Colloids and Surfaces A: Physicochem. Eng. Aspects 251 (2004) 5–17 Precoat filtration of a deflocculated mineral suspension in the presence of a dispersant Eugene Vorobiev ∗ , Thomas Mouroko-Mitoulou, Zied Soua D´ epartement du g´ enie chimique, Centre de Recherches de Royallieu, Universit´ e de Technologie de Compi` egne, BP 20529, F-60205 Compi` egne cedex, France Received 2 February 2004; accepted 23 July 2004 Abstract This article presents the study of the filtration of an aqueous calcium carbonate suspension in the presence of dispersants in order to obtain filter cakes in the form of highly concentrated liquefied dispersions. Two methods were used in this investigation. The first method consisted of the filtration of a deflocculated (via dispersants) suspension (FDS). The second method involved a precoated filter cake that was initially formed from a free-dispersant suspension and then deflocculated by a dispersants suspension (DS) that was filtered through the precoat. Both methods allowed the liquefaction of the filter cakes after homogenisation. The precoat filtration of the deflocculated suspension (PFDS) nevertheless showed noticeable advantages compared to FDS. Precoat formed from a free-dispersant suspension resulted in the protection of the filtrate from molecules of the dispersant and from fine particles of the DS. The filter cake obtained by PFDS had lower specific resistance and liquefied at lower concentrations of the dispersant. The results of this study show that the PFDS process may be a new way of obtaining highly concentrated liquefied dispersions. © 2004 Elsevier B.V. All rights reserved. Keywords: Filtration; Dispersion; Surfactant; Deflocculated suspension; Precoat; Colloidal phenomena 1. Introduction Fluidity of dispersions with high solid content is highly desirable in many practical applications, such us ceramic pro- cessing or paper coating [10,11]. For example, concentrated calcium carbonate (CaCO 3 ) suspensions with 72–75 wt.% are widely used as a white pigment, and impart high bright- ness, gloss and good printability on coated paper. To decrease the viscosity and increase the fluidity of highly concentrated dispersions, the aggregation of solid particles must be pre- vented, and existing flocs should be broken by the addition of special chemical agents like surfactants, wetting agents, dispersants [6]. A well-known method that makes the lique- Abbreviations: DC, deflocculated cake; DS, deflocculated suspension; FDS, filtration of deflocculated suspension; PFDS, precoat filtration of de- flocculated suspension ∗ Corresponding author. Tel.: +33 3 44 23 52 73; fax: +33 3 44 23 19 80. E-mail address: eugene.vorobiev@utc.fr (E. Vorobiev). faction of highly concentrated dispersions possible involves a colloidal processing technique that uses dispersants as de- flocculation agents. This method consists of the rehydration of dry powder to form an aqueous suspension with a high solid loading (approximately 60 wt.%) in presence of disper- sants [5,12,20]. Another method that produces a concentrated aqueous mineral suspension involves the dehydration of an initially diluted suspension, from approximately 25–35 wt.% before dehydration to 65–75 wt.% after dehydration. The standard technique involves a thermal dehydration (spray drying to evaporate excess water) [21] that consumes consid- erable power. An alternative method involves the mechanical dehydration of a diluted suspension by pressure filtration, followed by filter cake re-dispersion in the presence of dis- persants [8]. The dispersing of highly dehydrated filter cake (70–74 wt.%) unfortunately requires a considerable amount of energy and special equipment, like jaw crushers and blade mixers [9]. This explains why recent patents [7,13,15] em- ploy filtration to obtain partly dehydrated filter cake, which 0927-7757/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2004.07.020