Solid-Liquid Leaching

Definition Solid-liquid leaching is a basic operation to separate one or more components contained in a solid phase by a liquid phase or solvent. The components transferred from the solid to the luquid phase are called solutes,while the insoluble solid is called inert.

Important applications of the solid-liquid leaching in the food industry 1.Obtaining extracts from animal or vegetable materials:extraction of animal and vegetable oils (soybean, corn,and rice bran,rapeseeds, sunflower seeds) 2.Obitaining sugar(cane or beet) 3.Manufacturing tea and instant coffee 4.Separating useful ingredients from food processing waste and medicinal plants 5.Washing precipitates etc

Classification of leaching Physical leaching is a simple process to dissolve solute in the solvent.Water alcohol and other organic solvents often used as solvent in this process. Chemical leaching is a process to dissolve certain components by chemical reaction. Bacterial leaching is used to deal with some insoluble metallic ore.Transfering insoluble intermetallic compound to soluble compound by the oxidation of bacterium.

Steps of leaching Putting the solid material and the Solvent together. The separation of insoluble solids and Leaching solution. Reclaiming the soluble components that attached to the residue. Purification and concentration of the leaching solution. Recovering valuable solvents from the residue.

Pretreatment of leaching Comminution The purpose of this operation is to increase the leaching rate and the rate of leaching process. Drying This operation aim at improving the quality of leachate.

Leaching technology This type of operation may be performed in one or multiple stages,A stage refers to equipment in which the phases are in contact for a determined time,so that the mass transfer among the components of the phases are carried out,tending to equilibrium over time.Once the equilibrium is reached,a mechanical separation of phases is applied.

多级浸取工艺 单级浸取工艺

Leaching equipment The ways of operation used in extraction processes can be continuous or batch. Once or more stages can be employed for batch operation,with new solvent in each stage,or under countercurrent. A simple stage consists of an agitated mixer,where the solid and the solvent are in contact for atgiven time.then the mixture is transferred to a separator,where the phases,called extract and exhausted solids,are obtained after a specified standing time.The extraction and separation stages can be carried out in one piece of equipment instead of two;this type of equipment is called an extractor.

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