Table 1 Operational mechanisms, advantages, and limitations of heavy metal removal techniques.

Physical remediation

 Surface capping

Physical containment

Easy to install, low in cost, high security

Limited to small areas and certain geographic locations, loss of land cropping function

³³

 Encapsulation

Physical containment and isolation

High security, fast to install

Limited to small, shallow contamination areas, high cost, loss of land cropping function

^{33, 34}

Chemical remediation

 Chemical leaching

Contaminant removal by chemical solutions, and mechanical separation

High efficiency, fast effects, low cost, simple to install; suitable for severely contaminated matrix; minimal physiochemical disturbance

Best for coarse-textured matrix with high permeability; use of leaching agents incorrectly can result in pollution

^{33, 35, 36}

 Chemical stabilization

Contaminant deactivation by physiochemical transformation

Low-cost, effective, and convenient

Metal-specific, pollutants cannot be removed thoroughly, temporary effectiveness

^{37, 38}

 Electrokinetic remediation

Contaminant removal by electricity

Contaminant removal, minimal physiochemical disturbance

Time-consuming, low efficiency, best for a fine-textured matrix with low permeability, the physiochemical properties are changed

^{29, 39}

Biological remediation

Contaminant transformation by microorganisms

Low cost, simple to implement, minimal physiochemical disturbance

Low efficiency, high specificity, a certain concentration limit, difficult to implement at site

^{40, 41}

Phytoremediation

Contaminant removal and/or stabilization by plants

High public acceptance, low cost, easy to implement, suitable for large and low contamination areas

Limited to shallow contamination, metal-specific, time-consuming, low efficiency

^{42, 43}

Photocatalytic degradation/ treatment

Contaminant removal using photocatalyst

It is possible for several forms of contamination, particularly in mixed contaminated media

Time-consuming, highly reliant on power supply, incorrect supply of nutrients might have adverse effects on the ecosystem

^{41, 44}