Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewaters

• We reviewed adsorption works with thermodynamic parameters evaluations.
• Adsorption mechanisms reported for copper ions and methylene blue were listed.
• Adsorption works with low-cost adsorbents are nearly equilibrium.
• The standard enthalpy and entropy changes values reported are highly contestable.
• Suggestions were made on the works needed for adsorption thermodynamics.

This meta-analysis evaluates adsorption studies that report thermodynamic parameters for heavy metals and dyes from wastewaters. The adsorbents were derived from agricultural waste, industrial wastes, inorganic particulates, or some natural products. The adsorption mechanisms, derivation of thermodynamic relationships, and possible flaws made in such evaluation are discussed. This analysis shows that conclusions from the examined standard enthalpy and entropy changes are highly contestable. The reason for this flaw may be the poor physical structure of adsorbents tested, such that pore transport controlled the solute flux, leaving a surface reaction process near equilibrium.