Solid-liquid, suspension leaching

Dispersed-Solids Leaching Equipment for batch leaching of fine solids in a liquid suspension is now confined mainly to batch tanks with rotating impellers. For a detailed discussion of all aspects of the suspension of solid particles in fluids, refer to agitation of particle suspensions at the beginning of this subsection. 

Leaching has in the past been carried out mainly as a batch process although many continuous plants have also been developed. The type of equipment employed depends on the nature of the solid—whether it is granular or cellular and whether it is coarse or fine. The normal distinction between coarse and fine solids is that the former have sufficiently large settling velocities for them to be readily separable from the liquid, whereas the latter can be maintained in suspension with the aid of only a small amount of agitation. 

Batch leach experiments were performed on tailings material to determine the nature of contaminants distributed on sand and silt and clay-sized fractions. For the batch leach experiments, a mixture of tailings material was prepared using a chemical dispersant (sodium hexametaphosphate (NaPO ) ). The mixture was shaken and allowed to settle in covered beakers for sufficient time such that no particles with a diameter > 50 /im remained in suspension. The fines, which remained in suspension, represented the silt and clay-sized fraction of the samples. At the end of the settling period, the liquid was decanted from the beaker. The remaining sand-sized tailings were dried and transferred to a sealed vial. The decanted solution was passed through a 0.45 /im membrane filter, previously washed with distilled water, and the filtrate was collected and placed in a sealed container. The solids were dried and transferred to a sealed vial. The samples were then analyzed by instrumental neutron activation analysis. 

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