Abstract
The minerals calcium carbonate and talc were filtered under various conditions of filtrate flow rate and suspension concentration, using constant rate conditions with the aid of a peristaltic pump to draw the filtrate. Cake concentrations of between 0.41 and 0.53 v/v for calcium carbonate and 0.19 and 0.26 v/v for talc were recorded. The mean sizes of the two different minerals were very similar, but the average specific resistances obtained from the experiments were 5.9 × 1010 and 7.4 × 1011 m/kg for calcium carbonate and talc, respectively. These results do not agree with what would be predicted from an analytical equation for permeability, such as Kozeny-Carman. In addition, discontinuities were observed in all cases on the curves of filtrate volume with time for the initial stage of filtration. This behaviour is attributed to retarded packing compressibility (RPC) complicating the analysis of the filter medium resistance. RPC is an important component in determining the filter cake resistance and its functionality with cake forming pressure. It is found that there are additional effects that enhance the resistance to permeation in different cake materials, which is not recognised in the standard analytical approaches. These complexities can be related to shape, polydispersity, or agglomeration within the material sample and not to the experimental equipment or procedure. Furthermore, a complete and straightforward methodology is presented in this work for investigating the significance, or otherwise, of medium resistance on the later stages of the filtration.
Highlights
Cake filtration is important in many processes
When using calcium carbonate, the relative standard deviation (RSD) varies from is a small point of inflection near the origin followed by a rapid rise in pressure, before the rate of about ±2.4% (0.09 v/v) to less than ±1% (0.21 v/v)
The measured heights, calculated cake concentrations, and RSD for both solid materials are shown in Table 3a,b where the RSD of the cake concentration is determined from the variation in cake height measurements over the five measured data points
Summary
Cake filtration is important in many processes. the analysis and design of filtration operations is still largely dependent on heuristics and experimentation. There are a number of advantages to use CRF over the alternative of constant pressure filtration (CPF). The CRF provides more reliable data at the start of the filtration that can help to determine a value for the filter medium resistance (Rm ). The reliability of this data is greater than what is normally obtained from the alternative CPF, where a negative intercept on the classical t/V plot used for data analysis is often found [5,6]
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