the surface
doesn’t affect its affinity for neat pitch suggesting
that the pitch may be reforming on the surface. IJM
results show variation in the pitch shape on the model
surfaces. It is possible that molecular reorganization
of the components occurs at the surface and water
interfaces. On the hydrophilic surface the pitch
particle size for both salts is about 0.33-0.35 μm
while for the hydrophobic surface the particle size is
about 5 times more for the calcium salt than the
magnesium salt. Film thinning or spreading of the
pitch particles was observed to occur on the
hydrophobic surface with calcium and to a lesser
extent with magnesium salt. With time film thinning
will affect the chemistry expressed by the surface and
change the interaction of other process components in
the paper making process.

Item Type: Conference or Workshop Item (Paper)
Journal or Publication Title: 64th Appita Annual Conference Proceedings
Page Range: pp. 273-279
Date Deposited: 03 Mar 2011 02:00
Last Modified: 10 Sep 2013 05:27
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