Page 254 - Materials Chemistry, Second Edition

Technologies for Treatment of Heavy Metal–Contaminated Groundwater 235

part because of attractive interfaces between a surface and the compound being
retained.
In this context, adsorption has emerged as a promising method, with advantages
such as

• High efficiency even with low metal concentrations
• Low cost
• No additional nutrient requirements
• Easy operation
• Potential metal recovery
• No detrimental effects on the environment

Dependent on the type of intermolecular attractive forces, adsorption can take place
due to

• Physical adsorption
• Chemical adsorption
11.5.3.1 Physical Adsorption
This is a general occurrence and happens in any solid/fluid or solid/gas system.
Physical adsorption is a procedure in which the attachment of the adsorbate on the
adsorbent surface is brought about by van der Waals powers of attraction. The elec-
tronic structure of the atom or molecule is not really involved in physical adsorp-
tion. Van der Waals forces start from the associations between incited, perpetual, or
transient electric dipoles. Physical adsorption must involve low-temperature solids,
and under suitable conditions, gas-phase atoms can undergo multilayer adsorption.
Industrial adsorbents use physical adsorption for their surface attachment.
11.5.3.2 Chemical Adsorption
This is an after-effect of synthetic collaboration between the solid and the adsorbed
substance. It is additionally called actuated adsorption. It is irreversible. It is partic-
ularly essential in catalysis. In this way, the energy of chemisorption is considered as
a chemical reaction. It may be exothermic or endothermic, with procedures ranging
from small to extensive in size. The basic steps in chemisorption regularly include
high activation energy.

11.5.3.3 Low-Cost Adsorbents
Many minimal-effort adsorbents have been created and tried for heavy metal
removal, which reflect changing adsorption efficiencies relying on the sort of adsor-
bents used. Activated carbon has been the most used adsorbent, although it is gener-
ally costly. Scanning for minimal-effort and easily accessible adsorbents to remove
heavy metal particles has become a principal research focus. To date, many reviews
on the use of minimal-effort adsorbents have been distributed. Agricultural wastes,
industrial by-products and wastes, and natural substances have been examined as
adsorbents for heavy metal wastewater treatment.