Change of filtration properties of coal flotoconcentrate subjected to the centrifugal filtration after flocculant sonication

Abstract

Vacuum filtration is widely used in dehydration of the coal flotoconcentrate. Inspite of the application of flocculants, it gives post-filtration suspension humidity of ca. 27-28%. Suspension humidity may be significantly decreased as a result of the centrifugal filtration. Investigated flotoconcentrate suspension contained ca. 31% of solids and its density was ca. 1087 [kg/m3]. Flocculant Magnafloc 336 was added to the suspension in a proportion 70 g/l Mg of dry product. During the simultaneously performed investigation on vacuum filtration ([4]) it was shown that applied dosage is too small. Therefore, an additional flocculant portion of 40 g/l Mg of dry product is advisable. It enables one to obtain a product of less humidity. It was also stated that, in comparison to a nonsonicated flocculant, a treatment of the additional dosage by an ultrasound field of 20 [kHz] for 6 [s] results in an additional effect of dehydration. Investigations of the centrifugal filtration were carried out for the following parameters of a laboratory centrifuge: tau = 5-30 min, a/g = 251.3-1969.9. Investigation series for given suspension (without additional flocculant, addition of 40 g/l Mg and sonicated addition of 40 g/l Mg) included 7 centrifugation times and 6 values of the multiplication coefficient. It means 42 measurement points. All examinations were carried out for the same filtration cloth PT-912. Empirical triparametric correlations w(pl) = f (a/g,tau) were developed. The value of R-2 of the correlation is not lower than 0.9443 for investigated suspensions. Moreover, particle size distribution as well as sedimentation tests of examined suspensions were performed. It was stated that although addition of the extra flocculant dosage causes the decrease of humidity of the filtration cake significantly as a result of centrigugal filtration, the sonication of the flocculant was beneficial for final dehydration, however the changes were less noticable. For the most important working parameters of the centrifuge, i.e. a/g = 1970 and tau = 1800 s, for sonicated flocculant Magnafloc addition w(pl) approximate to 16.5% was obtained. Physical explanation of the flocculant sonication effect is a formation of smaller but more stable aggregates and the considerably lower amount of micrograins in comparison to a technological suspension. This suggestion is confirmed not only by sedimentation tests and grain analyses, but also by other coal flotoconcentrate investigations published in [7, 10], considering an influence of the flocculate sonication on w(pl) during the pressure filtration