Leaching

Leaching is the process by which soluble constituents are dissolved and transported from solid materials by a moving liquid, typically water or another solvent. This percolation can occur naturally, as rainfall or groundwater moves through soil and rock, or it can be induced by human activities, such as irrigation, mining, or waste disposal.

In soils and agriculture, leaching describes the downward movement of dissolved nutrients and contaminants from the root zone. Factors that influence leaching include the amount and timing of rainfall or irrigation, soil texture and structure, organic matter content, and ion exchange capacity. Leaching can deplete soil nutrients, alter pH, and contribute to groundwater contamination if soluble substances reach aquifers. Management practices such as precise irrigation, timed fertilizer applications, soil amendments, and mulching aim to minimize unwanted leaching.

In the context of waste disposal, landfill leachate is the liquid that forms when water filters through waste and dissolves a range of organic and inorganic compounds. Leachate can contain nutrients, dissolved salts, metals, ammonia, and various organic pollutants, posing environmental and public health risks if not collected and treated properly. Engineering measures include liners, leachate collection systems, and on-site treatment or transport to treatment facilities.

In mining and hydrometallurgy, leaching is used to extract metals from ores. Chemicals such as cyanide or sulfuric acid dissolve target metals, enabling their recovery. There are various approaches, including heap, dump, in situ, and bioleaching, the latter employing microorganisms to facilitate mineral dissolution. Leaching processes require careful handling to manage environmental impacts and regulatory compliance.