Harraz reported in 2016 that 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 wastes. 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, ponds, 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 be deadly.
- The main theory of leaching neglects mechanisms for holding the material 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 constituent away from an insoluble solid. An example is removing salt from sand by extraction with water.
- Countercurrent stage wise processes are frequently used in industrial leaching because they can deliver the highest possible concentration in the extract and can minimize the amount of solvent needed. The solvent phase becomes concentrated as it contacts in a stage wise fashion the increasing solute-rich solid. The raffinate becomes less concentrated in soluble material as it moves toward the fresh solvent stage.
The author concluded that:
In the most cases solution mining has a very high economic efficiency because:
 The investment costs are low. (We don‘t need a mine).
 The drilling of the bore holes are running costs.
 The demand of manpower is low.
 Solution mining can also used by difficult hydrogeological conditions.
 The first step of the potash mill (hot leaching) is in the underground. There are no costs for this equipment.
 Residue and high concentrated brine stays in the cavern, therefore there environmental burdens are low.
ï± If the geological and technical conditions are very difficult, the solution mining is not usable.
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