Cake Washing Research Articles

Slurry filtration and cake washing after the HCl-leach of magnesite and serpentine—continuous washing model

Four different ores of magnesite and serpentine were leached with hydrochloric acid to produce concentrated magnesium chloride liquors. The neutralized slurries were filtered at a constant pressure, and the cakes were washed with water. As for filtration, the mass balance was calculated based on magnesium analyses, while the Darcy-Ruth equation was used to investigate the kinetics and assess the specific resistance of cakes. As for washing, the mass balance and kinetics were accounted for in terms of a continuous mathematical model, which is compatible with the Moncrieff equation. This new model explains well the washing test results. Washing operations can be optimized only in economical terms, and a complete set of mathematical formulae was presented for the optimization procedure.

PARAMETER ESTIMATION IN CAKE WASHING

Abstract The uniform-film model for cake washing considers the cake to be composed of channels in which a stagnant film of solute-rich filtrate adheres to the surface of the channel. Two independent methods are presented for an unbiased evaluation of the uniform-film model parameters. The first is an iterative procedure which requires adjustment of only one model parameter, and the second is a direct analytical procedure based on the method of moments. Both require experimental data to identify the model parameters. Application of the two methods give wet-base porosities greater than unity which suggests that the experimental data used to determine the model parameters is beyond the domain of applicability of the uniform-film model.

Cycle Optimization Involving the Use of Filter Aids

ABSTRACT A method for optimizing the quantity of filter aid powders used In constant rate pumping operations In plate and frame, recessed plate, and leaf filters Is presented. In contrast to the usual assumption that there Is a fixed fraction of filter aid admix which yields the best results, we demonstrate that the optimum amount of filter aid varies with cake thickness, washing and dead times, and use of a membrane for expression or simply pressing out residual slurry In a filter press at the end of filtration. The specific problem treated in this paper relates to the adaptation of a constant rate pump to an existing filter equipped with cake squeezing membranes. The separation is limited by a specified pressure, and the maximum cake thickness Is fixed by the filter geometry. The optimum fraction of filter aid rises as cake thickness Increases.

Hydrodynamics of the cake washing process in filtering centrifuges

Washing the cake in industrial centrifuges is used widely in chemical engineering. This process is carried out most effectively in cylindrical filtering rotors in batch machines when using the filling method [i], a characteristic indication of which is the presence of a ring of liquid above the cake layer. In spite of the fact that the pressure at the cake surface has a marked influence on the rate and quality of the washing, up to the present time there are no accurate concepts in relation to the pattern of flow over the filtering medi~n. The solution to the Navier-Stokes equation as applied to similar problems in [2-4] remains ambiguous since, at assigned rotor angular velocities, flow and geometrical dimensions of the liquid ring, the angular velocity of the free surface is unknown~

Characterization and dewatering of Australian alumina trihydrate

This paper reports a study of the dewatering characteristics of Bayer alumina from three different processing plants. Particle characterization reveals that the surface area, exterior morphology, particle charge, and also the degree of hydration and temperature of dehydration, are similar for all three samples. However, significant differences in the pore size distribution of packed beds of particles are observed. The mercury intrusion porosimeter is shown to be a useful and versatile instrument for the simultaneous determination of surface area, particle size distribution and pore size distribution. The vacuum dewatering of alumina trihydrate filter cakes is shown to be influenced both by the particle size distribution of the feed slurry, and by the addition of anionic, cationic or nonionic surfactants to the cake wash water. Significant reductions in filter cake moisture content are obtained using all types of surfactant. The use of surfactants at concentrations much higher than typical industrial practice is also shown to result in further improvements in dewatering. The experimental results are interpreted in terms of the Laplace-Young equation for drainage from a saturated capillary.

Prediction of leaching and filtration performance of drum filters

The basic equations of filtration and cake washing are combined together to provide a complete model for a drum filter operating under floodwash conditions. The steady state operating data can be made to yield information on the performance of the unit under changing operating variables. For efficient washing of the cake the importance of vacuum, cake permeability and temperature control are indicated. Under floodwash conditions it is usually advantageous not to mix the feed pulp with excess wash water.

A structural model for filter cake washing

A mathematical model is developed to describe the washing performance of partially drained filter and centrifuge cakes. Washing experiments were carried out in vacuum and centrifugally drained beds and the experimental data compared with computed results from the model. The proposed model is compared with other models which have been used to describe the cake washing process.

Theoretical recoveries in filter cake reslurrying and washing

AbstractTheoretical equations and graphs are presented for filter cake reslurrying and washing with linear solute sorption.In the case of washing, the filter cake was represented by a model consisting of a number of mixing cells in series. Due to the complexity of the model, explicit algebraic solutions could not be obtained for countercurrent washing, but numerical data were generated using a computer.Practical application of the above is outlined.

Continuous filter cake washing performance

AbstractA previous report (1) has presented the derivation of new filter cake washing equations. This report presents the procedure for their application and contains an example of application to a specific batch washing system. It also presents the adaption of the equations to permit their use in predicting the performance of a continuous rotary‐drum filter.

A theoretical study of filter cake washing

A problem on filter cake washing assuming a geometrical model of the pore spaces, in which axial dispersion occurs in the flow channel and mass transfer through a resistance is taking place from the cross channels to the flow channel, is solved by deriving the differential equations and the auxiliary conditions corresponding to the geometrical model and solving the mathematical problem utilizing the Laplace transform and a method for its numerical inversion that utilizes positive values of the transform variable. The numerical results are checked by comparison with asymptotic expansions and by recalculating the results utilizing other values of the transform variable. The results are presented both numerically with four significant figures and graphically.

Filter cake washing performance

AbstractDifferential equations for a filter cake wash cycle are derived on the assumption that the wash liquor executes plug flow in the pores of the cake, with continuous mass transfer between the liquor and a boundary film of filtrate. These equations are solved and the solutions presented as performance charts. The solutions are compared with certain experimental results.

Liquid‐solid separation factors in hydrometallurgical leach circuit design

AbstractPractically all hydrometallurgical processes involve leaching of solids to dissolve valuable constituents. This usually is followed by a liquid‐solids separation before producing the final product. The liquid‐solids separation step requires careful investigation because: Soluble values must be recovered to a very high degree for economic purposes. Final liquor volume must be minimized to reduce capital and operating costs of later steps. Usually large amounts of gangue solids are associated with the digested pulp requiring care in minimizing wash volumes. The colloidal solids are strongly dispersed by retention times and pH conditions in leaching. This necessitates flocculation investigations to achieve desired results. Operation must be dependable under severe conditions of pH, abrasion, fast settling solids, temperature, etc. Equipment must have flexibility to allow efficient operation under even abnormal fluctuations. An appreciable percentage of initial investment is required for this portion of the plant. The two common liquid‐solids separation methods —countercurrent decantation and filtration with cake washing, are discussed. Investigation and correlation procedures for prediction of full scale results and design requirements are stressed. Emphasis is given to the influence of particle size distribution, temperature, pH, flocculation, repulping, solids concentration, and filter cake permeability.