Study of citric acid dispersant in the settling behavior of slate powder suspensions

•The areas of extraction can be seen by the map in the state of Minas Gerais — Brazil.•The paper provides a characterization of slate similar as the one used on our paper.•The authors are reference in Brazil about slate studies showing the situation of it in Brazil and the world.

The behavior of aqueous suspensions of slate stabilized with citric acid was investigated using sedimentation and rheological techniques. In order to determine the more effective dispersing agent concentration and the maximum loading of solids, a series of 12 suspensions were prepared with citric acid content between 0.5 and 2.5% w/v and solid percentages of 40, 55 and 70%. Light scattering techniques were used to obtain sedimentation data and particle size distribution; flow curves were obtained with a rheometer. The results indicated that the interaction between particle surfaces could either induce flocculation, at higher citric acid concentrations, or enhance the stabilization, at low dispersant concentration and pH values around 6. The highest sediment bed density was obtained for suspensions with 40% slate powder and 1.0% citric acid. This behavior was explained on the basis of the carboxyl groups of citric acid promoting higher dispersion of the particles resulting in lower settling rate, better stability and enhanced compact sediment bed.