Non-ideal behaviour in counter-current in-pulp adsorption cascades

Van der Walt T.J. ; Van Deventer J.S.J. (1992)


A stimulation algorithm was developed which solves a set of differential mass balance equations in order to predict the dynamic behaviour of an adsorbent-in-leach cascade. The kinetics of the process are described by a fundamental model, which assumes that three reactions can take place in the adsorption stages., i.e. adsorption, leaching and preg-robbing. Film transfer is assumed to be the rate-controlling mechanism in adsorption. The simulator can predict the behaviour of a multi-component system with competitive adsorption at the surface of the adsorbent. The effect of certain process conditions such as carbon distribution through the cascade, mode of carbon transfer and quantity of carbon in the adsorption stages can be investigated. This algorithm is also capable of simulating the effects of mixing efficiency and adsorptive competition between gold and other adsorbates. The optimal distribution of adsorbent through a cascade is normally represented by an even distribution between stages, whereas this is not necessarily the case when leaching occurs simultaneously with adsorption. The efficiency of mixing is extremely important in the last stages, while mixing in the first stage should be merely adequate to maintain the pulp and adsorbent in suspension. Preg-robbing and the extent to which leaching still occurs in the cascade have a detrimental effect on the loss of adsorbate in the ore phase. Competitive adsorption yields higher soluble losses, but does not change the loading on the adsorbent product significantly. The mode of interstage transfer of adsorbent does not affect the loading on product adsorbent significantly. Fouling of the adsorbent (a decrease in adsorptivity) results both in higher soluble losses and lower loadings on the product adsorbent. © 1992.

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