沥滤是什么？

沥滤是什么？

通过溶解将物质从固体中除去，这叫作沥滤。
化学加工业用到沥滤，但这个过程通常被称作淬取，而且常常使用有机溶剂。因为沥滤被用在分离金属与矿石以及从甜菜中抽取糖方面已经有很多年，所以其理论和实践已得到高度发展。近来，环境工程师给于沥滤更大的关注，因为垃圾倾倒场和垃圾填埋场含有有害有毒废料。一种有毒化学品的自然分解有时产生一种毒性更强的化学品。从这些物质间流过的雨水会流入地下水、湖泊、河流、井、池塘等等。

还有英文参考资料：
Removal of materials by dissolving them away from solids is called leaching .（这是沥滤的概念）
The chemical process industries use leaching but the process is usually called extraction, and organic solvents are often used. The theory and practice of leaching are well-developed because for many years leaching has been used to separate metals from their ores and to extract sugar from sugar beets. Environmental engineers have become concerned with leaching more recently because of the multitude of dumps and landfills that contain hazardous and toxic waste. Sometimes the natural breakdown of a toxic chemical results in another chemical that is even more toxic .Rain that passes through these materials enters ground water, lakes, streams,wells, pond, and the like.

Although many toxic materials have low solubility in water, the concentrations that are deemed hazardous are also very low. Furthermore, many toxic compounds are accumulated by living cells and can be more concentrated inside than outside a cell. This is why long-term exposure is a serious problem; encountering a low concentration of a toxic material a few times may not be dangerous, but having it in your drinking water day after day and year after year can ge deadly.

Heap leaching is a countercurrent process where the solid is in a stationary heap and the solvent percolates through the solid. An example is a dump or landfill. In industrial leaching, solvent and solid are mixed, allowed to approach eqilibrium, and the two phase are separated. Liquid and solids move countercurrently to the adjacent stages. The solvent phase ,called the extract, becomes more concentrated as it contacts in stagewise fasion the increaseingly solute -rich solid. The raffinate becomes less concentrated in soluble material as it moves toward the fresh solvent phase.

The main theory of leaching neglects mechanisms for holding the materials on the solid. Although adsorption and ion exchange can bind materials tightly to solids, we will simplify the analysis and consider only dissolving a soluble solid. An example is removing salt from sand by extraction with water.