Leaching: what is it?

The term lixiviation is used in various fields which are essentially the chemistry, pharmacy and soil science. It relates to the techniques of extraction of soluble substances by a solvent and in particular by water. By slow percolating, the latter makes it possible to dissolve certain materials. The resulting liquid is called leachate.

It is for example by leaching that water can be charged with toxic substances. When it crosses polluted ground. This may be the case in an industrial wasteland, for agricultural soil laden with pesticides or even for a discharge of household waste. In the leachate, we can then find nitrates, dioxins or some heavy metals, especially. As long as this leachate is contained, no problem. But if thesealing of the site is not guaranteed, these products will escape to the groundwater, watercourses or surface aquifers.

Leaching to recover metals

In the mining sector, leaching is used to recover metals of value such as silver, gold or copper. In situ leaching, for example, aims to dissolve metals directly in the deposit. It contributes to a part of the world uranium production. Because it is relatively easy to implement, as long as the deposit in question is sufficiently permeable to allow good circulation of the leaching solution. Other techniques also exist, such as tank or column leaching or heap leaching. The latter can facilitate the extraction from minerals weakly concentrated.

Note that the terms leaching and leaching refer to different processes. Leaching – the word comes from the Latin lixivium meaning to wash -, let us remember, relates to the vertical dragging of soluble elements. This is the case of nitrates, for example. the leaching applies to insoluble solid particles only. This is the case of clays, especially.

We also speak of phytolixiviation techniques to designate methods which make it possible to extract heavy metals at the heart of sorts of filtering gardens.