Microstructure and rheology of bentonite slurries containing multiple-charge phosphate-based additives

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Abstract

The multiple-charge phosphate-based additives affected the rheology of bentonite gels differently. The yield stress decreased with increasing concentration of additives. However for the triple-charge additives, PO4 3− and cyclic P3O9 3− the maximum extent of yield stress reduction was only about 50%. For the higher multiple-charge additives, P2O7 4−, P3O10 5− and (PO3 )17 the decrease was >95% where yield stress of <1 Pa was attained at high concentration. The cryo-SEM images of the bentonite gels under the influence of various phosphate additives showed similar microstructure as the untreated gels. An exception was that treated with 10 dwb% (NaPO3)17 where the microstructure showed evidence of structural collapse with more lying platelets facing up. A positive site per anion adsorption model for PO4 3− and the close proximity of charge sites was invoked to explain its poor performance in yield stress and viscosity reduction. The adsorption of PO4 3− on adjacent sites is not possible because of charge repulsion between the anions due their close proximity to explain the low adsorption. The number of positive sites per anion adsorption was larger for the higher multiple-charge additives such as 2 for P2O7 4− and 3 for P3O10 5− and a few more for the (PO3 )17 was responsible for their higher adsorption and this was responsible for the identical decreasing yield stress trend with additive concentration observed. The 6-member ring anion, P3O9 3−, adsorption is poor due to its low charge and bulky structure.

LanguageEnglish
Pages120-128
Number of pages9
JournalApplied Clay Science
Volume169
DOIs
Publication statusPublished - 1 Mar 2019

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Bentonite
Slurries
bentonite
rheology
Rheology
microstructure
Phosphates
Yield stress
phosphate
adsorption
Adsorption
Microstructure
Anions
anion
gel
Gels
Platelets
additive
viscosity
scanning electron microscopy

Cite this

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title = "Microstructure and rheology of bentonite slurries containing multiple-charge phosphate-based additives",
abstract = "The multiple-charge phosphate-based additives affected the rheology of bentonite gels differently. The yield stress decreased with increasing concentration of additives. However for the triple-charge additives, PO4 3− and cyclic P3O9 3− the maximum extent of yield stress reduction was only about 50{\%}. For the higher multiple-charge additives, P2O7 4−, P3O10 5− and (PO3 −)17 the decrease was >95{\%} where yield stress of <1 Pa was attained at high concentration. The cryo-SEM images of the bentonite gels under the influence of various phosphate additives showed similar microstructure as the untreated gels. An exception was that treated with 10 dwb{\%} (NaPO3)17 where the microstructure showed evidence of structural collapse with more lying platelets facing up. A positive site per anion adsorption model for PO4 3− and the close proximity of charge sites was invoked to explain its poor performance in yield stress and viscosity reduction. The adsorption of PO4 3− on adjacent sites is not possible because of charge repulsion between the anions due their close proximity to explain the low adsorption. The number of positive sites per anion adsorption was larger for the higher multiple-charge additives such as 2 for P2O7 4− and 3 for P3O10 5− and a few more for the (PO3 −)17 was responsible for their higher adsorption and this was responsible for the identical decreasing yield stress trend with additive concentration observed. The 6-member ring anion, P3O9 3−, adsorption is poor due to its low charge and bulky structure.",
keywords = "Bentonite, Microstructure, Phosphate, Polyphosphates, Pyrophosphate, Yield stress, Zeta potential",
author = "Mingyong Du and Jishan Liu and Peta Clode and Leong, {Yee Kwong}",
year = "2019",
month = "3",
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language = "English",
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T1 - Microstructure and rheology of bentonite slurries containing multiple-charge phosphate-based additives

AU - Du, Mingyong

AU - Liu, Jishan

AU - Clode, Peta

AU - Leong, Yee Kwong

PY - 2019/3/1

Y1 - 2019/3/1

N2 - The multiple-charge phosphate-based additives affected the rheology of bentonite gels differently. The yield stress decreased with increasing concentration of additives. However for the triple-charge additives, PO4 3− and cyclic P3O9 3− the maximum extent of yield stress reduction was only about 50%. For the higher multiple-charge additives, P2O7 4−, P3O10 5− and (PO3 −)17 the decrease was >95% where yield stress of <1 Pa was attained at high concentration. The cryo-SEM images of the bentonite gels under the influence of various phosphate additives showed similar microstructure as the untreated gels. An exception was that treated with 10 dwb% (NaPO3)17 where the microstructure showed evidence of structural collapse with more lying platelets facing up. A positive site per anion adsorption model for PO4 3− and the close proximity of charge sites was invoked to explain its poor performance in yield stress and viscosity reduction. The adsorption of PO4 3− on adjacent sites is not possible because of charge repulsion between the anions due their close proximity to explain the low adsorption. The number of positive sites per anion adsorption was larger for the higher multiple-charge additives such as 2 for P2O7 4− and 3 for P3O10 5− and a few more for the (PO3 −)17 was responsible for their higher adsorption and this was responsible for the identical decreasing yield stress trend with additive concentration observed. The 6-member ring anion, P3O9 3−, adsorption is poor due to its low charge and bulky structure.

AB - The multiple-charge phosphate-based additives affected the rheology of bentonite gels differently. The yield stress decreased with increasing concentration of additives. However for the triple-charge additives, PO4 3− and cyclic P3O9 3− the maximum extent of yield stress reduction was only about 50%. For the higher multiple-charge additives, P2O7 4−, P3O10 5− and (PO3 −)17 the decrease was >95% where yield stress of <1 Pa was attained at high concentration. The cryo-SEM images of the bentonite gels under the influence of various phosphate additives showed similar microstructure as the untreated gels. An exception was that treated with 10 dwb% (NaPO3)17 where the microstructure showed evidence of structural collapse with more lying platelets facing up. A positive site per anion adsorption model for PO4 3− and the close proximity of charge sites was invoked to explain its poor performance in yield stress and viscosity reduction. The adsorption of PO4 3− on adjacent sites is not possible because of charge repulsion between the anions due their close proximity to explain the low adsorption. The number of positive sites per anion adsorption was larger for the higher multiple-charge additives such as 2 for P2O7 4− and 3 for P3O10 5− and a few more for the (PO3 −)17 was responsible for their higher adsorption and this was responsible for the identical decreasing yield stress trend with additive concentration observed. The 6-member ring anion, P3O9 3−, adsorption is poor due to its low charge and bulky structure.

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KW - Phosphate

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