The accessibility of safe drinking water is becoming increasingly difficult to come by at the worldwide level. Only 0.003% of the globe's total water sources are freshwater, which is highly susceptible to pollution due to natural and anthropogenic activities [1]. For a healthy lifestyle, clean drinking water is essential, yet getting access to safe water can be difficult. Infectious diseases brought on by water contamination kill about 3,575,000 people annually and today, over two billion people lack access to safe water due to water pollution. Though the provision and access to potable water is the sixth goal of the 17 Sustainable Development Goals (SDGs), it is estimated that by 2050, this existing population is anticipated to reach six billion [[2], [3], [4]].

Although most lifeforms need modest levels of heavy metals like chromium, copper, zinc, nickel, boron, iron, and molybdenum, the majority of these heavy metals have harmful effects on living species, even at extremely low concentrations [[5], [6], [7]]. Numerous international organizations have acknowledged that heavy metals including lead, mercury, cadmium, and arsenic contribute to soil and water contamination through fertilization, discharges of industrial and municipal waste, and other anthropogenic influences [[8], [9], [10]]. Undoubtedly, the disposal of heavy metals polluted water into the soil and aquatic environments has led to a decline in water quality and health toxicity [11,12]. The majority of heavy metals are associated with cancers, birth defects, skin lesions, retardation of growth resulting in impairments, kidney, and liver damage, and other health-related issues. They can also damage cell membranes, alter enzyme activity, and alter the functioning of living cells [13,14].

One of the innovative wastewater treatment technologies is the adsorption of heavy metals through the application of natural and engineered adsorbents [[15], [16], [17]]. However, adsorption currently has setbacks that prevent its wider application for heavy metals sequestration from aquatic environments using various adsorbents, including difficulty in selecting suitable desorption eluent to recover adsorbed heavy metals and regeneration techniques to recycle the spent adsorbents for reusability and safe disposal. Desorption technology is practically utilized to recover as many adsorbed adsorbate molecules from the spent adsorbent as well as renew and re-utilize such adsorbent. When this process produces good retrievals of the heavy metal ions, it could cut down the quantity of waste generated, the amount of the adsorbent needed, as well as the expenses associated with waste disposal. One of the crucial steps in strengthening the efficiency of the adsorption technology and enabling the adsorbent's economic feasibility is the regeneration of the adsorbent for further use [18]. The merits of regeneration of the spent adsorbent and its storage/disposal disadvantages are presented in Fig. 1.

In the treatment of wastewater, the entire process of adsorption, desorption, regeneration, and reusability of exhausted adsorbents should be considered as a sustainable development strategy. This is because desorption and regeneration are often accomplished by physically or chemically removing the adsorbed heavy metal ions from the adsorbent without significantly harming the microstructure of the adsorbent. Presently, the majority of reviews have been conducted on the adsorption performance of various adsorbents in heavy metals remediation from aquatic systems [15,[20], [21], [22], [23], [24], [25], [26], [27]]. However, few reviews have been conducted on the desorption characteristics of heavy metal ions from spent adsorbents as well as the renewability and reusability of the spent adsorbents [28,29]. To the best of our knowledge, these reviews failed to comprehensively discuss the independent factors influencing heavy metals desorption, recovery, and adsorbent regeneration. In addition, isotherm and kinetic modeling that could have provided deep insights into the adsorption and desorption mechanisms of heavy metals and other contaminants from aqueous systems were not discussed in the various studies reviewed. Besides, the past reviews failed to comprehensively and critically evaluate current knowledge as well as important recommendations for future directions were not not provided.

Therefore, this study presents a state-of-the-art critical review to comprehensively provide insights and analysis on different desorption agents that could be used to retrieve heavy metals and regenerate the spent adsorbents for further adsorption-desorption processes. In addition, an attempt was made to provide an overview of some of the independent factors influencing heavy metals desorption, recovery, and adsorbent regeneration. Furthermore, isotherm and kinetic modeling have been summarized to provide comprehensive insights into the adsorption and desorption mechanisms of heavy metals from aqueous systems. Finally, the review provides future perspectives to provide room for researchers and industry players who are interested in heavy metals desorption, recovery, and spent adsorbents recycling to reduce the high cost of adsorbents reproduction, minimize secondary waste generation, and thereby safeguarding substantial economic and environmental benefits.