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1

Rheological properties of calcium carbonate concentrated suspensions: effects of solid content and dispersant concentration

Papo A., Piani L.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

393-397

EN

The aim of the present work is to study the flow behaviour of calcium carbonate suspensions in order to determine the effectiveness of some commercial dispersing agents. Three commercial deflocculants were used: a sodium polyphosphate, a sodium salt of benzenedisulfonic acid, and a sodium polyacrylate. Calcium carbonate aqueous suspensions were prepared at various solid volume fractions (0.31 to 0.46). Rheological tests were carried out at 25oC by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. All the suspensions prepared without deflocculant show a rheological behaviour of the shearthinning type; good correlations between relative viscosity and shear rate data were found by applying the Quemada model. The application of both static and oscillatory techniques permitted to evaluate the efficiency of dispersing agents. The sodium polyacrylate proved to be the most effective deflocculant for calcium carbonate slurries; the highest efficiency of sodium polyacrylate can be explained on the basis of its polymeric nature.

2

Rheological models for calcium carbonate/ kaolin suspensions for papercoating applications

Papo A., Piani L.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

387-392

EN

The rheological behaviour of calcium carbonate/kaolin aqueous suspensions has been studied. The mixes were prepared with a vane stirrer at various solid volume fractions (0.32 to 0.43). The tests were carried out at 25oC by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. Flow curves were determined by varying the shear rate from 0 to 1000 s-1 at constant shear acceleration. All systems show shearthinning flow behaviour. Some rheological models which correlate relative viscosity with shear rate and solid volume fraction were taken into consideration with the purpose of selecting one model suitable for describing the shear-dependent behaviour of calcite/kaolin suspensions. The Eilers-Robinson equation written in a modified form was checked at any solid volume fraction. An excellent fitting of the experimental data was also performed with the Quemada equation.

3

Influence of dispersant nature and concentration on the rheological properties of kaolin suspensions

Papo A., Piani L.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

381-385

EN

The aim of the present work is to evaluate the effectiveness of some commercial dispersing agents employed for maximizing the solid loading of kaolin suspensions. Two commercial deflocculants were used: a sodium polyacrylate (Reotan L) and a sodium benzenedisulfonate (Tiron). Kaolin aqueous suspensions were prepared at various solid contents (40 to 55 wt%). Rheological tests were carried out at 25oC by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. All the suspensions prepared without deflocculant show a rheological behaviour of the shearthinning type. The slurries prepared with Tiron present the same flow behaviour as the plain suspensions, whereas the addition of Reotan L brings about a shearthickening behaviour above a critical deflocculant concentration. The application of oscillatory techniques permitted to evaluate more accurately the efficiency of the dispersing agents. The sodium polyacrylate proved to be more effective than the benzenedisulfonate as dispersant for kaolin slurries.